# US 2016/0365902 A1 · Method and apparatus for channel estimation in massive mimo systems with dynamic training design > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2016/0365902 A1 - Document ID: US20160365902A1 - Status: Published application - Kind: A1 - Application number: 14/733,964 - Filed: 2015-06-09 - Published: 2016-12-15 - Earliest claimed: 2015-06-09 - Assignees: Hong Kong Applied Science and Technology Research Institute Company Limited - Applicants: Hong Kong Applied Science and Technology Research Institute Company Limited - Inventors: Yuxian ZHANG; Man Wai Victor KWAN; Eric Kong Chau TSANG - Web page: https://patentgrep.com/patent/US20160365902A1 ## CPC - H04B 17/346: {Noise values (signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR] H04B17/336)} - H04B 7/0413: MIMO systems - H04B 7/0691: {using subgroups of transmit antennas} - H04L 25/0202: {Channel estimation} - H04L 25/0204: {of multiple channels} - H04L 25/0224: {using sounding signals} - H04B: TRANSMISSION - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract This invention is concerned with estimating a massive multi-input multi-output (MIMO) channel. In one embodiment, the transmit antennas are first partitioned into antenna groups each comprising a subset of the transmit antennas such that a pre-determined level of channel-estimation accuracy is attainable. For each antenna group, training signals for estimating a group of channels associated with the antenna group are determined. In particular, the number of the antenna groups, the subset of the transmit antennas for forming the antenna group, and the training signals for the antenna group are determined based on spatial correlations of the massive MINO channel, a maximum allowable total number of training signals and a transmit signal-to-noise ratio such that the pre-determined level of channel-estimation accuracy is achievable. Advantageously, the number of antenna groups is determined by identifying a highest number of antenna groups under a constraint that the pre-determined level is achievable. ## Claims ### Claim 1 A method for estimating a massive MIMO channel on which a first communication device having plural transmit antennas communicates with a second communication device having a single receive antenna, the massive MIMO channel having a channel covariance matrix that characterizes spatial correlations among the transmit antennas, the method comprising: partitioning, by the first communication device, the transmit antennas into plural antenna groups each comprising a subset of the transmit antennas such that a pre-determined level of channel-estimation accuracy is attained; and for an individual antenna group, determining, by the first communication device, one or more training signals for estimating a group of channels associated with the subset of the transmit antennas belonging to the individual antenna group; wherein the number of the antenna groups, the subset of the transmit antennas for forming the individual antenna group, and the one or more training signals for the individual antenna group are determined based on the spatial correlations, a maximum allowable total number of training signals and a transmit signal-to-noise ratio (SNR) such that the pre-determined level of channel-estimation accuracy is achieved. ### Claim 2 (depends on 1) The method of claim 1, wherein the number of antenna groups is determined by identifying a highest number of antenna groups under a constraint that the pre-determined level of channel-estimation accuracy is achievable, with the identified highest number being less than or equal to the maximum allowable total number of training signals. ### Claim 3 (depends on 1) The method of claim 1, further comprising: transmitting, by the first communication device, the one or more training signals of the individual antenna group to the second communication device, whereby complex-channel gains for the subset of the transmit antennas belonging to the individual antenna group are estimable after the one or more training signals are received at the second communication device; proceeding the transmitting of the one or more training signals of the individual antenna groups for all the antenna groups one-by-one, so that complex-channel gains for all the transmit antennas are obtainable; and obtaining full channel estimation by combining estimation results of all the antenna groups. ### Claim 4 (depends on 3) The method of claim 3, wherein the complex-channel gains for the subset of the transmit antennas belonging to the individual antenna group are estimated by a minimum mean-square error (MMSE) estimator. ### Claim 5 (depends on 1) The method of claim 1, further comprising: estimating, by either the first or the second communication device, the channel covariance matrix before performing the partitioning of the transmit antennas. ### Claim 6 (depends on 1) The method of claim 1, wherein the partitioning of the transmit antennas comprises the steps of: (a) computing a first channel-estimation accuracy level achieved in an absence of partitioning the transmit antennas, whereby the pre-determined level of channel-estimation accuracy is calculated from the first channel-estimation accuracy level; (b) given a trial number of antenna groups, determining, for each antenna group, a candidate subset of the transmit antennas and a candidate number of the one or more training signals, so as to compute a second channel-estimation accuracy level attained by partitioning the transmit antennas into the trial number of antenna groups, wherein the second channel-estimation accuracy is computed based on the spatial correlations, the transmit SNR, the trial number of antenna groups, and the candidate number of the one or more training signals for each antenna group; (c) repeating the step (b) for different trial numbers; (d) identifying a subset of the trial numbers used in the step (c) such that each trial number in this subset has the second channel-estimation accuracy level better than the pre-determined performance level; (e) determining the number of antenna groups to be the highest trial number in the subset of the trial numbers; and (f) determining, for each antenna group, the subset of the transmit antennas for forming this antenna group to be the candidate subset therefor associated with the highest trial number. ### Claim 7 (depends on 1) The method of claim 1, wherein the partitioning of the transmit antennas comprises the steps of: (a) computing a first channel-estimation accuracy level achieved in an absence of partitioning the transmit antennas, whereby the pre-determined level of channel-estimation accuracy is calculated from the first channel-estimation accuracy level; (b) given a trial number of antenna groups, determining, for each antenna group, a candidate subset of the transmit antennas and a candidate number of the one or more training signals, so as to compute a second channel-estimation accuracy level attained by partitioning the transmit antennas into the trial number of antenna groups, wherein the second channel-estimation accuracy is computed based on the spatial correlations, the transmit SNR, the trial number of antenna groups, and the candidate number of the one or more training signals for each antenna group; (c) repeating the step (b) for different trial numbers in descending order starting from the maximum allowable total number of training signals until the second channel-estimation accuracy level achieved for one trial number is better than the pre-determined performance level, whereby the determined number of antenna groups is the aforesaid one trial number; and (d) determining, for each antenna group, the subset of the transmit antennas for forming this antenna group to be the candidate subset therefor associated with the aforesaid one trial number. ### Claim 8 (depends on 7) The method of claim 7, wherein the first channel-estimation accuracy level is computed as μ according to μ = ∑ i = 1 m  γλ i 2 γλ i + 1 , the second channel-estimation accuracy level obtained in the step (b) is computed as) {tilde over (μ)} according to μ ~ = ∑ g = 1 G  ∑ i = 1 m g  γλ g , i 2 γλ g , i + 1 . and the pre-determined level of channel-estimation accuracy is given by β×μ, where: β is a pre-determined number less than unity; m is the maximum allowable total number of training signals; γ is the transmit SNR; λi is the i th largest eigenvalue of R, R being the channel covariance matrix; G is the trial number of antenna groups; mg is the candidate number of the one or more training signals for the g th antenna group; and λg,i is the i th largest eigenvalue of Rg, Rg being a submatrix of R corresponding to the candidate subset of the transmit antennas for the g th antenna group. ### Claim 9 (depends on 8) The method of claim 8, wherein the determining of one or more training signals for estimating the subset of the transmit antennas belonging to the individual antenna group comprises computing, after the determined number of antenna groups is obtained, S′g=√{square root over (γ)}Qg(1:m′g), 1≦g≦G′ where: S′g is an N′g×m′g matrix representing the one or more training signals for the g th antenna group; G′ is the determined number of antenna groups; m′g is the determined number of the one or more training signals for the g th antenna group; N′g is the determined number of the transmit antennas belonging to the g th antenna group; and Qg(1:m′g) is formed by m′g eigen-vectors corresponding to the m′g largest eigenvalues of R′g, R′g being a submatrix of R corresponding to the determined subset of the transmit antennas for the g th antenna group. ### Claim 10 (depends on 9) The method of claim 9, further comprising: transmitting, by the first communication device, the one or more training signals for the g th antenna group from the first communication device to the second communication device, whereby the second communication device receives a signal represented by an m′g×1 matrix yg; estimating, by either the first or the second communication device, complex-channel gains for the subset of the transmit antennas belonging to the g th antenna group, by {tilde over (h)}g=R′gS′g(Img+S′gHR′gS′g)−1gg where {tilde over (h)}g is the estimated complex-channel gains; and proceeding the transmitting of the one or more training signals and the estimating of complex channel gains for 1≦g≦G′ so that complex-channel gains for all the transmit antennas are obtained. ### Claim 11 A base station (BS) for communicating with a user equipment (UE), the BS comprising plural radio antennas, a radio transceiving unit coupled to the radio antennas, and one or more processors configured to execute a process for estimating a massive multi-input multi-output (MIMO) channel when the radio antennas are configured to be transmit antennas to enable the BS to communicate with the UE and when the UE is configured to have one receive antenna, the process comprising: partitioning the transmit antennas into plural antenna groups each comprising a subset of the transmit antennas such that a pre-determined level of channel-estimation accuracy is attained; and for an individual antenna group, determining one or more training signals for estimating a group of channels associated with the subset of the transmit antennas belonging to the individual antenna group; wherein the number of the antenna groups, the subset of the transmit antennas for forming the individual antenna group, and the one or more training signals for the individual antenna group are determined based on the spatial correlations, a maximum allowable total number of training signals and a transmit signal-to-noise ratio (SNR) such that the pre-determined level of channel-estimation accuracy is achieved. ### Claim 12 (depends on 11) The BS of claim 11, wherein the number of antenna groups is determined by identifying a highest number of antenna groups under a constraint that the pre-determined level of channel-estimation accuracy is achievable, the identified highest number being less than or equal to the maximum allowable total number of training signals. ### Claim 13 (depends on 11) The BS of claim 11, wherein the radio transceiving unit is configured to: transmit the one or more training signals of the individual antenna group to the UE, whereby complex-channel gains for the subset of the transmit antennas belonging to the individual antenna group are estimable by BS after the one or more training signals are received at the UE; and proceed the transmitting of the one or more training signals of the individual antenna groups for all the antenna groups one-by-one, so that complex-channel gains for all the transmit antennas are obtained by the BS. ### Claim 14 (depends on 13) The BS of claim 13, wherein the process further comprises estimating the complex-channel gains for the subset of the transmit antennas belonging to the individual antenna group by a minimum mean-square error (MMSE) estimator. ### Claim 15 (depends on 11) The BS of claim 11, wherein the partitioning of the transmit antennas comprises the steps of: (a) computing a first channel-estimation accuracy level achieved in an absence of partitioning the transmit antennas, whereby the pre-determined level of channel-estimation accuracy is calculated from the first channel-estimation accuracy level; (b) given a trial number of antenna groups, determining, for each antenna group, a candidate subset of the transmit antennas and a candidate number of the one or more training signals, so as to compute a second channel-estimation accuracy level attained by partitioning the transmit antennas into the trial number of antenna groups, wherein the second channel-estimation accuracy is computed based on the spatial correlations, the transmit SNR, the trial number of antenna groups, and the candidate number of the one or more training signals for each antenna group; (c) repeating the step (b) for different trial numbers; (d) identifying a subset of the trial numbers used in the step (c) such that each trial number in this subset has the second channel-estimation accuracy level better than the pre-determined performance level; (e) determining the number of antenna groups to be the highest trial number in the subset of the trial numbers; and (f) determining, for each antenna group, the subset of the transmit antennas for forming this antenna group to be the candidate subset therefor associated with the highest trial number. ### Claim 16 (depends on 11) The BS of claim 11, wherein the partitioning of the transmit antennas comprises the steps of: (a) computing a first channel-estimation accuracy level achieved in an absence of partitioning the transmit antennas, whereby the pre-determined level of channel-estimation accuracy is calculated from the first channel-estimation accuracy level; (b) given a trial number of antenna groups, determining, for each antenna group, a candidate subset of the transmit antennas and a candidate number of the one or more training signals, so as to compute a second channel-estimation accuracy level attained by partitioning the transmit antennas into the trial number of antenna groups, wherein the second channel-estimation accuracy is computed based on the spatial correlations, the transmit SNR, the trial number of antenna groups, and the candidate number of the one or more training signals for each antenna group; (c) repeating the step (b) for different trial numbers in descending order starting from the maximum allowable total number of training signals until the second channel-estimation accuracy level achieved for one trial number is better than the pre-determined performance level, whereby the determined number of antenna groups is the aforesaid one trial number; and (d) determining, for each antenna group, the subset of the transmit antennas for forming this antenna group to be the candidate subset therefor associated with the aforesaid one trial number. ### Claim 17 (depends on 16) The BS of claim 16, wherein the first channel-estimation accuracy level is computed as μ according to μ = ∑ i = 1 m  γλ i 2 γλ i + 1 , the second channel-estimation accuracy level obtained in the step (b) is computed as {tilde over (μ)} according to μ ~ = ∑ g = 1 G  ∑ i = 1 m g  γλ g , i 2 γλ g , i + 1 , and the pre-determined level of channel-estimation accuracy is given by β×μ, where: β is a pre-determined number less than unity; m is the maximum allowable total number of training signals; γ is the transmit SNR; λi is the i th largest eigenvalue of R, R being the channel covariance matrix; G is the trial number of antenna groups; mg is the candidate number of the one or more training signals for the g th antenna group; and λg,i is the i th largest eigenvalue of Rg, Rg being a submatrix of R corresponding to the candidate subset of the transmit antennas for the g th antenna group. ### Claim 18 (depends on 17) The BS of claim 17, wherein the determining of one or more training signals for estimating the subset of the transmit antennas belonging to the individual antenna group comprises computing, after the determined number of antenna groups is obtained, S′g=√e,rad γQg(1;m′g), 1≦g≦G′ where: S′g is an N′g×m′g matrix representing the one or more training signals for the g th antenna group; G′ is the determined number of antenna groups; m′g is the determined number of the one or more training signals for the g th antenna group; N′g is the determined number of the transmit antennas belonging to the g th antenna group; and Qg(1:m′g) is formed by m′g eigen-vectors corresponding to the m′g largest eigenvalues of R′g, R′g being a submatrix of R corresponding to the determined subset of the transmit antennas for the g th antenna group. ### Claim 19 (depends on 18) The BS of claim 18, wherein the process further comprises: configuring the radio transceiving unit to transmit to the UE the one or more training signals for the g th antenna group, whereby the UE receives a signal represented by an m′g×1 matrix yg ; estimating, after the BS receives yg from the UE, complex-channel gains for the subset of the transmit antennas belonging to the g th antenna group by ĥg=R′gS′g(Img+S′gHR′gS′g)−1yg where ĥg is the estimated complex-channel gains; and repeating the configuring of the radio transceiving unit and the estimating of complex-channel gains for 1≦g≦G′ so that complex-channel gains for all the transmit antennas are obtained.