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

Abstract

The present application relates to a method for energy-efficient unicast and multicast transmission in a wireless communication system. A method for time-division multiplexing subframes on a serving cell to a user equipment (UE) wherein an eNodeB indicates the communication via a bitmap, wherein the bitmap indicates a set of subframes (501, 502, 503) operating with a legacy Long Term Evolution (LTE) transmission format using a first bit (bit "0") and another set of subframes (504) operating with an Evolved Transmission New Carrier Type (NCT) format using a second bit (bit "1"), including reduced density cell-specific reference signal (CRS) transmission without a physical downlink control channel (PDCCH) control region.

Description

[0001] This application is a divisional application of Chinese patent application No. 201480004621.5, entitled “Method for Energy-Efficient Unicast and Multicast Transmission in Wireless Communication Systems”, filed on January 21, 2014. Technical Field

[0002] The present invention relates to wireless communications, and in particular to user equipment connected to a base station. Background Art

[0003] A cellular communication network includes several wireless terminal devices and several base stations to provide communication services such as voice, data, video, messaging, chat, and broadcast. Several wireless terminals can connect to a serving cell controlled by a base station (BS). Typical access schemes 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 (SC-FDMA), or a combination thereof. A base station (BS) may also be referred to as a NodeB in a Universal Mobile Telecommunications System (UMTS) or an evolved NodeB (eNB) in a long-term evolution plan specified by the Third Generation Partnership Project (3GPP), a base transceiver system (BTS), an access point (AP), or some other similar technology.

[0004] Typically, the eNodeB hardware, when deployed, is fixed and static, but in some cases, for example, when deployed on a vehicle, it can also be mobile. In contrast to the eNodeB, a wireless end device can be portable hardware. Wireless end devices are commonly referred to as user equipment (UE), mobile workstations, cellular phones, personal digital assistants (PDAs), wireless modems, etc. Uplink (UL) communication refers to communication from a fixed or mobile UE to an eNodeB, while downlink (DL) communication refers to communication from an eNodeB to a fixed or mobile UE. Each eNodeB contains a radio frequency transmitter (one or more) and a receiver (one or more) that are used to communicate directly with a mobile device, where the mobile device is free to move around the eNodeB or is in a fixed position. Similarly, each UE contains a radio frequency transmitter (one or more) and a receiver (one or more) that are used to communicate directly with the eNodeB.

[0005] Figure 1An exemplary wireless communications network 100 is shown. This illustrative communications network includes base stations 101, 102, and 103, although in operation, the communications network will necessarily include many more base stations. Each of base stations 101, 102, and 103 (eNBs) is operable over a respective coverage area 104, 105, and 106. The coverage area of ​​each base station is further divided into cells. In this illustrative network, the coverage area of ​​each base station is divided into three cells. A mobile phone 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 transmits 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. Because UE 109 is synchronized with base station 101, UE 109 can use asynchronous random access to initiate a handover to base station 102.

[0006] Figure 2 Shown as Figure 1 The diagram shows the relationship between the Evolved Universal Terrestrial Radio Access Network (EUTRAN) 200 and the Core Network (CN) 210 in an LTE wireless network. eNodeBs 203 and 204 communicate with a Mobility Management Entity (MME) 211 and a Serving Gateway 212 via an S1 signaling interface 205. UEs 201 and 202 communicate with eNodeBs 203 and 204, respectively, over the air interface. Two eNodeBs are shown in this diagram, but in a deployed network, there may be more eNodeBs connected to the same MME, and one eNodeB may be connected to several MMEs. In the E-UTRAN, eNodeBs can communicate with each other via an X2 interface 206.

[0007] Description of the LTE system

[0008] The LTE wireless network (also known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN)) is being standardized by the 3GPP Working Group (WG). OFDMA and SC-FDMA access schemes are used for the downlink (DL) and uplink (UL) of E-UTRAN, respectively, as part of the Evolved Universal Terrestrial Radio Access (E-UTRA). Now referring to Figure 3, the legacy LTE DL transmission format is shown, which shows the time-frequency resource mapping of physical channels in a 1 millisecond (ms) transmission time interval (TTI), which is also called a subframe. Downlink control layer and user layer data are scheduled by the Physical Downlink Control Channel (PDCCH) or the Enhanced Physical Downlink Control Channel (EPDCCH), while the actual data is transmitted on the Physical Downlink Shared Channel (PDSCH). The minimum granularity of resource allocation for PDSCH and EPDCCH is a physical resource block (PRB) pair. The control region 301 contains DL control signaling, which includes the PDCCH, the Physical Hybrid Automatic Repeat Request Indicator Channel (PHICH), and the Physical Control Format Indicator Channel (PCFICH). Normal and dedicated control information is transmitted on the PDCCH, while dedicated control information is transmitted on the EPDCCH 305, 306, if present. A cell-specific reference signal (CRS) is 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 transmitted on the PDSCH. Alternatively, the UE is configured to demodulate the PDSCH (302, 303, 304) and / or EPDCCH (305, 306) using a dedicated demodulation reference signal (DMRS), which is transmitted only within the PRB containing data or control information. Key cell information required for initial UE access is transmitted on the physical broadcast channel (PBCH), while other system information and paging information are transmitted on the PDSCH. EPDCCH and PDSCH are frequency-division multiplexed across the system bandwidth, with Figure 3 showing the division into three PDSCH regions 302, 303, and 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.

[0009] Unicast and multicast data can be transmitted on the same carrier. Unicast includes bidirectional point-to-point or point-to-multipoint transmission between the network and each UE using a dedicated connection to each UE. The Evolved Multimedia Broadcast Multicast Service (E-MBMS) feature supports multicast data transmission to a group of UEs, and multicast data transmission includes 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) transmission. Figure 4 shows an MBSFN subframe 400. The non-MBSFN area 401 contains the PDCCH, PHICH, and PCFICH, where the PDCCH can be used to schedule uplink data transmission and to signal power control commands for the UE group. CRS is transmitted in the non-MBSFN area 401 for demodulation of the aforementioned channels. The MBSFN area 402 is used to transmit multicast data on the physical multicast channel (PMCH) of UEs, where these UEs subscribe to one or more MBMS services. In an MBSFN area, a group of synchronized eNodeBs can jointly transmit multicast data in an MBSFN subframe, thereby improving reception quality. Therefore, an MBSFN reference signal (MBSFN-RS) is used in the MBSFN area 402 for demodulating the PMCH.

[0010] The current and future trend in cellular networks is expected to be an exponential growth in data traffic, driven in part by the rapid adoption of mobile internet devices and related data-hungry applications. This increased traffic demand 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 any user equipment (UE) is actually being served in the cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 FIG. 1 is a schematic diagram of a traditional homogeneous network deployment of three macro cell sites, where each macro cell site includes three sectors.

[0012] Figure 2 Describe the relationship between E-UTRAN and the core network of LTE network.

[0013] FIG3 illustrates the current LTE DL transmission format, which shows the mapping of physical channels for unicast data and control.

[0014] Figure 3A The evolved LTE DL transmission format is shown, which shows the mapping of physical channels for unicast data and control.

[0015] FIG4 illustrates the current LTE DL transmission format showing the partitioning of MBSFN subframes into MBSFN and non-MBSFN areas.

[0016] Figure 5 The bitmap indicates allocation of subframes in radio frames of the legacy transport format and the evolved transport format.

[0017] Figure 6 Exemplary mapping of normal subframes and MBSFN subframes for the evolved transport formats for FDD and TDD is shown.

[0018] Figure 7 Mapping of channels and signals on the time-frequency grid is shown: (a) PSS / SSS is moved to avoid collision with the group-specific RS, and (b) the group-specific RS is moved to the EPBCH region to avoid collision with the PSS / SSS.

[0019] Figure 8 The mapping of PMCH and EPDCCH in the MBSFN subframe of the evolved transport format is shown.

[0020] Figure 9 、 Figure 10 and Figure 11 Several exemplary mappings of PSS and SSS with evolved transmission formats for both FDD and TDD are shown. DETAILED DESCRIPTION

[0021] As cellular networks evolve to handle this explosive growth in cellular data traffic, it has been discovered that bottlenecks are created because many services are localized to hotspots in both indoor and outdoor deployment scenarios. Homogeneous networks are becoming increasingly popular, in which small cells controlled by low-power base stations are deployed to increase hotspot capacity and / or increase cellular coverage. In the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system, base stations (also known as evolved NodeBs (eNBs)) often transmit cell-specific reference signals (CRSs) and time-division multiplexed physical downlink control channels (PDCCHs). However, the frequent transmission of cell-specific reference signals and time-division multiplexed physical downlink control channels (PDCCHs) has become a problem due to the increase in traffic and demand.

[0022] Description of the Evolved Transport Format

[0023] The 3GPP Radio Access Network (RAN) standardization body has adopted various measures to address the energy efficient transmission problem, involving the evolution from an "always on" DL transmission mode to an "on-demand" mode. One such technique is the introduction of an evolved DL transmission format, characterized by the absence of legacy downlink cell-specific reference signals and control channels (including PDCCH, PHICH, and PCFICH, which rely on CRS for demodulation). Figure 3A , PDSCH 312, 313 and 314 and EPDCCH 315, 316 span the entire subframe. CRS is sent in the time domain (optionally, in the frequency domain) with a reduced density. For example, CRS can be sent on a single antenna port with a 5ms periodicity and can occupy the entire system bandwidth or a reduced bandwidth. Removing legacy control signals and CRS can provide significant energy savings for lightly loaded cells or unloaded cells. When there is no UE in the cell, if one-fifth of the subframe is used for transmission, this means saving up to 80% of energy. In addition, removing legacy control signals and CRS frees up resources that can be used for data transmission, thereby increasing spectrum efficiency and peak data rate. The evolved transport format can also be referred to as a new carrier type (NCT). However, a significant problem is that UEs of previous LTE versions cannot attach to cells operating with the NCT structure.

[0024] The evolved transport format or NCT can be configured for a secondary cell (SCell) for carrier aggregation (CA) or can be configured for single cell operation (standalone mode). For SCell operation, all required system information for the NCT-SCell can be provided to the UE by dedicated signaling. A natural question to ask is whether the benefits of NCT can still be obtained if NCT is deployed in standalone mode. This means that the UE can attach to the NCT as the primary cell to start access or handover via a different cell. This will require new technologies to access the cell, including synchronization, broadcast transmission, and system information and mobility control. For both CA-based operation or standalone operation, new technologies are also needed to multiplex reference signals, synchronization signals and physical channels onto the OFDM time-frequency resource grid.

[0025] To achieve the goal of increasing energy conservation in wireless networks, it is desirable to constrain base station transmissions to periods when data transmission to user devices is available. For example, a small cell deployed within an office building could operate at full power during the day, while at night the small cell should operate at reduced power or be completely shut down when no one is in the building. Furthermore, reduced downlink (DL) signaling reduces DL inter-cell interference, which can become a bottleneck for capacity growth as more cells are added to the cellular topology.

[0026] Energy efficient transmission can be achieved by configuring NCT as 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, or a combination thereof in a homogeneous network (HetNet).

[0027] For the CA scenario, all system information necessary to receive SCell-related data and control information is provided to the UE 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 host information block and the system information block (SIB). System information that cannot be signaled to the UE (e.g., system frame number (SFN)), which changes every 10ms, is assumed by the UE to be the same for both the NCT SCell and the cell where the UE receives system information via dedicated signaling. Therefore, the PBCH may not be transmitted on the NCT. The eNodeB also provides an indication via RRC signaling whether the SCell is operating using the legacy LTE transport format or the evolved transport format. Alternatively, the UE can identify whether the SCell is operating using the legacy LTE transport format or the evolved transport format by the presence or absence of an existing or new signal. In one embodiment, the discovery signal can identify that the SCell is operating using the evolved transport format. The NCT indication determines the location of the DMRS, and this location in turn depends on the duplex mode (EDD or TDD), cyclic prefix, or subframe type (normal or special subframe). The NCT indication can also determine whether the PBCH is transmitted on the NCT. If not, the UE cannot rate match the resource element (RE), otherwise the resource element is reserved for PBCH transmission. Alternatively, in addition to the aforementioned NCT indication, additional RRC signaling can indicate whether the PBCH is transmitted, that is, whether to rate match the resource elements reserved for PBCH transmission.

[0028] If the SCell is NCT, the UE performs a cell search by detecting the legacy primary synchronization signal (PSS) and secondary synchronization signal (SSS) (in the legacy LTE transmission format). Alternatively, the UE may use the discovery signal for cell detection. The PSS / SSS is transmitted in the same time-frequency position in the legacy transmission format. In a different embodiment, the PSS / SSS position is different. For example, in yet another embodiment, the PSS / SSS may no longer be transmitted in every radio frame to improve energy efficiency and reduce inter-cell interference, and the UE will blindly detect the presence of the PSS / SSS or alternatively the network may notify the UE through explicit or implicit signaling on the subframes in which to search for the PSS / SSS.

[0029] Other variations of SCell operation are not excluded. For example, the SCell may be controlled by a second eNodeB that is different from the eNodeB that controls the primary serving cell. The two eNodeBs coordinate their scheduling and RRM decisions for the UE via the backhaul connection.

[0030] Evolved transmission formats in single cell operation

[0031] For stand-alone operation of the evolved transmission formats, new techniques are needed to achieve the goals of energy efficiency, reduced inter-cell interference, and increased spectral efficiency.

[0032] One such technique is to use a demodulation reference signal (DMRS) to transmit common control information on a shared downlink or broadcast channel. If the reduced density CRS is used only for tracking and not for data demodulation, new techniques are needed for transmitting system information, paging notifications, and common control information including UL power control commands based on DMRS. This technique uses a common control channel specification where all UEs or groups of UEs can monitor control messages that schedule common system information, paging information, and group power control commands. Another technique is to use DMRS-based transmission to send broadcast information where the UE needs to attach to the cell without the need for reception of existing handover commands (e.g., DL bandwidth and system timing reference (system frame number)). Yet another technique is to use transmission of UE-specific reference signals for radio resource management (RRM), including new mobility procedures and measurements; for radio link monitoring (RLM), including new RLM procedures and measurements; and channel state information (CSI) feedback, including new measurements and procedures based on, for example, CSI-RS.

[0033] Another technique is needed for cell identification and accessibility: one that prevents previous release UEs from accessing cells using the NCT format. In previous releases, the UE would obtain the MIB and at least SIB type 1 to determine if a cell is barred. If NCT follows this legacy procedure, previous release UEs will consume significant energy during cell search and intra-frequency and / or inter-frequency measurements, especially in high-density small cell deployments. Consequently, any energy savings on the network side are now offset by increased energy consumption on the terminal side.

[0034] Therefore, in order to enable a UE to access a cell operating with an evolved transport format, the following technologies are proposed:

[0035] In one embodiment, if the 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 uses the old transport format. On the one hand, if the RRC-IDLE UE finds that it has an RRC connection to the NCT within the last N (N is a fixed value) hours, the UE may perform an initial cell attachment to the NCT without handover via a cell operating with the old transport format. Otherwise, the UE searches for a cell operating with the old transport format and attaches to it. The UE may choose to camp on this cell in the RRC-IDLE state or may choose to transition to the RRC-CONNECTED state.

[0036] In another embodiment, the UE is in RRC-CONNECTED mode and is handed over to a cell operating with NCT. The handover is controlled by the network but assisted by the UE, i.e. the network may rely on the UE to discover and report cells operating with evolved transport mode. The eNodeB can assist the UE by providing a list of cells for which the UE should report radio resource management (RRM) measurements. For each cell in this list, the eNodeB indicates the transport format, either the legacy format or the NCT format. In yet another embodiment, the set of physical cell IDs (PCIs) is divided into several ranges, and the UE can infer the transport format used by the individual cells based on 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 with the legacy transport format, while the set not containing PCI 0 is associated with the NCT structure.

[0037] In one embodiment, RRM measurements including measurements of reference signal received power (RSRP) and reference signal received quality (RSRQ) are performed on a channel state information reference signal (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 should 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 performing said RRM measurements on the reduced density CRS, for example, performing the measurements in time and / or frequency resources. 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 reduced density CRS, CSI-RS or any other discovered signal.

[0038] In another embodiment, for RRM measurement purposes, the eNodeB may configure the UE with reporting criteria including periodic, event-triggered, or event-triggered / periodic measurements. The eNodeB may further configure the UE to report only the PCI that triggered the report. In another embodiment, the eNodeB configures the UE to report the PCI and related RRM measurement results. In addition, if the cell measurement value is better than a serving cell specific threshold, the reporting criteria may include an offset so that the UE only reports the cell ID and related measurement results. The eNodeB may then use the Neighbor Related List (NRT) to find out whether the reported cell ID is an NCT. For each neighboring cell included in the aforementioned PCI list, the eNodeB may also configure the UE with a system bandwidth. This helps to accurately perform RSRP or RSRQ measurements. Alternatively, the eNodeB indicates to the UE the measurement bandwidth of each neighboring cell included in the PCI list.

[0039] In yet another embodiment, the source eNodeB initiates a handover to the target eNodeB. If the target eNodeB affirmatively acknowledges the handover request, the target eNodeB provides the following handover information to the UE (which is relayed via the source eNodeB): RRC reconfiguration information including all system information related to the target cell; an indication of the transport format in the target cell; and the UE performs synchronization to the target cell based on the transport type.

[0040] In the current LTE specifications up to Release 11, the System Frame Number (SFN) is not exchanged between eNodeBs over the X2 interface. Consequently, the SFN is not part of the mobility information sent to the UE during handover preparation. If the PBCH is not sent for the NCT format, it does not mean that the target cell has deployed NCT to indicate the SFN to UEs arriving during or after the handover procedure. A new technique is needed to facilitate handovers from cells operating with the legacy transport format to cells operating with the NCT format.

[0041] To address this issue, an RRC information element is included in the mobility control information, which indicates 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 is used as the reference SFN for the target cell (determined by decoding the proxy cell's PBCH). The RRC information element may contain the PCI of the proxy cell operating with the legacy transport format. The mobility control information is prepared by the target eNB deploying NCT. The target eNB can determine the appropriate PCI through operations, administration, and maintenance (OAM) information or via its neighbor association table. In another embodiment, the source eNB implicitly provides a reference signal for the target cell's SFN, i.e., the SFN broadcast in the source cell's PBCH is the reference SFN for the target cell with 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, the offset that the UE should apply to the SFN of the proxy cell.

[0042] The mobility technique of providing a reference SFN for the target cell is also beneficial when the target eNB deploys a legacy carrier but operates in cell range extension (CRE). In this case, when the UE is handed over, it experiences severe interference and may not be able to reliably detect the PBCH of the target cell. This is especially the case when the UE is not equipped with a PBCN interference cancellation receiver. This mobility technique can allow the network to configure a larger CRE offset, which contributes to a larger offloading gain when the UE moves from a heavily loaded cell to a lightly loaded cell, especially for UEs without advanced receivers. Therefore, the SFN reference can be included in the mobility control information and is independent of whether the target cell deploys a legacy or NCT transmission format. More generally, the proposed mobility technique can be configured when the UE cannot reliably detect the PBCH of the target secondary serving cell, where the cell is controlled by a serving eNodeB or a different eNodeB. Moreover, the cell can operate with a legacy transmission mode and the PBCH is not sent by the eNodeB controlling such a cell. For example, the UE can be configured to send data to and receive data from multiple eNodeBs. In this case, only one eNodeB can transmit a broadcast channel (i.e., the master eNodeB) while the other eNodeBs (i.e., the slave eNodeBs) only transmit data or dedicated control information. In this deployment, the proposed technique is used to obtain the SFN of the cell controlled by the slave eNodeB from the PBCH transmitted by the master eNodeB.

[0043] Time division multiplexing of mixed subframes of both legacy and evolved transport formats

[0044] As mentioned previously, the NCT format is not backward compatible. Therefore, cellular operators may deploy this transmission format only in cells where all connected UEs in the cell support this feature. Furthermore, it appears to be more suitable for small cells rather than macro cells, where macro cells may not be shut down because they provide coverage and guarantee a minimum quality of service to all UEs. Furthermore, without PDCCH transmission, a new technology is needed to send common control signaling including broadcasts, system information, and paging.

[0045] One solution to these shortcomings of NCT is to run subframes of legacy and evolved transport formats through time domain multiplexing. The eNodeB can indicate to the UE the set of subframes that operate using the legacy or evolved transport structure. The subframe indication is conveyed to the UE by 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 in NCT format, while a bit value of "0" indicates that the subframe is in the legacy transport format, i.e., the subframe contains a time-division multiplexed control region and a unicast or multicast data region. Now referring to Figure 5, showing an exemplary bitmap of length 10 for one radio frame. Other bitmap sizes are also possible. Subframes 501, 502, 503 use the legacy transport format, where the UE monitors the PDCCH for common and dedicated control signaling and the CRS can be used to demodulate some channels transmitted in this subframe. The UE can also use these subframes for radio link monitoring (RLM) or radio resource management (RRM) measurements. The UE can also be configured to monitor the EPDCCH in subframes 501, 502, 503. Other subframes (such as 504) indicate the NCT format. Therefore, in these subframes, when the PDCCH is not sent, the UE only monitors the EPDCCH for downlink control information. In a different embodiment of the present invention, the UE is signaled a bitmap indicating a set of subframes where the UE monitors the PDCCH. The UE can be configured to monitor DL ​​allocations, UL grants and group power control commands, or only to monitor UL grants and group power control commands. This subframe indication concept is applied in different methods to enable efficient multiplexing of (a) unicast and multicast data and (b) transmissions utilizing legacy and evolved transmission formats within a cell.

[0046] Monitoring of control channels and PBCH

[0047] Subframes operating with the legacy transmission structure contain a PDCCH region and contain CRS transmissions with one, two, or four antenna ports. These legacy subframes are used to send common control information on the common search space of the PDCCH. The legacy subframe set should contain at least subframe 0 of each radio frame. Therefore, the PBCH is sent and can be detected by UEs of all LTE versions. DMRS is used to demodulate the PDSCH in all frames. Alternatively, the UE is configured to use CRS or DMRS for data demodulation in legacy subframes and only DMRS for data demodulation in NCT subframes. In another embodiment, the downlink control information (DCI) format received on the control channel indicates to the UE which reference signal to use for demodulation. However, the UE uses 1-port CRS, 2-port CRS, or 4-port CRS to demodulate the PBCH and PDCCH.

[0048] In a different embodiment, the UE may demodulate the PBCH and PDCCH using 1-port CRS, i.e., at most 1-port CRS is sent in a mixed subframe transmission format. RRM, RLM, and / or CSI measurements are performed in subframes carrying 1-port CRS.

[0049] Multiplexing of PMCH, PDSCH, EPDCCH and PDCCH

[0050] When two cells are deployed on the same carrier frequency, it is possible to operate using the NCT format in one cell and the legacy transport format in a different cell. The NCT format is used exclusively in all subframes of the small cell or only in those subframes configured for transmission using the evolved transport format. In this case, MBMS services can be provided in an MBSFN area consisting of cells operating using different transport formats. For example, in a homogeneous network, a macro cell and a small cell can operate using the legacy and evolved transport formats, respectively, on a shared carrier frequency. Therefore, if both the macro cell and the small cell eNB participate in MBSFN transmission, at least for the subframes carrying the PMCH in the small cell, the PMCH transmission should be synchronized with the PMCH transmission in the macro cell. Therefore, the first one or two OFDM symbols in the small cell layer are discarded to align the MBSFN transmission across the macro cell layer and the small cell layer, because the small cell does not contain a control region.

[0051] To address this abandonment, the small cell eNB can send PDCCH in the one or two OFDM symbols. This allows scheduling of uplink data transmission on PUSCH in future subframes. A bitmap is signaled to the UE to indicate which subframe is reserved for PMCH transmission, regardless of whether the UE subscribes to MBMS service (one or more) in a cell operating with an evolved transport structure. In subframes indicating PMCH, the UE monitors PDCCH as in the legacy transport structure. As a further embodiment, in order to reduce UE PDCCH processing, the UE can be configured to monitor only PDCCH in PMCH subframes for UL grants or group power control commands. In yet another embodiment, in subframes indicating PMCH, the UE monitors PDCCH for downlink control information scheduling DMRS-based PDSCH transmissions as in the legacy transport structure. The starting OFDM symbol of such PDSCH transmission is indicated by the PCFICH received in the legacy transport structure of such subframe or configured by a higher layer. This allows the network to schedule unicast transmissions in subframes where PMCH is indicated but not scheduled or where PMCH is scheduled but the eNodeB does not receive data due to congestion in the backhaul connection. In subframes where PMCH is not indicated, the UE monitors the EPDCCH.

[0052] Multiplexing of unicast / multicast data in evolved transport formats

[0053] In an MBSFN area, a set of synchronized eNodeBs jointly transmit multicast data in an MBSFN subframe. Because eNodeBs are geographically spread across various locations, an extended cyclic prefix (CP) length of 16.67 milliseconds has been specified in the LTE standard to support the large delay spread seen by UEs in an MBSFN area. Allowing even longer CPs would also support the expansion of MBSFN areas. This, in turn, increases the MBSFN combining gain at the UE, as more synchronized eNBs can participate in the multicast transmission. For example, the CP length can be doubled to 33.33 microseconds and the symbol length doubled to maintain the same CP overhead. This technology is not backward compatible, meaning that UEs of earlier LTE releases cannot enjoy MBMS services for enhanced MBSFN areas. This reduces the incentive for cellular operators to offer this feature, as the potential benefits do not justify the required capital investment. On the one hand, this benefits operators who are not concerned with backward compatibility. For example, the NCT format is deployed in frequency bands that are not currently supported by UEs of previous releases or that require special licenses for access. Therefore, we propose the following techniques to support multiplexing unicast and multicast data in cells operating with the evolved transport format.

[0054] In one embodiment, MBMS and unicast data are time-division multiplexed on the NCT transmission format. There are two types of subframes: normal subframes for transmitting unicast data (PDSCH and EPDCCH) and MBSFN subframes for multicast data. For both normal and MBSFN subframes, PDSCH and PMCH transmissions begin at symbol 0. Subframes 0 and 5 may not be configured as MBSFN subframes, meaning that MBSFN subframe utilization does not exceed 80%.

[0055] In another embodiment, the Evolved Physical Broadcast Channel (EPBCH) is transmitted in the second time slot of the first subframe of the radio frame. Alternatively, the EPBCH can be transmitted in the first time slot of the same subframe. In yet another embodiment, the EPBCH can span two time slots of 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 can 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 position of such a group-specific RS in the time-frequency resource grid of LTE is the same as that of the existing UE-specific RS. In a different embodiment, a new EPBCH RS set can be sent on one or two antenna ports, where the RS should be contained in an OFDM symbol and the PRB contains the EPBCH.

[0056] In yet another embodiment, for FDD, the primary and secondary synchronization signals (PSS / SSS) are transmitted in subframes 0 and 5, while for TDD, the SSS is in subframes 0 and 5 and the PSS is in 1 and 6. In yet another embodiment, the PMCH is transmitted in a subset of subframes. For FDD, the subset of MBSFN subframes is derived from {1, 2, 3, 4, 6, 7, 8, 9}, while for FDD, the subset of MBSFN subframes is derived from {3, 4, 7, 8, 9} because in the existing TDD UL-DL configuration, subframe 2 is always UL and subframe 6 transmits PSS. Alternatively, for TDD, PSS and SSS can be transmitted in TDD subframes 0 and 5, freeing subframes 1 and 6 as potential MBSFN subframes. Figure 6 An exemplary FDD and TDD mapping is shown. Figure 7 An exemplary mapping of EPBCH, PSS / SSS, and PMCH to the center 6 PRBs of the system bandwidth is shown. Figure 7 (a) shows a time division multiplexing scheme for mixed unicast and multicast data on NCT. The PSS and SSS are moved to symbols 1 and 2 respectively to avoid collision with the group-specific (demodulation) RS on symbols 5 and 6. Figure 7 (b) shows an alternative embodiment in which the demodulation RS for antenna ports 7 and 8 is moved from symbols 5 / 6 of slot 0 in subframe 0 to symbols 1 and 2 of slot 1. This maintains the same position of the PSS and SSS as the legacy transport format. This mapping design allows the coding rate of the EPBCH to be the same as that of the legacy PBCH because there are 8 resource elements per PRB (2 for 1-port CRS and 4 for group-specific RS) for RS. Note that the EPBCH may not require a PHICH configuration. By reducing the number of spare bits to 5, the payload of the master information block (MIB) can be reduced to 2 bytes (16 bits). This provides a lower coding rate - (16+16) / 480 = 1 / 60 (with 16 CRC bits) compared to the coding rate of 1 / 40 for the legacy PBCH.

[0057] In one embodiment, the length of the cyclic prefix of the PMCH transmission is extended to support a larger delay spread. In another embodiment, the CP is set to 33.33 microseconds.

[0058] In another embodiment, control information and control channels supporting the reception of multicast services (e.g., MBSFN subframe configuration and MCCH scheduling opportunities) are provided via the broadcast of system information in unicast subframes scheduled in a common search space on the enhanced physical downlink control channel (EPDCCH). Specifically, the EPDCCH is now a physical control channel supporting multicast transmissions, similar to the PDCCH in previous LTE releases.

[0059] In yet another embodiment, for FDD with paired UL carriers or for TDD with one or more UL subframes, a new technique is needed to support scheduling UL grants in MBSFN subframes. Two alternative techniques are: Option 1 : EPDCCH and PMCH are frequency multiplexed in MBSFN subframes. The bandwidth of PMCH transmission is Defined in system information broadcast, where (DL system bandwidth). EPDCCH is configured in a subset of PRBs that are not part of the PMCH bandwidth, such as Figure 8 As shown. Note that in a subframe containing a PMCH transmission, the eNodeB can schedule a PDSCH transmission, for example, using existing transmission modes TM 9 and 10, in the PRBs reserved for EPDCCH, following the procedure for PDSCH transmission, with the resource allocations for the PDSCH transmission not overlapping with those for the scheduled EPDCCH. In other words, unicast and PMCH transmissions are frequency-multiplexed in the MBSFN subframe. 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 of the paired carriers are scheduled as follows: UL grants for subframes 0-4 are transmitted in subframe 0, while UL grants for subframes 6-9 are transmitted in subframe 5.

[0060] Multiplexing EPDCCH, PRS and PMCH in the evolved transport format

[0061] When the system bandwidth is divided into M sets (where M-1 sets are allocated for EPDCCH transmission and one set is used for PMCH), EPDCCH and PMCH can be transmitted in the same subframe. These M-1 sets may partially overlap but be mutually disjoint with the Mth set, where the Mth set is not allocated for EPDCCH transmission but is used for PMCH transmission. If the M sets configured for PMCH and EPDCCH transmission do not span the entire system bandwidth, EPDCCH may schedule PDSCH in those PRBs not covered by the M sets. In addition, PDSCH transmission in a subframe configured for PMCH transmission may overlap some of the PRBs that are part of the M-1 sets allocated for EPDCCH transmission.

[0062] In one embodiment, the union of the 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 is used for EPDCCH in the frequency domain, while a bit value of "0" indicates that the corresponding PRB pair is allocated for PMCH. Other mappings are not excluded; the main idea is that the bitmap indicates which PRB pairs are used for EPDCCH and PMCH. Alternatively, a bit value of "0" can indicate that the corresponding PRB is used for EPDCCH in the frequency domain.

[0063] In another embodiment, the combination index is used to indicate to the UE the PRBs used for the PMCH in the frequency domain.

[0064] Multiplexing EPDCCH and PMCH in the frequency domain requires that both channels co-exist in an OFDM symbol, and since PMCH is dedicated only to the extended CP, EPDCCH is transmitted with an extended cyclic prefix (CP). Since the eNB may not know whether the UE is currently subscribed to MBMS and therefore receives PMCH, and since the UE needs to know the CP for demodulation, a method is needed to eliminate the ambiguity between the eNB and the UE regarding the CP used for a given OFDM symbol. The eNB can send EPDCCH according to a bitmap using a normal or extended cyclic prefix (CP), where the UE knows the bitmap by configuring it by higher layers. If a PDSCH transmission is scheduled in a subframe configured for PMCH transmission, the CP of the PDSCH also follows the aforementioned bitmap configured by higher layers. Alternatively, the CP of the PDSCH can follow the CP of the scheduled EPDCCH. However, this will require special handling of the case where the scheduling cell is different from the serving cell (cross-carrier scheduling). In other words, the PDSCH in the subframe of the EPDCCH scheduling configuration for the PMCH can be transmitted using a normal CP or an extended CP based on the subframe on the component carrier, where the PDSCH follows a bitmap provided by higher layers.

[0065] The length of such a bitmap can be 6, 10, 24, 40 or any other integer value. In one embodiment, "1" indicates that the extended CP is used in the relevant subframe. In another embodiment, "0" indicates that the extended CP is used in the relevant subframe. In a subframe where the extended CP is used for EPDCCH transmission, the subframe should contain at least all subframes where the PMCH is transmitted. In order to avoid the positioning reference signal (PRS) piercing the EPDCCH, if the frequency resources are divided into multiplexed PMCH and EPDCCH, the PRS can be transmitted only in those PRBs that are configured by higher layers for PRS transmission and are part of the PMCH partition in the subframe configured for PRS transmission. Alternatively, the PRS can be transmitted only in those PRBs that are configured by higher layers for PRS transmission and are part of the PMCH partition in the subframe configured for PRS transmission (which is also indicated for EPDCCH transmission with extended CP).

[0066] In an MBSFN area, participating eNBs must send PMCH over the same bandwidth. Therefore, the first eNB is able to send a message to the second eNB via a backhaul connection, informing the second eNB which PRBs it intends to use for transmitting PMCH. In one embodiment, this message is a bitmap of length {6, 15, 25, 50, 75, 100}, where "1" indicates that the relevant PRBs are used for PMCH in the frequency domain. Alternatively, "0" may indicate that the relevant PRBs are used for PMCH in the frequency domain. In another embodiment, a combination index is used to indicate that the PRBs are used for PMCH in the frequency domain in the form of such a message. The first eNB is also able to send a request for PMCH information to the second eNB via a backhaul connection, wherein the second eNB responds with a message informing the first eNB which PRBs it intends to use for transmitting PMCH.

[0067] Position of PSS / SSS / DMRS in the evolved transport format

[0068] In current LTE releases, DMRS is not transmitted in the middle six PRBs of the system bandwidth if it collides with the PSS and SSS. Since the reduced CRS may be unsuitable or insufficient for PDSCH demodulation, a new solution is needed to enable PDSCH demodulation using the UERS. For cells operating with evolved transport formats, the positions of the PSS and SSS change. In one embodiment, the relative positions of the PSS and SSS are changed compared to the legacy transport format to allow for easier differentiation between transport formats and duplex modes. Figure 9An exemplary mapping is described where for FDD, SSS precedes PSS by 2 symbols, where for TDD, PSS precedes SSS by 3 symbols. An additional benefit of this mapping for TDD is that it enables the transmission of reduced CRS in the first symbol of a special subframe. Figure 10 A different embodiment is shown in FIG. For 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., for normal CP, it is mapped to the 13th symbol, and for extended CP, it is mapped to the 11th symbol. Figure 11 Yet another embodiment of FDD is shown in FIG, where the PSS and SSS are moved to OFDM symbols 1 and 2, respectively.

Claims

1. A user equipment (UE), comprising: a processor configured to configure the UE to receive data on a secondary serving cell, wherein the secondary serving cell operates using a transmission format including a cell-specific reference signal (CRS) transmission transmitted with a periodicity of 5 milliseconds, the transmission format not including a physical downlink control channel (PDCCH) control region; and A receiver is configured to receive a transmission from the secondary serving cell according to the transmission format, wherein if a physical broadcast channel (PBCH) is not present on the transmission from the secondary serving cell, the UE does not rate match resource elements that are otherwise reserved for PBCH transmission.

2. The UE of claim 1, wherein the UE is provided with all system information required to receive data and control information. 3 . The UE of claim 1 , wherein the UE is provided with an indication of whether the secondary serving cell operates using a legacy transmission format or using the transmission format. The UE according to claim 3 , wherein the UE is configured to detect whether the PBCH exists on the secondary serving cell.

5. The UE of claim 1, wherein the UE is provided with information about which serving cell's sequential frame number is used as a reference for the secondary serving cell instead of for decoding a primary broadcast channel on the secondary serving cell.

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