# US 8,787,485 B2 · Method and apparatus for open loop transmission in a multiple antenna wireless communication system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,787,485 B2 - Document ID: US8787485B2 - Status: Granted - Kind: B2 - Application number: 14/042,393 - Filed: 2013-09-30 - Published: 2014-01-30 - Granted: 2014-07-22 - Earliest claimed: 2011-03-30 - Assignees: Huawei Technologies Co., Ltd. - Applicants: Huawei Technologies Co., Ltd. - Inventors: Jianghua Liu; Anahid Robert Safavi; Branislav Popovic - Web page: https://patentgrep.com/patent/US8787485B2 ## CPC - H04B 7/0486: {taking channel rank into account} - H04B 7/0621: {Feedback content} - H04J 13/00: Code division multiplex systems (for frequency hopping H04B1/713) - H04L 5/0001: {Arrangements for dividing the transmission path (two-way operation using the same type of signal, i.e. duplex H04L5/14)} - H04L 25/03942: {switching between different codebooks} - H04B: TRANSMISSION - H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S) - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract The invention concerns a method for precoding in an open loop transmission communications system, wherein the method includes precoding data at each of M REs with a precoding matrix, precoding each of DM-RSs with one column of a precoding matrix which is same as that used for precoding M data REs. The method is distinguished by using at least L≧2 different precoding matrices from a set of precoding matrices W to precode the M REs and the E allocated REs such that REs precoded with a first precoding matrix are interleaved with REs precoded with at least one additional, different precoding matrix and the number of used precoding matrices L is adapted to the transmission rank r and number N of available DM-RS. The invention further concerns a radio transmitter and a user equipment. ## Claims ### Claim 1 A method for precoding in an open loop transmission in a wireless multiple antenna radio communications system, wherein the system: provides for rank adaptation for data transmission with selected transmission rank r being 1≦r≦R, where R is a maximum available transmission rank of the communication system, communicates resource units (RU) containing resource elements (RE), provides N available Demodulation Reference Signals (DM-RS) for communication channel estimation in each RU, provides a number of M REs in each RU for data transmission, and provides a number of E REs in each RU allocated for DM-RS transmission, wherein the method comprises: applying a number, NUsed, of DM-RS:s, NUsed≦N, to the E allocated REs; precoding the data at each of the M REs within each RU with a precoding matrix and the same precoding matrix is used for all of the M REs within each RU; precoding each of NUsed DM-RSs over the E allocated REs within each RU with one column of the precoding matrix which is same as that used for precoding M data REs; and when precoding, using at least L≧2 different precoding matrices from a set of precoding matrices W to precode the M REs and the E allocated REs in at least one RU for at least one certain rank r transmission such that REs precoded with a first precoding matrix are interleaved with REs precoded with at least one additional, a second different precoding matrix, and wherein the number of used precoding matrices L is adapted to the transmission rank r and number N of available DM-RS. ### Claim 2 (depends on 1) The method according to claim 1, wherein the number N of available DM-RS depends on the number E of REs allocated for DM-RS:S in an RU and a length of code used for Code Division Multiplexing of DM-RS:S over the E REs. ### Claim 3 (depends on 1) The method according to claim 1, further comprising: using NUsed≦N available DM-RS for rank r transmission; and wherein number L of used precoding matrices for precoding data is a largest integer smaller than NUsed/r. ### Claim 4 (depends on 3) The method according to claim 3, wherein: E=12 REs are used in one resource unit for DM-RS, rank is chosen as either of 1 or 2, a length of CDM code is 4 and there are N=4 CDM DM-RS available, and number L of used precoding matrices is a largest integer smaller than N/r. ### Claim 5 (depends on 3) The method according to claim 3, wherein: E=24 REs are used in one resource unit for DM-RS, rank is chosen as either of 3 or 4, a length of CDM code is 4 and there are N=8 CDM DM-RS available, and number L of used precoding matrices is a largest integer smaller than N/r. ### Claim 6 (depends on 1) The method according to claim 1, wherein the number of E REs allocated for DM-RS in each RU depends on the selected transmission rank r. ### Claim 7 (depends on 1) The method according to claim 1, wherein: the same number N of available DM-RS:s are used for different rank r transmissions, and a number of used precoding matrices is a largest integer smaller than N/r. ### Claim 8 (depends on 1) The method according to claim 1, wherein: the number of available DM-RS for different rank r transmissions is Nr, same number of L precoding matrices is used for each transmission rank r, and Number NUsed of used DM-RS≦Nr available DM-RS for each rank r transmission is NUsed=L*r. ### Claim 9 (depends on 8) The method according to claim 8, wherein: the number of available DM-RS Nr for different rank r transmissions is the same. ### Claim 10 (depends on 1) The method according to claim 1, wherein: a number of NUsed DM-RS for rank r transmission is equal to r. ### Claim 11 (depends on 10) The method according to claim 10, wherein: the L precoding matrices used in one RU are obtained by permuting the columns or rows of one precoding matrix. ### Claim 12 (depends on 1) The method according to claim 1, wherein: multiple precoding matrices for only some available different transmission ranks is used in a resource unit. ### Claim 13 (depends on 1) The method according to claim 1, wherein: the resource unit is one Resource Block Pair in a Long Term Evolution mobile communications system, and the number of used precoding matrices in a number of consecutive Resource Block Pairs are at least the number of consecutive resource block pairs+1. ### Claim 14 (depends on 1) The method according to claim 1, further comprising: using cycling of L≧1 precoding matrices in a resource unit or in consecutive resource units. ### Claim 15 (depends on 14) The method according to claim 14, further comprising: performing layer permutation by permuting columns of the L precoding matrices and then use the permuted precoding matrices for precoding. ### Claim 16 (depends on 1) The method according to claim 1, wherein: each of NUsed DM-RS in a resource unit defines one antenna port, and there are NUsed defined antenna ports. ### Claim 17 (depends on 16) The method according to claim 16, wherein: each data transmission RE is associated with r of NUsed defined antenna ports when the transmission rank is r. ### Claim 18 (depends on 17) The method according to claim 17, wherein: each data transmission RE is associated with same antenna ports with different order. ### Claim 19 (depends on 1) The method according to claim 1, further comprising: signalling a scheme of used L precoding matrices to a receiver of precoded resource elements in the system. ### Claim 20 (depends on 1) The method according to claim 1, further comprising: computing received channel coefficients using non precoded reference signals; and extracting precoding matrices used for received precoded reference signals using the computed received channel coefficients. ### Claim 21 A radio transmitter configured to precode in an open loop transmission in a wireless multiple antenna radio communications system, wherein the system: provides for rank adaptation for data transmission with selected transmission rank r being 1≦r≦R, where R is a maximum available transmission rank of the communication system, communicates resource units (RU) containing resource elements (RE), provides N available Demodulation Reference Signals (DM-RS) for communication channel estimation in each RU, provides a number of M REs in each RU for data transmission, and provides a number of E REs in each RU allocated for DM-RS transmission, and wherein the radio transmitter is configured to: apply a number, NUsed, of DM-RS:s, NUsed≦N, to the E allocated REs; precode the data at each of the M REs within each RU with a precoding matrix and the same precoding matrix is used for all of the M REs within each RU; precode each of NUsed DM-RSs over the E allocated REs within each RU with one column of the precoding matrix which is same as that used for precoding M data REs; and when precoding, use at least L≧2 different precoding matrices from a set of precoding matrices W to precode the M REs and the E allocated REs in at least one RU for at least one certain rank r transmission such that REs precoded with a first precoding matrix are interleaved with REs precoded with at least one additional, a second different precoding matrix, and wherein the number of used precoding matrices L is adapted to the transmission rank r and number N of available DM-RS. ### Claim 22 A user equipment adapted to receive a transmission from a radio transmitter in a wireless multiple antenna radio communications system, wherein the system: provides for rank adaptation for data transmission with selected transmission rank r being 1≦r≦R, where R is a maximum available transmission rank of the communication system, communicates resource units (RU) containing resource elements (RE), provides N available Demodulation Reference Signals (DM-RS) for communication channel estimation in each RU, provides a number of M REs in each RU for data transmission, and provides a number of E REs in each RU allocated for DM-RS transmission, and wherein the user equipment is adapted to receive a precoded open loop transmission, wherein a number, NUsed, of DM-RS:s, NUsed≦N, is applied to the E allocated REs; wherein the data at each of the M REs within each RU is precoded with a precoding matrix and the same precoding matrix is used for all of the M REs within each RU; wherein each of NUsed DM-RSs over the E allocated REs within each RU is precoded with one column of the precoding matrix which is same as that used for precoding M data REs; and at least L≧2 different precoding matrices from a set of precoding matrices W are used to precode the M REs and the E allocated REs in at least one RU for at least one certain rank r transmission such that REs precoded with a first precoding matrix are interleaved with REs precoded with at least one additional, a second different precoding matrix, and wherein the number of used precoding matrices L is adapted to the transmission rank r and number N of available DM-RS.