Method and Apparatus for Multiple Transmission Points

A method of Transmission Configuration Indication (TCI) state mapping and (Quasi Co Location) (QCL) assumption for PDSCH transmission and reception under multiple transmission point (M-TRP) scheme with PDCCH repetition scheduling is proposed. New rules of TCI state mapping and QCL assumption are defined for PDSCH when there are two CORESETS with two corresponding TCI states under M-TRP scheme with PDCCH repetition scheduling. For M-TRP PDCCH scheduling S-TRP PDSCH, the TCI state of a CORESET with a lower ID is used as the TCI state. For M-TRP PDCCH scheduling M-TRP PDSCH, different TCI state mapping rules are defined, depending on the PDSCH transmission occasions are transmitted in CDM, FDM, or TDM.

TECHNICAL FIELD

The disclosed embodiments relate generally to wireless communication, and, more particularly, to PDCCH and PDSCH transmission involving multiple transmission points (TRPs) in new radio (NR) mobile communication networks.

BACKGROUND

The fifth generation (5G) radio access technology (RAT) will be a key component of the modern access network. It will address high traffic growth and increasing demand for high-bandwidth connectivity. It will address high traffic growth, energy efficiency and increasing demand for high-bandwidth connectivity. It will also support massive numbers of connected devices and meet the real-time, high-reliability communication needs of mission-critical applications. In the legacy wireless communication, a user equipment (UE) is normally connected to a single serving base station and communicates with the serving base station for control and data transmission. The 5G network is designed with dense base station deployment and heterogeneous system design are deployed. Multiple-connection technologies, such as coordinated multipoint (CoMP) transmission, is expected to get more widely deployment to get higher data rate and higher spectral efficiency gains. The multiple-connection model for the wireless communicate requires UEs to coordinate with multiple transmission points (M-TRPS) for reporting and control information reception.

In Rel-16, single downlink control information (DCI) based M-TRP scheme was introduced for ultra-reliable low-latency communications (URLLC) scheme. Two Physical Downlink Shared Channel (PDSCH) transmission occasions conveying the same transport block (TB) are transmitted from two TRPS to increase the reliability of downlink data. Resource allocation for two PDSCH transmission occasions can be done by single DCI from one TRP. For example, each PDSCH transmission occasion corresponds to the same or different redundancy versions (RVs) of the same TB. Each PDSCH transmission occasion can be transmitted in frequency division multiplexing (FDM), spatial division multiplexing (SDM), and time division multiplexing (TDM).

However, the reliability for Physical Downlink Control Channel (PDCCH) should be enhanced to fully use the benefit of multi-TRP based URLLC scheme in Rel-16 because the channel from the TRP sending PDCCH can be blocked. Multiple PDCCH transmissions from M-TRPS using different beams indicating the same allocation information for PDSCH transmission occasions can improve the reliability of PDCCH. These PDCCHs can convey the same DCI or different DCI, but indicate the same resource allocation.

Two antenna ports are said to be quasi-co-located if properties of the channel over which a symbol on one antenna port is conveyed can be inferred from the channel over which a symbol on the other antenna port is conveyed. Transmission Configuration Indicator (TCI) states are dynamically sent over in DCI, which includes configuration such as QCL (Quasi Co Location) information for PDSCH. UE can be configured with a list of TCI-State configurations within the higher layer parameter PDSCH-Config to decode PDSCH according to a detected PDCCH with DCI intended for the UE and the given serving cell. Each TCI-State contains parameters for configuring a quasi-co-location relationship between one or two downlink reference signals and the DM-RS ports of the PDSCH.

Traditionally, QCL of PDSCH can be configured to follow a TCI field in downlink DCI. Under M-TRP PDCCH repetition schedule, two control resource sets (CORSETS) associated with two search space sets including two PDCCH candidates are used. New rules of TCI state mapping for PDSCH need to be defined when there are two CORESETS with two corresponding TCI states.

SUMMARY

A method of Transmission Configuration Indication (TCI) state mapping and (Quasi Co Location) (QCL) assumption for PDSCH transmission and reception under multiple transmission point (M-TRP) scheme with PDCCH repetition scheduling is proposed. New rules of TCI state mapping and QCL assumption are defined for PDSCH when there are two CORESETS with two corresponding TCI states under M-TRP scheme with PDCCH repetition scheduling. For M-TRP PDCCH scheduling Single transmission point (S-TRP) PDSCH, the TCI state of a CORESET with a lower ID is used as the TCI state. For M-TRP PDCCH scheduling M-TRP PDSCH, different TCI state mapping rules are defined, depending on the PDSCH transmission occasions are transmitted in CDM, FDM, or TDM.

In one embodiment, a UE receives a first downlink control information (DCI) over a first physical downlink control channel (PDCCH) from a first transmission point (TRP) in a beamforming communication network. The UE is configured to operate under multiple transmission points (TRPs). The first DCI schedules a first physical downlink shared channel (PDSCH) transmission occasion. The UE receives a second DCI over a second PDCCH from a second TRP. The second DCI schedules a second PDSCH transmission occasion. The UE decodes the first DCI and the second DCI. The first and the second DCI does not carry any transmission configuration indicator (TCI) for the PDSCH transmission occasions. The UE determines TCI states for the PDSCH transmission occasions based at least on one of a) TCI states of corresponding to control resource set (CORESET) of the first and the second PDCCHs and b) a corresponding multiplexing scheme applied on the first and the second PDSCH transmission occasions. The UE receives the first and the second PDSCH transmission occasions using the determined TCI states.

DETAILED DESCRIPTION

FIG. 1illustrates a new radio (NR) beamforming wireless communication system supporting multiple transmission points (M-TRP) physical downlink control channel (PDCCH) repetition scheduling and transmission configuration indication (TCI) state determination in accordance with one novel aspect. NR beamforming wireless communication network100comprises a first base station BS or a TRP101, a second BS or a TRP102, and a user equipment UE103. In next 5G NR systems, a base station (BS) is referred to as a gNodeB or gNB. The base station performs beamforming in NR, e.g., in both FR1 (sub-6 GHz spectrum) or FR2 (Millimeter Wave frequency spectrum). The NR cellular network uses directional communications with beamformed transmission and can support up to multi-gigabit data rate. Directional communications are achieved via digital/analog beamforming, where multiple antenna elements are applied with multiple sets of beamforming weights to form multiple beams.

When there is a downlink packet to be sent from the BS to the UE, each UE gets a downlink assignment, e.g., a set of radio resources in a physical downlink shared channel (PDSCH). When a UE needs to send a packet to the BS in the uplink, the UE gets a grant from the BS that assigns a physical uplink shared channel (PUSCH) consisting of a set of uplink radio resources. The UE gets the downlink or uplink scheduling information from a PDCCH that is targeted specifically to that UE. In addition, broadcast control information is also sent in the PDCCH to all UEs in a cell. The downlink and uplink scheduling information and the broadcast control information, carried by the PDCCH, together is referred to as downlink control information (DCI).

In NR, beamforming-based directional links require fine alignment of the transmitter and receiver beams, achieved through a set of operations known as beam management. One mode of operation is beam management with indication, where quasi-co-location (QCL) is used to provide an instruction to the UE which it can use to adjust received settings. Two antenna ports are said to be quasi-co-located if properties of the channel over which a symbol on one antenna port is conveyed can be inferred from the channel over which a symbol on the other antenna port is conveyed. Transmission Configuration Indicator (TCI) states are dynamically sent over in DCI, which includes configuration such as QCL information for PDSCH. UE can be configured with a list of TCI-State configurations within the higher layer parameter PDSCH-Config to decode PDSCH according to a detected PDCCH with DCI intended for the UE and the given serving cell. Each TCI-State contains parameters for configuring a quasi-co-location relationship between downlink reference signals and the DM-RS ports of the PDSCH.

Traditionally, QCL of PDSCH can be configured to follow a TCI field in a downlink DCI carried by the corresponding PDCCH. However, under M-TRP PDCCH repetition schedule, two control resource sets (CORSETS) associated with two search space sets including two PDCCH candidates are used. In accordance with one novel aspect, new rules of TCI state mapping and QCL assumption are defined for PDSCH when there are two CORESETS with two corresponding TCI states under M-TRP scheme with PDCCH repetition scheduling (110). In the example ofFIG. 1, UE103receives PDCCH repetition scheduling under M-TRP scheme, e.g., PDCCH 0 from TRP #0 for scheduling PDSCH transmission occasion 0, and PDCCH 1 from TRP #1 for scheduling PDSCH transmission occasion 1. PDCCH 0 and PDCCH 1 using different beams indicating the same allocation information for PDSCH transmission occasions can improve the reliability of PDCCH. For M-TRP PDCCH scheduling S-TRP PDSCH, the TCI state of a CORESET with a lower ID is used as the TCI state. For M-TRP PDCCH scheduling M-TRP PDSCH, different TCI state mapping rules are defined, depending on the PDSCH transmission occasions are transmitted in CDM, FDM, or TDM.

FIG. 2is a simplified block diagram of a base station201and a user equipment202that carry out certain embodiments of this present invention. BS201has an antenna array211having multiple antenna elements that transmits and receives radio signals, one or more RF transceiver modules212, coupled with the antenna array, receives RF signals from antenna211, converts them to baseband signal, and sends them to processor213. RF transceiver212also converts received baseband signals from processor213, converts them to RF signals, and sends out to antenna211. Processor213processes the received baseband signals and invokes different functional modules to perform features in BS201. Memory214stores program instructions and data215to control the operations of BS201. BS201also includes multiple function modules and circuits220that carry out different tasks in accordance with embodiments of the current invention.

Similarly, UE202has an antenna array231, which transmits and receives radio signals. RF transceivers module232, coupled with the antenna array, receives RF signals from antenna array231, converts them to baseband signals and sends them to processor233. RF transceivers232also converts received baseband signals from processor233, converts them to RF signals, and sends out to antenna array231. Processor233processes the received baseband signals and invokes different functional modules to perform features in UE202. Memory234stores program instructions and data235to control the operations of UE202. UE202also includes multiple function modules and circuits240that carry out different tasks in accordance with embodiments of the current invention.

The functional modules and circuits can be implemented and configured by hardware, firmware, software, and any combination thereof. In one example, for UE202, connection handling circuit241handles the establishment and management of connections with the network, decoder242decodes received information such as DCI from PDCCH scheduling from M-TRP, configuration and control circuit243handles configuration and control parameters from the network, such as determining TCI state information for PDSCH transmission occasions.

FIG. 3illustrates PDCCH scheduling offset and corresponding TCI state determination or QCL assumption for PDSCH transmission and reception. Depending on a PDCCH scheduling offset (the time period from the PDCCH and the scheduled PDSCH) and a time duration for QCL (the time period for decoding DCI and obtain QCL info), different TCI state and QCL assumption may apply. When the scheduling offset is smaller or equal to the time duration for QCL, as depicted in310ofFIG. 3, there is not enough time for UE to obtain QCL information from the DL DCI. Therefore, for both cases when TCI-PresentInDCI is enabled and disabled, QCL of PDSCH follows the TCI state used for PDCCH of the lowest CORESET-ID in the latest slot in which one or more CORESETs are configured within the active BWP of the serving cell.

On the other hand, when scheduling offset is greater than the time duration for QCL, as depicted in320ofFIG. 3, QCL of PDSCH can be configured to follow a “TCI field” in the DL DCI. If TCI-PresentInDCI is enabled for the CORESET scheduling the PDSCH, QCL of PDSCH follows the TCI state presented in the DL DCI of the PDCCH transmitted on the CORESET. If TCI-PresentInDCI is disabled for the CORESET scheduling the PDSCH or the PDSCH is scheduled by a DCI format 1_0, UE assumes that the TCI state for the PDSCH is identical with the TCI state applied for the CORESET used for the PDCCH transmission. In one novel aspect, new rules of TCI state mapping and QCL assumption are defined for PDSCH when there are two CORESETS with two corresponding TCI states under M-TRP scheme with PDCCH repetition scheduling.

FIG. 4illustrates a first embodiment of TCI state determination or QCL assumption under M-TRP PDCCH scheduling for S-TRP PDSCH. In the embodiment ofFIG. 4, a UE receives PDCCH repetition scheduling under M-TRP scheme, e.g., PDCCH 0 from TRP #0 and PDCCH 1 from TRP #1, for scheduling a single PDSCH transmission occasion. TCI state 0 is used for PDCCH 0 over CORESET 0, and TCI state 1 is used for PDCCH 1 over CORESET 1. The TCI state or QCL assumption of a CORESET with lower ID (e.g., CORESET 0) is used for S-TRP PDSCH, when TCI-PresentInDCI is disabled for the CORESET scheduling the PDSCH or the PDSCH is scheduled by a DCI format 1_0.

FIG. 5illustrates a second embodiment of TCI state determination or QCL assumption under M-TRP PDCCH scheduling for M-TRP PDSCH in SDM. In the embodiment ofFIG. 5, a UE receives PDCCH repetition scheduling under M-TRP scheme, e.g., PDCCH 0 from TRP #0 for scheduling a first PDSCH transmission occasion 0 from TRP #0, and receives PDCCH 1 from TRP #1 for scheduling a second PDSCH transmission occasion 1 from TRP #1. TCI state 0 is used for PDCCH 0 over CORESET 0, and TCI state 1 is used for PDCCH 1 over CORESET 1. The two PDSCH transmission occasions are associated with two TCI states and transmitted in SDM, e.g., using different CDM (code division multiplexing) groups of different antenna ports. For the TCI states or QCL assumptions for the DM-RS port(s) within two CDM groups, the TCI state or the QCL assumption of a CORESET with lower ID corresponds to the CDM group of the first antenna port indicated by the antenna port indication table; and the TCI state or the QCL assumption of a CORESET with higher ID corresponds to the other CDM group, when TCI-PresentInDCI is disabled for the CORESET scheduling the PDSCH or the PDSCH is scheduled by a DCI format 1_0.

FIG. 6illustrates a third embodiment of TCI state determination or QCL assumption under M-TRP PDCCH scheduling for M-TRP PDSCH in FDM. In the embodiment ofFIG. 6, a UE receives PDCCH repetition scheduling under M-TRP scheme, e.g., PDCCH 0 from TRP #0 for scheduling a first PDSCH transmission occasion 0 from TRP #0, and receives PDCCH 1 from TRP #1 for scheduling a second PDSCH transmission occasion 1 from TRP #1. TCI state 0 is used for PDCCH 0 over CORESET 0, and TCI state 1 is used for PDCCH 1 over CORESET 1. The two PDSCH transmission occasions are associated with two TCI states and transmitted in FDM, e.g., over different PRBs along frequency domain. For M-TRP PDCCH repetition scheduling M-TRP PDSCH which is associated with two TCI states in FDM when TCI-PresentInDCI is disabled for the CORESET scheduling the PDSCH or the PDSCH is scheduled by a DCI format 1_0, the TCI states and QCL assumption for PDSCH are determined as follows.

In one example, if precoding granularity is ‘wideband’, e.g., the entire bandwidth, then the first ┌n_PRB/2┐ PRBs are assigned to the TCI state or the QCL assumption of a CORESET with lower ID, and the remaining └n_PRB/2┘ PRBs are assigned to the TCI state or the QCL assumption of a CORESET with higher ID, where n_PRB is the total number of allocated PRBs for the UE. In another example, if precoding granularity is determined as one of the values among {2, 4}, then even precoding resource groups (PRGs) within the allocated frequency domain resources are assigned to the TCI state or the QCL assumption of a CORESET with lower ID, and odd PRGs within the allocated frequency domain resources are assigned to the TCI state or the QCL assumption of a CORESET with higher ID. Note that for each PRG, all PRBs in one PRG are be precoded with the same precoding matrix. If the precoding granularity is either 2 or 4, then it means that the actual number of consecutive PRBs in each PRG can be either 2 or 4.

FIGS. 7A and 7Billustrate a fourth embodiment of TCI state determination or QCL assumption under M-TRP PDCCH scheduling for M-TRP PDSCH in TDM, either in the same slot, or across slots. In the embodiment ofFIGS. 7A and 7B, a UE receives PDCCH repetition scheduling under M-TRP scheme, e.g., PDCCH 0 from TRP #0 for scheduling a first PDSCH transmission occasion 0 from TRP #0, and receives PDCCH 1 from TRP #1 for scheduling a second PDSCH transmission occasion 1 from TRP #1. TCI state 0 is used for PDCCH 0 over CORESET 0, and TCI state 1 is used for PDCCH 1 over CORESET 1. The two PDSCH transmission occasions are associated with two TCI states and transmitted in TDM, e.g., over different OFDM symbols in the same slot, or across different slots.

For M-TRP PDCCH repetition scheduling M-TRP PDSCH which is associated with two TCI states in TDM in a slot when TCI-PresentInDCI is disabled for the CORESET scheduling the PDSCH or the PDSCH is scheduled by a DCI format 1_0, the TCI state or the QCL assumption of a CORESET with lower (or higher) ID is applied to the first PDSCH transmission occasion and resource allocation in time domain for the first PDSCH transmission occasion. The TCI state or the QCL assumption of a CORESET with higher (or lower) ID is applied to the second PDSCH transmission occasion.

For M-TRP PDCCH repetition scheduling M-TRP PDSCH which is associated with two TCI states in TDM across slots when TCI-PresentInDCI is disabled for the CORESET scheduling the PDSCH or the PDSCH is scheduled by a DCI format 1_0, the TCI states and QCL assumption for PDSCH are determined as follows. In this case, the multi-TRP PDSCH repetition has 4 repetition of PDSCH transmission occasions. That is, one PDSCH consists of 4 PDSCH transmission occasions/repetitions. Cyclic mapping or Sequential mapping determines the order of each TRP for corresponding PDSCH repetition.

When CycMapping is enabled, TRPS are mapped alternatively, as depicted in upper part ofFIG. 7B(0,1,0,1). The TCI state or the QCL assumption of a CORESET with lower (or higher) ID and the TCI state or the QCL assumption of a CORESET with higher (or lower) ID are applied to the first and second PDSCH transmission occasions, respectively, and the same TCI mapping pattern continues to the remaining PDSCH transmission occasions. When SeqMapping is enabled, TRPS are mapped alternatively, as depicted in lower part ofFIG. 7B(0,0,1,1). The TCI state or the QCL assumption of a CORESET with lower (or higher) ID is applied to the first and second PDSCH transmission occasions, and the TCI state or the QCL assumption of a CORESET with higher (or lower) ID is applied to the third and fourth PDSCH transmission occasions, and the same TCI mapping pattern continues to the remaining PDSCH transmission occasions.

FIG. 8is a message sequence flow between a UE and two TRPS for M-TRP PDCCH scheduling and corresponding TCI state mapping for PDSCH. In step811, UE801receives a first PDCCH 0 from TRP0, scheduling for a first PDSCH transmission occasion 0. In step812, UE801receives a second PDCCH 1 from TRP1, scheduling for a second PDSCH transmission occasion 1. PDCCH0 carries a first DCI over CORESET 0, and PDCCH1 carries a second DCI over CORESET 1. The TCI-PresentInDCI is disabled for the CORESET scheduling the PDSCH or the PDSCH is scheduled by a DCI format 1_0. In step821, UE801performs DCI decoding. In step822, UE801determines TCI states or QCL assumption for PDSCH transmission occasions, as illustrated earlier with respect toFIGS. 4-7. In step831, UE801receives the first PDSCH transmission occasion 0 from TRP0, using a first determined TCI state. In step832, UE801receives the second PDSCH transmission occasion 1 from TRP1, using a second determined TCI state.

FIG. 9is a flow chart of a method of TCI state mapping for PDSCH under M-TRP scheme with PDCCH repetition scheduling in accordance with one novel aspect. In step901, a UE receives a first downlink control information (DCI) over a first physical downlink control channel (PDCCH) from a first transmission point (TRP) in a beamforming communication network. The UE is configured to operate under multiple transmission points (TRPs). The first DCI schedules a first physical downlink shared channel (PDSCH) transmission occasion. In step902, the UE receives a second DCI over a second PDCCH from a second TRP. The second DCI schedules a second PDSCH transmission occasion. In step903, the UE decodes the first DCI and the second DCI. The first and the second DCI does not carry any transmission configuration indicator (TCI) for the PDSCH transmission occasions. In step904, the UE determines TCI states for the PDSCH transmission occasions based on at least on one of a) TCI states of corresponding to control resource set (CORESET) of the first and the second PDCCHs and b) a corresponding multiplexing scheme applied on the first and the second PDSCH transmission occasions. In step905, the UE receives the first and the second PDSCH transmission occasions using the determined TCI states.