Wireless communication system, base station, communication terminal

Abstract

To provide a communication system that can achieve data transmission at a relatively high speed and with relatively small delay, and that can accommodate a variety of communication terminal devices.SOLUTION: A wireless communication system includes a communication terminal and a base station, performs wireless communication between the communication terminal and the base station by adding cyclic prefixes to symbols, and the base station notifies the communication terminal of cyclic prefix settings. For example, the base station notifies the communication terminal of a cyclic prefix setting for each time domain.SELECTED DRAWING: Figure 7

Description

[Technical field]

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

[0002] In 3GPP (3rd Generation Partnership Project), a standardization organization for mobile communication systems, a communication method called Long Term Evolution (LTE) for wireless sections and System Architecture Evolution (SAE) for the overall system configuration including a core network and a wireless access network (hereinafter collectively referred to as a network) is being considered (see, for example, Non-Patent Documents 1 to 12). This communication method is also called a 3.9G (3.9 Generation) system.

[0003] LTE uses OFDM (Orthogonal Frequency Division Multiplexing) for downlink and SC-FDMA (Single Carrier Frequency Division Multiple Access) for uplink as its access method. Also, unlike W-CDMA (Wideband Code Division Multiple Access), LTE does not include circuit switching and is only a packet communication method.

[0004] The decisions made by 3GPP regarding the frame configuration in the LTE system, which are described in Non-Patent Document 1 (Chapter 5), will be described with reference to FIG. 1. FIG. 1 is an explanatory diagram showing the configuration of a radio frame used in an LTE communication system. In FIG. 1, one radio frame is 10 ms. The radio frame is divided into 10 equally sized subframes. The subframe is divided into two equally sized slots. The first and sixth subframes of each radio frame include a downlink synchronization signal. The synchronization signal includes a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS).

[0005] The decisions made by 3GPP regarding the channel configuration in the LTE system are described in Non-Patent Document 1 (Chapter 5). It is assumed that the same channel configuration as that of a non-CSG cell is used in a CSG (Closed Subscriber Group) cell.

[0006] The Physical Broadcast Channel (PBCH) is a channel for downlink transmission from a base station device (hereinafter, sometimes simply referred to as a "base station") to a communication terminal device (hereinafter, sometimes simply referred to as a "communication terminal") such as a mobile terminal device (hereinafter, sometimes simply referred to as a "mobile terminal"). A BCH transport block is mapped to four subframes in a 40 ms interval. There is no explicit signaling of the 40 ms timing.

[0007] The Physical Control Format Indicator Channel (PCFICH) is a channel for downlink transmission from a base station to a communication terminal. The PCFICH notifies the communication terminal of the number of OFDM (Orthogonal Frequency Division Multiplexing) symbols used for PDCCHs from the base station. The PCFICH is transmitted every subframe.

[0008] The Physical Downlink Control Channel (PDCCH) is a channel for downlink transmission from a base station to a communication terminal. The PDCCH reports resource allocation information for a Downlink Shared Channel (DL-SCH), which is one of the transport channels described below, resource allocation information for a Paging Channel (PCH), which is one of the transport channels described below, and Hybrid Automatic Repeat reQuest (HARQ) information for the DL-SCH. The PDCCH carries an uplink scheduling grant. The PDCCH carries Acknowledgement (Acknowledgement) / Nack (Negative Acknowledgement), which are response signals to uplink transmission. The PDCCH is also called an L1 / L2 control signal.

[0009] A physical downlink shared channel (PDSCH) is a channel for downlink transmission from a base station to a communication terminal. A downlink shared channel (DL-SCH), which is a transport channel, and a PCH, which is a transport channel, are mapped to the PDSCH.

[0010] A physical multicast channel (PMCH) is a channel for downlink transmission from a base station to communication terminals. A multicast channel (MCH), which is a transport channel, is mapped to the PMCH.

[0011] The Physical Uplink Control Channel (PUCCH) is a channel for uplink transmission from a communication terminal to a base station. The PUCCH carries Ack / Nack, which is a response signal to a downlink transmission. The PUCCH carries a CQI (Channel Quality Indicator) report. CQI is quality information that indicates the quality of received data or the quality of the communication path. The PUCCH also carries a Scheduling Request (SR).

[0012] A Physical Uplink Shared Channel (PUSCH) is a channel for uplink transmission from a communication terminal to a base station. An Uplink Shared Channel (UL-SCH), which is one of the transport channels, is mapped to the PUSCH.

[0013] The Physical Hybrid ARQ Indicator Channel (PHICH) is a channel for downlink transmission from a base station to a communication terminal. The PHICH carries Ack / Nack, which is a response signal to an uplink transmission. The Physical Random Access Channel (PRACH) is a channel for uplink transmission from a communication terminal to a base station. The PRACH carries a random access preamble.

[0014] Downlink reference signals (RS) are known symbols in LTE communication systems. The following five types of downlink reference signals are defined: Cell-specific Reference Signals (CRSs), MBSFN reference signals, UE-specific reference signals such as Demodulation Reference Signals (DM-RSs), Positioning Reference Signals (PRSs), and Channel-State Information Reference Signals (CSI-RSs). Reference signal received power (RSRP) measurement is one of the physical layer measurements of communication terminals.

[0015] The transport channel described in Non-Patent Document 1 (Chapter 5) will be explained. Among the downlink transport channels, the broadcast channel (BCH) is broadcast to the entire coverage of the base station (cell). The BCH is mapped to the physical broadcast channel (PBCH).

[0016] Retransmission control using HARQ (Hybrid ARQ) is applied to the Downlink Shared Channel (DL-SCH). DL-SCH can be broadcast to the entire coverage of a base station (cell). DL-SCH supports dynamic or semi-static resource allocation. Semi-static resource allocation is also called persistent scheduling. DL-SCH supports discontinuous reception (DRX) of communication terminals to reduce power consumption of communication terminals. DL-SCH is mapped to the physical downlink shared channel (PDSCH).

[0017] The Paging Channel (PCH) supports DRX of communication terminals to enable low power consumption of the communication terminals. The PCH is required to be broadcast to the entire coverage of the base station (cell). The PCH is mapped to physical resources such as the Physical Downlink Shared Channel (PDSCH) that can be dynamically used for traffic.

[0018] The Multicast Channel (MCH) is used for broadcasting to the entire coverage of a base station (cell). The MCH supports SFN combining of MBMS (Multimedia Broadcast Multicast Service) services (MTCH and MCCH) in multi-cell transmission. The MCH supports semi-static resource allocation. The MCH is mapped to the PMCH.

[0019] Among the uplink transport channels, the uplink shared channel (UL-SCH) is subject to retransmission control using HARQ (Hybrid ARQ). The UL-SCH supports dynamic or semi-static resource allocation. The UL-SCH is mapped to the physical uplink shared channel (PUSCH).

[0020] The Random Access Channel (RACH) is limited to control information. The RACH is subject to collision risk. The RACH is mapped to the Physical Random Access Channel (PRACH).

[0021] Let us explain about HARQ. HARQ is a technology that improves the communication quality of a transmission line by combining Automatic Repeat reQuest (ARQ) and Forward Error Correction. HARQ has the advantage that error correction works effectively by retransmission even for transmission lines whose communication quality changes. In particular, it is possible to obtain further quality improvement by combining the reception result of the initial transmission and the reception result of the retransmission when retransmitting.

[0022] An example of a retransmission method will be described below. If the received data cannot be decoded correctly on the receiving side, in other words, if a CRC (Cyclic Redundancy Check) error occurs (CRC=NG), the receiving side will send a "Nack" to the transmitting side. The transmitting side that receives the "Nack" will retransmit the data. If the received data can be decoded correctly on the receiving side, in other words, if no CRC error occurs (CRC=OK), the receiving side will send an "Ack" to the transmitting side. The transmitting side that receives the "Ack" will send the next data.

[0023] The logical channel described in Non-Patent Document 1 (Chapter 6) will be explained. The Broadcast Control Channel (BCCH) is a downlink channel for broadcast system control information. The logical channel BCCH is mapped to the broadcast channel (BCH) or the downlink shared channel (DL-SCH), which are transport channels.

[0024] The Paging Control Channel (PCCH) is a downlink channel for transmitting paging information and changes to system information. The PCCH is used when the network does not know the cell location of the communication terminal. The PCCH, which is a logical channel, is mapped to the Paging Channel (PCH), which is a transport channel.

[0025] A Common Control Channel (CCCH) is a channel for transmission control information between a communication terminal and a base station. CCCH is used when a communication terminal does not have an RRC connection with the network. In the downlink direction, CCCH is mapped to a transport channel, the Downlink Shared Channel (DL-SCH). In the uplink direction, CCCH is mapped to a transport channel, the Uplink Shared Channel (UL-SCH).

[0026] The Multicast Control Channel (MCCH) is a downlink channel for point-to-multipoint transmission. The MCCH is used for transmission of MBMS control information for one or several MTCHs from the network to communication terminals. The MCCH is used only by communication terminals receiving MBMS. The MCCH is mapped to the Multicast Channel (MCH), which is a transport channel.

[0027] A Dedicated Control Channel (DCCH) is a channel that transmits dedicated control information between a communication terminal and a network on a one-to-one basis. DCCH is used when a communication terminal is in an RRC connection. DCCH is mapped to an uplink shared channel (UL-SCH) in the uplink and to a downlink shared channel (DL-SCH) in the downlink.

[0028] A Dedicated Traffic Channel (DTCH) is a one-to-one communication channel for transmitting user information to an individual communication terminal. DTCH exists in both uplink and downlink. DTCH is mapped to an uplink shared channel (UL-SCH) in uplink and to a downlink shared channel (DL-SCH) in downlink.

[0029] A Multicast Traffic Channel (MTCH) is a downlink channel for transmitting traffic data from a network to a communication terminal. The MTCH is a channel used only by communication terminals receiving MBMS. The MTCH is mapped to a Multicast Channel (MCH).

[0030] CGI stands for Cell Global Identifier. ECGI stands for E-UTRAN Cell Global Identifier. CSG (Closed Subscriber Group) cells are introduced in LTE, LTE-A (Long Term Evolution Advanced) (described below), and UMTS (Universal Mobile Telecommunication System).

[0031] A CSG (Closed Subscriber Group) cell is a cell for which an operator has specified available subscribers (hereinafter sometimes referred to as a "specified subscriber cell"). The specified subscribers are permitted to access one or more cells in a PLMN (Public Land Mobile Network). The one or more cells to which the specified subscribers are permitted to access are called "CSG cell(s)". However, there are access restrictions in the PLMN.

[0032] A CSG cell is a part of a PLMN that broadcasts a unique CSG identity (CSG ID) and broadcasts a CSG indication of "TRUE". Members of a pre-registered and authorized subscriber group access the CSG cell using the CSG ID, which is access permission information.

[0033] The CSG ID is broadcast by a CSG cell or cells. There are a plurality of CSG IDs in an LTE communication system. The CSG ID is used by a communication terminal (UE) to facilitate access of CSG-related members.

[0034] The location of a communication terminal is tracked in units of an area consisting of one or more cells. Location tracking is performed to track the location of the communication terminal even when it is in standby mode and to enable the communication terminal to be called, in other words, to allow the communication terminal to receive calls. The area for tracking the location of this communication terminal is called a tracking area.

[0035] In 3GPP, base stations called Home-NodeB (Home-NB; HNB) and Home-eNodeB (Home-eNB; HeNB) are under consideration. HNB in ​​UTRAN and HeNB in ​​E-UTRAN are base stations for home, corporate and commercial access services, for example. Non-Patent Document 3 discloses three different modes of access to HeNB and HNB. Specifically, an open access mode, a closed access mode and a hybrid access mode are disclosed.

[0036] Each mode has the following characteristics: In the open access mode, the HeNB and the HNB are operated as normal cells of a normal operator. In the closed access mode, the HeNB and the HNB are operated as CSG cells, which are accessible only by CSG members. In the hybrid access mode, the HeNB and the HNB are operated as CSG cells to which non-CSG members are also allowed to access at the same time. In other words, a cell in the hybrid access mode (also called a hybrid cell) is a cell that supports both the open access mode and the closed access mode.

[0037] In 3GPP, among all physical cell identifiers (PCI), there is a PCI range reserved by the network for use in CSG cells (see Chapter 10.5.1.1 of Non-Patent Document 1). Dividing a PCI range is sometimes called PCI split. Information on PCI split (also called PCI split information) is notified by the base station to communication terminals under its control by system information. Being under the control of a base station means that the base station is the serving cell.

[0038] Non-Patent Document 4 discloses the basic operation of a communication terminal using PCI split. A communication terminal that does not have PCI split information must use all PCIs, for example, all 504 codes, to perform a cell search. On the other hand, a communication terminal that has PCI split information can perform a cell search using the PCI split information.

[0039] 3GPP is also working on the development of standards for Long Term Evolution Advanced (LTE-A) as Release 10 (see Non-Patent Documents 5 and 6). LTE-A is based on the LTE wireless communication method, and is configured by adding several new technologies to it.

[0040] In the LTE-A system, carrier aggregation (CA), which aggregates two or more component carriers (CCs) (also called "aggregation"), is being considered in order to support wider frequency bandwidths (transmission bandwidths) of up to 100 MHz.

[0041] When CA is configured, the UE has only one RRC connection with the network (NW). In the RRC connection, one serving cell provides NAS mobility information and security input. This cell is called a Primary Cell (PCell). In the downlink, the carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC). In the uplink, the carrier corresponding to the PCell is the Uplink Primary Component Carrier (UL PCC).

[0042] According to the capability of the UE, a secondary cell (SCell) is configured to form a pair of a PCell and a serving cell. In the downlink, the carrier corresponding to the SCell is a downlink secondary component carrier (DL SCC). In the uplink, the carrier corresponding to the SCell is an uplink secondary component carrier (UL SCC).

[0043] For one UE, a set of one PCell and a serving cell consisting of one or more SCells is configured.

[0044] New technologies for LTE-A include wider bandwidth extension and coordinated multiple point transmission and reception (CoMP). CoMP, which is being considered for LTE-A by 3GPP, is described in Non-Patent Document 7.

[0045] Mobile network traffic volume is on the rise, and communication speeds are also becoming faster. When LTE and LTE-A are fully operational, communication speeds are expected to increase further, leading to an increase in traffic volume.

[0046] In addition, the widespread use of smartphones and tablet devices has led to an explosive increase in traffic volume via cellular wireless communications, raising concerns about a shortage of wireless resources around the world.

[0047] To address the problem of increasing traffic volume, 3GPP is currently formulating the Release 12 standard. The Release 12 standard considers the use of small eNBs to handle the huge traffic volume that will be expected in the future. For example, technology is being considered that will increase communication capacity by installing many small eNBs to configure many small cells, thereby improving frequency utilization efficiency.

[0048] Among these, dual connectivity is discussed as a technology for connecting a communication terminal to both a macro cell and a small cell when the macro cell and the small cell overlap (see Non-Patent Document 11). Non-Patent Document 11 discloses dual connectivity as a technology for connecting a communication terminal to both a macro cell and a small cell when the macro cell and the small cell overlap.

[0049] Furthermore, in response to the increasing sophistication of mobile communications, fifth-generation (hereinafter sometimes referred to as "5G") wireless access systems are being considered, with services targeted to begin after 2020. For example, in Europe, an organization called METIS has compiled requirements for 5G (see Non-Patent Document 12).

[0050] Compared to the LTE system, the 5G wireless access system requires a system capacity that is 1,000 times greater, a data transmission speed that is 100 times greater, a data processing delay that is one-tenth (1 / 10), and 100 times the number of simultaneous connections of communication terminals, while also achieving further reductions in power consumption and reductions in equipment costs.

[0051] In order to satisfy the above requirements, the use of wideband frequencies to increase data transmission capacity, and the adoption of antenna beamforming technology that increases frequency utilization efficiency, increases data transmission capacity, and enables spatial multiplexing, are being considered.In addition, in order to secure wideband frequencies, the use of high frequencies such as the microwave (Super High Frequency: SHF) band of 3 to 30 GHz as frequencies to be used for wireless access is being considered.

[0052] When high frequencies are used, the wavelength becomes shorter, so there is a problem that the amount of attenuation of radio waves increases and the propagation distance of radio waves becomes shorter compared to conventional communication systems. Furthermore, the effect of Doppler shift becomes larger, and the moving speed of the communication terminal can have a significant impact on communication performance.

[0053] In addition, as various types of communication terminals will be accommodated in the 5G wireless access system, it will become necessary for the wireless access method to handle a wide range of communication terminals, from those compatible with high-speed data transmission such as 4K digital televisions to those compatible only with ultra-low-speed data transmission such as sensors, all in the same system.

[0054] Therefore, since it is difficult for the conventional LTE communication method to satisfy the requirements of 5G, new methods are being considered as 5G wireless access methods. [Prior art documents] [Non-patent literature]

[0055] [Non-Patent Document 1] 3GPP TS36.300 V11.7.0 [Non-Patent Document 2] 3GPP TS36.304 V11.2.0 [Non-Patent Document 3] 3GPP S1-083461 [Non-Patent Document 4] 3GPP R2-082899 [Non-Patent Document 5] 3GPP TR 36.814 V9.0.0 [Non-Patent Document 6] 3GPP TR 36.912 V10.0.0 [Non-Patent Document 7] 3GPP TR 36.819 V11.1.0 [Non-Patent Document 8] 3GPP TS 36.141 V11.1.0 [Non-Patent Document 9] 3GPP R1-134496 [Non-Patent Document 10] 3GPP R1-132236 [Non-Patent Document 11] 3GPP TR36.842 V0.2.0 [Non-Patent Document 12] "Scenarios, requirements and KPIs for 5G mobile and wireless system", [online], April 30, 2013, ICT-317669-METIS / D1.1, [Retrieved October 20, 2014], Internet<https: / / www.metis2020.com / documents / deliverables / > Summary of the Invention [Problem to be solved by the invention]

[0056] When trying to realize the above-mentioned requirements for a 5G wireless access system using the wireless access method used in LTE, there are some items that cannot be satisfied.

[0057] For example, when using high frequencies, the LTE specification OFDM subcarrier spacing of 15 kHz increases the effect of Doppler shift when moving at high speeds, resulting in significant degradation of communication performance. In addition, when processing a wide frequency band, the Fast Fourier Transform (FFT) size for OFDM modulation and demodulation increases, causing problems in implementation aspects such as circuit size and software processing volume. Here, FFT size refers to the number of sampling data in the time domain used when performing FFT.

[0058] In addition, since the LTE specifications process data in subframe (1 ms) units, in order to meet the requirement of low latency that is one-tenth (1 / 10) of that of LTE, the radio frame needs to be made smaller.

[0059] Therefore, it is impossible to apply the conventional LTE radio access method to a 5G radio access system without some ingenuity.

[0060] An object of the present disclosure is to provide a communication system capable of achieving data transmission at a relatively high speed and with a relatively small delay, and capable of accommodating a variety of communication terminal devices. [Means for solving the problem]

[0061] The wireless communication system of the present disclosure includes a communication terminal and a base station, and performs wireless communication between the communication terminal and the base station by adding a cyclic prefix to a symbol, and transmits a cyclic prefix to the communication terminal from the base station. Frequency domain The cyclic prefix setting is notified. Effect of the Invention

[0062] According to the communication system of the present disclosure, it is possible to obtain a communication system that can realize data transmission at a relatively high speed and with a relatively small delay, and that can accommodate various communication terminal devices.

[0063] The objects, features, aspects, and advantages of the present disclosure will become more apparent from the following detailed description and the accompanying drawings. [Brief description of the drawings]

[0064] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of a radio frame used in an LTE communication system. [Diagram 2] 1 is a block diagram showing the overall configuration of a communication system 200 based on the LTE standard that is being discussed in 3GPP. [Diagram 3] FIG. 3 is a block diagram showing a configuration of a mobile terminal 202 shown in FIG. 2, which is a communication terminal according to the present disclosure. [Figure 4] FIG. 3 is a block diagram showing a configuration of a base station 203 shown in FIG. 2 which is a base station according to the present disclosure. [Diagram 5] FIG. 2 is a block diagram showing the configuration of an MME according to the present disclosure. [Figure 6] 1 is a flowchart showing an overview of operations from cell search to standby performed by a communication terminal (UE) in an LTE communication system. [Figure 7] A diagram showing the concept of a cell configuration when macro eNBs and small eNBs are mixed. [Figure 8] FIG. 2 is a diagram showing an example of a signal used in the first embodiment of the present disclosure. [Figure 9] FIG. 11 is a diagram showing another example of signals used in the first embodiment of the present disclosure. [Figure 10] FIG. 1 is a diagram illustrating an example of a signal in which signals with different OFDM subcarrier intervals are mixed in time units. [Figure 11] FIG. 1 is a diagram illustrating an example of a signal in which signals with different OFDM subcarrier intervals are mixed in frequency units. [Figure 12]FIG. 1 is a diagram illustrating an example of a signal in which signals with different OFDM subcarrier intervals in time and frequency are mixed. [Figure 13] 13 is a diagram showing another example of a signal in the case where signals with different OFDM subcarrier intervals in time unit and frequency unit are mixed. FIG. [Figure 14] FIG. 11 is a diagram showing an example of a format used in the second embodiment of the present disclosure. [Figure 15] 1 is a diagram illustrating an example of the light-speed propagation distance of delay dispersion due to a direct wave and a reflected wave of a communication terminal. [Figure 16] FIG. 13 is a diagram illustrating an example of a resource block into which a known sequence is inserted. [Figure 17] FIG. 13 is a diagram illustrating an example of a resource block into which a known sequence is inserted. [Figure 18] FIG. 13 is a diagram for explaining a modified example of the second method. [Figure 19] FIG. 13 is a diagram showing an example of radio formats of cell #1 and cell #2. [Figure 20] FIG. 13 is a diagram showing an example of parameters of radio formats of cell #1 and cell #2. [Figure 21] FIG. 2 is a diagram showing an example of radio formats of cells #1 to #3. [Figure 22] FIG. 11 is a diagram showing an example of parameters of radio formats of cells #1 to #3. [Figure 23] FIG. 1 illustrates a system in which cells of different independent base stations are adjacent to each other. [Figure 24] FIG. 1 is a diagram showing a system in which one base station centrally manages multiple cells. [Diagram 25] A diagram showing a system in which small cells are overlaid on macro cells. [Figure 26] FIG. 13 is a diagram for explaining the timing for changing the data symbol length. [Figure 27] FIG. 1 is a diagram illustrating an example of an insertion ratio of a cell-specific reference signal (CRS). [Figure 28] FIG. 1 is a diagram illustrating an example of an insertion interval of a cell-specific reference signal (CRS). [Figure 29] 11 is a diagram showing an example of an insertion interval and an insertion ratio of CRS when the OFDM symbol length is different. FIG. [Diagram 30] FIG. 13 is a diagram illustrating an example of a control operation in a communication system according to a fifth embodiment. [Diagram 31] A diagram showing an example of the TTI period of UE#1 and UE#2. [Diagram 32] FIG. 11 is a diagram illustrating an example of a HARQ period when different TTIs are mixed. [Diagram 33] FIG. 2 is a diagram showing an example of data allocation to OFDM symbols within a TTI. [Diagram 34] FIG. 2 is a diagram showing an example of allocation of a synchronization signal (SS) and data. [Diagram 35] FIG. 2 is a diagram showing an example of an arrangement of synchronization signals (SS) in a frequency band. [Diagram 36] FIG. 11 is a diagram showing another example of an arrangement of synchronization signals (SS) in a frequency band. [Figure 37] 10 is a flowchart showing a processing procedure of a communication terminal relating to a synchronization signal detection process. [Figure 38] FIG. 1 is a diagram showing an example of a method for arranging a synchronization signal (SS) in the frequency domain. [Figure 39] FIG. 13 is a diagram illustrating a configuration of a communication system according to an eighth embodiment of the present disclosure. [Diagram 40] FIG. 23 is a block diagram showing a configuration of a communication system according to an eighth embodiment of the present disclosure. [Diagram 41] FIG. 5 is a block diagram showing the configuration of a base station transmission processing unit 5101 when a backhaul signal transmission method is used. [Diagram 42] FIG. 5 is a block diagram showing a configuration of a base station transmission processing unit 5101 when a dual connectivity signal transmission method is used. [Diagram 43] FIG. 5 is a block diagram showing the configuration of a base station transmission processing unit 5101 when a fronthaul signal transmission method is used. [Diagram 44] FIG. 5 is a block diagram showing the configuration of a base station reception processing unit 5102 when a backhaul signal transmission method is used. [Diagram 45]FIG. 5 is a block diagram showing a configuration of a base station reception processing unit 5102 when a dual connectivity signal transmission method is used. [Diagram 46] FIG. 5 is a block diagram showing the configuration of a base station reception processing unit 5102 when a fronthaul signal transmission method is used. [Figure 47] 5 is a block diagram showing the configuration of a base station mode reception processing unit 5105. FIG. [Figure 48] 13 is a block diagram showing the configuration of a mobile terminal mode reception processing unit 5106 when a backhaul signal transmission method is used. FIG. [Figure 49] 13 is a block diagram showing the configuration of a mobile terminal mode reception processing unit 5106 when the dual connectivity signal transmission method is used. FIG. [Figure 50] 13 is a block diagram showing the configuration of a mobile terminal mode reception processing unit 5106 when a fronthaul signal transmission method is used. FIG. [Figure 51] 13 is a block diagram showing the configuration of a base station mode transmission processing unit 5108 when a backhaul signal transmission method is used. FIG. [Figure 52] 13 is a block diagram showing the configuration of a base station mode transmission processing unit 5108 when a dual connectivity signal transmission method is used. FIG. [Figure 53] 13 is a block diagram showing the configuration of a base station mode transmission processing unit 5108 when a fronthaul signal transmission method is used. FIG. [Figure 54] 5109 is a block diagram showing the configuration of a mobile terminal mode transmission processing unit 5109. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] Embodiment 1 Fig. 2 is a block diagram showing the overall configuration of an LTE-based communication system 200 being discussed in 3GPP. Fig. 2 will now be described. The radio access network is called E-UTRAN (Evolved Universal Terrestrial Radio Access Network) 201. A mobile terminal device (hereinafter referred to as "mobile terminal (User Equipment: UE)") 202, which is a communication terminal device, is capable of wireless communication with a base station device (hereinafter referred to as "base station (E-UTRAN NodeB: eNB)") 203, and transmits and receives signals via wireless communication.

[0066] Here, the term "communication terminal device" includes not only mobile terminal devices such as mobile mobile phone terminal devices, but also stationary devices such as sensors. In the following description, the "communication terminal device" may be simply referred to as a "communication terminal."

[0067] If control protocols for mobile terminals 202, such as Radio Resource Control (RRC), and user plane protocols, such as Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC), and Physical layer (PHY), terminate in a base station 203, then E-UTRAN is composed of one or more base stations 203.

[0068] A control protocol RRC (Radio Resource Control) between the mobile terminal 202 and the base station 203 performs broadcast, paging, RRC connection management, etc. The states of the base station 203 and the mobile terminal 202 in RRC include RRC_IDLE and RRC_CONNECTED.

[0069] In RRC_IDLE, PLMN (Public Land Mobile Network) selection, system information (SI) broadcast, paging, cell re-selection, mobility, etc. are performed. In RRC_CONNECTED, the mobile terminal has an RRC connection and can transmit and receive data with the network. In addition, in RRC_CONNECTED, handover (HO), measurement of neighbor cells, etc. are performed.

[0070] The base station 203 is classified into an eNB 207 and a Home-eNB 206. The communication system 200 includes an eNB group 203-1 including a plurality of eNBs 207, and a Home-eNB group 203-2 including a plurality of Home-eNBs 206. A system including an EPC (Evolved Packet Core) which is a core network and an E-UTRAN 201 which is a radio access network is called an EPS (Evolved Packet System). The EPC which is a core network and the E-UTRAN 201 which is a radio access network may be collectively called a "network."

[0071] The eNB207 is connected to a Mobility Management Entity (MME), or a Serving Gateway (S-GW), or an MME / S-GW unit (hereinafter sometimes referred to as an "MME unit") 204 including an MME and an S-GW via an S1 interface, and control information is communicated between the eNB207 and the MME unit 204. A plurality of MME units 204 may be connected to one eNB207. The eNBs 207 are connected to each other via an X2 interface, and control information is communicated between the eNBs 207.

[0072] The Home-eNB 206 is connected to the MME unit 204 via an S1 interface, and control information is communicated between the Home-eNB 206 and the MME unit 204. A plurality of Home-eNBs 206 are connected to one MME unit 204. Alternatively, the Home-eNB 206 is connected to the MME unit 204 via a Home-eNB GateWay (HeNBGW) 205. The Home-eNB 206 and the HeNBGW 205 are connected to each other via an S1 interface, and the HeNBGW 205 and the MME unit 204 are connected to each other via the S1 interface.

[0073] One or more Home-eNBs 206 are connected to one HeNBGW 205, and information is communicated through an S1 interface. The HeNBGW 205 is connected to one or more MME units 204, and information is communicated through an S1 interface.

[0074] The MME unit 204 and the HeNBGW 205 are upper devices, specifically, upper nodes, and control connections between the eNB 207 and the Home-eNB 206, which are base stations, and the mobile terminal (UE) 202. The MME unit 204 constitutes the EPC, which is a core network. The base station 203 and the HeNBGW 205 constitute the E-UTRAN 201.

[0075] Furthermore, 3GPP is considering the following configuration. The X2 interface between Home-eNBs 206 is supported. That is, the Home-eNBs 206 are connected via the X2 interface, and control information is communicated between the Home-eNBs 206. From the MME unit 204, the HeNBGW 205 appears as the Home-eNB 206. From the Home-eNB 206, the HeNBGW 205 appears as the MME unit 204.

[0076] In either case where the Home-eNB 206 is connected to the MME unit 204 via the HeNBGW 205 or where the Home-eNB 206 is directly connected to the MME unit 204, the interface between the Home-eNB 206 and the MME unit 204 is the same, that is, the S1 interface.

[0077] The base station 203 may configure one cell or multiple cells. Each cell has a predetermined range as a coverage area in which communication with the mobile terminal 202 is possible, and performs wireless communication with the mobile terminal 202 within the coverage area. When one base station 203 configures multiple cells, each cell is configured to be able to communicate with the mobile terminal 202.

[0078] FIG. 3 is a block diagram showing the configuration of the mobile terminal 202 shown in FIG. 2, which is a communication terminal according to the present disclosure. The transmission process of the mobile terminal 202 shown in FIG. 3 will be described. First, the control data from the protocol processing unit 301 and the user data from the application unit 302 are stored in the transmission data buffer unit 303. The data stored in the transmission data buffer unit 303 is passed to the encoder unit 304, where encoding such as error correction is performed. There may be data that is directly output from the transmission data buffer unit 303 to the modulation unit 305 without encoding. The data that has been encoded by the encoder unit 304 is modulated by the modulation unit 305. The modulated data is converted into a baseband signal, and then output to the frequency conversion unit 306, where it is converted into a wireless transmission frequency. Then, a transmission signal is transmitted from the antenna 307 to the base station 203.

[0079] Moreover, the receiving process of the mobile terminal 202 is executed as follows. A radio signal from the base station 203 is received by the antenna 307. The received signal is converted from a radio receiving frequency to a baseband signal by the frequency conversion unit 306, and demodulated by the demodulation unit 308. The demodulated data is passed to the decoder unit 309, where decoding such as error correction is performed. Of the decoded data, the control data is passed to the protocol processing unit 301, and the user data is passed to the application unit 302. A series of processes of the mobile terminal 202 is controlled by the control unit 310. Therefore, although the control unit 310 is omitted in FIG. 3, it is connected to each of the units 301 to 309.

[0080] 4 is a block diagram showing a configuration of the base station 203 shown in FIG. 2 which is a base station according to the present disclosure. A transmission process of the base station 203 shown in FIG. 4 will be described. The EPC communication unit 401 transmits and receives data between the base station 203 and the EPC (MME unit 204, etc.), the HeNBGW 205, etc. The other base station communication unit 402 ... other base station. The EPC communication unit 401 and the other base station communication unit 402 each transmit and receive information to and from a protocol processing unit 403. The control data from the protocol processing unit 403, and the user data and control data from the EPC communication unit 401 and the other base station communication unit 402 are stored in a transmission data buffer unit 404.

[0081] The data stored in the transmission data buffer unit 404 is passed to the encoder unit 405, where it is subjected to encoding processing such as error correction. Some data may be output directly from the transmission data buffer unit 404 to the modulator unit 406 without being encoded. The encoded data is modulated in the modulator unit 406. The modulated data is converted into a baseband signal, and then output to the frequency converter unit 407, where it is converted into a radio transmission frequency. The transmission signal is then transmitted from the antenna 408 to one or more mobile terminals 202.

[0082] Moreover, the reception process of the base station 203 is executed as follows. A radio signal from one or more mobile terminals 202 is received by an antenna 408. The received signal is converted from a radio reception frequency to a baseband signal by a frequency conversion unit 407, and demodulated by a demodulation unit 409. The demodulated data is passed to a decoder unit 410, where a decoding process such as error correction is performed. Of the decoded data, the control data is passed to a protocol processing unit 403 or an EPC communication unit 401 or an other base station communication unit 402, and the user data is passed to the EPC communication unit 401 and the other base station communication unit 402. A series of processes of the base station 203 is controlled by a control unit 411. Therefore, although the control unit 411 is omitted in FIG. 4, it is connected to each unit 401 to 410.

[0083] FIG. 5 is a block diagram showing the configuration of the MME according to the present disclosure. FIG. 5 shows the configuration of the MME 204a included in the MME unit 204 shown in FIG. 2 described above. The PDN GW communication unit 501 transmits and receives data between the MME 204a and the PDN GW. The base station communication unit 502 transmits and receives data between the MME 204a and the base station 203 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 501 to the base station communication unit 502 via the user plane communication unit 503 and transmitted to one or more base stations 203. If the data received from the base station 203 is user data, the user data is passed from the base station communication unit 502 to the PDN GW communication unit 501 via the user plane communication unit 503 and transmitted to the PDN GW.

[0084] When the data received from the PDN GW is control data, the control data is passed from the PDN GW communication unit 501 to the control plane control unit 505. When the data received from the base station 203 is control data, the control data is passed from the base station communication unit 502 to the control plane control unit 505.

[0085] The HeNBGW communication unit 504 is provided when a HeNBGW 205 is present, and transmits and receives data via an interface (IF) between the MME 204a and the HeNBGW 205 depending on the information type. Control data received from the HeNBGW communication unit 504 is passed from the HeNBGW communication unit 504 to a control plane control unit 505. A result of processing in the control plane control unit 505 is transmitted to the PDN GW via the PDN GW communication unit 501. In addition, a result of processing in the control plane control unit 505 is transmitted to one or more base stations 203 by the S1 interface via the base station communication unit 502, and is also transmitted to one or more HeNBGW 205 via the HeNBGW communication unit 504.

[0086] The control plane control unit 505 includes a NAS security unit 505-1, an SAE bearer control unit 505-2, an idle state mobility management unit 505-3, etc., and performs general processing for the control plane. The NAS security unit 505-1 performs security for NAS (Non-Access Stratum) messages, etc. The SAE bearer control unit 505-2 performs management of SAE (System Architecture Evolution) bearers, etc. The idle state mobility management unit 505-3 performs mobility management in the idle state (also called the LTE-IDLE state or simply idle), generation and control of paging signals in the idle state, addition, deletion, update, search, tracking area list management, etc. for one or more mobile terminals 202 under its control.

[0087] The MME 204a distributes a paging signal to one or more base stations 203. The MME 204a also performs mobility control in an idle state. The MME 204a manages a tracking area list when the mobile terminal is in an idle state and in an active state. The MME 204a initiates a paging protocol by transmitting a paging message to a cell that belongs to a tracking area in which the UE is registered. The idle state mobility management unit 505-3 may manage the CSG and CSG ID of the Home-eNB 206 connected to the MME 204a, and manage the whitelist.

[0088] Next, an example of a cell search method in a communication system is shown. Fig. 6 is a flow chart showing an outline of a process from cell search to standby operation performed by a communication terminal (UE) in an LTE communication system. When the communication terminal starts a cell search, in step ST601, the communication terminal synchronizes slot timing and frame timing using a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS) transmitted from a surrounding base station.

[0089] P-SS and S-SS are collectively called the Synchronization Signal (SS). The Synchronization Signal (SS) is assigned a synchronization code that corresponds one-to-one to the PCI assigned to each cell. 504 different PCIs are being considered. These 504 different PCIs are used to achieve synchronization and to detect (identify) the PCI of the synchronized cell.

[0090] Next, in step ST602, for the synchronized cell, a cell-specific reference signal (CRS), which is a reference signal (RS) transmitted from the base station for each cell, is detected and the RS received power (Reference Signal Received Power: RSRP) is measured. A code that has a one-to-one correspondence with the PCI is used for the reference signal (RS). By correlating with the code, it is possible to separate the cell from other cells. By deriving the code for the RS of the cell from the PCI identified in step ST601, it is possible to detect the RS and measure the RS received power.

[0091] Next, in step ST603, the cell with the best RS reception quality, for example the cell with the highest RS reception power, that is, the best cell, is selected from among one or more cells detected up to step ST602.

[0092] Next, in step ST604, the PBCH of the best cell is received to obtain the BCCH, which is broadcast information. A MIB (Master Information Block) including cell configuration information is mapped to the BCCH on the PBCH. Therefore, the MIB can be obtained by receiving the PBCH and obtaining the BCCH. Examples of MIB information include the downlink system bandwidth (abbreviated as dl-bandwidth), the number of transmitting antennas, and the number of system frames (System Frame Number: SFN). The downlink system bandwidth is also called the transmission bandwidth configuration.

[0093] Next, in step ST605, the DL-SCH of the cell is received based on the cell configuration information in the MIB, and SIB (System Information Block) 1 in the broadcast information BCCH is obtained. SIB 1 includes information on access to the cell, information on cell selection, and scheduling information of other SIBs (SIBk; k is an integer ≧2). SIB 1 also includes a tracking area code (TAC).

[0094] Next, in step ST606, the communication terminal compares the TAC of the SIB1 received in step ST605 with the TAC portion of the tracking area identity (TAI) in the tracking area list that the communication terminal already holds. The tracking area list is also called a TAI list. The TAI is identification information for identifying a tracking area, and is composed of a MCC (Mobile Country Code), an MNC (Mobile Network Code), and a TAC (Tracking Area Code). The MCC is a country code. The MNC is a network code. The TAC is a code number of the tracking area.

[0095] If the TAC received in step ST605 is the same as the TAC included in the tracking area list as a result of the comparison in step ST606, the communication terminal enters standby mode in the cell. If the TAC received in step ST605 is not included in the tracking area list as a result of the comparison, the communication terminal requests a core network (EPC) including an MME, etc., to change the tracking area in order to perform a Tracking Area Update (TAU) through the cell.

[0096] An apparatus constituting a core network (hereinafter sometimes referred to as a "core network side apparatus") updates the tracking area list based on an identification number (such as a UE-ID) of a communication terminal sent from the communication terminal together with a TAU request signal. The core network side apparatus transmits the updated tracking area list to the communication terminal. The communication terminal rewrites (updates) the TAC list held by the communication terminal based on the received tracking area list. After that, the communication terminal enters standby mode in the cell.

[0097] The spread of smartphones and tablet devices has led to an explosive increase in traffic via cellular wireless communications, raising concerns about a shortage of wireless resources around the world. In response to this, efforts are being made to create smaller cells and promote spatial separation in order to improve frequency utilization efficiency.

[0098] In a conventional cell configuration, a cell configured by an eNB has a relatively wide coverage area. Conventionally, a cell is configured to cover a certain area by the relatively wide coverage areas of a plurality of cells configured by a plurality of eNBs.

[0099] In the case of small cell configuration, the cell configured by the eNB has a narrower coverage range than the coverage of the cell configured by the conventional eNB. Therefore, as in the past, in order to cover a certain area, a large number of small cell eNBs are required compared to the conventional eNBs.

[0100] In the following description, a cell with a relatively large coverage, such as a cell configured by a conventional eNB, is referred to as a "macro cell," and an eNB that configures the macro cell is referred to as a "macro eNB." Also, a cell with a relatively small coverage, such as a cell that has been made into a small cell, is referred to as a "small cell," and an eNB that configures the small cell is referred to as a "small eNB."

[0101] The macro eNB may be, for example, a “Wide Area Base Station” as described in Non-Patent Document 8.

[0102] The small eNB may be, for example, a low power node, a local area node, a hotspot, etc. Also, the small eNB may be a pico eNB constituting a pico cell, a femto eNB constituting a femto cell, a HeNB, a remote radio head (RRH), a remote radio unit (RRU), a remote radio equipment (RRE), or a relay node (RN). Also, the small eNB may be a "local area base station" or a "home base station" as described in Non-Patent Document 8.

[0103] 7 is a diagram showing the concept of a cell configuration when macro eNBs and small eNBs are mixed. A macro cell configured by a macro eNB has a relatively wide coverage area 701. A small cell configured by a small eNB has a coverage area 702 that is smaller than the coverage area 701 of the macro eNB (macro cell).

[0104] When multiple eNBs are mixed, the coverage of a cell configured by one eNB may be included in the coverage of a cell configured by another eNB. In the cell configuration shown in Fig. 7, as shown by reference numerals "704" and "705", the coverage 702 of a small cell configured by a small eNB may be included in the coverage 701 of a macro cell configured by a macro eNB.

[0105] Also, as indicated by reference numeral "705," the coverage of multiple, for example, two, small cells 702 may be included within the coverage of one macro cell 701. A mobile terminal (UE) 703 is included, for example, within the coverage 702 of the small cell and communicates via the small cell.

[0106] Furthermore, in the cell configuration shown in FIG. 7, as indicated by reference numeral "706," there may be cases where coverage 701 of a macro cell formed by a macro eNB and coverage 702 of a small cell formed by a small eNB overlap in a complex manner.

[0107] Also, as indicated by reference numeral "707," there may be cases where coverage 701 of a macro cell configured by a macro eNB and coverage 702 of a small cell configured by a small eNB do not overlap.

[0108] Furthermore, as indicated by reference numeral "708," there may be cases where the coverage 702 of multiple small cells formed by multiple small eNBs is formed within the coverage 701 of one macro cell formed by one macro eNB.

[0109] As a fifth-generation wireless access system that is aimed at commercialization between 2018 and 2020, a system that can accommodate various communication terminals is being considered, as disclosed in Non-Patent Document 12.

[0110] For example, in the dense urban scenario (TC2) described in ICT-317669-METIS / D6.11 (Chapter 9.2) and non-patent document 12 (Chapter 8), the communication capacity per unit area considering the number of communication terminals is 700Gbps / km, with a download speed of 300Mbps and an upload speed of 60Mbps per communication terminal. 2 The movement speed when used indoors is nearly 0km / h, and when used outdoors while moving, the movement speed is 3 to 50km / h. The allowable latency is 0.5 seconds per web page for web browsing, and 2 to 5 ms is required to launch augmented reality.

[0111] In addition, in the scenario (TC8) for high-speed mobile terminals described in Non-Patent Document 12 (Chapter 14), the downlink speed is 100 Mbps and the uplink speed is 20 Mbps per communication terminal, and the communication capacity per unit area considering the number of communication terminals is 60 Gbps / km. 2 The required travel speed is 350km / h and the allowable delay time is 10ms.

[0112] As described above, since the requirements differ depending on the usage form, an optimal wireless format for each communication form is required to improve frequency utilization efficiency. However, in the current LTE / LTE-A wireless format, the spacing between OFDM subcarriers that are transmitted simultaneously is fixed, which causes a problem that the frequency utilization efficiency deteriorates depending on the usage form.

[0113] In order to solve the above problems, this embodiment discloses a technique for a base station to receive a notification of the moving speed of a communication terminal when the base station starts communication with the communication terminal and set an OFDM subcarrier spacing according to the moving speed. By using this technique, it is possible to improve frequency utilization efficiency.

[0114] The base station here may be an evolved NodeB (eNB) of 3GPP, or a Master eNB (MeNB) or a Secondary eNB (SeNB) in dual connectivity. It may also be what is called a Relay Node (RN), a Remote Radio Head (RRH), or a concentrator. It may also be a Component Carrier (CC) in carrier aggregation.

[0115] It is known that the Doppler fading characteristic of moving objects causes a carrier offset according to the moving speed. The carrier offset is expressed by the following formula, "v × f / c," where v is the moving speed of the moving object, f is the carrier frequency, and c is the speed of light. In other words, the faster the object is moving, the larger the carrier offset becomes.

[0116] Fig. 8 is a diagram showing an example of a signal used in the first embodiment of the present disclosure. Fig. 9 is a diagram showing another example of a signal used in the first embodiment of the present disclosure. Fig. 8 shows, as an example, a signal when the OFDM subcarrier spacing is K1 (Hz). For comparison, Fig. 9 shows a signal when the OFDM subcarrier spacing is K2 (Hz), which is twice K1. In Figs. 8 and 9, the known sequence signal is shown with hatching.

[0117] The horizontal axis in Fig. 8(a) and Fig. 9(a) represents frequency f, and the vertical axis represents time t. Moreover, the horizontal axis in Fig. 8(b) and Fig. 9(b) represents frequency f, and the vertical axis represents power P. In both cases of Fig. 8 and Fig. 9, a known-sequence signal, for example a reference signal, that has the same energy, i.e., the same area on the drawing, is transmitted and used for synchronous detection. In this case, when the OFDM subcarrier interval is K1 (Hz), the known-sequence signal interval is J1, but when the OFDM subcarrier interval is K2 (Hz), which is twice K1, the known-sequence signal interval is J2, which is half J1 (J1 / 2).

[0118] This shows that the larger the OFDM subcarrier spacing, the shorter the known sequence signal spacing, making it easier to detect time fluctuations in the carrier offset, and therefore more resistant to high-speed movement, i.e., demodulation is possible on the receiving side even when the signal is moving at high speed.

[0119] Taking advantage of this property, the OFDM subcarrier spacing is made smaller for communication terminals moving slowly indoors, for example, and the OFDM subcarrier spacing is made larger for communication terminals moving at high speeds, such as on a Shinkansen train.

[0120] In addition, in the case of a communication terminal such as a sensor with a data rate of about 125 bytes / 5 minutes (see Chapter 4.11 of ICT-317669-METIS / D6.1), reducing the OFDM subcarrier spacing enables the transmission amplifier of the communication terminal to be narrowed in bandwidth, thereby enabling lower power consumption.

[0121] As described above, in this embodiment, signals with various OFDM subcarrier intervals can be mixed. Fig. 10 is a diagram showing an example of signals when signals with different OFDM subcarrier intervals are mixed in time units. The horizontal axis of Fig. 10 represents frequency f, and the vertical axis represents time t. In the range from time t9 to time t14, the OFDM subcarrier interval is K1 (Hz), and in the remaining time range, the OFDM subcarrier interval is K2 (Hz), which is twice K1.

[0122] By mixing signals with different OFDM subcarrier spacing in time units as shown in Figure 10, it becomes possible to modulate and demodulate OFDM signals with a single FFT size in time. This makes it possible to reduce the hardware scale or processing volume of communication terminals and base stations.

[0123] Fig. 11 is a diagram showing an example of signals in the case where signals with different OFDM subcarrier spacing are mixed in frequency units. The horizontal axis in Fig. 11(a) represents frequency f, and the vertical axis represents time t. The horizontal axis in Fig. 11(b) and Fig. 11(c) represents frequency f, and the vertical axis represents power P. In the frequency range from frequency f3 to frequency f6, the OFDM subcarrier spacing is K1 (Hz), and in the remaining frequency range, the OFDM subcarrier spacing is K2 (Hz), which is twice K1.

[0124] As shown in Figure 11, by mixing signals with different OFDM subcarrier spacing on a frequency basis, it becomes possible to modulate and demodulate OFDM signals for each frequency using the same processing. In this case, if the OFDM subcarrier spacings to be mixed are n times or 1 / n times the spacing of each other, it becomes possible to process OFDM subcarriers located at distant frequencies using the same Inverse Fast Fourier Transform (IFFT) or Fast Fourier Transform (FFT). This makes it possible to reduce the scale of hardware or the amount of processing.

[0125] Also, it is possible to perform IFFT including the portion enclosed by the dashed lines in Fig. 11 and transmit without allocating power to f3+f4 and f5+f6. Similarly, in the reception process, it is possible to perform FFT including the portion enclosed by the dashed lines in Fig. 11 and discard the data of f3+f4 and f5+f6.

[0126] Also, for frequencies where inter-symbol interference occurs at the boundary between adjacent different OFDM subcarrier intervals, it is effective to not assign data. The signals f1+f2 and f3 interfere with each other. That is, at the peak of f3 indicated by the arrow in Fig. 11, the power of the signal f1+f2 is not 0, and becomes interference power P1 for f3. Therefore, it is effective not to use f3, or not to use f1+f2. In order to reduce the number of unusable frequency bands, it is more preferable not to use f3, which has a small OFDM subcarrier interval.

[0127] In addition, even if interference occurs at the boundary between adjacent OFDM subcarrier intervals, it is effective to simplify the processing by transmitting the same data as when the subcarriers are not adjacent. This is effective when the signal power of f3 is greater than the interference power, or when the receiving side is equipped with an interference removal function.

[0128] Fig. 12 is a diagram showing an example of signals in the case where signals with different OFDM subcarrier intervals are mixed in time units and frequency units. The horizontal axis of Fig. 12 represents frequency f, and the vertical axis represents time t. Fig. 12 shows an example in which signals with different OFDM subcarrier intervals are mixed for each communication terminal in the arrangement of time units and frequency units.

[0129] Resource blocks (hereinafter sometimes referred to as "RB") 11 and 23 have an OFDM subcarrier spacing of K2 (Hz), which is twice K1, and one resource block is "6 subcarriers x 14 OFDM symbols." The rest have an OFDM subcarrier spacing of K1 (Hz), and one resource block is "12 subcarriers x 7 OFDM symbols." In the example shown in Fig. 12, two types of resource blocks are mixed, but three or more types of resource blocks may be mixed.

[0130] Here, a "resource block" does not include information of multiple communication terminals and is the smallest unit for communication between communication terminals. Therefore, a resource block is the smallest unit of data including a signal of a known sequence for channel estimation on the receiving side. A resource block may also be the smallest unit for transmitting data to be error-correcting coded. A resource block may also be the smallest unit for performing delivery confirmation such as Automatic Repeat reQuest (ARQ) or Hybrid ARQ (HARQ) depending on whether a Cyclic Redundancy Check (CRC) is successful.

[0131] Fig. 13 is a diagram showing another example of signals in the case where signals with different OFDM subcarrier intervals are mixed in time and frequency units. The horizontal axis of Fig. 13 represents frequency f, and the vertical axis represents time t. Fig. 12 shows an example in which the total of frequency widths K1, K2 and the total of OFDM symbol length (SL) of each resource block are the same, but as shown in Fig. 13, a resource block may be defined according to the amount of data generated per event.

[0132] An example of the amount of data generated per event is 125 bytes as a chunk of data transmitted by the aforementioned sensor. Examples of resource blocks that correspond to this include 4 subcarriers x 14 OFDM symbols, 1 subcarrier x 7 OFDM symbols, etc.

[0133] By appropriately allocating OFDM subcarrier spacing for each resource block defined as above in response to changes in the movement speed of communication terminals such as mobile terminals, it is possible to flexibly respond to time and frequency, thereby improving frequency utilization efficiency.

[0134] In order to achieve the above, in this embodiment, a communication terminal such as a mobile terminal measures the moving speed of its own device using a global positioning system (GPS), and a base station uses the measurement result received from the communication terminal by RRC or the like to determine the OFDM subcarrier spacing. The moving speed may be calculated from the difference with the previous position information by notifying only the position information such as GPS from the communication terminal such as a mobile terminal to the base station. The moving speed may also be calculated from the amount of change in the round-trip time, for example, the round-trip time using a random access signal, or the angle information of the arriving wave, measured in the base station.

[0135] Alternatively, it is also effective to have the communication terminal measure the Doppler frequency from the phase rotation of the known sequence and report the measured Doppler frequency to the base station. The base station determines the OFDM subcarrier spacing using the measurement results received from the communication terminal by RRC or the like. Alternatively, it is also effective to have the communication terminal report to the base station the phase rotation amount of the known sequence within a specified time such as one slot or one subframe, or its average value.

[0136] Alternatively, the capability of a communication terminal (hereinafter sometimes referred to as "UE capability") may be set to indicate whether or not it can handle high speed movement. Even if the communication terminal is not actually moving at high speed, if the UE capability indicates that high speed movement is possible, the base station sets a large OFDM subcarrier spacing. Similarly, if the UE capability indicates that the UE is moving at low speed or cannot move, the base station sets a small OFDM subcarrier spacing.

[0137] It is preferable to classify the above-mentioned moving speed, Doppler frequency, known sequence phase rotation amount in a specified time, or compatible moving speed (UE capability) into several stages and report them. This makes it possible to reduce the amount of information. For example, it is effective to classify them into three stages: high speed [Shinkansen / train / car], low speed [pedestrian], and fixed. Alternatively, it is also effective to classify them into two stages: moving and fixed.

[0138] The OFDM subcarrier spacing to be used for communication is determined based on this reported value. It is advisable to set the OFDM subcarrier spacing to the actual moving speed, or to an OFDM subcarrier spacing proportional to the inverse of the corresponding moving speed, or to a value close to this.

[0139] In addition, signals used for monitoring and common control of neighboring cells of a communication terminal, such as CRS (Cell-specific Reference Signal), are set to a fixed OFDM subcarrier interval regardless of the moving speed of the communication terminal. This is effective because it enables transmission and reception without the need to exchange control information between the communication terminal and the base station.

[0140] As with the signals used for monitoring neighboring cells of the communication terminals and for common control, it is also effective to use a fixed OFDM subcarrier spacing with a long subcarrier spacing for the common channel, regardless of the moving speed, and to allow the OFDM subcarrier spacing for the individual channels to be changed depending on the moving speed.

[0141] Also, for individual channels, it is effective to use a fixed OFDM subcarrier spacing with a long subcarrier spacing for the common channel (PDCCH in LTE) associated with the individual channel, regardless of the moving speed, and to make the data section channel (PDSCH in LTE) changeable for each communication terminal.

[0142] It is also effective to configure the broadcast channel (PMCH in LTE) to use a fixed OFDM subcarrier spacing with a long subcarrier spacing, regardless of the moving speed.

[0143] The OFDM subcarrier spacing fixed for monitoring the surrounding cells of the communication terminal and for common control is relatively large, and for example, is set to an OFDM subcarrier spacing that corresponds to high speed movement in order to ensure communication quality. This is effective in enabling transmission and reception regardless of the moving speed.

[0144] Furthermore, the OFDM subcarrier spacing corresponding to low-speed movement is relatively small, but it may be possible to do the following: increase the transmission power, use a modulation method with a low modulation depth such as BPSK (Binary Phase Shift Keying), increase the error correction capability of the error correction coding, for example, lower the coding rate, or use code gain such as Hadamard code and Zadoff-chu code to guarantee the communication quality to a communication terminal moving at high speed. This makes it possible to reduce the OFDM subcarrier spacing and reduce the power consumption of the communication terminal.

[0145] Next, a method will be described in which a communication terminal, for example a mobile terminal, notifies a base station of at least one of its own location, the above-mentioned moving speed, Doppler frequency, and the amount of phase rotation of a known sequence at a specified time.

[0146] An example of random access is shown below. At the time of initial connection or when starting communication with a destination base station by handover, the communication terminal transmits a synchronization signal, for example, a random access preamble in chapters 10.1.5.1 and 10.1.5.2 of Non-Patent Document 1 (3GPP TS36.300), to the base station.

[0147] When the base station receives the synchronization signal transmitted from the communication terminal, it transmits a signal as a random access response notifying the communication terminal that it has received the synchronization signal, and corrects the transmission timing of the communication terminal, adjusting it so that the communication terminal can transmit at the timing the base station is waiting for.

[0148] A communication terminal that receives a signal transmitted from a base station transmits an RRC (Radio Resource Control) connection request as control information for enabling individual communication with the communication terminal. This RRC connection request should include the above-mentioned communication terminal's moving speed, Doppler frequency, and known sequence phase rotation amount at a specified time.

[0149] The base station that receives the RRC connection request considers the status of the base station's radio resources used for other communication terminals, for example, whether there are free resources, and then transmits a radio format change instruction corresponding to the moving speed, for example, an instruction to change the OFDM subcarrier spacing. After transmitting the change instruction, the base station starts transmission and reception in the new radio format after receiving a response from the communication terminal acknowledging the change instruction.

[0150] In a communication terminal, as in CoMP, there are cases where the terminal is simultaneously communicating with other base stations and cannot change the wireless format because the same signal is being transmitted. Therefore, the communication terminal returns a response to the base station to accept or reject the change instruction, taking into account the communication situation.

[0151] The above procedure makes it possible to reliably change the wireless format, but it requires a large number of exchanges between the base station and the communication terminal. To avoid this, the base station may start transmission and reception in the wireless format specified by the change instruction as soon as the base station sends the wireless format change instruction to the communication terminal. In this case, it is unclear whether the communication terminal has received the change instruction from the base station, and even if it has received it, the change may not have been approved depending on the communication status of the communication terminal.

[0152] Therefore, it is effective to provide a timer so that if communication cannot be established after the wireless format is changed, the original wireless format is restored and transmission and reception are performed.Specifically, it is effective to use a timer that measures the time from when the base station sends a wireless format change instruction to the communication terminal, until when the communication terminal sends a change acknowledgement message (RRC) after the wireless format change to the base station using the new wireless format, and until the change acknowledgement message can be received by the base station.

[0153] As an example different from the above example, the process up to receiving the random access response is the same as the above example, but the RRC connection request after receiving the random access response may include a change in the wireless format calculated by the communication terminal from the moving speed, Doppler frequency, and amount of phase rotation of a known sequence at a specified time.

[0154] In the above example of random access, a method was shown in which at least one of the position, moving speed, Doppler frequency, and amount of phase rotation of a known sequence at a specified time of the communication terminal was notified in an exchange with the communication terminal, but the following may also be used: For example, when a handover request is transmitted from the source base station to the destination base station via the X2 interface, at least one of the position, moving speed, Doppler frequency, and amount of phase rotation of a known sequence at a specified time of the communication terminal, or a wireless format determined therefrom, for example, an OFDM symbol interval, may be notified.

[0155] Instead of via the X2 interface, the notification may be made via the S1 interface, i.e., a Handover Required via the MME, or via a Handover Request via the Xn interface in dual connectivity.

[0156] When setting up a wireless channel as a random access response to a synchronization signal transmitted by a communication terminal to the destination base station, the destination base station may notify the wireless format, for example, OFDM symbol interval, instructed in the handover request or handover required from the source base station as the setting value of each physical channel, specifically, the setting value of the physical configuration. At this time, the destination base station considers the status of the wireless resources of the base station used for other communication terminals, for example, whether there are free resources, and if there are free resources, notifies the instructed wireless format.

[0157] Next, an example of measurement configuration is shown. When a base station and a communication terminal are communicating with each other, it is also effective to use a method in which the base station transmits a measurement configuration (RRC) and the communication terminal transmits a measurement report (RRC) according to this setting.

[0158] A communication terminal reports at least one of its own location, moving speed, Doppler frequency, and known sequence phase rotation amount at a specified time in a measurement report. The base station that receives this reports the status of the base station's radio resources used for other communication terminals, for example, whether there are free resources, and then transmits a radio format change instruction corresponding to the moving speed, for example, a reconfiguration.

[0159] After receiving the change instruction, the communication terminal considers the communication status with other base stations, for example, whether CoMP is being used, and if it is not communicating with other base stations or is using the same wireless format, it transmits a change instruction acceptance response and starts transmission and reception using the new wireless format. After receiving the change instruction acceptance response, the base station starts transmission and reception using the new wireless format.

[0160] After transmitting the change instruction, the base station starts transmission and reception in the new wireless format after receiving a change instruction acceptance response from the communication terminal. After transmitting the change instruction acceptance response, the communication terminal starts transmission and reception in the new wireless format.

[0161] Next, an example of transmitting a request to change the wireless format from a communication terminal is shown. In addition to random access and measurement configuration, the communication terminal may detect its own location, moving speed, Doppler frequency, and moving speed from a known sequence phase rotation amount at a specified time, and transmit a request to change the wireless format, for example, the OFDM symbol interval.

[0162] After receiving the change request, the base station considers the status of the base station's wireless resources used for other communication terminals, for example, whether there are free resources, and if there are free resources, transmits a change acceptance response and starts transmission and reception in the new wireless format. After receiving the change acceptance response, the communication terminal starts transmission and reception in the new wireless format.

[0163] In the above, we have shown an example of instructing a change in the wireless format, for example, the OFDM subcarrier spacing, by RRC, but to switch more quickly, it is also effective to transmit and receive the type of wireless format by MAC. It is also effective to notify the type of wireless format by physical signaling together with the transmission data.

[0164] Furthermore, in the above description, an example has been given in which a wireless format, for example, an OFDM subcarrier spacing, is set for each communication terminal, but it is also effective to set a wireless format for each communication terminal group.

[0165] It is also effective to group communication terminals into three types, high speed, low speed, and fixed, as mentioned above. For example, it is also effective to notify three types of wireless formats for the settings of each physical channel notified at the time of channel establishment, have the communication terminal switch the wireless format according to the moving speed of the device itself, and have the base station blindly decode from the three types and use the wireless format that gives an OK CRC.

[0166] Alternatively, it is effective to notify three types of wireless formats in the settings of each physical channel notified at the time of channel establishment, and when the communication terminal switches the wireless format according to the moving speed of the device, to attach the number of the wireless format being used to the data in a physical signal. In this case, it is effective for the physical signal to fix the wireless format.

[0167] As described above, according to the present embodiment, the base station device is configured to be able to set the radio format of signals transmitted and received between the base station device and the communication terminal device for each communication terminal device. The radio format is set for each communication terminal device according to the usage mode including, for example, the moving speed of the communication terminal device. Therefore, it is possible to obtain a communication system that can realize data transmission at a relatively high speed and with a relatively small delay, and can accommodate various communication terminal devices.

[0168] In this embodiment, the wireless format is set for each communication terminal device based on the usage pattern including the moving speed of the communication terminal device. This makes it possible to set an appropriate wireless format according to the usage pattern of each communication terminal device. Therefore, it is possible to obtain a communication system that can realize data transmission at higher speed and with smaller delay.

[0169] In this embodiment, the base station apparatus and the communication terminal apparatus perform wireless communication using orthogonal frequency division multiplexing (OFDM). Signals transmitted and received between the base station apparatus and the communication terminal apparatus include a plurality of wireless formats with different at least one of the OFDM symbol length (SL), which is the length of the OFDM signal symbol, and the CP length (CPL), which is the length of the cyclic prefix (CP). This allows data transmission at a relatively high speed and with a relatively small delay as described above, and also allows a communication system that can accommodate various communication terminal apparatuses to be realized with a simple configuration.

[0170] Embodiment 2 The CP length (CPL) in the OFDM access method can be shortened when the distance between the communication terminal and the base station is short. Also, the CP length can be shortened when the spread of delay dispersion in the transmission path between the communication terminal and the base station is small.

[0171] The fifth generation wireless access system, which is aimed to be commercialized between 2018 and 2020, will require microwave (SHF) to millimeter wave (Extra High Frequency: EHF) bands that can utilize unused frequencies to achieve wide bandwidth, and as the frequency increases, propagation loss will increase. Furthermore, not only will propagation loss increase, but it will also be necessary to make the service area of ​​base stations smaller in order to increase the communication capacity per unit area. Therefore, if OFDM is used in the fifth generation, the above circumstances mean that the CP length may be able to be shortened.

[0172] However, in rural areas with relatively low population density, base stations with large capacity and large cell radius are expected to be required, and technologies that enable transmission as far as possible using, for example, multi-element antennas are being considered.

[0173] In addition, when the carrier frequency becomes higher, the OFDM subcarrier spacing must be longer than that of LTE / LTE-A to ensure resistance to Doppler frequencies. In other words, since the OFDM symbol length is the reciprocal of the OFDM subcarrier spacing, the OFDM symbol length must be shorter. Therefore, the overhead of the CP length has a significant impact on frequency utilization efficiency.

[0174] Furthermore, if the CP length is too short, problems such as (1) interference between symbols will occur, deteriorating communication quality, and (2) when a communication terminal operates in a low-power consumption mode such as discontinuous reception, insufficient synchronization accuracy will result in deteriorating communication quality.

[0175] As described above, among various possible usage patterns, in the current LTE / LTE-A radio format, the CP length of the downlink PDSCH transmitted simultaneously is fixed in one cell. In this case, for example, a communication terminal blindly detects the CP length by using a secondary synchronization signal S-SS transmitted from a base station. When the downlink CP length is fixed in one cell in this way, there is a possibility that communication quality or frequency utilization efficiency will be significantly deteriorated.

[0176] As a technique to prevent such deterioration, this embodiment discloses a technique to use signals with different CP lengths for each communication terminal according to the mode of use when using the OFDM access method. By using this technique, it is possible to improve the frequency utilization efficiency.

[0177] Fig. 14 is a diagram showing an example of a format used in the second embodiment of the present disclosure. The horizontal axis of Fig. 14 represents frequency f, and the vertical axis represents time t. Fig. 14 shows an example in which resource blocks with different CP lengths are used depending on the distance from the communication terminal to the base station. Fig. 15 is a diagram showing an example of the light-speed propagation distance of delay dispersion due to a direct wave (DW) and a reflected wave (RW) of a communication terminal.

[0178] 14, resource block (RB) 1 is composed of 8 subcarriers × 11 OFDM symbols = 88 OFDM symbols. If the clock period Ts, which is the reciprocal of the clock frequency, is 1 / 245.76 MHz and the OFDM subcarrier spacing is 120 kHz, then, for example, the OFDM symbol length (SL) is 2048Ts (= 245.76 MHz / 120 kHz), the CP length (CPL) at the beginning of the resource block is 768Ts, the other CP lengths (CPL) are 128Ts, and the total length of the resource block is 24576Ts = 0.1 ms.

[0179] The spread of delay dispersion that can be handled is equal to the minimum CP length, so this format can be used up to 128Ts=0.52μs, or approximately 150m at the speed of light. The light-speed propagation distance of the delay dispersion due to the direct wave (DW) and reflected wave (RW) of communication terminal A (UE A) shown in Figure 15 is the distance between communication terminal A (UE A) and the base station (BS), so the target cell radius that can be handled is 150m. Resource block (RB) 1 shown in Figure 14 is for communication terminals located closer than 150m.

[0180] In addition, resource block (RB) 2 is composed of 8 subcarriers x 10 OFDM symbols = 80 OFDM symbols, with an OFDM symbol length (SL) of 2048 Ts, a CP length (CPL) at the beginning of the resource block of 512 Ts, and other CP lengths (CPLs) of 384 Ts, for a total resource block length of 24576 Ts = 0.1 ms.

[0181] The spread of delay spread that can be handled is equal to the minimum CP length, so this format can be used up to 384Ts=1.56μs, or approximately 450m at the speed of light. The light-speed propagation distance of the delay spread due to the direct wave (DW) and reflected wave (RW) of communication terminal B (UE B) shown in Figure 15 is the distance between communication terminal B (UE B) and base station (BS), so the target cell radius that can be handled is 450m. Resource block (RB) 2 shown in Figure 14 is for communication terminals located closer than 450m.

[0182] In this way, by configuring resource blocks appropriately depending on the distance from the base station to the communication terminal, the amount of data that can be transmitted with resource block (RB) 1 can be increased by 10% even with the same resource block size, compared to when only resource block (RB) 2 is used uniformly.

[0183] As described above, in this embodiment, resource blocks with two types of CP lengths are transmitted at different frequencies, but the CP lengths of the resource blocks may be three or more. Also, resource blocks with different CP lengths may be used at different times.

[0184] In the format example of Fig. 14, both the CP length (CPL) and the OFDM symbol length (SL) are integer multiples of 128Ts. This corresponds to 245.76MHz / 1.92MHz=128, and means that it is an integer multiple of 1.92MHz, which is the sampling clock (hereinafter sometimes referred to as the "reference clock") of a communication terminal with a 1.4MHz bandwidth in LTE. This also means that it is an integer multiple of the sampling clock of 7.68MHz for a 5MHz bandwidth, the sampling clock of 15.36MHz for a 10MHz bandwidth, and the sampling clock of 30.72MHz for a 20MHz bandwidth.

[0185] From this, it can be seen that by using the format shown in Figure 14, a dual-mode communication terminal with LTE / LTE-A can be made with a single clock source, thereby realizing low-cost communication terminals.

[0186] The method of determining the distance between the base station and the communication terminal is effective as follows.

[0187] For example, a communication terminal notifies a base station of location information of a GPS installed in the communication terminal. The base station calculates the distance between the base station and the communication terminal from the difference between its own station location information written in a memory in the base station or in a device that maintains and monitors the base station when the base station is installed and the GPS location information notified from the communication terminal. Alternatively, the base station calculates the distance between the base station and the communication terminal from the difference between the GPS location information installed in the base station and the GPS location information notified from the communication terminal.

[0188] For example, it is also effective to use a signal transmitted from a communication terminal to convert the time difference into distance. In this case, the base station receives a random access signal and converts the time difference into distance, similar to the timing advance control in LTE / LTE-A.

[0189] Also, for example, a method may be used in which the communication terminal measures the delay dispersion of the downlink signal and reports the result to the base station, regardless of the actual distance between the communication terminal and the base station. In this case, even if the communication terminal is located relatively far from the base station, if the line of sight from the base station is good and the environment is relatively small in reflected waves, the CP length can be set short to improve the frequency utilization efficiency.

[0190] For the format of the uplink signal, the base station measures the delay spread, determines the CP length of the uplink signal based on the result, and the base station indicates the CP length to the communication terminal. This can improve frequency utilization efficiency. Alternatively, when the uplink and downlink are on the same frequency, such as in Time Division Duplex (TDD), the base station can measure the delay spread of the uplink signal from the communication terminal and set the CP length of the downlink signal accordingly.

[0191] Also, for example, the CP length may be determined for each beam by the same base station or a multi-element antenna in the same cell, regardless of the actual distance between the communication terminal and the base station. In this case, for example, when the directivity of the beam in the elevation angle direction is controlled and the directivity of the beam is narrowed to a point relatively close to the base station, the CP length is shortened. Conversely, when the beam reaches a point relatively far from the base station, the CP length is lengthened.

[0192] In addition, for example, when many element antennas are used and the beam is very narrow, the delay dispersion is reduced, so that the delay dispersion report value from the communication terminal can be used to determine and control whether the CP length can be shortened even if the communication terminal is far from the base station.

[0193] Next, a method for setting the CP length will be described. In this embodiment, the following first to third methods are disclosed as a method for setting the CP length.

[0194] The first method is to detect the CP length on the receiving side without notifying a message. Figures 16 and 17 are diagrams showing an example of a resource block into which a known sequence has been inserted. The horizontal axis in Figures 16 and 17 represents frequency f, and the vertical axis represents time t. Figures 16 and 17 show the case where a known sequence has been inserted into a resource block of 8 subcarriers × 11 OFDM symbols.

[0195] In the example shown in Fig. 16, all OFDM subcarriers at the beginning of each of the two resource blocks, t1 and t12, are known sequences. In this case, the receiving device can calculate the CP length when it receives the first symbol of the resource block. This also makes it possible to change the CP length for each resource block.

[0196] In the example shown in Figure 17, a known sequence is transmitted intermittently only at t1 of frequency f4 and at t1 of frequency f8, so the receiving side detects the CP length from this signal. This increases the amount of transmitted data and improves frequency utilization efficiency.

[0197] In the second method, the CP length of the resource for notifying a message including the CP length control information is set to a fixed or relatively long CP length, and the CP length of the resource for transmitting and receiving data is set to a CP length that matches the CP length control information. The CP length control information includes the CP length of the data to be transmitted and information on the CP length used by the communication terminal.

[0198] The resource allocation for notifying the message including the CP length control information should be periodically, for example, every 10 ms, and should be a resource block including a frequency near the center of the OFDM subcarrier to be transmitted. This allows control information to be exchanged at the same frequency even with narrowband communication terminals that only use the center of the OFDM subcarrier.

[0199] In particular, when the CP length is set for each beam, it is advisable to notify the CP length control information by setting the CP length of the common channel for each beam, such as a broadcast channel, to a fixed or relatively long CP length. This allows a communication terminal using this beam to know the CP length to be used for data transmission and reception by receiving the common channel. Therefore, the CP length can be set according to the beam setting situation, such as directing the beam to a position close to the base station, thereby improving frequency utilization efficiency.

[0200] Fig. 18 is a diagram for explaining a modified example of the second method. The horizontal axis of Fig. 18 represents frequency f, and the vertical axis represents time t. Fig. 18 shows a modified example of the second method in which the CP length is specified in advance according to the arrangement of time resources used for communication. In the example shown in Fig. 18, there are 24 resource blocks in the direction of frequency f, and the same setting is repeated in units of 10 resource blocks in the direction of time t. In Fig. 18, the repetition period of the CP length setting is represented as Tcp.

[0201] For example, the CP length is 128Ts for resource block groups (RBG) 1 and 3, and 384Ts for resource block groups (RGB) 2 and 4. This resource allocation information and the repetition period of the settings are notified to the communication terminal using a broadcast channel.

[0202] When the MAC scheduler allocates resources to a communication terminal near the base station, it selects from resource block groups (RBG) 1 and 3. For example, it specifies that f2 and t2 are to be used.

[0203] The communication terminal to which the resource is allocated can identify the CP length from the broadcast information and the allocated resource location information from the scheduler. If the communication terminal moves significantly and needs to lengthen the CP length the next time the resource is allocated from the scheduler, the CP length is selected from resource block groups (RBG) 2 and 4.

[0204] As described above, the CP length can be set simply by specifying resource allocation, eliminating the need to exchange control information for setting the CP length every time. Although the explanation in Fig. 18 is for time resources, it is also effective to specify the CP length for each frequency resource or resource block.

[0205] In the above example, two different CP lengths have been used, but three or more lengths are also effective.

[0206] The above-described CP length setting repetition period is preferably an integer division of the broadcast information repetition period.

[0207] When carrier aggregation is performed, different settings may be used for each carrier component.

[0208] The third method is to use a wireless format with a longer CP length, and change the CP length after the usage situation and usage conditions are satisfied.

[0209] For example, in the initial stage of communication, during the DRX operation period (active time), and immediately after the end of DRX, a wireless format with a longer CP length is used, and the communication terminal notifies the base station that sufficient time synchronization has been achieved, after which the base station changes the CP length. Conversely, the base station lengthens the CP length in response to a DRX start command.

[0210] As described above, in this embodiment, the base station device is configured to be able to change the wireless format for the communication terminal device in response to changes in the environment for wireless communication with the communication terminal device and change information including the location of the communication terminal device. This makes it possible to set a more appropriate wireless format for each communication terminal device. Therefore, it is possible to obtain a communication system that can realize data transmission at higher speeds and with smaller delays.

[0211] In addition, in the current 3GPP message, the uplink CP length can be changed by RRC connection reconfiguration, but the downlink CP length cannot be changed. In contrast, in the present embodiment, even in the downlink signal, (1) the CP length can be changed according to the distance from the base station to the communication terminal, and (2) the OFDM symbol length can be changed according to the moving speed of the communication terminal. Therefore, a good communication environment can be maintained in response to the change in communication situation caused by the increase in frequency and the decrease in symbol length that occurs in the 5G wireless access system.

[0212] As in the first embodiment, the procedure for changing the wireless format (CP length) in the second embodiment will be described below.

[0213] A method for a communication terminal to notify a base station of at least one of its location, its distance from the base station, and a delay spread measurement value will be described.

[0214] An example of random access is shown below. At the time of initial connection or when starting communication with a destination base station by handover, the communication terminal transmits a synchronization signal, for example, a random access preamble in chapters 10.1.5.1 and 10.1.5.2 of Non-Patent Document 1 (3GPP TS36.300), to the base station.

[0215] When the base station receives the synchronization signal transmitted from the communication terminal, it transmits a signal as a random access response notifying the communication terminal that it has received the synchronization signal, and corrects the transmission timing of the communication terminal, adjusting it so that the communication terminal can transmit at the timing the base station is waiting for.

[0216] A communication terminal that receives a signal transmitted from a base station transmits an RRC (Radio Resource Control) connection request as control information for enabling individual communication with the communication terminal. This RRC connection request should include at least one of the above-mentioned communication terminal's location, distance from the base station, and delay dispersion measurement value.

[0217] The base station that receives this transmits an instruction to change the wireless format corresponding to the moving speed, for example, an instruction to change the OFDM subcarrier spacing, after considering the status of the wireless resources of the base station that are being used for other communication terminals, for example, whether there are free resources. After transmitting the instruction to change, the base station starts transmission and reception in the new wireless format after receiving a response from the communication terminal acknowledging the instruction to change.

[0218] In a communication terminal, as in CoMP, there are cases where the terminal is simultaneously communicating with other base stations and cannot change the wireless format because the same signal is being transmitted. Therefore, the communication terminal returns a response to the base station to accept or reject the change instruction, taking into account the communication situation.

[0219] The above procedure makes it possible to reliably change the wireless format, but it requires a large number of exchanges between the base station and the communication terminal. To avoid this, the base station may start transmission and reception in the wireless format specified by the change instruction as soon as the base station sends the wireless format change instruction to the communication terminal. In this case, it is unclear whether the communication terminal has received the change instruction from the base station, and even if it has received it, the change may not have been approved depending on the communication status of the communication terminal.

[0220] Therefore, it is effective to provide a timer so that if communication cannot be established after the wireless format is changed, the original wireless format is restored and transmission and reception are performed.Specifically, it is effective to use a timer that measures the time from when the base station sends a wireless format change instruction to the communication terminal, until when the communication terminal sends a change acknowledgement message (RRC) after the wireless format change to the base station using the new wireless format, and until the change acknowledgement message can be received by the base station.

[0221] As another example, the process is the same as above up to the point where the random access response is received, but the RRC connection request after receiving the random access response may include a change in the wireless format, for example a change in the CP length, calculated from at least one of the position of the communication terminal, the distance from the base station, and the delay dispersion measurement value.

[0222] In the above example of random access, a method was shown in which at least one of the position of the communication terminal, the distance from the base station, and the delay dispersion measurement value was notified in an exchange with the communication terminal, but the following may also be used: For example, when a handover request is transmitted from the source base station to the destination base station via the X2 interface, at least one of the position of the communication terminal, the distance from the base station, and the delay dispersion measurement value, or a wireless format determined from these, such as the CP length, may be notified.

[0223] Instead of via the X2 interface, the notification may be made via the S1 interface, i.e., a Handover Required via the MME, or via a Handover Request via the Xn interface in dual connectivity.

[0224] When setting up a wireless channel, the destination base station may notify the setting value of each physical channel as a random access response to a synchronization signal transmitted by the communication terminal to the destination base station. Specifically, the destination base station may notify the wireless format, for example, the CP length, instructed by the source base station in a handover request or handover required as a setting value of the physical configuration. At this time, the destination base station considers the status of the wireless resources of the base station used for other communication terminals, for example, whether there are free resources, and if there are free resources, notifies the instructed wireless format.

[0225] Next, an example of measurement configuration is shown. When a base station and a communication terminal are communicating with each other, it is also effective to use a method in which the base station transmits a measurement configuration (RRC) and the communication terminal transmits a measurement report (RRC) according to this setting.

[0226] A communication terminal reports at least one of its own location, distance from the base station, and delay dispersion measurement value in a measurement report. The base station that receives this reports the status of the base station's radio resources used for other communication terminals, for example, whether there are free resources, and then transmits a radio format change instruction corresponding to the moving speed, for example, a reconfiguration.

[0227] After receiving the change instruction, the communication terminal considers the communication status with other base stations, for example, whether CoMP is being used, and if it is not communicating with other base stations or is using the same wireless format, it transmits a change acceptance response and starts transmission and reception in the new wireless format. After receiving the change acceptance response, the base station starts transmission and reception in the new wireless format.

[0228] After transmitting the change instruction, the base station starts transmission and reception in the new wireless format after receiving a change instruction acceptance response from the communication terminal. After transmitting the change instruction acceptance response, the communication terminal starts transmission and reception in the new wireless format.

[0229] Next, an example of transmitting a wireless format change request from a communication terminal is shown. In addition to random access and measurement configuration, the communication terminal may transmit a request to change a wireless format, for example, a CP length, derived from at least one of the location of the terminal itself, the distance from the base station, and the delay dispersion measurement value.

[0230] After receiving the change request, the base station considers the status of the base station's wireless resources used for other communication terminals, for example, whether there are free resources, and if there are free resources, transmits a change acceptance response and starts transmission and reception in the new wireless format. After receiving the change acceptance response, the communication terminal starts transmission and reception in the new wireless format.

[0231] In the above, we have shown an example of indicating the wireless format, for example the CP length, by RRC, but to switch more quickly, it is also effective to transmit and receive the type of wireless format by MAC. It is also effective to notify the type of wireless format by physical signaling together with the transmission data.

[0232] Also, in the above example, the wireless format, for example the CP length, is set for each communication terminal, but it is also effective to set the wireless format for each communication terminal group.

[0233] It is also effective to group communication terminals into three types: large, medium, and small delay spread.For example, it is also effective to notify three types of wireless formats for the settings of each physical channel notified at the time of channel establishment, have the communication terminal switch the wireless format according to the moving speed of the device, and have the base station blindly decode from the three types and use the format that gives OK CRC.

[0234] Alternatively, it is effective to notify three types of wireless formats in the settings of each physical channel notified at the time of channel establishment, and when the communication terminal switches the wireless format according to the moving speed of the device, to attach the number of the wireless format being used to the data in a physical signal. In this case, it is effective for the physical signal to fix the wireless format.

[0235] Embodiment 3 Enhanced Inter-cell Interference Coordination (eICIC), which is being discussed in 3GPP, is a technology for controlling interference between adjacent cells that use the same frequency. To apply this technology, the units of time and frequency for data control between cells must match. In the LTE system, a 1 ms subframe is defined as the smallest unit of time. Here, the time for data control is the smallest unit of data transmission and reception, and corresponds to the 3GPP LTE resource block (RB).

[0236] If there is a time lag between cells, the signals in the shifted portions will interfere with each other's cell signals, degrading communication performance such as data throughput.

[0237] In 5G wireless systems, it is expected that various communication terminals will be connected to a base station. In that case, it is expected that a different wireless format will be set for each communication terminal. Wireless formats are parameters related to OFDM symbols, such as OFDM symbol length, OFDM subcarrier frequency interval, and CP length (Cyclic Prefix). When wireless formats are mixed, the time and frequency units for data control will not match, and it is thought that interference control between cells will not be able to be performed with good performance.

[0238] In this embodiment, in order to cope with the above-mentioned problem, when wireless formats are mixed, the data symbol length defined in each wireless format is made the same. Here, the data symbol length is the sum of the OFDM symbol length and the CP length. Fig. 19 is a diagram showing an example of the wireless formats of cell #1 and cell #2. The horizontal axis in Fig. 19 represents time t. Fig. 20 is a diagram showing an example of the parameters of the wireless formats of cell #1 and cell #2. Figs. 19 and 20 show a case where the data symbol length (TL) is the same in cell #1 and cell #2.

[0239] For example, as shown in FIG. 20, when two wireless formats are mixed, in the first wireless format shown as No. 1, the OFDM symbol length SL is set to 4.18 microseconds (μs), the CP length (CPL) is set to 5.15 μs, and the total data symbol length (TL) is set to 9.33 μs. In the second wireless format shown as No. 2, the OFDM symbol length SL is set to 8.33 μs, the CP length (CPL) is set to 1.00 μs, and the total data symbol length (TL) is set to 9.33 μs. In this way, interference control for each data symbol length (TL) is possible, and communication that is resistant to inter-cell interference is possible. For example, as shown in FIG. 19, the wireless format No. 1 is used in cell #2, and the wireless format No. 2 is used in cell #1.

[0240] There is also a method of setting the data symbol length to an integer multiple of the reference data symbol length when wireless formats are mixed. In this case, by performing interference control in time units that are the least common multiple of the data symbol lengths used in the wireless formats, communication becomes possible without degrading interference cancellation performance.

[0241] Furthermore, by setting the data symbol length to an integer multiple of the reference data symbol length, the time unit of the least common multiple can be made smaller than in the case where the symbol length is freely determined for each wireless format, which has the effect of making it possible to shorten the interference control unit time.

[0242] Fig. 21 is a diagram showing an example of radio formats of cells #1 to #3. Fig. 22 is a diagram showing an example of parameters of the radio formats of cells #1 to #3. Figs. 21 and 22 show a case where the data symbol of each radio format is an integer multiple of the reference data symbol length.

[0243] In Fig. 21, A indicates the minimum control unit time for performing interference control between cell #1 and cell #2. B indicates the minimum control unit time for performing interference control between cell #1 and cell #3. C indicates the minimum control unit time for performing interference control between cell #2 and cell #3. Ra in Fig. 22 indicates the ratio of data symbol lengths when the data symbol length L of cell #1 is taken as the reference (=1).

[0244] 21 and 22, the data symbol length of the wireless format used in cell #2 is 2L, which is twice the data symbol length L of the wireless format used in cell #1. Moreover, the data symbol length of the wireless format used in cell #3 is 3L, which is three times the data symbol length L of the wireless format used in cell #1.

[0245] As a method of determining the unit time for interference control when the data symbol length differs between the above-mentioned cells, there is a method of sharing information on the data symbol length between adjacent cells performing interference control, and a method of using a fixed value. When the data symbol length is shared, the unit time for interference control can be set to the minimum time according to the state of the adjacent cell, which enables efficient data transmission and reception scheduling, and as a result, it is possible to increase the frequency utilization efficiency. In addition, when a fixed value is used, it is not necessary to transmit information on the data symbol length in a control message between adjacent cells, so that control can be simplified. As a method of determining the fixed value, for example, there is a method of statically determining the fixed value in advance according to a standard.

[0246] The method of sharing data symbol length between cells differs depending on the cell configuration. Three examples of cell configurations that perform interference control between cells are given below. Fig. 23 is a diagram showing a communication system in which cells of different independent base stations are adjacent to each other. Fig. 24 is a diagram showing a communication system in which one base station centrally manages multiple cells. Fig. 25 is a diagram showing a communication system in which small cells are overlaid on a macro cell.

[0247] A communication system in which cells of different independent base stations are adjacent to each other as shown in Fig. 23 will be described. The communication system shown in Fig. 23 includes an MME / S-GW unit (hereinafter sometimes referred to as an "MME unit") 3201, a base station (E-UTRAN NodeB: eNB) 3202, and a mobile terminal (User Equipment: UE) 3203 which is a communication terminal device. In the example shown in Fig. 23, the communication system includes a plurality of eNBs 3202, specifically, two eNBs 3202. The MME unit 3201 includes a mobility management entity (Mobility Management Entity: MME), or a serving gateway (S-GW), or an MME and an S-GW.

[0248] The UE 3203 is capable of wireless communication with the eNB 3202, and transmits and receives signals via wireless communication. The eNB 3202 is connected to the MME unit 3201 via an S1 interface, and control information is communicated between the eNB 3202 and the MME unit 3202. A plurality of MME units 3201 may be connected to one eNB 3202.

[0249] The eNBs 3202 are connected to each other via an X2 interface, and control information is communicated between the eNBs 3202. The eNBs 3202 form cells 3204. In the example shown in Fig. 23, the cells 3204 of two eNBs 3202, which are independent and different base stations, are adjacent to each other.

[0250] In a communication system in which the cells of different independent base stations are adjacent to each other, when interference control is performed, the data symbol length is transmitted to each base station using signaling on the interface between the base stations. Here, the signaling on the interface between the base stations can be performed via the MME unit using the S1 interface, or directly using the X2 interface. There are three methods for coordination between cells:

[0251] In the first method, the timing for changing the data symbol length in each base station is arbitrary. After changing the data symbol length, the data symbol length is notified by signaling on the interface provided between the base stations, and after the notification is completed, interference control is performed in the new time unit. In this configuration, the data symbol length with the communication terminal can be changed as quickly as possible, so it is possible to change the data symbol length according to the wireless environment and the state of the communication terminal, and it is possible to maintain high wireless quality.

[0252] In the second method, when the data symbol length is notified to adjacent base stations in advance, the timing of changing the data symbol length is also notified, and the unit time of interference control is changed at both base stations from the timing of changing the data symbol length. In this case, the interference control is synchronized with the timing of changing the data symbol length, so it is possible to suppress the deterioration of interference removal performance immediately after switching the data symbol length.

[0253] In the third method, a common data symbol length changeable timing is determined in advance as a system or between adjacent base stations, and the data symbol length is changed according to that timing. When a data symbol length change notification is received from another cell, it is recognized that the change will occur from the data symbol length changeable timing immediately thereafter. It is recognized that the change will occur from the first interference control time after the data symbol length changeable timing. In this case, since it is only necessary to notify the execution of the data symbol length change, there is an effect that the information size of signaling between base stations can be reduced.

[0254] A communication system in which one base station centrally manages multiple cells will be described, as shown in Fig. 24. The communication system shown in Fig. 24 includes one centralized control base station (hereinafter sometimes referred to as "ICBS") 3301 as a base station, and multiple remote base stations (Remote Radio Equipment: RRE) 3302.

[0255] The centralized control base station 3301 performs baseband signal processing and mobility control for a plurality of remote base stations 3302. The remote base station 3302 performs radio control processing. The centralized control base station 3301 and the remote base station 3302 are connected by, for example, optical fiber. The remote base station 3302 may be equipped with a baseband signal processing unit. The mobile terminal 3203 communicates with the remote base station 3302. Each remote base station 3302 forms a cell 3303 having a relatively small coverage.

[0256] In this configuration, the centralized control base station 3301 has data symbol information of all cells 3303, so the information on the data symbol length is always shared. Therefore, even if the data symbol length changes, it can be quickly reflected in the interference control. Also, the minimum time unit for interference control can be calculated in real time and reflected in the control. Furthermore, it is preferable to change the data symbol length in each cell at the interval of the minimum time of the previous interference control.

[0257] A communication system in which small cells are overlaid on a macro cell will be described below, as shown in Fig. 25. The communication system shown in Fig. 25 is configured to include an MME unit 3201, a UE 3203, a macro eNB 3401 which is a macro base station, and a small eNB 3402 which is a small base station. In the example shown in Fig. 25, the communication system includes a plurality of small eNBs 3402, specifically, two small eNBs 3402.

[0258] The macro eNB 3401 configures a macro cell 3403 having a relatively wide coverage. The small eNB 3402 configures a small cell 3404 having a relatively small coverage. The communication system shown in Fig. 25 is configured such that the small cell 3404, which is the cell of the small eNB 3402, is superimposed (overlayed) on the macro cell 3403, which is the cell of the macro eNB 3401.

[0259] The macro eNB3401 and the small eNB3402 may use different carrier frequencies or may use the same carrier frequency. The macro eNB3401 and the UE3203 may communicate control information, and the small eNB3402 and the UE3203 may communicate user data. In this configuration, interference control is mainly performed between adjacent small eNB3402.

[0260] When performing interference control for the UE 3203, information sharing of data symbol length between the small eNBs 3402 may be performed via an X2 interface between the small eNBs 3402, or may be performed using an Xn interface via the macro eNB 3401.

[0261] The data symbol length can be dynamically changed depending on the status of the communication terminal. The timing for changing the data symbol length is determined by calculating the minimum control time when performing interference control between adjacent cells before and after the change, and setting the timing to the least common multiple of the minimum control time. The target minimum control time may be for all adjacent cells, or may be calculated for the cell performing interference control.

[0262] 26 is a diagram for explaining the timing for changing the data symbol length. This is an example of changing the data symbol length of cell #2 from the original setting: cell #2(1) to a new setting: cell #2(2). In this example, the data symbol length combining the CP length (CPL) and OFDM symbol length (SL) is L for cell #1, 2L for cell #2(1), and 3L for cell #2(2).

[0263] In FIG. 26, A represents the minimum control time when performing interference control between cell #1 and cell #2 (1), which is equivalent to 2L. B represents the minimum control time when performing interference control between cell #1 and cell #2 (2), which is equivalent to 3L. C is the least common multiple of A and B, which is equivalent to 6L. When changing the data symbol, by changing the data symbol length at the time period of C, for example, at the timing of arrow D, interference control between cells can be performed seamlessly.

[0264] In addition, for example, the data symbol length may be determined for each beam by a multi-element antenna. The present disclosure can also be applied to cases where interference control is performed between beams in the same cell and between a beam of the own cell and a beam of another cell.

[0265] An example of a method for generating information that can identify the timing of data symbol length between base stations is shown below. Each base station acquires GPS time and generates subframe timing synchronized with GPS. The subframe counter of each base station is preset with the transmission period of the broadcast information. This allows subframe counters synchronized with GPS to be generated in all base stations, enabling synchronization between base stations. The timing for notifying the change in data symbol length is the current subframe counter value plus a processing delay and margin. This makes it possible to synchronize the timing for changing the data symbol length between base stations.

[0266] In the configuration as shown in Fig. 24, the GPS may be located in the centralized control base station 3301 or in each remote base station 3302. In the configuration as shown in Fig. 25, the GPS may be located in the macro eNB 3401 or in the small eNB 3402.

[0267] In addition, in the above, a method of generating a subframe counter to synchronize between base stations by synchronizing with GPS has been shown, but time may also be synchronized using a Network Time Protocol (NTP) server, a communication terminal, or IEEE1588 instead of GPS.

[0268] There are three methods for changing the data symbol length at a communication terminal:

[0269] In the first method, the base station in communication notifies the communication terminal of the timing to change the data symbol length, for example, the subframe number, and both the base station and the communication terminal change the data symbol length from the timing of notification. In this case, any change timing can be specified, and information can be sent and received individually from each communication terminal to be set, so that the change information of the data symbol length can be transmitted at high speed, and it becomes possible to perform rapid interference control in response to changes in the wireless environment, etc.

[0270] Methods of reporting information between a base station and a communication terminal include a method of adding information that can identify the timing of changing the data symbol length to an RRC message, and a method of adding information that can identify the timing of changing the data symbol length to L1 / L2 control information such as a PDCCH. There is also a method of adding information that can identify the timing of changing the data symbol length to broadcast information.

[0271] In the above example, the base station notifies the communication terminal of the change timing, but the communication terminal may also notify the base station. For example, there is a method of adding information that can identify the data symbol length change timing to L1 / L2 control information such as PUCCH.

[0272] In the second method, a common timing for changing the data symbol length is determined in advance as a system or between a base station and a communication terminal, and the data symbol length is changed according to that timing. When a data symbol length change notification is received from a base station or a communication terminal, it is recognized that the change will occur from the data symbol length changeable timing immediately thereafter. In this case, it is only necessary to notify the execution of the data symbol length change, which has the effect of reducing the information size of signaling between the base station and the communication terminal.

[0273] In the third method, the base station changes the data symbol length without notifying the communication terminal of the timing of changing the data symbol length. The communication terminal needs to blindly detect that the data symbol length has been changed. As a method for doing so, there is a method for detecting the corresponding wireless format from the insertion position of a known signal or the period of a known signal, and calculating the data symbol length. There is also a method for adding changed information to the L1 / L2 control information of the PDCCH after changing the data symbol length at the base station, and a method for notifying the base station of the data symbol length being used by using broadcast information. In the third method, since there is no need to strictly match the timing of changing the data symbol length between the base station and the communication terminal, it is possible to simplify the processing.

[0274] Here, the communication terminal is the UE 3203, and the base station can be applied to any of the configurations of the eNB 3202, the RRE 3302, and the small eNB 3402. Also, for the setting information of the data symbol length, an interface for notifying the change timing can be used. The interface used may be the same for the setting information and the change timing, or may be different. For example, the setting information is configured to use L1 / L2 control information such as PDCCH, and the change timing is configured to use broadcast information. Also, the notification timing may be simultaneous for the setting information and the change timing information, or may be different. If they are different, it is necessary to notify the setting information prior to the change timing.

[0275] The data symbol lengths of the uplink and downlink do not need to be the same. Therefore, the CP length can be changed by changing only the uplink data symbol length or only the downlink data symbol length.

[0276] By making the data symbol length in a cell variable per subframe, per TTI, or per RB, control according to the modulation / demodulation processing unit becomes possible, and the modulation / demodulation processing can be simplified. In addition, the interference control time has the data symbol length as the smallest unit, but it is preferable to set it to an integer fraction of a subframe (e.g., 1 / 2) or an integer fraction of a TTI time (e.g., 1 / 4). This makes it possible to perform interference control according to the control time of the modulation / demodulation processing, and has the effect of simplifying the MAC scheduling processing, etc.

[0277] Embodiment 4 In wireless systems such as 5G systems, it is expected that wireless formats with different OFDM symbol lengths or CP lengths will coexist. It is also possible that the OFDM symbol length and CP length will change dynamically. In the LTE system, when considering the time direction, two symbols of cell-specific reference signals (CRS) are inserted for every seven OFDM symbols. These are the 0th symbol (first symbol) and the 4th symbol (fifth symbol).

[0278] When radio formats are mixed, the position where a cell-specific reference signal (CRS) is inserted is considered to be defined as the optimum position for each radio format. For example, in order to simplify modulation / demodulation processing, the insertion ratio of CRS to data may be constant. FIG. 27 is a diagram showing an example of the insertion ratio of a cell-specific reference signal (CRS). The horizontal axis in FIG. 27 represents time t. T1 and T2 are symbols into which data is inserted. For example, as shown in FIG. 27, CRS is inserted at a rate of 1 symbol for every 4 symbols. In that case, the insertion interval of CRS is the sum of the CRS length and the data length, that is, CRS length + T1 and CRS length + T2.

[0279] FIG. 28 is a diagram showing an example of an insertion interval of a cell-specific reference signal (CRS). The horizontal axis in FIG. 28 represents time t. T3 and T4 are symbols into which data is inserted. T5 represents the insertion interval of the CRS. In the above-mentioned situation, even when wireless formats are mixed, the insertion interval T5 in the time direction of the cell-specific reference signal (CRS) is made the same for multiple wireless formats. By doing so, the control timing of CRS generation in the base station becomes the same, and the device can be simplified, and even when one communication terminal communicates simultaneously using multiple wireless formats, the processing can be simplified.

[0280] In addition, by determining the CRS insertion interval according to the characteristics of the communication terminals accommodated in the cell, rather than inserting CRS at a fixed rate into all OFDM symbols, it is possible to reduce the occupancy rate of CRS in all OFDM symbols and improve frequency utilization efficiency. The characteristics of the communication terminals include, for example, the movement speed of mobile terminals and the influence of the installation location of the base station.

[0281] In the case of moving speed, for cells where the moving speed is slow and the effect of Doppler shift is small, the CRS insertion interval is increased to reduce the CRS occupancy rate. Conversely, for cells where the moving speed is fast and the effect of Doppler shift is large, the CRS insertion interval is decreased to improve reception performance. When the moving speed increases, CRS is inserted into all OFDM symbols of a certain frequency at maximum.

[0282] In addition, when the moving speed is very slow, it is effective to increase the CRS insertion interval in the frequency direction as well as the time direction. When the moving speed is very slow, not only is the effect of Doppler shift small, but the change in the radio propagation environment is also small, so even if the CRS insertion rate is small, the degradation of reception performance is small.

[0283] Therefore, even if the CRS insertion interval in the frequency direction is increased, the reception performance does not deteriorate, and it is possible to improve the frequency utilization efficiency. If the CRS insertion interval in the frequency direction is increased, the reception performance may deteriorate at a specific frequency when frequency selective fading occurs. In that case, it is possible to reduce the deterioration of the reception performance by changing the CRS allocation frequency every CRS insertion time or by performing frequency hopping operation.

[0284] When installing a base station, in places such as cities with many buildings and people and poor visibility, the wireless propagation environment changes greatly due to the effects of frequency selective fading, so one method is to reduce the CRS insertion interval to improve reception performance.

[0285] FIG. 29 is a diagram showing an example of an insertion interval and an insertion ratio of CRS when the OFDM symbol length is different. The horizontal axis of FIG. 29 represents time t, and the vertical axis represents frequency f. The diagram shows a state in which radio formats REF#1, REF#2, and RFE#3 with different OFDM symbol lengths SL and OFDM subcarrier intervals SCI are mixed. When the OFDM symbol lengths are different, if the insertion intervals in the time direction of CRS are made the same, in the case of a radio format with a short OFDM symbol length, the combined power of CRS becomes small, and there is a possibility that the required reception performance such as SNR (Signal Noise Ratio) cannot be ensured in the reception of CRS at a communication terminal. To achieve this, there are methods such as increasing the insertion ratio of CRS in the frequency direction (increasing the number of CRS insertion subcarriers) or increasing the transmission power of the CRS insertion symbol relative to other OFDM symbols.

[0286] The CRS insertion ratio in the frequency direction may be determined for each beam by a multi-element antenna. When forming a beam with a multi-element antenna, it is also possible to change the transmission power and the beam radiation angle depending on the number of elements forming the beam. Therefore, for example, for a beam with a large number of elements, there is a method of increasing the resources used for data transmission and improving frequency utilization efficiency by reducing the CRS insertion ratio in the frequency direction and satisfying the required SNR.

[0287] As for the UE-specific reference signals, DM-RSs (Demodulation Reference Signals), the same radio format can be used for different UEs, as with the CRS. This simplifies the control of the base station and the communication terminal. As for the DM-RSs, the DM-RSs can be set for each communication terminal, so the DM-RSs insertion interval can be determined for each communication terminal according to the reception performance, reception quality information, antenna configuration, amount of data transmitted and received, and allowable processing delay of the communication terminal.

[0288] One method for notifying communication terminals of the CRS insertion interval and insertion ratio is to transmit the insertion interval and insertion ratio in broadcast information. By inserting the insertion interval and insertion ratio in broadcast information, it is possible to notify all communication terminals at the same time, and it is also possible to respond to changes in the CRS insertion interval and insertion ratio settings by changing the SI (System Information).

[0289] The DM-RSs insertion interval and insertion rate can be dynamically changed for each communication terminal according to the reception quality, etc. There are two methods for changing the DM-RSs insertion interval and insertion rate in a communication terminal:

[0290] In the first method, the base station in communication notifies the communication terminal of the DM-RSs setting change content and timing (e.g., subframe number), and both the base station and the communication terminal change the DM-RSs setting from the notified timing. In this case, any change timing can be specified, and information can be sent and received individually from each communication terminal, so that change information of the data symbol length can be transmitted at high speed, and rapid control can be performed in response to changes in the wireless environment, etc.

[0291] Methods of reporting information between a base station and a communication terminal include a method of adding information that can identify the change content and change timing of the DM-RSs setting to an RRC message, and a method of adding information that can identify the DM-RSs setting to L1 / L2 control information such as a PDCCH. There is also a method of adding information that can identify the change content and change timing of the DM-RSs setting to broadcast information.

[0292] The above is an example in which the base station notifies the communication terminal of the change contents and change timing of the DM-RSs setting, but the communication terminal may also notify the base station in the opposite manner. For example, there is a method of adding information that can identify the change contents and change timing of the DM-RSs setting to L1 / L2 control information such as PUCCH.

[0293] In the second method, a timing at which the data symbol length can be changed is determined in advance as a system or common between a base station and a communication terminal, and the data symbol length is changed according to that timing. When a notification of a change in the DM-RSs setting is received from a base station or a communication terminal, it is recognized that the change will occur from the next timing at which the DM-RSs setting can be changed. In this case, it is only necessary to notify the execution of the change in the DM-RSs setting, which has the effect of reducing the information size of signaling between the base station and the communication terminal.

[0294] Embodiment 5. In wireless systems such as 5G systems, various communication terminals will be connected. For example, it is expected that devices used in FA (Factory Automation) will also be connected to the same system as communication terminals. Some FA devices place importance on real-time performance, and old data may not be usable as valid data.

[0295] A major cause of processing delays in wireless systems is retransmission in HARQ or retransmission in RLC. In the case of the above-mentioned FA equipment, data retransmitted by HARQ or the like is considered to be treated as invalid data. However, in the LTE system, HARQ is a required function, and radio resources for HARQ are secured regardless of the type of communication terminal to be connected. Therefore, even for communication terminals that do not require HARQ retransmission, resources for returning HARQ ACK / NACK and instructions for scheduling information associated with retransmission are generated, resulting in waste of radio resources.

[0296] In the future, 5G systems will be required to connect 100 times as many communication terminals as current wireless systems, using MMC (Massive Machine Connection) etc. Therefore, it is clear that the occupation rate of wireless resources related to retransmission control such as HARQ will also increase.

[0297] Fig. 30 is a diagram showing an example of a control operation in a conventional communication system. The horizontal axis in Fig. 30 represents time t. A base station BS is connected to a device, and the device has a device control unit UE_C having the functions of a UE and a communication control unit UE. This is an example in which the control operation is changed based on event information from the base station BS.

[0298] An event occurs in Step ST3901, and the base station BS transmits event information to the equipment as Data(1) in Step ST3903. The communication control unit UE of the equipment demodulates the data, but the demodulation fails, and Data(1) cannot be reflected in Step ST3909, and a HARQ NACK is returned to the base station BS in Step ST3904.

[0299] The base station BS retransmits Data(1) in step ST3905. Since the communication control unit UE of the equipment successfully demodulates the data, it returns an ACK in step ST3906.

[0300] However, from the viewpoint of the control of the device control unit UE_C, the reception of Data(1) is late and therefore unusable data, and is discarded in Step ST3910. At that time, in Step ST3912, the device control unit UE_C operates autonomously.

[0301] In step ST3902, a new event occurs, and the base station BS transmits Data(2) in step ST3907. Since the communication control unit UE of the equipment correctly receives Data(2), it reflects this to the equipment control unit UE_C in step ST3911, and the equipment control unit UE_C executes a control operation based on the information in Data(2) in step ST3913. Also, it returns an ACK in step ST3908. In the example of FIG. 30, the operations in steps ST3904, ST3905, and ST3906 are not necessary.

[0302] In order to solve the above problem, a mode that does not execute HARQ control is added for each communication terminal or for each radio bearer. By making it possible to mix a mode that executes HARQ and a mode that does not execute HARQ in the same system, unnecessary HARQ processing can be reduced, and radio resources associated with unnecessary HARQ can be used for data communication, etc., thereby improving frequency utilization efficiency. In addition, since the processing of communication terminals that do not require HARQ processing is reduced, it can also contribute to power saving.

[0303] The unit for selecting whether or not to execute HARQ processing is (1) for each communication terminal, (2) for each radio bearer, (3) at certain intervals, (4) for each transmission data (packet), (5) for each LCG (Logical Channel Group), (6) for each CC in the case of a cell for carrier aggregation CA, (7) for each MeNB or SeNB in ​​a dual connectivity DC configuration, (8) for each type of communication terminal, (9) for each QoS, (10) switching the presence or absence of HARQ at a predetermined timing, etc. In addition, the method for sharing the setting of whether or not to execute HARQ processing between the base station and the communication terminal is L1 / L2 control information, MAC control information, and RRC control information.

[0304] As an example of the selection method for each communication terminal in (1) above, there is a method in which the communication terminal determines whether or not to use HARQ depending on the processing capacity and usage environment of the communication terminal, and notifies the base station using UE capability or the like.

[0305] As an example of the method of selection for each radio bearer in (2) above, there is a method in which bearers for video and audio are selected without HARQ in order to emphasize real-time performance, and bearers for data packet transmission are selected with HARQ in order to emphasize reliability.

[0306] The method of selecting every certain time period in (3) above is, for example, a method of using HARQ during the transmission time of a control signal and not using HARQ during the transmission time of a user data signal.

[0307] As a selection method for each transmission data (packet) in (4) above, for example, there is a method in which communication quality is monitored, and if the communication conditions are good (e.g., SNR is high), HARQ is not performed to increase the frequency utilization efficiency, and conversely, if the communication conditions are poor, HARQ is performed to increase the communication quality by HARQ operation.

[0308] As an example of the selection method for each LCG in (5) above, there is a method in which HARQ is enabled for LCGs with high priority to ensure communication quality, and HARQ is disabled for LCGs with low priority to reduce the occupied bandwidth of wireless resources.

[0309] As a selection method for each CC in the case of a CA cell in (6) above, for example, there is a method of realizing low latency by not using HARQ for CCs with good communication quality, or by not using HARQ for CCs to which communication terminals requiring low latency, such as FA equipment, are assigned.

[0310] As a selection method for each MeNB and each SeNB when configuring DC in (7) above, there is a method in which the MeNB handles control information and therefore ensures quality by using HARQ, and the SeNB does not use HARQ to achieve low latency for user data.

[0311] As a selection method for each type of communication terminal in (8) above, for example, since the communication environment of a stationary terminal does not change, there is a method in which HARQ is not used to achieve low latency, whereas since the communication environment of a moving terminal changes, HARQ is used to achieve quality maintenance even when the communication environment changes suddenly.

[0312] As an example of the selection method for each QoS in (9) above, there is a method of enabling HARQ when it is necessary to ensure high quality, and disabling HARQ when low quality is acceptable, thereby improving frequency utilization efficiency.

[0313] As a method of switching the presence or absence of HARQ at a predetermined timing as described in (10) above, for example, there is a method of using HARQ for control information until the initial communication is established, and not using HARQ for subsequent user data communication.

[0314] In the LTE system, the L1 / L2 control information is the physical downlink control channel (PDCCH). By adding information indicating whether or not to execute HARQ to the L1 / L2 control information, it becomes possible to select whether or not to execute HARQ for each piece of transmission data. For downlink transmission, whether or not to execute HARQ may be added to the allocation information of the downlink shared channel. For uplink transmission, whether or not to execute HARQ may be added to the information of the uplink scheduling grant. Notification in the PDCCH has the advantage of enabling instantaneous response and applying changes only to the corresponding PDSCH.

[0315] In this case, any of the following changes are possible: (1) for each communication terminal, (2) for each radio bearer, (3) at certain intervals, (4) for each transmission data (packet), (5) for each LCG (Logical Channel Group), (6) for each CC in the case of a cell for carrier aggregation CA, (7) for each MeNB or SeNB in ​​a dual connectivity DC configuration, (8) for each type of communication terminal, (9) for each QoS, and (10) switching the presence or absence of HARQ at a predetermined timing (for example, with HARQ for control information when performing the first connection, and without HARQ thereafter). In this case, the base station notifies the communication terminal of the setting.

[0316] The MAC control information is information for performing initial setting and reconfiguration at the Layer 2 level, for example, HARQ setting information is added to the MAC-CE (Medium Access Control - Control Element) to change whether or not to perform HARQ at the timing of setting. In the LTE system method, this corresponds to the RRC control information of RRC Connection Reconfiguration.

[0317] In this case, it is possible to change the presence or absence of HARQ (for example, with HARQ for control information for initial connection execution, and without HARQ thereafter) (1) for each communication terminal, (2) for each radio bearer, (3) at certain intervals, (5) for each LCG (Logical Channel Group), (6) for each CC in the case of a cell for carrier aggregation CA, (7) for each MeNB or SeNB in ​​a dual connectivity DC configuration, (8) for each type of communication terminal, (9) for each QoS, and (10) at a predetermined timing. In this case, the base station notifies the communication terminal of the setting.

[0318] The RRC control information is added to UE capability information to set whether or not to execute HARQ when setting up a wireless connection for a communication terminal. In this case, it can be set (1) for each communication terminal, or (8) for each type of communication terminal. In this case, the communication terminal notifies the base station of the setting.

[0319] In addition, in the LTE system, the Quality of Service (QoS) for each radio bearer is specified by Quality Class Identifiers (QCIs). In some configurations, the QCIs table can be configured to include the presence or absence of HARQ execution, making it possible to set this for each radio bearer (2).

[0320] Although the method for setting the availability of HARQ has been described above, once the availability of HARQ has been set, it is also effective to continue the set state until the next trigger comes in. In the LTE system method, various L1 / L2 control information is set for each PDSCH transmission, but if the setting is continued, it is not necessary to execute the setting for each PDSCH transmission, making it possible to reduce the amount of control information, reducing the overhead of the control information and improving frequency utilization efficiency.

[0321] The following methods can be used as triggers to stop the continuation of the setting. (1) A HARQ setting continuation timer is provided and the setting continues until the timer expires. The timer value is assumed to have been set in advance. It may be fixedly determined in a setting file for each standard or base station. (2) The setting continues until a request for a change is received from a communication terminal, a base station, or a higher-level device of the base station. For example, if the reception performance deteriorates, the state without HARQ is stopped and a request for a change to the state with HARQ is issued. Methods for detecting deterioration of reception performance include, for example, a method of finding the error rate from a CRC check of data and a method of measuring the SNR (Signal Noise Ratio) from a known signal.

[0322] It is also effective to determine a default value for the presence or absence of HARQ. When communication is started and there is no setting for the presence or absence of HARQ, for example, HARQ is set to be present. By setting a default value, it is possible to further reduce the overhead of control information. The default value may be fixedly determined by the standard or a setting file for each base station. Also, the default value for the presence or absence of HARQ may be made known by broadcast information.

[0323] Whether or not to execute the above-mentioned HARQ can also contribute to power saving of communication terminals such as sensor devices. For example, by executing HARQ only for necessary information such as control information and not executing HARQ for other information, it is possible to eliminate the transmission of unnecessary HARQ-ACK / NACK. As a method for reducing HARQ processing, there is a method of transmitting only HARQ-ACK when data demodulation is successful and not transmitting HARQ-NACK when data demodulation is incorrect. In this case, retransmission is automatically repeated until HARQ-ACK is received. In this case, the retransmission can be stopped by an RRC message or the like, or when the maximum number of retransmissions is reached.

[0324] Embodiment 6 It is expected that MTC (Machine Type Communication) will be fully implemented in the 5G system. MTC will include communication terminals with very strict requirements such as a processing delay (latency) regulation of 30 seconds or more. In the LTE system specifications, the TTI (Transmission Time Interval) interval is standardized to one subframe (1 ms) for all communication terminals, and even in the case of MTC, it is necessary to operate in accordance with one subframe.

[0325] The TTI in the sixth embodiment is a unit time for determining ACK / NACK of HARQ. In other words, it is a unit time for transmitting channel-coded data. A CRC is added to data for 1 TTI, and HARQ is returned. Therefore, a CRC is not added to data for 2 TTI, and HARQ ACK / NACK is not executed. Therefore, even in the case of MTC, which has loose processing delay regulations, it is necessary to operate in units of 1 subframe, and retransmission operations by HARQ must be processed in the same cycle as other communication terminals.

[0326] In the uplink of the LTE system specification, the retransmission period of HARQ is 8 subframes. Here, TTI in the LTE system specification is the time to check CRC (Cyclic Redundancy Check) when executing HARQ, and the retransmission process of HARQ is performed in data units allocated to 1 TTI.

[0327] Therefore, even MTC communication terminals need instantaneous high-speed processing, and it is necessary to adopt high-performance devices that can process it. Also, since the transmission timing of retransmission data in HARQ is fixed and it is scheduled preferentially, even low-priority data such as MTC may momentarily have a higher priority than other data, hindering the transmission of other high-priority data.

[0328] In order to overcome the above-mentioned problem, the TTI period can be set for each mobile terminal or for each radio bearer, and they can be mixed. FIG. 31 is a diagram showing an example of the TTI period of the mobile terminal UE#1 and the mobile terminal UE#2. The OFDM symbol length is SL. For example, as shown in FIG. 31, a certain mobile terminal UE#1 operates at 1 TTI of T11, for example, 0.1 ms, in order to operate with low processing delay, and a mobile terminal UE#2 such as MTC operates at 1 TTI of T12, for example, 1000 ms, in a system that can be set long. In addition, by making all the mixed TTI lengths an integer multiple of the reference TTI length, there is an effect that the scheduling control of the RB resource allocation when communication terminals with different TTI lengths are mixed is simplified.

[0329] By doing so, a mobile terminal such as an MTC can also extend the HARQ period, thereby resolving momentary loads on the mobile terminal and momentary shortages of radio resources.

[0330] Fig. 32 is a diagram showing an example of a HARQ cycle when different TTIs are mixed. The horizontal axis in Fig. 32 represents time t. A short TTI is set for mobile terminal UE#1, and a long TTI is set for mobile terminal UE#2.

[0331] In step ST4101, the base station BS transmits data to the mobile terminal UE#1. Step ST4102 indicates the TTI length (hereinafter may be referred to as "TTIL") of the mobile terminal UE#1, which is the data length for executing the HARQ process. The mobile terminal UE#1 demodulates the data during the period of step ST4102, and returns a HARQ ACK / NACK to the base station BS in step ST4103. The base station BS checks the result of step ST4103, and in the case of a NACK, retransmits the next data in step ST4101.

[0332] As in the example of mobile terminal UE#1, the mobile terminal UE#2 transmits data to the mobile terminal UE#2 in step ST4104, receives the data in step ST4105, and returns the demodulated result to the base station BS in step ST4106.

[0333] As shown in Fig. 32, depending on the mobile terminal, the HARQ cycle can be changed, and retransmission of low priority data does not need to be performed at the same time interval as retransmission of high priority data, making it possible to reduce the disruption of data transmission by high priority mobile terminals such as mobile terminal UE#1. Note that by allowing arbitrary RB resource allocation for data to be transmitted during one TTI and allowing the amount of data to be controlled, more flexible scheduling becomes possible when multiple mobile terminals are present, making it easier to realize priority control for each mobile terminal.

[0334] As a method of mixing TTI periods, a reference TTI (a TTI with the shortest time) is determined, and TTIs that are integer multiples of the reference TTI can be set. In this case, the base station device operates in accordance with the reference TTI, which simplifies scheduling.

[0335] Data allocation to OFDM symbols within a TTI does not need to be continuous like the downlink signal of the LTE system, and by reducing the amount of processing per unit time, it is possible to allocate data that can be processed by low-speed devices used in MTC, etc. FIG. 33 is a diagram showing an example of data allocation to OFDM symbols within a TTI. FIG. 33 shows an example in which the amount of processing per unit time is reduced. Specifically, this is an example in which 4 symbols of data are transmitted per 40 ms.

[0336] FIG. 33(a) shows an example in which the TTI length T21 is 1 ms, and FIG. 33(b) shows an example in which the TTI length T23 is 40 ms. When the TTI length T21 is 1 ms, the amount of data processed per subframe is a maximum of 4 symbols. In addition, when HARQ retransmission is performed, the load is concentrated in the first half of 40 ms. For example, when retransmission data (RTD) is received after T22, for example 7 ms, 8 symbols are processed in 9 ms. On the other hand, when the TTI length T23 is set to 40 ms, the amount of data processed per subframe is a maximum of 1 symbol, and even if HARQ retransmission occurs, retransmission is performed at a timing 40 ms above. For example, FIG. 33(b) shows an example in which retransmission is performed after TTI, for example 7 ms, at T24.

[0337] In Fig. 33(b), in order to further reduce the power consumption of the mobile terminal, it is effective to activate the mobile terminal and execute processing only for symbols that have data, like DRX (Discontinuous Reception) in the LTE system. In that case, there are a method of executing fixed scheduling so that it is not necessary to decode the PDCCH (scheduling information), a method of notifying the allocation of data within 1 TTI in advance by the PDCCH (scheduling information), and a method of allocating RBs in the time direction at a fixed cycle.

[0338] The TTI can be set for (1) each mobile terminal, (2) each radio bearer, (3) every certain period of time, or (4) each piece of transmission data (packet). The method for sharing the TTI setting between the base station and mobile terminal includes L1 / L2 control information, MAC control information, and RRC control information.

[0339] In the LTE system, the L1 / L2 control information is the physical downlink control channel (PDCCH). By adding information indicating the TTI setting to the L1 / L2 control information, it becomes possible to select the TTI setting for each transmission data. For downlink transmission, the TTI setting may be added to the allocation information of the downlink shared channel, and for uplink transmission, the TTI setting may be added to the information of the uplink scheduling grant. In this case, it becomes possible to change the TTI for each mobile terminal (1), for each radio bearer (2), for each fixed time interval, or for each transmission data (packet).

[0340] As for the MAC control information, the TTI setting is added to the information for executing the initial setting or reconfiguration at the Layer 2 level, and the TTI setting is changed at the setting timing. In the LTE system method, this corresponds to RRC connection reconfiguration, etc. In this case, it is possible to change (1) for each mobile terminal, (2) for each radio bearer, and (3) at certain regular intervals.

[0341] The RRC control information is added to the UE capability information to set whether or not to execute HARQ when setting up a radio connection for a mobile terminal. In this case, (1) it can be set for each mobile terminal.

[0342] In addition, in the LTE system, the Quality of Service (QoS) for each radio bearer is specified by QCIs (Quality Class Identifiers). There is also a configuration in which the TTI setting can be added to this QCIs table to make it possible to set (2) for each radio bearer.

[0343] In addition, in a system that forms beams using a multi-element antenna, it is also effective to change the TTI setting for each beam. For example, when communicating with a mobile terminal that moves at high speed and when a thin beam is used, the mobile terminal moves out of the irradiation range of the beam in a short time, so it is necessary to shorten the TTI period and feed back the strength of the received power of the beam at the mobile terminal and channel information of the wireless transmission section to precoding of MIMO (Multiple Input and Multiple Output) to control the direction of the beam. Conversely, when a thick beam is used, the mobile terminal is less likely to move out of the irradiation range of the beam even if the TTI period is longer than when a thin beam is used. Generally, when the number of antenna elements is large, the beam width becomes narrow, and when the number of elements is small, the beam width becomes wide. Therefore, it is also effective to determine the TTI length based on the number of antenna elements.

[0344] Methods for notifying a mobile terminal of the TTI length include a method of notifying the mobile terminal using L1 / L2 control information such as a PDCCH, a method of notifying the mobile terminal using MAC scheduling information, and a method of notifying the mobile terminal using an RRC message.

[0345] Embodiment 7 In the LTE system, the downlink synchronization signal is allocated only to the central 72 subcarriers (1.08 MHz bandwidth) of the transmission frequency. Figure 34 is a diagram showing an example of the allocation of the synchronization signal (SS) and data. Since the frequency band BW used in the 5G system is wider (e.g., 500 MHz), if it is allocated only to the subcarriers of the center frequency W1, all mobile terminals must synchronize with the center frequency and then move to the frequency band W2 used for data transmission and reception.

[0346] In the systems described above, even devices that use only narrow frequency bands need to support two frequency bands, which requires the use of RF devices that support wide frequency bands or the inclusion of circuits that switch between the two frequencies, leading to increased costs.

[0347] Furthermore, when there are many mobile terminals that can only support one narrow frequency band, all low-speed communication devices must be allocated around the central frequency, which can lead to resource shortages when a large number of mobile terminals are connected, such as in Massive Machine Connection (MMC).

[0348] One possible solution to the above problem is the LTE-A system's Carrier Aggregation (CA). In the CA system, a wideband of 100 MHz or the like is realized by arranging up to five 20 MHz band CCs (Component Carriers). In this case, since the center frequency can be allocated every 20 MHz, it is possible to arrange a synchronization signal (SS) every 20 MHz. However, a mobile terminal capable of high-speed transmission needs to perform processing such as FFT every 20 MHz, which makes the processing complicated. In the 5G system, since a band exceeding 500 MHz is used, it is considered that the processing unit such as FFT will be large in order to simplify the processing. In that case, problems such as the shortage of resources compatible with MMC mentioned above will occur.

[0349] To solve the above-mentioned problem, the synchronization signal (SS) is arranged not only at the center frequency but also at regular frequency intervals in the entire band or in the frequency band used by mobile terminals that support narrow frequency bands such as sensors (for example, 20 MHz intervals). This allows the mobile terminal to synchronize with the synchronization signal (SS) close to the frequency used for data communication, eliminating the need to support two frequency bands. Also, in systems where a large number of mobile terminals are connected, such as MMC, resource allocation can be performed freely.

[0350] Fig. 35 is a diagram showing an example of the arrangement of synchronization signals (SS) in a frequency band. The horizontal axis in Fig. 35 represents frequency f. Fig. 35 shows an example in which synchronization signals (SS) are allocated to the entire frequency band BW. A synchronization signal (SS) of a center frequency is shown in 4401, and a synchronization signal (SS) in which an SS arrangement is additionally arranged at frequency intervals AFI is shown in 4402. 4403 is data of a frequency used by a certain mobile terminal. A mobile terminal demodulating the data of 4403 does not need to synchronize with the synchronization signal (SS) 4401 of the center frequency, but can synchronize with the additional synchronization signal (SS) 4402 adjacent to the data, and communication is possible with only a narrowband frequency.

[0351] The method of arranging the synchronization signal (SS) is to allow the position of the synchronization signal (SS) to be freely changed in a configuration file. For example, in a base station that does not need to accommodate a large number of mobile terminals that only support narrow frequency bands such as MMC environments, the synchronization signal (SS) is arranged only at the center frequency, while in a base station that needs to accommodate a large number of mobile terminals that only support narrow frequency bands such as MMC environments, the synchronization signal (SS) is arranged over the entire band or over a wide band.

[0352] An example of a configuration file is held by each base station, and contains information on the frequency direction to which the synchronization signal (SS) is assigned, such as the subcarrier frequency of the synchronization signal (SS) allocation and the frequency allocation period of the same signal (SS) (e.g., 20 MHz period), as well as information on the time direction, such as the time position of the synchronization signal (SS) allocation (subframe position, etc.) and the time direction allocation period of the synchronization signal (SS) (e.g., 10 ms period).Each base station reads the above information from the file when it starts up, and applies it to the synchronization signal allocation settings and the notification information of the broadcast information.

[0353] Alternatively, instead of using a configuration file, the setting may be made from the MME / S-GW, which is the host device of the base station. In this case, in the case of Assisted configuration such as CA (Carrier Aggregation) and DC (Dual Connectivity), the synchronization signal allocation information of the surrounding cells can also be set from the MME / S-GW, eliminating the need to notify between base stations and simplifying the control interface.

[0354] Fig. 36 is a diagram showing another example of the arrangement of the synchronization signal (SS) in the frequency band. The horizontal axis in Fig. 36 represents frequency f. Fig. 36 shows an example in which the synchronization signal (SS) is arranged only in the frequency band allocated for MMC. In this example, the additional synchronization signal (SS) is not arranged in the entire frequency band BW, but the additional synchronization signal (SS) 4503 is arranged only in the frequency band used for MMC as the SS arrangement frequency AF for MMC. In this way, the synchronization signal (SS) is not arranged in the frequency domain used by a mobile terminal capable of normal wideband data transmission and reception, and therefore there is no need to arrange an unnecessary synchronization signal (SS).

[0355] There are two methods for a mobile terminal to synchronize with a base station. One is blind detection, and the other is a method of obtaining, from a PCell and MeNB (Master eNB), when connecting to an SCell and SeNB (Secondary eNB) in an Assisted configuration such as CA (Carrier Aggregation) and DC (Dual Connectivity), information on the frequency direction to which a synchronization signal (SS) is assigned, such as the frequency of the subcarrier allocated to the synchronization signal (SS) and information on the frequency allocation period (e.g., 20 MHz period) of the same signal (SS), and information on the time direction, such as the time position (subframe position, etc.) of the synchronization signal (SS) allocation and information on the time direction allocation period (e.g., 10 ms period) of the synchronization signal (SS).

[0356] The allocation information of the synchronization signal of the SCell and SeNB may be included in the broadcast information as the neighboring cell information of the PCell and MeNB. In addition, the SIB information of the SCell and SeNB may also be notified by the broadcast information of the PCell and MeNB. In this way, the mobile terminal does not need to perform the process of acquiring the SIB information of the SCell and SeNB after synchronization with the communication of the SCell and SeNB, and only needs to perform the process corresponding to the frequency band used in the data communication, which can simplify the device and reduce the cost. In addition, since the SIB acquisition process in the SCell and SeNB is eliminated, there is also an effect that it is possible to start the data communication immediately.

[0357] In the case of blind detection, the synchronization signal (SS) of the frequency band used for data communication is first searched, and if the synchronization signal (SS) is captured, the synchronization signal (SS) is used for frame synchronization and communication control is carried out. If the synchronization signal (SS) of the frequency band cannot be captured, the synchronization signal (SS) of the center frequency is used to perform synchronization with the base station.

[0358] In the Assisted configuration, the mobile terminal obtains information (frequency and time) on the insertion position of the synchronization signal (SS) for the cell and CC to be added from the master base station. For example, this is notified as a neighboring cell list in the RRC information. Then, the mobile terminal performs a search process for the synchronization signal (SS) at the corresponding frequency and time for the cell and CC to be added.

[0359] Fig. 37 is a flowchart showing a processing procedure of a communication terminal related to a synchronization signal detection process. Each process of the flowchart shown in Fig. 37 is executed by the communication terminal. When the communication terminal starts a cell search, the process of the flowchart shown in Fig. 37 starts and proceeds to step ST4601.

[0360] In step ST4601, a communication terminal judges whether or not it is in an Assisted configuration. If it is judged to be in an Assisted configuration, it moves to step ST4602, and if it is judged not to be in an Assisted configuration, it moves to step ST4604.

[0361] In step ST4602, the communication terminal checks whether or not the frequency band (hereinafter sometimes referred to as the "synchronization signal (SS) insertion frequency band") into which the synchronization signal (SS) of the cell to be added (hereinafter sometimes referred to as the "additional cell") is inserted has been designated by the master base station. Specifically, the communication terminal determines whether or not synchronization signal insertion frequency band information indicating the synchronization signal (SS) insertion frequency band is obtained, thereby determining whether or not the synchronization signal (SS) insertion frequency band has been designated.

[0362] If it is determined that the synchronization signal (SS) insertion frequency band is specified, the process proceeds to step ST4603, and if it is determined that the synchronization signal (SS) insertion frequency band is not specified, the process proceeds to step ST4604.

[0363] In step ST4603, the communication terminal performs synchronization processing by using a synchronization signal (SS) in a specified frequency band.

[0364] If it is determined in step ST4601 that the configuration is not Assisted, and if it is determined in step ST4602 that synchronization signal (SS) insertion frequency band information of the additional cell is not obtained and the synchronization signal (SS) insertion frequency band is not specified, the communication terminal performs blind detection in steps ST4604 to ST4606.

[0365] First, in step ST4604, the communication terminal attempts synchronization processing using a synchronization signal (SS) of the frequency band used in data communication. In step ST4605, the communication terminal judges whether or not synchronization has been achieved. If it is judged that synchronization has been achieved, the synchronization processing of the synchronization signal (SS) is terminated, and the process moves to RS detection and data communication. If it is judged that synchronization is not achieved, the synchronization processing is performed using a synchronization signal (SS) of the center frequency of the frequency band used in data communication. Thereafter, the synchronization processing of the synchronization signal (SS) is terminated, and the process moves to RS detection and data communication.

[0366] Since the synchronization signal (SS) of the center frequency is commonly used, it is inserted at the minimum time unit (for example, 1 ms period), but as a method of inserting a synchronization signal (SS) of a frequency other than the center frequency, it is possible to transmit it thinned out (for example, 1 second period) according to the mobile terminal to be accommodated. For example, by using a synchronization signal (SS) of a frequency other than the center frequency with a mobile terminal such as MTC, it is possible to use a synchronization signal (SS) of a long period since it does not matter how long it takes to acquire synchronization. In that case, by transmitting a synchronization signal (SS) of a frequency other than the center frequency with a long period, it is possible to reduce the resources of the synchronization signal (SS), which has the effect of increasing the radio resources that can be allocated to data transmission.

[0367] Fig. 38 is a diagram showing an example of a method of arranging a synchronization signal (SS) in the frequency direction. The horizontal axis of Fig. 38 represents frequency f, and the vertical axis represents time t. A synchronization signal (SS) 4701 of a center frequency is transmitted, for example, every 10 ms. A synchronization signal (SS) 4702 for MMC-1 is arranged in a frequency band that accommodates a mobile terminal that operates at a relatively low frequency, by specifying an SS arrangement frequency AF1 for MMC-1, and the synchronization signal (SS) is arranged, for example, at a cycle of 40 ms.

[0368] The synchronization signal (SS) 4703 for MMC-2 is allocated by specifying the SS allocation frequency AF2 for MMC-2 in a frequency band that accommodates a mobile terminal that operates at a relatively high cycle, and allocation is performed, for example, at a cycle of 20 ms. The additionally allocated synchronization signal (SS) 4702 and synchronization signal (SS) 4703 may be transmitted at the same timing as the center frequency. The allocation of the synchronization signal (SS) 4702 is an example. In that case, in an Assisted configuration, etc., the master base station synchronizes with the center frequency, and the added cell detects and processes the synchronization signal (SS) only at the timing synchronized with the center frequency, thereby saving power.

[0369] Also, it may be shifted in the time direction like the synchronization signal (SS) 4703. In this case, by lowering the synchronization signal (SS) allocation occupancy rate per time, it becomes possible to speed up resource allocation to mobile terminals performing high-speed transmission. This is because when high-speed transmission is performed during the time occupied by the synchronization signal (SS), data cannot be allocated and there is a possibility that it will move to the next slot.

[0370] In addition, in systems that use multi-element antennas to form beams, it is also effective to change the location of the synchronization signal (SS) added to each beam. For example, when communicating with a mobile terminal that moves at high speed or when using a narrow beam, it is possible to make it easier for the mobile terminal to synchronize by increasing the proportion of the synchronization signal (SS) added in the time direction or shortening the synchronization signal (SS) insertion period in the frequency direction.

[0371] The configuration disclosed in this embodiment may be used as a synchronization signal (SS) for network listening, in which a base station detects base stations in neighboring cells.

[0372] In addition, when a base station transmits a measurement configuration (RRC) and a mobile terminal transmits a measurement report (RRC) in accordance with this setting, it is possible to reduce the processing load on the mobile terminal by applying the configuration disclosed in this embodiment and measuring only the SS allocation frequency band.

[0373] Embodiment 8 The fifth generation requires many base stations capable of large-volume communication outdoors, but wired lines, especially optical lines, are mainly installed indoors or underground, and it can be difficult to install equipment that requires an optical communication interface on building walls and utility poles. In addition, when many base stations are installed, simple repeaters cannot adapt to changes in the wireless environment, and there is a problem that they cannot sufficiently reduce interference.

[0374] Fig. 39 is a diagram illustrating a configuration of a communication system according to an eighth embodiment of the present disclosure. With reference to Fig. 39, an example in which a base station is installed on a utility pole on which an optical communication device cannot be installed will be described.

[0375] SGW and MME (hereinafter referred to as "SGW / MME") 5001 connects to base station (hereinafter sometimes referred to as "BS") 5002 and BS 5003, and transmits and receives data between each BS and controls and manages each BS. BS 5002 communicates with mobile terminals (UE) within its own area, and also communicates with BS 5003. The antenna of BS 5003 forms directional beams 5007 and 5008.

[0376] All information that would normally be required by BS5003 is transmitted and received wirelessly from BS5002. By using the wireless interface described below and using directional beams, time, and space resources in a manner that avoids interference, it is possible to set up a base station that does not require the installation of optical communication equipment.

[0377] FIG. 40 is a block diagram showing a configuration of a communication system according to an eighth embodiment of the present disclosure. A method of connecting base stations wirelessly will be described with reference to FIG. 40. The communication system according to the present embodiment includes an SGW / MME 5001, a BS 5002, a BS 5003, and UEs 5004, 5005, and 5006. The BS 5002 includes a base station transmission processing unit 5101 and a base station reception processing unit 5102. The BS 5003 includes a receiving antenna unit 5103, a base station mode reception processing unit 5105, a mobile terminal mode reception processing unit 5106, a base station management control unit 5107, a base station mode transmission processing unit 5108, a mobile terminal mode transmission processing unit 5109, a transmitting antenna unit 5110, and a scheduler 5111.

[0378] The SGW / MME 5001 and the BS 5002 are connected by an S1 interface in LTE / LTE-A. A signal input from the SGW / MME 5001 is subjected to transmission processing by a base station transmission processing unit 5101 of the base station 5002 as data (DSCH) of the user plane (U-plane).

[0379] In base station 5003, it is desirable to perform beam control in receiving antenna unit 5103 to direct the directivity toward base station 5002 in accordance with instruction 5124 from scheduler 5111. Furthermore, a signal determined to be data transmitted from base station 5002 by instruction 5118 from scheduler 5111 is provided to mobile terminal mode receiving processing unit 5106.

[0380] The mobile terminal mode reception processing unit 5106 performs the same signal processing, such as decoding processing, as the downlink signal reception processing performed by the UEs 5004, 5005, and 5006. The mobile terminal mode reception processing unit 5106 also measures reception quality, or receives feedback information 5119 of the reception quality at the base station 5002, and provides this to the scheduler 5111.

[0381] Signal 5115 that has been signal processed by mobile terminal mode reception processing unit 5106 is provided to base station mode transmission processing unit 5108. Base station mode transmission processing unit 5108 performs the same signal processing, such as coding processing, as that performed by base station transmission processing unit 5101 of BS 5002. Base station mode transmission processing unit 5108 also performs resource mapping in accordance with instruction 5120 from scheduler 5111, and transmits the signal to UEs 5004, 5005, and 5006 via transmitting antenna unit 5110.

[0382] At this time, it is desirable for the transmitting antenna unit 5110 to perform beam control to direct the directivity toward the UEs 5004, 5005, and 5006 in response to an instruction 5125 from the scheduler 5111. Furthermore, the signal 5112 determined by the mobile terminal mode reception processing unit 5106 to be a control signal such as base station maintenance management data, S1AP (S1 Application Protocol), X2AP (X2 Application Protocol), or the like is provided to the base station management control unit 5107.

[0383] Signals transmitted from UEs 5004, 5005, and 5006 are received by the receiving antenna section 5103 of the BS 5003 with beams directed toward each UE, in accordance with instructions 5124 from the scheduler 5111.

[0384] Signals that are determined to be data transmitted from UEs 5004 , 5005 , and 5006 according to instruction 5116 of scheduler 5111 are provided to base station mode reception processing section 5105 .

[0385] The base station mode reception processing unit 5105 performs the same signal processing as the uplink signal reception processing performed in the base station, such as decoding processing. The base station mode reception processing unit 5105 also measures reception quality, or receives feedback information 5117 of the reception quality in the UEs 5004, 5005, and 5006, and provides this to the scheduler 5111.

[0386] Signal 5114 processed by base station mode reception processing unit 5105 is provided to mobile terminal mode transmission processing unit 5109. Mobile terminal mode transmission processing unit 5109 performs the same signal processing as the UE, such as coding processing, together with base station maintenance management data, and control signals 5113 such as S1AP and X2AP. Mobile terminal mode transmission processing unit 5109 also performs resource mapping according to instruction 5122 from scheduler 5111, and provides the mapping to BS 5002 via transmission antenna unit 5110.

[0387] At this time, it is desirable for the transmitting antenna unit 5110 to perform beam control to direct the directivity towards the BS 5002 in response to an instruction 5125 from the scheduler 5111 .

[0388] As described above, according to the communication system of this embodiment, even when a large number of base stations are installed, it is possible to easily add more base stations.

[0389] The wireless interface methods between BS5002 and BS5003 are divided into the following three types: a method for transmitting backhaul signals (hereinafter sometimes referred to as the "backhaul signal transmission method"), a method for transmitting signals between MeNB and SeNB that are transmitted by dual connectivity (hereinafter sometimes referred to as the "dual connectivity signal transmission method"), and a method for transmitting fronthaul signals (hereinafter sometimes referred to as the "fronthaul signal transmission method"). The differences in functional block diagrams of the three signal transmission methods are shown in Figures 41 to 54.

[0390] 41 is a block diagram showing a configuration of a base station transmission processing unit 5101 when using a backhaul signal transmission method. When using the backhaul signal transmission method, the base station transmission processing unit 5101 includes an IP unit 5201, a UDP (User Datagram Protocol) / SCTP (Stream Control Transmission Protocol) / TCP (Transmission Control Protocol) unit 52021, a GTP-U (General Packet Radio Service Tunneling Protocol for User Plane) unit 5203, a PDCP (Packet Data Convergence Protocol) unit 52041, an RLC (Radio Link Control) unit 5205, a MAC (Medium Access Control) unit 5206, a CRC adding unit 5207, a channel coding unit 5208, a modulation unit 5209, a precoding unit 5210, an OFDM (Orthogonal Frequency Division Multiplexing) unit 5211, and a wireless transmission processing unit 5212.

[0391] 42 is a block diagram showing the configuration of a base station transmission processing unit 5101 when using the dual connectivity signal transmission method. It includes an IP unit 5201, a UDP / SCTP / TCP unit 52022, a GTP-U unit 5203, a PDCP equivalent unit 52242, an RLC unit 5205, a MAC unit 5206, a CRC adding unit 5207, a channel coding unit 5208, a modulation unit 5209, a precoding unit 5210, an OFDM unit 5211, and a wireless transmission processing unit 5212. The PDCP equivalent unit 52242 has a function equivalent to the PDCP unit.

[0392] 43 is a block diagram showing the configuration of a base station transmission processing unit 5101 when using the fronthaul signal transmission method. The base station transmission processing unit 5101 includes an IP unit 5201, a UDP / TCP unit 52023, a GTP-U unit 5203, a PDCP unit 52041, an RLC unit 5205, a MAC unit 5206, a CRC adding unit 5207, a channel coding unit 5208, a modulation unit 5209, a precoding unit 5210, an OFDM unit 5211, and a wireless transmission processing unit 5212.

[0393] 44 is a block diagram showing the configuration of the base station reception processing unit 5102 when the backhaul signal transmission method is used. The base station reception processing unit 5102 includes a wireless reception processing unit 5213, an OFDM unit 5214, a postcoding unit 5215, a demodulation unit 5216, a channel decoding unit 5217, a CRC check unit 5218, a MAC unit 5219, an RLC unit 5220, a PDCP unit 52211, a GTP-U unit 5222, a UDP / SCTP / TCP unit 52231, and an IP unit 5224.

[0394] 45 is a block diagram showing a configuration of the base station reception processing unit 5102 when using the dual connectivity signal transmission method. The base station reception processing unit 5102 includes a wireless reception processing unit 5213, an OFDM unit 5214, a postcoding unit 5215, a demodulation unit 5216, a channel decoding (Ch Decoding) unit 5217, a CRC check unit 5218, a MAC unit 5219, an RLC unit 5220, a PDCP equivalent unit 52212, a GTP-U unit 5222, a UDP / SCTP / TCP unit 52232, and an IP unit 5224.

[0395] 46 is a block diagram showing the configuration of the base station reception processing unit 5102 when the fronthaul signal transmission method is used. The base station reception processing unit 5102 includes a wireless reception processing unit 5213, an OFDM unit 5214, a postcoding unit 5215, a demodulation unit 5216, a channel decoding (Ch Decoding) unit 5217, a CRC check unit 5218, a MAC unit 5219, an RLC unit 5220, a PDCP unit 52211, a GTP-U unit 5222, a UDP / TCP unit 52233 and an IP unit 5224.

[0396] 47 is a block diagram showing the configuration of the base station mode reception processing unit 5105. The base station mode reception processing unit 5105 includes a radio reception processing unit 5213, an OFDM unit 5214, a postcoding unit 5215, a demodulation unit 5216, a channel decoding (Ch Decoding) unit 5217, a CRC check unit 5218, a MAC unit 5219, an RLC unit 5220, and a PDCP unit 5221.

[0397] 48 is a block diagram showing a configuration of the mobile terminal mode reception processing unit 5106 when the backhaul signal transmission method is used. The mobile terminal mode reception processing unit 5106 includes a wireless reception processing unit 5313, an OFDM unit 5314, a postcoding unit 5315, a demodulation unit 5316, a channel decoding (Ch Decoding) unit 5317, a CRC check unit 5318, a MAC unit 5319, an RLC unit 5320, and a PDCP unit 5321.

[0398] 49 is a block diagram showing a configuration of the mobile terminal mode reception processing unit 5106 when using the dual connectivity signal transmission method. The mobile terminal mode reception processing unit 5106 includes a wireless reception processing unit 5313, an OFDM unit 5314, a postcoding unit 5315, a demodulation unit 5316, a channel decoding unit 5317, a CRC check unit 5318, a MAC unit 5319, an RLC unit 5320, and a PDCP equivalent unit 5322.

[0399] 50 is a block diagram showing the configuration of mobile terminal mode reception processing unit 5106 when the fronthaul signal transmission method is used.

[0400] 51 is a block diagram showing a configuration of a base station mode transmission processing unit 5108 when using a backhaul signal transmission method. The base station mode transmission processing unit 5108 includes a PDCP unit 5304, an RLC unit 5305, a MAC unit 5306, a CRC adding unit 5307, a channel coding unit 5308, a modulation unit 5309, a precoding unit 5310, an OFDM unit 5311, and a wireless transmission processing unit 5312.

[0401] 52 is a block diagram showing a configuration of a base station mode transmission processing unit 5108 when using the dual connectivity signal transmission method. The base station mode transmission processing unit 5108 includes a PDCP equivalent unit 5303, an RLC unit 5305, a MAC unit 5306, a CRC adding unit 5307, a channel coding unit 5308, a modulation unit 5309, a precoding unit 5310, an OFDM unit 5311, and a wireless transmission processing unit 5312.

[0402] 53 is a block diagram showing the configuration of base station mode transmission processing unit 5108 when the fronthaul signal transmission method is used.

[0403] 54 is a block diagram showing the configuration of the mobile terminal mode transmission processing unit 5109. The mobile terminal mode transmission processing unit 5109 includes a PDCP unit 5324, an RLC unit 5325, a MAC unit 5326, a CRC adding unit 5327, a channel coding unit 5328, a modulation unit 5329, a precoding unit 5330, an OFDM unit 5331, and a radio transmission processing unit 5332.

[0404] First, the difference in base station transmission processing unit 5101 of BS 5002 will be described with reference to FIGS.

[0405] In the backhaul signal transmission method, when the BS5003 is connected to the SGW / MME5001 via an optical line, signals that can operate as a base station, specifically, S1AP signals, S1-U signals, X2AP signals, X2-U signals, and signals between maintenance devices, are processed into wireless signals and transmitted wirelessly from the BS5002. For example, if the UDP / SCTP / TCP unit 52021 in FIG. 41 uses UDP (User Datagram Protocol), it determines that the signal is an S1-U signal or an X2-U signal, and separates each user by port number. For example, it associates the signal with a wireless resource ID such as a user ID. These are processed by the GTP-U unit 5203 as GTP-U (GPRS (General Packet Radio Service) Tunneling Protocol for User Plane).

[0406] Next, if the UDP / SCTP / TCP unit 52021 is SCTP, it associates it with an S1AP signal or an X2AP signal for each session. This data is also treated as a type of user, and all parameters required for PDCP to L1 are generated, and the PDCP unit 52041 performs PDCP processing.

[0407] Similarly, if the UDP / SCTP / TCP unit 52021 determines that the signal is TCP, it determines that it is a maintenance signal, and as a type of user, generates all parameters required for PDCP to L1, and performs PDCP processing in the PDCP unit 52041.

[0408] Other components, such as IP (Internet Protocol) unit 5201 and RLC (Radio Link Control) unit 5205 to wireless transmission processing unit 5212, are the same in all systems.

[0409] Similarly, the difference between the methods in base station reception processing unit 5102 of BS 5002 is that the above-mentioned reverse processing is performed. After PDCP processing is performed in PDCP 52211 in Fig. 44, the association with the wireless resource is reversed and returned to UDP / SCTP / TCP unit 52231. Other components such as IP unit 5224 and wireless reception processing unit 5213 to RLC unit 5220 are the same in all methods.

[0410] In the dual connectivity signal transmission method, all signals transmitted between the MeNB and SeNB, specifically, XnAP signals, Xn-U signals [equivalent to PDCP], and signals between maintenance devices, are processed as wireless signals and transmitted wirelessly from the BS 5002. Since the corresponding signals are different, the UDP / SCTP / TCP unit 52022 in Fig. 42 processes them differently from the backhaul signal transmission method.

[0411] The difference with the backhaul signal transmission method is not PDCP, but functions equivalent to PDCP, such as a new control plane (C-Plane) control by dividing the equipment and upstream sequence control.

[0412] Similarly, the difference between the methods in base station reception processing unit 5102 of base station 5002 is that the above-mentioned reverse processing is performed. After performing PDCP-equivalent processing in PDCP-equivalent unit 52212 in Fig. 45, the association with the wireless resource is reversed and returned to UDP / SCTP / TCP unit 52232. Other components including IP unit 5224 and wireless reception processing unit 5213 to RLC unit 5220 are the same for all methods.

[0413] In the fronthaul signal transmission method, the L1 signal and the signal between the maintenance equipment are processed into a wireless signal and transmitted wirelessly from the BS 5002. The L1 signal is, for example, a downstream DA input signal and an upstream AD output signal, or a downstream pre-coded signal and an upstream pre-post-coded signal, or an L1-MAC signal. Since the corresponding signals are different, the UDP / TCP unit 52023 in Fig. 43 processes the signal differently from the backhaul signal transmission method.

[0414] Similarly, the difference between the methods in base station reception processing unit 5102 of BS 5002 is that the above-mentioned reverse processing is performed. After PDCP processing is performed in PDCP 52211 in Fig. 46, the association with the wireless resource is reversed and returned to UDP / TCP unit 52233. Other components such as IP unit 5224 and wireless reception processing unit 5213 to RLC unit 5220 are the same in all methods.

[0415] 47 to 53 show base station mode reception processing unit 5105, mobile terminal mode reception processing unit 5106, base station mode transmission processing unit 5108, and mobile terminal mode transmission processing unit 5109 of BS 5003. For the fronthaul signal transmission method, an example of functional blocks in which a signal after downlink precoding and before uplink postcoding is radio-signalized is shown.

[0416] As described above in detail, in the resource management function unit of each method, signals between BS 5002 and BS 5003 and signals between BS and UE can be multiplexed in time, frequency, and space within the same radio frequency band.

[0417] For example, UE 5006 is in the same direction as BS 5002 and spatial separation is not possible, but stable communication can be provided by using resource region 5011 that is divided in time and frequency.

[0418] In addition, even if there is a lot of radio interference between BS5002 and BS5003 in the surrounding area and a certain frequency cannot be used, if that frequency can be used in the vicinity of BS5003 with less radio interference, stable communication with mobile terminals can be achieved by flexibly allocating radio resources, unlike a repeater.

[0419] In addition, the following method is effective for realizing the backhaul signal transmission method.

[0420] The first method is to wirelessly transmit some or all of the five types of signals (S1AP signal, S1-U signal, X2AP signal, X2-U signal, and signal between maintenance equipment) input to base station 5003 as one mobile terminal. Wireless encryption processing is also consolidated into one. For example, since it is known that there is only one communication partner, there is no need to process antenna directivity control for each signal.

[0421] The second method is to wirelessly transmit the five types of signals input to the base station 5003 as separate mobile terminals. This method has the same ID as separate mobile terminals, performs different wireless encryption, and transmits and receives using wireless transmission procedures with different parameters (PDCP, RLC, MAC). Since the base station does not need a function to merge signals with different connection destinations, it is only necessary to add or delete the relevant signals in response to an increase or decrease in the number of connected surrounding base stations (the number of connected X2s), for example.

[0422] As with the backhaul signal transmission method, the dual connectivity signal transmission method can be effectively implemented by wirelessly transmitting some or all of the three types of signals (XnAP signal, Xn-U signal [equivalent to PDCP], and signal between maintenance equipment) as a single mobile terminal, or by using them as separate mobile terminals.

[0423] As with the backhaul signal transmission method, the fronthaul signal transmission method can use either a method of wirelessly transmitting two types of signals (L1 signal and signal between maintenance equipment) as one mobile terminal or a method of transmitting them as separate mobile terminals.

[0424] Eighth embodiment, variant 1 To disclose a method for enabling a base station to be used even when a wired line is cut off due to a disaster or the like and the base station becomes unusable.

[0425] In addition to the function of the eighth embodiment that can eliminate the need for a wired line, the BS5003 in the eighth embodiment may be provided with a function to search for the same surrounding cell as the mobile terminal when it detects that its own station has lost its wired line or that a base station that normally operates without a wired line has lost its connection with a base station to which it is normally connected. The wired line may be determined to be lost based on the loss of a signal that can confirm that the line is normal, such as a TCP or SCTP heartbeat, or LOF (Loss of Frame) at the Ethernet (registered trademark) level.

[0426] Furthermore, it is preferable to have a function for increasing the effective radiated power (EIRP) by increasing the number of elements in a multi-element antenna when searching.

[0427] It is also a good idea to have a function to self-diagnose whether the wired line can be used when it is restored. An effective alternative is to have a function to loop back and receive test transmission data. If the self-diagnosis result is good, it is a good idea to have a function to periodically transmit a signal indicating this. It is effective for this signal to be a signal other than P-SS or S-SS. In this case, it is a good idea to transmit the signal while changing the directivity using a multi-element antenna.

[0428] It is also desirable to have the ability to execute a plug-and-play connection sequence when a wirelessly connectable backhaul, dual connectivity interface, or fronthaul is found.

[0429] In addition, when starting communication with neighboring cells, since voice is the main communication during a disaster, it is also effective to have a function to increase the MCS (Modulation and channel coding scheme) and the required BLER (Block Error Rate), which is the standard for transmission power control. The required BLER is, for example, 10 -6 By increasing the required BLER, for example, -2 It will be raised to.

[0430] In the eighth embodiment, the BS5002 may be provided with a function to allow the BS5003 to eliminate the need for a wired line, and a function to search for nearby cells that are disconnected from the wired line. It is preferable to change the directivity while receiving signals by using the time and frequency when communication is not in use.

[0431] In addition, when a nearby cell with a wired connection failure is detected but the wired line cannot be restored, it is advisable to have a function for expanding the service area of ​​the own station and allocating beams to the nearby cell with a wired connection failure.

[0432] The base station 5002 is a so-called capacity cell, and during normal operation, it is preferable that the beam has a function of transmitting a common channel even when the base station 5002 is not transmitting a common channel such as a broadcast channel.

[0433] The above-described embodiments and their modifications are merely examples of the present disclosure, and the embodiments and their modifications can be freely combined within the scope of the present disclosure. In addition, any component of the embodiments and their modifications can be modified or omitted as appropriate.

[0434] Although the present disclosure has been described in detail, the above description is illustrative in all respects and does not limit the present disclosure. It is understood that countless variations not illustrated can be assumed without departing from the scope of the present disclosure. [Explanation of symbols]

[0435] 3201 MME / S-GW unit, 3202 eNB, 3203 UE, 3204 cell, 3301 ICBS, 3302 RRE, 3303 RRE cell, 3401 macro eNB, 3402 small eNB, 3403 macro cell, 3404 small cell.

Claims

1. A communication terminal and a base station, performing wireless communication between the communication terminal and the base station by adding a cyclic prefix to a symbol; The base station notifies the communication terminal of a setting of the cyclic prefix for each frequency domain.

2. The wireless communication system according to claim 1 , wherein the setting of the cyclic prefix for each time domain is notified from the base station to the communication terminal.

3. 2. The wireless communication system of claim 1, wherein the cyclic prefix configuration is one of a plurality of cyclic prefix configurations having different lengths.

4. The wireless communication system according to claim 3 , wherein the cyclic prefix used in a common channel has a fixed length.

5. A base station that performs wireless communication between a communication terminal and the base station by adding a cyclic prefix to a symbol, A base station that notifies the communication terminal of a setting of the cyclic prefix for each frequency domain.

6. A communication terminal that performs wireless communication with a base station by adding a cyclic prefix to a symbol, A communication terminal that receives the configuration of the cyclic prefix for each frequency region notified from the base station.

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