Method for channel adaptive SRS pattern selection

Abstract

Described is a UE apparatus (302) is configured to: obtain sounding reference signal, SRS, information (303) from a base station, BS, apparatus (301), the SRS information (303) comprising: a UE capability enquiry comprising one or more SRS resource pattern enquiries; an indication that flexible SRS resource is used for SRS resource group configuration; an SRS resource set configuration comprising locations for the SRS resource; and a channel state information, CSI, reporting configuration for the SRS resource pattern. In this way, the UE is configured to compute SRS resource pattern adapted to the selectivity of the channel, report SRS resource pattern to BS, and transmit SRS based on granted SRS resource pattern received from BS. BS estimates channel more accurately with transmitted SRS with less or equal SRS resource than uniform SRS resource pattern.

Description

[0001] METHOD FOR CHANNEL ADAPTIVE SRS PATTERN SELECTION

[0002] TECHNICAL FIELD

[0003] This disclosure relates to an apparatuses and methods for SRS resource pattern selection.

[0004] BACKGROUND

[0005] In Time Division Duplex (TDD) systems, the base station (BS) estimates downlink channel directly from the uplink sounding reference signals (SRS) transmitted by the user equipment (UE). Based on the estimated channel state information, the BS can perform optimized downlink transmissions by precoding and scheduling.

[0006] The performance of the downlink transmissions relies on accuracy of channel estimation by the BS. The wireless channel must be estimated for each transmit-receive antenna pair across each resource element of the whole frequency band and OFDM symbols within the transmit-time-interval. SRS are placed on the time-frequency grid with a fixed transmission “comb” structure where reference signals are mapped at every k-th subcarrier at a given OFDM symbol [3GPP TS 38.214], To avoid pilot contamination and achieve sufficiently accurate channel estimation, the reference signals are orthogonal at the receiver either in time, frequency or code domain. The expected increasing number of antennas in massive multiple-input-multiple- output (mMIMO) systems and high number of users significantly increase the demand for more SRS resource pattern to support accurate channel estimation by the BS.

[0007] A number of state-of-the-art solutions to estimate channels in massive MIMO systems exist, including:

[0008] Solution 1 : SRS Resource Regular Structure: 3GPP defines a regular SRS resource pattern structure in the frequency domain, the comb structure to multiplex SRS from different SRS ports belonging to same user or different users across the whole frequency band. In addition, 3GPP also defines cyclic shifts of Zadoff-Chu (ZC) sequences to multiplex SRS from different SRS ports in the same time-frequency resource belonging to same user or different users in the code domain.

[0009] Solution 2: Frequency Hopping SRS Resource Structure: 3GPP defines a frequency hopping procedure where SRS are transmitted in multiple narrowband transmissions hopping from sub-band to sub-band on each OFDM symbol to increase the power spectral density of the transmitted signal and thus reach receiver with more power to improve channel estimation.

[0010] Solution 3: Adapt periodicity in time domain of regular SRS Resource: 3GPP defines a time-domain channel property (TDCP) in CSI report to indicate the degree of time variability of the channel. UE provides TDCP to BS to adapt periodicity / fixed configurations of SRS (or other reference signals) allocated to the UE. BS adapts density of SRS pilots in time-domain with periodicity and time-offset.

[0011] These solutions may have the following disadvantages:

[0012] Solution 1 : SRS Resource Regular Structure: Current SRS resource pattern is uniform across the whole frequency band where the SRS for each user or layer are required to be orthogonal to guarantee channel estimation performance. Since each user transmits with the same uniform SRS structure where different users may have different channel characteristics, the demand of SRS resource pattern is high due to the high number of antennas and high number of users in a massive MIMO system.

[0013] Solution 2: Frequency Hopping SRS Resource: The SRS frequency hopping procedure hops from one sub-band to another subband per time slot. In time-selective channel, channel estimation performance will reduce significantly due to channel aging. Solution 3: Adapt periodicity in time domain of regular SRS resource structure: UE adapts density of SRS pilots in time-domain (i.e., periodicity) with TDCP information from CSI where different users have different channel characteristics (e.g., different selectivity in the time domain). In addition, in scenarios with many users or a significantly time-selective channel, channel estimation performance may reduce significantly due to channel aging.

[0014] Figure 2 shows a current state-of-the-art procedure 200. In TDD systems, the BS 201 may estimate 207 downlink channel directly from the uplink sounding reference signals (SRS) 206 transmitted by UE 202, to perform 208, 209: Precoding, Scheduling and Beam Management, etc. This may have followed DL data 203 being provided to the UE 202, estimation 204 by the UE 202, and CSI reporting 205.

[0015] It is desirable to develop an apparatus and method that overcomes the above problems.

[0016] SUMMARY

[0017] According to a first aspect, there is provided a user equipment, UE, apparatus, the UE apparatus comprising one or more processors and a memory storing in non-transient form data defining program code executable by the one or more processors, wherein the program code is executable by the one or more processors so that the UE apparatus is configured to: obtain sounding reference signal, SRS, information from abase station, BS, apparatus, the SRS information comprising: a UE capability enquiry comprising one or more SRS resource pattern enquiries; an indication that flexible SRS resource is used for SRS resource group configuration; an SRS resource set configuration comprising locations for the SRS resource; and a channel state information, CSI, reporting configuration for the SRS resource pattern. In this way, the UE is configured to compute SRS resource pattern adapted to the selectivity of the channel, report SRS resource pattern to BS, and transmit SRS based on granted SRS resource pattern received from BS. BS estimates channel more accurately with transmitted SRS with less or equal SRS resource than uniform SRS resource pattern. This may reduce the demand of SRS resource while maintaining or improving channel estimation performance of BSs in a massive MIMO system.

[0018] In some implementations, the UE apparatus may be configured to receive reference signals from the BS apparatus. In some implementations, the UE apparatus may be configured to carry out channel estimation in dependence on the reference signals to obtain channel estimates to compute SRS resource pattern. In some implementations, the UE apparatus may be configured to compute CSI information for the estimated channels in dependence on the reference signals. In this way, UE may be able to acquire an accurate initial channel estimate and CSI information to guide the computation of the SRS resource pattern.

[0019] In some implementations, the UE apparatus may be configured to obtain an SRS pilot allocation request from the BS apparatus. In this way, the BS may request the UE for assistance to allocate SRS resource pattern based on selectivity of the channel.

[0020] In some implementations, the UE apparatus may be configured to compute an SRS resource pattern in dependence on the CSI information and the estimated channels. In this way, the UE apparatus may determine an SRS resource pattern based on the more accurate channel estimate.

[0021] In some implementations, the UE apparatus may be configured to send an SRS resource pattern indication to BS apparatus, the SRS resource pattern indication corresponding to the SRS resource pattern computed by the UE apparatus. In this way, the UE apparatus may provide the SRS resource pattern selected according to the selectivity of the channel to the BS.

[0022] In some implementations, the UE apparatus may be configured to obtain an SRS resource pattern grant from the BS apparatus, the SRS resource pattern grant being computed by the BS apparatus in dependence on the SRS resource pattern indication and SRS resource pattern availability, the SRS resource pattern grant comprising the SRS resource pattern for transmission by the UE apparatus. In this way, the BS may select and coordinate the SRS resource to avoid pilot contamination between SRS of different users or layers.

[0023] In some implementations, the UE apparatus may be configured to transmit SRS to the BS apparatus in dependence on the SRS resource pattern. In this way, the BS may perform more accurate channel estimation with less or equal number of SRS resource.

[0024] In some implementations, the UE apparatus may be configured to receive a downlink data transmission from the BS apparatus, the downlink data transmission being precoded by the BS apparatus, wherein the precoder is computed with the channel estimate obtained with the transmitted SRS. In this way, the UE may receive more data pay load with more optimized precoding of downlink data transmissions.

[0025] According to a second aspect, there is provided a base station, BS, apparatus, the BS apparatus comprising one or more processors and a memory storing in non-transient form data defining program code executable by the one or more processors, wherein the program code is executable by the one or more processors so that the BS apparatus is configured to: send sounding reference signal, SRS, information to a user equipment, UE, apparatus, the SRS information comprising: a UE capability enquiry comprising one or more SRS resource pattern enquiries; an indication that flexible SRS resource is used for SRS resource group configuration; an SRS resource set configuration comprising locations for the SRS resource; and a channel state information, CSI, reporting configuration for the SRS resource pattern. In this way, the UE is configured to compute the SRS resource pattern adapted to the selectivity of the channel, report SRS resource pattern to BS, and transmit SRS based on granted SRS resource pattern received from BS. BS estimates channel more accurately with transmitted SRS with less or equal SRS resource than uniform SRS resource. This may reduce the demand of SRS resource while maintaining or improving channel estimation performance of BSs in a massive MIMO system.

[0026] According to a third aspect, there is provided a system comprising the UE apparatus and the BS apparatus. In this way, both the UE and BS apparatus may be configured.

[0027] According to a fourth aspect, there is provided a system further comprising one or more further UE apparatuses. In this way, multiple UEs may be configured.

[0028] According to a fifth aspect, there is provided a method, carried out by a user equipment, UE, apparatus, comprising the steps of: obtaining sounding reference signal, SRS, information from a base station, BS, apparatus, the SRS information comprising: a UE capability enquiry comprising one or more SRS resource pattern enquiries; an indication that flexible SRS resource is used for SRS resource group configuration; an SRS resource set configuration comprising locations for the SRS resource; and a channel state information, CSI, reporting configuration for the SRS resource pattern. In this way, the UE is configured to compute the SRS resource pattern adapted to the selectivity of the channel, report SRS resource pattern to BS, and transmit SRS based on granted SRS resource pattern received from BS. BS estimates channel more accurately with transmitted SRS with less or equal SRS resource than uniform SRS resource. This may reduce the demand of SRS resource while maintaining or improving channel estimation performance of BSs in a massive MIMO system.

[0029] According to a sixth aspect, there is provided a method, carried out by a base station, BS, apparatus, comprising the steps of: sending sounding reference signal, SRS, information to a user equipment, UE, apparatus, the SRS information comprising: a UE capability enquiry comprising one or more SRS resource pattern enquiries; an indication that flexible SRS resource is used for SRS resource group configuration; an SRS resource set configuration comprising locations for the SRS resource; and a channel state information, CSI, reporting configuration for the SRS resource pattern. In this way, the UE is configured to compute the SRS resource pattern adapted to the selectivity of the channel, report SRS resource pattern to BS, and transmit SRS based on granted SRS resource pattern received from BS. BS estimates channel more accurately with transmitted SRS with less or equal SRS resource than uniform SRS resource. This may reduce the demand of SRS resource while maintaining or improving channel estimation performance of BSs in a massive MIMO system.

[0030] BRIEF DESCRIPTION OF THE FIGURES

[0031] The present disclosure will now be described by way of example with reference to the accompanying drawings. In the drawings:

[0032] Figure 1 is a schematic illustration of a flexible SRS resource pattern in the time-frequency grid.

[0033] Figure 2 is a schematic illustration of a procedure of the prior art.

[0034] Figure 3 is a schematic illustration of a procedure of the present system.

[0035] Figure 4 is a schematic illustration of a procedure of the present system for multiple UEs.

[0036] Figure 5a shows exemplary information elements for UE capability information. Figure 5b shows exemplary information elements for CSI reporting configuration. Figure 5c shows exemplary information elements for SRS resource set configuration.

[0037] Figure 6a is an exemplary code for DCI format 0_l (uplink scheduling grant). Figure 6b is an exemplary code for DCI format 1_1 (downlink scheduling grant). Figure 6c is an exemplary code for UCI format 0_l (CSI report).

[0038] Figure 7 shows an example of a computer implemented method of the procedure of the present system.

[0039] Figure 8 shows an example of a computer apparatus configured to perform the methods described herein.

[0040] DETAILED DESCRIPTION

[0041] The apparatuses and methods described herein concern SRS resource pattern selection.

[0042] Embodiments of the present disclosure may tackle one or more of the problems previously mentioned by: obtaining sounding reference signal, SRS, information from abase station, BS, apparatus, the SRS information comprising: a UE capability enquiry comprising one or more SRS resource pattern enquiries; an indication that flexible SRS resource is used for SRS resource group configuration; an SRS resource set configuration comprising locations for the SRS resource; and a channel state information, CSI, reporting configuration for the SRS resource pattern. In this way, the UE is configured to compute SRS resource pattern adapted to the selectivity of the channel, report SRS resource pattern to BS, and transmit SRS based on granted SRS resource pattern received from BS. BS estimates channel more accurately with transmitted SRS with less or equal SRS resource than uniform SRS resource. This may reduce the demand of SRS resource pattern while maintaining or improving channel estimation performance of BSs in a massive MIMO system.

[0043] The following acronyms are used herein:

[0044] Fifth-generation mobile network 5G

[0045] Long Term Evolution LTE

[0046] New Radio NR

[0047] Radio Access Network RAN

[0048] Base Station BS

[0049] User Equipment UE Time Division Duplex TDD

[0050] Multiple-Input-Multiple-Output MIMO

[0051] Sounding Reference Signal SRS

[0052] Zadoff-Chu ZC

[0053] Resource element RE

[0054] Sub-carrier SC

[0055] Delay Spread DS

[0056] Doppler Spread DOS

[0057] Resource block RB

[0058] Physical uplink control channel PUCCH

[0059] Uplink control information UCI physical downlink control channel PDCCH

[0060] Downlink control information DCI

[0061] Channel State Information - Reference Signals CSI-RS

[0062] SRS Resource Pattern Indicator SRPI

[0063] The following key terms are used herein:

[0064] Pilot signals: Known signals both to transmitter and receiver used in modem communication systems to perform channel estimation, Multiple-Input Multiple-Output (MEMO) precoding, Adaptive Modulation and Coding (AMC), scheduling, beammanagement, and other procedures related to adapting the transmission to the current channel conditions. These signals are typically “scrambled” with data signals in time and frequency domains so the channel conditions experienced by pilots and data are as identical as possible.

[0065] Sounding Reference Signals (SRS): These are pilot signals used in Time Division Duplex (TDD) and sent by the UE to the gNB. SRS are typically allocated in frequency regions not currently used for uplink (UL) data transmission between a particular UE and gNB. This information, together with the assumption of channel reciprocity in TDD systems, allows the gNB to know the channel conditions in frequency bands outside of the current UL ones for one UE. With this information, the gNB can perform downlink (DL) precoding, scheduling, etc., without the need of explicit Channel State Information (CSI) feedback from the UE.

[0066] Pilot Contamination: Phenomenon which occurs when reference signals from transmitter A reach receiver and are interfered by signals of other transmitters. As a consequence, channel estimation performance degrades significantly as the composite received signal differs significantly from the known reference signal due to interference.

[0067] The present system may enable the adaptation of the location of SRS resource within the time-frequency resource 100 grid per UE according to the selectivity of their respective channel in the frequency 104 and / or time 103 domain. As an example, as shown in Figure 1, SRS resource pattern allocation 101a, 101b is given for two UEs where each UE has different channel characteristics. L denotes the number of layers 102, and F the number of subcarriers (SC) 104, and T the number of slots 103.

[0068] Depending on characteristics of the channel, such as signal-to-noise ratio (SNR), prior estimations of the channel matrix, statistics of the channel, delay spread (DS) and / or doppler spread (DOS), locations of the SRS resource may be adapted to the selectivity of the channel in the frequency and / or time domain.

[0069] The intuition behind the present system is that, UEs with flat and / or static channel require few SRS, while UEs with dynamic channel may require more SRS in the time-frequency resource grid. More peaks / selectivity of the channel may require more resolution, and less peaks / selectivity may require less resolution of SRS resource. For example, in a significantly selective charnel, the optimized location of SRS resource could be determined according to peaks in the channel amplitude along frequency or time domain to adaptively track changes of the channel. If the selectivity of the channel is non-uniform, then the SRS resource pattern would be accordingly non-uniform to achieve best channel estimation performance while decreasing the demand for SRS resource.

[0070] The BS may obtain sufficiently accurate or better channel estimation with optimized locations of SRS resource in the timefrequency resource grid with potentially less SRS resource. With a fixed SRS resource pattern structure, unbalanced channel estimation performance may be achieved for different selectivity of the channel in the frequency and / or time domain, while increasing the demand of SRS resource.

[0071] BSs may coordinate SRS resource of UEs to handle pilot contamination. BSs may use freed SRS resources to allocate SRS resources multiplexed in the frequency or time domain according to the channel characteristics of users to support more accurate estimation of their respective channels. BSs, with more accurate channel estimates of users, perform more optimized precoding of downlink data transmissions.

[0072] The procedure 300, 400 of the present system is shown in Figures 3 and 4. The system may comprise a base station (BS) apparatus 301, and one or more user equipment (UE) apparatus 302a, 302b. The BS 301 and the one or more UE 302 may communicate with one another. Figure 3 is for a single UE 302 and Figure 4 is for a plurality of UEs 302a, 302b. The following steps may be applied to a BS 301 and a single UE 302 or a plurality of UEs 302a, 302b.

[0073] The signalling procedure 300, 400 may enable channel-adaptive SRS resource pattern selection in a 3GPP system with one user 302, or multiple users 302a, 302b. More specifically the procedure 300, 400 relates to the extension / modifications of message fields in the RRC protocol for UE Capability Enquiry (TS 38.331), SRS configuration (TS 38.331) and CSI Reporting Configuration (TS 38.331). Moreover, it relates to the extension / modification of message fields within the Uplink Control Information (UCI) in the Physical Uplink Control Channel (PUCCH) or Physical Uplink Shared Channel (PUSCH), more specifically, a SRS Resource Pattern Indicator (SRPI) in CSI report. In addition, it also relates to the extension / modification of message fields within the Downlink Control Information (DCI) in the Physical Downlink Control Channel (PDCCH), specifically for dynamic CSI request (TS 38.214) and dynamic SRPI (TS 38.214) in scheduling grant. Finally, the procedure also relates to the mapping of SRS to physical resources following SRPI by UE (TS 38.211).

[0074] In step 0, the BS 301 verifies UE 302 capability and configures UE 302 to compute SRS resource pattern. The BS 301 verifies the capability of UE 302 to compute flexible SRS resource pattern as well as configures reporting parameters of UE 302 so that said UE 302 reports computed flexible SRS resource pattern. The BS 301 may send SRS information 303 to the UE 302. The SRS information 303 may comprise one or more of: a UE capability enquiry comprising one or more SRS resource pattern enquiries; an indication that flexible SRS resource is used for SRS resource group configuration; an SRS resource set configuration comprising locations for the SRS resource; and a channel station state information, CSI, reporting configuration for the SRS resource pattern.

[0075] The SRS information 303 may be included in an RRC reconfiguration message 303. The gNB 301 communicates the RRC reconfiguration message 303 containing one or more of the following information elements.

[0076] RRCConfiguration:UECapabilityEnquiry:srsFlexibleResourceCapabilityEnquiry: srsFlexibleResourceCapability: indicates whether UE 302 has the capability to compute flexible SRS resource and map SRS to flexible resources. RRCConfiguration:SRS-Resource:srsFlexibleResourceFlag: srsFlexibleResourceFlag: indicates UE 302 that flexible locations are used for SRS resource in the time-frequency resource grid for a particular SRS resource configuration group.

[0077] RRCConfiguration:CSI-ReportConfig:reportQuantity::srsFlexibleResourceFlag(cri-RI-LI-PMI-CQI-SRPI): csi-srsResourcePattemlndicatorFlag (e.g., cri-RI-LI-PMI-CQI-SRPI): indicates UE 302 that the SRS resource pattern indicator will be reported in its pre-configured reports with a given configuration (e.g., periodically, semi-periodically or upon request). csi-srsResourcePattemlndicator ( {0,1 }AR): an R-bit bitmap R which indicates the presence of at least one SRS resource on R regions where each region has size K_region. K_region spans one or multiple SCs. Configuration is indicated during session establishment. csi-RegionComb-offset (K_f): a region offset that indicates a frequency domain shift per region where SRS resource is allocated, where K_rA'<K_region. Configuration is indicated during session establishment.

[0078] Csi-srsRegionSize (K_region): an integer that indicates the size in number of SCs per region of R.

[0079] The present system relates to the detailed description of the extension / modifications of message fields in the RRC protocol for UE Capability Enquiry (TS 38.306, Clause 4.2.7.10), SRS configuration (TS 38.331) and CSI Reporting Configuration (TS 38.331).

[0080] Figure 5a shows the information elements 501 for the UE capability information - RRC UECapabilitylnformation. Similar to the specification in TS 38.306 Clause 4.2.7.10 for UE Capability information, UE 302, upon a UECapabilityEnquiry request from gNB 301 via RRC signalling 303, responds with a UECapabilitylnformation message including the information elements in 501.

[0081] Figure 5b shows the information elements 502 for the CSI reporting configuration. Similar to the specification in TS 38.331 Clause 6.2.3 for RRC Configuration, gNB 301 sends a RRCConfigurationMessage via RRC signaling 303 to UE 302 with the information elements in 502. UE 302 configures its configuration based on RRCConfigurationMessage 303 and responds with RRCConfigurationComplete.

[0082] Figure 5c shows the information elements 503 for the SRS resource set configuration. Similar to the specification in TS 38.331 for RRC Configuration, gNB 301 sends a RRCConfigurationMessage via RRC signaling 303 to UE 302 with the information elements in 503.

[0083] In step 1, the BS 301 sends reference signals 304 to the UE 302. The reference signals 304 may be CSI or DMRS signals, the gNB 301 may transmit bursts of CSI-related reference signals (e.g., CSI-RS) 304 and are received by UEs 302. Said reference signals 304 may be transmitted with high transmission power and are potentially more dense in the frequency- and or timedomain than SRS.

[0084] In step 2, the UE 302 may carry out channel estimation 305a. The channel estimation may be based on the reference signals 304. The UEs 302 perform accurate channel estimation 305 with said reference signals 304. The channel estimation 305a may obtain channel estimates to compute SRS resource pattern. The UE 302 may also compute CSI-related information 305b. The CSI related information may be for the estimated channels 305a. The CSI related information 305b may be determined based on the reference signals 304. The CSI information 305b may include one or more of: Channel Quality Indicator (CQI), Rank Indicator (RI), Reference Signal Received Power (RSRP), Signal-to-Noise Ratio (SNR), etc.

[0085] In step 3, BS 301 requests assistance 306 to UE 302 for SRS resource pattern selection. The BS 301 requests 306 UE 302 to compute SRS resource pattern adapted to the characteristics of the channel, due to more accurate channel estimate available at UE 302. The request 306 may be a CSI request. The gNB 301 may request 306 UE 302 within the DCI type 0_l via the PDCCH the following information elements.

[0086] DCI: :CSIRequest: : srsFlexibleResourceRequest: srsFlexibleResourceRequest: indicates UE 302 to compute SRS resource pattern and report it BS 301 based on preconfigured reporting configuration. The reporting behaviour may be aperiodic, periodic or semi-persistent CSI report. If the reporting is aperiodic, the request 306 may be an SRS pilot allocation request 306.

[0087] Figure 6a shows the information element 601 for the DCI format 0_l (Uplink Scheduling Grant).

[0088] In step 4, the UE 302 may compute 307 an SRS resource pattern. The UE 302 may compute 307 the resource pattern based on the estimated channels 305a and the CSI information 305b. The UE 302 may obtain the estimated channels 305a from the previous estimate. The UE 302, with estimated channel 305a from previous measurements, may compute SRS resource pattern P' 307a using iterative algorithm. UE 302 may map 307c the computed SRS resource pattern to an SRS resource pattern R. The UE 302 may report said resource pattern to BS 301. The UE 302 computes SRS resource pattern using the information including but not limited the following information: UE’s 302 pre-estimated channel matrix estimate per subcarrier, delay spread of UE 302, doppler spread of UE 302, SINR of UE 302, covariance matrix of UE’s 302 channel, number of taps, UE’s 302 velocity information (position and direction), and other relevant statistical information about UE’s 302 channel conditions.

[0089] The following iterative algorithms may be used to compute SRS resource pattern and how to map said SRS resource pattern to a SRPI:

[0090] Gradient-based Algorithm

[0091] Initiate P G {0,l}LxTxFwith baseline fixed SRS resource pattern and channel matrix H by transposing the downlink channel matrix from downlink measurements. H denotes an accurate channel estimate obtained with a burst of downlink reference signals such as CSI-RS. We allow P to be any value between [0,1], so it is differentiable.

[0092] While not converged, do:

[0093] 1. Compute H based on pilot signals ypfollowing pattern P.

[0094] 2. Compute CrossCorr between U and U where U denotes left eigenmatrix per RE for H and H respectively.

[0095] 5. Project P* <- round(P).

[0096] The output of the iterative algorithm is P*. UE maps P* to the srsResourcePattemlndicator R pre-configured with length R and region size Kreglonduring RRCConfiguration::SRS-Resource. R has equal or less resolution than P*, therefore if R has less resolution than P*, UE downsamples P* by determining whether an SRS resource has been selected on SC k G {1, ... , F} Vk (i.e., P*(l,t, k) == 1) within region r G {1, .. , R} (i.e., check if k is within interval [kr, kr+1] Vr ). Each region spans kr+1= kr+ KregionSCs. Process is repeated for every layer 1 and optionally for every time slot t.

[0097] In step 5, the UE 302 may send an SRS resource pattern indication 308 to the BS 301. The SRS resource pattern indication 308 may correspond to the SRS resource patten 307b computed by the UE 302. The SRS resource pattern indication 308 may be a CSI report. The BS 301 receives the SRS resource pattern indication 308 from UEs 302. BS 301 receives resource pattern indicator reported by UE 302a and collects SRS resource patterns from other UEs 302b. In particular, UE 302 reports gNB 301 within the UCI type 0_l via the PUCCH / PUSCH the following information elements.

[0098] UCI: :CSIReport: :csi-srsResourcePattemIndicator:

[0099] Figure 6c shows the code 603 for the UCI Format 0_l (CSI Report of cri-RI-LI-PMI-CQI-SRPI).

[0100] In step 6, the BS 301 selects resource 309. The BS 301 may compute an SRS resource pattern grant 310 by selecting the resource 309. The BS 301 may select the resource 309 based on the SRS resource pattern indication 308 and the SRS resource pattern availability. Depending on SRS resource pattern availability, SRS resource pattern 308 selected by other UEs 302 and channel characteristics of UEs 302, the BS 301 may select the final SRS resource pattern 309 for each UE 302. This may handle pilot contamination and fairness in the overall channel estimation performance.

[0101] DCI: :Grant: :csi-srsResourcePattemIndicator: grant-srsResourcePattemlndicator ({0,1 }AR): an R-bit bitmap R which indicates the presence of at least one SRS resource on R regions where each region has size K_region. K_region spans one or multiple SCs. Grant is indicated dynamically.

[0102] In particular, the scheduling grant in downlink includes Grant: :csi-srsResourcePattemIndicatorCombOffset

[0103] K'T. grant-RegionComb-offset (K_f): a region offset that indicates a frequency domain shift per region where SRS resource(s) is allocated, where K_rAI< K_region. Grant is indicated dynamically.

[0104] Figure 6b shows the exemplary information element 602 for the DCI Format 1_1 (Downlink Scheduling Grant).

[0105] In step 8, the UE 302 may transmit SRS 311 to the BS 301. The SRS transmission 311 may be based on the SRS resource pattern 309 in the grant 301. UEs 302 may transmit SRS 311 on selected resource 309. UEs 302 receive the SRS resource pattern indication 310 from BS 301 and maps SRS following indicated resource pattern for transmission. UE 302 transmits SRS 311. In particular, UE 302 maps SRS to physical resources following the received SRPI similar for the specification for SRS sequence generation in TS 38.211 Clause 6.4.1.4.3.

[0106] In step 9, the BS 301 estimates 312 channel more accurately. BS 301 receives SRS 311 and estimates the channel more accurately. BS 301 computes precoders of UEs 302 with more accurate channel estimates. The BS 301 may compute the precoder 312 based on the channel state estimate obtained with the transmitted SRS 311. In particular, gNB 301 receives transmitted SRS 311 from UEs 301 and computes the estimated channel matrix 312 per RE with an implementation-specific channel estimation algorithm (e.g., practical filter-based channel estimation) with increased cross-correlation between the left eigenmatrix of the real and estimated channel. gNB 301 computes downlink precoders of UEs 302.

[0107] In step 10, the BS 301 precodes downlink data transmission 313 to UEs 302. In particular, gNB 301 precodes downlink data transmissions 313 to UEs 302 with more accurate estimated channel matrices 312 of UEs 302.

[0108] The present system may be applied to the 5G Radio Access Network architecture defined by 3GPP and are documented in TS 38.214, TS 38.211 and TS 38.331331 or in a communication network in the future.

[0109] The present system may have the following innovative points, and corresponding advantageous effects:

[0110] BS 301 verify 303 UE 302 capability and configure said UE 301 to compute SRS resource pattern. This may configure new reporting quantities in CSI report to report an SRS resource pattern, as well as configure pilot resource set (e.g., SRS resource pattern set) with flexibility in the frequency domain.

[0111] BS 301 requests assistance 306 to UE 302 for SRS resource pattern selection. This may allow timely request flexible SRS resource pattern and trigger SRS computation at the UE 302.

[0112] UE 302 compute SRS resource pattern 307. This may enable the computation of optimized SRS resource patterns to exploit time-frequency-space selectivity of the channel and improve channel estimates that assists the next optimization action of BS 301 (e.g., downlink precoding).

[0113] BS 301 receive SRS resource pattern sets 308 from UEs 302 and select SRS resource pattern 309 to notify 310 UE 302. This may enable notification of selected SRS resource pattern 309 at BS 301. BS 301 selects SRS resource pattern 309 to avoid pilot contamination. BS 301 notifies 310 the selected SRS resource pattern 309 to UE 302.

[0114] Tx of SRS at flexible positions in resource grid. This may improve channel estimation performance at the BS 301 according to the time-frequency selectivity of the channels of users.

[0115] Figure 7 summarises an example of a method 700. At step 701, the method 700 comprises obtaining sounding reference signal, SRS, information from a base station, BS, apparatus, the SRS information comprising: a UE capability enquiry comprising one or more SRS resource pattern enquiries; an indication that flexible SRS resource is used for SRS resource group configuration; an SRS resource set configuration comprising locations for the SRS resource; and a channel state information, CSI, reporting configuration for the SRS resource pattern.

[0116] An example of computer apparatus 301, 302 configured to implement the method 700 is schematically illustrated in Figure 8. The computer apparatus 301, 302 may carry out the procedures 300 and 400 illustrated in Figures 3 and 4. The computer apparatus 301, 302 in Figure 8 may correspond to the BS 301 or the UE 302. The computer apparatus 301, 302 may be implemented on an electronic device, such as a computer, a computer for a vehicle, laptop, tablet, or smart phone. The computer apparatus 301, 302 may be connected to the internet.

[0117] The computer apparatus 301, 302 comprises a processor 801 configured to process the datasets in the manner described herein.

[0118] For example, the processor 801 may be implemented as a computer program running on a programmable device such as a Central Processing Unit (CPU). The computer apparatus 301, 302 comprises a memory 802 which is arranged to communicate with the processor 801. Memory 802 may be a non-volatile memory . The processor 801 may also comprise a cache (not shown in Figure 8), which may be used to temporarily store data from memory 802. The computer apparatus 301, 302 may comprise more than one processor 801 and more than one memory 802. The memory 802 may store data that is executable by the processor 801. The processor 801 may be configured to operate in accordance with a computer program stored in non-transitory form on a machine-readable storage medium. The computer program may store instructions for causing the processor to perform its methods in the manner described herein. The method steps described herein may be carried out by a computer- readable storage medium. The method steps described herein may be carried out by a computer program product.

[0119] The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present disclosure may consist of any such individual feature or combination of features. In view of the foregoing description, it will be evident to a person skilled in the art that various modifications may be made within the scope of the disclosure.

Claims

CLAIMS1. A user equipment, UE, apparatus (302), the UE apparatus (302) comprising one or more processors (801 ) and a memory (802) storing in non-transient form data defining program code executable by the one or more processors (801), wherein the program code is executable by the one or more processors (801) so that the UE apparatus (302) is configured to: obtain sounding reference signal, SRS, information (303) from a base station, BS, apparatus (301), the SRS information (303) comprising: a UE capability enquiry comprising one or more SRS resource pattern enquiries; an indication that flexible SRS resource is used for SRS resource group configuration; an SRS resource set configuration comprising locations for the SRS resource; and a channel state information, CSI, reporting configuration for the SRS resource pattern.

2. A UE apparatus (302) according to claim 1, wherein the UE apparatus (302) is configured to receive reference signals (304) from the BS apparatus (301).

3. A UE apparatus (302) according to claim 2, wherein the UE apparatus (302) is configured to carry out channel estimation (305a) in dependence on the reference signals (304) to obtain channel estimates to compute SRS resource pattern.

4. A UE apparatus (302) according to claim 3 when dependent on claim 2, wherein the UE apparatus (302) is configured to compute CSI information (305b) for the estimated channels (305a) in dependence on the reference signals (304).

5. A UE apparatus (302) according to any preceding claim, wherein the UE apparatus (302) is configured to obtain an SRS pilot allocation request (306) from the BS apparatus (301).

6. A UE apparatus (302) according to claim 5 when dependent on claim 4, wherein the UE apparatus (302) is configured to compute an SRS resource pattern (307) in dependence on the CSI information (305b) and the estimated channels (305a).

7. A UE apparatus (302) according to claim 6, wherein the UE apparatus (302) is configured to send an SRS resource pattern indication (308) to BS apparatus (301), the SRS resource pattern indication (308) corresponding to the SRS resource pattern (307) computed by the UE apparatus (302).

8. A UE apparatus (302) according to claim 7, wherein the UE apparatus (302) is configured to obtain an SRS resource pattern grant (310) from the BS apparatus (301), the SRS resource pattern grant (310) being computed by the BS apparatus (301 ) in dependence on the SRS resource pattern indication (308) and SRS resource availability, the SRS resource pattern grant (310) comprising the SRS resource pattern (309) for transmission by the UE apparatus (302).

9. A UE apparatus (302) according to claim 8, wherein the UE apparatus (302) is configured to transmit SRS (311 ) to the BS apparatus (301) in dependence on the SRS resource pattern (309).

10. A UE apparatus (302) according to claim 9, wherein the UE apparatus (302) is configured to receive a downlink data transmission (313) from the BS apparatus (301), the downlink data transmission (313) being precoded by the BS apparatus (301), wherein the precoder is computed with the channel estimate (312) obtained with the transmitted SRS (311).

11. A base station, BS, apparatus (301), the BS apparatus (301) comprising one or more processors (801) and a memory (802) storing in non-transient form data defining program code executable by the one or more processors (801), wherein the program code is executable by the one or more processors (801) so that the BS apparatus (301) is configured to: send sounding reference signal, SRS, information (303) to a user equipment, UE, apparatus (302), the SRS information (303) comprising: a UE capability enquiry comprising one or more SRS resource pattern enquiries; an indication that flexible SRS resource is used for SRS resource group configuration; an SRS resource set configuration comprising locations for the SRS resource; and a channel state information, CSI, reporting configuration for the SRS resource pattern.

12. A system (300, 400) comprising the UE apparatus (302) and the BS apparatus (301) of any of claims 1 to 11.

13. A system (400) according to claim 12, further comprising one or more further UE apparatuses (302) of any of claims 1 to 10.

14. A method (700), carried out by a user equipment, UE, apparatus (302), comprising the steps of: obtaining (701) sounding reference signal, SRS, information from a base station, BS, apparatus, the SRS information comprising: a UE capability enquiry comprising one or more SRS resource pattern enquiries; an indication that flexible SRS resource is used for SRS resource group configuration; an SRS resource set configuration comprising locations for the SRS resource; and a channel state information, CSI, reporting configuration for the SRS resource pattern.

15. A method (700), carried out by a base station, BS, apparatus (301), comprising the steps of: sending (701) sounding reference signal, SRS, information to a user equipment, UE, apparatus, the SRS information comprising: a UE capability enquiry comprising one or more SRS resource pattern enquiries; an indication that flexible SRS resource is used for SRS resource group configuration; an SRS resource set configuration comprising locations for the SRS resource; and a channel state information, CSI, reporting configuration for the SRS resource pattern.

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