Method for energy-efficient unicast and multicast transmission in wireless communication system

Abstract

To provide a method for transmitting using an evolved transmission format.SOLUTION: In a method for time multiplexing subframes on a serving cell to user equipment (UE), an eNodeB communicates by bitmap indication using a first bit (bit "0") of a set of subframes (501, 502, 503) operating using a legacy Long Term Evolution (LTE) transmission format and using a second bit (bit "1") of another set of subframes (504) operating using an evolved transmission NCT (New Carrier Type) format including reduced density cell-specific reference signal (CRS) transmission without a physical downlink control channel (PDCCH) control region.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] This application relates to wireless communications, and more particularly to user equipment connected to base stations. [Background technology]

[0002] A cellular communication network incorporates a large number of wireless terminal devices and a large number of base stations to provide communication services such as telephony, data, video, messaging, chat, and broadcasting. A large number of wireless terminals can be connected to a serving cell controlled by a base station (BS). Typical access methods used in widely used cellular networks include frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), orthogonal frequency division multiple access (OFDMA), single-carrier frequency division multiple access (FDMA), or a combination thereof. A base station (BS) may also be called a NodeB in the Universal Mobile Telecommunications System (UMTS), an evolved NodeB (eNB) in the Long Term Evolution specified by the Third Generation Partnership Project (3GPP), a base transceiver system (BTS), an access point (AP), or some other equivalent term.

[0003] When deployed, eNodeB hardware is generally fixed and stationary, but may be mobile in some cases, such as when deployed in a car. In contrast to eNodeBs, wireless terminal devices may be portable hardware. Wireless terminal devices are typically referred to as user equipment (UE), mobile stations, mobile phones, personal digital assistants (PDAs), wireless modem cards, etc. Uplink (UL) communication refers to communication from fixed or mobile UEs to eNodeBs, while downlink (DL) communication refers to communication from eNodeBs to fixed or mobile UEs. Each eNodeB includes a radio frequency transmitter and receiver used to communicate directly with mobile terminals, which may be free to move around in its vicinity or at a fixed location. Similarly, each UE includes a radio frequency transmitter and receiver used to communicate directly with eNodeBs.

[0004] FIG. 1 illustrates an exemplary wireless telecommunications network 100. This exemplary telecommunications network includes base stations 101, 102, and 103, although in operation, a telecommunications network will necessarily include many more base stations. Each of the base stations 101, 102, and 103 (eNBs) is operable over a corresponding coverage area 104, 105, and 106. The coverage area of ​​each base station is further divided into cells. In the illustrated network, the coverage area of ​​each base station is divided into three cells. A handset or other user equipment (UE) 109 is shown in cell A 108. Cell A 108 is within the coverage area 104 of base station 101. Base station 101 sends transmissions to and receives transmissions from UE 109. As UE 109 moves out of cell A 108 and into cell B 107, UE 109 is handed over to base station 102. Since the UE 109 is synchronized with the base station 101, the UE 109 can use unsynchronized random access to initiate a handover to the base station 102.

[0005] Figure 2 shows the relationship between an E-UTRAN (Evolved Universal Terrestrial Radio Access) 200, such as that illustrated in Figure 1, and a core network (CN) 210 in an LTE wireless network. eNodeBs 203 and 204 communicate with an MME (Mobility Management Entity) 211 and a serving gateway 212 via an S1 signaling interface 205. UEs 201 and 202 communicate with eNodeBs 203 and 204, respectively, via an air interface. This illustration shows two eNodeBs, but there are more eNodeBs connected to the same MME in a deployed network, and one eNodeB can be connected to several MMEs. In E-UTRAN, eNodeBs can communicate with each other via an X2 interface 206.

[0006] <Description of LTE System> LTE wireless networks, also known as E-UTRAN (Evolved Universal Terrestrial Radio Access), are being standardized by 3GPP working groups (WGs). OFDMA and SC-FDMA access schemes are used for the downlink (DL) and uplink (UL) of E-UTRAN, respectively, as part of E-UTRA. Referring now to FIG. 3, a legacy LTE DL transmission format is illustrated, showing the time-frequency resource mapping of physical channels in a 1 millisecond (ms) transmission time interval (TTI), also known as a subframe. Downlink control-plane and user-plane data are scheduled by the Physical Downlink Control Channel (PDCCH) or the Enhanced Physical Downlink Control Channel (EPDCCH), while actual data is transmitted on the Physical Downlink Shared Channel (PDSCH). The minimum granularity for resource allocation for the PDSCH and EPDCCH is a physical resource block (PRB) pair. The control domain 301 contains DL control signaling, including the PDCCH, the Physical Hybrid Automatic Repeat reQuest Indicator Channel (PHICH), and the Physical Control Format Indicator Channel (PCFICH). Common and dedicated control information is transmitted on the PDCCH, while dedicated control information, if present, is transmitted on the EPDCCHs 305 and 306. Cell-specific reference signals (CRS) are transmitted on one or more antenna ports and can be used for radio resource management (RRM) and radio link monitoring (RLM) functions, as well as for demodulating control information on the PDCCH and data transmission on the PDSCH. Alternatively, the UE is configured to demodulate the PDSCHs (302, 303, 304) and / or EPDCCHs (305, 306) using dedicated demodulation reference signals (DMRS), which are transmitted only within PRBs containing data or control information.Important cell information required for initial access by UEs is transmitted on the Physical Broadcast Channel (PBCH), while other system and paging information is transmitted on the PDSCH. The EPDCCH and PDSCH are frequency multiplexed across the system bandwidth, and Figure 3 illustrates their partitioning into three PDSCH regions 302, 303, 304 and two EPDCCH regions 305 and 306. Additional signals, such as a Channel State Information Reference Signal (CSI-RS) or a Positioning Reference Signal (PRS), may also be transmitted in a subframe.

[0007] Unicast and multicast data can be transmitted on the same carrier. Unicast consists of bidirectional point-to-point or point-to-multipoint transmission between the network and each UE, with a dedicated connection to each UE. Multicast data transmission to a group of UEs is supported by the Evolved Multimedia Broadcast Multicast Service (E-MBMS) feature and consists of a downlink-only multipoint-to-multipoint connection. Only UEs subscribed to the MBMS service receive the content. Time sharing of unicast and multicast data is achieved by defining a subset of subframes to support MBMS Single Frequency Network (MBSFN) transmissions. Figure 4 shows an MBSFN subframe 400. The non-MBSFN region 401 includes the PDCCH, PHICH, and PCFICH. The PDCCH can be used to schedule uplink data transmissions and signal power control commands for a group of UEs. The CRS is transmitted in the non-MBSFN region 401 for demodulation of these channels. The MBSFN area 402 is used to transmit multicast data on a physical multicast channel (PMCH) for UEs subscribed to one or more MBMS services. In an MBSFN area, a set of unsynchronized eNodeBs may jointly transmit multicast data in MBSFN subframes, thereby improving reception quality. Therefore, an MBSFN reference signal (MBSFN-RS) is used in the MBSFN area 402 for demodulating the PMCH. Summary of the Invention

[0008] Current and future trends in cellular networks predict exponential growth in data traffic, due in part to the rapid adoption of mobile internet devices and associated data-demanding applications. Increased traffic demands will drive the need for energy conservation, especially as more cells are deployed in the network. Unfortunately, current base stations typically transmit control channels and cell-specific reference signals regardless of whether there are actually any user equipment (UE) being served in the cell. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagrammatic illustration of a conventional homogenous network deployment of three macrocell sites, each consisting of three sectors.

[0010] [Figure 2] 1 is a description of the relationship between E-UTRAN and the core network of an LTE network.

[0011] [Figure 3] 1 shows the current LTE DL transmission format and illustrates the mapping of physical channels for unicast data and control.

[0012] [Figure 3A] 1 shows an Evolved LTE DL transmission format and illustrates physical channel mapping for unicast data and control.

[0013] [Figure 4] 1 shows the current LTE DL transmission format and illustrates the partitioning of MBSFN subframes into MBSFN and non-MBSFN regions.

[0014] [Figure 5]1 is a bitmap showing the allocation of subframes in a radio frame for legacy and evolved transmission formats.

[0015] [Figure 6] 1 shows an example mapping of regular and MBSFN subframes for evolved transmission formats for both FDD and TDD.

[0016] [Figure 7] 1 shows the mapping of channels and signals on a time-frequency grid, i.e., (a) moving PSS / SSS to avoid collision with group-specific RS, and (b) moving group-specific RS to the EPBCH region to avoid collision with PSS / SSS.

[0017] [Figure 8] 1 shows mapping of PMCH and EPDCCH in an MBSFN subframe of the evolved transmission format.

[0018] [Figure 9] 1 illustrates some example mappings of PSS and SSS for both FDD and TDD in the Evolved Transmission Format. [Figure 10] 1 illustrates some example mappings of PSS and SSS for both FDD and TDD in the Evolved Transmission Format. [Figure 11] 1 illustrates some example mappings of PSS and SSS for both FDD and TDD in the Evolved Transmission Format. DETAILED DESCRIPTION OF THE INVENTION

[0019] As cellular networks evolve to accommodate this rapid growth in cellular data traffic, they are finding bottlenecks because much of the traffic is localized in hotspots in both indoor and outdoor deployment scenarios. Heterogeneous networks are becoming increasingly common, where small cells controlled by low-power base stations are deployed to increase capacity in hotspots and / or improve cellular coverage. In 3GPP (Third Generation Partnership Project) Long Term Evolution (LTE) systems, base stations, also known as evolved NodeBs (eNBs), constantly transmit cell-specific reference signals (CRSs) and time-multiplexed physical downlink control channels (PDCCHs). However, constantly transmitting cell-specific reference signals and time-multiplexed physical downlink control channels (PDCCHs) becomes problematic as traffic and demand increases.

[0020] <Explanation of evolved transmission format> The 3GPP Radio Access Network (RAN) standardization body has taken various measures to address energy-efficient transmission, which involves the evolution from an "always-on" DL transmission mode to an "on-demand" mode. One such approach is the introduction of the evolved DL transmission format, which is characterized by the absence of legacy downlink cell-specific reference signals and control channels, including the PDCCH, PHICH, and PCFICH, which rely on CRS for demodulation. Referring now to FIG. 3A, the PDSCHs 312, 313, and 314 and the EPDCCHs 315 and 316 span the entire subframe. The CRS is transmitted with reduced density in the time domain and, optionally, in the frequency domain. For example, the CRS may be transmitted on a single antenna port with a 5 ms periodicity and may occupy either the full system bandwidth or a reduced bandwidth. Removing the legacy control signals and CRS can provide significant energy savings for lightly or unloaded cells. This translates to energy savings of up to 80% when one in five subframes is used for transmission when there are no UEs in the cell. Additionally, removing legacy control signals and CRS frees up resources that can be used for data transmission, thereby increasing spectral efficiency and peak data rates. The evolved transmission format may also be known as NCT (New Carrier Type). However, a major drawback is that UEs of earlier LTE releases may not be able to attach to cells operating using the NCT structure.

[0021] The evolved transmission format, or NCT, can be configured for a secondary cell (SCell) in carrier aggregation (CA) or for single-cell operation (standalone mode). In SCell operation, all system information required for the NCT-SCell can be provided to the UE by dedicated signaling. A natural question is whether the benefits of NCT can be obtained even when the NCT is deployed in standalone mode. This means that a UE can attach to the NCT as its primary cell either at initial access or via handover from a different cell. This may require new approaches to cell access, including synchronization, broadcast and system information transmission, and mobility control. In both CA-based and standalone operation, new approaches are also needed to multiplex reference signals, synchronization signals, and physical channels onto the OFDM time-frequency resource grid.

[0022] Toward the goal of improving energy conservation in wireless networks, it is desirable to limit base station transmissions to periods of time during which data is transmitted to user equipment. For example, a small cell located in an office building may operate at full power during the day, but at night, the small cell should operate at reduced power or be turned off entirely when no one is in the building. Reduced downlink (DL) signaling also reduces DL inter-cell interference, which is becoming a bottleneck for capacity improvements as more cells are added to cellular topologies.

[0023] Energy-efficient transmission is possible by configuring the NCT as an SCell in carrier aggregation. One embodiment of the present invention describes a method for configuring an evolved transmission format for SCell operation, small cell operation in a heterogeneous network (HetNet), or a combination thereof.

[0024] In the CA case, the UE is provided with all system information necessary to receive data and control information for the SCell via dedicated radio resource control (RRC) signaling. The eNodeB configures the UE for PDSCH reception on a secondary serving cell (SCell) configured as an NCT. The eNodeB provides all system information to the UE via RRC signaling, including system information contained in the Master Information Block and System Information Block (SIB). System information that cannot be signaled to the UE, such as the System Frame Number (SFN), which changes every 10 ms, is assumed by the UE to be the same for both the NCT SCell and the cell from which the UE receives system information via dedicated signaling. Therefore, the PBCH may not be transmitted in the NCT. The eNodeB also provides an indication of whether the SCell is operating using a legacy LTE transmission format or an evolved transmission format via RRC signaling. Alternatively, the UE can identify whether the SCell is operating using a legacy LTE transmission format or an evolved transmission format via the presence or absence of existing or new signals. In one embodiment, the discovery signal may identify the SCell as operating using an evolved transmission format. The NCT indication determines the location of the DMRS, which depends on the duplexing mode (FDD or TDD), cyclic prefix, or subframe type (normal or special subframe). The NCT indication may also determine whether the PBCH is transmitted in the NCT, in which case the UE does not rate-match to resource elements otherwise reserved for PBCH transmission. Alternatively, additional RRC signaling in addition to the aforementioned NCT indication may indicate whether the PBCH is transmitted, i.e., whether it rate-matches to resource elements reserved for PBCH transmission.

[0025] If the SCell is an NCT, the UE performs cell search by detecting legacy primary and secondary synchronization signals (PSS, SSS), as in the legacy LTE transmission format. Alternatively, the UE may use discovery signals for cell search. The PSS / SSS are transmitted at the same time-frequency locations as in the legacy transmission format. In different embodiments, the locations of the PSS / SSS are different. In yet another embodiment, for example, for improved energy efficiency and inter-cell interference reduction, the PSS / SSS may not be transmitted in every radio frame, and the UE may blindly detect the presence of the PSS / SSS, or alternatively, may be informed by the network via explicit or implicit signaling of the subframes in which to search for the PSS / SSS.

[0026] Other variants of SCell operation are not excluded, for example, the SCell may be controlled by a second eNodeB different from the eNodeB that controls the primary serving cell, with both NodeBs coordinating their scheduling and RRM decisions with respect to the UE backhaul connection.

[0027] <Evolved transmission format for single cell operation> Standalone operation of evolved transmission formats requires a variety of new approaches to achieve the goals of energy efficiency, reduced inter-cell interference, and increased spectral efficiency.

[0028] One such approach is to use demodulation reference signals (DMRS) to transmit common control information on a shared downlink or broadcast channel. If a reduced-density CRS is used only for tracking and not for data demodulation, a new approach is needed for DMRS-based transmission of common control information, including system information, paging notifications, and UL power control commands. Such an approach uses the common control channel, in which all UEs or groups of UEs can monitor control message scheduling common system information, paging information, and group power control commands. Another approach is to use DMRS-based transmission to transmit broadcast information that a UE needs to belong to a cell without prior receipt of a handover command, such as DL bandwidth and system timing reference (system frame number). Yet another approach is to use UE-specific reference signal transmission for radio resource management (RRM), including new mobility procedures and measurements, for radio link monitoring (RLM), including new RLM procedures and measurements, and for channel state information (CSI) feedback, including new measurements and procedures, e.g., based on CSI-RS.

[0029] Further approaches are needed for cell identification and accessibility, and some approach is needed to bar access of previous release UEs to cells that use the NCT format. In previous releases, the UE may obtain the MIB and at least SIB Type 1 to determine if a cell is barred. If this legacy procedure for NCT is followed, previous release UEs may expend significant energy during cell search and intra-frequency and / or inter-frequency measurements, especially in highly dense small cell deployments. Thus, energy consumption savings on the network side are offset by increased energy consumption on the terminal side.

[0030] Therefore, the following approach is proposed to enable a UE to access a cell operating using the evolved transmission format.

[0031] In one embodiment, when a UE is in the RRC_IDLE state, cell attachment follows conventional LTE procedures, e.g., Releases 8, 9, 10, and 11. The UE may not be able to camp on or attach to this cell because it assumes a legacy transmission format. On the other hand, if an RRC_IDLE UE finds an NCT to which it has had an RRC connection within the last N hours (where N is a fixed value), the UE may perform initial cell attachment to the NCT without handover through a cell operating using a legacy transmission format. Otherwise, the UE searches for and attaches to a cell operating using a legacy transmission format. The UE may choose to camp on this cell in the RRC_IDLE state or may choose to transition to the RRC_CONNECTED state.

[0032] In another embodiment, the UE is in RRC_CONNECTED mode and is handed over to a cell operating using NCT. The handover is network-controlled but UE-assisted; that is, the network may rely on the UE to find and report cells operating in evolved transmission mode. The eNodeB may assist the UE by providing a list of cells to which the UE may report radio resource management (RRM) measurements. For each cell in this list, the eNodeB indicates the transmission format, legacy or NCT. In yet another embodiment, the set of physical cell identities (PCIs) is divided into several ranges, and the UE may infer which transmission format is used by each cell from the provided list of PCIs. For example, if the range of valid PCIs is divided into two ranges, each containing consecutive cell IDs in increasing order, the set containing PCI 0 is associated with cells operating using the legacy transmission format, while the set not including PCI 0 is associated with the NCT structure.

[0033] In one embodiment, RRM measurements, including measurements of Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ), are performed on Channel State Information Reference Signals (CSI-RS). The CSI-RS configuration is configured by RRC signaling from the eNodeB to the UE. In one embodiment, the eNodeB provides the corresponding CSI-RS configuration in a list of cells on which the UE may perform RRM measurements. In a different embodiment, the RRM measurements are performed on a reduced-density CRS. In yet another different embodiment, the network provides additional assistance information for the RRM measurements performed on a reduced-density CRS, such as time and / or frequency resources for performing the measurements. In yet another embodiment, the UE is configured with several such configurations, sometimes referred to as CSI processes, regardless of whether the measurements are performed using a reduced-density CRS, CSI-RS, or any other discovery signal.

[0034] In another embodiment, the eNodeB may configure the UE with reporting criteria for RRM measurement purposes, including periodic, event-triggered, or event-triggered / periodic measurements. The eNodeB may further configure the UE to report only PCIs for which reporting is triggered. In another embodiment, the eNodeB configures the UE to report not only PCIs but also associated RRM measurement results. The reporting criteria may also include an offset so that the UE only reports cell IDs and associated measurements if the cell measurements are better than the serving cell by a certain threshold. The eNodeB may then use a Neighbor Relation Table (NRT) to look up whether the reported cell ID is an NCT. The eNodeB may also configure the UE with system bandwidths for each neighbor cell included in the list of PCIs. This facilitates accurate RSRP or RSRQ measurements. Alternatively, the NodeB may indicate to the UE the measurement bandwidth for each neighbor cell included in the list of PCIs.

[0035] In yet another embodiment, the source eNodeB initiates handover to the target eNodeB. If the target eNodeB acknowledges the handover request, it provides the UE with the following handover information: RRC reconfiguration information including all system information about the target cell, an indication of the transmission format in the target cell, which is relayed via the source eNodeB, and the UE performs synchronization to the target cell according to the transmission type.

[0036] In current LTE specifications up to Release 11, the System Frame Number (SFN) is not exchanged between eNodeBs over the X2 interface. Therefore, the SFN is not part of the mobility information sent to the UE during handover preparation. If the PBCH is not transmitted for the NCT format, there is no means for a target cell using NCT to indicate the SFN to the incoming UE during or after the handover procedure. A new approach is needed to facilitate handover from a cell operating using a legacy transmission format to a cell operating using the NCT format.

[0037] To solve this problem, an RRC information element is included in the mobility control information to indicate which cell's SFN the UE can use as the reference SFN for the target cell. In other words, the UE is signaled the proxy cell whose SFN, determined by decoding the proxy cell's PBCH, is to be used as the reference SFN for the target cell. The RRC information element may include the PCI of the proxy cell operating using a legacy transmission format. The mobility control information is provided by the target eNB using NCT. The target eNB can determine the appropriate PCI through Operation and Maintenance Function (OAM) information or via its Neighbor Relation Table (NRT). In another embodiment, the reference cell for the target cell's SFN is explicitly provided by the source eNB. That is, the SFN broadcast in the source cell's PBCH is the reference SFN for the target cell using NCT. In yet another embodiment, the RRC information element included in the mobility control information indicates the actual SFN of the target cell, or alternatively, an offset that the UE can apply to the SFN of the proxy cell.

[0038] The mobility approach providing a reference SFN for the target cell is also advantageous when the target eNB uses a legacy carrier but operates in cell area extension (CRE). In such a scenario, when the UE is handed over, it may experience heavy interference and be unable to reliably detect the target cell's PBCH, especially if the UE does not have a PBCH interference cancellation receiver. This mobility approach may allow the network to configure a larger CRE bias, thereby facilitating greater offload gains when the UE is moved from a heavily loaded to a lightly loaded cell, especially for UEs without advanced receivers. Therefore, the SFN reference may be included in the mobility control information regardless of whether the target cell uses a legacy or NCT transmission format. More generally, this proposed mobility technique may be configured whenever the UE cannot reliably detect the PBCH of a target secondary serving cell, whether the cell is controlled by the serving eNodeB or a different eNodeB. Alternatively, the cell may be operated using a legacy transmission mode, but the PBCH is not transmitted by the eNodeB controlling such a cell. For example, a UE may be configured to transmit data to and receive data from multiple eNodeBs. In such a case, only one eNodeB may transmit the broadcast channel (i.e., the master eNodeB), while the other eNodeBs (i.e., the secondary eNodeBs) transmit only data or dedicated control information. In such an arrangement, the proposed approach is used to derive the SFN for the cell controlled by the secondary eNodeB from the PBCH transmitted by the master eNodeB.

[0039] <Time multiplexing of mixed subframes of both legacy and evolved transmission formats> As mentioned above, the NCT format is not backward compatible. Therefore, cellular operators may not use this transmission format in cells where all connected UEs support this feature. Also, it seems more appropriate for small cells rather than macrocells, where they may not be turned off since they provide coverage and ensure a minimum quality of service to all UEs. Also, in the absence of PDCCH transmission, new techniques are needed to send common control signaling, including broadcast, system information, and paging.

[0040] One solution to address these shortcomings of NCT is time-domain multiplexing of subframes that operate with both legacy and evolved transmission formats. The eNodeB can indicate to the UE the set of subframes that operate using either the legacy or evolved transmission structure. This subframe indication is communicated to the UE via RRC signaling. In one embodiment, the subframe indication is in the form of a bitmap. A bit value of '1' indicates that the subframe is of the NCT format, while a bit value of '0' indicates that the subframe is of the legacy transmission format. That is, the subframe includes a time-multiplexed control region and either a unicast or multicast data region. Referring now to FIG. 5, an exemplary bitmap of length 10 for one radio frame is shown. Other bitmap sizes are possible. Subframes 501, 502, and 503 use the legacy transmission format, where the UE monitors the PDCCH for common and dedicated control signaling, and the CRS can be used to demodulate some of the channels transmitted in this subframe. The UE may also use these subframes for radio link monitoring (RLM) or radio resource management (RRM) measurements. The UE may also be configured to monitor the EPDCCH in subframes 501, 502, and 503. Other subframes, such as 504, indicate the NCT format. Therefore, in these subframes, the UE monitors only the EPDCCH for downlink control information, since no PDCCH is transmitted. In different embodiments of the present invention, the UE is signaled a bitmap indicating the set of subframes in which the UE monitors the PDCCH. The UE may be configured to monitor both DL assignments, UL grants, and group power control commands, or to monitor only UL grants and group power control commands. This subframe indication concept is applied in different ways for energy-efficient multiplexing of (a) unicast and multicast data, and (b) transmissions using legacy and evolved transmission formats in a cell.

[0041] <Monitoring of Control Channel and PBCH> Subframes operating using a legacy transmission structure are composed of a PDCCH region and include CRS transmission on one, two, or four antenna ports. These legacy subframes are used to transmit common control information in the common search space of the PDCCH. The set of legacy subframes includes at least subframe 0 of each radio frame. Therefore, the PBCH can be transmitted and detected by UEs of all LTE releases. The PDSCH is demodulated using DMRS in all subframes. Alternatively, the UE is configured for data demodulation using CRS in legacy subframes and only DMRS in NCT subframes. In yet another embodiment, the downlink control information (DO) format received on the control channel indicates to the UE which reference signal to use for demodulation. However, the UE demodulates the PBCH and PDCCH using 1-, 2-, or 4-port CRS.

[0042] In different embodiments, the UE may demodulate the PBCH and PDCCH using 1-port CRS. That is, at most 1-port CRS is transmitted in a mixed subframe transmission format. RRM, RLM, and / or CSI measurements are performed in subframes carrying 1-port CRS.

[0043] <Multiplexing of PMCH, PDSCH, EPDCCH, and PDCCH> It is possible to operate using the NCT format in one cell and the legacy transmission format in a different cell when both cells are deployed on the same carrier frequency. The NCT format may be used exclusively in all subframes in the small cell or only in subframes configured for transmission using the evolved transmission format. In such a scenario, MBMS services may be provided in an MBSFN area consisting of cells operating using different transmission formats. For example, in a heterogeneous network, a macro cell and a small cell may operate using legacy and evolved transmission formats, respectively, on a shared carrier frequency. Therefore, if eNBs in both the macro cell and the small cell participate in MBSFN transmission, PMCH transmission should be synchronized with PMCH transmission in the macro cell, at least for subframes carrying the PMCH in the small cell. As a result, because the small cell does not include a control region, the first one or two OFDM symbols in the small cell layer are wasted to align MBSFN transmission across the macro and small cell layers.

[0044] To address this waste, the eNB of a small cell may transmit a PDCCH in the one or two OFDM symbols. This allows scheduling of uplink data transmissions on the PUSCH in future subframes. A bitmap is signaled to the UE to indicate which subframes are reserved for PMCH transmission, regardless of whether the UE subscribes to an MBMS service in a cell operating using the evolved transmission structure. In subframes where the PMCH is indicated, the UE monitors the PDCCH as in the legacy transmission structure. As a further example to reduce UE PDCCH processing, the UE may be configured to monitor only the PDCCH in PMCH subframes for either UL grants or group power control commands. In yet another example, in subframes where the PMCH is indicated, the UE monitors the PDCCH as in the legacy transmission structure for downlink control information that schedules DMRS-based PDSCH transmissions. The starting OFDM symbol of such PDSCH transmission is indicated by the PCFICH received in the legacy transmission structure for such subframe, or configured by a higher layer. This allows the network to schedule unicast transmissions in subframes where a PMCH is indicated but the PMCH is not scheduled, or where a PMCH is scheduled but no data is being received by the eNodeB due to congestion on the backhaul connection. In subframes where a PMCH is not indicated, the UE monitors the EPDCCH.

[0045] <Unicast / Multicast Data Multiplexing in Evolved Transmission Format> In an MBSFN area, a set of synchronized eNodeBs jointly transmit multicast data in MBSFN subframes. Because eNodeBs are geographically dispersed, the LTE standard specifies an extended cyclic prefix (CP) length of 16.67 μs to support the large delay spread seen by UEs in the MBSFN area. Enabling a longer CP can also support an increased MBSFN area. This increases the MBSFN combining gain at the UE because more unsynchronized eNBs can participate in multicast transmissions. For example, the CP length can be doubled to 33.33 μs, and the symbol length can also be doubled to maintain the same CP overhead. This approach is not backward compatible; MBMS services for an extended MBSFN area cannot be enjoyed by UEs running earlier LTE releases. This reduces the incentive for cellular operators to offer such a feature, as the potential revenue may not offset the required capital investment. On the other hand, it is beneficial for operators for whom backward compatibility is not an issue. For example, the NCT format is used in frequency bands that are not currently supported by UEs of previous releases or that require special permissions for access. Therefore, the applicant proposes the following approach to support multiplexing of unicast and multicast data in cells operating using the evolved transmission format.

[0046] In one embodiment, MBMS and unicast data are time multiplexed in an NCT transmission format. There are two types of subframes: normal subframes for carrying unicast data (PDSCH and EPDCCH) and MBSFN subframes for multicast data. For both normal and MBSFN subframes, PDSCH and PMCH transmission begins with symbol 0. Subframes 0 and 5 may not be configured as MBSFN subframes; that is, MBSFN subframe utilization is capped at 80%.

[0047] In another embodiment, an evolved physical broadcast channel (EPBCH) is transmitted in the second slot of the first subframe of a radio frame. Alternatively, the EPBCH may be transmitted in the first slot of the same subframe. In yet another embodiment, the EPBCH may span both slots in a PRB pair. The EPBCH is demodulated by a group-specific reference signal on one or two antenna ports. In one embodiment, the group-specific RS may use the same waveform and random number generator as the UE-specific RS in LTE Release 11 on antenna ports {7}, {8}, or {7, 8}. Other combinations, such as {7, 9} or {9, 10}, are not excluded. The location of this group-specific RS in the LTE time-frequency resource grid is the same as the existing UE-specific RS. In a different embodiment, a new set of EPBCH RSs may be transmitted on one or two antenna ports, and the RSs may be included in the PRB containing the OFDM symbol and the EPBCH.

[0048] In yet another embodiment, primary and secondary synchronization signals (PSS / SSS) are transmitted in subframes 0 and 5 for FDD and TDD, in subframes 0 and 5 for SSS, and in subframes 1 and 6 for PSS. In yet another embodiment, the PMCH is transmitted in a subset of subframes. For FDD, the subset of MBSFN subframes is taken from {1, 2, 3, 4, 6, 7, 8, 9}, and for TDD, the subset of MBSFN subframes is taken from {3, 4, 7, 8, 9}. This is because subframe 2 is always UL and subframe 6 carries PSS in the existing TDD UL-DL configuration. Alternatively, for TDD, PSS and SSS can be carried in subframes 0 and 5 for TDD, freeing up subframes 1 and 6 as potential MBSFN subframes. Figure 6 shows example mappings for FDD and TDD. Figure 7 illustrates an example mapping of the EPBCH, PSS / SSS, and PMCH to one of the six central PRBs of the system bandwidth. Figure 7(a) shows a time-multiplexing scheme for mixed unicast and multicast data in the NCT. The PSS and SSS are moved to symbols 1 and 2, respectively, to avoid collisions with the group-specific (demodulation) RSs on symbols 5 and 6. Figure 7(b) shows an alternative embodiment in which the demodulation RSs for antenna ports 7 and 8 are shifted from symbols 5 / 6 of slot 0 to symbols 1 and 2 of slot 1 in subframe 0. This maintains the same PSS and SSS positions as in the legacy transmission format. This mapping design allows for the same coding rate for the EPBCH as for the legacy PBCH, since eight resource elements per PRB (two for the one-port CRS and four for the group-specific RSs) are used for the RSs. Note that the EPBCH may not require a PHICH configuration. By reducing the number of spare bits to 5, the payload for the MIB (Master Information Block) can be reduced to 2 octets (16 bits).This provides a lower coding rate of (16+16) / 480=1 / 60 (with 16 CRC bits) compared to the 1 / 40 coding rate for the legacy PBCH.

[0049] In one embodiment, the length of the cyclic prefix for PMCH transmission is extended to support a larger delay spread, hi another embodiment, the CP is set to 33.33 microseconds.

[0050] In another embodiment, control information to support reception of multicast traffic and control channels (e.g., in the case of MBSFN subframe configuration and MCCH scheduling) is provided via broadcast of system information in unicast subframes scheduled with a common search space on an enhanced physical downlink control channel (EPDCCH). Specifically, the EPDCCH is a physical control channel that supports multicast transmissions similar to the PDCCH in previous LTE releases.

[0051] In yet another embodiment, a new approach is needed to support scheduling of UL grants in MBSFN subframes for FDD with paired UL carriers or for TDD with one or more UL subframes. Two alternatives are Option 1 and Option 2. Option 1 is the frequency at which EPDCCH and PMCH are multiplexed in MBSFN subframes. Bandwidth for PMCH transmission JPEG2025138843000002.jpg1318 is specified in the system information broadcast, where: JPEG2025138843000003.jpg1036, which is the DL system bandwidth. The EPDCCH is configured in a subset of PRBs that are not part of the PMCH bandwidth, as shown in Figure 8. Note that in subframes containing PMCH transmission, the eNodeB may schedule PDSCH transmission in PRBs reserved for the EPDCCH following the procedures for PDSCH transmissions whose resource allocation does not overlap with that of the scheduled EPDCCH, e.g., using existing transmission modes TM9 and TM10. In other words, unicast and PMCH transmissions are multiplexed in the frequency domain in MBSFN subframes. In Option 2, scheduling of UL grants occurs only in subframes of the legacy transmission format. For example, if the MBSFN subframe configuration for a radio frame in FDD is {1, 2, 3, 4, 6, 7, 8, 9}, the UL subframes for the paired carriers are scheduled as follows: The UL grant for subframes 0 to 4 is transmitted in subframe 0, and the UL grant for subframes 6 to 9 is transmitted in subframe 5.

[0052] <Multiplexing of EPDCCH, PRS, and PMCH in evolved transmission format> The EPDCCH and PMCH may be transmitted in the same subframe when the system bandwidth is partitioned into M sets, with M-1 sets assigned to EPDCCH transmission and 1 set assigned to PMCH. These M-1 sets may overlap but are disjoint, and the Mth set used for PMCH transmission is not assigned to EPDCCH transmission. If the M sets configured for PMCH and EPDCCH transmission do not span the entire system bandwidth, the EPDCCH may schedule the PDSCH in PRBs not covered by the M sets. Also, PDSCH transmission in a subframe configured for PMCH transmission may overlap some of the PRBs that are part of the M-1 sets assigned for EPDCCH transmission.

[0053] In one embodiment, the union of M-1 sets is signaled to the UE via a bitmap of length {6, 15, 25, 50, 75, 100}, where a bit value of "1" indicates that the corresponding PRB pair in the frequency domain is used for the EPDCCH, and a bit value of "0" indicates that the corresponding PRB pair is assigned to the PMCH. Other mappings are not excluded; the main idea is that the bitmap indicates which PRB pairs are used for the EPDCCH and the PMCH. Alternatively, a bit value of "0" may indicate that the corresponding PRB in the frequency domain is used for the EPDCCH.

[0054] In another embodiment, a combination index is used to indicate to the UE the PRB in the frequency domain that is used for the PMCH.

[0055] Multiplexing the EPDCCH and PMCH in the frequency domain requires that the EPDCCH be transmitted with an extended cyclic prefix (CP) whenever the two channels coexist in an OFDM symbol, since the PMCH is identified only because of the extended CP. Because the eNB may not know whether the UE is currently subscribed to MBMS and therefore receives the PMCH, and because the UE needs to know the CP for demodulation, a method is needed to remove any ambiguity between the eNB and the UE regarding the CP used in a given OFDM symbol. The eNB may transmit the EPDCCH with a normal or extended cyclic prefix (CP) according to a bitmap known to the UE through configuration by higher layers. If a PDSCH transmission is scheduled in a subframe configured for PMCH transmission, the CP of the PDSCH also follows the bitmap configured by higher layers. Alternatively, the CP of the PDSCH can follow the CP of the scheduling EPDCCH. However, this may require special handling when the scheduling cell is different from the serving cell (cross-carrier scheduling). In other words, EPDCCH scheduling in subframes configured for PMCH. PDSCH may be transmitted with normal CP or extended CP depending on the subframe on its component carriers, while PDSCH follows a bitmap provided by higher layers.

[0056] The length of such a bitmap may be 6, 10, 24, 40, or any other integer value. In one embodiment, a "1" indicates the use of an extended CP in the associated subframe. In another embodiment, a "0" indicates the use of an extended CP in the associated subframe. The subframes in which the extended CP is used for EPDCCH transmission may include at least all subframes in which the PMCH is transmitted. To avoid puncturing of the EPDCCH by a Positioning Reference Signal (PRS), when frequency resources are partitioned to multiplex the PMCH and EPDCCH, the PRS may be transmitted only in PRBs that are configured for PRS transmission by higher layers and that are part of the PMCH segment in the subframe configured for PRS transmission. Alternatively, the PRS may be transmitted only in PRBs that are configured for PRS transmission by higher layers and that are part of the PMCH segment in the subframe configured for PRS transmission that is also indicated for EPDCCH transmission with the extended CP.

[0057] In an MBSFN area, participating eNBs must transmit PMCHs over the same bandwidth. Therefore, a first eNB may transmit a message to a second eNB over a backhaul connection informing the second eNB of which PRBs it intends to use for PMCH transmission. In one embodiment, this message is a bitmap of length {6, 15, 25, 50, 75, 100}, where a "1" indicates that the associated PRB in the frequency domain is used for the PMCH. Alternatively, a "0" may indicate that the associated PRB in the frequency domain is used for the PMCH. In another embodiment, a combination index is used in such a message to indicate the PRB in the frequency domain that is used for the PMCH. A first eNB may also transmit a PMCH information request to a second eNB over a backhaul connection, in which case the second eNB responds with a message informing the first eNB of which PRBs it intends to use for PMCH transmission.

[0058] <PSS / SSS / DMRS location for evolved transmission formats> In the current LTE release, the DMRS is not transmitted in the central six PRBs of the system bandwidth if it conflicts with the PSS and SSS. Because the reduced CRS may not be adequate or sufficient for PDSCH demodulation, a new solution is needed to enable PDSCH demodulation in the UERS. The locations of the PSS and SSS are changed for cells operating with the evolved transmission format. In one embodiment, the relative locations of the PSS and SSS are changed compared to legacy transmission formats to allow for easy differentiation between transmission formats and duplexing modes. Figure 9 illustrates an example mapping, in which the SSS precedes the PSS by two symbols for FDD and the PSS by three symbols for TDD. A further advantage of this mapping for TDD is that it allows the possibility of the reduced CRS being transmitted in the first symbol of a special subframe. A different embodiment is shown in Figure 10. In FDD, the SSS is mapped to the last symbol of subframes 0 and 5, while the PSS is mapped to the symbol preceding the SSS, i.e., the 13th symbol for normal CP and the 11th symbol for extended CP. Yet another example for FDD is shown in Figure 11, where the PSS and SSS are moved to OFDM symbols 1 and 2, respectively.

Claims

1. 1. A method comprising: Implementing a serving cell for a user equipment (UE), The method, wherein the serving cell operates using an evolved transmission format including reduced density CRS transmission without a PDCCH control region.

2. 10. The method of claim 1, A method wherein the serving cell is a secondary serving cell and the UE is provided with all system information needed to receive data and control information.

3. 10. The method of claim 1, 11. The method of claim 10, wherein the UE is provided with an indication of whether the serving cell operates using the legacy transmission format or the evolved transmission format.

4. 4. The method of claim 3, A method in which the UE is configured to assume or not assume the presence of a PBCH on an attached serving cell.

5. 5. The method of claim 4, The method, wherein the UE does not rate-match resource elements otherwise reserved for PBCH transmission when the PBCH is not present on the attached serving cell.

6. 10. The method of claim 1, The method, wherein the UE is provided with information about which sequence frame number of the added serving cell to use as a reference for the added serving cell instead of decoding a primary broadcast channel on the added serving cell.

7. 1. A method comprising: time multiplexing subframes on a serving cell to a user equipment (UE); one set of subframes operates using a legacy LTE transmission format; A method in which one set of subframes operates using an evolved transmission format including reduced density CRS transmission without a PDCCH control region.

8. 8. The method of claim 7, A bitmap indicating the set of subframes for a legacy or evolved transmission format is signaled to the UE.

9. 8. The method of claim 7, A bitmap indicating the set of subframes for monitoring a PDCCH is signaled to the UE.

10. 8. The method of claim 7, A PBCH is transmitted in the set of subframes operating using the legacy transmission format.

11. 1. A method comprising: multiplexing unicast and multicast data and control in an evolved LTE transmission format including frequency multiplexing of data and control information from the first symbol of a subframe; A method comprising:

12. 12. The method of claim 11, A method in which an evolved PBCH is transmitted in subframe 0 and decoded using DMRS on one or two antenna ports.

13. 12. The method of claim 11, The EPDCCH and the PMCH are frequency multiplexed over a system bandwidth in a subframe, and the method includes: Partitioning the system bandwidth into M non-overlapping sets of physical resource blocks; and indicating by a bitmap which of the sets may include a PMCH and which of the sets may include an EPDCCH; A method comprising:

14. 12. The method of claim 11, A method in which the PMCH is transmitted with a longer cyclic prefix.

15. 12. The method of claim 11, A method in which PSS, SSS, and DMRS are mapped to different symbols of a subframe.

16. 1. A method comprising: Connecting a user equipment (UE) to a legacy LTE cell; configuring the user equipment (UE) to receive data and control on a New Carrier Type (NCT) cell; Including, constructing the UE, receiving information on a control channel regarding radio resource management (RRM) measurements; demodulating the information to generate a list of cells for providing radio resource management (RRM) measurements, a transmission format being indicated for each cell in the list; receiving reporting references for RRM measurements via radio resource control to construct a channel state information (CSI) reference signal (RS); transmitting the RRM report; A method comprising:

17. 17. The method of claim 16, The method, wherein the transmission format is selected from one of the group: legacy and NCT.

18. 1. A method comprising: Operating a cellular communication system using time-multiplexed legacy and New Carrier Type (NCT) formats; and receiving a list indicating which format is used by each of a plurality of subframes; A method comprising:

19. 20. The method of claim 18, The method, wherein the list is communicated by radio resource control (RRC) signaling.

20. 20. The method of claim 18, wherein the list is composed of bit values ​​"0" and "1", with a bit value of "1" indicating that the subframe is of one transmission format and a bit value of "0" indicating that the subframe is of the other transmission format.

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