Mobile communication system and base station

Abstract

To suppress interference between base stations (between cells).SOLUTION: A mobile communication system includes a mobile terminal and a plurality of base stations that perform wireless communication with the mobile terminal. When a first base station among the plurality of base stations is an interference control base station that should control interference occurring with a second base station among the plurality of base stations, the first base station is caused to synchronize with the second base station, and the first base station transmits a specific type of signal at timing excluding timing at which the second base station transmits the specific type of signal.SELECTED DRAWING: Figure 17

Description

[Technical Field]

[0001] The present disclosure relates to a mobile communication system and a base station. [Background technology]

[0002] Among the third-generation communication systems, the Wideband Code Division Multiple Access (W-CDMA) system has been commercially available in Japan since 2001. Furthermore, the High Speed ​​Downlink Packet Access (HSDPA) service has been launched, which achieves even faster data transmission speeds on the downlink by adding a packet transmission channel (HS-DSCH: High Speed-Downlink Shared Channel) to the downlink (dedicated data channel, dedicated control channel). Furthermore, the High Speed ​​Uplink Packet Access (HSUPA) service has also been launched to further increase the speed of data transmission in the uplink. W-CDMA is a communication system defined by the 3rd Generation Partnership Project (3GPP), a standardization organization for mobile communication systems, and Release 8 of the standard is currently being compiled.

[0003] 3GPP is also considering a new communication method other than W-CDMA, called "Long Term Evolution (LTE)" for the radio section and "System Architecture Evolution (SAE)" for the overall system configuration, including the core network (also simply referred to as the network). LTE's access method, radio channel configuration, and protocols will be completely different from those of the current W-CDMA (HSDPA / HSUPA). For example, while W-CDMA uses Code Division Multiple Access (CDMA), LTE uses Orthogonal Frequency Division Multiplexing (OFDM) for the downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) for the uplink. Furthermore, while W-CDMA uses a 5 MHz bandwidth, LTE allows base stations to select from 1.4, 3, 5, 10, 15, or 20 MHz. In addition, LTE does not include circuit switching like W-CDMA, and is only a packet communication method.

[0004] Because the LTE communication system is configured using a new core network different from the W-CDMA core network (GPRS), it is defined as an independent radio access network separate from the W-CDMA network. Therefore, to distinguish it from the W-CDMA communication system, in the LTE communication system, the base station that communicates with mobile terminals (UE: User Equipment) is called the eNB (E-UTRAN NodeB), and the base station control device (Radio Network Controller) that exchanges control data and user data with multiple base stations is called the EPC (Evolved Packet Core) (sometimes called the aGW: Access Gateway). This LTE communication system provides unicast service and E-MBMS service (Evolved Multimedia Broadcast Multicast Service). The E-MBMS service is a broadcast-type multimedia service and is sometimes simply called MBMS. It transmits large-capacity broadcast content such as news, weather forecasts, and mobile broadcasts to multiple mobile terminals. This is also called a point-to-multipoint service.

[0005] Current decisions made by 3GPP regarding the overall architecture of the LTE system are described in Non-Patent Document 1. The overall architecture (Chapter 4 of Non-Patent Document 1) will be explained using FIG. 1. FIG. 1 is an explanatory diagram showing the configuration of an LTE communication system. In FIG. 1, if a control protocol (e.g., RRC (Radio Resource Management)) for a mobile terminal 101 and a user plane (e.g., PDCP: Packet Data Convergence Protocol, RLC: Radio Link Control, MAC: Medium Access Control, PHY: Physical layer) terminate at a base station 102, an E-UTRAN (Evolved Universal Terrestrial Radio Access) is composed of one or more base stations 102. The base station 102 schedules and transmits paging signals (also referred to as paging messages) notified from an MME (Mobility Management Entity) 103. The base stations 102 are connected to each other via an X2 interface. The base station 102 is also connected to the EPC (Evolved Packet Core) via an S1 interface, more specifically to the MME 103 (Mobility Management Entity) via an S1_MME interface, and to the S-GW 104 (Serving Gateway) via an S1_U interface. The MME 103 distributes paging signals to multiple or a single base station 102. The MME 103 also performs mobility control in the idle state. The MME 103 manages a tracking area list when a mobile terminal is in the idle state or active state. The S-GW 104 transmits and receives user data to one or more base stations 102.The S-GW 104 acts as a local mobility anchor point during handover between base stations. There is also a P-GW (PDN Gateway), which performs packet filtering for each user and assigns UE-ID addresses.

[0006] The current decisions regarding the frame structure in the LTE system at 3GPP are described in Non-Patent Document 1 (Chapter 5). This will be explained using Figure 2. Figure 2 is an explanatory diagram showing the structure of a radio frame used in an LTE communication system. In Figure 2, one radio frame is 10 ms long. The radio frame is divided into 10 equally sized subframes. Each subframe is divided into two equally sized slots. The first (#0) and sixth (#5) subframes of each radio frame contain a downlink synchronization signal (SS). The synchronization signals include a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS). Channels for MBSFN (Multimedia Broadcast Multicast Service Single Frequency Network) and channels other than MBSFN are multiplexed on a subframe-by-subframe basis. Hereinafter, subframes for MBSFN transmission are referred to as MBSFN subframes. Non-Patent Document 2 describes an example of signaling when allocating MBSFN subframes. Fig. 3 is an explanatory diagram showing the structure of an MBSFN frame. In Fig. 3, MBSFN subframes are allocated to each MBSFN frame. A cluster of MBSFN frames (MBSFN frame cluster) is scheduled. A repetition period for the cluster of MBSFN frames is allocated.

[0007] Current decisions made by 3GPP regarding the channel configuration in the LTE system are described in Non-Patent Document 1. It is assumed that the same channel configuration as that of non-CSG cells is used in CSG (Closed Subscriber Group) cells. Physical channels (Chapter 5 of Non-Patent Document 1) are explained using Figure 4. Figure 4 is an explanatory diagram illustrating physical channels used in an LTE communication system. In Figure 4, a Physical Broadcast Channel (PBCH) 401 is a downlink channel transmitted from a base station 102 to a mobile terminal 101. A BCH transport block is mapped to four subframes within a 40 ms interval. There is no explicit signaling of the 40 ms timing. A Physical Control Format Indicator Channel (PCFICH) 402 is transmitted from the base station 102 to the mobile terminal 101. The PCFICH informs the mobile terminal 101 of the number of OFDM symbols used for PDCCHs. The PCFICH is transmitted every subframe. The physical downlink control channel 403 (PDCCH) is a downlink channel transmitted from the base station 102 to the mobile terminal 101. The PDCCH reports resource allocation, HARQ information related to DL-SCH (a downlink shared channel, which is one of the transport channels shown in FIG. 5), and PCH (a paging channel, which is one of the transport channels shown in FIG. 5). The PDCCH carries an uplink scheduling grant. The PDCCH carries ACK / Nack, which are response signals to uplink transmission. The PDCCH is also called an L1 / L2 control signal. The physical downlink shared channel 404 (PDSCH) is a downlink channel transmitted from the base station 102 to the mobile terminal 101.The PDSCH is mapped with the DL-SCH (downlink shared channel) which is a transport channel and the PCH which is a transport channel. The physical multicast channel 405 (PMCH) is a downlink channel transmitted from the base station 102 to the mobile terminal 101. The PMCH is mapped with the MCH (multicast channel) which is a transport channel.

[0008] The physical uplink control channel (PUCCH) 406 is an uplink channel transmitted from the mobile terminal 101 to the base station 102. The PUCCH carries ACK / Nack, which is a response signal to downlink transmission. The PUCCH carries a CQI (Channel Quality indicator) report. The CQI is quality information indicating the quality of received data or the quality of the communication path. The PUCCH also carries a scheduling request (SR). The physical uplink shared channel (PUSCH) 407 is an uplink channel transmitted from the mobile terminal 101 to the base station 102. The UL-SCH (uplink shared channel, which is one of the transport channels shown in FIG. 5) is mapped to the PUSCH. The physical HARQ indicator channel (PHICH) 408 is a downlink channel transmitted from the base station 102 to the mobile terminal 101. The PHICH carries ACK / Nack, which is a response to uplink transmission. A physical random access channel (PRACH) 409 is an uplink channel transmitted from the mobile terminal 101 to the base station 102. The PRACH carries a random access preamble.

[0009] Downlink reference signals, known as symbols in mobile communication systems, are inserted into the first, third, and last OFDM symbols of each slot. Reference symbol received power (RSRP) is one of the physical layer measurements of a mobile terminal.

[0010] The transport channel (Transport Channel) will be explained using Figure 5 (Chapter 5 of Non-Patent Document 1). Figure 5 is an explanatory diagram of the transport channels used in an LTE communication system. Figure 5A shows the mapping between downlink transport channels and downlink physical channels. Figure 5B shows the mapping between uplink transport channels and uplink physical channels. For the downlink transport channel, the broadcast channel (BCH) is broadcast to the entire base station (cell). The BCH is mapped to the physical broadcast channel (PBCH). Retransmission control using hybrid ARQ (HARQ) is applied to the downlink shared channel (DL-SCH). Broadcast to the entire base station (cell) is possible. Dynamic or semi-static resource allocation is supported. Semi-static resource allocation is also called persistent scheduling. Discontinuous reception (DRX) of mobile terminals is supported to reduce power consumption of mobile terminals. The DL-SCH is mapped to the physical downlink shared channel (PDSCH). The paging channel (PCH) supports DRX of mobile terminals to enable low power consumption of mobile terminals. Notification to the entire base station (cell) is required. It is mapped to physical resources such as the physical downlink shared channel (PDSCH) that can be dynamically used for traffic, or to physical resources such as the physical downlink control channel (PDCCH) of other control channels. The multicast channel (MCH) is used for notification to the entire base station (cell). It supports SFN combining of MBMS services (MTCH and MCCH) in multi-cell transmission. It supports semi-static resource allocation. The MCH is mapped to the PMCH.

[0011] Retransmission control using HARQ (Hybrid ARQ) is applied to the uplink shared channel (UL-SCH). Dynamic or semi-static resource allocation is supported. The UL-SCH is mapped to the physical uplink shared channel (PUSCH). The random access channel (RACH) shown in Figure 5B is limited to control information and there is a risk of collision. The RACH is mapped to the physical random access channel (PRACH). HARQ will now be explained.

[0012] HARQ is a technology that improves the communication quality of a transmission channel by combining Automatic Repeat reQuest (ARRQ) and Forward Error Correction (FEC). Its advantage is that error correction works effectively even on transmission channels with variable communication quality. In particular, combining the reception results of the initial transmission and the retransmission can further improve quality. Here is an example of a retransmission method. If the receiving side is unable to decode the received data correctly (if a CRC Cyclic Redundancy Check error occurs (CRC=NG)), the receiving side sends a "Nack" to the transmitting side. Upon receiving the "Nack," the transmitting side retransmits the data. If the receiving side is able to decode the received data correctly (if no CRC error occurs (CRC=OK)), the receiving side sends an "Ack" to the transmitting side. Upon receiving the "Ack," the transmitting side transmits the next data. One example of a HARQ method is "Chase Combining." Chase combining is a method of transmitting the same data sequence for the initial transmission and retransmission, and improving the gain by combining the initial transmission data sequence with the retransmission data sequence during retransmission. This is based on the idea that even if the initial transmission data contains errors, it may contain some correct data, and by combining the correct parts of the initial transmission data with the retransmission data, data can be transmitted with higher accuracy. Another example of a HARQ method is IR (Incremental Redundancy). IR increases redundancy by transmitting parity bits during retransmission, combining them with the initial transmission to increase redundancy and improve quality through error correction.

[0013] Logical channels (Non-Patent Document 1, Chapter 6) will be explained using Figure 6. Figure 6 is an explanatory diagram explaining logical channels used in an LTE communication system. Figure 6A shows the mapping between downlink logical channels and downlink transport channels. Figure 6B shows the mapping between uplink logical channels and uplink transport channels. The broadcast control channel (BCCH) is a downlink channel for broadcast system control information. The logical channel BCCH is mapped to the transport channel broadcast channel (BCH) or the downlink shared channel (DL-SCH). The paging control channel (PCCH) is a downlink channel for transmitting paging signals. The PCCH is used when the network does not know the cell location of the mobile terminal. The logical channel PCCH is mapped to the transport channel paging channel (PCH). The common control channel (CCCH) is a channel for transmission control information between the mobile terminal and the base station. The CCCH is used when the mobile terminal does not have an RRC connection with the network. In the downlink direction, the CCCH is mapped to a transport channel, the Downlink Shared Channel (DL-SCH). In the uplink direction, the CCCH is mapped to a transport channel, the Uplink Shared Channel (UL-SCH).

[0014] The Multicast Control Channel (MCCH) is a downlink channel for point-to-multipoint transmission. It is a channel used to transmit MBMS control information for one or several MTCHs from the network to mobile terminals. The MCCH is a channel used only by mobile terminals receiving MBMS. The MCCH is mapped to the downlink shared channel (DL-SCH) or the multicast channel (MCH), which are transport channels. The Dedicated Control Channel (DCCH) is a channel for transmitting dedicated control information between mobile terminals and the network. The DCCH is mapped to the uplink shared channel (UL-SCH) in the uplink and to the downlink shared channel (DL-SCH) in the downlink. The Dedicated Traffic Channel (DTCH) is a channel for point-to-point communication to individual mobile terminals for transmitting user information. DTCH exists in both the uplink and downlink. The DTCH is mapped to the uplink shared channel (UL-SCH) in the uplink and to the downlink shared channel (DL-SCH) in the downlink. The Multicast Traffic Channel (MTCH) is a downlink channel for transmitting traffic data from the network to mobile terminals. The MTCH is a channel used only by mobile terminals receiving MBMS. The MTCH is mapped to the Downlink Shared Channel (DL-SCH) or the Multicast Channel (MCH).

[0015] GCI stands for Global Cell Identity. Closed Subscriber Group (CSG) cells are introduced in LTE and UMTS (Universal Mobile Telecommunication System). CSGs are described below (see Non-Patent Document 4, Chapter 3.1). A Closed Subscriber Group (CSG) is a cell for which an operator identifies available subscribers (a designated subscriber cell). The designated subscribers are permitted to access one or more E-UTRAN cells in a PLMN (Public Land Mobile Network). The one or more E-UTRAN cells to which designated subscribers are permitted access are called "CSG cell(s)." However, PLMNs have access restrictions. A CSG cell is a part of a PLMN that broadcasts a unique CSG identity (CSG ID, CSG-ID). Members of a pre-registered and authorized subscriber group access the CSG cell using the CSG-ID, which is access permission information. The CSG-ID is broadcast by the CSG cell or cells. Multiple CSG-IDs exist in a mobile communication system. The CSG-ID is used by the terminal (UE) to facilitate access to CSG-related members. The 3GPP meeting is discussing using a Tracking Area Code (TAC) instead of the CSG-ID to broadcast information from a CSG cell or cell. Mobile terminal location tracking is performed in units of an area consisting of one or more cells. This location tracking is intended to enable tracking and calling (receiving calls) of a mobile terminal even when the mobile terminal is in standby mode. The area used for tracking the mobile terminal location is called a tracking area. The CSG White List is a list stored in the USIM that records all CSG IDs of the CSG cells to which the subscriber belongs. The white list in the mobile terminal is provided by a higher layer. This allows the base station of the CSG cell to allocate radio resources to the mobile terminal.

[0016] The term "suitable cell" is explained below (Chapter 4.3 of Non-Patent Document 4). A "suitable cell" is a cell on which a UE can camp to receive normal service. Such a cell is one that (1) is part of the selected PLMN, the registered PLMN, or a PLMN in the "Equivalent PLMN List," and (2) further satisfies the following conditions in the latest information provided by the NAS (non-access stratum): (1) the cell is not a barred cell, and (2) the cell is not part of the "barred LAs for roaming" list and is part of at least one Tracking Area (TA). In that case, the cell must satisfy (1) above, (3) the cell must satisfy the cell selection evaluation criteria, and (4) for cells identified by System Information (SI) as CSG cells, the CSG-ID must be part of the UE's "CSG WhiteList" (included in the UE's CSG WhiteList).

[0017] An "acceptable cell" is defined below (NPL 4, Chapter 4.3). This is a cell on which a UE can camp to receive limited services (emergency calls). Such a cell shall fulfill all of the following requirements. That is, the minimum set of requirements for initiating an emergency call in an E-UTRAN network is as follows: (1) The cell is not a barred cell. (2) The cell meets the cell selection evaluation criteria.

[0018] 3GPP is studying base stations called Home-NodeB (Home-NB, HNB) and Home-eNodeB (Home-eNB, HeNB). HNB / HeNB are base stations for access services in UTRAN / E-UTRAN, for example, for homes, businesses, and commercial use. Non-Patent Document 6 discloses three different modes of access to HeNBs and HNBs: open access mode, closed access mode, and hybrid access mode. Each mode has the following characteristics. In open access mode, a HeNB or HNB is operated as a normal cell of a regular operator. In closed access mode, a HeNB or HNB is operated as a CSG cell. This is a CSG cell that can only be accessed by CSG members. In hybrid access mode, it is a CSG cell that is simultaneously accessible to non-CSG members. In other words, a hybrid access mode cell is a cell that supports both open access mode and closed access mode.

[0019] 3GPP is studying operation methods for HNBs or HeNBs (Non-Patent Document 8). Non-Patent Document 8 describes five operation methods, A to E. In Type A, the HNB / HeNB operates using CSG, a dedicated channel, and fixed power. In Type B, the HNB / HeNB operates using CSG, a dedicated channel, and adaptive power. In Type C, the HNB / HeNB operates using CSG, a co-channel, and adaptive power. In Type D, the HNB / HeNB operates using CSG and partial co-channel. In Type E, the HNB / HeNB operates in open access mode and using a dedicated channel or a co-channel. Operation using a dedicated channel is an operation method in which the HNB / HeNB uses a dedicated frequency that is different from that of the macrocell (NB or eNB). Co-channel operation is an operation method in which the HNB / HeNB uses the same frequency as the macrocell (NB or eNB). Partially co-channel operation is an operation method in which the frequency used by the HNB / HeNB is a part of the frequency used by the macrocell (NB or eNB). [Prior art documents] [Non-patent literature]

[0020] [Non-Patent Document 1] 3GPP TS36.300 V8.6.0 [Non-patent document 2] 3GPP R1-072963 [Non-patent document 3] TR R3.020V0.6.0 [Non-patent document 4] 3GPP TS36.304 V8.3.0 [Non-patent document 5] 3GPP R2-082899 [Non-patent document 6] 3GPP S1-083461 [Non-Patent Document 7] 3GPP R2-086246 [Non-patent document 8] 3GPP TR25.820 V8.2.0 [Non-Patent Document 9] 3GPP TS36.413 V8.4.0 Chapter 8, Chapter 9 [Non-Patent Document 10] 3GPP TS36.423 V8.4.0 Chapter 8, Chapter 9 [Non-Patent Document 11] 3GPP TS36.331 V8.4.0 Chapter 5.2, Chapter 5.5, Chapter 6.3.1 [Non-Patent Document 12] 3GPP TR36.814 V1.5.0 Chapter 5 [Non-Patent Document 13] 3GPP R1-094415 [Non-Patent Document 14] 3GPP R1-094659 Summary of the Invention [Problem to be solved by the invention]

[0021] HeNBs and HNBs are required to support various services. For example, operators allow mobile terminals to register with specific HeNBs and HNBs and allow only registered mobile terminals to access HeNB and HNB cells, thereby increasing the radio resources available to the mobile terminals and enabling high-speed communication. To compensate for this, operators charge higher fees than usual. To realize such services, CSG (Closed Subscriber Group) cells, which can only be accessed by registered (subscribed or member) mobile terminals, have been introduced. Many CSG (Closed Subscriber Group) cells are required to be installed in shopping districts, apartment buildings, schools, companies, and so on. For example, a CSG cell is required for each store in a shopping district, each room in an apartment building, each classroom in a school, and each section in a company, and only users registered to each CSG cell can use the CSG cell. HeNBs / HNBs are required not only to complement communications outside the coverage area of ​​a macrocell, but also to support the various services mentioned above. For this reason, there are cases where a HeNB / HNB is installed within the coverage of a macro cell. When a HeNB / HNB is installed within the coverage of a macro cell, interference occurs between the HeNB / HNB and the macro cell. A mobile terminal (UE) communicating with a HeNB / HNB within the HeNB / HNB coverage area experiences interference from radio waves from the macro cell, which hinders communication with the HeNB / HNB, and if the interference power becomes large, the UE will be unable to communicate. Conversely, if a mobile terminal communicating with a macro cell within the macro cell coverage area moves into the coverage of a HeNB / HNB installed within the macro cell coverage area, radio waves from the HNB / HeNB will interfere, which hinders communication with the macro cell, and if the interference power becomes large, the UE will be unable to communicate.

[0022] Generally, when interference power from other cells becomes large within the coverage of a certain cell, a mobile terminal is allowed to perform handover (HO) or cell reselection to the other cell or another appropriate cell to prevent communication from being interrupted. However, if a mobile terminal is unable to perform handover or reselection to the other cell, the interference power from the other cell increases, resulting in a problem of communication being interrupted. For example, consider the case where an HNB / HeNB is a CSG cell in closed access mode as described above in 3GPP. If the CSG cell is installed within the coverage of a macro cell, interference occurs between the macro cell and the CSG cell within the CSG coverage, as described above. In such a case, a mobile terminal that is not user-registered in the CSG cell is unable to communicate with the macro cell due to interference from the CSG cell.

[0023] Figure 13 shows a conceptual diagram of a situation in which a CSG cell is installed within the coverage of a macrocell and the received signal-to-interference ratio (SIR) at a mobile terminal in that situation. As shown in Figure 13(a), a CSG cell 1303 is installed within the coverage 1301 of a macrocell 1302. When a mobile terminal 1305 communicating with the macrocell 1302 within the macrocell coverage 1301 moves into the coverage 1304 of the CSG cell 1303 installed within the macrocell coverage 1301, radio waves from the CSG cell 1303 cause interference, hindering communication with the macrocell 1302. Figure 13(b) shows the SIR at the mobile terminal before a HeNB (corresponding to the CSG cell 1303) is installed, and Figure 13(c) shows the SIR at the mobile terminal when the HeNB 1303 is installed. The horizontal axis represents the distance from the macrocell base station (eNB), and the vertical axis represents the SIR. It is assumed that the mobile terminal is not registered as a user with the CSG cell. As shown in FIG. 13(b), when a HeNB is not installed, the SIR gradually decreases as the mobile terminal moves away from the eNB. When the SIR is greater than threshold a, communication is possible, and when it is smaller, communication is impossible. As shown in FIG. 13(c), when a HeNB 1303 is installed within the coverage of an eNB (corresponding to macro cell 1302), radio waves from HeNB 1303, indicated by the dashed line, become strong near HeNB 1303. For a mobile terminal communicating with eNB 1302, the radio waves from HeNB 1303 cause interference, and the SIR from eNB 1302 deteriorates significantly near the HeNB. As a result, the SIR of the mobile terminal near the HeNB may become smaller than threshold a. The mobile terminal attempts to handover to HeNB 1303 or reselect a cell, but because HeNB 1303 is a CSG cell in closed access mode, handover is not possible and communication is disconnected.

[0024] 14 shows a situation in which a CSG cell 1404 is installed within the coverage areas 1402 and 1406 of multiple (here, two) macrocells 1401 and 1407, and a conceptual diagram of the received signal-to-interference ratio (SIR) at a mobile terminal in that situation. As shown in FIG. 14(a), when a CSG cell 1404 is installed within the coverage areas 1402 and 1406 of two macrocells 1401 and 1407, and a mobile terminal 1403 communicating with macrocells 1401 and 1407 within macrocell coverage areas 1402 and 1406 moves into the coverage area of ​​CSG cell 1404 installed within macrocell coverage area 1405, radio waves from CSG cell 1404 cause interference, hindering communication with macrocells 1401 and 1407. Figure 14(b) shows the SIR of a mobile terminal before a HeNB is installed, and Figure 14(c) shows the SIR of a mobile terminal when a HeNB is installed. It is assumed that the mobile terminal is not registered as a user with the CSG. As shown in Figure 14(b), when a HeNB is not installed, the SIR gradually decreases as the mobile terminal moves away from eNB#1. During this time, the radio waves from eNB#2 become stronger, and before the SIR due to the radio waves from eNB#1 falls below threshold a, the mobile terminal performs handover or cell reselection to eNB#2. On the other hand, as shown in Figure 14(c), when HeNB 1404 is installed within the coverage of two cells 1401 and 1407 (eNB#1 and eNB#2 in Figure 14(c)), radio waves from the HeNB indicated by the dashed line become strong near the HeNB, and for a mobile terminal communicating with eNB#1 or eNB#2, the radio waves from this HeNB cause interference, causing the SIR from eNB#1 or eNB#2 to deteriorate significantly near the HeNB. As a result, there are cases where the SIR of a mobile terminal near the HeNB becomes smaller than threshold a.

[0025] When a mobile terminal communicating with eNB#1 has its SIR lower than threshold a near a HeNB, it attempts handover to eNB#2 or cell reselection, but because the SIR of eNB#2 is also lower than threshold a, handover or cell reselection becomes impossible. Furthermore, the mobile terminal attempts handover or cell reselection to HeNB1404, but cannot access that HeNB because it is a CSG cell in closed access mode, and handover or cell reselection is not possible. Therefore, communication is disconnected.

[0026] In the above example, we have described a problem that occurs when a mobile terminal communicating in a macrocell (eNB) cannot hand over to a CSG cell. However, a similar problem occurs when a mobile terminal communicating in a CSG cell cannot hand over to a macrocell (eNB), in which communication is interrupted.

[0027] To address these issues, Non-Patent Document 8 describes a method of operating an HNB / HeNB that serves as a CSG cell with adaptive output. However, simply adjusting the output power of the CSG cell according to the degree of interference only increases or decreases the coverage of the CSG cell. As a result, in either case, there will be areas where interference between the CSG cell and the macro cell becomes significant. This still leaves a problem of mobile terminals moving into such areas being unable to communicate. [Means for solving the problem]

[0028] The mobile communication system disclosed herein is a mobile communication system including a mobile terminal and a plurality of base stations that perform wireless communication between the mobile terminal and the mobile terminal, and when a first base station among the plurality of base stations is an interference control base station that should control interference occurring between the first base station and a second base station among the plurality of base stations, the first base station is synchronized with the second base station, and transmits a specific type of signal at the first base station at a timing other than the timing at which the second base station transmits a specific type of signal. The base station of the present disclosure is a base station that performs wireless communication with a mobile terminal, and when it is an interference control base station that should control interference occurring with another base station, is characterized in that it synchronizes with the other base station and transmits a specific type of signal at a timing other than the timing at which the specific type of signal is transmitted at the other base station. [Effects of the Invention]

[0029] According to the present disclosure, it is possible to suppress interference between base stations (between cells). [Brief explanation of the drawings]

[0030] [Figure 1] 1 is an explanatory diagram showing the configuration of an LTE communication system. 2 is an explanatory diagram showing the configuration of an LTE communication system. [Figure 2] FIG. 1 is an explanatory diagram showing the configuration of a radio frame used in an LTE communication system. [Figure 3] FIG. 1 is an explanatory diagram showing the structure of an MBSFN (Multimedia Broadcast multicast service Single Frequency Network) frame. [Figure 4] FIG. 1 is an explanatory diagram illustrating physical channels used in an LTE communication system. [Figure 5] FIG. 1 is an explanatory diagram illustrating transport channels used in an LTE communication system. [Figure 6] FIG. 1 is an explanatory diagram illustrating logical channels used in an LTE communication system. [Figure 7] 1 is a block diagram showing the overall configuration of a mobile communication system currently being discussed in 3GPP. [Figure 8] FIG. 2 is a block diagram showing the configuration of a mobile terminal. [Figure 9] FIG. 2 is a block diagram showing the configuration of a base station. [Figure 10] FIG. 2 is a block diagram illustrating the configuration of an MME. [Figure 11] FIG. 2 is a block diagram showing the configuration of a HeNBGW. [Figure 12] 1 is a flowchart showing an outline of a cell search performed by a mobile terminal (UE) in an LTE communication system. [Figure 13] 1 is a conceptual diagram showing a situation in which a CSG cell is installed within the coverage of a macro cell and the received signal-to-interference ratio (SIR) at a mobile terminal in that situation. [Figure 14] FIG. 1 is a conceptual diagram showing a situation in which a CSG cell is installed within the coverage of multiple (here, two) macro cells, and the received signal-to-interference ratio (SIR) at a mobile terminal in that situation. [Figure 15] FIG. 1 is a diagram illustrating a frame structure and non-schedulable signals in LTE. [Figure 16] FIG. 1 is a diagram illustrating the frame structure of two cells (cell #1 and cell #2). [Figure 17] 10 is a diagram illustrating a case where an n-subframe offset is provided in a physical resource onto which a non-schedulable signal is mapped, as disclosed in this embodiment. FIG. [Figure 18] FIG. 1 is a conceptual diagram of a received signal-to-interference ratio (SIR) at a mobile terminal in a situation where a HeNB operating as a CSG cell is installed within the coverage of a macro cell. [Figure 19] FIG. 1 is a diagram illustrating physical resources onto which L1 / L2 control signals are mapped, as determined by 3GPP. [Figure 20] FIG. 10 is a diagram illustrating a case where symbols are mapped from the 10th symbol to the 12th symbol in each subframe. [Figure 21] 10 is a diagram illustrating an example of a frame configuration between two cells when an n-symbol offset is provided according to this modification. FIG. [Figure 22] FIG. 10 is a diagram illustrating an example of a frame configuration shown in this modified example. [Figure 23] FIG. 10 is a diagram illustrating an example of mapping of symbols within a subframe in this modification. [Figure 24] FIG. 10 is a diagram for explaining transmission timing between two cells when one frame configuration is used for all cells in the system, as disclosed in this modification. [Figure 25] FIG. 10 is a diagram illustrating a method for mapping symbols within one subframe in this modified example. [Figure 26] FIG. 10 is a diagram illustrating transmission timing between two cells when the above-described symbol mapping method within a subframe is used, as shown in this modified example. [Figure 27] FIG. 11 is a sequence diagram showing how an offset amount is determined in a mobile communication system according to a third embodiment. [Figure 28] FIG. 13 is a sequence diagram showing how an offset amount is determined in a mobile communication system according to a first modification of the third embodiment. [Figure 29] FIG. 13 is a sequence diagram showing how an offset amount is determined in a mobile communication system according to a second modification of the third embodiment. [Figure 30] FIG. 13 is a sequence diagram showing how an offset amount is determined in a mobile communication system according to a third modification of the third embodiment. [Figure 31] FIG. 13 is a sequence diagram showing how an offset amount is determined in a mobile communication system according to a fourth modification of the third embodiment. [Figure 32] FIG. 13 is a sequence diagram showing how an offset amount is determined in a mobile communication system according to a fifth modification of the third embodiment. [Figure 33] FIG. 13 is a sequence diagram showing how an offset amount is determined in a mobile communication system according to a sixth modification of the third embodiment. [Figure 34] FIG. 10 is a conceptual diagram of a problem to be solved in the fourth embodiment. [Figure 35] FIG. 10 is a conceptual diagram of a result of reducing the amount of downlink interference. [Figure 36] 13 is a flowchart of a mobile terminal illustrating a problem in the first modification of the fifth embodiment. [Figure 37] FIG. 10 is a sequence diagram for setting a CSG cell (HeNB / HNB) to be compatible with the open access mode when the CSG cell (HeNB / HNB) makes a decision. [Figure 38] FIG. 10 is a sequence diagram for setting a CSG cell (HeNB / HNB) to be compatible with the open access mode when determined by the core network. [Figure 39] This shows a conceptual diagram of the received signal-to-interference ratio (SIR) at a mobile terminal in a situation where a HeNB operating as a CSG cell is installed within the coverage of a macro cell. [Figure 40] 13 is a flowchart of a mobile terminal for explaining a problem of the seventh embodiment. [Figure 41] 13 is a flowchart of a mobile terminal when performing a handover to a cell having the same CSG-ID according to the seventh embodiment. [Figure 42] 1 is a conceptual diagram of the frequency band configuration of the LTE-A system. [Figure 43] FIG. 1 is a conceptual diagram of an extension carrier. [Figure 44] FIG. 13 is a conceptual diagram of a solution according to a sixth modification of the first embodiment. [Figure 45] FIG. 10 is an explanatory diagram of a specific example in which a copy of a signal that cannot be scheduled is provided in the first embodiment. [Figure 46] FIG. 10 is an explanatory diagram of a specific example in which a copy of a signal that cannot be scheduled is provided in the first modification of the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0031] Embodiment 1 FIG. 7 is a block diagram showing the overall configuration of an LTE-based mobile communication system currently being discussed in 3GPP. Currently, 3GPP is studying the overall configuration of a system including CSG (Closed Subscriber Group) cells (e-UTRAN Home-eNodeBs (Home-eNBs, HeNBs), UTRAN Home-NBs (HNBs)) and non-CSG cells (e-UTRAN eNodeBs (eNBs), UTRAN NodeBs (NBs), and GERAN BSSs), and for e-UTRAN, configurations such as those shown in FIG. 7(a) and (b) have been proposed (Non-Patent Document 1, Non-Patent Document 3). Now, FIG. 7(a) will be explained. A mobile terminal (UE) 71 transmits and receives data to and from a base station 72. The base station 72 is divided into an eNB (non-CSG cell) 72-1 and a Home-eNB (CSG cell) 72-2. The eNB 72-1 is connected to an MME 73 via an interface S1, and control information is communicated between the eNB and the MME. Multiple MMEs are connected to one eNB. The Home-eNB 72-2 is connected to the MME 73 via an interface S1, and control information is communicated between the Home-eNB and the MME. Multiple Home-eNBs are connected to one MME.

[0032] Next, Fig. 7(b) will be described. A mobile terminal (UE) 71 transmits and receives data to and from a base station 72. The base station 72 is classified into an eNB (non-CSG cell) 72-1 and a Home-eNB (CSG cell) 72-2. As in Fig. 7(a), the eNB 72-1 is connected to an MME 73 via an interface S1, and control information is communicated between the eNB and the MME. Multiple MMEs are connected to one eNB. Meanwhile, a Home-eNB 72-2 is connected to the MME 73 via a HeNBGW (Home-eNB Gateway) 74. The Home-eNB and HeGW are connected via an interface S1, and the HeNBGW 74 and MME 73 are connected via an interface S1_flex. One or more Home-eNBs 72-2 are connected to one HeNBGW 74, and information is communicated via S1. The HeNBGW 74 is connected to one or more MMEs 73, and information is communicated via S1_flex.

[0033] By connecting one HeNBGW74 to Home-eNBs belonging to the same CSG-ID using the configuration of Fig. 7(b), when the same information, such as registration information, is transmitted from the MME73 to multiple Home-eNBs72-2 belonging to the same CSG-ID, the signaling efficiency can be improved by first transmitting the information to the HeNBGW74 and then transmitting it from there to the multiple Home-eNBs72-2, rather than transmitting the information directly to each of the multiple Home-eNBs72-2. On the other hand, when each Home-eNB72-2 communicates individual information with the MME73, the information is transmitted via the HeNBGW74, but by simply passing (transmitting) the information without processing it there, it becomes possible for the Home-eNB72-2 and the MME73 to communicate as if they were directly connected.

[0034] FIG. 8 is a block diagram showing the configuration of a mobile terminal (terminal 71 in FIG. 7). The transmission process of the mobile terminal shown in FIG. 8 will be described. First, control data from protocol processing unit 801 and user data from application unit 802 are stored in transmission data buffer unit 803. The data stored in transmission data buffer unit 803 is passed to encoder unit 804, where it undergoes encoding processes such as error correction. Some data may be output directly from transmission data buffer unit 803 to modulation unit 805 without undergoing encoding processes. The data encoded by encoder unit 804 is modulated by modulation unit 805. The modulated data is converted into a baseband signal, and then output to frequency conversion unit 806, where it is converted into a radio transmission frequency. A transmission signal is then transmitted from antenna 807 to base station 312. The reception process of mobile terminal 311 is performed as follows. A radio signal from base station 312 is received by antenna 807. The received signal is converted from a radio reception frequency to a baseband signal by frequency conversion unit 806, and demodulated by demodulation unit 808. The demodulated data is passed to a decoder unit 809, where decoding processing such as error correction is performed. Of the decoded data, control data is passed to a protocol processing unit 801, and user data is passed to an application unit 802. A series of processes in the mobile terminal are controlled by a control unit 810. Therefore, although the control unit 810 is omitted from the drawing, it is connected to each unit (801 to 809).

[0035] FIG. 9 is a block diagram showing the configuration of a base station (the base station 72 in FIG. 7). The transmission processing of the base station shown in FIG. 9 will be described. The EPC communication unit 901 transmits and receives data between the base station 72 and the EPC (the MME 73, the HeNBGW 74, etc.). The other base station communication unit 902 transmits and receives data with other base stations. The EPC communication unit 901 and the other base station communication unit 902 each exchange information with a protocol processing unit 903. Control data from the protocol processing unit 903, as well as user data and control data from the EPC communication unit 901 and the other base station communication unit 902, are stored in a transmission data buffer unit 904. The data stored in the transmission data buffer unit 904 is passed to an encoder unit 905, where it is subjected to encoding processing such as error correction. Some data may be output directly from the transmission data buffer unit 904 to a modulation unit 906 without being subjected to encoding processing. The encoded data is modulated in the modulation unit 906. The modulated data is converted into a baseband signal and then output to a frequency conversion unit 907, where it is converted into a radio transmission frequency. Then, a transmission signal is transmitted from antenna 908 to one or more mobile terminals 71. Furthermore, reception processing in the base station 72 is executed as follows. A radio signal from one or more mobile terminals 311 is received by antenna 908. The received signal is converted from a radio reception frequency to a baseband signal by frequency conversion unit 907, and demodulated by demodulation unit 909. The demodulated data is passed to decoder unit 910, where decoding processing such as error correction is performed. Of the decoded data, control data is passed to protocol processing unit 903 or EPC communication unit 901 or other base station communication unit 902, and user data is passed to EPC communication unit 901 or other base station communication unit 902. A series of processes in the base station 72 is controlled by control unit 911. Therefore, although the control unit 911 is omitted from the drawing, it is connected to each unit (901 to 910).

[0036] 10 is a block diagram showing the configuration of an MME (Mobility Management Entity). A PDN GW communication unit 1001 transmits and receives data between the MME 73 and the PDN GW. A base station communication unit 1002 transmits and receives data between the MME 73 and the base station 72 via the S1 interface. If the data received from the PDN GW is user data, the user data is passed from the PDN GW communication unit 1001 to the base station communication unit 1002 via a user plane processing unit 1003, and transmitted to one or more base stations 72. If the data received from the base station 72 is user data, the user data is passed from the base station communication unit 1002 to the PDN GW communication unit 1001 via the user plane processing unit 1003, and transmitted to the PDN GW.

[0037] If the data received from the PDN GW is control data, the control data is passed from the PDN GW communication unit 1001 to the control plane control unit 1005. If the data received from the base station 72 is control data, the control data is passed from the base station communication unit 1002 to the control plane control unit 1005. The HeNBGW communication unit 1004 is provided when a HeNBGW 74 is present, and transmits and receives data via an interface (IF) between the MME 73 and HeNBGW 74 depending on the information type. The control data received from the HeNBGW communication unit 1004 is passed from the HeNBGW communication unit 1004 to the control plane control unit 1005. The result of processing in the control plane control unit 1005 is transmitted to the PDN GW via the PDN GW communication unit 1001. Furthermore, the results processed in the control plane control unit 1005 are transmitted to one or more base stations 72 via the base station communication unit 1002 over the S1 interface, and also transmitted to one or more HeNBGWs 74 via the HeNBGW communication unit 1004.

[0038] The control plane control unit 1005 includes a NAS security unit 1005-1, an SAE bearer control unit 1005-2, an idle state mobility management unit 1005-3, and the like, and performs overall processing for the control plane. The NAS security unit 1005-1 performs security for NAS (Non-Access Stratum) messages, etc. The SAE bearer control unit 1005-2 performs management of SAE (System Architecture Evolution) bearers, etc. The idle state mobility management unit 1005-3 performs mobility management in the standby state (LTE-IDLE state, also simply referred to as idle), generation and control of paging signals in the standby state, addition, deletion, update, and search of tracking areas (TAs) of one or more mobile terminals 71 under its control, and management of the tracking area list (TA List). The MME initiates the paging protocol by sending a paging message to a cell belonging to the tracking area (TA) where the UE is registered. The idle state mobility management unit 1005-3 may manage the CSGs and CSG-IDs of the Home-eNB 72-2 connected to the MME, as well as the whitelist. In the CSG-ID management, the relationship between the mobile terminal corresponding to the CSG-ID and the CSG cell is managed (added, deleted, updated, searched). For example, the relationship may be between one or more mobile terminals registered for user access to a certain CSG-ID and the CSG cell belonging to that CSG-ID. In the whitelist management, the relationship between the mobile terminal and the CSG-ID is managed (added, deleted, updated, searched). For example, the whitelist may store one or more CSG-IDs registered by a user for a certain mobile terminal. While these CSG-related management tasks may be performed by other parts of the MME 73, performing them in the idle state mobility management unit 1005-3 allows for efficient implementation of the method of using tracking area codes instead of CSG-IDs, which is currently being discussed in the 3GPP meeting. The series of processes in the MME 313 is controlled by the control unit 1006.Therefore, although the control unit 1006 is omitted in the drawing, it is connected to each unit (1001 to 1005).

[0039] FIG. 11 is a block diagram showing the configuration of the HeNBGW. The EPC communication unit 1101 transmits and receives data between the HeNBGW 74 and the MME 73 via the S1_flex interface. The base station communication unit 1102 transmits and receives data between the HeNBGW 74 and the Home-eNB 72-2 via the S1 interface. The location processing unit 1103 performs processing to transmit, to multiple Home-eNBs, data such as registration information that is part of the data from the MME 73 that is passed via the EPC communication unit 1101. The data processed by the location processing unit 1103 is passed to the base station communication unit 1102 and transmitted to one or more Home-eNBs 72-2 via the S1 interface. Data that does not require processing by the location processing unit 1103 and that only needs to be passed (transmitted) is passed from the EPC communication unit 1101 to the base station communication unit 1102 and transmitted to one or more Home-eNBs 72-2 via the S1 interface. A series of processes by the HeNBGW 74 is controlled by the control unit 1104. Therefore, although the control unit 1104 is omitted in the drawing, it is connected to each unit (1101 to 1103).

[0040] Next, an example of a general cell search method in a mobile communication system is shown. FIG. 12 is a flowchart showing an outline of the process from cell search to standby operation performed by a mobile terminal (UE) in an LTE communication system. When a cell search is started in the mobile terminal, in step ST1201, slot timing and frame timing are synchronized using a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS) transmitted from a surrounding base station. A synchronization code that corresponds one-to-one with a PCI (Physical Cell Identity) assigned to each cell is assigned to the synchronization signal (SS) together with the P-SS and S-SS. Currently, 504 different PCIs are considered to be possible, and synchronization is achieved using these 504 PCIs, and the PCI of the synchronized cell is detected (identified). Next, in step ST1202, for the synchronized cell, a reference signal (RS) transmitted from the base station for each cell is detected and the received power is measured. A code that corresponds one-to-one with the PCI is used for the reference signal RS, and by correlating with this code, it is possible to separate the cell from other cells. By deriving the RS code of the cell from the PCI identified in ST1201, it is possible to detect the RS and measure the RS reception power. Next, in ST1203, from one or more cells detected up to ST1202, the cell with the best RS reception quality (for example, the cell with the highest RS reception power, i.e., the best cell) is selected. Next, in ST1204, the PBCH of the best cell is received and a BCCH, which is broadcast information, is obtained. The BCCH on the PBCH carries a MIB (Master Information Block) containing cell configuration information. Examples of MIB information include the DL (downlink) system bandwidth, the number of transmit antennas, and the SFN (System Frame Number).

[0041] Next, in step ST1205, the mobile terminal receives the DL-SCH of the cell based on the cell configuration information in the MIB and obtains SIB (System Information Block) 1 from the broadcast information BCCH. SIB 1 contains information about access to the cell, information about cell selection, and scheduling information for other SIBs (SIBk; k is an integer greater than or equal to 2). SIB 1 also contains a Tracking Area Code (TAC). Next, in step ST1206, the mobile terminal compares the TAC received in step ST1205 with the TAC it already possesses. If the comparison results in a match, the mobile terminal enters standby mode in the cell. If the comparison results in a mismatch, the mobile terminal requests a change of TA to the core network (EPC) (including MME, etc.) via the cell to perform a Tracking Area Update (TAU). The core network updates the TA based on the mobile terminal's identification number (e.g., UE-ID) sent from the mobile terminal along with the TAU request signal. After updating the TA, the core network transmits a TAU acceptance signal to the mobile terminal. The mobile terminal rewrites (updates) the TAC (or TAC list) that it holds with the TAC of the cell, and then enters standby mode in the cell.

[0042] The introduction of Closed Subscriber Group (CSG) cells is being considered for LTE and Universal Mobile Telecommunication System (UMTS). As mentioned above, access is permitted only to one or more mobile terminals registered with a CSG cell. A CSG cell and one or more registered mobile terminals constitute a single CSG. Each CSG configured in this way is assigned a unique identification number called a CSG-ID. Note that a single CSG may have multiple CSG cells. A mobile terminal can register with one CSG cell and access other CSG cells in the CSG to which that CSG cell belongs. Home-eNBs in LTE and Home-NBs in UMTS may also be used as CSG cells. A mobile terminal registered with a CSG cell has a whitelist. Specifically, the whitelist is stored in the SIM / USIM. The whitelist contains CSG information for the CSG cells to which the mobile terminal has registered. Specific examples of CSG information include CSG-ID, Tracking Area Identity (TAI), and TAC. As long as the CSG-ID and TAC are associated, either one is sufficient. Furthermore, a Global Cell Identity (GCI) may be used as long as it is associated with a CSG-ID or TAC. Therefore, a mobile terminal that does not have a whitelist (which in the present disclosure includes a case where the whitelist is empty) cannot access a CSG cell and can only access non-CSG cells. On the other hand, a mobile terminal that has a whitelist can access both a CSG cell with a registered CSG-ID and a non-CSG cell.

[0043] In 3GPP, there is discussion about dividing all PCIs (Physical Cell Identities) into those for CSG cells and those for non-CSG cells (referred to as PCI split) (Non-Patent Document 5). There is also discussion about PCI split information being broadcast from a base station to mobile terminals under its control in system information. The basic operation of a mobile terminal using PCI split will be disclosed. A mobile terminal that does not have PCI split information needs to perform a cell search using all PCIs (for example, using all 504 codes). On the other hand, a mobile terminal that has PCI split information can perform a cell search using the PCI split information.

[0044] When a CSG cell is introduced, for example, an HNB / HeNB may be operated as a CSG cell in closed access mode, and the CSG cell may be installed within the coverage of a macro cell. In such a case, interference occurs between the macro cell and the CSG cell within the CSG coverage, causing a problem in which a mobile terminal that is not registered with the CSG cell is unable to communicate with the macro cell due to interference from the CSG cell. Similarly, if a mobile terminal communicating with a CSG cell cannot handover to the macro cell (eNB), the communication may be rendered impossible. Generally, when interference power from other cells becomes large within the coverage of a certain cell, the mobile terminal is able to perform handover (HO) or cell reselection to the other cell or another appropriate cell to prevent communication from being interrupted. However, if the mobile terminal is unable to perform handover or reselection to the other cell, the interference power from the other cell increases, causing a problem in which communication is interrupted.

[0045] Non-Patent Document 8 describes a method of operating an HNB / HeNB that is a CSG cell with adaptive output. However, with this method, there are still areas where interference between the CSG cell and the macro cell is large, and mobile terminals that move into such areas are unable to communicate, so the above problem remains unresolved. In order to resolve these problems, the present disclosure discloses a method of preventing overlapping of physical resources for signals that cannot be scheduled between cells. In the first embodiment, for example, the time (timing) or frequency of physical resources onto which signals that cannot be scheduled are mapped, or both, are prevented from overlapping between cells.

[0046] In a mobile communication system, there are signals that can be scheduled, such as by changing the timing or frequency of the physical resources to which the signals are mapped, and conversely, signals that cannot be scheduled, such that the timing or frequency of the physical resources to which the signals are mapped is predetermined for the system. When the coverage areas of multiple cells overlap, signals transmitted from other cells can cause interference to the cell in question. In this case, for signals that can be scheduled, the base station can avoid interference from other cells by scheduling the signals, such as by dynamically or semi-statically mapping the signals to physical resources, so as to avoid interference from other cells. However, for signals that cannot be scheduled, the physical region to which the signals are mapped is predetermined, so the base station cannot map the signals to physical resources so as to avoid interference from other cells, and therefore, there are cases where interference cannot be avoided.

[0047] For example, there is a signal that is mapped to a specific subframe in a radio frame in a specific frequency region. Because cells are asynchronous, when multiple cells exist, the signal is mapped to physical resources in a specific frequency region and a specific subframe, which can cause the transmission timing of the signals from multiple cells to overlap. As a result, signals from other cells interfere with the signal from the cell itself. This interference can cause a mobile terminal to be unable to receive signals from the desired cell.

[0048] Therefore, in this embodiment, an offset is provided in the time domain so that the physical resources to which non-schedulable signals are mapped do not overlap between cells. An example of the offset is an offset of n subframes in subframe units. LTE is shown as an example. FIG. 15 shows the frame structure and non-schedulable signals in LTE. Reference numeral 1501 denotes the primary synchronization signal (P-SS), 1502 denotes the secondary synchronization signal (S-SS), and 1503 denotes the physical broadcast channel (PBCH). The PBCH carries broadcast information. As described above, in LTE, downlink synchronization signals (P-SS, S-SS) are mapped to the first (#0) and sixth (#5) subframes of each radio frame, and the PBCH is mapped to the first (#0) subframe of each radio frame. Furthermore, the frequency domain to which the synchronization signals and PBCH are mapped is determined to be 1.08 MHz, the center of the cell frequency band, in all cells. Therefore, these signals (P-SS, S-SS, PBCH) in LTE are non-schedulable signals.

[0049] Next, we will discuss the case where the coverage of multiple cells overlaps. As an example, Figure 16 shows the frame configuration of two cells (cell #1 and cell #2). In Figure 16, 1601 is the primary synchronization signal (P-SS), 1602 is the secondary synchronization signal (S-SS), and 1603 is the physical broadcast channel (PBCH). Since they are in the same system, the two cells have the same frame configuration. However, because the cells are asynchronous, the transmission timing differs from cell to cell. Therefore, the transmission timing at which the radio frame begins (the transmission timing at which subframe #0 begins) differs from cell to cell. If the two transmission timings are offset as shown in the figure, some of the physical resources onto which PBCH 1603 is mapped will be transmitted at the same time. Since the frequency domain of the physical resources onto which PBCH 1603 is mapped is also predetermined and cannot be scheduled, if the coverage of these two cells overlap, the physical resources transmitted simultaneously will interfere with each other. If a mobile terminal served by cell #1 moves into an area where the coverage of cell #1 and cell #2 overlap, the PBCH of cell #1 received by the mobile terminal will be interfered with by the PBCH transmitted from cell #2. Depending on the received power of the PBCH of cell #1 and the interference power of the PBCH from cell #2, the PBCH of cell #1 will not be received. The PBCH is a signal that carries information necessary for communication with the cell, such as system information. Therefore, a mobile terminal that cannot receive this signal will not be able to communicate with the cell.

[0050] FIG. 17 shows an example of a case where an n-subframe offset is provided in the physical resources onto which non-schedulable signals are mapped, as disclosed in this embodiment. In this example, n=2. In FIG. 17, 1701 denotes a primary synchronization signal (P-SS), 1702 denotes a secondary synchronization signal (S-SS), and 1703 denotes a physical broadcast channel (PBCH). Cells are synchronized so that the start timing of the radio frames of cell #1 (first cell) and cell #2 (second cell) is the same. By synchronizing cells where interference is a problem, it is possible to align the frame timing of each cell, thereby enabling the transmission timing of desired transmission signals for each cell to be coordinated. A method of synchronizing cells where interference is a problem is disclosed in embodiment 3. In cell #1, downlink synchronization signals (P-SS, S-SS) are mapped to subframe #0 (first subframe) and subframe #5 (second subframe) for each radio frame, as in the conventional case, and the PBCH is mapped to subframe #0 (first subframe) for each radio frame. Unlike conventional techniques, in cell #2, downlink synchronization signals (P-SS, S-SS) are mapped to subframe #2 (third subframe) and subframe #7 (fourth subframe) in each radio frame, and the PBCH is mapped to subframe #2 in each radio frame. In other words, an offset is provided between the cells, and cell #2 transmits synchronization signals and PBCH in subframes that are offset from cell #1. In this way, by providing an offset in the time domain of the physical resources onto which signals that cannot be scheduled in two interference-prone cells are mapped, the transmission timings of the signals from the two cells do not overlap, thereby preventing the signals from interfering with each other. Therefore, even if handover or cell reselection between the two cells is not possible, a mobile terminal can receive these signals that cannot be scheduled.

[0051] In the above example, the offset set for the physical resource onto which the non-schedulable signal is mapped is set in subframe units, but it may also be set in time units, symbol units, or slot units. When set in time units, symbol units, or slot units, the offset amount can be set for each unit, which has the effect of enabling more detailed adjustments to prevent overlapping of transmission timings depending on the unit. However, when the offset is set in time units, symbol units, or slot units, the configuration within the subframe will differ for each cell. When the offset is set in subframe units as disclosed in the above example, it is not necessary to change the configuration of the physical resource onto which the non-schedulable signal within the subframe is mapped for each cell, which simplifies system control, avoids complexity in the control circuitry in the base station or mobile terminal, and enables lower power consumption.

[0052] The offset value may be predetermined or may be changed semi-statically. Alternatively, several offset values ​​may be predetermined, and one cell (e.g., cell #2 in the example of FIG. 17) may select one from among them. For example, when a CSG cell is installed within the coverage of a macrocell (eNB), the macrocell may have a conventional frame configuration, and an offset may be set for the CSG cell. This allows the macrocell's frame configuration to remain conventional, and only the CSG cell in question needs to have an offset, resulting in fewer cells requiring an offset. Alternatively, the offset may be set in a cell to be installed later. For example, when a CSG cell is installed within the coverage of a macrocell (eNB), the above offset is set in the frame configuration of the CSG cell. This allows the frame configuration of the first installed cell (here, the macrocell) to use a conventional frame configuration, reducing the number of offsets. This results in the effect of enabling mobile terminals and base stations to receive synchronization signals and PBCH signals without increasing the complexity of the receiving circuits or power consumption of these signals.

[0053] At the transmission timing of the physical resource to which the synchronization signal or PBCH of cell #1 is mapped, a schedulable signal is mapped to the physical resource in cell #2. Therefore, to avoid interference with the synchronization signal or PBCH of cell #1, appropriate scheduling can be performed in cell #2, such as avoiding scheduling of control signals or data, at the transmission timing of cell #1. This makes it possible to eliminate or reduce interference with the synchronization signal or PBCH of cell #1, thereby ensuring communication in cell #1. The same applies to the transmission timing of the physical resource to which the synchronization signal or PBCH of cell #2 is mapped.

[0054] For example, assume that the CSG cell is installed within the coverage of the macro cell. If a mobile terminal that is communicating with the macro cell and not registered with the CSG cell moves into the coverage of the CSG cell, the mobile terminal cannot handover to the CSG cell. Therefore, in order for the mobile terminal to communicate, it must be able to receive unschedulable signals from the macro cell. Therefore, to eliminate interference from the CSG cell, the above method is applied. The CSG cell avoids scheduling control signals, data, etc. at the transmission timing of the unschedulable signals of the macro cell. This allows the mobile terminal to receive the unschedulable signals of the macro cell and enable communication with the macro cell. Meanwhile, even at the transmission timing of the physical resources to which the CSG cell's synchronization signal or PBCH is mapped, the macro cell maps schedulable signals to the physical resources. If handover from the CSG cell to the macro cell is possible, there is no need to avoid scheduling control signals, data, etc. at the transmission timing of the macro cell. However, it is preferable not to map control signals or data of mobile terminals with poor communication quality (CQI) at the transmission timing of the macro cell. This is because the poor CQI may be due to interference from a synchronization signal or PBCH transmitted from the CSG cell. Therefore, a mobile terminal with poor CQI may be located within or near the coverage of the CSG cell. Furthermore, the macro cell transmits a PDSCH with high transmission power to a mobile terminal with poor CQI. This increases interference with the synchronization signal or PBCH of the CSG cell. To prevent this from happening, it is preferable not to map control signals or data of mobile terminals with poor communication quality at the transmission timing of the macro cell.

[0055] By adopting the configuration disclosed in this embodiment, inter-cell interference of non-schedulable signals is reduced, allowing a mobile terminal to receive the signals. This makes it possible to obtain the effect that, when handover or cell reselection to those cells is not permitted, the mobile terminal will not lose communication with those cells. For example, FIG. 18 shows a conceptual diagram of the received signal-to-interference ratio (SIR) at a mobile terminal in a situation where a HeNB operating as a CSG cell is installed within the coverage of a macro cell. FIG. 18(a) shows the SIR in a conventional case. Since FIG. 18(a) is the same as FIG. 13(c), its description will be omitted. On the other hand, by adopting the configuration disclosed in this embodiment, as shown in FIG. 18(b), interference from the CSG cell to non-schedulable signals of an eNB is reduced even in the vicinity of the HeNB, and the SIR of the mobile terminal becomes greater than threshold a, as indicated by the dashed dotted line. Therefore, the mobile terminal can receive the non-schedulable signals and continue communication with the eNB without loss of communication. By adopting the configuration disclosed in this embodiment, as described above, for example, in LTE, when handover-unable cells are arranged in an overlapping manner or when a CSG cell is arranged within a macro cell, the inter-cell interference of signals that cannot be scheduled is reduced, and the mobile terminal is able to receive the signals, making it possible to continue communication with the macro cell without interruption.

[0056] Variation 1. In the first embodiment, it is disclosed that an offset of n subframes is provided so that physical resources onto which unschedulable signals are mapped do not overlap between cells. In this modification, it is disclosed that physical resources of the unschedulable signals do not overlap between cells.

[0057] As mentioned above, in a mobile communication system, there are schedulable signals, which can be scheduled by changing the timing or frequency of the physical resources to which the signals are mapped, and conversely, non-schedulable signals, which are mapped to the timing and frequency of the physical resources to which the signals are mapped in advance for the system. Non-schedulable signals include signals that are mapped to specific symbols in each subframe in a specific frequency domain. For example, in LTE, L1 / L2 control signals such as PDCCH, PHICH, and PCFICH are mapped to physical resources across the entire frequency band (system band) of a cell within the first to third symbols of each subframe. For such signals, the method of providing an n-subframe offset disclosed in the first embodiment cannot be applied. This is because even if signals are transmitted with an n-subframe offset, the L1 / L2 control signals mapped to those subframes will be transmitted simultaneously, resulting in mutual interference. To solve the above problem, in this modification, physical resources of non-schedulable signals are offset so that they do not overlap between cells within a single subframe. As an example of the offset to be provided, an offset of m symbols is used in symbol units.

[0058] FIG. 19 shows the physical resources onto which L1 / L2 control signals are mapped, as determined by 3GPP. L1 / L2 control signals (PDCCH, PHICH, PCFICH) are mapped to the physical resources of the entire cell bandwidth within three symbols from the beginning of each subframe. In the figure, 1901 is the primary synchronization signal (P-SS), 1902 is the secondary synchronization signal (S-SS), and 1903 is the PBCH. 1904 is the L1 / L2 control signal. In this modification, physical resources for signals that cannot be scheduled are prevented from overlapping between cells within a single subframe. For example, in LTE, the L1 / L2 control signals are mapped to symbols excluding the first three symbols from each subframe. FIG. 20 shows an example of mapping to the 10th to 12th symbols in each subframe. 2001 is the primary synchronization signal (P-SS), 2002 is the secondary synchronization signal (S-SS), and 2003 is the PBCH. 2004 indicates the L1 / L2 control signal. The frequency is mapped to the entire bandwidth of the cell. The symbols to be mapped may be any symbols excluding the first three symbols of each subframe. Alternatively, an offset of m symbols may be provided, shifting the symbols from the first symbol by the offset. In the example shown in the figure, m=9. By offsetting the symbols, the mapping method of the L1 / L2 control signal to the physical resources within the three symbols can be made the same as the conventional method. Simply shifting the symbols by the offset amount suffices, resulting in a simplified control method. Furthermore, since only the offset value can be used as a parameter, the control method is simplified. Furthermore, the amount of information required for signaling the offset value between the network side, base station, and mobile terminal can be reduced, thereby improving the signaling efficiency of the system. This also results in the effect of enabling mobile terminals to receive these signals without significantly complicating the L1 / L2 control signal receiving circuitry or increasing power consumption compared to conventional methods.

[0059] As described in the first embodiment, there may be a case where a non-schedulable signal is mapped to a specific symbol in a specific subframe in a radio frame. Therefore, to avoid simultaneous transmission of these signals with L1 / L2 control signals, the specific symbol is excluded from the mapping. In this way, it is possible to avoid interference between a non-schedulable signal that is mapped to the entire bandwidth of a cell (system bandwidth) and a non-schedulable signal that is mapped to a partial frequency band of the cell bandwidth. In LTE, for example, as shown in Figures 19 and 20, a synchronization signal and a PBCH are mapped to 1.08 MHz, which is the center of the band of the fourth to ninth symbols from the beginning. Therefore, to avoid simultaneous transmission of these signals with L1 / L2 control signals, it is preferable to map the signals excluding the fourth to ninth symbols from the beginning.

[0060] FIG. 21 shows an example of a frame configuration between two cells when an m-symbol offset is provided as shown in this modification. To prevent overlap between the physical resources onto which non-schedulable signals are mapped, the physical resources are the first to third symbols at the beginning of the entire bandwidth of each subframe in cell #1 as shown in FIG. 19, and the 10th to 12th symbols at the beginning of the entire bandwidth of each subframe in cell #2 as shown in FIG. 20. That is, cell #2 provides an m-symbol offset from cell #1, mapping the signal to the physical resource with m=9 and transmitting it. Synchronization is achieved between cells so that the start timing of the radio frames of cell #1 and cell #2 are the same. In this way, by providing an m-symbol offset in the transmission timing of the physical resources onto which non-schedulable signals are mapped in two interference-prone cells, and preventing the transmission timing of the signals from the two cells from overlapping, it is possible to prevent the signals from interfering with each other. Therefore, even if handover or cell reselection between the two cells is not possible, a mobile terminal can receive these non-schedulable signals.

[0061] In the above example, the offset set for the physical resource onto which the non-schedulable signal is mapped is set in units of symbols, but it may also be set in units of time or slots. Setting the offset in units of time allows the offset amount to be set for each unit, resulting in the advantage of more precise adjustment to prevent overlapping transmission timing. Setting the offset in units of slots does not allow for fine adjustment, but it does not require changing the slot configuration for each cell, which simplifies system control, avoids complicating the control circuitry in the base station or mobile terminal, and also enables lower power consumption. However, setting the offset in units of slots reduces the number of offset values ​​that can be set. Setting the offset in units of symbols allows for fine adjustment, easy control, and the simultaneous setting of many offset values.

[0062] The offset value may be predetermined or may be changed semi-statically. Alternatively, several offset values ​​may be predetermined, and one cell (e.g., cell #2 in the example of FIG. 21) may select one from among them. For example, when a CSG cell is installed within the coverage of a macrocell (eNB), the macrocell may have a conventional frame configuration, and an offset may be set for the CSG cell. This allows the macrocell's frame configuration to remain conventional, and only the CSG cell in question needs to have an offset, resulting in fewer cells requiring an offset. Alternatively, the offset may be set in a cell to be installed later. For example, when a CSG cell is installed within the coverage of a macrocell (eNB), the offset is set in the frame configuration of the CSG cell. This allows the frame configuration of the first installed cell (here, the macrocell) to use the conventional frame configuration, reducing the number of offsets. This results in the mobile terminal and base station being able to receive these signals without significantly complicating the receiving circuitry for L1 / L2 control signals or increasing power consumption.

[0063] At the transmission timing of the physical resource to which the L1 / L2 control signal of cell #1 is mapped, a schedulable signal is mapped to the physical resource in cell #2. Therefore, to avoid interference with the L1 / L2 control signal of cell #1, appropriate scheduling can be performed in cell #2, such as avoiding scheduling of control signals and data, at the transmission timing of cell #1. This makes it possible to eliminate or reduce interference with the L1 / L2 control signal of cell #1, thereby ensuring communication in cell #1. The same applies to the transmission timing of the physical resource to which the L1 / L2 control signal of cell #2 is mapped. For example, assume that the CSG cell is installed within the coverage of the macro cell. If a mobile terminal communicating with the macro cell and not registered with the CSG cell moves into the coverage of the CSG cell, the mobile terminal cannot handover to the CSG cell. Therefore, in order for the mobile terminal to be able to communicate, it must be able to receive non-schedulable signals from the macro cell. Therefore, the above method is applied to eliminate interference from the CSG cell. At the transmission timing of a signal that cannot be scheduled by the macrocell, the CSG cell avoids scheduling control signals, data, etc. This allows the mobile terminal to receive the signal that cannot be scheduled by the macrocell, enabling communication with the macrocell.

[0064] On the other hand, even at the transmission timing of the physical resource to which the L1 / L2 control signal of the CSG cell is mapped, a schedulable signal is mapped to the physical resource in the macro cell. Assuming that handover from a CSG cell to a macro cell is possible, there is no need to avoid scheduling control signals, data, and the like at the transmission timing of the macro cell. However, it is preferable not to map control signals and data of a mobile terminal with poor communication quality (CQI) at the transmission timing of the macro cell. This is because interference from L1 / L2 control signals transmitted from the CSG cell is considered to be a reason for the poor CQI. Therefore, a mobile terminal with poor CQI may be located within or near the coverage of the CSG cell. Furthermore, the macro cell transmits a PDSCH with high transmission power to a mobile terminal with poor CQI. This increases interference with the L1 / L2 control signal of the CSG cell. To prevent this from happening, it is preferable not to map control signals and data of a mobile terminal with poor communication quality at the transmission timing of the macro cell.

[0065] By adopting the configuration disclosed in this modification, inter-cell interference of non-schedulable signals is reduced, enabling a mobile terminal to receive the signals. In particular, when a non-schedulable signal is mapped to a specific subframe in a specific frequency region every subframe, applying this modification reduces inter-cell interference of the non-schedulable signal, enabling a mobile terminal to receive the signals. This provides the advantage that, when handover or cell reselection to those cells is not permitted, the mobile terminal will not lose communication with those cells. For example, a conceptual diagram of the signal-to-interference ratio (SIR) received at a mobile terminal in a situation where a HeNB operating as a CSG cell is installed within the coverage of a macrocell is shown in FIG. 18 , similar to the first embodiment described above. As shown in FIG. 18(b), interference from the CSG cell to non-schedulable signals from an eNB is reduced even in the vicinity of the HeNB, and the SIR of the mobile terminal becomes greater than threshold a, as indicated by the dashed-dotted line. Therefore, the mobile terminal can receive the non-schedulable signal, enabling continuous communication with the eNB without loss of communication. By adopting the configuration disclosed in this embodiment, as described above, for example, in LTE, when handover-unavailable cells are arranged in an overlapping manner or when a CSG cell is arranged within a macro cell, the inter-cell interference of signals that cannot be scheduled is reduced, and the mobile terminal is able to receive the signals, making it possible to continue communication with the macro cell without interruption.

[0066] When there are both non-schedulable signals that are mapped to a specific subframe in a radio frame in a specific frequency region and signals that are mapped to a specific symbol in every subframe in a specific frequency region, a method is disclosed for preventing the physical resources of the non-schedulable signals from overlapping between cells within a single subframe in order to prevent the signals from interfering with each other. In this case, the method disclosed in the first embodiment and the method disclosed in the first modification may be combined. For signals that are mapped to a specific subframe in a radio frame in a specific frequency region, an n-subframe offset is provided so that the physical resources to which the signals are mapped do not overlap between cells. For signals that are mapped to a specific symbol in every subframe in a specific frequency region, the physical resources of the signals are not overlapped between cells within a single subframe. Furthermore, the physical resources of the signals are not overlapped with the physical resources of signals mapped to a specific subframe in a radio frame.

[0067] For example, in LTE, the mapping of signals within a subframe is as shown in Figures 19 and 20. Synchronization signals (P-SS, S-SS) and PBCH, which are signals mapped to specific subframes within a radio frame in a specific frequency domain, are mapped to the same symbols in both configurations. To prevent interference between cells, these signals are provided with an offset in the subframes to which they are mapped. For L1 / L2 control signals, which are signals mapped to specific symbols in each subframe across the entire frequency domain of a cell, the physical resources of these signals are not overlapped between cells within a single subframe. Furthermore, they are not overlapped with the symbols in a specific subframe to which the synchronization signal and PBCH are mapped. Figure 20 shows, for example, a case where a 9-symbol offset is provided.

[0068] An example frame configuration is shown in Figure 22. Physical resources onto which non-schedulable signals are mapped are made to not overlap between cells. In cell #1, as shown in Figure 19, L1 / L2 control signals are mapped to the first through third symbols from the beginning of the entire bandwidth of every subframe, while synchronization signals (P-SS, S-SS) and PBCH are mapped to the fourth through ninth symbols from the beginning. Synchronization signals (P-SS, S-SS) and PBCH are mapped to subframe #0 rather than every subframe, and synchronization signals (P-SS, S-SS) are further mapped to subframe #5. In cell #2, as shown in Figure 20, L1 / L2 control signals are mapped to the tenth through twelfth symbols from the beginning of every subframe, while synchronization signals (P-SS, S-SS) and PBCH are mapped to the fourth through ninth symbols from the beginning, the same as in cell #1. However, unlike cell #1, the synchronization signals (P-SS, S-SS) and PBCH are mapped to subframe #2, and the synchronization signal is further mapped to subframe #7. In other words, non-schedulable signals mapped to every subframe are offset by m symbols within the subframe, and non-schedulable signals mapped to a specific subframe are offset by n subframes within the radio frame, and are each mapped to physical resources and transmitted.

[0069] The cells are synchronized so that the transmission timings of the radio frames of cell #1 and cell #2 are the same. This prevents the transmission timings of the non-schedulable signals from the two cells from overlapping, making it possible to prevent the signals from interfering with each other. Therefore, even if handover or cell reselection between the two cells is not possible, the mobile terminal can receive these non-schedulable signals. The offset value may be determined using the methods disclosed in the first embodiment or this modification. Furthermore, when a non-schedulable signal is transmitted from one cell, the method of transmitting a signal from another cell may be determined using the methods disclosed in the first embodiment or this modification.

[0070] By using the method disclosed above, even in a communication system in which there are both signals that cannot be scheduled, such as a signal that is mapped to a specific subframe in a radio frame in a specific frequency region and a signal that is mapped to a specific symbol in every subframe in a specific frequency region, the signals can be prevented from interfering with each other and the mobile terminal can receive the signals, thereby enabling communication with the macro cell to continue without being interrupted. This method makes it possible to support a wider variety of frame configurations.

[0071] Variation 2. In the first embodiment and the first modification, we have disclosed that an offset of n subframes or a predetermined number of symbols within one subframe is provided so that the physical resources onto which non-schedulable signals are mapped do not overlap between cells. In other words, this means that cells with different frame configurations exist within a certain system. This results in more complex transmission and reception circuits in base stations and mobile terminals than in a system with only one frame configuration, and also increases the amount of information signaled between the network side, base stations, and mobile terminals. For example, if there are two frame configurations, the base station and mobile terminal must configure transmission and reception circuits compatible with these two frame configurations. This increases the circuit complexity and leads to increased power consumption. Furthermore, signaling is required between the network side, base stations, and mobile terminals to determine the frame configuration used by each cell. This increases the amount of signaling and reduces signaling efficiency. To solve this problem, this modification discloses that the physical resources of the non-schedulable signals do not overlap between cells, and the system has a single frame configuration.

[0072] FIG. 23 shows an example of symbol mapping within a subframe in this modification. A non-schedulable signal mapped within each subframe in a specific frequency domain is mapped to the first, third, and fifth symbols. It is not necessary to map the signal to all three symbols; it is sufficient to map the signal within these three symbols. A non-schedulable signal mapped to a specific subframe in a specific frequency domain is mapped to the seventh to twelfth symbols from the beginning. Furthermore, in a specific subframe within a radio frame, as shown in FIG. 23, a synchronization signal and a PBCH are mapped to 1.08 MHz, which is the center of the band from the seventh symbol to the twelfth symbol from the beginning. For example, in LTE, L1 / L2 control signals (PDCCH, PHICH, PCFICH) are mapped to the first, third, and fifth symbols from the beginning of each subframe. In the figure, 2301 denotes a primary synchronization signal (P-SS), 2302 denotes a secondary synchronization signal (S-SS), and 2303 denotes a PBCH. 2304 denotes the PDCCH among the L1 / L2 control signals. This allows all cells in the system to use only one frame structure and prevents the physical resources of non-schedulable signals from overlapping between cells.

[0073] FIG. 24 shows the transmission timing between two cells when all cells in the system use a single frame configuration, as disclosed in this modification. To prevent overlapping between cells in the physical resources to which non-schedulable signals are mapped, a subframe configuration such as that shown in FIG. 23 is used, and cell #2 transmits with a time interval td offset from cell #1. td may be expressed in symbol units. In FIG. 24, for example, the time is 15 symbols (1 subframe and 1 symbol). By using the subframe configuration shown in FIG. 23 and shifting the transmission timing by one symbol between cells, non-schedulable signals mapped to the same symbol in each subframe are prevented from being transmitted simultaneously when two cells use the same frame configuration. Furthermore, as shown in FIG. 24, shifting the transmission timing by one subframe prevents non-schedulable signals mapped to a specific subframe in a radio frame from being transmitted simultaneously. Therefore, as shown in Figure 24, by setting td to, for example, a time equivalent to 15 symbols (1 subframe and 1 symbol), it is possible to prevent any non-schedulable signals from being transmitted simultaneously from two cells.

[0074] This makes it possible to prevent the unschedulable signals from interfering with each other. Therefore, even if handover or cell reselection between two cells is not possible, a mobile terminal can receive these unschedulable signals. The offset value, which is the time interval for shifting, is not limited to 15 symbols. For example, in the case of the subframe configuration shown in FIG. 23, it can be 29 symbols, 43 symbols, etc. Furthermore, in addition to the subframe configuration shown in FIG. 23, for example, unschedulable signals mapped in every subframe in a specific frequency region can be mapped to the 8th, 10th, and 12th symbols from the beginning, and unschedulable signals mapped in a specific subframe in a specific frequency region can be mapped to the 1st to 6th symbols from the beginning. In this case, td can be set to, for example, 13 symbols. That is, when one frame configuration is transmitted with a certain time shift, it is sufficient that the transmission timings of the unschedulable signals do not overlap. The offset value may be determined using the methods disclosed in the first embodiment or the first modification. Furthermore, the method for transmitting a signal from another cell at the transmission timing of the unschedulable signal in a certain cell may also be determined using the methods disclosed in the first embodiment or the first modification.

[0075] By using the method disclosed above, it is possible to obtain the same effects as in embodiment 1 and variant 1, and since it is possible to have a single frame configuration as a system, it is possible to solve the problem of the transmission and reception circuits in base stations and mobile terminals becoming complex, and further, it is possible to solve the problem of the increase in the amount of information signaled on the network side, between base stations and mobile terminals.

[0076] In this modification, we have shown that by providing an offset in the transmission timing between cells so that non-schedulable signals do not overlap between cells where interference is a problem, it is not necessary to change the frame configuration or the symbol configuration within a subframe for each cell. This modification can also be applied to the case where the non-schedulable signals shown in the first embodiment are mapped to a specific subframe in a specific frequency domain. For example, instead of providing an offset between cells in the subframe to which the non-schedulable signals are mapped, it is possible to keep the frame configuration the same between cells and provide an offset in the transmission timing for transmission. This suffices because only one frame configuration is required, which simplifies system control, simplifies the configuration of the transmission and reception circuits in the base station or mobile terminal, and enables reductions in control delay and power consumption.

[0077] The unit of the transmission timing offset may be time, symbol, slot, or subframe. When the unit is time, symbol, or slot, an offset amount can be set for each unit, resulting in the effect of enabling more precise adjustments to prevent overlapping of transmission timings according to the unit. This modification is also applicable to the case where a non-schedulable signal, as shown in Modification 1, is mapped to each subframe in a specific frequency domain. For example, instead of providing an offset between cells for the symbol onto which the non-schedulable signal is mapped and transmitting, it is possible to transmit the signal by providing an offset to the transmission timing while keeping the symbol configuration within the subframe the same between cells. This allows for a single symbol configuration within the subframe, simplifying system control, simplifying the configuration of the transceiver circuits in the base station or mobile terminal, and enabling reduced control delay and power consumption. The unit of the transmission timing offset may be time, symbol, or slot. When the unit is time, an offset amount can be set for each unit, resulting in more precise adjustments to prevent overlapping of transmission timings. When using symbol units or slot units, fine adjustments are not possible, but the adjustment control is simplified, which has the effect of preventing the control circuit in the base station or mobile terminal from becoming complicated and also enabling low power consumption.

[0078] Variation 3. In the first embodiment to the second modification, in order to prevent overlap between cells of physical resources for non-schedulable signals, the transmission times (timings) of physical resources onto which non-schedulable signals are mapped are made to not overlap between cells. Simply preventing overlap between the transmission timings between cells results in a limited number of frame configuration patterns and time interval patterns for shifting the transmission timing. To increase the number of patterns, an offset is also provided in frequency to prevent overlap between cells of physical resources onto which non-schedulable signals are mapped. Non-Patent Document 8 discloses a partially shared channel operation in which the physical resources onto which the signals are mapped on the frequency axis are made different for each cell in order to prevent overlap between synchronization signals and PBCHs between multiple cells. This is an operation method in which the frequencies used by the HNB / HeNB are made part of the frequencies used by a macrocell (NB or eNB), and the frequency domain onto which the synchronization signals and PBCH of the HNB / HeNB are mapped is made different from the frequency domain onto which the synchronization signals and PBCH of the macrocell are mapped. However, Non-Patent Document 8 does not include the concept of non-schedulable signals, nor does it mention the existence of non-schedulable signals that are mapped across the entire frequency band of a cell. It also does not mention providing a frequency offset, much less how to set the offset in each cell. If a signal is mapped across the entire frequency band of a cell, even if the frequency domains in which only the synchronization signal and the PBCH are mapped are different between multiple cells as shown in Non-Patent Document 8, the non-schedulable signals mapped across the entire frequency band of a cell will overlap between multiple cells. Therefore, operation using the partially shared channel method described in Non-Patent Document 8 alone cannot prevent increased interference between cells, and mobile terminals will be unable to receive non-schedulable signals mapped across the entire frequency band, resulting in communication being cut off.

[0079] To solve these problems, in this variant, for signals that cannot be scheduled and are mapped to a portion of the frequency range of a cell, the frequency range is made to not overlap between cells, and for signals that cannot be scheduled and are mapped across the entire frequency band of a cell, the transmission times (timings) of the physical resources to which the signals are mapped are made to not overlap between cells.

[0080] A first method for preventing overlap between cells of signals that cannot be scheduled but are mapped to a portion of a cell's frequency range is to make the entire frequency band of the cells the same but make the frequency ranges different. For example, in cell #1 and cell #2, which have a frequency band of 20 MHz, the frequency range of cell #1 is set to 1.08 MHz, which is the center of the entire cell band, and the frequency range of cell #2 is set to 1.08 MHz from the lower frequency end of the cell. This makes it possible to prevent overlap between the frequency ranges regardless of the transmission timing, thereby preventing increased interference between cells due to the signals. Furthermore, since the entire frequency band of the cells can be made the same, the widest frequency bandwidth permitted by the system can be applied to the cells, enabling high-capacity communications.

[0081] As a second method, the total bandwidth of the cells is made different, and the center frequency (carrier) of the cells is made different so that the frequency ranges between the cells do not overlap. For example, the frequency ranges of both cells in cell #1 and cell #2 are set to 1.08 MHz, the center of the cell's total band. Then, the total bandwidth of cell #1 is set to 20 MHz, and the total bandwidth of cell #2 is set to 10 MHz. Then, the center frequency (carrier) of cell #1 and the center frequency (carrier) of cell #2 are made to differ by 5 MHz. By doing this, it is possible to prevent the frequency ranges from overlapping regardless of the transmission timing, and it is possible to prevent increased interference between the cells due to the signals.

[0082] As a third method, the total bandwidth of the cells is made different, and the center frequency (carrier) of the cells is made different so that the frequency ranges of the cells do not overlap, and the frequency band of one cell is made different from the frequency range of another cell. For example, in cell #1 and cell #2, the frequency ranges of both cells are set to 1.08 MHz, the center of the total bandwidth of the cells. Then, the total bandwidth of cell #1 is set to 20 MHz, and the total bandwidth of cell #2 is set to 5 MHz. Then, the center frequency (carrier) of cell #1 and the center frequency (carrier) of cell #2 are made to differ by 5 MHz. This not only achieves the effects described above, but also makes it possible to prevent overlapping between non-schedulable signals mapped across the entire frequency band of one cell and non-schedulable signals mapped to the frequency range of another cell, regardless of the transmission timing, thereby preventing an increase in interference between cells.

[0083] Although the above-mentioned method has been shown as an example of two cells, this method can also be used in the case of three or more cells. For example, in the third method, the frequency bandwidth of cell #1 is set to 20 MHz, the frequency bandwidth of cells #2 and #3 is set to 5 MHz, and the center frequency of cell #2 is set to differ from cell #1 by -5 MHz, and the center frequency of cell #2 is set to differ from cell #1 by +5 MHz.

[0084] However, in some systems, non-schedulable signals include not only signals mapped to a portion of the frequency range of a cell, but also signals mapped across the entire frequency band of the cell. In such cases, the method disclosed above alone cannot prevent non-schedulable signals mapped across the entire frequency band of a cell from overlapping between cells. Therefore, when the coverage areas of multiple cells overlap, interference caused by non-schedulable signals mapped across the entire frequency band between the cells increases, making it impossible for mobile terminals to receive the signals and resulting in communication being cut off. To solve this problem, for non-schedulable signals mapped across the entire frequency band of a cell, the transmission times (timings) of the physical resources to which the signals are mapped are made to not overlap between cells. As a method for this, the methods disclosed in the first embodiment, the first modification, and the second modification can be applied.

[0085] Figure 25 shows a method for mapping symbols within one subframe in this modification. The total bandwidth of each cell is made different, and the frequency domains of signals that cannot be scheduled and are mapped to a portion of the cell's frequency domain are made non-overlapping between cells, so that the frequency domain of one cell is made different from that of the other cell. For example, in cell #1 and cell #2, the frequency domains of both cells are set to 1.08 MHz, the center of the cell's total bandwidth. The total bandwidth of cell #1 is set to 20 MHz, and the total bandwidth of cell #2 is set to 5 MHz. The center frequency (carrier) of cell #1 and the center frequency (carrier) of cell #2 are made to differ by 5 MHz. For example, in LTE, the non-schedulable signals that are mapped to a portion of the cell's frequency domain include a synchronization signal and a PBCH. 2501 is a P-SS, 2502 is an S-SS, and 2503 is a PBCH. As shown in the figure, these signals are mapped to the fourth through ninth symbols from the beginning of a specific subframe.

[0086] By doing this, it is possible to prevent overlapping of the frequency domains of signals that cannot be scheduled and are mapped to part of the frequency domain of a cell between cells. Signals that are mapped across the entire frequency band of a cell are mapped within the third symbol from the beginning of each subframe. In LTE, for example, an L1 / L2 control signal is an example of a signal that is mapped across the entire frequency band of a cell. In the figure, 2504 is the L1 / L2 control signal. Cell #1 and cell #2 have the same frame structure. This alone does not prevent overlapping of signals that are mapped across the entire frequency band of a cell between cells.

[0087] Figure 26 shows the transmission timing between two cells when the above-described intra-subframe symbol mapping method is used. In the figure, 2601 denotes P-SS, 2602 denotes S-SS, 2603 denotes PBCH, and 2604 denotes L1 / L2 control signals. To prevent overlapping of non-schedulable signals mapped across the entire frequency band between cells, cell #2 transmits with a time offset of td relative to cell #1. td may be measured in symbol units. In Figure 26, for example, a time equivalent to three symbols is used. This prevents overlapping of non-schedulable signals mapped across the entire frequency band between cells, as shown in the figure. Although the transmission timing of signals mapped to some frequency domains of cells may overlap between cells, these signals are mapped to different frequency domains between cells, resulting in no overlap between cells. Therefore, even if two cells have the same frame structure, non-schedulable signals from the two cells will not be transmitted in the same frequency-time domain. This makes it possible to prevent mutual interference between the non-schedulable signals. The mobile terminal will be able to receive these non-schedulable signals even if handover or cell reselection between the two cells is not possible.

[0088] Even if the transmission timings of signals mapped to some frequency domains of cells overlap between cells, the signals will not overlap between cells because the frequency domains to which they are mapped are different between cells. Therefore, there is no need to prevent overlap between cells for the signals. Furthermore, the signals and non-schedulable signals mapped across the entire frequency band will also not overlap between cells. As a result, it is possible to increase the number of patterns that prevent overlapping transmission of non-schedulable signals from multiple cells. Therefore, even if the number of cells where interference is a problem increases, by increasing the number of patterns, it is possible to prevent overlapping transmission of non-schedulable signals from multiple cells, and a mobile terminal will be able to receive these non-schedulable signals even if handover or cell reselection between multiple cells is not possible.

[0089] The methods disclosed in the first embodiment, the first modification, and the second modification can be applied as a method for preventing overlap between cells in the transmission times (timings) of physical resources onto which signals mapped across the entire frequency band of a cell are mapped. This provides equivalent effects. The offset value may also be determined using the methods disclosed in the first embodiment, the first modification, and the second modification. Furthermore, at the transmission timing of a signal that cannot be scheduled in a certain cell, the method for transmitting a signal from another cell may also be determined using the methods disclosed in the first embodiment, the first modification, and the second modification. This provides equivalent effects.

[0090] In FIG. 25 , the total bandwidths of the cells are made different, and the frequency domains of signals that cannot be scheduled and are mapped to a portion of the frequency domain of the cells do not overlap between the cells, so that the frequency band of one cell is different from the frequency domain of another cell. However, other methods, such as making the total frequency bands of the cells the same and making the frequency domains different, may also be used. This allows for a larger cell bandwidth, thereby enabling higher-capacity communication. In the method of making the total bandwidths of the cells different and making the frequency domains of signals that cannot be scheduled and are mapped to a portion of the frequency domain of the cells not overlap between the cells, the frequency offset may be the frequency difference between the center frequencies (carriers) of the cells. Also, in the method of making the total frequency bands of the cells the same and making the frequency domains different, the frequency offset may be the frequency difference between the center frequencies of the frequency domains of the cells. The frequency offset value may be set based on the center frequency of one of the cells. By using the frequency difference between the cells as the offset value, it is possible to obtain the effect that signaling between the network, base stations, and mobile terminals can be performed with a small amount of information when setting or changing the offset value. Furthermore, the methods for setting the subframe and symbol offset values ​​and the transmission timing offset values ​​disclosed in the first embodiment, the first modification, and the second modification can also be applied to these frequency offsets. This makes it possible to obtain the same effect. In practice, these frequency offset values ​​can be determined by taking into consideration the frequencies (frequency rasters) that can be taken by carriers in the system, the subcarrier frequencies in the case of OFDMA (for example, 15 kHz in the case of LTE), and the like.

[0091] The method disclosed in this modification can achieve the same effects as those described in the first to second embodiments, and can also increase the number of patterns that prevent overlapping transmission of non-schedulable signals from multiple cells. Therefore, even if the number of cells in which interference is a problem increases, increasing the number of patterns can prevent overlapping transmission of non-schedulable signals from multiple cells. Even if handover or cell reselection between multiple cells is not possible, a mobile terminal can receive these non-schedulable signals. For example, when multiple CSG cells are installed within the coverage of a macro cell, interference between the CSG cells can become a problem. Furthermore, even if the macro cell and the CSG cell each use a separate dedicated channel (frequency), interference between the CSG cells can become a problem if multiple CSG cells are installed. In such cases, applying the method described in this modification can prevent overlapping transmission of non-schedulable signals from those cells. Therefore, even if handover or cell reselection between multiple cells is not possible, a mobile terminal can receive these non-schedulable signals, enabling communication.

[0092] In the present disclosure, an example has been described in which the number of symbols in one subframe is 14. However, the number of symbols in one subframe does not have to be 14 and may be another value. For example, the number of symbols may be determined by the following relational expression: The number of symbols required for signals that are mapped to each subframe among non-schedulable signals is set to x. The number of symbols required for signals that are mapped to each subframe among non-schedulable signals is set to y. Furthermore, the transmission timings of physical resources for non-schedulable signals are set to not overlap among z cells. In this case, the number of symbols in one subframe may be determined by the following relational expression (1) ns≧x*z+y.

[0093] By using this relational expression, it is possible to provide a z-pattern frame structure for the system in the first embodiment or the first modification, and to provide a z-pattern time offset in the second modification. Therefore, it is possible to prevent the transmission timings of physical resources of signals that cannot be scheduled from overlapping among z cells. For example, in a case where two CSG cells are installed within the coverage of a macro cell and the coverages of the two CSG cells also overlap, by setting z=3 and setting the number of symbols in a subframe to a value that satisfies the above relational expression, it is possible to prevent the transmission timings of physical resources of signals that cannot be scheduled from overlapping among the three cells. This makes it possible to reduce interference between a large number of cells where handover is not possible, thereby achieving the effect of enabling communication between a mobile terminal and the cells.

[0094] Variation 4. As disclosed in Non-Patent Document 12, 3GPP is currently developing the Long Term Evolution Advanced (LTE-A) standard as Release 10. The LTE-A system is expected to support frequency bandwidths larger than the transmission bandwidths of the LTE system (Chapter 5 of Non-Patent Document 12). Therefore, an LTE-A-compatible mobile terminal is expected to simultaneously receive one or multiple component carriers (CCs). An LTE-A-compatible mobile terminal is expected to have the capability to simultaneously receive and transmit, or only receive, or only transmit on multiple component carriers, i.e., carrier aggregation.

[0095] FIG. 42 is a conceptual diagram of the frequency band configuration of the LTE-A system. 4201 in FIG. 42 indicates a physical downlink control channel (PDCCH). While FIG. 42 illustrates an example in which the physical downlink control channel is mapped to each of all component carriers, this is not a limitation. As another example, there may be a mixture of component carriers to which the physical downlink control channel is mapped and component carriers to which the physical downlink control channel is not mapped. 4202, 4203, 4204, 4205, and 4206 indicate a downlink synchronization signal (SS) and a physical broadcast channel (PBCH). While FIG. 42 illustrates an example in which the downlink synchronization signal and the physical broadcast channel (or broadcast information) are mapped to each component carrier, this is not a limitation. As another example, there may be a mixture of component carriers to which the downlink synchronization signal and the physical broadcast channel are mapped and component carriers to which the downlink synchronization signal and the physical broadcast channel are not mapped.

[0096] In Figure 42, consider a base station in an LTE-A system with five component carriers, each with a bandwidth of 20 MHz. The carrier frequencies of each component carrier are fa, fb, fc, fd, and fe. In other words, consider a base station with a downlink transmission bandwidth of 100 MHz. The component carrier bandwidth is not limited to 20 MHz, and discussions at 3GPP meetings have suggested that it may be 20 MHz or less. Furthermore, the bandwidth of component carriers supported by a single base station is not limited to one type. Furthermore, discussions at 3GPP meetings have suggested that the downlink transmission bandwidth of a base station in an LTE-A system is not limited to 100 MHz, and may be 100 MHz or less. Furthermore, while Figure 42 shows the case where the component carriers are contiguous, this is not limited to this case, and carrier aggregation is possible on the receiving side even if the component carriers are discontinuous.

[0097] The following three types of component carriers are under consideration (Non-Patent Document 13).

[0098] The first is a backwards compatible carrier, which can be accessed by mobile terminals that support all existing LTE standards.

[0099] The second type is a non-backwards compatible carrier. Such a carrier cannot be accessed by mobile terminals that support existing LTE standards, but is easily accessible to mobile terminals that support the standards that define the non-backwards compatible carrier. If a carrier is non-backwards compatible due to duplex distance, the carrier can operate either stand-alone or as part of a carrier aggregation.

[0100] The third type is an extension carrier. This carrier allows additional resources to be aggregated into one component carrier. A carrier segment is always adjacent to a component carrier. A carrier segment is associated with one component carrier. A carrier segment does not exist independently of a component carrier. A carrier segment does not provide downlink synchronization signals, system information (or broadcast information), or paging signals.

[0101] Figure 43 shows a conceptual diagram of an extension carrier. In Figure 43, 4301 indicates a physical downlink control channel (PDCCH). 4302 and 4303 indicate carrier segments. 4304 indicates a downlink synchronization signal (SS) and a physical broadcast channel (PBCH). As mentioned above, the downlink synchronization signal, system information (or broadcast information), and paging signals are not provided in the carrier segment.

[0102] Non-Patent Document 14 discloses that a newly switched-on base station selects a primary component carrier for downlink transmission when it is switched on, based on interference from neighboring cells, etc. This is for the purpose of interference management.

[0103] The number of component carriers supported by one base station is determined by the downlink transmission bandwidth of the base station and the bandwidth of the component carriers, as shown in Figure 42. In Figure 42, the number of component carriers supported by the base station is five. In this way, there is a limit to the number of component carriers that one base station can support.

[0104] Since the number of component carriers that can be used as substitutes for component carriers with large interference is limited, it is not possible to avoid downlink interference with many surrounding base stations using Non-Patent Document 14. As mentioned above, it is expected that many HeNBs will be installed. Therefore, when many HeNBs are installed under a macrocell using Non-Patent Document 14, the problem of not being able to solve the downlink interference problem arises.

[0105] The solution in this fourth modification is disclosed below. The first embodiment, the first modification of the first embodiment, the second modification of the first embodiment, or the third modification of the first embodiment is used for each component carrier. Alternatively, if a component carrier with a low level of interference exists, a component carrier may be selected based on interference from neighboring cells, and if no component carrier with a low level of interference exists, the first embodiment, the first modification of the first embodiment, the second modification of the first embodiment, or the third modification of the first embodiment may be used for each component carrier.

[0106] A threshold value may be used as a criterion for determining whether to use the first embodiment, the first modification of the first embodiment, the second modification of the first embodiment, or the third modification of the first embodiment. As a specific example of the determination, when there is no component carrier whose interference amount is equal to or less than the threshold (or less), the first embodiment, the first modification of the first embodiment, the second modification of the first embodiment, or the third modification of the first embodiment is used. The threshold value may be determined statically or may be broadcast as system information.

[0107] The following effects can be obtained by this fourth modification. Compared to Non-Patent Document 14, it is possible to increase the number of patterns for avoiding overlapping transmission of unschedulable signals. Therefore, even if the number of cells where interference is a problem increases, it is possible to avoid overlapping transmission of unschedulable signals from multiple cells. By avoiding overlapping transmission of unschedulable signals, as in the first embodiment, etc., a mobile terminal can receive these unschedulable signals even if handover or cell reselection between multiple cells is not possible.

[0108] Variation 5. The method described in the fourth modification of the first embodiment has the following problem. If the frame configuration differs for each component carrier, or if the transmission timing differs for each component carrier, the load for carrier aggregation on the receiving side, i.e., on the mobile terminal, increases. The increased processing load on the mobile terminal leads to the problem of increased power consumption.

[0109] The solution in this fifth modification is disclosed below. The first embodiment, the first modification of the first embodiment, the second modification of the first embodiment, and the third modification of the first embodiment are used for each aggregated carrier that aggregates component carriers that can be used for carrier aggregation, for each node, or for each base station.

[0110] Alternatively, if there is a component carrier with low interference, the component carrier may be selected based on interference from neighboring cells, and if there is no component carrier with low interference, embodiment 1, variant 1 of embodiment 1, variant 2 of embodiment 1, or variant 3 of embodiment 1 may be used for each aggregate carrier, for each node, or for each base station.

[0111] A threshold value may be used as a criterion for determining whether to use the first embodiment, the first modification of the first embodiment, the second modification of the first embodiment, or the third modification of the first embodiment. As a specific example of the determination, when there is no component carrier whose interference amount is equal to or less than the threshold (or less), the first embodiment, the first modification of the first embodiment, the second modification of the first embodiment, or the third modification of the first embodiment is used. The threshold value may be determined statically or may be broadcast as system information.

[0112] In addition to the effects of Modification 4 of Embodiment 1, Modification 5 can provide the following effects. The same frame structure or the same transmission timing is used for each aggregate carrier, etc. This reduces the processing load and power consumption for mobile terminals that perform carrier aggregation.

[0113] Variation 6. This sixth modification discloses a solution for downlink interference avoidance in LTE-A that is different from that in Non-Patent Document 14. In this sixth modification, one node maps an unschedulable signal using a frequency band of physical resources to which the unschedulable signal of the other node is not mapped. Alternatively, one node uses a frequency band of physical resources to which the unschedulable signal of the other node is mapped as a frequency band of physical resources to which the unschedulable signal is not mapped.

[0114] Alternatively, a component carrier may be selected based on interference from neighboring cells, and if there is no component carrier with a small amount of interference, modification 6 may be implemented.

[0115] A node may also be a cell.

[0116] Specific examples of signals that cannot be scheduled in LTE and LTE-A include a synchronization signal (SS), a physical broadcast channel (PBCH), and L1 / L2 control signals such as PDCCH, PHICH, and PCFICH.

[0117] An example of a frequency band of a physical resource to which non-schedulable signals in LTE-A are not mapped is a carrier segment of an extension carrier. Examples of a frequency band of a physical resource to which non-schedulable signals are mapped include the transmission bandwidth of a base station in LTE, a backwards compatible carrier in LTE-A, a non-backwards compatible carrier, and a band to which L1 / L2 control signals in an extension carrier are mapped.

[0118] A specific example of the solution of the sixth modification of the first embodiment will be described using Figure 44. The component carrier configuration within the downlink transmission bandwidth of cell #1 (first cell) will be described. It has extension carrier 1 and backward compatible carriers 1-1 and 1-2. Extension carrier 1 has band 4405 and carrier segments 4401 and 4402 in which L1 / L2 control signals in the extension carrier are mapped. A synchronization signal (SS) and a physical broadcast channel (PBCH) are mapped in band 4405.

[0119] The component carrier configuration within the downlink transmission bandwidth of cell #2 (second cell) will be described. It has backward compatible carrier 2-1 and extension carrier 2. Extension carrier 2 has band 4406, to which L1 / L2 control signals in the extension carrier are mapped, and carrier segments 4403 and 4404. A synchronization signal (SS) and a physical broadcast channel (PBCH) are mapped within band 4406.

[0120] One node (cell #2) maps the non-schedulable signals (PDCCH and SS in FIG. 44) using the frequency bands of physical resources (4401 and 4402 in FIG. 44) to which the non-schedulable signals of the other node (cell #1) are not mapped. Alternatively, one node (cell #2) uses the frequency bands of physical resources (4405 in FIG. 44, backward compatible carrier 1-1) to which the non-schedulable signals of the other node (cell #1) are mapped, as the frequency bands of physical resources (4403 and 4404 in FIG. 44) to which the non-schedulable signals are not mapped.

[0121] In addition to the effects of Modification 4 of Embodiment 1, Modification 6 can provide the following effects. It is possible to separate, in the frequency domain, signals that cannot be scheduled between multiple cells where interference is a problem. This provides the same effects as in Embodiment 1. That is, inter-cell interference of signals that cannot be scheduled is reduced, and mobile terminals can receive these signals. This provides the effect that, when handover or cell reselection to those cells is not permitted, mobile terminals will no longer lose communication with those cells.

[0122] Furthermore, since only one symbol structure is required within a subframe, only one type of receiving and transmitting circuit is required for signals that cannot be scheduled at the mobile terminal and base station, which enables reception and transmission of these signals without increasing complexity or power consumption.Furthermore, since there is no need to synchronize between multiple cells, where interference is a problem, it is possible to avoid complexity in the mobile communication system.

[0123] This variant 6 can be used in combination with embodiment 1, variant 1 of embodiment 1, variant 2 of embodiment 1, variant 3 of embodiment 1, variant 4 of embodiment 1, and variant 5 of embodiment 1.

[0124] Variation 7. In the first embodiment, the first modification of the first embodiment, the third modification of the first embodiment, the fourth modification of the first embodiment, and the fifth modification of the first embodiment, an offset is provided in the time domain for the physical resources onto which an unschedulable signal is mapped. However, in the seventh modification, the same unschedulable signal is mapped in both the original time domain and the time domain with the offset. In other words, the unschedulable signal is transmitted in the original time domain, and a replica of the unschedulable signal is provided in the time domain with the offset. Alternatively, the unschedulable signal may be transmitted in the time domain with the offset, and a replica of the unschedulable signal may be provided in the original time domain. Furthermore, the replica may be transmitted in both of the two cells (cell #1 and cell #2) that cause downlink interference, or may be transmitted in only one of them (only cell #1 or only cell #2).

[0125] Furthermore, the transmission power may be changed between the signal in the original time domain and the signal in the time domain to which an offset is provided.

[0126] A specific example of the time domain of the base in LTE is described below.

[0127] The downlink synchronization signals (P-SS, S-SS) are mapped to the first (#0) and sixth (#5) subframes of each radio frame (see FIG. 15). They are also mapped to the sixth (#5) and seventh (#6) symbols from the beginning of each subframe. Therefore, the original time domain of the downlink synchronization signal is the first (#0) and sixth (#5) subframes of each radio frame. The sixth and seventh symbols from the beginning of each subframe are also the original time domain of the downlink synchronization signal.

[0128] The PBCH is mapped to the first subframe (#0) of each radio frame (see FIG. 15). It is also mapped to the fourth symbol (#3), fifth symbol (#4), eighth symbol (#7), and ninth symbol (#8) from the beginning of the subframe. Therefore, the original time domain of the PBCH is the first subframe (#0) of each radio frame. The original time domain of the PBCH is the fourth, fifth, eighth, and ninth symbols from the beginning of the subframe.

[0129] The L1 / L2 control signals (PDCCH, PHICH, PCFICH) are mapped within three symbols from the beginning of each subframe (see FIG. 19). Therefore, the original time domain of the L1 / L2 control signals is three symbols from the beginning of each subframe.

[0130] As a result, even if the receiving side (i.e., the mobile terminal side) does not have a receiving circuit for receiving a signal that cannot be scheduled in the time domain with an offset, it is possible to receive a signal that cannot be scheduled in the original time domain. In other words, even if it does not have a receiving circuit for multiple frame configurations, it is possible to receive a signal that cannot be scheduled. Therefore, for example, even if a mobile terminal conforming to an existing standard does not have a receiving circuit for receiving a signal that cannot be scheduled in the time domain with an offset, it is possible to obtain the effect that it can receive services of a mobile communication system under the umbrella of a base station in which interference avoidance measures have been taken.

[0131] Using Figure 45, a specific example in which a copy of a signal that cannot be scheduled in embodiment 1 is provided will be described. The same numbers as in Figure 17 indicate corresponding parts, and therefore the description will be omitted. Assume that cell #1 transmits P-SS, S-SS, and PBCH in subframe #0, and P-SS and S-SS in subframe #5. Cell #2 transmits P-SS, S-SS, and PBCH in subframe #0, and P-SS and S-SS in subframe #5. Also, in subframe #2, a copy of subframe #0, i.e., P-SS, S-SS, and PBCH, is transmitted, and in subframe #7, a copy of subframe #5, i.e., P-SS and S-SS, is transmitted. In Figure 45, the solid line indicates the original time domain signal, and the dashed line indicates the copy signal in the time domain with an offset.

[0132] Using Figure 46, a specific example will be described in which a copy of a signal that cannot be scheduled in cell #2 is provided in Variant 1 of Embodiment 1. The same numbers as in Figure 20 indicate corresponding parts. Therefore, the description will be omitted. Assume that cell #1 transmits an L1 / L2 control signal in the first to third symbols in every subframe. Cell #2 transmits an L1 / L2 control signal in the first to third symbols in every subframe. Furthermore, copies of the first to third symbols, i.e., the L1 / L2 control signal, are transmitted in the tenth to twelfth symbols in every subframe. In Figure 46, the solid line indicates the original time domain signal, and the dashed line indicates the copy signal in the time domain with an offset.

[0133] The above-mentioned method of mapping the same non-schedulable signal in both the original time domain and the time domain with an offset can also be applied to the second modification of the first embodiment. The second modification of the first embodiment is a solution that does not require multiple frame configurations in one system. When the receiving side (i.e., the mobile terminal side) searches for cells other than the serving cell on the assumption that synchronization is achieved between cells, the presence of non-schedulable signals, P-SS, S-SS, and L1 / L2 control signals, in the original time domain can provide an advantage of simplifying the search operation. Specifically, it is possible to omit the process of synchronizing slot timing and frame timing using the primary synchronization signal (P-SS) and secondary synchronization signal (S-SS) transmitted from neighboring base stations in step ST1201 of FIG. 12.

[0134] Embodiment 2 In the first embodiment, it has been disclosed that the time (timing) and / or frequency of physical resources onto which non-schedulable signals are mapped do not overlap between cells. It has also been disclosed that offsets are provided between cells in the physical resources onto which non-schedulable signals are mapped, the transmission timing of the physical resources, and the frequencies onto which non-schedulable signals are mapped. The range of these offsets is limited depending on the system and the method disclosed in the first embodiment. This is because, for example, among non-schedulable signals, there are signals that are mapped across the entire frequency band to specific symbols in each subframe. For example, in LTE, there are L1 / L2 control signals. If the method of the first modification of the first embodiment is applied to such signals and the symbol offset m is set to m=12, the signals will be mapped to the first to third symbols at the beginning of a subframe in one cell, and to the first, thirteenth, and fourteenth symbols at the beginning of a subframe in another cell. In such a case, the leading symbols will overlap between cells. Therefore, the range of the offsets is limited.

[0135] In the second embodiment, the physical resources provided between cells onto which non-schedulable signals are mapped, the transmission timing of the physical resources, and the possible range of offset of the frequency onto which the non-schedulable signals are mapped will be disclosed.

[0136] This section discloses a method for providing an n-subframe offset when a non-schedulable signal is mapped to a specific subframe in a radio frame, as disclosed in the first embodiment. Let nsub be the number of subframes in a radio frame, and let the subframe numbers range from #0 to #(nsub-1). Let xk be the k specific subframe numbers to which the non-schedulable signal is mapped. Let xa and xb be the specific subframe numbers of any cell. In this case, the range of n that can be taken is a value of n that satisfies the following equation (2). xa≠(xb+n)mod(nsub), xa, xb∈{xk} (2)

[0137] For example, let us consider the case of LTE. The number of subframes in a radio frame is 10. The subframes to which either or both of the synchronization signal and the PBCH, which cannot be scheduled, are mapped are #0 and #5. Therefore, the range of possible offsets is n=1, 2, 3, 4, 6, 7, 8, and 9. Note that the offset may be negative; since there are 10 subframes in a radio frame, for example, offset n=9 is the same as offset n=-1. By doing this, even when a signal that cannot be scheduled is mapped to a specific subframe in a radio frame, it is possible to prevent the physical resources to which the signal is mapped from overlapping between cells. This makes it possible to eliminate interference between cells for the signal.

[0138] Next, we will disclose a method of providing an m-symbol offset when a non-schedulable signal is mapped to a specific symbol in each subframe in a radio frame, as disclosed in Variant 1 of Embodiment 1. Let nsym be the number of symbols in a subframe, and the symbol numbers range from #0 to #(nsym-1). Let xk be the number of k specific symbols to which a non-schedulable signal is mapped. Let xa and xb be the specific symbol numbers of any cell. In this case, the range of m that can be taken is a value of m that satisfies the following equation (3). xa≠(xb+m)mod(nsym), xa, xb∈{xk} (3) Furthermore, when a non-schedulable signal is mapped to a specific subframe in a radio frame and further, when a non-schedulable signal is mapped to a specific symbol in each subframe in the radio frame, n is derived using the relational expression (2) to map the non-schedulable signal to a specific subframe in the radio frame, and the symbol number of the non-schedulable signal mapped to the specific subframe in the radio frame is included in xa in the relational expression (3), and an m symbol offset is set using the relational expression (3).

[0139] For example, let us consider the case of LTE. The number of symbols in a subframe is 14. The symbols onto which non-schedulable L1 / L2 control signals are mapped are within the first symbol (symbol #0) to the third symbol (symbol #2) at the beginning of each subframe. Furthermore, the symbols onto which non-schedulable signals are mapped in a specific subframe within a radio frame are within the fourth symbol (symbol #3) to the ninth symbol (symbol #8) from the beginning. Therefore, the possible range of offsets is m = 9, 10, and 11. For example, if m = 11, then in a cell with an offset, the signal is mapped within the twelfth symbol (symbol #11) to the fourteenth symbol (symbol #13) from the beginning of each subframe. In a cell without an offset, the signal is mapped within the first symbol (symbol #0) to the third symbol (symbol #2) at the beginning of each subframe. Note that the offset may be negative; since the number of symbols in a subframe is 14, for example, an offset m = 14 is the same as an offset m = -1. In this way, even when a non-schedulable signal is mapped to a specific symbol in each subframe of a radio frame, it is possible to prevent the physical resources to which the signal is mapped from overlapping between cells, thereby eliminating interference between the signals.

[0140] Next, we will disclose the method disclosed in the second modification of the first embodiment, in which an offset td is provided in the transmission timing between cells in one frame configuration. For example, we will disclose a case in which symbols in a subframe are mapped as shown in Figure 23. There are 10 subframes in a radio frame, and 14 symbols in a subframe. The subframes are numbered #0 to #9, and the symbol numbers are #0 to #13. Furthermore, certain subframes in a radio frame into which signals that cannot be scheduled are numbered #0 and #5. In this case, the offset td is given by the following equation (4). Here, the unit of the offset td is symbols. td=n×14+1, where n=1, 2, 3, 4, 6, 7, 8, 9 (4) Although the unit of the offset td is a symbol, the symbol may be converted into time and the unit may be time.

[0141] Also, although specific subframes in a radio frame are numbered #0 and #5, this is not a limitation. In this case, the value of n in equation (4) only needs to be such that there is no overlap even when an offset is added. For example, the value of n may be derived using the relational expression in equation (2). In this way, even in the case of a method in which an offset td is provided in the transmission timing between cells in a single frame configuration, it is possible to prevent the physical resources to which the signal is mapped from overlapping between cells. Therefore, it is possible to eliminate interference between the cells of the signal.

[0142] Next, we will disclose a case where the method disclosed in the third modification of the first embodiment is used to prevent overlapping of frequency regions of signals that are mapped to a portion of a cell among unschedulable signals between cells. The first method disclosed in the third modification of the first embodiment makes the entire frequency band of the cells the same while making the frequency regions different, so that the offset fd of the portion of the frequency region to which the unschedulable signals are mapped is expressed by the following relational expression (5): BW is the system bandwidth of the cell, and SBW is the bandwidth of the portion of the frequency region to which the unschedulable signals are mapped. -(BW / 2-SBW / 2)≦fd≦-SBW or SBW≦fd≦BW / 2-SBW / 2 (5)

[0143] For example, let us assume that the system bandwidth (total frequency bandwidth) of cell #1 and cell #2 is 20 MHz, and the bandwidth of the partial frequency region where the non-schedulable signals are mapped is 1.08 MHz. The partial frequency region where the non-schedulable signals of cell #1 are mapped is the center of the system band. In this case, the offset fd of the partial frequency region where the non-schedulable signals of cell #2 are mapped relative to cell #1 is -9.46 MHz ≦ fd ≦ -1.08 MHz or 1.08 MHz ≦ fd ≦ 9.46 MHz. The second method disclosed in the third modification of the first embodiment makes the total bandwidths of the cells different and makes the center frequencies (carriers) of the cells different so that the frequency regions of the cells do not overlap. Therefore, the offset fc of the center frequencies (carriers) of the cells is expressed by the following relational expression (6): SBW is the bandwidth of the partial frequency region of the cells where the non-schedulable signals of each cell are mapped. fc≦-SBW or SBW≦fc (6)

[0144] Furthermore, the range of fc may be restricted based on the system bandwidth of each cell so that the system bandwidth of a cell having a narrow system bandwidth is included in the system bandwidth of a cell having a wide system bandwidth. For example, the system bandwidth of cell #1 is 20 MHz. The system bandwidth of cell #2 is 10 MHz. The bandwidth of a portion of the frequency region to which non-schedulable signals are mapped is 1.08 MHz, which is the center of the system band. In this case, the offset fc of the center frequency (carrier) of cell #2 relative to cell #1 is -5 MHz≦fc≦-1.08 MHz or 1.08 MHz≦fd≦5 MHz. The third method disclosed in the third modification of the first embodiment makes the entire bandwidths of the cells different, and makes the center frequencies (carriers) of the cells different so that the frequency regions of the cells do not overlap, and the frequency band of one cell is different from the frequency regions of the other cells. Therefore, the offset fc of the center frequency (carrier) of the cell is expressed by the following relational expression (7): SBW is the bandwidth of the portion of the frequency region of the cell to which the non-schedulable signals of each cell are mapped. fc≦-SBW-BW2 / 2 or SBW+BW2 / 2≦fc However, BW2≦(BW1-SBW) / 2 (7)

[0145] Furthermore, the range of fc may be limited based on the system bandwidth of each cell so that the system bandwidth of a cell with a narrow system bandwidth is included in the system bandwidth of a cell with a wide system bandwidth. For example, the system bandwidth of cell #1 is 20 MHz. The system bandwidth of cell #2 is 5 MHz. The bandwidth of a portion of the frequency region to which non-schedulable signals are mapped is set to 1.08 MHz, which is the center of the system band. In this case, the offset fc of the center frequency (carrier) of cell #2 relative to cell #1 is -7.5 MHz≦fc≦-3.58 MHz or 3.58 MHz≦fd≦7.5 MHz.

[0146] As for the method disclosed in the third modification of the first embodiment for preventing overlapping of signals mapped across the entire frequency band of a cell between cells, the method in the case of the first embodiment, the method in the case of the first modification of the first embodiment, and the method in the case of the second modification of the first embodiment disclosed in this embodiment may be used. By setting the offset shown in the third modification of the first embodiment as described above, it is possible to prevent overlapping of physical resources onto which signals that cannot be scheduled are mapped between cells. Therefore, it is possible to eliminate interference between the cells of the signals.

[0147] As disclosed in this embodiment, by setting the offset within the possible range of the physical resource on which the non-schedulable signal is mapped, the transmission timing of the physical resource, and the frequency on which the non-schedulable signal is mapped, the offset can be prevented from being set incorrectly. In other words, by prohibiting the setting of the offset to a value different from the possible range of the offset, it is possible to ensure that the physical resource on which the non-schedulable signal is mapped does not overlap between cells. This makes it possible to reliably eliminate interference between the cells of the signal. Furthermore, by selecting the offset value within this possible range, the range of selection is narrowed, and the amount of information required for selection is reduced. This results in the effects of reducing the memory required in the mobile terminal and the base station and simplifying the configuration of the control circuit.

[0148] Embodiment 3 Interference between downlink signals becomes a problem between cells that cannot perform handover or between cells that operate in closed access mode. As a solution to this problem, the first embodiment discloses that radio resources of signals that cannot be scheduled do not overlap between the cells. As a method for this, synchronization between the cells and shifting resources of signals that cannot be scheduled between the cells (providing an offset) are disclosed. Furthermore, the second embodiment discloses what value to use for the offset amount to solve the downlink inter-cell interference problem. The third embodiment discloses a method for determining the offset amount (or a frame configuration). In this specification, a cell that has already been installed is referred to as a "first cell". A newly installed cell, i.e., a cell that is installed after the installation of the first cell, is referred to as a "second cell". Specific examples of the first cell and the second cell include an eNodeB, a NodeB, a macro cell, a HeNB, an HNB, a pico cell, a micro cell, and a CSG cell.

[0149] A method for an entity on the network side to determine the offset amount (or a frame configuration) will be disclosed. As a specific example, in an LTE system, possible network side entities that determine the offset amount include an EPC (Evolved Packet Core), an S-GW (Serving Gateway), an aGW (Access Gateway), and an MME (Mobility Management Entity). FIG. 27 shows an example of a sequence for determining the offset amount in a mobile communication system according to the third embodiment. In FIG. 27, an LTE system will be used as a specific example. Furthermore, a macro cell will be used as the first cell, a CSG cell will be used as the second cell, and the EPC will be used as the network side entity that determines the offset amount. When a new CSG cell is installed, the network side (EPC in FIG. 27) will be notified that the cell has been installed (step ST2701). When notifying the fact that the cell has been installed, information that identifies the cell itself, specifically, a PCI or a GCI, may be notified. By the second cell notifying the information that identifies its own cell, it becomes easy to determine which cell is the newly installed cell or to notify the same in subsequent processing. In step ST2702, the EPC receives notification of installation from the CSG cell. A specific example of the notification of installation may be location information of the CSG cell. The CSG cell can obtain the location information using existing technology such as the Global Positioning System (GPS). A specific example of a method of notification from the CSG cell to the EPC may be the S1 interface. By notifying the location information, which is new information, using the S1 interface, which is an existing interface (Non-Patent Document 9), it is possible to achieve the effect of avoiding complexity in the mobile communication system.

[0150] It is also possible to add location information as a new element to the information element (IE) in the "S1 SETUP REQUEST" message of the S1 interface. Including location information as an information element in the "S1 SETUP REQUEST" would provide the following benefits. Currently, 3GPP is moving toward mapping messages in the "S1 SETUP REQUEST" to exchange data necessary for the eNodeB and network entities to properly use the S1 interface. Therefore, when a new cell is installed in a mobile communication system, the initial data exchange can be performed using the same message. This means that a new message does not need to be created, which avoids the complexity of the mobile communication system's operation and prevents control delays. It is also possible to add location information as a new element to the information element in the "ENB CONFIGURATION UPDATE" message of the S1 interface. Including location information as an information element in the "ENB CONFIGURATION UPDATE" would provide the following benefits. Currently, 3GPP is moving toward mapping data necessary for updating the base station configuration in the "ENB CONFIGURATION UPDATE." Therefore, when a new cell is installed in a mobile communication system, the base station settings can be updated using the same message, meaning that there is no need to create a new message, which has the effect of avoiding complexity in the operation of the mobile communication system and preventing control delays.

[0151] In Step ST2703, the EPC determines whether or not there is a first cell that will interfere with the installation of the CSG cell. By using the method of notifying the installation and determining whether or not there is an interfering cell as disclosed herein, it becomes possible to selectively determine the cell in which to set an offset. It becomes possible to select a cell that requires offset amount setting or synchronization processing. If an interfering first cell exists, the EPC proceeds to Step ST2704; if not, the processing ends. Also, if no interfering first cell exists, the EPC may notify information indicating "no consideration required," "none," "0," or the like as the offset amount in Step ST2710. This has the effect of unifying the processing regardless of the result of the determination in Step ST2703. Furthermore, regardless of the result of the determination in Step ST2703, the second cell receives some information about the offset amount from the network side. As a result, if the CSG cell cannot receive the offset amount, it can recognize that there is a communication error indicating that the CSG cell has been installed from the EPC or a communication error in the offset amount from the EPC to the CSG cell. This has the effect of enabling early detection of communication errors. A specific example of a method for determining whether an interfering first cell exists may be determining whether a CSG cell is installed within the coverage area of ​​a previously installed cell (first cell). As a specific example, the EPC determines whether a CSG cell is installed within the coverage area of ​​a macro cell. The EPC can use the information received in step ST2702 for this determination. As a specific example, the EPC can use location information of the CSG cell.

[0152] In Step ST2704, the EPC performs processing so that resources of signals that cannot be scheduled do not overlap between cells. As a specific example, resources of signals that cannot be scheduled are shifted between cells (by providing an offset). The EPC determines the offset amount. The configuration for preventing resources of signals that cannot be scheduled from overlapping between cells can use the method of Embodiment 1, including its modified example. The offset amount can also use the method of Embodiment 2, including its modified example. The offset amount may be set to the same value in base stations within an MBSFN synchronization area (Multimedia Broadcast multicast service Single Frequency Network Synchronization Area). The offset amount may also be set to the same value in base stations within MBSFN areas. When the offset amount is set to the same value in base stations within an MBSFN synchronization area or within an MBSFN area, the following effects can be obtained. In a mobile terminal receiving MBMS data, it is necessary to transmit MBSFN subframes at the same timing to improve reception quality. When MBSFN subframes are controlled to be at the same timing, if the offset amounts are the same, the effect of simplifying processing on the network side can be obtained. Furthermore, when MIMO (Multiple Input Multiple Output), a wireless technology that combines multiple antennas to widen the bandwidth for data transmission and reception, is implemented using antennas from different cells, the offset amount may be set to the same value in the multiple cells. This has the following advantages: In order to widen the bandwidth for transmission and reception between multiple cells and mobile terminals, it is necessary to transmit data to the mobile terminals at the same timing. When controlling the transmission timing to mobile terminals to be the same, if the offset amount is the same, the effect of simplifying processing on the network side can be obtained.

[0153] In Step ST2705, the EPC performs synchronization processing. Here, "synchronization" refers to using a time managed by the network in the first cell and the second cell. Alternatively, a certain timing may be derived from the time managed by the network in the first cell and the second cell. Specific examples of the certain timing include the beginning of a radio frame used in the first cell and the second cell, a system frame number (SFN), and the like. As a specific example of the synchronization processing in Step ST2705, the EPC notifies the macro cell and the CSG cell of the time managed by the EPC. By performing the synchronization processing in Step ST2705, an effect can be obtained in which the second cell can know the timing used in the first cell (specific examples include transmission timing, SFN, and the like). Knowing the timing used in the first cell in the second cell can have the effect of enabling control of the time (timing) of the physical resources disclosed in the first embodiment so as not to overlap. As a specific example of a method of notification from the EPC to the macro cell or the CSG cell, the S1 interface can be considered. It is also possible to notify the time from the EPC to the macro cell or CSG cell using Layer 1 of the S1 interface.

[0154] It is also possible to add this time as a new element to the information elements in the "S1 SETUP RESPONSE" message of the S1 interface. Including this time as an information element in the "S1 SETUP RESPONSE" would provide the following benefits. Currently, 3GPP is moving toward mapping messages in the "S1 SETUP RESPONSE" to exchange data necessary for the eNodeB and network entities to properly use the S1 interface. Therefore, when a new cell is established in a mobile communication system, the initial data exchange can be performed using the same message. This means that a new message is not required, which avoids the complexity of the mobile communication system's operation and prevents control delays. It is also possible to add this time as a new element to the information elements in the "ENB CONFIGURATION UPDATE ACKNOWLEDGE" message of the S1 interface. Including this time as an information element in the "ENB CONFIGURATION UPDATE ACKNOWLEDGE" would provide the following benefits. In the current 3GPP, "ENB CONFIGURATION UPDATE ACKNOWLEDGE" is intended to be used as a response to "ENB CONFIGURATION UPDATE," which maps the data required to update the base station settings. Therefore, when a new cell is installed in a mobile communication system, the network side can respond to the update of the base station settings using the same message. In other words, there is no need to create a new message, which has the effect of avoiding complexity in the operation of the mobile communication system and preventing control delays.

[0155] It is also possible to add this time as a new element to the information elements in the "MME CONFIGURATION UPDATE" message on the S1 interface. If this time is included as an information element in "MME CONFIGURATION UPDATE," the following effects can be achieved. Currently, 3GPP is moving toward mapping the data required to update the MME configuration to "MME CONFIGURATION UPDATE." This makes it possible for the mobile communication system to perform network-side updates using the same message, which means that there is no need to create a new message, thereby avoiding complexity in the operation of the mobile communication system and preventing control delays.

[0156] In Step ST2706, the macro cell receives the time managed by the EPC notified by the EPC. In Step ST2707, the CSG cell receives the time managed by the EPC notified by the EPC. In Step ST2708, the macro cell performs synchronization processing using the time managed by the network side received in Step ST2706. As a specific example of synchronization processing, the macro cell derives the timing to be used in the first cell (specific examples include transmission timing and SFN) using the time managed by the network side in the same way as the network side. Furthermore, the SFN to be used in the macro cell is derived from the time managed by the network side. As a specific example of derivation, the following equation (1) can be used. Equation (1) SFN = (time) mod (SFN period) The (time) in equation (1) is the time managed by the network side and received in step ST2706. The (SFN period) is the period at which the SFN is repeated. This period may be a statically defined value, or may be notified to the macro cell or the CSG cell from the network side as a quasi-static value. In step ST2709, the CSG cell performs synchronization processing using the time managed by the network side and received in step ST2707. A specific example is the same as in step ST2708, so a description thereof will be omitted. Using the same time managed by the network side in steps ST2708 and ST2709 to derive the timing used in the first cell and the second cell (specific examples include transmission timing, SFN, etc.) in the same way as on the network side can provide the following advantages. An advantage can be obtained that the second cell can know the timing used in the first cell (specific examples include transmission timing, SFN, etc.). Knowing the timing used in the first cell in the second cell has the effect of enabling control so that the time (timing) of the physical resources disclosed in the first embodiment does not overlap. In Step ST2710, the EPC notifies the CSG cell of the offset amount determined in Step ST2704. As a notification method, the method shown in Step ST2705 can be used. Steps ST2705 and ST2710 may be performed simultaneously. The order is also arbitrary. In Step ST2711, the CSG cell receives the offset amount from the EPC. In Step ST2712, the CSG cell starts communication in accordance with the offset amount received in Step ST2711, that is, by shifting the timing by the offset amount. Alternatively, the CSG cell starts communication in accordance with the frame configuration received in Step ST2711.

[0157] According to the third embodiment, when a new cell is installed, it becomes possible to operate the resources of signals that cannot be scheduled so as not to overlap with those of an already installed cell. This can provide the effect of reducing downlink inter-cell interference. Furthermore, when MIMO (Multiple Input Multiple Output), a radio technology that widens the bandwidth for data transmission and reception by combining multiple antennas as described above, is implemented using the antenna of another cell, the determination of whether or not there are any interfering cells in the multiple cells may be performed in steps ST2701 to ST2703. This can provide the following effect. By selectively determining a cell to set an offset in, it becomes possible to set the offset in a cell that requires the operation of the MIMO. Furthermore, synchronization processing may be performed in steps ST2705 to ST2709. This can provide the following effect. It can provide the effect of enabling multiple cells to mutually know the timings used (for example, transmission timing, SFN, etc.). It can derive the timings used in multiple cells (for example, transmission timing, SFN, etc.) using time managed on the same network side. This means that when the transmission timing to the mobile terminal is controlled to be the same, if the timing is the same, the processing on the network side can be simplified.

[0158] Variation 1. The synchronization process described in the third embodiment has the following problem. When a new cell is installed, it may become necessary for a previously installed cell to perform synchronization. When a previously installed cell performs synchronization, it is necessary to derive the timing to be used in the cell (specifically, the beginning of a radio frame, SFN, etc.) from the time managed on the network side and use it for communication in the cell. If the timing differs before and after the execution of synchronization, a problem occurs in which communication between the cell and a mobile terminal served by the cell is interrupted. In this first modification, in order to solve the above problem, a method different from the synchronization process disclosed in the third embodiment is disclosed.

[0159] FIG. 28 shows an example of a sequence up to determining an offset amount in the mobile communication system according to the first modification. In FIG. 28, the same steps as those in FIG. 27 execute the same or equivalent processing, and therefore description thereof will be omitted. In step ST2801 of FIG. 28, the EPC transmits a synchronization instruction to the macro cell. As a method for notifying the synchronization instruction, the method shown in step ST2705 can be used. Information for identifying the second cell, specifically, PCI or GCI, may be included in the synchronization instruction. By including the information for identifying the second cell, the first cell can identify which cell it should perform step ST2803 for. In step ST2802, the macro cell receives the synchronization instruction from the EPC. Here, "synchronization" means that the second cell uses the time managed by the first cell. Also, the second cell may derive a certain timing from the time managed by the first cell. A specific example of a certain timing may be the beginning of a radio frame used in the second cell, a system frame number (SFN), or the like. In Step ST2803, the macro cell notifies the CSG cell of the time managed by the macro cell. A specific example of a method of notification from the macro cell to the CSG cell can be the X2 interface. By notifying the time managed by the macro cell, which is new information, using the X2 interface (Non-Patent Document 10), which is an existing interface, it is possible to obtain the effect of avoiding complexity in the mobile communication system.

[0160] In addition, it is possible to add this time as a new element to the information elements of the "X2 SETUP REQUEST" and "X2 SETUP RESPONSE" messages of the X2 interface. Including this time as an information element in the "X2 SETUP REQUEST" and "X2 SETUP RESPONSE" messages can achieve the following benefits. Currently, 3GPP is moving toward mapping "X2 SETUP REQUEST" and "X2 SETUP RESPONSE" messages to messages for exchanging data necessary for the eNodeB to properly use the X2 interface. Therefore, when a new cell is established in a mobile communication system, the initial data exchange can be performed using the same message. In other words, there is no need to create a new message, which can avoid complexity in the operation of the mobile communication system and prevent control delays. In addition, it is possible to add this time as a new element to the information elements of the "ENB CONFIGURATION UPDATE" and "ENB CONFIGURATION UPDATE ACKNOWLEDGE" messages of the X2 interface. If this time is used as an information element in "ENB CONFIGURATION UPDATE" and "ENB CONFIGURATION UPDATE ACKNOWLEDGE," the following effects can be achieved. Currently, 3GPP is moving toward mapping the data required to update base station settings in "ENB CONFIGURATION UPDATE" and "ENB CONFIGURATION UPDATE ACKNOWLEDGE." Therefore, when a new cell is installed in a mobile communication system, it will be possible to update the base station settings using the same message, which means that there is no need to create a new message, and this will avoid complexity in the operation of the mobile communication system and prevent control delays.

[0161] As another specific example of the method of notifying the CSG cell from the macro cell, a method in which the macro cell first notifies the EPC of the "time" and then the EPC notifies the CSG cell can be considered. In this case, the method shown in step ST2701 can be used as a specific example of the method of notifying the EPC from the macro cell. Furthermore, the method shown in step ST2705 can be used as a method of notifying the CSG cell from the EPC. In step ST2804, the CSG cell receives the time managed by the macro cell from the macro cell. In step ST2805, the CSG cell performs synchronization processing using the time managed by the macro cell that was received in step ST2804. As a specific example of the synchronization processing, the timing to be used in the CSG cell (specific examples include transmission timing and SFN) is derived in the same manner as the first cell, using the time managed by the macro cell. Furthermore, the SFN to be used in the CSG cell is derived from the time managed by the macro cell. As a specific example of the derivation, the same method as in step ST2708 of the third embodiment can be used.

[0162] In addition to the effects of Embodiment 3, Modification 1 can achieve the following effects. The timing used in the second cell can be derived using the time managed by the first cell. In other words, there is no need to change the timing of the first cell through synchronization processing. Even if interference occurs due to the installation of the second cell, it is possible to reduce downlink inter-cell interference without interrupting communication in the first cell. Furthermore, when implementing MIMO (Multiple Input Multiple Output), a wireless technology that widens the bandwidth for data transmission and reception by combining multiple antennas, using an antenna of another cell, the multiple cells may determine whether or not there are any interfering cells in steps ST2701 to ST2703. This achieves the following effects. By selectively determining a cell to set an offset in, it is possible to set the offset in a cell that requires the operation of the MIMO. Furthermore, the multiple cells may undergo synchronization processing from steps ST2801 to ST2805. This achieves the following effects. It is possible to achieve the effect of enabling multiple cells to mutually know the timings used in each cell (specifically, transmission timing, SFN, etc.). Using the same time managed on the network side, it is possible to derive timing (specifically, transmission timing, SFN, etc.) to be used in multiple cells. This means that when controlling transmission timing to mobile terminals to the same timing, if the timing is the same, it is possible to obtain the effect of simplifying processing on the network side.

[0163] Variation 2. In this second modification, a method for performing synchronization processing in the second cell is described, and another solution to the same problem as in the first modification is disclosed. FIG. 29 shows an example of a sequence for determining an offset amount in a mobile communication system according to this second modification. In FIG. 29, the same steps as those in FIG. 27 execute the same or corresponding processing, and therefore description thereof will be omitted. In step ST2901, the EPC transmits a synchronization instruction to the CSG cell. As a method for notifying the synchronization instruction, the method shown in step ST2705 can be used. In step ST2902, the CSG cell receives the synchronization instruction from the EPC. Here, "synchronization" includes the second cell knowing a certain timing of the first cell. A specific example of the certain timing may be the beginning of a radio frame used in the first cell, a system frame number (SFN), or the like. In step ST2903, the CSG cell performs synchronization processing. A specific example of synchronization processing is knowing a certain timing of the macro cell (radio frame, SFN, etc.). A specific example of knowing the timing is the CSG cell performing processing similar to cell search for a mobile terminal. Specifically, as in step ST1201 in Fig. 12, the slot timing and radio frame timing are determined using the primary synchronization signal (P-SS) and secondary synchronization signal (S-SS) transmitted from the macrocell. Furthermore, the BCCH on the PBCH may be received to obtain MIB (Master Information Block) information mapped to the BCCH, and the SFN in the MIB information may be obtained.

[0164] In step ST2904, the CSG cell starts communication in accordance with the offset amount received in step ST2711 from the timing of the macro cell obtained in step ST2903, that is, by shifting the timing by the offset amount. Alternatively, the CSG cell starts communication in accordance with the frame configuration received in step ST2711.

[0165] In addition to the effects of Embodiment 3, Modification 2 can achieve the following effects. By performing a cell search by the second cell, the second cell can learn the timing (radio frame, SFN) of the first cell. In other words, there is no need to change the timing of the first cell through synchronization processing. Even if interference occurs due to the installation of the second cell, an effect can be achieved in which downlink inter-cell interference can be reduced without interrupting communication in the first cell. Furthermore, when implementing MIMO (Multiple Input Multiple Output), a wireless technology that broadens the bandwidth for data transmission and reception by combining multiple antennas as described above, using an antenna of another cell, the multiple cells may determine whether or not there are any interfering cells in steps ST2701 to ST2703. This achieves the following effects. By selectively determining a cell to set an offset in, it becomes possible to set the offset in a cell that requires the operation of the MIMO. Furthermore, the multiple cells may perform synchronization processing from steps ST2901 to ST2903. This achieves the following effects. An effect can be achieved in which the timings used in multiple cells (specifically, transmission timing, SFN, etc.) can be known from one another. Using the same time managed on the network side, it is possible to derive timing (specifically, transmission timing, SFN, etc.) to be used in multiple cells. This means that when controlling transmission timing to mobile terminals to the same timing, if the timing is the same, it is possible to obtain the effect of simplifying processing on the network side.

[0166] Variation 3. In step ST2703 of the third embodiment, "location information" is used as a specific example of a method for determining whether an interfering first cell exists. In this third modification, another method for determining whether an interfering first cell exists is disclosed. A specific example of a method for determining whether an interfering first cell exists may be determining whether a CSG cell has been installed within the range of a cell (first cell) that has already been installed. A specific example is determining whether a CSG cell has been installed within the range of a macrocell. The EPC may use the status of neighboring cells measured by the CSG cell to make this determination.

[0167] Figure 30 shows an example of a sequence for determining the offset amount (or frame configuration) of a mobile communication system in this third modification. In Figure 30, the same steps as in Figure 27 execute the same or corresponding processing, so their explanation will be omitted. In step ST3001, the CSG cell synchronizes slot timing and frame timing using a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS) transmitted from a neighboring base station. It also detects (identifies) the PCI of the synchronized cell. In step ST3002, the CSG cell measures the communication quality of each base station for the synchronized cells (neighboring cells). Examples of quality include (1) the received power (RSRP Reference signal received power) measured by detecting the cell-specific reference signal RS (Reference Signal) transmitted for each cell, (2) the ratio of the received power of the cell-specific reference signal RS transmitted for each cell to the received power strength at the carrier frequency of the system (RSRQ Reference signal received quality), (3) the received signal strength (desired signal received power RSSI Received Signal Strength Indicator), (4) the ratio of the desired signal to the interference signal (SIR Signal Interference Ratio), (5) the received power (DL RS TX power) of the cell-specific reference signal RS transmitted for each cell in the resource element (RE), and (6) the amount of interference.

[0168] In step ST3003, the CSG cell selects the cell with the best quality (best cell) from among the one or more cells detected in steps ST3001 and ST3002. Specifically, the best cell is assumed to be (1) the cell with the highest received power when detecting a cell-specific reference signal RS (Reference Signal) transmitted for each cell, (2) the cell with the highest ratio between the received power of the cell-specific reference signal RS transmitted for each cell and the received power strength at the carrier frequency of the system, (3) the cell with the highest received signal strength, (4) the cell with the highest ratio between desired waves and interference waves, (5) the cell with the highest received power of the cell-specific reference signal RS transmitted for each cell in a resource element (RE), and (6) the cell with the smallest amount of interference.

[0169] When a new CSG cell is installed, the network side (EPC in FIG. 30) is notified of the fact that the cell has been installed (step ST3004). When notifying of the fact that the cell has been installed, information for identifying the cell itself, as a specific example, the PCI or GCI, may be notified. By the second cell notifying of the information for identifying the cell itself, it becomes easier to determine which cell is the newly installed cell or to notify it in subsequent processing. A specific example of the fact that the cell has been installed can be the situation of the neighboring cells measured in steps ST3001 to ST3003. As a notification method, the method shown in step ST2701 can be used. Also, specific examples of the situation of the neighboring cells can be the PCI (or GCI) of the neighboring cells, the communication quality of the neighboring cells (specific examples of communication quality are as described above), the timing of the neighboring cells, and so on. Also, in order to notify the timing of the neighboring cells, a reference cell may be selected from the neighboring cells, and the timing offset between the reference cell and neighboring cells other than the reference cell may be notified. A specific example of the reference cell can be the best cell. A specific example of the timing can be the radio frame, the SFN, and so on. In order to notify the network side of the reference cell, the PCI (or GCI) of the reference cell is notified.

[0170] In Step ST3005, the EPC determines whether or not there is a first cell that will interfere with the installation of the CSG cell. If there is, the EPC proceeds to Step ST2704; if there is not, the EPC terminates the process. If there is not, the EPC may notify information indicating "no consideration required," "none," "0," or the like as the offset amount in Step ST2710. This provides an advantage of unifying the process regardless of the result of the decision in Step ST3005. Furthermore, regardless of the result of the decision in Step ST3005, the second cell receives some information about the offset amount from the network side. As a result, if the CSG cell cannot receive the offset amount, it can recognize that there is a communication error indicating that the CSG cell has been installed to the EPC or a communication error in the offset amount from the EPC to the CSG cell. This provides an advantage of enabling early detection of communication errors. A specific example of a method for determining whether or not there is an interfering first cell is to determine whether or not the CSG cell is installed within the coverage area of ​​a previously installed cell (first cell). As a specific example, the EPC determines whether or not the CSG cell is installed within the coverage area of ​​a macrocell. The EPC can use the information received in Step ST2702 for this determination. As a specific example, the EPC can use the status of cells surrounding the CSG cell.

[0171] In Step ST3006, the CSG cell starts communication in accordance with the offset amount received in Step ST2711, that is, by shifting the timing by the offset amount. Alternatively, the CSG cell starts communication in accordance with the frame configuration received in Step ST2711. Alternatively, if the EPC has determined the offset amount from the timing of the reference cell in Step ST2704, the CSG cell may start communication in accordance with the offset amount received in Step ST2711, that is, by shifting the timing by the offset amount from the timing of the reference cell obtained in Steps ST3001 to ST3003.

[0172] Furthermore, the timing for measuring the communication quality of neighboring cells of the CSG cell in step ST3002 may be when a new CSG cell is installed. The notification of the neighboring cell status from the CSG cell to the EPC in step ST3004 and the determination by the EPC in step ST3005 may also be performed when a new CSG cell is installed. As a result, after the CSG cell starts communication in step ST3006, the CSG cell does not measure the communication quality of neighboring cells. Therefore, after the CSG cell starts communication, the offset amount of the CSG cell is not changed in accordance with the communication quality measurement results. This has the effect of preventing communication interruptions with mobile terminals served by the CSG cell due to changes in the offset amount or due to measurements of the communication quality of neighboring cells during CSG cell operation. Furthermore, the timing for measuring the communication quality of neighboring cells of the CSG cell in step ST3002 may be periodically measured. The notification of the neighboring cell status from the CSG cell to the EPC in step ST3004 and the determination by the EPC in step ST3005 may also be performed periodically. After the CSG cell starts communication, the situation of a neighboring cell may change, causing the problem of overlapping radio resources of signals that cannot be scheduled between cells again, resulting in downlink interference between the cells. By periodically performing measurement and notification by the CSG cell and determination by the EPC, the network side can know the situation of the neighboring cell even if the situation of the neighboring cell changes after the CSG cell starts communication in step ST3006. This makes it possible to operate the system so that radio resources of signals that cannot be scheduled do not overlap between cells, even after the CSG cell starts communication. A flexible mobile communication system can be obtained.

[0173] Furthermore, the timing for measuring the communication quality of a cell neighboring the CSG cell in step ST3002 may be considered to be when the situation of the neighboring cell changes. The notification of the situation of the neighboring cell from the CSG cell to the EPC in step ST3004 and the determination by the EPC in step ST3005 may also be considered to be performed when the situation of the neighboring cell changes. Similar to the case where the CSG cell periodically measures and notifies the EPC and periodically makes a determination, a flexible mobile communication system can be obtained. Furthermore, since the CSG cell measures and notifies the EPC and periodically makes a determination only when the situation of the neighboring cell changes, it is possible to obtain the effects of reducing the load on the CSG cell and the EPC and reducing power consumption. When a new cell is installed near the CSG cell, it is considered that the newly installed cell or the EPC notifies the CSG cell of whether the situation of the neighboring cell has changed using the S1 interface or the X2 interface. This third modification can be used in combination with embodiment 3. This third modification can be used in combination with the first modification. This third modification can also be used in combination with the second modification.

[0174] In addition to the effects of embodiment 3, modification 3 can achieve the following effects. In embodiment 3, whether or not an interfering first cell exists is determined based on location information of the second cell. In a determination based on location information, even if the second cell is installed outside the range of the first cell, it is possible that under actual communication conditions the second cell may be within the range of the first cell due to reflections from buildings, etc. In modification 3, whether or not an interfering first cell exists is determined based on the surrounding cell conditions actually measured by the second cell. Therefore, an effect can be achieved in which a determination can be made more appropriately based on actual communication conditions than in embodiment 3.

[0175] Variation 4. In this fourth modification, a method for determining an offset amount different from that in the third embodiment is disclosed, in which a second cell determines an offset amount. As a specific example, in an LTE system, the second cell for which an offset amount is determined may be an eNodeB, a NodeB, a macrocell, a HeNB, an HNB, a picocell, a microcell, a CSG cell, or the like. FIG. 31 shows an example of a sequence for determining an offset amount (or a frame configuration) in a mobile communication system in this fourth modification. In FIG. 31, the same steps as those in FIG. 30 execute the same or corresponding processes, and therefore description thereof will be omitted. In step ST3101, the CSG determines whether or not there is a first cell that will interfere with the installation of the CSG cell. If there is, the process proceeds to step ST3102, and if there is not, the process ends. As a specific example of a method for determining whether or not there is an interfering first cell, it can be considered to determine whether or not the CSG cell has been installed within the range of a cell (first cell) that has already been installed. As a specific example, the CSG determines whether or not the CSG cell has been installed within the range of a macrocell. For this determination, the CSG can use the conditions of neighboring cells measured in steps ST3001 and ST3002.

[0176] In step ST3102, the CSG cell performs processing so that resources of signals that cannot be scheduled do not overlap between cells. The details are the same as in step ST2704, so a description thereof will be omitted. In step ST3103, the CSG cell starts communication in accordance with the offset amount determined in step ST3102, that is, by shifting the timing by the offset amount. Alternatively, the CSG cell starts communication in accordance with the frame configuration determined in step ST3102. Alternatively, the CSG cell may start communication in accordance with the offset amount determined in step ST3102 from the timing of the reference cell obtained in steps ST3001 to ST3003, that is, by shifting the timing by the offset amount. The description of the reference cell is the same as that of the third modification, so a description thereof will be omitted. Furthermore, synchronization processing between the CSG cell and the macro cell may be performed. The third embodiment, the first modification, and the second modification can be used as specific examples of the synchronization processing. The offset amount determined in step ST3102 may also be notified from the CSG cell to either the macro cell or the EPC, or to both.

[0177] In addition to the effects of Embodiment 3, Modification 4 can achieve the following effects. When a new cell is installed, it is possible to operate the resources of signals that cannot be scheduled so that they do not overlap with those of previously installed cells, without any processing on the network side or on the previously installed cells, thereby reducing interference between downlink signals. In other words, when a new cell is installed, it is possible to operate the resources of signals that cannot be scheduled so that they do not overlap with those of previously installed cells, with processing only on the second cell, thereby reducing interference between downlink signals. This makes it possible to achieve the effect of enabling the installation of a new cell while reducing interference between downlink signals without affecting the existing mobile communication system. This achieves the effect of avoiding complexity in the mobile communication system and enabling flexible cell installation.

[0178] Variation 5. When the offset amount of the second cell is determined using the fourth modification, there is a possibility that the offset amount (transmission timing) may differ even between cells located within the same first cell. This fifth modification discloses a method for operating second cells located within the same first cell so that they have the same offset amount (or frame configuration). Figure 32 shows an example of a sequence for determining the offset amount (or frame configuration) of a mobile communication system according to the fifth modification. In Figure 32, the same steps as those in Figures 30 and 31 execute the same or corresponding processes, and therefore, description thereof will be omitted. In step ST3201, the CSG cell receives the PBCH of the first cell (or the best cell) and obtains the BCCH, which is broadcast information. The BCCH on the PBCH carries a Master Information Block (MIB), which includes cell configuration information. After receiving the PBCH, the CSG cell may receive the DL-SCH of the cell based on the cell configuration information in the MIB, and receive a System Information Block (SIB) 1 in the broadcast information BCCH. In addition, other SIBs (SIBk; k is an integer greater than or equal to 2) may be received based on the scheduling information of other SIBs included in SIB1.

[0179] In Step ST3202, the CSG cell checks whether the MIB, SIB1, or other SIB received in Step ST3201 includes an offset amount of the macro cell. If an offset amount is not included, it moves to Step ST3101. If an offset amount is included, it moves to Step ST3206. In Step ST3203, the CSG cell notifies the first cell of the offset amount determined in Step ST3102. As a notification method, the method disclosed in Step ST2803 can be used. When notifying the offset amount, information identifying the first cell, such as PCI or GCI, may be notified. By the second cell notifying information identifying its own cell, it becomes easier to determine which cell is a newly installed cell or to notify it in subsequent processing. The CSG cell may also notify the EPC of the offset amount. In Step ST3204, the macro cell receives the offset amount from the CSG cell. In Step ST3205, the macro cell notifies its own cell of the offset amount received in Step ST3204. The following notification methods are possible. The offset amount (or frame configuration) applied by a cell newly established within the cell is mapped to the broadcast information BCCH. A specific example of the offset amount is the amount of deviation from the timing (radio frame, SFN) of the cell. When the offset amount is mapped to the BCCH, the following effects can be obtained. Because it is broadcast information, it can be notified within the range of the cell.

[0180] An offset amount is newly added as an information element of the existing MIB (Master Information Block) (Non-Patent Document 11) in the broadcast information. When an offset amount is mapped to the MIB, the following effects can be obtained. For example, in an LTE communication system, the MIB is mapped to the PBCH, so it can be received at an early stage of a search operation (a specific example is step ST1204 in FIG. 12). Therefore, by mapping the offset amount to the MIB information, it is possible to prevent control delays and reduce power consumption. An offset amount is newly added as an information element of the existing SIB (System Information Block) (Non-Patent Document 11) in the broadcast information BCCH. Furthermore, an offset amount is newly added as an information element of SIB1. When an offset amount is mapped to SIB1, the following effects can be obtained. For example, in an LTE communication system, it can be received at an early stage of a search (a specific example is step ST1205 in FIG. 12). Therefore, by mapping the offset amount to the MIB information, it is possible to prevent control delays and reduce power consumption. Furthermore, an offset amount is newly added as an information element of SIB2. When an offset amount is mapped to SIB2, the following effects can be obtained. Currently, 3GPP is moving towards mapping radio resource settings to SIB2. Adding the offset, which is a parameter used to configure radio resources, to SIB2, which contains similar parameters, makes it possible to obtain similar parameters by receiving the same system information. This can avoid complexity in the mobile communication system and prevent control delays.

[0181] In step ST3206, the CSG cell starts communication in accordance with the offset amount determined in step ST3102, that is, by shifting the timing by the offset amount. Alternatively, the CSG cell may start communication in accordance with the offset amount determined in step ST3102 from the timing of the reference cell obtained in steps ST3001 to ST3003, that is, by shifting the timing by the offset amount. Note that the description of the reference cell is the same as that of Modification 3, so a description thereof will be omitted. Alternatively, the CSG cell starts communication in accordance with the offset amount received in step ST3201, that is, by shifting the timing by the offset amount. Alternatively, the CSG cell starts communication in accordance with the offset amount received in step ST3201 from the timing of the reference cell obtained in steps ST3001 to ST3003, that is, by shifting the timing by the offset amount. Alternatively, the CSG cell starts communication in accordance with the frame configuration determined in step ST3102. Alternatively, the CSG cell starts communication in accordance with the frame configuration received in step ST3201. Modification 5 can obtain the following effects in addition to the effects of Modification 4. According to the fifth modification, the second cell determines whether the first cell has notified (broadcast) the "offset amount to be applied by a cell newly installed within the first cell," and if so, the second cell follows the notified offset amount. This provides the advantage of being able to set the same offset amount for a second cell installed within the same first cell. Similarly, even when MIMO (Multiple Input Multiple Output), a wireless technology that combines multiple antennas to expand the bandwidth for data transmission and reception, is implemented using the antenna of another cell, the same offset amount can be set for a second cell installed within the first cell. This provides the following advantages: The second cell can learn the timing (specifically, transmission timing, SFN, etc.) used in the first cell. This means that when controlling transmission timing to mobile terminals to the same timing, if the timing is the same, the processing on the network side can be simplified.

[0182] Furthermore, using the method of this fifth modification (step ST3205), the first cell may notify the MBSFN (Multimedia Broadcast Multicast Service Single Frequency Network) synchronization area number to which the first cell belongs or which the first cell knows, and the offset amount used in the MBSFN synchronization area. A specific example of the offset amount is the offset amount from the timing of the first cell (if the offset amount is "0", the offset amount does not need to be notified). This allows the new cell, when installed, to know the timing of the MBSFN synchronization area without any processing on the network side or on the previously installed cell (step ST3201). Therefore, when a new cell is installed, it is possible to achieve synchronization required for belonging to the MBSFN synchronization area only through processing on the new cell, thereby achieving the effects of avoiding complexity in the mobile communication system and enabling flexible cell installation. Also, using the method of this fifth modification (step ST3205), the first cell may notify the MBSFN area number to which the first cell belongs or which the first cell knows, and the offset amount used in the MBSFN area. A specific example of the offset amount is the offset amount from the timing of the first cell (if the offset amount is "0", the offset amount does not need to be notified). As a result, when a new cell is installed, the new cell can know the timing of the MBSFN area without any processing on the network side or on the previously installed cell (step ST3201). Therefore, when a new cell is installed, it is possible to achieve the synchronization required to belong to the MBSFN area only by processing the new cell, thereby achieving the effects of avoiding complexity in the mobile communication system and enabling flexible cell installation.

[0183] Variation 6. In this sixth modification, a method for determining an offset amount different from that in the third embodiment is disclosed, in which a first cell determines an offset amount (or a frame configuration). As a specific example, in an LTE system, the first cell for determining an offset amount may be an eNodeB, a NodeB, a macrocell, a HeNB, an HNB, a picocell, a microcell, or a CSG cell. FIG. 33 shows an example of a sequence for determining an offset amount (or a frame configuration) in a mobile communication system in this sixth modification. In FIG. 33, the same steps as those in FIG. 27 execute the same or corresponding processes, and therefore, description thereof will be omitted. In Step ST3301, the EPC instructs the macrocell to determine an offset amount. As a notification method, the method shown in Step ST2705 can be used. In Step ST3302, the macrocell receives the offset amount determination instruction from the EPC. In Step ST3303, the macrocell performs processing so that resources of signals that cannot be scheduled do not overlap between cells. As a specific example, resources of signals that cannot be scheduled are shifted between cells (offset amounts are provided). The macrocell determines the offset amount. The detailed description is the same as that of step ST2704, and therefore will not be repeated. In step ST3304, the macro cell notifies the CSG cell of the offset amount determined in step ST3303. As a notification method, the method shown in step ST2803 of FIG. 28 can be used. In step ST3305, the CSG cell receives the offset amount from the macro cell. In step ST3306, the CSG cell starts communication in accordance with the offset amount received in step ST3305, that is, by shifting the timing by the offset amount. Alternatively, the CSG cell starts communication in accordance with the frame configuration received in step ST3305. This sixth modification can use the third embodiment, the first modification, and the second modification in the synchronization procedure. Furthermore, this sixth modification can be used in combination with the third modification. The sixth modification can achieve the same effects as those of the third embodiment.

[0184] Furthermore, in step ST2701, the CSG cell may notify the macro cell. The decision in step ST2703 may be made by the macro cell. Also, variant 1 may be used for the synchronization procedure. This makes it possible to omit the instruction from the EPC to the macro cell to determine the offset amount (steps ST3301 and ST3302) and the synchronization process in the EPC (step ST2705). This makes it possible to obtain the effect of avoiding complexity in the mobile communication system.

[0185] Variation 7. In this seventh modification, a specific example of a criterion for determining whether an interfering first cell exists when a new cell is installed is disclosed. A threshold is used as the criterion. Specific examples of the threshold are shown below. When "location information" is used to determine whether an interfering first cell exists, the distance between the second cell and the first cell (or multiple cells) can be considered as the threshold. For example, if the distance between the first cell and the second cell is equal to or greater than a threshold (or greater than the threshold), it is determined that the first cell and the second cell do not interfere with each other. Also, if the distance between the first cell and the second cell is less than a threshold (or less than the threshold), it is determined that the first cell and the second cell interfere with each other. When "surrounding cell conditions" are used to determine whether an interfering first cell exists, communication quality can be considered as the threshold. As shown in the third modification, specific examples of communication quality include (1) the received power of the RS, (2) the ratio of the received power of the RS to the received power strength of the carrier frequency, (3) the received signal strength, (4) the ratio of the desired wave to the interference wave, (5) the received power of the RS in the RE, and (6) the amount of interference. For example, if the measurement result of the communication quality of the surrounding cell conditions measured by the second cell does not include any cells that are equal to or greater than the threshold, it is determined that the first cell that interferes with the second cell does not exist.Furthermore, if the measurement result of the communication quality of the surrounding cell conditions measured by the second cell includes any cells that are equal to or greater than the threshold, it is determined that the first cell that interferes with the second cell exists.

[0186] Furthermore, the second cell may use the threshold to determine the measurement results of the surrounding cell situations, and if it determines that an interfering first cell exists, it may notify the entity that determines the offset amount of the surrounding cell situations. As a result, if the second cell determines that an interfering first cell does not exist, it is possible to omit notification of the surrounding cell situations. This can achieve the effects of avoiding complexity in the mobile communication system and effectively utilizing radio resources. The threshold may be determined statically. By determining the threshold statically, notification due to threshold changes is unnecessary. This can achieve the effect of avoiding complexity in the mobile communication system. The threshold may also be configurable. In this case, the network side notifies the entity that determines whether an interfering first cell exists of the threshold. As a notification method, the method shown in step ST2705 can be used. Depending on changes in the maximum permitted transmission power of each cell and communication conditions, it is possible that whether an interfering first cell exists may differ even if the second cell is installed in the same location. By making the threshold configurable, it is possible to achieve the effect of providing a flexible mobile communication system that can handle such cases. Furthermore, the first cell may notify the threshold value to an entity that determines whether or not there is an interfering first cell. As a notification method, the method shown in step ST2803 can be used. Since it is possible to set a unique threshold value for each cell, it is possible to set a threshold value according to the installation location of the first cell. Therefore, a flexible mobile communication system can be obtained.

[0187] Similarly, a threshold value can be used as a criterion for determining whether or not a cell is installed within the range of another cell. Similarly, when a second cell is installed, a threshold value can be used as a criterion for determining whether or not to perform processing to prevent channels that cannot be scheduled from using the same radio resource. This seventh modification can be used in combination with the third embodiment, the third modification, the fourth modification, the fifth modification, and the sixth modification. This seventh modification can achieve the same effects as those of the third embodiment.

[0188] Embodiment 4 Interference between downlink signals becomes a problem between cells that cannot perform handover or between cells that operate in closed access mode. As a solution to this problem, the first embodiment discloses that radio resources of signals that cannot be scheduled do not overlap between the cells. As a method for this, synchronization between the cells and shifting resources of signals that cannot be scheduled between the cells (providing an offset) are disclosed. The second embodiment discloses what value to use for the offset amount to solve the downlink inter-cell interference problem. The third embodiment discloses a method for determining the offset amount. Below, consider the case where a new cell is installed in a location where interference occurs between downlink signals from multiple cells.

[0189] FIG. 34 shows a conceptual diagram of the problem of the fourth embodiment. There are macrocell 3401 (eNB#1) and macrocell 3403 (eNB#2). Coverage area (within range) 3402 of macrocell 3401 and coverage area 3404 of macrocell 3403 are as shown in FIG. 34. Consider a case where CSG cell 3405 (eNB#3) is newly installed within the coverage areas of both eNB#1 and eNB#2, i.e., in the area belonging to 3402 and 3404. Coverage area (within range) 3406 of CSG cell 3405 is as shown in FIG. 34. Mobile terminal 3407 is located within this coverage area 3406. FIG. 34(b) shows the SIR of mobile terminal 3407 under communication conditions before CSG cell 3405 (eNB#3) is installed. The area above the dashed line indicates the SIR in which communication is possible. Even if mobile terminal 3407 moves from eNB#1 to eNB#2, mobile terminal 3407 can obtain the SIR shown by the dashed line in (b) by handing over from eNB#1 to eNB#2. As a result, even if mobile terminal 3407 moves from eNB#1 to eNB#2, mobile terminal 3407 is always able to communicate. Figure 34(c) shows the SIR for mobile terminal 3407 under communication conditions after eNB#3 is installed. The area above the dashed line indicates the SIR at which communication is possible. The thick dashed line indicates the SIR that mobile terminal 3407 receives from eNB#3. eNB#3 is a CSG cell. Also, consider the case where mobile terminal 3407 is not registered with eNB#3. Mobile terminal 3407 is unable to communicate with eNB#3 and is therefore unable to hand over to eNB#3. Therefore, when mobile terminal 3407 moves from eNB#1 to eNB#2, it will obtain the SIR shown by the dashed line in (c), which will not satisfy the SIR required for communication around eNB#3, meaning that communication will become impossible.

[0190] When a new eNB#3 is installed, it may be necessary to prevent the radio resources of signals that cannot be scheduled from eNB#1 or eNB#2 from overlapping between the cells. In this case, without any special measures, it is possible to prevent the radio resources of signals that cannot be scheduled from eNB#3 and eNB#1 from overlapping between the cells, or to prevent the radio resources of signals that cannot be scheduled from eNB#3 and eNB#2 from overlapping between the cells. Figure 35 shows conceptual diagrams of the results of downlink interference reduction in each case. Figure 35(a) shows a case in which the radio resources of signals that cannot be scheduled from eNB#3 and eNB#1 do not overlap between the cells. In this case, even if mobile terminal 3407 moves from eNB#1 to eNB#2, handover from mobile terminal 3407 from eNB#1 to eNB#2 allows the SIR indicated by the dashed-dotted line in (a) to be obtained. This ensures that mobile terminal 3407 can always communicate, even when it moves from eNB#1 to eNB#2. FIG. 35(b) shows a case where the radio resources of signals that cannot be scheduled by eNB#3 and eNB#2 do not overlap between the cells. In this case, when mobile terminal 3407 moves from eNB#1 to eNB#2, even if mobile terminal 3407 hands over from eNB#1 to eNB#2, only the SIR indicated by the dashed line in (b) can be obtained, which does not satisfy the SIR that allows communication around eNB#3, that is, communication becomes impossible. In other words, when a new cell is installed in a location where downlink signals from multiple cells interfere with each other, the question is how to coordinate to achieve the most effective downlink interference reduction. Specific examples of "coordination" here include synchronization processing, timing shift processing, and processing to set a timing offset. In this fourth embodiment, we will disclose how to coordinate to reduce downlink inter-cell interference when multiple first cells exist.

[0191] In the fourth embodiment, when a new cell is installed in a location where downlink signals from a plurality of first cells interfere with each other, the new cell is coordinated with the most interfering cell. The configuration for preventing overlap of resources of signals that cannot be scheduled between cells can use the method of the first embodiment, including its modified examples. The offset amount can also be the method of the second embodiment, including its modified examples. The offset amount (or frame configuration) can also be determined using the method of the third embodiment, including its modified examples. A specific example of a method for determining the most interfering cell (hereinafter referred to as a cooperative cell) is disclosed below. When "location information" is used in determining whether or not there is an interfering first cell (for example, step ST2703 in FIG. 27), the distance between the second cell and the first cell is used as the determination criterion. For example, the first cell with the shortest distance between it and the second cell among multiple first cells is determined to be the cooperative cell. When "surrounding cell conditions" are used in determining whether or not there is an interfering first cell, the communication quality of the surrounding cell conditions measured by the second cell is used as the determination criterion. As shown in Modification 3 of Embodiment 3, specific examples of communication quality include (1) the received power of the RS, (2) the ratio of the received power of the RS to the received power strength of the carrier frequency, (3) the received signal strength, (4) the ratio of the desired wave to the interference wave, (5) the received power of the RS in the RE, and (6) the amount of interference. For example, the cell with the highest measurement result of communication quality of the surrounding cell conditions measured by the second cell is determined to be the cooperative cell. When the "surrounding cell conditions" are used, the second cell notifies the entity that determines the offset amount of the surrounding cell conditions.

[0192] According to this fourth embodiment, when a new cell is installed in a location where interference occurs between downlink signals from multiple cells, it is possible to obtain a method for reducing downlink interference most efficiently. As a result, it is possible to obtain an effect that the area where communication is impossible can be reduced by installing a new cell.

[0193] Variation 1. This first modification discloses another solution to the same problem as in the fourth embodiment. This first modification discloses that when a new cell is installed in a location where downlink signals from a plurality of first cells interfere with each other, the new cell is coordinated with all of the first cells. That is, the timing (radio frame, SFN, etc.) is shifted (offset is provided) with respect to all of the first cells. The method of the first embodiment including the modification can be used for the configuration to prevent overlap of resources of signals that cannot be scheduled between cells. Furthermore, the method of the second embodiment including the modification can be used for the amount of offset. Furthermore, the method of the third embodiment including the modification can be used for the method of determining the amount of offset (or the frame configuration).

[0194] Consider a case where the number of first cells is large and exceeds the offset amount settable range (limited range of offset amounts) shown in embodiment 2. In this case, coordination is performed with the cell that causes the most interference. The specific method is the same as in embodiment 4. Furthermore, the timing is not shifted from that of the cell that causes the least interference, that is, the same timing is used. A specific example of a method for determining the cell that causes the least interference is disclosed below. When "location information" is used to determine whether or not there is an interfering first cell, the distance between the second cell and the first cell is used as the determination criterion. For example, the first cell that is the longest distance from the first cell among multiple first cells is determined to be the cell that causes the least interference. When "surrounding cell conditions" are used to determine whether or not there is an interfering first cell, the communication quality of the surrounding cell conditions measured by the second cell is used as the determination criterion. As shown in Modification 3, specific examples of communication quality include (1) RS reception power, (2) ratio of RS reception power to carrier frequency reception power strength, (3) received signal strength, (4) ratio of desired wave to interference wave, (5) RS reception power in RE, and (6) interference level. For example, the cell with the smallest measurement result of communication quality of the surrounding cell conditions measured by the second cell is determined to be the cell that causes the least interference. When the "surrounding cell conditions" are used, the second cell notifies the entity that determines the offset amount of the surrounding cell conditions. Modification 1 can achieve the following effects in addition to the effects of Embodiment 4. It is possible to reduce downlink interference with all first cells that cause interference between downlink signals within the offset amount configurable range. This makes it possible to achieve the effect of building a mobile communication system that further suppresses downlink interference.

[0195] Embodiment 5. Interference between downlink signals becomes a problem between cells that cannot perform handover or between cells operating in closed access mode. As a solution to this problem, the first embodiment discloses preventing overlap between the cells in either the time (timing) or the frequency, or both, of the physical resources onto which non-schedulable signals are mapped. As a method for achieving this, synchronization between the cells and shifting the resources of non-schedulable signals between the cells (providing an offset) are disclosed. Furthermore, the second embodiment discloses what value to use for the offset amount to solve the downlink inter-cell interference problem. Furthermore, the third embodiment discloses a method for determining the offset amount. The fourth embodiment discloses that, when a new cell is installed in a location where interference occurs between downlink signals from multiple first cells, the new cell is coordinated with the cell that causes the most interference. Using the solution of the first embodiment may result in the existence of cells with different frame configurations within the system. Specific examples of this solution include the first embodiment and the first modification of the first embodiment. When cells with different frame configurations exist within the system, a mobile terminal cannot communicate unless it knows the frame configuration used by the serving cell, the handover destination cell, or the cell to which it is reselected. Therefore, in the fifth embodiment, a specific method for notifying the frame configuration (or the offset amount) to the mobile terminal will be disclosed.

[0196] In the fifth embodiment, the second cell notifies a mobile terminal being served by the second cell of an offset amount of radio resources allocated to a signal causing interference between the first cell and the second cell, or information indicating a frame configuration. As a specific example, the second cell notifies a mobile terminal being served by the second cell of an offset amount of radio resources allocated to a signal causing interference between the first cell and the second cell, or information indicating a frame configuration, as an element of MIB (Master Information Block) information mapped to BCCH on PBCH. By notifying a mobile terminal being served by the second cell of an offset amount of a signal causing interference between the first cell and the second cell, or information indicating a frame configuration, as an element of MIB (Master Information Block) information mapped to BCCH on PBCH, the following effects can be obtained. For example, in an LTE communication system, the MIB is mapped to the PBCH, so that it can be received at an early stage of a search operation (a specific example is step ST1204 in FIG. 12 ). Therefore, by mapping the offset amount or information indicating the frame configuration to the MIB information, it is possible to prevent control delays and reduce power consumption. Furthermore, the offset amount or information indicating the frame configuration of the second cell can be notified only from the second cell, which eliminates the need for notification from the first cell, resulting in the effect of efficient use of radio resources.

[0197] As another method, the PCI of the second cell and the offset amount of the radio resources allocated to the signal that causes interference between the first cell and the second cell, or the PCI of the second cell and information indicating the frame configuration of the second cell are associated with each other. For example, the offset amount or the frame configuration may be calculated in the mobile terminal using the following equation:

[0198] Offset amount = PCI mod N (N: integer) Frame configuration information = PCI mod N (N: integer) By associating the PCI of the second cell with the offset amount of the radio resources allocated to the signal that causes interference between the first cell and the second cell, or by associating the PCI of the second cell with information indicating the frame configuration of the second cell, the following effects can be obtained. When the mobile terminal learns the PCI, it can also learn the offset amount or the frame configuration. The PCI of the cell can be learned at an early stage of the search operation (as a specific example, step ST1201 in FIG. 12). Compared to the first method, the second method allows the mobile terminal to learn the offset amount or the frame configuration of the second cell at an earlier stage of the search operation. This further prevents control delays and reduces power consumption. Furthermore, additional information is not required for the base station to notify the mobile terminal of the offset amount or the frame configuration. This results in an effective use of radio resources.

[0199] Another possible method is to statically determine the offset amount or frame configuration of radio resources allocated to signals that cause interference between the first cell and the second cell as a mobile communication system. As a specific example, the offset amount or frame configuration used in the second cell, and the offset amount or frame configuration when a CSG cell is installed within the macrocell area, are determined in advance by a standard. The determined offset amount or frame configuration may be one or more. In the case of multiple offset amounts or frame configurations, the mobile terminal can detect the offset amount or frame configuration used in the second cell using blind detection. By statically determining the offset amount or information indicating the frame configuration of radio resources allocated to signals that cause interference between the first cell and the second cell as a mobile communication system, the following advantages can be achieved. Specifically, since additional information indicating the offset amount or frame configuration is not required from the base station to the mobile terminal, the advantage of efficient utilization of radio resources can be achieved. Furthermore, since the mobile terminal does not use radio resources to learn the offset amount or frame configuration, the advantage of preventing reception errors can be achieved.

[0200] This fifth embodiment can be used in combination with the first embodiment including modifications, the second embodiment including modifications, the third embodiment including modifications, and the fourth embodiment including modifications. The fifth embodiment can provide the following effects. When an offset amount is provided between the first cell and the second cell in order to reduce downlink interference, it is possible to obtain an effect that a mobile terminal being served by the second cell can communicate even if the frame configurations of the first cell and the second cell are changed.

[0201] Variation 1. In the first embodiment, a method for preventing the existence of cells with different frame configurations within a system even when a solution is used has been disclosed. Specific examples of such a method include Modification 2 of the first embodiment and Modification 3 of the first embodiment. When downlink inter-cell interference is reduced without the existence of cells with different frame configurations within a system, it is possible to obtain an effect that the frame configuration (or offset amount) of the second cell does not need to be notified to the mobile terminal. That is, it is possible to obtain an effect that communication is possible with only a general search operation. In other words, since additional information indicating the offset amount or frame configuration is not required from the base station to the mobile terminal, it is possible to obtain an effect of efficient use of radio resources. Furthermore, since the mobile terminal does not use radio resources to know the offset amount or frame configuration, it is possible to obtain an effect that reception errors do not occur. On the other hand, during handover, etc., shortening the search time is an essential issue to prevent control delays. In this first modification, a method is disclosed that can be used to shorten the search time even with an interference mitigation method that enables communication with only a general search operation of the mobile terminal (as a specific example, see FIG. 12). The issue of shortening the search operation becomes apparent in the following specific example. FIG. 36 shows an example of the operation in this case until the mobile terminal determines that a cell is a "suitable cell."

[0202] In Figure 36, Steps ST3601 to ST3606 correspond to the processes of Steps ST1201 to ST1206 in Figure 12, and therefore description thereof will be omitted. If the UE that has received the TAC broadcast from the selected cell determines in Step ST3606 that the TAC in SIB1 is not the same as the TAC in the TA list of the UE, the UE moves to Step ST3607 and determines whether or not the cell is a CSG cell. To determine whether or not the cell is a CSG cell, the UE may use a CSG indicator that is currently proposed in 3GPP and that is broadcast by the cell by including it in broadcast information. If the UE determines in Step ST3607 that the cell is not a CSG cell, the UE moves to Step ST3610. If the UE determines in Step ST3603 that the TAC in SIB1 is the same as the TAC in the TA list of the UE, the UE moves to Step ST3610.

[0203] If it is determined in Step ST3607 that the cell is a CSG cell, the mobile terminal proceeds to Step ST3608. In Step ST3608, the mobile terminal determines whether it has a whitelist. If it has a whitelist, in Step ST3609, the mobile terminal compares the TAC (CSG-ID) included in the received SIB1 with the TAC (CSG-ID) in the whitelist it has. If the comparison reveals that the TAC (CSG-ID) is the same, the mobile terminal determines in Step ST3610 that the CSG cell is a "suitable cell." However, if the comparison of the TAC (CSG-ID) included in the SIB1 received in Step ST3609 with the CSG-ID (TAC) in the whitelist it has reveals that the same TAC (CSG-ID) is not found, the mobile terminal determines in Step ST3611 that the cell is not a "suitable cell" and is therefore prohibited from accessing the cell. Therefore, the mobile terminal must perform a cell search again in Step ST3612. Also, if the UE does not have a whitelist in Step ST3608, the UE is prohibited from accessing the cell in Step ST3611 because the cell is not an "appropriate cell." In this case, the UE is also unable to access the cell and must perform a cell search again in Step ST3612.

[0204] As described above, the introduction of CSG cells requires time to determine whether the target cell is a "suitable cell" during cell reselection and handover. CSG cells are being introduced in mobile communication systems such as LTE and UMTS. It is expected that a large number of CSG cells will be installed in the future. Interruptions to ongoing communications, especially during handover, are a major problem. Therefore, shortening the time it takes for a mobile terminal to determine whether a cell is a "suitable cell" is a major challenge for mobile communication systems.

[0205] This first modification discloses a method for solving the above problem. The serving cell notifies mobile terminals of offset information of neighboring cells (which may be information indicating the frame configuration). A specific example of the notification method is disclosed below. The serving cell notifies mobile terminals served by it of the offset information of neighboring cells as broadcast information. When the offset information is mapped to the BCCH, the following effects can be obtained. Because it is broadcast information, it can be notified within the coverage area of ​​the cell. Furthermore, the broadcast information is information that can be received even by mobile terminals that do not have a dedicated channel established with the serving cell, i.e., mobile terminals in idle state. Therefore, it is possible to obtain the effect of shortening the time required for a mobile terminal to determine whether a cell is "appropriate" when reselecting a cell. The offset information is newly added as an information element in the MIB (Master Information Block) in the broadcast information. The offset information is newly added as an information element in the SIB (System Information Block) in the broadcast information BCCH. Furthermore, the offset information is newly added as an information element in the SIB4. When the offset information is mapped to the SIB4, the following effects can be obtained. Currently, 3GPP is moving towards mapping the intra-frequency neighboring cell list to SIB4. Under such circumstances, the mobile terminal will be able to obtain the parameters used in the process of obtaining the status of neighboring cells by receiving the same system information, which will reduce the complexity of the mobile terminal's operation and prevent control delays.

[0206] In addition, offset information is newly added as an information element of SIB5. Mapping the offset information to SIB5 can achieve the following effects. In the current 3GPP, an inter-frequency neighboring cell list is planned to be mapped to SIB5. Under such circumstances, a mobile terminal can obtain parameters used in the process of obtaining the status of neighboring cells by receiving the same system information, thereby achieving the effects of avoiding complexity in the mobile terminal's operation and preventing control delays. In addition, if the second cell is a HeNB, offset information is newly added as an information element of SIB9. Mapping the offset information to SIB9 can achieve the following effects. In the current 3GPP, an HeNB identifier (a home eNB identifier (HNBID)) is planned to be mapped to SIB9. Under such circumstances, a mobile terminal can obtain parameters used in the process of obtaining information about a HeNB by receiving the same system information, thereby achieving the effects of avoiding complexity in the mobile terminal's operation and preventing control delays.

[0207] Furthermore, the offset information of neighboring cells may be mapped to a logical channel such as a shared control channel (CCCH), a dedicated control channel (DCCH), a multicast control channel (MCCH), or a multicast traffic channel (MTCH), and may further be mapped to a transport channel such as a downlink shared channel (DL-SCH) or a physical channel such as a physical downlink shared channel (PDSCH), and then notified to mobile terminals. Broadcast information is information that is periodically broadcast. Therefore, reducing the amount of broadcast information is an important issue from the perspective of effective utilization of radio resources. Therefore, when the offset information of neighboring cells is notified using a downlink shared channel, it is possible to notify mobile terminals of the offset information of neighboring cells without increasing the amount of broadcast information, thereby achieving the effect of effective utilization of radio resources.

[0208] Furthermore, offset information is newly added to control information (sometimes referred to as measurement control information) for measurements of neighboring cells that is notified from the serving cell to the mobile terminal. This allows the mobile terminal to obtain the parameters used in the process of measuring neighboring cells from the same information, thereby achieving the effects of avoiding complexity in the mobile terminal's operation and preventing control delays. Furthermore, it becomes possible to notify the mobile terminal of the offset information of neighboring cells without increasing the amount of information in the broadcast information, thereby achieving the effect of efficiently utilizing radio resources. As a specific example, it is possible to newly add the offset information as a new element to the existing information element (Meas Object EUTRA information element) (Non-Patent Document 11). This eliminates the need to create a new message, thereby achieving the effects of avoiding complexity in the operation of the mobile communication system and preventing control delays. Furthermore, as described above, the issue of Modification 1 is particularly noticeable during handover. Therefore, offset information is newly added as an information element for measurement control that is notified from the serving cell during handover processing. This allows the mobile terminal to obtain the parameters used in the handover process from the same information, which can avoid complexity in the mobile terminal's operation and prevent control delays.In addition, it allows the mobile terminal to be notified of offset information of neighboring cells without increasing the amount of information in the broadcast information, which can result in effective use of radio resources.

[0209] Specific examples of offset information are disclosed below. In specific example 1, a serving cell notifies an offset amount of a neighboring cell in coordination with its own cell. Specific examples of "coordination" here include synchronization processing, timing shifting processing, and setting an offset amount in the timing. If there are multiple neighboring cells, the offset amount may be notified for each PCI (or GCI). In specific example 2, a serving cell notifies an offset amount of a second cell within the serving cell's coverage area. Also, the serving cell notifies an offset amount of a CSG cell within the serving cell's coverage area. If there are multiple second cells, the offset amount may be notified for each PCI (or GCI). Specific example 2 is particularly effective in reducing the time required for handover processing from a macro cell to a CSG cell installed within the macro cell's coverage area. In specific example 3, a serving cell notifies an offset amount from a first cell. Also, the serving cell notifies an offset amount from a macro cell having the same coverage. If there are multiple first cells, the offset amount may be notified for each PCI (or GCI). Specific example 3 is particularly effective in shortening the time required for handover processing from a CSG cell to a macro cell having the same coverage. Specific example 4 is a case in which the serving cell notifies the first cell whether or not there is a cell other than the own cell that has the same offset amount as the own cell. Specific example 4 is particularly effective in shortening the time required for handover processing from a CSG cell to another CSG cell within the same macro cell area. Specific examples 1 to 4 can be used in combination. Furthermore, this modified example 1 can be used in combination with embodiment 1 including a modified example, embodiment 2 including a modified example, embodiment 3 including a modified example, embodiment 4 including a modified example, and embodiment 5 including a modified example.

[0210] The present modification 1 can provide the following effects. The serving cell notifies the mobile terminal of offset information of neighboring cells or information indicating the frame configuration. If the serving cell does not notify the mobile terminal of offset information of neighboring cells, the mobile terminal must perform blind detection of timing synchronization in step ST3601. Taking the LTE system as a specific example, the mobile terminal must perform blind detection of slot timing using P-SS in step ST3601. The present modification 1 allows the mobile terminal to obtain offset information of neighboring cells, making it possible to reduce the blind detection in step ST3601. This provides the effect of shortening the time required to determine whether a cell is a "suitable cell" at the time of cell reselection and handover.

[0211] The methods disclosed in the first to fifth embodiments, including the modifications, can be used as solutions to the following cases. When a macrocell, HeNB, HNB, picocell, or microcell that does not allow handover is installed as the second cell, the methods disclosed in the first to fifth embodiments, including the modifications, can be used as a method for reducing interference of downlink signals between a first cell and a second cell. By using the first to fifth embodiments, including the modifications, it is possible to prevent overlap between the first cell and the second cell in resources for signals that cannot be scheduled in the first cell and the second cell, thereby realizing interference reduction of downlink signals. Furthermore, when a macrocell, HeNB, HNB, picocell, or microcell that operates in a closed mode is installed as the second cell, the methods disclosed in the first to fifth embodiments, including the modifications, can be used as a method for reducing interference of downlink signals between a first cell and a second cell. By using the first to fifth embodiments, including the modifications, it is possible to prevent overlap between the first cell and the second cell in resources for signals that cannot be scheduled in the first cell and the second cell, thereby realizing interference reduction of downlink signals.

[0212] Furthermore, the methods disclosed in the first to fifth embodiments, including their modifications, can be used as a method for reducing interference between downlink signals between CSG cells (which may be HeNBs, HNBs, picocells, or microcells) when operating a dedicated channel, a co-channel, or a partial co-channel. By using the first to fifth embodiments, including their modifications, interference between downlink signals can be reduced by preventing overlap between CSG cells (HeNBs, HNBs, picocells, and microcells) of resources for signals that cannot be scheduled between CSG cells (HeNBs, HNBs, picocells, and microcells). While the above description focuses on the OFDM communication system, the first to fifth embodiments, including their modifications, can also be applied to the TDM communication system. By using the first to fifth embodiments, including their modifications, interference between downlink signals can be reduced by preventing overlap between the first cell and the second cell of resources for signals that cannot be scheduled between the first cell and the second cell of the TDM communication system. In the TDM communication system, the radio resources used for uplink transmission and the radio resources used for downlink transmission are separated in time. It is also possible to set an offset so that the radio resources used for downlink transmission of a first cell are used as the uplink radio resources of a second cell, and the radio resources used for uplink transmission of the first cell become the radio resources used for downlink transmission of the second cell, thereby making it possible to set a wide range of offset amounts that are effective in reducing downlink interference. As such, the solutions disclosed in the first to fifth embodiments, including the modified examples, are methods that are highly compatible with the TDM system.

[0213] Embodiment 6 Generally, when interference power from other cells becomes large within the coverage of a certain cell, a mobile terminal is allowed to perform handover (HO) or cell reselection to the other cell or another appropriate cell to prevent communication from being interrupted. However, if a mobile terminal is unable to perform handover or cell reselection to the cell, the interference power from the other cell increases, resulting in a problem of communication being interrupted. For example, when a CSG cell is introduced, an HNB / HeNB may be operated as a CSG cell in closed access mode, and the CSG cell may be installed within the coverage of a macro cell. In such a case, interference occurs between the macro cell and the CSG cell within the CSG coverage, causing a problem in that a mobile terminal that is not user-registered in the CSG cell cannot communicate with the macro cell due to interference from the CSG cell. Similarly, if a mobile terminal communicating in a CSG cell cannot handover to the macro cell (eNB), the same problem of communication being interrupted occurs. To solve these problems, Non-Patent Document 8 describes operation method E in which a cell is operated in open access mode. However, there is no mention of a method for setting this mode, for example, a method for determining which cells should be set to open access mode. A common thought would be to set all HeNBs / HNBs to open access mode, but this would cause a problem in that it would be impossible to operate as a CSG, such as setting closed access mode to allow access only to registered mobile terminals. Therefore, in this embodiment, in order to solve these problems, it is disclosed that cells where interference is a problem are made compatible with open access mode. Furthermore, a method for setting the mode when making a cell compatible with access mode is disclosed.

[0214] In the present embodiment, a determination is made as to whether interference is a problem in a cell, and if interference is a problem in a cell, the access mode is set to open access mode. First, to determine whether interference is a problem in a cell, part of the method for determining the offset amount disclosed in the third embodiment can be applied. For example, when a core network (CN, EPC) (MME, HeNBGW) makes the determination, ST2701 to ST2703 in FIG. 27 may be applied. If the result in ST2703 is YES, the CSG cell (HeNB / HNB) that has notified its installation in ST2701 may be set to open access mode. Also, for example, ST3001 to ST3005 in FIG. 30 may be applied. If the result in ST3005 is YES, the CSG cell (HeNB / HNB) that has notified its installation in ST3004 may be set to open access mode. Also, for example, when a CSG cell (HeNB / HNB) makes the determination, ST3001 to ST3101 in FIG. 31 may be applied. If the answer is YES in ST3101, the CSG cell (HeNB / HNB) may be set to open access mode. As a determination index, the method disclosed in the seventh modification of the third embodiment may be used. For example, the determination may be made using the location, downlink received power from other cells, and a threshold value of the received power for determining whether communication is possible.

[0215] Next, a method for setting a CSG cell (HeNB / HNB) to be compatible with the open access mode will be disclosed. For example, when the CSG cell (HeNB / HNB) makes the determination, the method shown in FIG. 37 is used. The CSG cell (HeNB / HNB) that determined the presence or absence of interference in ST3101 of FIG. 31 instructs the owner of the HeNB / HNB by, for example, displaying the determination result. The owner enables the mode setting (change) of the HeNB / HNB it owns. As a result, the owner sets (changes) the mode of the HeNB / HNB, as shown in ST3701 of FIG. 37. The HeNB / HNB that has set (changed) the mode notifies the core network of the set mode in ST3702. The core network notifies the HeNB / HNB of TAC in ST3703 according to the set mode. If the HeNB / HNB determines YES in ST3101 of FIG. 31, the owner, instructed of the result, sets (changes) the mode to be compatible with the open access mode. Open access mode is supported in open access mode or hybrid access mode. A HeNB / HNB that has been set (changed) to support open access mode notifies the core network of the mode in ST7102. The core network notifies the TAC for the mode in ST7103.

[0216] For example, when the core network makes the judgment, the method shown in Fig. 38 is used. The core network that has judged the presence or absence of interference in ST2703 of Fig. 27 sets (changes) the mode of the HeNB / HNB that has notified its installation in ST2701, based on the judgment result. In ST3801, the core network notifies the HeNB / HNB of the set (changed) mode, thereby setting (changing) the mode of the HeNB / HNB. The HeNB / HNB that has been notified of the set (changed) mode from the core network in ST3801 may set (change) the mode. Furthermore, the core network notifies the HeNB / HNB of the TAC in ST3802 depending on the set mode. The HeNB / HNB that has made the mode setting (change) may display the mode in ST3803 to indicate to its owner and users of mobile terminals located nearby in which mode the HeNB / HNB is operating. If the answer is YES in ST2703 of Fig. 27, the core network sets (changes) in ST3801 the mode of the HeNB / HNB notified in ST2701 that it has been installed to open access mode compatible. In addition, the core network notifies the TAC compatible with open access mode in ST3703. The HeNB / HNB that has been set (changed) to be compatible with open access mode displays the mode in ST3703 to indicate to its owner and users of mobile terminals located nearby that the HeNB / HNB is operating in open access mode compatible.

[0217] The interface used for notifying the access mode shown in ST3702 and ST3701 may be the S1 interface, as a specific example. By notifying the location information, which is new information, using the S1 interface, which is an existing interface, it is possible to obtain the effect of avoiding complexity in the mobile communication system. The method of notifying using the S1 interface may be the method of notifying the location information from the CSG cell to the EPC, or the method of notifying from the EPC to the macro cell or CSG cell for synchronization processing, as disclosed in the third embodiment. Furthermore, the notification of the access mode may be performed via a broadband line, etc.

[0218] The timing for setting (changing) the access mode may be when the HeNB / HNB is installed or when the power is changed from off to on. Alternatively, the setting may be semi-static, such as when a new interfering cell is installed. Furthermore, if it is known in advance that the HeNB / HNB will be installed in an area where interference will be a problem, only HeNBs / HNBs that are pre-configured to support the open access mode may be installed, or the owner and operator may decide in advance to set the HeNB / HNB to support the open access mode.

[0219] By using the access mode setting method disclosed in this embodiment, it is no longer necessary to set all HeNBs / HNBs to the open access mode regardless of whether inter-cell interference exists, and it is possible to make an appropriate HeNB / HNB compatible with the open access mode depending on whether inter-cell interference exists. Therefore, an effect is obtained that operation as a CSG is also possible. Note that even if a HeNB / HNB that is also intended to operate in the closed access mode is subject to inter-cell interference, it can be made compatible with both the closed access mode and the open access mode by setting (changing) it to the hybrid access mode in the above-mentioned mode setting method. When inter-cell interference becomes a problem, it is possible to solve the problem of communication being disconnected even when a mobile terminal cannot handover to or reselect a cell to those cells.

[0220] For example, Figure 39 shows a conceptual diagram of the received signal-to-interference ratio (SIR) at a mobile terminal in a situation where a HeNB operating as a CSG cell is installed within the coverage of a macrocell. Figure 39(a) shows the SIR in a conventional case. The horizontal axis represents the distance from the macrocell base station (eNB), and the vertical axis represents the SIR. A threshold a is set such that communication is possible when the SIR is greater than a and impossible when the SIR is less than a. Assume that the mobile terminal is not registered as a user with the CSG cell. When a CSG cell is installed within the coverage of a macrocell, and a mobile terminal communicating with the macrocell within the macrocell coverage moves into the coverage of a CSG cell installed within the macrocell coverage, radio waves from the CSG cell cause interference, hindering communication with the macrocell. As shown in Figure 39(a), when a HeNB is installed within the coverage of an eNB, the SIR of a mobile terminal communicating with the eNB in ​​the vicinity of the HeNB is extremely degraded. As shown by the dashed-dotted line, the SIR of the mobile terminal falls below threshold a near the HeNB. Therefore, the mobile terminal attempts to handover or reselect a cell to the HeNB. However, because the HeNB is a CSG cell in closed access mode, the mobile terminal is unable to perform handover or cell reselection to the CSG cell, resulting in communication being disconnected. However, by using the method disclosed in this embodiment, as shown in FIG. 39(b), any mobile terminal can be handed over to a HeNB that is configured (changed) to support open access mode near the HeNB. Therefore, the SIR of the mobile terminal does not fall below threshold a, as shown by the dashed-dotted line. Therefore, the mobile terminal can continue communication with the eNB or HeNB without being disconnected.

[0221] In the above example, the first cell and the second cell where interference is a problem are a macro cell and a HeNB / HNB, but not only these cells but also any cell capable of setting the access mode to open access mode may be used. Also, in the above example, the open access mode is set, but not only the setting to this mode but also a setting that enables handover may be used.

[0222] Variation 1. This modification discloses a method for setting or restricting either or both of the system bandwidth (full frequency bandwidth) and the center frequency (carrier) of a cell when inter-cell interference is a problem. Modification 3 of Embodiment 1 discloses a method for preventing overlap between cells in frequency domains to which unschedulable signals are mapped. Also, a method for providing a frequency offset to prevent overlap between cells in frequency domains to which unschedulable signals are mapped. This modification shows a method for setting the offset. First, to determine whether a cell is subject to interference, part of the method for determining the offset amount disclosed in Embodiment 3 can be applied, as in Embodiment 6. First, the method for determining the offset amount is determined based on either or both of the system bandwidth and the center frequency (carrier) of the interfering cell, within the allowable frequency offset range disclosed in Embodiment 2. The offset amount may be determined by, for example, a HeNB / HNB or a core network. If the core network recognizes the system bandwidth and the center frequency (carrier) of the interfering cell, the core network can determine the offset amount based on either or both of the system bandwidth and the center frequency (carrier) of the interfering cell. On the other hand, since the HeNB / HNB and the macro cell do not recognize the system bandwidth and center frequency (carrier) of the interfering cell, when the offset amount is determined by the HeNB / HNB or the macro cell, the core network may notify the HeNB / HNB or the macro cell of either or both of the system bandwidth and the center frequency (carrier). When the HeNB / HNB determines the offset amount, as another method, the method disclosed in Modification 2 of Embodiment 3, of acquiring either or both of the center frequency (carrier) of the cell by cell search and the system bandwidth of the cell in MIB (Master Information Block) information may be used. Furthermore, there are cases where the core network does not recognize the system bandwidth and center frequency (carrier) of the interfering cell.In this case, each cell that has determined that interference is a problem by the method disclosed in the third embodiment may notify the core network of either or both of its own cell's system bandwidth and center frequency (carrier). Next, as for the method of notifying the set offset amount, the offset amount notifying method disclosed in the third embodiment may be applied.

[0223] By using the method disclosed in this modification, it is possible to prevent overlapping of frequency domains in which signals that cannot be scheduled are mapped between cells. Furthermore, by using a method that combines the method disclosed in this modification with Embodiments 1 to 5, it is possible to obtain the same effects as those of Embodiments 1 to 5.

[0224] The frequency offset setting method disclosed in this modification can also be applied to cases where the CSG cell and the macro cell are operated in different dedicated frequency bands, or where some of the frequencies are operated in overlapping bands. In the above example, the first cell and the second cell where interference is a problem are a macro cell and a HeNB / HNB, but these cells are not the only cells that can be affected by interference.

[0225] Variation 2. This modification discloses that the first cell, the second cell, and the core network each determine whether to permit or deny installation of the second cell. For a cell to be installed later where interference is a problem, installation is denied to reduce interference, thereby preventing mobile terminals served by a cell installed earlier from being unable to communicate. The same method as in the sixth embodiment can be applied to determine whether interference is a problem for a cell. The method disclosed in the seventh modification of the third embodiment can be used as a determination indicator. For example, the determination indicator may be the location, downlink received power from other cells, or a received power threshold for determining whether communication is possible. Furthermore, the determination may be based on one or more of the number of mobile terminals present within the coverage area when the second cell is installed. The threshold for determining whether interference is present may be the same as or different from the threshold disclosed in the sixth or third embodiment. A separate threshold for permitting or denying installation may be set. This enables multiple stages of operation for the second cell, such as an operation in which installation is permitted but with an offset, or an operation in which installation is not permitted. Furthermore, by making a determination based on the number of mobile terminals present within the coverage when the second cell is installed, it is possible to avoid installation in areas where mobile terminals are densely packed, thereby enabling precise operation, such as avoiding situations where many mobile terminals are unable to communicate. The method of notifying whether installation is permitted / denied to the second cell, the interface used for the notification, or the notification timing can also be the same as the method disclosed in the access mode setting method of the sixth embodiment. In this case, it is also possible to notify only installation permission, rather than installation permission / denial. It is sufficient to set the cell to be operable only when an installation permission notification is received.

[0226] By using the above method, there is no need to adjust offsets between cells, which makes it possible to avoid making the system complicated. Also, since control at base stations and mobile terminals is simplified, it is possible to reduce the scale of control circuits and lower power consumption. Another effect is that it becomes possible to reduce the signaling load on the system.

[0227] Variation 3. As an interference reduction method when a cell where interference is a problem is installed, if a second cell is installed and the second cell interferes with the first cell, the first cell or the core network may instruct a mobile terminal located within the coverage of the second cell to perform handover or reselection to a cell operating on a different frequency (channel) from that of the second cell before the second cell starts operating. The method disclosed in the third embodiment can be applied to determine whether the second cell interferes with the first cell. A determining entity that determines that the second cell is interfering with the first cell notifies the first cell or the network of the interference. This allows the first cell to instruct the mobile terminal to perform handover or reselection in a cell-initiated or network-initiated manner. Furthermore, the first cell or the core network may determine which mobile terminals are located within the coverage of the second cell. This determination can be made based on location information of the location where the second cell is installed, which the first cell or the core network acquires. The method of obtaining or notifying the location information may be the same as that disclosed in the third embodiment.

[0228] Embodiment 7 The problems of the seventh embodiment are as follows. For example, there may be a service in which cells with the same CSG-ID are owned by the same owner, or cells with the same CSG-ID offer the same preferential charging treatment, or cells with the same CSG-ID offer the same preferential treatment in terms of communication speed. As a result, it is conceivable that a user would prefer to hand over to a cell having the same CSG-ID when performing a handover. In the current standard trend, a CSG-ID is associated with a TAC. A TAC is mapped to SIB1. Therefore, FIG. 40 shows the processing of a mobile terminal when performing a handover to a cell having the same CSG-ID without any special measures. In FIG. 40, steps with the same numbers as those in FIG. 36 execute the same or corresponding processing, and therefore, a description of the parts with the same step numbers will be omitted. In Step ST4001, the mobile terminal determines whether the CSG-ID (or TAC, TA) of the cell included in SIB1 is the same as that of the serving cell. If it determines that they are different, it moves to Step ST4002. If it determines that they are the same, it moves to Step ST4003. In Step ST4002, the UE deletes the cell from the cell search or measurement targets and proceeds to Step ST3601. In Step ST4003, the UE determines the cell as a handover destination. That is, the CSG-ID of the target cell at the time of handover is determined after receiving SIB1 in Step ST3605. If it is determined in Step ST4001 that the CSG-ID is different, the processes in Steps ST3601 to ST3605 are wasted. In a location where CSG cells with CSG-IDs different from that of the serving cell are densely installed, it is determined in Step ST4001 that the cell has a different CSG-ID many times, and the processes in Steps ST3601 to ST3605 are repeated. This causes problems such as exceeding the allowed handover time, interrupting ongoing communication, handover failure, or performing handover to a CSG-ID different from that of the serving cell that the user does not want due to the allowed time even though there is a cell with the same CSG-ID as the serving cell nearby. Therefore, a major challenge for a mobile communication system is to shorten the time it takes for a mobile terminal to obtain the CSG-ID of the target cell.

[0229] This embodiment discloses a method for solving the above-mentioned problems. A CSG cell having the same CSG-ID (or TAC, TA) as the serving cell is notified to a mobile terminal. As a specific example of the notifying method, the method of notifying offset information according to Variant 1 of Embodiment 5 can be used. As a specific example of the notified information, notifying the PCI (or list) of cells having the same CSG-ID as the serving cell can be considered. FIG. 41 shows the processing of a mobile terminal when performing a handover to a cell having the same CSG-ID as Embodiment 7. In FIG. 41, steps with the same numbers as those in FIGS. 36 and 40 execute the same or corresponding processing, and therefore descriptions of the same step numbers will be omitted. In Step ST4101, the mobile terminal determines whether or not the PCI of the cell obtained in Step ST3601 is the "PCI of a cell having the same CSG-ID as that of the serving cell" notified by the serving cell. Alternatively, the mobile terminal determines whether or not the PCI of the cell obtained in Step ST3601 is included in the "PCI list of cells having the same CSG-ID as that of the serving cell" notified by the serving cell. If it is the same PCI or if it exists in the list, the process proceeds to step ST3602, whereas if it is not the same PCI or if it does not exist in the list, the process proceeds to step ST4002.

[0230] This makes it possible to determine whether or not a cell has the same CSG-ID as the serving cell at the initial stage of handover operation (step ST4101). It is possible to eliminate unnecessary steps ST3602 to ST3605 for a cell having a CSG-ID different from that of the serving cell, which occurs in conventional techniques. Therefore, according to embodiment 7, it is possible to obtain the effect that handover to a cell having the same CSG-ID can be realized without causing a control delay.

[0231] Although the present disclosure has been described mainly in relation to an LTE system (E-UTRAN), it is also applicable to W-CDMA systems (UTRAN, UMTS) and LTE Advanced (LTE-Advanced). Furthermore, it is also applicable to mobile communication systems that employ a Closed Subscriber Group (CSG) and communication systems in which, like a CSG, an operator identifies subscribers and the identified subscribers are permitted access. In LTE Advanced and the like, not only base stations (eNB, HNB, HeNB, etc.) but also various types of devices or nodes are being considered for transmitting and receiving at multiple points and for multi-hopping. When interference becomes a problem due to the installation of these various devices or nodes, the present disclosure can be applied as a method for coordinating these devices or nodes to reduce interference. The interface disclosed in the third embodiment may be an interface provided between the devices or nodes. [Explanation of symbols]

[0232] 101 mobile terminal, 102 base station, 103 MME (Mobility Management Entity), 104 S-GW (Serving Gateway).

Claims

1. A mobile communication system including a mobile terminal and a plurality of base stations that perform wireless communication between the mobile terminal and the mobile terminal, A mobile communication system characterized in that, when a first base station among the plurality of base stations is an interference control base station that should control interference occurring between the first base station and a second base station among the plurality of base stations, the first base station is synchronized with the second base station, and a specific type of signal is transmitted from the first base station at a timing other than a timing at which the second base station transmits the specific type of signal.

2. A base station that performs wireless communication with a mobile terminal, A base station characterized in that, when it is an interference control base station that should control interference occurring with another base station, it synchronizes with the other base station and transmits a specific type of signal at a timing other than the timing at which the other base station transmits a specific type of signal.

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