Controlling DL MIMO transmissions in communication systems

Abstract

To control transmissions to a user equipment (UE) via a downlink (DL) multiple-input multiple-output (MIMO) channel, the base station determines that the UE is configured to support N DL MIMO layers and transmit reference signals via L antenna chains (852). In response to determining that L < N (870), the base station generates channel information for the DL MIMO channel using (i) L uplink reference signals, each of which is transmitted by the UE via a corresponding one of the L antenna chains (880) and (ii) one or more additional transmissions received from the UE (882). The base station transmits a data stream via the DL MIMO channel based on the generated channel information.

Description

Technical Field

[0001] The present disclosure relates generally to wireless communications, and more particularly to efficiently using a multiple-input multiple-output communication channel in a downlink direction from a base station to a user equipment. Background Art

[0002] One of the technologies that allows wireless communication devices to more efficiently utilize available bandwidth is multiple-input, multiple-output (MIMO) communication. According to MIMO technology, a transmitting device transmits through multiple antennas, and a receiving device receives through multiple antennas. For example, a base station supporting 5G New Radio (NR) radio access technology (RAT) can use multiple transmit (Tx) antenna chains to send multiple data streams to a user equipment (UE) equipped with multiple receive (Rx) antenna chains through a downlink (DL) MIMO channel. The UE can send to multiple Rx chains of the base station through multiple Tx chains through an uplink (UL) MIMO channel.

[0003] In order for the base station to effectively utilize the DL MIMO channel, the base station and / or the UE may perform channel estimation for coherent demodulation and interference suppression. To this end, the base station is able to "sound" the channel by sending predefined reference signals (such as demodulation reference signals (DM-RS) and / or channel state information reference signals (CSI-RS)) to the UE through various Tx chains in the downlink direction, and the UE can measure the quality of the received reference signal and report the channel state to the base station, for example, in the form of so-called channel state information (CSI). The CSI information consists of various parameters including an indication of how many streams or DL ​​MIMO layers the UE recommends the base station to use. For example, the UE may include four Rx chains and recommends that the base station use four DL MIMO layers. Using the CSI information, the base station can select or generate a suitable precoding matrix, or indicate which weights (e.g., phase, gain) the base station should apply to the data stream during the transmission of the DL MIMO channel through a given precoding matrix. The CSI may also include a channel quality indicator (CQI) to help the base station identify an appropriate modulation and coding scheme (MCS).

[0004] In some cases, the base station and UE share the same frequency for downlink and uplink transmissions, for example using time division duplexing (TDD). To evaluate the DL channel, the base station and UE can exploit channel reciprocity. More specifically, the UE can "probe" the MIMO channel by sending reference signals in the uplink direction, and the base station can measure the quality of these uplink reference signals to evaluate the quality of the UL MIMO channel, and use this evaluation to estimate the quality of the DL MIMO channel.

[0005] However, the UE does not always have the same number of Rx chains and Tx chains, for example, the UE may have more Rx chains than Tx chains. The UE may include a switch to operate one or more Rx antennas in a transmission mode for the purpose of sending uplink reference signals. For example, the UE may have a one-transmitter-four-receiver (1T4R) configuration and a pair of four-antenna switch selectors, which allow the UE to send the same or different information via each of the Rx antennas in different time periods (e.g., OFDM symbols, time slots, subframes, frames). In another embodiment, the switching capability of the UE is limited to a subset of the Rx chains, for example, the UE may use only two of the four Rx chains for transmission.

[0006] Due to these implementation constraints, the base station and the UE cannot always use the uplink reference signal to estimate all layers of the DL MIMO channel. As a more specific example, the UE may include four Rx chains and support four DL MIMO layers, but the switch allows the UE to operate only two of these chains as Tx chains and therefore only send uplink reference signals through two of these chains. Therefore, the base station estimates the DL MIMO channel only for two layers and sends information to the UE through the DL MIMO channels of the two layers instead of the DL MIMO channels of the four layers. Summary of the invention

[0007] In general, the technology disclosed in the present invention improves channel estimation for coherent demodulation and suppresses interference from multiple transmission antennas. Specifically, the base station determines how many DL MIMO layers (N) the UE supports and how many Rx chains (L) the UE can use to send uplink reference signals. The number of DL MIMO layers supported by the UE corresponds to the number of Rx chains, and the UE can implement antenna switching to send uplink reference signals through some or all of the Rx chains. The base station can, for example, receive an indication of the UE MIMO capability from the UE, another base station, or a core network. Then, taking into account the parameters N and L, the base station configures the UE to send uplink reference signals, receive downlink reference signals, and generate channel state information, or both. The base station obtains channel information based on the uplink reference signal sent by the UE through L Rx chains together with one or more other transmissions (such as, additional uplink reference signals sent by some of the same L Rx chains, one or more transmissions through a physical uplink channel, channel state information generated based on downlink reference signals, etc.).

[0008] The uplink reference signal may be a sounding reference signal (SRS), and the downlink reference signal may be a CSI-RS. In some embodiments, the base station configures the UE to send corresponding SRS transmissions for L Rx chains and to generate CSI based on NL CSI-RS transmissions. In other embodiments, the base station configures the UE to send corresponding SRS transmissions for L Rx chains and to generate CSI based on N CSI-RS transmissions. In yet other embodiments, the base station may use transmissions over a physical uplink channel, such as a scheduling request, a HARQ positive acknowledgment, or a HARQ negative acknowledgment.

[0009] The base station can generate a V_PMI precoding matrix based on the CSI, generate multiple precoding matrices V' based on (i) SRS transmission and (ii) predefined values ​​for lost matrix elements (e.g., 1+j, 1-j) or other transmissions (additional SRS transmissions, data units transmitted through physical uplink channels, etc.), and select the precoding matrix V that is closest to the V_PMI matrix.

[0010] In addition, in various implementations, the base station may configure the UE to send an SRS, receive a CSI-RS, etc. before determining that L<N or after determining that L<N.

[0011] An example embodiment of these techniques is a method in a base station for controlling transmissions to a UE via a downlink DL MIMO channel. The method includes determining that the UE is configured to support N DL MIMO layers and to send reference signals via L antenna chains. In response to determining that L < N, the method includes: using (i) L uplink reference signals, each uplink reference signal is sent by the UE via a corresponding Rx chain in the L Rx chains, and (ii) one or more additional transmissions received from the UE to generate channel information for the DL MIMO channel. The method also includes sending a data stream via the DL MIMO channel based on the generated channel information.

[0012] Another embodiment of the techniques is a base station comprising processing hardware configured to implement the above method. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1A is a block diagram of an example communication system in which a base station can send one or more data streams to a UE via a downlink (DL) multiple-input multiple-output (MIMO) channel;

[0014] Figure 1B Shows Figure 1A The base station may send a downlink reference signal for estimating the beamforming of the DL MIMO channel;

[0015] Figure 2A It shows that it can be Figure 1A or Figure 1B Example antenna configuration implemented in a UE for receiving through four receive (Rx) chains and transmitting a reference signal through four of the transmit chains;

[0016] Figure 2B It shows that it can be Figure 1A or Figure 1B Example antenna configuration implemented in a UE for receiving through four Rx chains and transmitting reference signals through three of the chains;

[0017] Figure 2C It shows that it can be Figure 1A or Figure 1B An example antenna configuration implemented in a UE according to receiving through four Rx chains and transmitting a reference signal through two of the chains;

[0018] Figure 2D It shows that it can be Figure 1A or Figure 1B Example antenna configuration implemented in a UE for receiving through four Rx chains and transmitting a reference signal through one of the chains;

[0019] Figure 3A Yes, you can Figure 1A or Figure 1B Block diagram of an example DL MIMO operation using codebook-based precoding implemented in a UE of FIG. 1 ;

[0020] Figure 3B Yes, you can Figure 1A or Figure 1B Block diagram of an example DL MIMO operation using non-codebook based precoding implemented in a UE of FIG. 1 ;

[0021] Figure 4A Yes, you can Figure 1A or Figure 1B Message diagram of an example scenario implemented in a system of , wherein a base station determines channel information of a DL MIMO channel using an uplink reference signal and a downlink reference signal;

[0022] Figure 4B Yes, you can Figure 1A or Figure 1B A flowchart of an example method implemented in a base station of for determining channel information of a DL MIMO channel using an uplink reference signal alone or together with a downlink reference signal;

[0023] Figure 5A Yes, you can Figure 1A or Figure 1B Message diagram of an example scenario implemented in a system of , wherein a base station determines channel information of a DL MIMO channel using an uplink reference signal sent over multiple time periods;

[0024] Figure 5B Yes, you can Figure 1A or Figure 1B A flowchart of an example method implemented in a base station of FIG. 1 for determining channel information of a DL MIMO channel using an uplink reference signal;

[0025] Fig. 6A Yes, you can Figure 1A or Figure 1B Message diagram of an example scenario implemented in a system of wherein a base station determines channel information for a DL MIMO channel using an uplink reference signal and one or more transmissions over one or more physical uplink channels;

[0026] Figure 6B Yes, you can Figure 1A or Figure 1B A flowchart of an example method implemented in a base station of for determining channel information of a DL MIMO channel using an uplink reference signal and one or more transmissions over one or more physical uplink channels;

[0027] Fig. 7A Yes, you can Figure 1A or Figure 1B A message diagram of an example scenario implemented in a system of wherein a base station determines channel information of a DL MIMO channel using an uplink reference signal or a downlink reference signal;

[0028] Figure 7B Yes, you can Figure 1A or Figure 1B A flowchart of an example method implemented in a base station of FIG. 1 for determining channel information of a DL MIMO channel using an uplink reference signal or a downlink reference signal;

[0029] Figure 7C Yes, you can Figure 1A or Figure 1B A flowchart of an example method implemented in a base station of for determining whether a UE should send an uplink reference signal during a process of determining channel information of a DL MIMO channel;

[0030] Fig.7D Yes, you can Figure 1A or Figure 1BA flowchart of an example method implemented in a base station of FIG. 1 for determining whether a UE should send an uplink reference signal or process a downlink reference signal during a process of determining channel information of a DL MIMO channel;

[0031] Figure 8 Yes, you can Figure 1A or Figure 1B A flowchart of an example method implemented in a base station of for controlling transmissions over a DL MIMO channel; and

[0032] Fig. 9 Yes, you can Figure 1A or Figure 1B Flowchart of an example method implemented in a UE for receiving transmissions over a DL MIMO channel. DETAILED DESCRIPTION

[0033] Figure 1A An example wireless communication network 100 is depicted in which a UE 102 capable of antenna switching can receive multiple data streams from a base station 104 over a DL MIMO channel 106. To improve channel estimation for coherent demodulation and to suppress interference for the DL MIMO channel 106, the base station 104 generates channel information using reference signals and, in some cases, transmissions other than reference signals. As described below, the base station 104 can use signals sent in the downlink (from the base station 104 to the UE 102) and / or uplink (from the UE 102 to the base station 104) directions.

[0034] In this example embodiment, the base station 104 operates as a 5G Node B (gNB) supporting 5G NR. The base station 104 is directly or indirectly connected to the 5G core network (5GC) 110 to access various core network functions, services, components, etc. In another embodiment, the base station 104 operates as a next-generation evolved Node B eNB (ng-eNB) and supports the Evolved Universal Terrestrial Radio Access (EUTRA) radio interface and is connected to the 5GC 100. In yet another embodiment, the base station 104 operates as an eNB and is connected to the Evolved Packet Core (ECP) instead of the 5GC. More generally, the base station 104 can support any appropriate RAT and be connected to any appropriate core network.

[0035] The base station 104 is equipped with multiple antennas 112 accessible via corresponding antenna Tx ports 114. In an example embodiment, the base station 104 is capable of transmitting CSI-RS and / or DM-RS through 32 antenna ports in a beamformed or non-beamformed manner. The base station 104 also includes processing hardware 120, which may include one or more general-purpose processors such as a central processing unit (CPU) and a non-transitory computer-readable memory storing machine-readable instructions that can be executed on one or more general-purpose processors and / or dedicated processing units. The processing hardware 120 may include a DL MIMO controller 122 coupled to a CSI-RS controller 124, an SRS processor 126, and an uplink TX processor 128. The base station 104 may also store a codebook 130 including a precoding matrix.

[0036] In operation, the DL MIMO controller 122 performs channel estimation for the DL MIMO channel 106 to identify appropriate DL MIMO precoding information, such as transmission layers and precoding matrices, to eliminate correlation between the antennas 112. For simplicity, this disclosure refers to the downlink data stream information generated by the DL MIMO controller 122 and applied for coherent demodulation and interference suppression as "channel information."

[0037] In some cases, the DL MIMO controller 122 may generate channel information using only the CSI, and the CSI-RS controller 124 may receive the CSI from the UE 102. More specifically, the CSI-RS controller 124 may configure the UE 102 to receive one or more CSI-RS (or, in some embodiments, DM-RS) according to a particular CSI-RS resource set selection, send the CSI-RS to the UE 102 according to the configuration, and receive CSI information from the UE 102. The UE 102 may include in the CSI a Rank Indicator (RI) for specifying the number of recommended transmission layers to the base station 104, a precoding matrix indicator (PMI) for suggesting a suitable MIMO precoding matrix for the specified RI, and a Channel Quality Indicator (CQI) for specifying a modulation and channel coding scheme (MCS) suitable for the specified PMI. In addition, when the CSI-RS controller 124 generates a beamformed CSI-RS transmission, the CSI information from the UE may include a CSI-RS resource indicator (CRI) to identify the beam. Therefore, when the CSI-RS controller 124 transmits multiple beams, the UE 102 may scan the CSI-RS transmission, evaluate the signal quality of each beam, generate the corresponding CSI for each beam, and report the CSI information for each beam using the CRI as a beam identifier.

[0038] When the base station 104 is a gNB or an eNB, the UE 102 may include the RI, PMI, and CQI in the CSI. However, when the base station 104 is a gNB, the UE 102 may additionally include a layer indicator (L1) in the CSI to inform the base station 104 which DL MIMO layer the UE 102 has identified as the best DL MIMO layer, as well as a synchronization signal block (SSB) physical broadcast channel (PBCH) block resource indicator (SSBRI) and layer 1 reference signal received power (L1-RSRP) that the base station 104 may use in beam management and mobility procedures.

[0039] Therefore, in some scenarios, the CSI-RS controller 124 configures the UE 102 to process CSI-RS transmissions, the base station 104 transmits the CSI-RS through the corresponding antenna or antenna group 112, the UE 102 transmits the CSI information to the base station 104, and the DL MIMO controller 122 generates channel information using the received CSI. The DL MIMO controller 122 then uses the generated channel information when transmitting a data stream to the UE 102 via the corresponding Tx chain (e.g., by applying corresponding phase and gain weights to the antenna 112).

[0040] The DL MIMO controller 122 uses the results of processing the SRS transmission from the UE 102 and, in some cases, one or more other transmissions from the UE 102 to generate channel information in other scenarios. In general, the SRS processor 126 can use the SRS transmission to estimate the state of the uplink counterpart of the DL MIMO channel 106. When the downlink and uplink transmissions share the same frequency or multiple frequencies using time division multiplexing such as time division duplexing (TDD), the SRS processor 126 can estimate the channel information of the DL MIMO channel 106 based on the estimated state of the corresponding UL MIMO channel by exploiting channel reciprocity. The SRS processor 126 can select SRS from one or more SRS resource sets based on whether the UE 102 will transmit the SRS at different times or at the same time, and instruct the UE 102 to generate the SRS transmission based on these selections.

[0041] When the antenna switching capability of the UE 102 allows the UE 102 to receive through N Rx antenna chains (or simply "Rx chains") but to transmit uplink reference signals through only L of these Rx chains (L<N), the L SRS transmissions from the UE 102 are insufficient for the base station 104 to accurately estimate the DL MIMO channel 106 having N DL MIMO layers. As discussed in more detail below, the DL MIMO controller 122 can use the L SRS transmissions with (i) some or all of the CSI that the CSI-RS controller 124 can generate as described above, (ii) additional one or more SRS that the UE 102 can transmit through some of the same L Rx chains during different time periods (e.g., time slots), or (iii) one or more transmissions over a physical uplink channel or several such channels. One or more transmissions over the physical uplink channel may include, for example, a medium access control (MAC) protocol data unit (PDU), a scheduling request, a hybrid automatic repeat request (HARQ) positive acknowledgement, or a HARQ negative acknowledgement, etc. The uplink TX processor 128 may process these transmissions and provide corresponding measurements to the DL MIMO controller 122.

[0042] In some cases, the base station 104 uses codebook-based precoding to transmit data streams to the UE 102 over the DL MIMO channel 106. The DL MIMO controller 122 can use the determined channel information to select a precoding matrix from a plurality of precoding matrices stored in a memory of the base station 104 as part of the codebook 130. In other cases, the base station 104 generates the precoding matrix without using the codebook 130. Figure 3A and Figure 3B These two methods are discussed further.

[0043] Continue to refer Figure 1A , UE 102 is equipped with multiple antennas 140. Using antennas 140, UE 102 can receive downlink data streams from base station 1034 via Rx ports and send uplink data streams to base station 104 via Tx ports (as described below with reference to FIG. 2A to FIG. 2B As discussed, the number of Tx ports may be less than the number of Rx ports.) UE 102 is also equipped with processing hardware 141, which may include one or more general-purpose processors (such as central processing units (CPUs)) and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors and / or special-purpose processing units. Figure 2A-2DAs discussed, the processing hardware 141 includes a CSI-RS processor 142, an SRS controller 144, and a Tx switch controller 146 for switching some or all of the antennas 140 between a Tx mode of operation and an Rx mode of operation.

[0044] In operation, the CSI-RS processor 142 receives CSI-RS transmissions from the base station 104 according to the configuration that the CSI-RS controller 124 has provided, determines one or more CSIs as described above, and provides CSI information to the base station 104. In some cases, the CSI-RS processor 142 also processes the DM-RS. The SRS controller 144 generates SRS transmissions according to the configuration that the SRS processor 126 has provided.

[0045] Figure 1B A wireless communication network 100 is shown when a base station 104 transmits a beamformed CSI-RS or other suitable downlink reference signal for a UE 102 to estimate a DL MIMO channel 106. In this scenario, the base station 104 transmits one or more CSI-RS to form a beam 152 having a first orientation, one or more CSI-RS to form a beam 154 having a second orientation, and one or more CSI-RS to form a beam 156 having a third orientation. The base station 104 can generally generate any suitable number of beams. As a more specific example, beam 152 can correspond to a CSI-RS transmitted through the first eight Tx ports 114, beam 154 can correspond to a CSI-RS transmitted through the last eight Tx ports 114, and so on. The CSI-RS processor 142 can determine the corresponding CSI for each of beam 152, beam 154, and beam 156, and provide the determined CSI to the base station 104. Using this feedback, base station 104 can determine that beam 154 is most closely oriented toward UE 102 , and accordingly transmit a data stream to UE 102 via a beam that is oriented similarly to beam 154 .

[0046] More generally, using the channel information, the base station 104 may perform beamforming or spatial multiplexing for DL ​​MIMO operations involving one, two, or more DL MIMO layers.

[0047] Next, Figure 2A-2D Several example configurations of antenna 140 in UE 102 are shown. In each of these embodiments, UE 102 has fewer Tx ports than Rx ports. In addition, UE 102 in each of these configurations has four Rx paths, at least one of which UE 102 can switch to Tx mode to transmit SRS. However, because the ability of UE 102 to switch Rx paths is limited in Figure 2A-2DThe configurations of the UE 102 are different, so each of these configurations requires the UE 102 to report its handover capabilities to the base station 104 differently and generate SRS transmissions based on the reported capabilities and the configuration received from the base station 104.

[0048] according to Figure 2A In the configuration 202 of FIG. 1 , the UE 102 has four Rx paths 212, 214, 216, and 218. Therefore, the UE 102 can receive four data streams through the DL MIMO channel 106. In other words, the UE 102 supports four N=4 DL MIMO layers. The Rx path 212 also operates as a main SRS transmission Rx chain or path, and thus can be referred to as an Rx / Tx path 212. A pair of four switches 220A allows the Tx switch controller 146 to send SRS through L=4 Rx paths 212, 214, 216, and 218 during a specific time period. Therefore, the Rx paths 214, 216, and 218 can operate as diversity SRS transmission Rx paths or chains, and can be referred to as SRS transmission Rx chains or paths. For example, the Tx switch controller 146 may cause the UE 102 to transmit an SRS through the Rx / Tx path 212 in a particular OFDM symbol S1, then operate the switch 220A to cause the UE 102 to transmit an SRS through the Rx path 214 during the next (second) OFDM symbol S2, then operate the switch 220A again to cause the UE 102 to transmit an SRS through the Rx path 216 during another (third) OFDM symbol S3, and again operate the switch 220A to cause the UE 102 to transmit an SRS through the Rx path 218 during the fourth OFDM symbol S4. More generally, the Tx switch controller 146 may select any suitable time period for SRS transmission. In other embodiments, the UE 102 may transmit an SRS simultaneously through two or more of the Rx chains 212, 214, 216, and 218.

[0049] exist Figure 2B In the configuration 204 of FIG. 1 , the UE 102 also has four Rx paths 212, 214, 216, and 218, and can therefore receive four data streams through the DL MIMO channel 106. The one-to-three switch 220B allows the Tx switch controller 146 to send SRS through L=3 Rx paths 212, 214, and 216. However, the UE 102 cannot send SRS through the Rx path 218, which can be referred to as a non-SRS transmission Rx path or chain. Using the Tx switch controller 146, the UE 102 can send SRS signals through the paths 212, 214, or 216 during different time periods (e.g., OFDM symbols) or during the same time period.

[0050] Further, in Figure 2CIn configuration 206 of FIG. 1 , UE 102 also has four Rx paths 212, 214, 216, and 218, and can therefore receive four data streams through DL MIMO channel 106. One-to-two switch 220C allows Tx switch controller 146 to send SRS through L=2 Rx paths 212 and 214, but not through Rx paths 216 or 218. Similar to configurations 202 and 205, UE 102 can use Tx switch controller 146 to send SRS through paths 212 and 214 during different time periods or during the same time period.

[0051] Furthermore, Figure 2D Configuration 208 also includes four Rx paths 212, 214, 216, and 218, but switch 220D allows Tx switch controller 146 to send SRS only through Rx / Tx path 212 (ie, L=1). In this configuration, UE 102 cannot send SRS through Rx paths 214, 216, or 218.

[0052] For configuration 202, UE 102 may report to base station 104 that its Tx / Rx capability is “one Tx chain, four Rx chains” (1T4R). For configuration 204, UE 102 may report to base station 104 that its Tx / Rx capability is “one Tx chain, three Rx chains” (1T3R). For configuration 206, UE 102 may report to base station 104 that its Tx / Rx capability is “one Tx chain, two Rx chains” (1T2R). For configuration 208, UE 102 may report to base station 104 that its Tx / Rx capability is “one Tx chain, one Rx chain” (1T1R). Therefore, UE 102 communicating with base station 104 via 5G NR may use the information element (IE) of supportedSRS-TxPortSwitch described in 3GPP TS 38.331. UE 102 may include this IE in the BandParameters IE and, in turn, include the BandParameters IE in the BandCombinationList IE. In addition, UE 102 may use the FeatureSetCombination IE to report that UE 102 supports N=4 DL MIMO layers. More specifically, UE 102 may utilize the FeatureSet IE included in the FeatureSetCombination IE, where UE 102 may select a FeatureSetDownlinkID value on a per-band basis to indicate a particular supported feature set. UE 102 may link the value of FeatureSetDownlinkID to a particular FeatureSetDownlinkPerCC, where the MIMO-LayersDL field indicates how many DL MIMO layers UE 102 supports.

[0053] When UE 102 communicates with base station 104 via EUTRA, according to TS 36.331, UE 102 can report its antenna switching capability to base station 104 using BandParameters IE included in UE-EUTRA-Capability UE. BandParameters IE can in turn include IEs such as SRS-1T4R, SRS-2T4R-2Pairs, or SRS-2T4R-3Pairs. For example, in order to report "two Tx chains, four Rx chains with two pairs" or 2T4R-2Pairs capability according to a specific antenna configuration (not shown), UE 102 can include, for example, Tx0←→{Rx0, Rx1} parameters as a pair to indicate that UE 102 can switch SRS transmission between Rx0 and Rx1 chains, and include Tx1←→{Rx2, Rx3} parameters as another pair to indicate that UE 102 can also switch SRS transmission between Rx2 and Rx3. In another example, to report "two Tx chains, four Rx chains with three pairs" or 2T4R-3Pairs capability according to a specific antenna configuration (not shown), the UE 102 may include, for example, a Tx0←→{Rx0} parameter for indicating that the UE 102 may switch SRS transmission only for the Rx0 chain, and a Tx1←→{Rx1, Rx2, Rx3} parameter for indicating that the UE 102 may also switch SRS transmission between Rx1-Rx3. To report the number of supported DL MIMO layers through EUTRA, the UE 102 may use the supportedMIMO-CapabilityDL IE included in the CA-MIMO-ParameterDL, or use the FeatureSetDL-PerCC IE included in the FeatureSet IE.

[0054] Before discussing several example techniques that base station 104 may implement to efficiently control transmissions over DL MIMO channel 106 based on DL MIMO layer capabilities and switching capabilities reported by UE 102, example DL MIMO operations using precoding matrices are briefly considered next for additional clarity.

[0055] First reference Figure 3A, the example four-layer DL MIMO operation mode 302 uses codebook-based precoding. The DL MIMO controller 122 obtains channel information based on one or more of a downlink reference signal, an uplink reference signal, an uplink non-reference signal, etc., and selects an appropriate precoding matrix from the codebook 130. The base station 104 then indicates to the UE 102 which precoding matrix the base station 104 has selected from the codebook. To this end, the base station 104 may send downlink control information (DCI) on at least one physical downlink control channel (PDCCH). The base station 104 applies the selected precoding matrix to data streams DS1, DS2, DS3, and DS4 in a precoding operation 310. The base station 104 may multiplex the precoded data streams DS1-DS4 with or without a downlink reference signal (e.g., CSI-RS or cell-specific reference signal (CRS)), and perform a modulation and RF up-conversion operation 312. Then, the base station 104 sends the data stream on a physical downlink shared channel (PDSCH) with or without multiplexing a downlink reference signal.

[0056] On the other hand, Figure 3B In the example DL MIMO operation mode 304 of FIG. 304 , the base station 104 does not use codebook-based precoding. Similar to the operation mode 302 , the DL MIMO controller 122 obtains channel information based on one or more of a downlink reference signal, an uplink reference signal, an uplink non-reference signal, etc. Instead of selecting a precoding matrix from the codebook 130 , the DL MIMO controller 122 determines the precoding matrix based on the estimated channel information. Depending on the scenario, the precoding matrix may correspond to one of the precoding matrices in the codebook 130 , or may not correspond to any of these matrices. Before performing the precoding operation 310 , the base station 104 adds the corresponding DM-RS to each data stream. The base station 104 then performs modulation and RF upconversion operation 312 and transmits the data stream on the PDSCH with or without multiplexing the CSI-RS. The base station 104 may also send a DCI on the PDCCH to notify the UE 102 of at least one PDSCH transmission. Unlike the operation mode 302 discussed above, according to the operation mode 304, the base station 104 does not include an indication of the precoding matrix in the DCI.

[0057] In any case, the DL MIMO transmission from base station 104 to UE 102 can be modeled as

[0058] Y = HX + N (Equation 1),

[0059] Where X is the signal sent by base station 104, Y is the signal received by UE 102, H is channel information, and N is additive Gaussian white noise (AGWN). For example, when base station 104 configures UE 102 for four-layer DL MIMO transmission, the general model of equation 1 becomes:

[0060]

[0061] In the downlink direction, the CSI-RS processor 142 of the UE 102 can use, for example, the least square (LS) or minimum mean square error (MMSE) technique to obtain channel information H based on the CSI-RS or DM-RS. Then, the CSI-RS processor 142 can use, for example, singular value decomposition (SVD) to decompose the estimated channel information H into the product of three matrices UDV T The rank of the matrix D corresponds to the rank of the channel information matrix H and the number of DL MIMO layers. The CSI-RS processor 142 can derive an estimated precoding matrix from V. In some embodiments, the UE 102 stores a codebook similar to the codebook 130 of the base station 104 and can compare each matrix in the codebook with V to identify the closest matrix as the PMI and report the PMI to the base station 104.

[0062] In the uplink direction, the DL MIMO controller 122 may also use LS or MMSE techniques to obtain channel information H using SRS or one or more other transmissions from the UE 102 as discussed in more detail below. Similar to the method discussed above, the DL MIMO controller 122 may apply SVD to decompose H into the product UDV T , and derive the estimated precoding matrix from V. Depending on whether the base station 104 uses codebook-based precoding or non-codebook-based precoding, the base station 104 may notify the UE 102 of the precoding matrix or omit notification.

[0063] To determine the distance between two matrices, for example, UE 102 or base station 104 may calculate a matrix norm or matrix similarity. More specifically, for a pair of matrices

[0064] and

[0065] In matrix norm, the distance between A and B is the norm of (A - B), and in matrix similarity, the distance between A and B is a1b1 + a2b2 + a3b3 + a4b4.

[0066] Next, referring to Figure 4A-Figure 9 discuss several example techniques for controlling transmission through the DL MIMO channel 106. In some cases, for example, the base station may implement Figure 4A-Figure 9 more than one of the techniques in

[0067] Although Figures 4A-7D the discussion specifically relates to CSI-RS and SRS transmissions, in general, the base station may use any suitable uplink reference signal and / or downlink reference signal to determine the channel information of the DL MIMO channel. Additionally, the base stations involved in the following scenarios generally support any suitable RAT and are coupled to any suitable type of core network, but for convenience, Figures 4A-7D the examples in

[0068] First referring to Figure 4A , the gNB 104 in scenario 400 first determines (402) how many DL MIMO layers (N) the UE 102 supports and how many in its Rx path the UE 102 can switch for SRS transmission (L). For convenience, the number of supported DL MIMO layers may be referred to as the DL MIMO capability, and the ability to switch the Rx path for the purpose of SRS transmission may be referred to as the SRS-Tx-switching capability. In this case, N < L (e.g., N = 4 and L = 2, as shown in Figure 2C ). The value N may be less than or equal to a certain predefined maximum value N of the DL MIMO layers max . N in the example implementation max is four.

[0069] In one embodiment, the gNB 104 receives the DL MIMO capability and the SRS-Tx-Switch capability from the UE 102. The gNB 104 may, for example, receive a Radio Resource Control (RRC) message including an IE specifying the capabilities of the UE 102. More specifically, the gNB 104 may receive an NR RRC UECapability Information message including a UE-NR-Capability IE. When the base station 104 is implemented as an eNB or ng-eNB, the RRC message may be an EUTRA RRC UE Capability Information message including a UE-EUTRA-Capability IE.

[0070] In another embodiment, the gNB 104 receives the DL MIMO capability and the SRS-Tx-switching capability from another base station. In another embodiment, the gNB 104 receives the DL MIMO capability and the SRS-Tx-switching capability from a Mobility Management Entity (MME), an Access and Management Function (AMF), or other suitable components of the core network such as the 5GC 110.

[0071] Based on the determined DL MIMO capability and SRS-Tx-switching capability of UE 102, gNB 104 determines (404) that UE 102 should transmit at least one SRS. For example, when N=4 and L=2, gNB may determine to configure UE 102 to transmit two SRS corresponding to two of the four supported DL MIMO layers. Then, gNB 104 selects two SRS from one or more SRS resource sets and transmits (406) the one or more SRS configurations to UE 102.

[0072] Since L < N, gNB 104 determines that L SRS transmissions will not be sufficient to obtain channel information for all N DL MIMO layers. Therefore, gNB 104 determines (408) to configure UE 102 to process one or more CSI-RS transmissions. gNB 104 then provides (410) the CSI-RS configuration to UE 102. In the above example, where N = 4 and L = 2, as Figure 2C As shown, gNB 104 can configure UE 102 to process two CSI-RS.

[0073] According to scenario 400, UE 102 transmits (412) one or more SRS to gNB 104, and gNB 104 transmits (414) one or more CSR-RS. Events 412 and 414 may occur in either order. UE 102 measures one or more CSI-RS to generate one or more CSIs, and transmits (416) one or more CSI reports to gNB 104 on at least one physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH) via one or more Tx chains.

[0074] The gNB 104 may then generate (432) channel information using the received one or more SRSs and the one or more received CSIs. The gNB 104 may also determine the number of DL MIMO layers or ranks that the gNB 104 should configure the UE 102 to use. Further, the gNB 104 may determine a precoding matrix and an MCS. The gNB 104 may then transmit 440 a data stream to the UE 102 over the DL MIMO channel via one or more PDSCHs based on the determined channel information. The gNB 104 may use codebook-based precoding or non-codebook-based precoding, as described above with reference to each of the foregoing. Figure 3A and 3B discussed.

[0075] Continuing with the above example, when N=4 and L=2, gNB 104 may configure UE 102 to receive four CSI-RS and transmit two SRS. Then, gNB 104 transmits CSI-RS through four different antenna Tx ports 114. UE 102 transmits CSI-RS through Rx chains 212 and 214 (e.g., see Figure 2C ) sends SRS. UE 102 processes the four CSI-RS transmissions to estimate channel information, selects a four-by-four precoding matrix V_PMI, and reports (416) the corresponding PMI to gNB 104.

[0076] Because in this scenario, gNB 104 receives only two SRSs, gNB 104 cannot use the SRSs to generate a four-by-four precoding matrix. However, gNB 104 uses the two SRSs together with the PMI to improve the selection of a suitable precoding matrix. Specifically, channel H can be modeled as

[0077] H = [H1H2H2H4] (Equation 3)

[0078] in, and gNB 104 may use two SRS transmissions to obtain the (eight) values ​​of only H1 and H2. To obtain complete channel information, gNB 104 may use the matrix H Each unknown element of (i.e., element h of matrices H3 and H4) 1,3 、h 2,3 ,…h 4,4 ) uses any predefined value with finite levels. More specifically, for example, gNB 104 can use four levels of predefined values, such as 1+j, 1-j, -1+j, or -1-j.

[0079] gNB 104 may calculate 4 for the complete channel configuration 8 A precoded four-by-four matrix V'. 8 The matrix spans the vector space S, and gNB 104 can map the matrix V_PMI onto the vector space. If V_PMI is already in the vector space S, gNB 104 can use V_PMI as the estimated precoding matrix V. Otherwise, if V_PMI is not in the vector space S, gNB 104 can map V_PMI to the vector space S with V_project 8 Each of the matrices V' is compared, and the closest distance matrix with respect to V_project is selected from these matrices as the estimated precoding matrix V.

[0080] In another example scenario, gNB 104 configures UE 102 to process two CSI-RS and transmit two SRS. gNB 104 transmits two CSI-RS through two corresponding antenna ports 114. UE 102 transmits two SRS through chains 212 and 214. In this case, V_PMI is a 2 by 2 matrix V_PMI = [V1 V2], where V1 = [v 1,1 v 1,2 ] and V2=[v 2,1 v 2,2 ]. gNB 104 may generate 4 8 A four-by-four matrix V', and select V_PMI and the elements of V' (v' 1,1 ,v' 1,2 ,v' 2,1 ,v' 2,2 ,) to determine the estimated precoding matrix V.

[0081] According to a specific example, the DL MIMO capability of UE 102 is four, and gNB 104 configures three CSI-RS and one SRS for UE 102. UE 102 transmits CSI corresponding to the three CSI-RS and SRS. gNB 104 can calculate up to three ranks using CSI and up to one rank using SRS. If gNB 104 obtains three ranks from CSI and one rank from SRS, gNB 104 can use these four ranks to generate channel information and implement four-layer DL MIMO operation on at least one PDSCH to send data streams to UE 102.

[0082] According to another specific example, the DL MIMO capability of UE 102 is four, and gNB 104 configures two CSI-RS and two SRS for UE 102. UE 102 transmits CSI corresponding to the two CSI-RS and the two SRS. gNB 104 can calculate up to two ranks using CSI and up to two ranks using SRS. gNB 104 can generate channel information using the four ranks and implement four-layer DL MIMO operation on at least one PDSCH to transmit data streams to UE 102.

[0083] According to yet another specific example, the DL MIMO capability of UE 102 is four, and gNB 104 configures one CSI-RS and three SRS for UE 102. UE 102 transmits CSI corresponding to the CSI-RS and three SRS. gNB 104 can calculate up to one rank using the CSI and up to three ranks using the SRS. Similar to the above example, gNB 104 can use these four ranks to generate channel information and implement four-layer DL MIMO operation on at least one PDSCH to send data streams to UE 102.

[0084] Figure 4B An example method 450 for determining channel information for a DL MIMO channel using an uplink reference signal alone or in combination with a downlink reference signal is shown. The method 450 may be implemented in a gNB 104 (as a more specific example, in a DL MIMO controller 122). The method 450 begins at block 452, where the gNB 104 configures the UE 102 to transmit one or more SRSs. In particular, the gNB 104 may configure the UE 102 to transmit as many SRSs as there are SRS transmission Rx paths at the UE 102.

[0085] Next, at block 454, the gNB 104 receives one or more SRS transmissions from the UE 102. At block 456, the gNB 104 configures the UE 102 to measure the one or more CSI-RS transmissions. After the gNB 104 transmits on the one or more CSI-RS to the UE 102, the gNB 104 receives one or more CSI corresponding to these CSI-RS transmissions at block 458. The gNB 104 may perform blocks 452, 454 before performing blocks 456, 458, or in another embodiment, perform blocks 452, 454 after performing blocks 456, 458.

[0086] At block 470, gNB 104 determines whether the number of SRS-transmission Rx paths, L, is less than the number of DL MIMO layers, N, and if so, proceeds to block 472. For example, gNB 104 may determine that N = 4 and L = 2. gNB 104 at block 472 determines channel information for the DL MIMO channel using the one or more SRS transmissions and the CSI data or one or more CSIs corresponding to the transmitted CSI-RS.

[0087] Otherwise, if L=N (or if the number of SRS transmission Rx paths L exceeds the number of DL MIMO layers N), flow proceeds from block 470 to block 474. More specifically, at block 474, the gNB 104 may determine that SRS transmission provides a more accurate estimate of channel information and elect to use only SRS transmission to generate channel information without using CSI(s) at all.

[0088] Therefore, according to method 470, when the SRS-Tx-switching capability of UE 102 is lower than the DL MIMO capability, gNB 104 can use one or more CSIs (CSI generated by UE 102 based on one or more CSI-RS transmissions with or without DM-RS) and one or more SRS transmissions to generate full-rank channel information, so that the SRS transmission does not take into account the full rank of the DL MIMO channel.

[0089] Reference now Figure 5A , gNB 104 in scenario 500 first determines (502) the DL MIMO capability (N) and SRS-Tx-switching capability (L) of UE 102. Similar to event 402 described above, gNB 104 may obtain this information from UE 102, another base station, or the core network. Also similar to scenario 400, gNB 104 determines that N < L.

[0090] The gNB 104 then determines (504) that the UE 102 should send at least one SRS. For example, when N=4 and L=2, the gNB may determine to configure the UE 102 to send two SRSs corresponding to two of the four supported DL MIMO layers. In addition, to obtain channel information for the remaining two DL MIMO layers, the gNB 104 may also configure the UE 102 to send two additional SRSs during another time period (e.g., another OFDM symbol). Thus, after the gNB 104 selects one or more SRSs from the (multiple) SRS resource sets and provides (506) the corresponding SRS configuration to the UE 102, the UE 102 sends (512) one or more SRSs to the gNB 104, and then sends (518) one or more additional SRSs to the gNB 104. Continuing with the above example, where N=4 and L=2 (refer to Figure 2C ), UE 102 may transmit SRS1 and SRS2 (506) during the first one or more OFDM symbols, respectively, through SRS transmission Rx paths 212 and 214. During the second one or more OFDM symbols, UE 102 may transmit (506) SRS'1 and SRS'2, respectively, through the same SRS transmission Rx paths 212 and 214. The first one or OFDM symbols and the second one or more OFDM symbols may belong to the same time period or different time periods.

[0091] The gNB 104 generates 534 channel information using the SRS sent as part of event 512 and the SRS sent as part of event 518. For example, as described above, when N=4 and L=2, the gNB 104 may process the four SRS transmissions as a vector.

[0092]

[0093] To determine the channel H and derive the appropriate precoding matrix.

[0094] Then, gNB 104 may transmit (540) a data stream to UE 102 via a DL MIMO channel via one or more PDSCHs based on the determined channel information. Figure 3A and Figure 3B As discussed, the gNB 104 may use codebook-based precoding or non-codebook-based precoding.

[0095] For further clarity, Figure 5B An example method 550 is shown for determining channel information for a DL MIMO channel using an uplink reference signal when the SRS-Tx-switching capability of the UE 102 is lower than the DL MIMO capability of the UE 102 .

[0096] The method 550 may be implemented in the gNB 104 (e.g., in the DL MIMO controller 122). The method 550 begins at block 552, where the gNB 104 configures the UE 102 to transmit one or more SRSs during a time period and to transmit one or more SRSs during another time period. Specifically, the gNB 104 may configure the UE 102 to transmit as many SRSs as there are SRS-transmission Rx paths at the UE 102, and to transmit the remaining SRSs through the same SRS-transmission Rx path during another time period, such that the total number of SRS transmissions reaches at least the number of DL MIMO layers supported by the UE 102.

[0097] Next, at block 554, gNB 104 receives one or more SRS transmissions from UE 102 during the first time period. Then, at block 555, gNB 104 receives one or more SRS transmissions from UE 102 during the second time period. At block 576, gNB 104 determines channel information for the DL MIMO channel using the one or more SRS transmissions received during the first time period and the one or more SRS transmissions received during the second time period.

[0098] and Figure 4A The scene and Figure 4A In contrast to the approach where gNB 104 uses CSI data to compensate for the non-SRS transmission path of UE 102, Figure 5A The scene and Figure 5B In the method, the gNB 104 uses only SRS transmissions during multiple time periods (e.g., OFDM symbols) to obtain full-rank channel information, even if L<N. In this embodiment, the gNB 104 does not rely on CSI-RS or other downlink reference signals.

[0099] Next, Fig. 6A Scenario 600 is shown, according to which gNB 104 first determines (602) the DL MIMO capability (N) and SRS-Tx-switching capability (L) of UE 102. Similar to events 402 and 502 discussed above, gNB 104 may obtain this information from UE 102, another base station, or the core network. Also similar to scenarios 400 and 500, gNB 104 determines that N < L.

[0100] Then, gNB 104 determines (604) that UE 102 should transmit at least one SRS. For example, when N=4 and L=2, gNB 104 may determine to configure UE 102 to transmit two SRS corresponding to two of the four supported DL MIMO layers. Then, gNB 104 selects two SRS from one or more SRS resource sets and transmits (606) the one or more SRS configurations to UE 102. To obtain channel information for the remaining two DL MIMO layers, gNB 104 may use one or more transmissions over one or more physical uplink channels.

[0101] However, gNB 104 optionally also determines (608) that UE 102 is configured to process one or more CSI-RS transmissions. gNB 104 then provides (610) the CSI-RS configuration to UE 102. In the above example, where N=4 and L=2, Figure 2C As shown, gNB 104 can configure UE 102 to process four CSI-RS so that the UE can generate full-rank CSI data.

[0102] UE 102 then sends (612) one or more SRS to gNB 104. When optional events 608 and 610 occur, UE 102 also measures one or more CSI-RS to generate one or more CSIs, and sends (616) one or more CSI reports on at least one PUCCH or PUSCH via one or more Tx chains to gNB 104. gNB 104 may generate an MCS based on the CSI(s) and send a DCI to UE 102 to configure time and frequency resources and the MCS for PUSCH or PDSCH transmissions.

[0103] UE 102 transmits (619) data on at least one uplink physical channel, such as a PUSCH or PUCCH. More specifically, UE 102 may transmit a MAC PDU over the PUSCH or a scheduling request and a HARQ positive acknowledgement or a HARQ negative acknowledgement over the PUCCH. gNB 104 generates (636) channel information using the SRS transmitted as part of event 612 and one or more transmissions transmitted over the physical uplink channel corresponding to event 619. In some embodiments, event 612 occurs during a first OFDM symbol or other suitable time period, and event 619 occurs during a second OFDM symbol or other suitable time period.

[0104] In the example scenario, gNB 104 generates (636) channel information using the SRS sent as part of event 612 and the data sent as part of event 619. For example, as described above when N=4 and L=2, gNB 104 may transmit four SRS as vectors Processing is performed to determine the channel H and derive a suitable precoding matrix.

[0105] Then, gNB 104 may transmit (640) a data stream to UE 102 via the DL MIMO channel via one or more PDSCHs based on the determined channel information. Figure 3A and 3B As discussed, the gNB 104 may use codebook-based precoding or non-codebook-based precoding.

[0106] Figure 6B An example method 650 is shown for determining channel information for a DL MIMO channel using uplink reference signals alone or in combination with (multiple) transmissions over one or more uplink physical channels. The method 650 may be implemented in a gNB 104 (as a more specific example, in a DL MIMO controller 122). The method 650 begins at block 652, where the gNB 104 configures the UE 102 to transmit one or more SRSs. In particular, the gNB 104 may configure the UE 102 to transmit as many SRSs as there are SRS-transmission Rx paths at the UE 102.

[0107] Next, at block 654, the gNB 104 receives one or more SRS transmissions from the UE 102. At block 660, the gNB 104 receives the transmission(s) over one or more physical uplink channels. As described above, these transmissions may occur on the PUSCH and / or PUCCH and may include MAC PDUs, scheduling requests, HARQ positive acknowledgments, HARQ negative acknowledgments, etc.

[0108] At block 670, gNB 104 determines whether the number of SRS-transmission Rx paths, L, is less than the number of DL MIMO layers, N, and if so, proceeds to block 676. For example, gNB 104 may determine that N = 4 and L = 2. As described above, gNB 104 determines channel information for the DL MIMO channel at block 676 using one or more SRS transmissions and one or more transmissions over one or more physical uplink channels.

[0109] Otherwise, if L=N (or if the number of SRS transmission Rx paths L exceeds the number of DL MIMO layers N), flow proceeds from block 670 to block 674. More specifically, gNB 104 may determine that SRS transmissions provide a more accurate estimate of channel information and elect to use only SRS transmissions to generate channel information and not use other transmissions at all.

[0110] With reference above Figure 4A-Figure 5B The technologies discussed are different. Fig. 6A The scene and Figure 6B The gNB 104 in the method uses SRS and transmission of reference signals in neither the downlink or uplink direction to obtain full rank channel information when L < N. In this embodiment, the gNB 104 does not need CSI-RS or additional SRS (although the gNB 104 can optionally use CSI-RS for further accuracy).

[0111] Next, Fig. 7A Another example scenario 700 is shown in which the gNB 104 determines whether the gNB 104 should use an uplink reference signal or a downlink reference signal to obtain channel information for a DL MIMO channel based on the SRS-Tx-switching capability of the UE 102. In this scenario, the gNB 104 first determines (702) the DL MIMO capability (N) and the SRS-Tx-switching capability (L) of the UE 102. Similar to events 402, 502, and 602 described above, the gNB 104 may obtain this information from the UE 102, another base station, or the core network.

[0112] The gNB 104 determines (704) that the UE 102 should transmit at least one SRS based on the SRS-Tx-switching capability of the UE 102. For example, when N=4 and L=2, the gNB may determine to configure the UE 102 to transmit two SRSs corresponding to two of the four supported DL MIMO layers. As another example, when N=4 and L=4, the gNB may configure the UE 102 to transmit four SRSs corresponding to the four supported DL MIMO layers, respectively. The gNB 104 then selects an SRS from one or more SRS resource sets and transmits (706) the one or more SRS configurations to the UE 102.

[0113] The gNB 104 also determines (708) to configure the UE 102 to process CSI-RS transmissions based on the DL MIMO capabilities of the UE 102. The gNB 104 then provides (710) the CSI-RS configuration to the UE 102. In the above example, where N=4, the gNB 104 may configure the UE 102 to process four CSI-RSs so that the UE can generate full-rank CSI data. The UE 102 then sends (712) one or more SRSs to the gNB 104 via at least one PUCCH or PUSCH. The gNB sends (714) the one or more CSI-RSs to the UE 104, and the UE 102 sends (716) the one or more CSIs to the gNB 104 in response.

[0114] The gNB 104 determines (730) whether the gNB 104 should use CSI(s) or SRS transmission to generate channel information based on the SRS-Tx-switching capability of the UE 102. When the SRS-Tx-switching capability is less than the DL MIMO capability of the UE 102, the gNB 104 generates (738) the channel information using the CSI(s) received during event 716. However, when the SRS-Tx-switching capability is equal to or exceeds the DL MIMO capability of the UE 102, the gNB 104 generates (736) the channel information using the SRS received during event 712. The gNB 104 may then transmit (740) a data stream to the UE 102 over a DL MIMO channel over one or more PDSCHs based on the determined channel information and using codebook-based precoding or non-codebook-based precoding.

[0115] Next, Figure 7B-7D Several example methods for determining channel information for a DL MIMO channel are shown, wherein the gNB 104 can send a downlink reference signal, process an uplink reference signal, and select a transmission for determining the channel information based on several example sequences.

[0116] First reference Figure 7B, method 750B begins at block 752, where the gNB 104 configures the UE 102 to transmit one or more SRS (e.g., as many SRS as there are SRS transmission Rx paths at the UE 102). At block 754, the gNB 104 receives the one or more SRS transmissions from the UE 102. Then, at block 756, the gNB 104 configures the UE 102 to measure one or more CSI-RS transmissions, and after the gNB 104 transmits to the UE 102 on the one or more CSI-RS, the gNB 104 receives one or more CSI corresponding to these CSI-RS transmissions at block 758. The gNB 104 may perform blocks 752, 754 before performing blocks 756, 758, or in another embodiment, perform blocks 752, 754 after performing blocks 756, 758.

[0117] At block 770, the gNB 104 determines whether the number of SRS-transmit Rx paths, L, is less than the number of DL MIMO layers, N, and if so, proceeds to block 778. For example, the gNB 104 may determine that N=4 and L=2. The gNB 104 determines channel information for the DL MIMO channel using only the CSI data at block 778. Otherwise, if L=N (or if the number of SRS-transmit Rx paths, L, exceeds the number of DL MIMO layers, N), the process proceeds from block 770 to block 774, where the gNB 104 generates channel information using only the SRS.

[0118] Reference now Figure 7C In method 750C, the gNB 104 in this embodiment configures (756) the UE 102 to measure one or more CSI-RS transmissions, and after the gNB 104 sends to the UE 102 on the one or more CSI-RSs, the gNB 104 receives in block 758 one or more CSIs corresponding to these CSI-RS transmissions.

[0119] At block 770, gNB 104 determines whether the number of SRS-transmission Rx paths L is less than the number of DL MIMO layers N, and if so, the flow proceeds to block 753. For example, gNB 104 may determine that N = 4 and L = 2. gNB 104 determines at block 753 not to configure UE 102 to transmit SRS, and at block 778 uses only CSI data to generate channel information for the DL MIMO channel.

[0120] However, when the gNB 104 determines at block 770 that the number of SRS-transmission Rx paths, L, is equal to or greater than the number of DL MIMO layers, N, the flow proceeds to block 752. The gNB 104 configures the UE 102 to transmit one or more SRSs (e.g., as many SRSs as there are SRS transmission Rx paths at the UE 102) at block 752. At block 754, the gNB 104 receives one or more SRS transmissions from the UE 102. Then, at block 774, the gNB 104 uses the SRS transmissions to determine channel information (because the UE 102 has a sufficient number of SRS transmission Rx paths to obtain full-rank channel information in this case).

[0121] Further, Fig.7D Another example method 750D is shown for determining whether a UE should send an uplink reference signal or process a downlink reference signal during a process of determining channel information for a DL MIMO channel. The method 750D begins at block 770, where the gNB determines whether the number of SRS-transmission Rx paths, L, is equal to or greater than the number of DL MIMO layers, N. The flow proceeds to block 756 when L<N, or proceeds to block 752 when L≥N.

[0122] The gNB 104 configures the UE 102 to transmit one or more SRSs (e.g., as many SRSs as there are SRS transmission Rx paths at the UE 102) at block 752. The gNB 104 receives the one or more SRS transmissions from the UE 102 at block 754. Then, at block 774, the gNB 104 determines channel information using the SRS transmissions (because the UE 102 has a sufficient number of SRS transmission Rx paths to obtain full-rank channel information in this case).

[0123] At block 756, gNB 104 configures UE 102 to measure one or more CSI-RS transmissions, and after gNB 104 transmits on the one or more CSI-RS to UE 102, gNB 104 receives one or more CSI corresponding to these CSI-RS transmissions at block 758. At block 778, gNB 104 generates channel information for the DL MIMO channel using only the CSI data.

[0124] For further clarity, Figure 8 A method for controlling the MIMO signal transmitted through a DL MIMO channel (eg, Figure 1A An example method 800 for transmitting a datagram via a channel 106) may be implemented in the base station 104, or more generally, in any suitable base station.

[0125] Method 850 begins at block 852, where base station 104 determines how many (N) DL MIMO layers the UE supports and how many chains or paths (L) the UE can use to transmit uplink reference signals, such as SRS (e.g., referring to Figure 4A event 402 of Figure 5A event 502 of Fig. 6A event 602 of Fig. 7A or event 702 of ). As described above, base station 104 can obtain this information from the UE (via one or more RRC messages), another base station, the core network, etc.

[0126] Next, at block 870, base station 104 can determine whether L < N (e.g., referring to Figure 4B block 470 of Figure 6B block 670 of FIG. 7B to FIG. 7D or block 770 of ). When L ≥ N, the process proceeds to block 884, where gNB 106 can use SRS transmissions to obtain full-rank channel information without relying on other transmissions (referring to, for example, Figure 6B block 674 of ).

[0127] However, when L < N, the process proceeds to block 880 and block 882 in either order. At block 880, base station 104 can use the uplink reference signals transmitted by the UE through each of its L antenna chains (e.g., L SRS transmission Rx chains or paths). For example, these uplink reference signals can correspond to SRS (referring to, for example, Figure 4A event 412 of Figure 5A event 512 of Fig. 6A event 612 of Fig. 7A event 712 of ; also referring to Figure 4B block 454 of Figure 5B block 554 of Figure 5B block 654 of Figure 7B-7D or block 754 of ).

[0128] At block 882, base station 104 uses one or more additional transmissions from the UE to compensate for the number of SRS transmission paths at the UE, which is less than the number required to generate full-rank channel information. In some cases, base station 104 can use the channel state information generated by the UE based on downlink reference signals. The UE can report one or more CSIs based on one or more CSI-RS transmissions, for example (referring to, for example, Figure 4A event 416 of Fig. 6A event 616 of Fig. 7A event 716 of ; also referring to Figure 4B block 458 of Figure 7B-7DIn other cases, the one or more additional transmissions include uplink reference signals (e.g., reference signals) transmitted by the UE at block 880 via some of the same L antenna chains through which the UE transmitted the “original” uplink reference signal. Figure 5A Event 518 and Figure 5B The UE may transmit these additional uplink reference signals during new time periods or time slots (such as one or more new OFDM symbols). In other cases, the one or more additional transmissions include non-reference signal transmissions, such as MAC PDUs, scheduling requests, HARQ positive or negative acknowledgements, etc. (See, for example, Fig. 6A Event 619, Figure 6B Block 660).

[0129] At block 890, the base station 104 generates channel information (eg, reference Figure 4A Event 432, Figure 5A Event 534, Fig. 6A Event 636; also refer to Figure 4B Block 472, Figure 5B Block 576, Figure 6B Finally, at block 892, the base station 104 transmits multiple data streams (e.g., referring to event 676) through the DL MIMO channel according to the determined channel information. Figure 4A Event 440, Figure 5A Event 540, Fig. 6A Event 640, Fig. 7A Event 740).

[0130] Next, Fig. 9 It shows that it can be Figure 1A or Figure 1B An example method 900 for receiving transmissions over a DL MIMO channel implemented in a UE 102 of FIG. 900 begins at optional block 902, where the UE 102 indicates to the base station 104 how many (N) DL MIMO layers the UE supports and how many links or paths (L) the UE may send uplink reference signals, such as SRS (reference e.g. Figure 4A Event 402, Figure 5A Event 502, Fig. 6A Event 602 or Fig. 7A As discussed above, in some cases, UE 102 does not report this information to base station 104, and base station 104 obtains parameters N and L from another base station or the core network.

[0131] At block 904, UE 102 receives CSI and / or SRS configuration from base station 104 (see, e.g., Figure 4A Events 406 and 410, Figure 5A Event 506, Fig. 6A Events 606 and 610, Fig. 7A Events 706 and 710 of Figure 4B Blocks 452 and 456, Figure 5B Block 552, Figure 6B Block 652, Figure 7B Block 752, Figure 7C Block 756 and Fig.7D ).

[0132] Next, the UE 102 performs one or more of blocks 906 , 908 , or 910 .

[0133] At block 906, UE 102 sends an uplink reference signal (e.g., reference Figure 4A Event 412, Figure 5A Event 512, Fig. 6A Event 612, Fig. 7A Event 712; also refer to Figure 4B Block 454, Figure 5B Block 554, Figure 6B Block 654, Figure 7B-7D As described above, in some cases, UE 102 transmits additional uplink reference signals (e.g., reference signals 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, Figure 5A Event 518 and Figure 5B Block 555).

[0134] At block 908, UE 102 receives a downlink reference signal (e.g., a reference Figure 4A Event 414, Fig. 6A Event 614, Fig. 7A Event 714; also refer to Figure 4B 456), and at block 912, channel state information is sent to the base station 104 based on these downlink reference signals (e.g., reference Figure 4A Event 416, Fig. 6A Event 616, Fig. 7A Event 716; also refer to Figure 4B Block 458, Figure 7B-7D At block 910, the UE 102 sends information other than the reference signal via one or more uplink physical channels, such as a MAC PDU, a scheduling request, a HARQ positive or negative acknowledgement, etc. (e.g., a reference signal). Fig. 6A Event 619, Figure 6B Block 660).

[0135] Finally, UE 102 receives at block 914 a data stream transmitted according to the channel information determined by the base station using the transmissions at blocks 906, 910, and 912 (see, e.g., Figure 4A Event 440, Figure 5A Event 540, Fig. 6A Event 640, Fig. 7A Event 740).

[0136] The following additional considerations apply to the above discussion.

[0137] The user equipment (e.g., UE 102) in which the technology of the present disclosure can be implemented can be any suitable device capable of wireless communication, such as a smart phone, a tablet computer, a laptop computer, a mobile game console, a point of sale (POS) terminal, a health monitoring device, a drone, a camera, a media streaming dongle or other personal media device, a wearable device (such as a smart watch), a wireless hotspot, a femtocell, or a broadband router. In addition, the user equipment can be embedded in an electronic system (such as a vehicle's audio body or an advanced driver assistance system (ADAS)) in some cases. Further, the user equipment can be operated as an Internet of Things (IoT) device or a mobile Internet device (MID). Depending on the type, the user device may include one or more general-purpose processors, a computer-readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0138] Certain embodiments are described in the present disclosure as including logic or multiple components or modules. A module may be a software module (e.g., a code or machine-readable instruction stored on a non-transitory machine-readable medium) or a hardware module. A hardware module is a tangible unit that is capable of performing a specific operation and may be configured or arranged in a specific manner. A hardware module may include dedicated circuits or logic that are permanently configured (e.g., as a dedicated processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), a digital signal processor (DSP), etc.) to perform certain operations. A hardware module may also include programmable logic or circuits (e.g., contained within a general-purpose processor or other programmable processor) that are temporarily configured by software to perform certain operations. The decision to implement a hardware module in a dedicated and permanently configured circuit or in a temporarily configured circuit (e.g., configured by software) may be driven by cost and time considerations.

[0139] When implemented in software, the techniques may be provided as part of an operating system, a library used by multiple applications, a specific software application, etc. The software may be executed by one or more general-purpose processors or one or more special-purpose processors.

[0140] The following list of aspects reflects various embodiments expressly contemplated by the present disclosure.

[0141] Aspect 1. A method in a base station for controlling transmissions to a UE via a DL MIMO channel, comprising: determining, by processing hardware, that the UE is configured to support N DL MIMO layers and to send reference signals via L antenna chains; in response to determining that L<N, generating, by the processing hardware, channel information for the DL MIMO channel using: (i) L uplink reference signals, each uplink reference signal being sent by the UE via a corresponding one of the L antenna chains, and (ii) one or more additional transmissions received from the UE; and sending, by the processing hardware, multiple data streams via the DL MIMO channel based on the generated channel information.

[0142] Aspect 2. The method according to aspect 1 further includes: sending one or more downlink reference signals to the UE, wherein the one or more additional transmissions received from the UE include channel state information generated by the UE based on the one or more downlink reference signals.

[0143] Aspect 3. The method according to aspect 2, wherein the UE generates the channel state information based on exactly NL downlink reference signals.

[0144] Aspect 4. The method according to aspect 2 or 3, wherein sending one or more downlink reference signals to the UE comprises sending each of the one or more downlink reference signals via a different corresponding antenna port of the base station.

[0145] Aspect 5. The method according to aspect 2, wherein the UE generates the channel state information based on exactly N downlink reference signals.

[0146] Aspect 6. The method according to aspect 5, wherein generating the channel information comprises: receiving a precoding matrix indicator (PMI) generated based on the N downlink reference signals from the UE; using the received PMI to generate an N-by-N precoding matrix V_PMI; using L uplink reference signals and predefined values ​​to replace unknown matrix elements to generate multiple candidate matrices V'; selecting a precoding matrix V closest to the precoding matrix V_PMI from the multiple candidate matrices V'; and associating the precoding matrix V with the channel information.

[0147] Aspect 7. The method according to any one of aspects 2-6, wherein the downlink reference signal comprises a CSI-RS.

[0148] Aspect 8. The method according to aspect 1, wherein the one or more additional transmissions from the UE include an additional uplink reference signal sent by the UE via one of the L antenna chains.

[0149] Aspect 9. The method according to aspect 8, wherein generating the channel information comprises: receiving one of L uplink reference signals during a first time slot, and receiving an additional uplink reference signal during a second time slot.

[0150] Aspect 10. The method according to aspect 8 or 9, wherein the one or more additional transmissions from the UE include exactly NL additional uplink reference signals.

[0151] Aspect 11. The method according to aspect 1, wherein the one or more additional transmissions received from the UE include transmissions on a physical uplink channel.

[0152] Aspect 12. The method according to aspect 11, wherein the transmission on the physical uplink channel comprises one of a medium access control (MAC) protocol data unit (PDU) sent on a PUSCH, a first hybrid automatic repeat request (HARQ) positive acknowledgement, or a HARQ negative acknowledgement.

[0153] Aspect 13. The method according to aspect 11, wherein the transmission on the physical uplink channel comprises one of a scheduling request transmitted on a PUCCH, a second HARQ positive acknowledgement, or a second HARQ negative acknowledgement.

[0154] Aspect 14. The method according to aspect 1 further comprises: before determining L<N, sending configuration information to the UE by the processing hardware so that the UE sends an uplink reference signal and receives a downlink reference signal.

[0155] Aspect 15. The method according to aspect 1 further includes: before determining L<N, sending configuration information to the UE by the processing hardware to enable the UE to receive a downlink reference signal; and in response to determining L<N, enabling the UE not to send an uplink reference signal.

[0156] Aspect 16. According to the method of aspect 13, wherein it is determined that L<N occurs in a first instance and the configuration information is first configuration information, the method further comprises: in response to determining that L>=N in a second instance, sending second configuration information to the UE to enable the UE to send an uplink reference signal.

[0157] Aspect 17. The method according to aspect 1 further includes: in response to determining that L<N in the first instance, sending, by the processing hardware, first configuration information to the UE so that the UE receives a downlink reference signal; and in response to determining that L>=N in the second instance, sending, by the processing hardware, second configuration information to the UE so that the UE sends an uplink reference signal.

[0158] Aspect 18. The method according to any one of the preceding aspects, further comprising: receiving an indication of how many of the N receive (Rx) chains the UE can switch to operate as L antenna chains for transmitting reference signals.

[0159] Aspect 19. A method according to any one of the preceding aspects, wherein determining that the UE is configured to support N DL MIMO layers and is equipped with L transmit chains comprises receiving an indication of the N DL MIMO layers and the L chains from at least one of: (i) the UE, (ii) another base station, or (iii) a core network to which the base station is connected.

[0160] Aspect 20. The method according to any one of the preceding aspects, wherein the uplink reference signal comprises a sounding reference signal (SRS).

[0161] Aspect 21. The method according to any one of the preceding aspects, wherein the multiple data streams are transmitted via a physical downlink shared channel (PDSCH).

[0162] Aspect 22. The method according to any one of the preceding aspects, comprising receiving the channel state information via a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH).

[0163] Aspect 23. The method according to any one of the preceding aspects, wherein the channel information includes a precoding matrix and a modulation and coding scheme (MCS).

[0164] Aspect 24. The method of any of the preceding aspects, wherein generating the channel information comprises selecting a precoding matrix from a predetermined set of codebooks.

[0165] Aspect 25. The method according to any one of aspects 2-6, wherein sending the downlink reference signal comprises beamforming to apply different directions to beams associated with respective subsets of the downlink reference signal.

[0166] Aspect 26. The method according to any one of the preceding aspects, wherein transmitting the plurality of data streams over the DL MIMO channel according to the generated channel information comprises beamforming.

Claims

1. A method in a base station for controlling transmission to a user equipment UE via a downlink DL multiple-input multiple-output MIMO channel, the method comprising: Determining, by processing hardware, that the UE is configured to support N DL MIMO layers and to transmit reference signals via L antenna chains; receiving, by the processing hardware, L uplink reference signals, each uplink reference signal being sent by the UE via a corresponding one of the L antenna chains; receiving, by the processing hardware, one or more additional transmissions from the UE including a hybrid automatic repeat request (HARQ) positive or negative acknowledgement message or a scheduling request; In response to determining that L<N, generating, by the processing hardware, channel information for the DL MIMO channel using (i) the L uplink reference signals, and (ii) the HARQ positive or negative acknowledgement message or scheduling request; as well as Multiple data streams are transmitted by the processing hardware over the DL MIMO channel based on the generated channel information.

2. The method according to claim 1, further comprising: sending one or more downlink reference signals to the UE, The one or more additional transmissions received from the UE include channel state information generated by the UE based on the one or more downlink reference signals.

3. The method according to claim 2, wherein: The UE generates the channel state information based on exactly NL downlink reference signals.

4. The method according to claim 2 or 3, wherein: Sending one or more downlink reference signals to the UE includes sending each of the one or more downlink reference signals via a different corresponding antenna port of the base station.

5. The method according to claim 2, wherein: The UE generates the channel state information based on exactly N downlink reference signals.

6. The method according to claim 5, wherein: Generating the channel information includes: receiving, from the UE, a precoding matrix indicator PMI generated based on the N downlink reference signals; Generate an N by N precoding matrix V_PMI using the received PMI; generating a plurality of candidate matrices V' using the L uplink reference signals and predefined values ​​replacing unknown matrix elements, Selecting a precoding matrix V closest to the precoding matrix V_PMI from among the plurality of candidate matrices V', and The precoding matrix V is associated with the channel information.

7. The method according to claim 1, wherein: The one or more additional transmissions from the UE include an additional uplink reference signal sent by the UE via one of the L antenna chains.

8. The method according to claim 7, wherein: Generating the channel information includes: receiving one of L uplink reference signals during a first time slot, and The additional uplink reference signal is received during a second time slot.

9. The method according to claim 7 or 8, wherein: The one or more additional transmissions from the UE include exactly NL additional uplink reference signals.

10. The method according to claim 1, wherein: The one or more additional transmissions received from the UE include a transmission on a physical uplink channel.

11. The method according to claim 10, wherein: The transmission on the physical uplink channel comprises: One of a medium access control MAC protocol data unit PDU transmitted on a physical uplink shared channel PUSCH, a first hybrid automatic repeat request HARQ positive acknowledgement or a HARQ negative acknowledgement, or One of a scheduling request transmitted on a physical uplink control channel PUCCH, a second HARQ positive acknowledgement, or a second HARQ negative acknowledgement.

12. The method according to claim 1, further comprising: Before determining that L<N, the processing hardware sends configuration information to the UE so that the UE sends an uplink reference signal and receives a downlink reference signal.

13. The method according to claim 1, further comprising: Before determining that L<N, the processing hardware sends configuration information to the UE so that the UE receives a downlink reference signal; as well as In response to determining that L<N, causing the UE to not send an uplink reference signal.

14. The method according to claim 13, wherein: Determining that L<N occurs in a first instance and the configuration information is first configuration information, the method further includes: In response to determining that L>=N in the second instance, second configuration information is sent to the UE to enable the UE to send an uplink reference signal.

15. The method according to claim 1, further comprising: In response to determining that L<N in a first instance, sending, by the processing hardware, first configuration information to the UE to enable the UE to receive a downlink reference signal; as well as In response to determining that L>=N in a second instance, second configuration information is sent, by the processing hardware, to the UE to cause the UE to send an uplink reference signal.

16. The method according to claim 1, further comprising: An indication of how many of the N reception Rx chains the UE can switch to operate as the L antenna chains for sending reference signals is received.

17. A base station comprising processing hardware and configured to implement the method according to any one of the preceding claims.

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