# US 11,451,274 B2 · Adaptive downlink multi user multiple input multiple output (MU-MIMO)precoding using uplink signal subspace tracking for active antenna systems AAS > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,451,274 B2 - Document ID: US11451274B2 - Status: Granted - Kind: B2 - Application number: 17/055,806 - Filed: 2018-06-29 - Published: 2021-07-29 - Granted: 2022-09-20 - Earliest claimed: 2018-05-16 - Assignees: Telefonaktiebolaget LM Ericsson (publ) - Applicants: Telefonaktiebolaget LM Ericsson (publ) - Inventors: Amr El-Keyi; Svante Bergman; Yongquan Qiang - Web page: https://patentgrep.com/patent/US11451274B2 ## CPC - H04B 7/0456: Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting - H04L 25/0204: {of multiple channels} - H04B 7/0452: Multi-user MIMO systems - H04B 15/00: Suppression or limitation of noise or interference (by means associated with receiver H04B1/10) - H04B: TRANSMISSION - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract A method, base station and user equipment are disclosed. A base station configured to communicate with a plurality of user equipments is provided. The base station includes processing circuitry configured to: track a downlink signal subspace for each UE of the plurality of UEs, and determine a Multi-User Multiple-Input Multiple-Output, MU-MIMO, precoders based on the downlink signal subspace for each UE of the plurality of UEs. The MU-MIMO precoders are configured to at least in part suppress intra-cell MU-MIMO interference. ## Claims ### Claim 1 A base station configured to communicate with a plurality of user equipments, UEs, the base station comprising processing circuitry configured to: track a downlink signal subspace for each UE of the plurality of UEs; and determine a Multi-User Multiple-Input Multiple-Output, MU-MIMO, precoders based on the tracked downlink signal subspace for each UE of the plurality of UEs, the MU-MIMO precoders being configured to at least in part suppress intra-cell MU-MIMO interference. ### Claim 2 (depends on 1) The base station of claim 1, wherein the determining of the MU-MIMO precoders includes determining MU-MIMO beamforming vectors of paired UEs of the plurality of UEs, the beamforming vectors are configured to at least in part suppress intra-cell MU-MIMO interference. ### Claim 3 (depends on 1) The base station of claim 1, wherein the downlink signal subspace includes significant eigenvectors and eigenvalues of a covariance matrix of the downlink channel for each UE of the plurality of UEs. ### Claim 4 (depends on 3) The base station of claim 3, wherein the tracking of the downlink signal subspace for each UE of the plurality of UEs includes: estimating an M×R matrix whose columns are R significant eigenvectors of the covariance matrix, where M and R are positive integers; and estimating an R×R diagonal matrix corresponding to eigenvalues of the covariance matrix. ### Claim 5 (depends on 3) The base station of claim 3, wherein a plurality of dimensions of the covariance matrix are less than or equal to a number of antennas of the base station. ### Claim 6 (depends on 3) The base station of claim 3, wherein the covariance matrix corresponds to the covariance matrix for an antenna polarization. ### Claim 7 (depends on 1) The base station of claim 1, wherein the tracking of the downlink signal subspace is based on at least one of an uplink demodulation reference signal, DMRS, and an uplink sounding reference signal, SRS. ### Claim 8 (depends on 1) The base station of claim 1, wherein the processing circuitry is further configured to: determine a Single User, SU, -MIMO precoder for a UE of the plurality of UEs based on the tracked downlink signal subspace; estimate signal leakage between two UEs of the plurality of UEs based on the SU-MIMO precoders; and pair at least two UEs of the plurality of UEs if the estimated leakage is below a predefined threshold. ### Claim 9 (depends on 1) The base station of claim 1, wherein the MU-MIMO precoders are for the at least two UEs of the plurality of UEs that are paired for MU-MIMO co-scheduling. ### Claim 10 (depends on 1) The base station of claim 1, wherein the tracking of the downlink signal subspace for each UE of the plurality of UEs is performed iteratively. ### Claim 11 A method for a base station configured to communicate with a plurality of user equipments, UEs, the method comprising: tracking a downlink signal subspace for each UE of the plurality of UEs; and determining a Multi-User Multiple-Input Multiple-Output, MU-MIMO, precoder based on the tracked downlink signal subspace for each UE of the plurality of UEs, the MU-MIMO precoders being configured to at least in part suppress intra-cell MU-MIMO interference. ### Claim 12 (depends on 11) The method of claim 11, wherein the determining of the MU-MIMO precoders includes determining MU-MIMO beamforming vectors of paired UEs of the plurality of UEs, the beamforming vectors are configured to at least in part suppress intra-cell MU-MIMO interference. ### Claim 13 (depends on 11) The method of claim 11, wherein the downlink signal subspace includes significant eigenvectors and eigenvalues of a covariance matrix of the downlink channel for each UE of the plurality of UEs. ### Claim 14 (depends on 13) The method of claim 13, wherein the tracking of the downlink signal subspace for each UE of the plurality of UEs includes: estimating an M×R matrix whose columns are R significant eigenvectors of the covariance matrix, where M and R are positive integers; and estimating an R×R diagonal matrix corresponding to eigenvalues of the covariance matrix. ### Claim 15 (depends on 13) The method of claim 13, wherein a plurality of dimensions of the covariance matrix are less than or equal to a number of antennas of the base station. ### Claim 16 (depends on 13) The method of claim 13, wherein the covariance matrix corresponds to the covariance matrix for an antenna polarization. ### Claim 17 (depends on 11) The method of claim 11, wherein the tracking of the downlink signal subspace is based on at least one of an uplink demodulation reference signal, DMRS, and an uplink sounding reference signal, SRS. ### Claim 18 (depends on 11) The method of claim 11, further comprising: determining a Single User, SU, -MIMO precoder for a UE of the plurality of UEs based on the tracked downlink signal subspace; estimating signal leakage between two UEs of the plurality of UEs based on the SU-MIMO precoders; and pairing at least two UEs of the plurality of UEs if the estimated leakage is below a predefined threshold. ### Claim 19 (depends on 11) The method of claim 11, wherein the MU-MIMO precoders are for the at least two of the plurality of UEs that are paired for MU-MIMO co-scheduling. ### Claim 20 (depends on 11) The method of claim 11, wherein the tracking of the downlink signal subspace for each UE of the plurality of UEs is performed iteratively. ### Claim 21 A first user equipment, UE, configured to communicate with a base station, the first UE comprising processing circuitry configured to: perform wireless communication using Multi-User Multiple-Input Multiple-Output, MU-MIMO, precoders, the MU-MIMO precoders being based on tracking of a downlink signal subspace for each UE of a plurality of UEs, the plurality of UEs including the first UE, the MU-MIMO precoders being configured to at least in part suppress intra-cell MU-MIMO interference. ### Claim 22 A method of a first user equipment, UE, configured to communicate with a base station, the method comprising: performing wireless communication using Multi-User Multiple-Input Multiple-Output, MU-MIMO, precoders, the MU-MIMO precoders being based on tracking of a downlink signal subspace for each UE of a plurality of UEs, the plurality of UEs including the first UE, the MU-MIMO precoders being configured to at least in part suppress intra-cell MU-MIMO interference.