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

Abstract

The invention relates to a method for energy efficient unicast and multicast transmission in a wireless communication system. A method of time division multiplexing subframes on a serving cell to a user equipment (UE) in which an eNodeB indicates communication through a bitmap, wherein the bitmap indication indicates a set of subframes (501, 502, 503) operating with a legacy long term evolution (LTE) transport 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, in the absence of a physical downlink control channel (PDCCH) control region, determining whether or not the first bit (bit '0') indicates a set of subframes (501, 502, 503) operating with the legacy long term evolution (LTE) transport format using the second bit (bit '1'). The invention relates to cell-specific reference signal (CRS) transmission with reduced density.

Description

[0001] This application is a divisional application of Chinese patent application 201480004621.5 entitled "Method for high-efficiency unicast and multicast transmission in wireless communication system", filed on January 21, 2014, and is a divisional application of 202110187483.0. Technical Field

[0002] This invention relates to wireless communication, and more particularly to user equipment connected to a base station. Background Technology

[0003] Cellular communication networks comprise several wireless terminal devices and several base stations to provide communication services, such as voice, data, video, messaging, chat, and broadcasting. 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 combinations thereof. A base station (BS) may also be referred to as a NodeB in the Universal Mobile Telecommunications System (UMTS) or as an evolved NodeB (eNB) in the 3rd Generation Partnership Project (3GPP), Base Transceiver System (BTS), Access Point (AP), or other long-term evolution plans specifying the same technology.

[0004] Typically, eNodeB hardware, when deployed, is fixed and static, but in some cases, such as when deployed in a vehicle, it can also be mobile. In contrast to eNodeBs, wireless terminal devices can be portable hardware. Wireless terminal devices are commonly referred to as User Equipment (UE), mobile workstations, cellular phones, personal digital assistants (PDAs), wireless modem cards, 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 one or more radio frequency transmitters and one or more receivers for direct communication with a mobile device, which may move freely around the eNodeB or be in a fixed location. Similarly, each UE contains one or more radio frequency transmitters and one or more receivers for direct communication with an eNodeB.

[0005] Figure 1An exemplary wireless communication network 100 is illustrated. This illustrative communication network includes base stations 101, 102, and 103, although in operation, the communication network necessarily includes many more base stations. Each of base stations 101, 102, and 103 (eNB) is operable in a corresponding 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 A108. Cell A108 is within the coverage area 104 of base station 101. Base station 101 transmits and receives transmission signals from and from UE 109. As UE 109 moves out of cell A108 and into cell B107, UE 109 is handed over to base station 102. Because UE 109 is synchronized with base station 101, UE 109 is able to initiate a handover to base station 102 using asynchronous random access.

[0006] Figure 2 As shown Figure 1 The diagram illustrates the relationship between the Evolved Universal Terrestrial Radio Access Network (EUTRAN) 200 and the core network (CN) 210 in the LTE radio network. eNodeBs 203 and 204 communicate with the Mobility Management Entity (MME) 211 and the Serving Gateway 212 via the S1 signaling interface 205. UEs 201 and 202 communicate with eNodeBs 203 and 204 respectively via the air interface. While only two eNodeBs are shown in this diagram, more eNodeBs may be connected to the same MME in the deployed network, and one eNodeB may be connected to several MMEs. In EUTRAN, eNodeBs can communicate with each other via the X2 interface 206.

[0007] Description of 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 Network (E-UTRA). Referring now to Figure 3, the legacy LTE DL transmission format is shown, illustrating the time-frequency resource mapping of the physical channels within a 1-millisecond (ms) transmission time interval (TTI), also known as 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 smallest granularity of resource allocation for PDSCH and EPDCCH is the Physical Resource Block (PRB) pair. Control area 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). General and dedicated control information is transmitted on the PDCCH, while dedicated control information is transmitted on EPDCCH 305 and 306, if present. 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 transmitted on the PDSCH. Alternatively, the UE is configured to use dedicated demodulation reference signals (DMRS) to demodulate the PDSCH (302, 303, 304) and / or EPDCCH (305, 306), where the DMRS is transmitted only within the PRB containing data or control information. Critical 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. The EPDCCH and PDSCH cross-system bandwidth is frequency-division multiplexed, as shown in Figure 3, which divides the bandwidth into three PDSCH regions 302, 303, and 304, and two EPDCCH regions 305 and 306. Additional signals (such as Channel State Information Reference Signal (CSI-RS) or Position Reference Signal (PRS)) can also be transmitted in subframes.

[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 downlink-only multipoint-to-multipoint connections. Only UEs subscribed to the MBMS service receive this content. Time sharing of unicast and multicast data is achieved by defining subsets of subframes to support MBMS Single Frequency Network (MBSFN) transmission. Figure 4 shows MBSFN subframe 400. Non-MBSFN area 401 contains PDCCH, PHICH, and PCFICH, where PDCCH can be used to schedule uplink data transmission and to signal power control commands for UE groups. CRS is transmitted in non-MBSFN area 401 for demodulating the aforementioned channels. 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 the MBSFN area, a group of synchronized eNodeBs can jointly transmit multicast data in MBSFN subframes, thereby improving reception quality. Therefore, the MBSFN Reference Signal (MBSFN-RS) is used in MBSFN area 402 for demodulating the PMCH.

[0010] The current and future trend in cellular networks is expected to be exponential growth in data services, driven in part by the rapid adoption of mobile internet devices and related data-intensive applications. This increased demand will spur 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 present in the cell receiving service. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of a traditional homogeneous network deployment with three macrocell sites, each of which includes three sectors.

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

[0013] Figure 3 illustrates the current LTE DL transmission format, showing the mapping of physical channels used for unicast data and control.

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

[0015] Figure 4 shows the current LTE DL transmission format, which illustrates the division of MBSFN subframes into MBSFN and non-MBSFN regions.

[0016] Figure 5 The bitmap indicates the allocation of subframes in radio frames for legacy and evolved transmission formats.

[0017] Figure 6 An exemplary mapping of ordinary subframes and MBSFN subframes for evolved transport formats for FDD and TDD is shown.

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

[0019] Figure 8 This shows the mapping of PMCH and EPDCCH in an MBSFN subframe of the evolved transport format.

[0020] Figure 9 , Figure 10 and Figure 11 Several exemplary mappings of PSS and SSS with evolved transport formats are shown for both FDD and TDD. Detailed Implementation

[0021] With the development of cellular networks to cope with the explosive growth of cellular data services, bottlenecks have been identified due to the localization of many services 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 improve hotspot capacity and / or increase cellular coverage. In 3GPP Long Term Evolution (LTE) systems, base stations (also known as evolved NodeBs (eNBs)) often transmit Cell Specific Reference Signals (CRS) and Time Division Multiplexed Physical Downlink Control Channels (PDCCHs). However, the frequent transmission of CRS and PDCCHs has become problematic due to increased traffic and demands.

[0022] Description of Evolved Transmission Format

[0023] The 3GPP Radio Access Network (RAN) standardization body employs various measures to address the issue of energy-efficient transmission, involving the evolution from "always-on" DL transmission mode to "on-demand" mode. One such technology introduces 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 the CRS used for demodulation). Now referencing... Figure 3A PDSCH 312, 313, and 314, and EPDCCH 315 and 316 span the entire subframe. CRS is transmitted in the time domain (optionally, in the frequency domain) at a reduced density. For example, CRS can be transmitted on a single antenna port with a 5ms period 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 or unloaded cells. When there are no UEs in a cell, using one-fifth of the subframe for transmission translates to energy savings of up to 80%. Furthermore, removing legacy control signals and CRS frees up resources available for data transmission, thus increasing spectral efficiency and peak data rate. The evolved transmission format can also be referred to as New Carrier Type (NCT). However, a significant problem is that UEs from previous LTE versions cannot be attached to cells operating using the NCT structure.

[0024] Evolved Transport Format (ETC) or NCT can be configured for use in secondary cells (SCells) of Carrier Aggregation (CA) or for single-cell operation (standalone mode). For SCell operation, all necessary system information for the NCT-SCell can be provided to the UE via dedicated signaling. A natural question is whether the benefits of NCT can still be obtained if deployed in standalone mode. This implies that the UE can attach to the NCT as the primary cell for initial access or handover via a different cell. This will require new technologies for cell access, including synchronization, broadcast transmission, and system information and mobility control. For both CA-based and 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 energy savings in wireless networks, it is desirable to constrain base station transmission to the time periods during which data is transmitted to user equipment. For example, small cells deployed within an office building can operate at full power during the day, while at night they should operate at reduced power or be completely shut down when no one is in the building. Furthermore, reduced downlink (DL) signaling also reduces DL inter-cell interference, which becomes a bottleneck for capacity improvement as more cells are added to the cellular topology.

[0026] Energy-efficient transmission can be achieved by configuring NCT as a 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] In the CA scenario, the eNodeB provides the UE with all the system information necessary for receiving SCell-related data and control information via dedicated radio resource control (RRC) signaling. The eNodeB configures the UE to receive PDSCH on the secondary serving cell (SCell) configured as NCT. The eNodeB provides all system information to the UE via RRC signaling, including system information contained in the Host Information Block and System Information Block (SIB). System information that cannot be signaled to the UE (e.g., System Frame Number (SFN)) changes every 10ms, and is assumed to be the same for both the NCT SCell and the cell where the UE receives system information via dedicated signaling. Therefore, 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 existing or new signals. In one embodiment, a detection signal can identify that the SCell is operating using the evolved transport format. The NCT indication determines the location of the DMRS, which 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, supplementary RRC signaling can indicate whether the PBCH is transmitted, that is, whether rate-matching is used for resource elements reserved for PBCH transmission.

[0028] If the SCell is NCT, the UE performs cell search by detecting the legacy Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS) (in the legacy LTE transmission format). Alternatively, the UE can use a discovery signal for cell detection. The PSS / SSS is transmitted in the same time-frequency location in the legacy transmission format. In a different embodiment, the PSS / SSS location differs. 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 will notify the UE via explicit or implicit signaling about subframes in which the UE searches for the PSS / SSS.

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

[0030] Evolved transmission formats in single cell operation

[0031] For stand-alone operation of evolved transmission formats, new technologies 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 over 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 and schedule control messages for common system information, paging information, and group power control commands. Another technique is to use DMRS-based transmissions to send broadcast information, where the UE needs this broadcast information to attach to the cell without requiring the reception of existing handover commands (e.g., DL bandwidth and system timing reference (system frame number)). Yet another technique is to use UE-specific reference signal transmissions 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 based on, for example, CSI-RS.

[0033] Another technology is needed for cell identification and accessibility: a technology required to block access to cells using the NCT format, as was necessary in previous versions of UE. In previous versions, the UE had to obtain the MIB and at least SIB Type 1 to determine if a cell was blocked. If NCT followed this legacy procedure, previous version UEs would consume significant energy during cell search and intra-frequency and / or inter-frequency measurements (especially in high-density small cell deployments). Therefore, the energy savings on the network side are now offset by the increased energy consumption on the terminal side.

[0034] Therefore, in order to enable UEs to access cells operating using evolved radii, the following technologies are proposed:

[0035] In one embodiment, if the UE is in RRC-IDLE state, cell attachment follows standard LTE procedures, such as versions 8, 9, 10, and 11. The UE may not be able to wait for or attach to this cell because it uses an older transport format. On the one hand, if the RRC-IDLE UE discovers it has an RRC connection to the NCT within the last N (N is a fixed value) hours, the UE can perform initial cell attachment to the NCT without handover via a cell operating with an older transport format. Otherwise, the UE searches for and attaches to a cell operating with an older transport format. The UE can choose to wait for the cell in RRC-IDLE state or transition to RRC-CONNECTED state.

[0036] In another embodiment, the UE is in RRC-CONNECTED mode and is handed over to a cell operating using NCT. This handover is network-controlled but assisted by the UE; that is, the network may rely on the UE to discover and report cells operating using evolved transport modes. The eNodeB can assist the UE by providing a list of cells for which its UE should report Radio Resource Management (RRM) measurements. For each cell in this list, the eNodeB indicates the transport format, legacy format or NCT format. In yet another embodiment, the set of Physical Cell IDs (PCIs) is divided into ranges, and the UE can infer the transport format used by each cell 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 ascending order, the set containing PCI 0 is associated with cells operating using legacy transport formats, while the set not containing PCI 0 is associated with NCT structures.

[0037] 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 Signal (CSI-RS). The CSI-RS configuration is configured via RRC signaling from the eNodeB to the UE. In one embodiment, the eNodeB provides the appropriate CSI-RS configuration from a list of cells where the UE should perform RRM measurements. In a different embodiment, RRM measurements are performed on a reduced-density CRS. In yet another embodiment, the network provides additional assistance information for performing the RRM measurements on a reduced-density CRS, for example, performing the measurement in time and / or frequency resources. In yet another embodiment, the UE is configured with several such configurations, sometimes referred to as CSI procedures, regardless of whether the measurement is performed using a reduced-density CRS, CSI-RS, or any other discovered signal.

[0038] In another embodiment, for RRM measurement purposes, the eNodeB can configure the UE to have reporting criteria, including periodic, event-triggered, or event-triggered / periodic measurements. The eNodeB can further configure the UE to only report PCIs that trigger reporting. In another embodiment, the eNodeB configures the UE to report PCIs and associated RRM measurement results. Furthermore, if a cell measurement value is better than a serving cell-specific threshold, the reporting criteria can include a cancellation amount, so the UE only reports the cell ID and associated measurement results. The eNodeB can then use a Neighbor-Related List (NRT) to look up whether the reported cell ID is an NCT. For each neighboring cell included in the aforementioned PCI list, the eNodeB can also configure the UE to have system bandwidth. This facilitates accurate RSRP or RSRQ measurements. Alternatively, the eNodeB indicates the measurement bandwidth of each neighboring cell included in the PCI list to the UE.

[0039] In 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 (relayed via the source eNodeB): RRC reconfiguration information including all system information related to the target cell; an indication of the transmission format in the target cell; and the UE performs synchronization to the target cell based on the transmission type.

[0040] In the current LTE specification up to version 11, the System Frame Number (SFN) is not exchanged between eNodeBs via 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 imply that the target cell deploys NCT to indicate the SFN to UEs arriving during or after the handover procedure. A new technology is needed to facilitate handover from cells operating using legacy transport formats to cells operating using the NCT format.

[0041] To address this issue, an RRC information element is included in the mobility control information, indicating which cell's SFN the UE can use as the reference SFN for the target cell. In other words, the UE is signaled to the proxy cell (determined by decoding the proxy cell's PBCH) that the proxy cell's SFN 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 transport format. The mobility control information is prepared by the target eNB deploying NCT. The target eNB can determine the appropriate PCI through Operation, Administration and Maintenance (OAM) information or via its neighbor correlation 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 with NCT for the target cell. 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 amount of offset the UE should apply to the proxy cell's SFN.

[0042] Mobility techniques that provide a reference SFN for the target cell are also beneficial when the target eNB deploys legacy carriers 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 true when the UE is not equipped with a PBCN interference cancellation receiver. This mobility technique allows the network to configure a larger CRE offset, which contributes to a greater offload 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, regardless of whether the target cell deploys legacy or NCT transmission formats. More generally, the proposed mobility technique can be configured when the UE cannot reliably detect the PBCH of the target secondary serving cell, which is controlled by the serving eNodeB or a different eNodeB. Moreover, the cell can operate using legacy transmission modes, and the PBCH is not transmitted 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 configuration, only one eNodeB can transmit the broadcast channel (i.e., the primary eNodeB), while the other eNodeBs (i.e., the secondary 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 secondary eNodeB from the PBCH transmitted by the primary eNodeB.

[0043] Time Division Multiplexing of Hybrid Subframes Combining Old and Evolved Transmission Formats

[0044] As previously mentioned, the NCT format is not backward compatible. Therefore, cellular operators can deploy only this transmission format within a cell, where all connected UEs within the cell support this feature. Furthermore, it appears to be better suited 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. Additionally, without PDCCH transmission, a new technology is needed to send common control signaling, including broadcast, system information, and paging.

[0045] One solution to address these drawbacks of NCT is to run subframes in legacy and evolved transport formats using time-domain multiplexing. The eNodeB can indicate to the UE the set of subframes operating using legacy or evolved transport structures. The subframe indication is transmitted 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 in NCT format, while a bit value of "0" indicates that the subframe is in a legacy transport format, i.e., the subframe contains a time-division multiplexed control area and a unicast or multicast data area. Now refer to... Figure 5The diagram shows an exemplary bitmap of length 10 for a single radio frame. Other bitmap sizes are also possible. Subframes 501, 502, and 503 use legacy transmission formats, 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 Detection (RLM) or Radio Resource Management (RRM) measurements. The UE can 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, when no PDCCH is transmitted, the UE only monitors the EPDCCH for downlink control information. In a different embodiment of the invention, the UE is signaled to a bitmap indicating a set of subframes where the UE monitors the PDCCH. The UE can be configured to monitor DL ​​allocation, UL grant, and group power control commands, or only to monitor UL grant and group power control commands. This subframe indication concept is applied in various approaches to enable efficient multiplexing of (a) unicast and multicast data and (b) transmissions within a cell utilizing legacy and evolved transmission formats.

[0046] Monitoring of control channels and PBCH

[0047] Subframes operating using legacy transmission structures contain PDCCH regions and CRS transmissions with 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 should contain at least subframe 0 of each radio frame. Therefore, the PBCH is transmitted and can be detected by the UE in all LTE versions. The PDSCH is demodulated using DMRS in all frames. Alternatively, the UE is configured to use either CRS or DMRS for data demodulation in legacy subframes and only DMRS for data demodulation in NCT subframes. In yet 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 a 1-port CRS, a 2-port CRS, or a 4-port CRS to demodulate the PBCH and PDCCH.

[0048] In one different embodiment, the UE can use a 1-port CRS to demodulate the PBCH and PDCCH; that is, a maximum of 1-port CRS is transmitted in a hybrid subframe transmission format. RRM, RLM, and / or CSI measurements are performed in the subframe carrying the 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 different cells. 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 service can be provided in an MBSFN area composed of cells operating using different transport formats. For example, in a homogeneous network, macro cells and small cells can operate using 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 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 MBSFN transmissions across the macro cell layer and the small cell layer, since the small cell does not contain a control area.

[0051] To address this obsolescence, the small cell eNB can transmit the PDCCH in one or two OFDM symbols. This allows for scheduling uplink data transmission on the PUSCH in future subframes. A bitmap is signaled to the UE indicating which subframe is reserved for PMCH transmission, regardless of whether the UE is subscribed to MBMS services (one or more) in a cell operating with an evolved transport architecture. In the subframe indicating the PMCH, the UE monitors the PDCCH as in the legacy transport architecture. As a further embodiment, to reduce UE PDCCH processing, the UE can be configured to monitor the PDCCH only in the PMCH subframe for UL grants or group power control commands. In yet another embodiment, in the subframe indicating the PMCH, the UE monitors the PDCCH to obtain downlink control information for scheduling DMRS-based PDSCH transmissions, as in the legacy transport architecture. The starting OFDM symbol for such PDSCH transmission is indicated by the PCFICH received in the legacy transport architecture of this subframe or configured by a higher layer. This allows the network to schedule unicast transmissions in subframes where a PMCH is indicated but not scheduled, or where the PMCH is scheduled but the eNodeB does not receive data due to congestion in the backhaul connection. In subframes where no PMCH is indicated, the UE monitors the EPDCCH.

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

[0053] Within the MBSFN area, synchronized sets of eNodeBs jointly transmit multicast data in MBSFN subframes. Because eNodeBs are geographically distributed, a 16.67-millisecond extended cyclic prefix (CP) is already specified in the LTE standard to support the large delay propagation seen by the UE within the MBSFN area. Allowing even longer CPs will also support the expansion of the MBSFN area. This, in turn, increases the MBSFN combining gain at the UE, as more synchronized eNBs can participate in multicast transmission. For example, the CP length can be doubled to 33.33 microseconds and the symbol length can also be doubled to maintain the same CP overhead. This technique is not backward compatible; that is, UEs from earlier LTE versions cannot enjoy MBMS services for the enhanced MBSFN area. This reduces the incentive for cellular operators to offer this feature, as the potential benefits do not outweigh the required capital investment. On the other hand, this benefits operators who do not consider backward compatibility. For example, the NCT format is deployed in frequency bands not currently supported by previous versions of UEs or in frequency bands requiring special licenses for access. Therefore, we propose the following techniques to support multiplexed unicast and multicast data in cells operating using evolved transport formats.

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

[0055] In another embodiment, the Evolved Physical Broadcast Channel (EPBCH) is transmitted in the second slot of the first subframe of the radio frame. Alternatively, the EPBCH can be transmitted in the first slot of the same subframe. In yet another embodiment, the EPBCH can span two slots of a PRB pair. The EPBCH is demodulated by a group-specific reference signal on one or both 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 version 11 on antenna ports {7}, {8}, or {7, 8}. Other combinations, such as {7, 9} or {9, 10}, are not excluded. The location of such a group-specific RS in the LTE time-frequency resource grid is the same as that of existing UE-specific RSs. In a different embodiment, a new set of EPBCH RSs can be transmitted on one or two antenna ports, wherein the RS should be contained in an OFDM symbol and the PRB contains the EPBCH.

[0056] In yet another embodiment, for FDD, the primary synchronization signal and secondary synchronization signal (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 subframes 1 and 6. In yet another embodiment, the PMCH is transmitted in subsets of subframes. For FDD, the subset of MBSFN subframes is obtained from {1,2,3,4,6,7,8,9}, while for FDD, the subset of MBSFN subframes is obtained from {3,4,7,8,9}, because in the existing TDD UL-DL configuration, subframe 2 is always UL and subframe 6 transmits the PSS. Alternatively, for TDD, the PSS and SSS can be transmitted in subframes 0 and 5 of the TDD, freeing up subframes 1 and 6 as potential MBSFN subframes. Figure 6 An example FDD and TDD mapping is shown. Figure 7 An exemplary mapping of the PRBs from the EPBCH, PSS / SSS, and PMCH to the central 6 PRBs of the system bandwidth is shown. Figure 7 (a) illustrates the time-division multiplexing scheme for mixed unicast and multicast data on NCT. PSS and SSS are moved to symbols 1 and 2 respectively to avoid conflicts with group-dedicated (demodulation) RS on symbols 5 and 6. Figure 7 (b) illustrates an alternative embodiment in which the demodulated RSs at antenna ports 7 and 8 are moved from symbols 5 / 6 of slot 0 in subframe 0 to symbols 1 and 2 of slot 1. This maintains the same positions for the PSS and SSS as in the legacy transmission format. This mapping design allows the EPBCH to have the same coding rate as the legacy PBCH, since each PRB has 8 resource elements (2 for port 1 CRS and 4 for group-dedicated RS) for the RS. Note that the EPBCH may not require PHICH configuration. By reducing the number of spare bits to 5, the payload of the main information block (MIB) can be reduced to 2 bytes (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 of the legacy PBCH.

[0057] In one embodiment, the length of the cyclic prefix transmitted in the PMCH is extended to support greater delay propagation. In another embodiment, the CP is set to 33.33 microseconds.

[0058] In another embodiment, control information and control channels supporting multicast service reception (e.g., MBSFN subframe configuration and MCCH scheduling timing) are provided via broadcasting system information in unicast subframes with common search space scheduling on the enhanced physical downlink control channel (EPDCCH). Specifically, the EPDCCH is now a physical control channel supporting multicast transmission, similar to the PDCCH in previous LTE versions.

[0059] In 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. PMCH transmission bandwidth... The system information broadcast is limited to, among which (DL system bandwidth). EPDCCH is configured in a subset of PRBs, where the PRB is not part of the PMCH bandwidth, such as... Figure 8 As shown. Note that in subframes containing PMCH transmissions, the eNodeB can schedule PDSCH transmissions, for example, using existing transmission modes TM 9 and 10. Following the PDSCH transmission procedure in the PRB reserved for EPDCCH, the resource allocation for PDSCH transmissions does not overlap with those resource allocations scheduled for EPDCCH. In other words, unicast and PMCH transmissions are multiplexed in the frequency domain within MBSFN subframes. Option 2 UL grant scheduling only occurs in subframes of the legacy transmission format. For example, if the MBSFN subframes used for radio frames in an FDD are configured as {1,2,3,4,6,7,8,9}, the UL subframes for 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] EPDCCH, PRS, and PMCH, multiplexed evolved transport formats

[0061] When the system bandwidth is divided into M sets (where M-1 sets are allocated for EPDCCH transmission and one set is allocated for PMCH), EPDCCH and PMCH can be transmitted in the same subframe. These M-1 sets may partially overlap but do not intersect with each other, where the M-th set is not allocated for EPDCCH transmission but 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 PRBs not covered by the M sets. Furthermore, PDSCH transmissions in subframes configured for PMCH transmission may overlap with some PRBs that are part of the M-1 sets allocated for EPDCCH transmission.

[0062] In one embodiment, the union of M-1 sets is communicated to the UE via a bitmap signal of length {6, 15, 25, 50, 75, 100}, where a bit value "1" indicates that the corresponding PRB pair is used for EPDCCH in the frequency domain, and a bit value "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 "0" can indicate that the corresponding PRB is used for EPDCCH in the frequency domain.

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

[0064] In the frequency domain, multiplexing EPDCCH and PMCH requires both channels to coexist in an OFDM symbol. Since PMCH is dedicated solely to the extended CP, EPDCCH is transmitted using the extended cyclic prefix (CP). Because the eNB may not know whether the UE is currently subscribed to MBMS and therefore receives PMCH, and because the UE needs to know the CP used for demodulation, a method is needed to eliminate the ambiguity between the eNB and UE regarding the CP used for a given OFDM symbol. The eNB can transmit EPDCCH according to a bitmap using either the normal or extended cyclic prefix (CP), where the UE knows the bitmap through configuration by a higher layer. If PDSCH transmission is scheduled in a subframe configured for PMCH transmission, the CP of that PDSCH also follows the aforementioned bitmap configured by a higher layer. Alternatively, the CP of the PDSCH can follow the CP that schedules the EPDCCH. However, this would require special handling for cases where the scheduling cell differs from the serving cell (cross-carrier scheduling). In other words, the PDSCH in the subframes used for PMCH scheduling configuration can be transmitted using normal CP or extended CP based on subframes on member carriers, where the PDSCH follows a bitmap provided by a higher layer.

[0065] The length of this bitmap can be 6, 10, 24, 40, or any other integer value. In one embodiment, "1" indicates the use of extended CP in the relevant subframe. In another embodiment, "0" indicates the use of extended CP in the relevant subframe. In subframes where extended CP is used for EPDCCH transmission, the subframe should contain at least all subframes transmitting PMCH. To prevent the Positioning Reference Signal (PRS) from piercing the EPDCCH, if frequency resources are divided into multiplexed PMCH and EPDCCH, the PRS can be transmitted only in those PRBs that are configured for PRS transmission at a higher layer and are part of the PMCH division in subframes configured for PRS transmission. Alternatively, the PRS can be transmitted only in those PRBs that are configured for PRS transmission at a higher layer and are part of the PMCH division in subframes configured for PRS transmission (which are also indicated for EPDCCH transmission using extended CP).

[0066] Within an MBSFN area, participating eNBs must transmit the PMCH over the same bandwidth. Therefore, a first eNB can send a message to a second eNB via a backhaul connection, informing the second eNB which PRBs it intends to use for transmitting the PMCH. In one embodiment, this message is a bitmap of length {6, 15, 25, 50, 75, 100}, where "1" indicates that the associated PRB is used for the PMCH in the frequency domain. Alternatively, "0" can indicate that the associated PRB is used for the PMCH in the frequency domain. In another embodiment, a combined index is used to indicate the PRB's use for the PMCH in the frequency domain in this message format. The first eNB can also send a request for PMCH information to the second eNB via a backhaul connection, wherein the second eNB responds using a message informing the first eNB which PRBs it intends to use for transmitting the PMCH.

[0067] Location of PSS / SSS / DMRS in evolved transport formats

[0068] In current LTE versions, if the DMRS conflicts with the PSS and SSS, the DMRS is not transmitted in the middle six PRBs of the system bandwidth. 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 transmission formats, the positions of the PSS and SSS change. In one embodiment, the relative positions of the PSS and SSS change compared to the legacy transmission format to allow for easy distinction between transmission formats and duplex modes. Figure 9An exemplary mapping is described, in which for FDD, SSS precedes PSS by 2 symbols, and for TDD, PSS precedes SSS by 3 symbols. An additional benefit of this mapping for TDD is that it allows for the transmission of reduced CRS in the first symbol of a particular subframe. Figure 10 A different implementation is shown. 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; that is, for normal CP, it is mapped to the 13th symbol, and for extended CP, it is mapped to the 11th symbol. Figure 11 In another embodiment of FDD shown, the PSS and SSS are moved to OFDM symbols 1 and 2, respectively.

Claims

1. A method comprising: Implement a serving cell for a user equipment (UE), wherein the serving cell operates using an evolved transport format, which includes reduced-density cell-specific reference signal transmission (CRS) transmission in the absence of a physical downlink control channel control area (PDCCH control area).

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

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

4. The method of claim 3, wherein the UE is configured to assume whether the physical broadcast channel, i.e., the PBCH, exists on the added serving cell.

5. The method according to claim 4, wherein if the PBCH does not exist on the added serving cell, the UE is not rate-matched with the resource element; otherwise, the resource element is reserved for PBCH transmission.

6. The method of claim 1, wherein the UE is provided with information about which serving cell's sequence frame number is used as a reference for the additional serving cell in place of decoding the primary broadcast channel on the additional serving cell.

7. A method comprising: Subframes on the serving cell are time-division multiplexed to the user equipment, where: A set of subframes operates using the legacy LTE transport format; and A set of subframes operates using an evolved transmission format that includes reduced-density CRS transmission in the absence of a PDCCH control region.

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

9. The method of claim 7, wherein the bitmap is signaled to the UE to indicate the set of subframes to the PDCCH monitor.

10. The method of claim 7, wherein the PBCH is transmitted in a set of subframes operating using the legacy transport format.

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