Method and device for detecting downlink channel information

Description

[0001] This application claims priority to Chinese Patent Application No. 201711386200.5, filed with the Chinese Patent Office on December 20, 2017 and entitled "METHOD AND APPARATUS FOR OBTAINING DOWNLINK CHANNEL INFORMATION" .TECHNICAL FIELD

[0002] This application relates to the field of communications technologies, and in particular, to a method and an apparatus for obtaining downlink channel information.BACKGROUND

[0003] A multiple-input multiple-output (multiple-input multiple-output, MIMO) technology means that a plurality of transmit antennas and a plurality of receive antennas are respectively used at a transmit end and a receive end, so that a signal is transmitted and received by using the plurality of antennas at the transmit end and the receive end, thereby improving communication quality. In a MIMO beamforming technology (MIMO beamforming, MIMO-BF), a base station performs weighting on sent data based on downlink channel information, to form a narrow transmit beam, and aligns energy at a target user, thereby improving communication quality.

[0004] In a time division duplex (English: time division duplex, TDD for short) system, a same channel is used for uplink transmission and downlink transmission. Therefore, the base station can estimate the downlink channel information by measuring the uplink channel based on channel reciprocity. The channel reciprocity means that the uplink transmission and the downlink transmission use the same channel. When the time interval between the uplink transmission and the downlink transmission is sufficiently short, it may be considered that fading of the uplink channel is basically the same as that of the downlink channel.

[0005] However, because receiving and transmitting are unbalanced on a user equipment (user equipment, UE) side, for example, the UE is usually a 2T4R (that is, the UE includes four antenna ports, uplink transmission is performed by using two of the four antenna ports and downlink receiving is performed by using the four antenna ports), a 4T8R (that is, the UE includes eight antenna ports, uplink transmission is performed by using four of the eight antenna ports and downlink receiving is performed by using the eight antenna ports), or the like. Currently, a common method for obtaining a downlink channel is as follows: Using the 2T4R UE as an example, the UE first sends a sounding reference signal (Sounding Reference Signal, SRS) to the base station by using two antenna ports, so that the base station obtains, based on reciprocity between uplink and downlink channels, downlink channel information corresponding to the two antenna ports. Then, the UE sends the SRS to the base station by using the other two antenna ports, so that the base station obtains, based on the reciprocity between uplink and downlink channels, downlink channel information corresponding to the other two antenna ports. Because the UE needs a specific time interval between two times of sending the SRS, real-time performance is relatively poor, and accuracy of downlink channel information obtained by the base station is relatively low.

[0006] Document AU 2016 264 412 A1 relates to the field of wireless communication technology, in particular to a method in the wireless communication system, which implements a two-stage channel estimation and feedback scheme and a two-step precoding scheme.

[0007] Document EP 3 588 794 A1 falls within the terms of Art. 54(3) EPC and relates to a channel state information transmission method.SUMMARY

[0008] This application provides a method and an apparatus for obtaining downlink channel information, to resolve a problem in the prior art that obtained downlink channel information is of low accuracy.

[0009] According to a first aspect, this application provides a method for obtaining downlink channel information. The method includes: receiving, by a network side device, a first pilot signal sent by user equipment by using N first antenna ports, and determining, based on the received first pilot signal, a downlink channel gain matrix corresponding to the N first antenna ports; determining, based on the downlink channel gain matrix corresponding to the N first antenna ports, a first weight matrix corresponding to the N first antenna ports, where the first weight matrix is used to represent downlink channel information corresponding to the N first antenna ports; sending, by the network side device, a second pilot signal to the user equipment, and receiving a precoding matrix indicator PMI fed back by the user equipment, where the PMI is determined by the user equipment based on a second pilot signal received by using P antenna ports; and the P antenna ports include M second antenna ports and at least one first antenna port, or the P antenna ports include the M second antenna ports; determining a second weight matrix based on the PMI, where the second weight matrix is used to represent downlink channel information corresponding to the P receiving ports; and determining, by the network side device based on the first weight matrix and the second weight matrix, downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports.

[0010] In this embodiment of this application, the network side device receives, in an uplink slot, a first pilot signal to measure an uplink channel, to obtain the downlink channel information; and sends, in a downlink slot, a second pilot signal to measure a downlink channel, and then obtains all downlink channel information by combining the downlink channel information obtained by using the first pilot signal and the downlink channel information measured by using the second pilot signal. As compared with a manner in the prior art in which the uplink channel information is obtained by continuously sending an SRS in two uplink slots to measure the uplink channel, because a time interval between the adjacent uplink slot and downlink slot is less than a time interval between two adjacent uplink slots, in this embodiment of this application, real-time performance is relatively good when the downlink channel information is obtained, and accuracy of obtaining the downlink channel information can be effectively improved.

[0011] In a possible design, the PMI is determined by the user equipment based on the second pilot signal received by using the M second antenna ports. The network side device concatenates the first weight matrix and the second weight matrix to obtain the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports. The first weight matrix used to represent the downlink channel information corresponding to the N first antenna ports may be combined with the second weight matrix used to represent the downlink channel information corresponding to the M receive ports in the concatenating manner, to obtain the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports.

[0012] In a possible design, the PMI is determined by the user equipment based on the second pilot signal received by using the M second antenna ports and the at least one first antenna port. The network side device may determine an m-column matrix in the second weight matrix, and concatenates the first weight matrix and the m-column matrix in the second weight matrix, to obtain the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports. As compared with a manner in the prior art in which the user equipment sends, in a second uplink slot, an SRS pilot to the network side device by using the M second antenna ports to enable the network side device to obtain the downlink channel information corresponding to the M second antenna ports, in the foregoing design, downlink channel information corresponding to a plurality of antenna ports including the M second antenna ports may be obtained in a downlink slot having a shorter time interval with the first uplink slot, so that more accurate downlink channel information corresponding to the M second antenna ports can be obtained.

[0013] In a possible design, before the receiving, by the network side device, a first pilot signal sent by user equipment by using N first antenna ports, the network side device may receive the first pilot signal sent by the user equipment by using the M second antenna ports, and determine, based on the received first pilot signal, a downlink channel gain matrix corresponding to the M second antenna ports. The network side device then determines, based on the downlink channel gain matrix corresponding to the M second antenna ports, a third weight matrix corresponding to the M second antenna ports, where the third weight matrix is used to represent the downlink channel information corresponding to the M second antenna ports. Subsequently, the network side device determines the m-column matrix in the second weight matrix based on the third weight matrix, where a rank of the m-column matrix is equal to a rank of the third weight matrix. The third weight matrix is used to represent the downlink channel information corresponding to the M second antenna ports, and real-time performance of the second weight matrix is better than that of the third weight matrix. Therefore, the m-column matrix that is in the second weight matrix and that has a rank is equal to the rank of the third weight matrix can more accurately reflect a downlink channel status corresponding to the M second antenna ports.

[0014] In a possible design, the PMI is determined by the user equipment based on the second pilot signal received by using the M second antenna ports and the N first antenna ports. After the receiving, by the network side device, a first pilot signal sent by user equipment by using N first antenna ports, the network side device may receive the first pilot signal sent by the user equipment by using the M second antenna ports, and determine, based on the received first pilot signal, a downlink channel gain matrix corresponding to the M second antenna ports. The network side device then determines, based on the downlink channel gain matrix corresponding to the M second antenna ports, a fourth weight matrix corresponding to the M second antenna ports, where the fourth weight matrix is used to represent the downlink channel information corresponding to the M second antenna ports. Subsequently, the network side device concatenates the first weight matrix and the fourth weight matrix to obtain a fifth weight matrix, and adjusts the fifth weight matrix based on the second weight matrix, to obtain the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports. Because the second weight matrix is obtained through measurement in one downlink slot, and the fifth weight matrix is obtained through measurement in two consecutive uplink slots, the second weight matrix has better real-time performance than the fifth weight matrix. In the foregoing design, that the fifth weight matrix is adjusted based on the second weight matrix with better real-time performance can improve real-time performance of obtaining the downlink channel information, so that accuracy of obtaining the downlink channel information can be effectively improved.

[0015] In a possible design, the network side device multiplies the second weight matrix by the fifth weight matrix, to adjust the fifth weight matrix based on the second weight matrix. In this way, a phase of a transmit beam corresponding to the fifth weight matrix may be corrected, so that a transmit beam formed based on the corrected fifth weight matrix is more accurate.

[0016] In a possible design, the network side device adjusts a size of a matrix element in the second weight matrix and / or the fifth weight matrix, and then multiplies the adjusted second weight matrix by the adjusted fifth weight matrix, to adjust the fifth weight matrix based on the second weight matrix. In this way, a phase and an amplitude of a transmit beam corresponding to the fifth weight matrix may be corrected, so that a transmit beam formed based on the corrected fifth weight matrix is more accurate.

[0017] In a possible design, the network side device determines an H*H-order orthogonal matrix of the downlink channel gain matrix corresponding to the N first antenna ports, and a rank of the downlink channel gain matrix corresponding to the N first antenna ports, where H is a quantity of receiving ports of the network side device; and then determines first n columns of the H*H-order orthogonal matrix as the first weight matrix, where n is equal to the rank of the downlink channel gain matrix corresponding to the N first antenna ports. In this way, the downlink channel gain matrix corresponding to the N first antenna ports may be normalized, so that the downlink channel gain matrix may be combined with the second weight matrix, to improve accuracy of obtaining the downlink channel information.

[0018] In a possible design, the network side device performs precoding weighting on the second pilot signal based on a preset weight matrix, and then sends the weighted second pilot signal to the user equipment. Subsequently, the network side device multiplies the preset weight matrix by the PMI to obtain the second weight matrix. In this way, the PMI may be normalized, and may be further combined with the first weight matrix to improve accuracy of obtaining the downlink channel information.

[0019] According to a second aspect, this application provides an apparatus for obtaining downlink channel information. The apparatus includes: a receiving module, configured to receive a first pilot signal sent by user equipment by using N first antenna ports; a determining module, configured to: determine, based on the first pilot signal received by the receiving module, a downlink channel gain matrix corresponding to the N first antenna ports, where N is an integer greater than 0, and determine, based on the downlink channel gain matrix corresponding to the N first antenna ports, a first weight matrix corresponding to the N first antenna ports, where the first weight matrix is used to represent downlink channel information corresponding to the N first antenna ports; and a sending module, configured to send a second pilot signal to the user equipment. The receiving module is further configured to receive a precoding matrix indicator PMI fed back by the user equipment, where the PMI is determined by the user equipment based on a second pilot signal received by using P antenna ports. The P antenna ports include M second antenna ports and at least one first antenna port, or the P antenna ports include M second antenna ports. The determining module is further configured to: determine a second weight matrix based on the PMI received by the receiving module, where the second weight matrix is used to represent downlink channel information corresponding to the P receiving ports; and determine, based on the first weight matrix and the second weight matrix, downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports.

[0020] In a possible design, the PMI is determined by the user equipment based on the second pilot signal received by using the M second antenna ports. When determining, based on the first weight matrix and the second weight matrix, the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports, the determining module is specifically configured to concatenate the first weight matrix and the second weight matrix, to obtain the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports.

[0021] In a possible design, the PMI is determined by the user equipment based on the second pilot signal received by using the M second antenna ports and the at least one first antenna port. When determining, based on the first weight matrix and the second weight matrix, the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports, the determining module is specifically configured to: determine an m-column matrix in the second weight matrix, and concatenate the first weight matrix and the m-column matrix in the second weight matrix, to obtain the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports, where m is an integer greater than 0 and less than a quantity of columns of the second weight matrix.

[0022] In a possible design, before the receiving a first pilot signal sent by user equipment by using N first antenna ports, the receiving module is further configured to receive the first pilot signal sent by the user equipment by using the M second antenna ports. The determining module is further configured to: determine, based on the first pilot signal received by the receiving module, a downlink channel gain matrix corresponding to the M second antenna ports, and determine, based on the downlink channel gain matrix corresponding to the M second antenna ports, a third weight matrix corresponding to the M second antenna ports. The third weight matrix is used to represent the downlink channel information corresponding to the M second antenna ports. When determining the m-column matrix in the second weight matrix, the determining module is specifically configured to determine the m-column matrix in the second weight matrix based on the third weight matrix, where a rank of the m-column matrix is equal to a rank of the third weight matrix.

[0023] In a possible design, the PMI is determined by the user equipment based on the second pilot signal received by using the M second antenna ports and the N first antenna ports. After the receiving a first pilot signal sent by user equipment by using N first antenna ports, the receiving module is further configured to receive the first pilot signal sent by the user equipment by using the M second antenna ports. The determining module is further configured to: determine, based on the first pilot signal received by the receiving module, a downlink channel gain matrix corresponding to the M second antenna ports, and determine, based on the downlink channel gain matrix corresponding to the M second antenna ports, a fourth weight matrix corresponding to the M second antenna ports. The fourth weight matrix is used to represent the downlink channel information corresponding to the M second antenna ports. When determining, based on the first weight matrix and the second weight matrix, the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports, the determining module is specifically configured to: concatenate the first weight matrix and the fourth weight matrix to obtain a fifth weight matrix, and adjust the fifth weight matrix based on the second weight matrix to obtain the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports.

[0024] In a possible design, when adjusting the fifth weight matrix based on the second weight matrix, the determining module is specifically configured to multiply the second weight matrix by the fifth weight matrix.

[0025] In a possible design, when adjusting the fifth weight matrix based on the second weight matrix, the determining module is specifically configured to: adjust a size of a matrix element in the second weight matrix and / or the fifth weight matrix and multiply the adjusted second weight matrix by the adjusted fifth weight matrix.

[0026] In a possible design, when determining, based on the downlink channel gain matrix corresponding to the N first antenna ports, the first weight matrix corresponding to the N first antenna ports, the determining module is specifically configured to: determine an H*H-order orthogonal matrix of the downlink channel gain matrix corresponding to the N first antenna ports, and a rank of the downlink channel gain matrix corresponding to the N first antenna ports. H is a quantity of receiving ports of the network side device. Then the determining module determines first n columns of the H*H-order orthogonal matrix as the first weight matrix. n is equal to the rank of the downlink channel gain matrix corresponding to the N first antenna ports.

[0027] In a possible design, the apparatus further includes an encoding module, configured to perform precoding weighting on the second pilot signal based on a preset weight matrix. When sending the second pilot signal to the user equipment, the sending module is specifically configured to send the weighted second pilot signal to the user equipment. When determining the second weight matrix based on the PMI, the determining module is specifically configured to multiply the preset weight matrix by the PMI to obtain the second weight matrix.

[0028] According to a third aspect, this application provides an apparatus for obtaining downlink channel information, including a transceiver, a memory, and a processor. The memory is configured to store program code that needs to be executed by the processor. The transceiver is configured to receive and send data. The processor is configured to execute the program code stored in the memory, and is specifically configured to perform the method according to the first aspect or any one of the designs of the first aspect.

[0029] According to a fourth aspect, this application further provides a computer-readable storage medium, configured to store a computer software instruction used to perform the first aspect and any one of the designed functions of the first aspect, and the computer software instruction includes a program designed to perform the first aspect or any one of the designs of the first aspect.

[0030] According to a fifth aspect, an embodiment of this application provides a computer program product including an instruction. When the computer program product is run on a computer, the computer is enabled to perform the method according to the first aspect or any one of the designs of the first aspect.

[0031] According to a sixth aspect, an embodiment of this application provides a chip. The chip is connected to a memory, and is configured to read and execute a software program stored in the memory, to implement the method according to the first aspect or any one of the designs of the first aspect.BRIEF DESCRIPTION OF DRAWINGS

[0032] FIG. 1A is a schematic architectural diagram of a SISO system according to this application; FIG. 1B is a schematic architectural diagram of a MISO system according to this application; FIG. 1C is a schematic architectural diagram of a SIMO system according to this application; FIG. 1D is a schematic architectural diagram of a MIMO system according to this application; FIG. 2 is a schematic flowchart of a method for obtaining downlink channel information according to this application; FIG. 3 is a schematic architectural diagram of a MIMO system according to this application; FIG. 4 is a schematic flowchart of a method for obtaining downlink channel information according to this application; FIG. 5 is a schematic flowchart of a method for obtaining downlink channel information according to this application; FIG. 6 is a schematic flowchart of a method for obtaining downlink channel information according to this application; FIG. 7 is a schematic structural diagram of an apparatus for obtaining downlink channel information according to this application; and FIG. 8 is a schematic structural diagram of an apparatus for obtaining downlink channel information according to this application. DESCRIPTION OF EMBODIMENTS

[0033] To make the objectives, technical solutions, and advantages of this application clearer, the following further describes this application in detail with reference to the accompanying drawings.

[0034] The network architecture and the service scenario described in the embodiments of this application are intended to describe the technical solutions in the embodiments of this application more clearly, and do not constitute a limitation on the technical solutions provided in the embodiments of this application. A person of ordinary skill in the art may learn that: With the evolution of the network architecture and the emergence of new service scenarios, the technical solutions provided in the embodiments of this application are also applicable to similar technical problems.

[0035] A communications system may be classified into a single-input single-output (single-input single-output, SISO) system, a multiple-input single-output (multiple-input single-output, MISO) system, a single-input multiple-output (single-input multiple-output, SIMO) system, or a multiple-input multiple-output (multiple-input multiple-output, MIMO) system. Both a network side device and user equipment in the SISO system include one antenna, as shown in FIG. 1A. In the MISO system, the network side device includes a plurality of antennas, and the user equipment includes one antenna, as shown in FIG. 1B. In the SIMO system, the network side device includes one antenna, and the user equipment includes a plurality of antennas, as shown in FIG. 1C. In the MIMO system, the network side device includes a plurality of antennas, and the user equipment includes a plurality of antennas, as shown in FIG. 1D. The embodiments of this application may be applied to the MIMO system shown in FIG. 1D. The MIMO system in the embodiments of this application may be various communications systems, for example, may be a long term evolution (long term evolution, LTE) system, may be a fifth-generation (5G) communications system, or may be a hybrid architecture of the LTE and the 5G.

[0036] The network side device may be a common base station (for example, a NodeB or an eNB), a new radio controller (new radio controller, NR controller), a gNode B (gNB) in a 5G system, a centralized network element (centralized unit), a new radio base station, a radio remote unit, a micro base station, a distributed network element (distributed unit), a transmission reception point (transmission reception point, TRP), a transmission point (transmission point, TP), or any other radio access device. This is not limited in the embodiments of this application.

[0037] The user equipment (user equipment, UE), namely, a terminal device, is a device providing voice and / or data connectivity to a user, for example, a handheld device or a vehicle-mounted device having a wireless connection function. A common terminal includes, for example, a mobile phone, a tablet computer, a notebook computer, a palmtop computer, a mobile internet device (mobile internet device, MID), and a wearable device such as a smartwatch, a smart band, or a pedometer.

[0038] In the MIMO system, the network side device (for example, a base station) may send data to the UE by using the MIMO beamforming (MIMO beamforming, MIMO-BF) technology. In the MIMO-BF, the network side device performs weighting on the sent data based on downlink channel information, to form a narrow transmit beam, and aligns energy at target UE, thereby improving communication quality.

[0039] The MIMO system may be classified into a frequency division duplex (frequency division duplex, FDD) system or a time division duplex (English: time division duplex, TDD for short) system. In the FDD system, two channels that are independent of each other are respectively used for uplink transmission and downlink transmission. In the TDD system, a same channel is used for the uplink transmission and the downlink transmission. Therefore, in the TDD system, the network side device can estimate the downlink channel information by measuring an uplink channel based on channel reciprocity. The channel reciprocity means that the same channel is used for the uplink transmission and the downlink transmission. When the time interval between the uplink transmission and the downlink transmission is sufficiently short, it may be considered that fading of the uplink channel is basically the same as that of the downlink channel.

[0040] However, receiving and transmitting of the UE are usually unbalanced, for example, the UE is usually a 2T4R (that is, the UE includes four antenna ports, uplink transmission is performed by using two of the four antenna ports and downlink receiving is performed by using the four antenna ports), a 4T8R (that is, the UE includes eight antenna ports, uplink transmission is performed by using four of the eight antenna ports and downlink receiving is performed by using the eight antenna ports), or the like. Therefore, in the TDD system, in a manner in which the network side device estimates the downlink channel information by measuring the uplink channel, only downlink channel information corresponding to some antenna ports included in the UE can be obtained. To obtain downlink channel information corresponding to all antennas included in the UE, currently, a common method for obtaining a downlink channel information is as follows. In an existing solution 1, using the 2T4R UE as an example, four antenna ports of the UE are respectively an antenna port 0 to an antenna port 3. The UE sends a sounding reference signal (Sounding Reference Signal, SRS) to the base station by using the antenna port 0 and the antenna port 2 in one uplink slot, so that the base station determines uplink channel information that corresponds to the antenna port 0 and that corresponds to the antenna port 2 after receiving the SRS from the antenna port 0 and the antenna port 2. Then, the UE obtains downlink channel information that corresponds to the antenna port 0 and that corresponds to the antenna port 2 based on reciprocity between uplink and downlink channels. Then, the UE sends the SRS to the base station by using the antenna port 1 and the antenna port 3 in a next uplink slot, so that the base station determines uplink channel information that corresponds to the antenna port 1 and that corresponds to the antenna port 3 after receiving the SRS from the antenna port 1 and the antenna port 3. Then, the UE obtains downlink channel information that corresponds to the antenna port 1 and that corresponds to the antenna port 3 based on the reciprocity between uplink and downlink channels. Because the UE needs a specific time interval between two times of sending the SRS, in other words, there is a specific time interval between two consecutive uplink slots, real-time performance of the downlink channel information that corresponds to the antenna port 0 and that corresponds to the antenna port 2 and that is first obtained is relatively poor, and accuracy of the downlink channel information obtained by the base station is relatively low.

[0041] In addition to the existing solution 1, currently, a common method for obtaining the downlink channel includes an existing solution 2. Using the 2T4R UE as an example, the network side device sends a channel state measurement pilot (CSI reference signals, CSI-RS) to the UE, after receiving the CSI-RS by using the four antenna ports, the UE feeds back a precoding matrix indicator (Precoding Matrix Indicator, PMI) to the network side device, so that the network side device obtains the downlink channel information based on the PMI fed back by the UE. However, a quantity of PMIs specified in the 3rd generation partnership project (3rd generation partnership project, 3GPP) protocol is relatively limited. Therefore, the downlink channel information obtained by the network side device based on the PMI fed back by the UE can only approximate to an actual downlink channel status, but cannot accurately reflect the actual downlink channel status, and accuracy is relatively low.

[0042] Based on this, this application provides a method and an apparatus for obtaining downlink channel information, to resolve a problem in the prior art that obtained downlink channel information is of low accuracy. The method and the apparatus are based on a same inventive concept. Because principles of the method and the apparatus for resolving a problem are similar, mutual reference may be made between implementations of the apparatus and the method. Repeated descriptions are omitted.

[0043] To make the embodiments of this application easier to be understood, the following first describes some descriptions in the embodiments of this application. These descriptions should not be considered as a limitation on the protection scope claimed in this application.

[0044] An uplink channel gain matrix includes a plurality of uplink channel gains, where a quantity of rows of the uplink channel gain matrix represents a quantity of antenna ports used by the network side device to receive data, and a quantity of columns of the uplink channel gain matrix represents a quantity of antenna ports used by the UE to send data. Therefore, a matrix element h i,j in an i th< row and a j th< column in the uplink channel gain matrix represents a channel gain of an uplink channel between an i th< antenna port of the network side device and a j th< antenna port of the UE, and h i,j may meet the following formula requirement: y i , j = h i , j × s i , j + n y i,j represents a received signal that is from the j th< antenna port of the UE and that is received by the i th< antenna port of the network side device, h i,j represents the channel gain of the uplink channel between the i th< antenna port of the network side device and the j th< antenna port of the UE, and s i,j represents a transmitted signal sent by the UE by using the i th< antenna port, and n indicates noise of the network side device.

[0045] A downlink channel gain matrix includes a plurality of downlink channel gains, where a quantity of rows of the downlink channel gain matrix represents a quantity of antenna ports used by the UE to receive data, and a quantity of columns of the downlink channel gain matrix represents a quantity of antenna ports used by the network side device to send data. Therefore, a matrix element in an r th< row and a k th< column in the downlink channel gain matrix represents a channel gain of a downlink channel between an r th< antenna port of the UE and a k th< antenna port of the network side device.

[0046] The channel reciprocity means that a same channel is used for uplink transmission and downlink transmission. When a time interval between the uplink transmission and the downlink transmission is sufficiently short, it may be considered that fading of the uplink channel is basically the same as that of the downlink channel. Therefore, the channel gain of the uplink channel between the i th< antenna port of the network side device and the j th< antenna port of the UE is the same as the channel gain of the downlink channel between the j th< antenna port of the UE and the i th< antenna port of the network side device.

[0047] Singular value decomposition (Singular Value Decomposition, SVD): SVD is performed on a matrix M of an order a*b. In other words, the matrix M is decomposed into a product of three matrices: SVD M = USV ;

[0048] U is an a*a-order orthogonal matrix of the matrix M, S is a diagonal matrix of the matrix M, and V is a b*b-order orthogonal matrix of the matrix M.

[0049] Rank: a maximum order of a non-zero subdeterminant of the matrix is a rank of the matrix.

[0050] "Multiple" refers to two or more than two.

[0051] In addition, it should be understood that, in descriptions of this application, terms such as "first" and "second" are merely used for purposes of distinguishing descriptions and are neither intended to indicate or imply relative importance nor intended to indicate or imply a sequence.

[0052] The following further describes in detail the embodiments of this application with reference to accompanying drawings.

[0053] FIG. 2 shows a method for obtaining downlink channel information according to an embodiment of this application. The method may be applied to a TDD system in a MIMO system, and the method may specifically include the following steps.

[0054] S201. UE sends a first pilot signal to a network side device (for example, a base station) by using N first antenna ports in a first uplink slot. The first uplink slot may be any uplink slot. N is an integer greater than 0. The first antenna port may be an antenna port that is used to send data in the first uplink slot and that is in the antenna ports included in the UE. If the UE is a 2T4R, the UE may send the first pilot signal to the network side device (for example, the base station) by using any two antenna ports in the first uplink slot. If the UE is the 4T8R, the UE may send the first pilot signal to the network side device (for example, the base station) by using any four antenna ports in the first uplink slot. The first pilot signal may be an SRS.

[0055] S202. The network side device determines, based on the first pilot signal from the N first antenna ports, a downlink channel gain matrix corresponding to the N first antenna ports.

[0056] In a possible implementation, the network side device may determine, based on the first pilot signal from the N first antenna ports, an uplink channel gain matrix H UL (H*N-order matrix) corresponding to the N first antenna ports, and then determine, based on reciprocity between uplink and downlink channels, a downlink channel gain matrix H DL (N*H-order matrix) corresponding to the N first antenna ports. H is a quantity of antenna ports used to receive and send data in the network side device.

[0057] S203. The network side device determines, based on the downlink channel gain matrix corresponding to the N first antenna ports, a first weight matrix V 1 corresponding to the N first antenna ports. The first weight matrix V 1 is used to represent downlink channel information corresponding to the N first antenna ports.

[0058] The first weight matrix V 1 may be determined in the following manner. The network side device determines an H*H-order orthogonal matrix of H DL and a rank of H DL , and determines first n columns of the H*H-order orthogonal matrix as the first weight matrix V 1 . n is equal to the rank of H DL . The network side device may determine the H*H-order orthogonal matrix of H DL and the rank of H DL in a manner of performing the SVD on H DL , which is as follows: SVD H DL = U HDL S HDL V HDL ; V HDL represents the H*H-order orthogonal matrix of H DL , S HDL represents a diagonal matrix of H DL , and a quantity of non-zero rows in S HDL is the rank of H DL .

[0059] S204. The network side device sends a second pilot signal to the UE in a first downlink slot. The first downlink slot may be before the first uplink slot, or may be after the first uplink slot. The second pilot signal may be a CSI-RS, may be a cell-specific pilot (cell-specific RS, CRS), or the like. This is not specifically limited in this embodiment of this application.

[0060] In a possible implementation, when sending the second pilot signal to the UE, the network side device may first perform precoding weighting on the second pilot signal based on a preset weight matrix V, and then send the weighted second pilot signal to the UE. A quantity of rows of the preset weight matrix is equal to H, and a quantity of columns of the preset weight matrix is equal to a quantity of antenna ports that are included in the UE and that are used to receive data.

[0061] S205. The UE feeds back a PMI to the network side device. The PMI is determined by the UE based on the second pilot signal received by P antenna ports. The P antenna ports include M second antenna ports and at least one first antenna port, or the P antenna ports include the M second antenna ports. P and M are integers greater than 0, and P is greater than or equal to M. The second antenna port may be an antenna port that is not used to send data in the first uplink slot and that is in the antenna ports included in the UE, that is, an antenna port other than the N first antenna ports in the antenna ports included in the UE.

[0062] S206. The network side device determines a second weight matrix V 2 based on the PMI. The second weight V 2 matrix is used to represent downlink channel information corresponding to the P receiving ports.

[0063] In a possible implementation, the network side device may determine the second weight matrix V 2 by multiplying the preset weight matrix by the PMI.

[0064] S207. The network side device determines, based on the first weight matrix V 1 and the second weight matrix V 2 , downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports.

[0065] In this embodiment of this application, the network side device receives, in an uplink slot, a first pilot signal to measure an uplink channel, to obtain the downlink channel information; and sends, in a downlink slot, a second pilot signal to measure a downlink channel, and then obtains all downlink channel information by combining the downlink channel information obtained by using the first pilot signal and the downlink channel information measured by using the second pilot signal. As compared with a manner in the prior art in which the uplink channel information is obtained by continuously sending an SRS in two uplink slots to measure the uplink channel, because a time interval between the adjacent uplink slot and downlink slot is less than a time interval between two adjacent uplink slots, in this embodiment of this application, real-time performance is relatively good when the downlink channel information is obtained, and accuracy of obtaining the downlink channel information can be effectively improved.

[0066] In a possible implementation, after the network side device sends the second pilot signal to the UE in the first downlink slot, the UE may receive the second pilot signal by using the M second antenna ports. In this case, the preset weight matrix V is an H*M-order matrix.

[0067] Based on the foregoing implementation, when determining the PMI, the UE may determine the PMI based on the second pilot signal received by the M second antenna ports.

[0068] Based on the foregoing manner of determining the PMI, when determining the second weight matrix V 2 , the network side device may determine the second weight matrix V 2 by multiplying the H*M order preset weight matrix by the determined PMI. The second weight matrix V 2 may be as follows: V 2 = V × PMI = ν 1 , N + 1 ⋯ ν 1 , N + M ⋯ ⋯ ⋯ ν H , N + 1 ⋯ ν H , N + M ;

[0069] Based on the manner of determining the second weight matrix V 2 , when determining downlink channel information V DL that corresponds to the N first antenna ports and that corresponds to the M second antenna ports, the network side device may implement the determining in a manner of concatenating the first weight matrix V 1 and the second weight matrix V 2 . For example, the first weight matrix V 1 and the second weight matrix V 2 are respectively as follows: V 1 = ν 1 1 ⋯ ν 1 N ⋯ ⋯ ⋯ ν H 1 ⋯ ν H N ; V 2 = ν 1 , N + 1 ⋯ ν 1 , N + M ⋯ ⋯ ⋯ ν H , N + 1 ⋯ ν H , N + M ;

[0070] The downlink channel information V DL that corresponds to the N first antenna ports and that corresponds to the M second antenna ports is as follows: V DL = ν 1 1 ⋯ ν 1 N ν 1 , N + 1 ⋯ ν 1 , N + M ⋯ ⋯ ⋯ ⋯ ⋯ ⋯ ν H 1 ⋯ ν H N ν H , N + 1 ⋯ ν H , N + M .

[0071] In another possible implementation, after the network side device sends the second pilot signal to the UE in the first downlink slot, the UE may further receive the second pilot signal by using the M second antenna ports and the at least one first antenna port. In this case, the preset weight matrix V is an H*(M+x)-order matrix, and x is a quantity of the at least one first antenna port.

[0072] Based on the another implementation, the UE may determine the PMI in the following two manners, but the manners are not limited thereto.

[0073] In a first implementation, the UE determines the PMI based on the second pilot signal received by the M second antenna ports.

[0074] Based on the first implementation, the network side device may determine the second weight matrix V 2 in the following manner. The network side device first determines an M-column matrix in the H*(M+x)-order preset weight matrix, and multiplies the M-column matrix by the determined PMI to determine the second weight matrix V 2 . The M-column matrix may include any M columns of matrix elements in the second weight matrix V 2 . The second weight matrix V 2 may be as follows: V 2 = M columns of matrix in V × PMI .

[0075] Based on the first implementation, when determining the downlink channel information V DL that corresponds to the N first antenna ports and that corresponds to the M second antenna ports, the network side device may implement the determining in a manner of concatenating the first weight matrix V 1 and the second weight matrix V 2 . Herein, a method similar to the foregoing method in which the V 1 and the V 2 are concatenated to obtain the V DL may be used. Details are not described again in this embodiment of this application.

[0076] In a second implementation, the UE may determine the PMI based on the second pilot signal received by the M second antenna ports and the at least one first antenna port.

[0077] Based on the second implementation, when determining the second weight matrix V 2 , the network side device may implement the determining in a manner of multiplying the H*(M+x)-order preset weight matrix by the PMI. The second weight matrix V 2 may be as follows: V 2 = V × PMI = ν 1 , N + 1 ⋯ ν 1 , N + M + x ⋯ ⋯ ⋯ ν H , N + 1 ⋯ ν H , N + M + x .

[0078] Based on the second implementation, the downlink channel information V DL that corresponds to the N first antenna ports and that corresponds to the M second antenna ports may be determined by the network side device in the following manner. The network side device first determines the m-column matrix in the second weight matrix V 2 , and then concatenates the first weight matrix V 1 and the m-column matrix in the second weight matrix V 2 . m is an integer greater than 0 and less than a quantity of columns of the second weight matrix. For example, the first weight matrix V 1 and the second weight matrix V 2 are respectively as follows: V 1 = ν 1 1 ⋯ ν 1 N ⋯ ⋯ ⋯ ν H 1 ⋯ ν H N ; V 2 = ν 1 , N + 1 ⋯ ν 1 , N + M + x ⋯ ⋯ ⋯ ν H , N + 1 ⋯ ν H , N + M + x ;

[0079] The downlink channel information V DL that corresponds to the N first antenna ports and that corresponds to the M second antenna ports is as follows: V DL = V 1 , and m − column matrix in V 2 = ν 1 1 ⋯ ν 1 N ν 1 , N + 1 ⋯ ν 1 , N + m ⋯ ⋯ ⋯ ⋯ ⋯ ⋯ ν H 1 ⋯ ν H N ν H , N + 1 ⋯ ν H , N + m ; the m-column matrix may include any M columns of matrix elements in the second weight matrix V 2 . Alternatively, the m-column matrix may include an m-column matrix element in the second weight matrix V 2 , and a rank of the m-column matrix element is equal to a rank of a third weight matrix V 3 . The third weight matrix V 3 is used to represent the downlink channel information corresponding to the M second antenna ports.

[0080] The network side device may determine the third weight matrix V 3 in the following manner. The UE sends the first pilot signal to the network side device by using the M second antenna ports in a second uplink slot. The second uplink slot may be before the first uplink slot. Then, the network side device determines, based on the received first pilot signal from the M second antenna ports, a downlink channel gain matrix corresponding to the M second antenna ports, and determines, based on the downlink channel gain matrix corresponding to the M second antenna ports, the third weight matrix V 3 corresponding to the M second antenna ports. The network side device may determine the downlink channel gain matrix corresponding to the M second antenna ports by using a method similar to the method for determining the downlink channel gain matrix corresponding to the N first antenna ports. The network side device may also determine the third weight matrix by using a method similar to the method for determining the first weight matrix. Details are not described again in this embodiment of this application.

[0081] Based on the second implementation, when the quantity of the at least one first antenna port is N, that is, when the UE receives the second pilot signal by using the M second antenna ports and the N first antenna ports, and determines the PMI based on the second pilot signal received by using the M second antenna ports and the N first antenna ports, the network side device may further determine the downlink channel information V DL that corresponds to the N first antenna ports and that corresponds to the M second antenna ports in the following manner.

[0082] The network side device concatenates the first weight matrix V 1 and the third weight matrix V 3 to obtain a fourth weight matrix, and adjusts the fourth weight matrix based on the second weight matrix, to obtain the downlink channel information V DL that corresponds to the N first antenna ports and that corresponds to the M second antenna ports. In this manner, the second uplink slot may be before the first uplink slot, or may be after the first uplink slot.

[0083] The network side device may adjust the fourth weight matrix based on the second weight matrix in the following manners, but the manners are not limited thereto.

[0084] Manner 1. The network side device multiplies the second weight matrix V 2 by the fourth weight matrix V 4 . The downlink channel information V DL that corresponds to the N first antenna ports and that corresponds to the M second antenna ports is as follows: V DL = V 2 × V 4 .

[0085] Manner 2. The network side device adjusts a size of a matrix element in the second weight matrix and / or the fourth weight matrix, and then multiplies the adjusted second weight matrix V 2 ' by the adjusted fourth weight matrix V 4 '. The downlink channel information V DL that corresponds to the N first antenna ports and that corresponds to the M second antenna ports is as follows: V DL = V ′ 2 × V ′ 4 .

[0086] To better understand this embodiment of this application, for example, in the MIMO system shown in FIG. 3, the first pilot signal is an SRS, and the second pilot signal is a CIS-RS. The MIMO system includes one 2T4R UE and one network side device. The UE includes four antenna ports 0, which are respectively U 0 to U 3 . The N first antenna ports are U 0 and U 2 , the M second antenna ports are U 1 and U 3 . The network side device includes 64 antenna ports used to receive and send data, and for example, the 64 antenna ports are respectively E 0 to E 63 . The following describes in detail the method for obtaining downlink channel information with reference to a specific application scenario. FIG. 3 is merely a schematic diagram, and does not specifically limit a communications system to which the embodiments of this application are applied.

[0087] FIG. 4 shows a process of obtaining downlink channel information.

[0088] S401. UE sends an SRS to a network side device by using U 0 and U 2 .

[0089] S402. The network side device determines, based on the SRS received from U 0 and U 2 by E 0 to E 63 , an uplink channel gain matrix H UL(0,2) that corresponds to U 0 and that corresponds to U 2 , where H UL(0,2) is as follows: H UL 0 , 2 = h E 0 , U 0 h E 0 , U 2 h E 1 , U 0 h E 1 , U 2 ⋯ ⋯ h E 62 , U 0 h E 62 , U 2 h E 63 , U 0 h E 63 , U 2

[0090] S403. The network side device determines, based on reciprocity between uplink and downlink channels, the downlink channel gain matrix H DL(0,2) that corresponds to U 0 and that corresponds to U 2 , where H DL(0,2) is as follows: H DL 0 , 2 = h E 0 , U 0 h E 1 , U 0 ⋯ h E 62 , U 0 h E 63 , U 0 h E 0 , U 2 h E 1 , U 2 ⋯ h E 62 , U 2 h E 63 , U 2

[0091] S404. The network side device determines, based on H DL(0,2) , a corresponding weight matrix V SRS(0,2) .

[0092] Specifically, the network side device may perform SVD on H DL(0,2) (2*64- order ), and SVD(H DL(0, 2) )=U (0,2) S (0,2) V (0,2) . U (0,2) is a 2*2-order orthogonal matrix of H DL(0, 2) , V (0,2) is a 64*64-order orthogonal matrix of H DL(0,2) , and S (0,2) is a diagonal matrix of H DL(0, 2) . A quantity of non-zero rows in the network side device S (0,2) is a rank of H DL(0, 2) . It is assumed that the rank of H DL(0, 2) is 2, and then first two columns in V (0,2) are used as V SRS(0,2) (64*2-order).

[0093] S405. The network side device sends a CSI-RS to U 1 and U 3 of the UE by using E 0 to E 63 .

[0094] Specifically, the network side device performs precoding weighting on the CSI-RS based on a preset weight matrix V(64*2-order), and sends the weighted CSI-RS to U 1 and U 3 of the UE by using E 0 to E 63 .

[0095] There is no strict sequence between step S405 and step S401. Step S405 may be performed before step S401, or may be performed after step S401. This is not specifically limited in this embodiment of this application.

[0096] S406. The UE feeds back a PMI to the network side device based on the CSI-RS received by U 1 and U 3 .

[0097] S407. The network side device determines a corresponding weight matrix V PMI(1,3) based on the PMI.

[0098] Specifically, the network side device multiplies V(64*2-order) by the PMI that is fed back, to obtain V PMI(1,3) (64*2-order).

[0099] S408. The network side device concatenates V SRS(0,2) and V PMI(1,3) , to obtain downlink channel information V DL corresponding to U 0 to U 3 .

[0100] FIG. 5 shows another process of obtaining downlink channel information.

[0101] For S501 to S504, refer to step S401 to step S404 shown in FIG. 4. Details are not described again in this embodiment of this application.

[0102] S505. The network side device sends the CSI-RS to U 0 to U 3 of the UE by using E 0 to E 63 .

[0103] Specifically, the network side device performs precoding weighting on the CSI-RS based on a preset weight matrix V(64*4-order), and sends the weighted CSI-RS to U 0 to U 3 of the UE by using E 0 to E 63 .

[0104] There is no strict sequence between step S505 and step S501. Step S505 may be performed before step S501, or may be performed after step S501. This is not specifically limited in this embodiment of this application.

[0105] S506. The UE feeds back the PMI to the network side device based on the CSI-RS received by U 0 to U 3 .

[0106] S507. The network side device determines a corresponding weight matrix V PMI based on the PMI.

[0107] Specifically, the network side device multiplies the V(64*4-order) by the PMI that is fed back, to obtain V PMI (64*4-order).

[0108] S508. The network side device determines an m-column matrix V PMI ' in V PMI , and concatenates V PMI ' and V SRS(0,2) to obtain V DL .

[0109] FIG. 6 shows another process of obtaining downlink channel information.

[0110] For S601 to S604, refer to step S401 to step S404 shown in FIG. 4. Details are not described again in this embodiment of this application.

[0111] S605. The UE sends an SRS to the network side device by using U 1 and U 3 .

[0112] There is no strict sequence between step S605 and step S601. Step S605 may be performed before step S601, or may be performed after step S601. This is not specifically limited in this embodiment of this application.

[0113] S606. The network side device determines, based on the SRS received from U 1 and U 3 by E 0 to E 63 , an uplink channel gain matrix H UL(1,3) that corresponds to U 1 and that corresponds to U 3 .

[0114] For details of a method for determining H UL(1,3) by the network side device, refer to step S402 shown in FIG. 4. Details are not described again in this embodiment of this application.

[0115] S607. The network side device determines a downlink channel gain matrix H DL(1,3) that corresponds to U 1 and that corresponds to U 3 , where H DL(1,3) is as follows: H UL 1 , 3 = H DL 1 , 3

[0116] For details of a method for determining H DL(1,3) by the network side device, refer to step S403 shown in FIG. 4. Details are not described again in this embodiment of this application.

[0117] S608. The network side device determines a corresponding weight matrix V SRS(1,3) based on H DL(1,3) .

[0118] For details of a method for determining V SRS(1,3) by the network side device, refer to step S404 shown in FIG. 4. Details are not described again in this embodiment of this application.

[0119] For S609 to S611, refer to step S505 to step S507 shown in FIG. 5. Details are not described again in this embodiment of this application.

[0120] S612. The network side device determines V DL in any one of the following manners based on V SRS(0,2) , V SRS(1,3) , and V PMI .

[0121] Manner 1. The network side device concatenates V SRS(0,2) and V SRS(1,3) to obtain V SRS ', and multiplies V SRS ' by V PMI to obtain V DL .

[0122] Manner 2. The network side device concatenates V SRS(0,2) and V SRS(1,3) to obtain V SRS ', adjusts a size of a matrix element in V SRS ', and multiplies the adjusted V SRS ' by V PMI to obtain V DL .

[0123] Manner 3. The network side device concatenates V SRS(0,2) and V SRS(1,3) to obtain V SRS ', adjusts a size of a matrix element in V PMI , and multiplies V SRS ' by the adjusted V PMI to obtain V DL .

[0124] Manner 4. The network side device concatenates V SRS(0,2) and V SRS(1,3) to obtain V SRS ', adjusts a size of a matrix element in V SRS ' and a size of a matrix element in V PMI , and multiplies the adjusted V SRS ' by the adjusted V PMI to obtain V DL .

[0125] Manner 5. When step S605 is performed before step S601, the network side device may further determine an m-column matrix in V PMI , where a rank of the m-column matrix is equal to a rank of V SRS(1,3) .

[0126] Based on a same inventive concept as the method embodiments, an embodiment of this application provides an apparatus for obtaining downlink channel information, and the apparatus is specifically configured to implement the methods described in the embodiments in FIG. 2 to FIG. 6. The apparatus may be applied to a network side device. A structure of the apparatus is shown in FIG. 7, and the apparatus includes: a receiving module 701, a determining module 702, and a sending module 703. The receiving module 701 is configured to receive a first pilot signal sent by user equipment by using N first antenna ports. The determining module 702 is configured to: determine, based on the first pilot signal received by the receiving module 701, a downlink channel gain matrix corresponding to the N first antenna ports, where N is an integer greater than 0, and determine, based on the downlink channel gain matrix corresponding to the N first antenna ports, a first weight matrix corresponding to the N first antenna ports. The first weight matrix is used to represent downlink channel information corresponding to the N first antenna ports. The sending module 703 is configured to send a second pilot signal to the user equipment. The receiving module 701 is further configured to receive a precoding matrix indicator PMI fed back by the user equipment, where the PMI is determined by the user equipment based on a second pilot signal received by using P antenna ports. The P antenna ports include M second antenna ports and at least one first antenna port, or the P antenna ports include M second antenna ports. The determining module 702 is further configured to: determine a second weight matrix based on the PMI received by the receiving module 701, where the second weight matrix is used to represent downlink channel information corresponding to the P receiving ports; and determine, based on the first weight matrix and the second weight matrix, downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports.

[0127] If the PMI is determined by the user equipment based on the second pilot signal received by using the M second antenna ports, when determining, based on the first weight matrix and the second weight matrix, the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports, the determining module 702 is specifically configured to concatenate the first weight matrix and the second weight matrix, to obtain the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports.

[0128] If the PMI is determined by the user equipment based on the second pilot signal received by using the M second antenna ports and the at least one first antenna port, when determining, based on the first weight matrix and the second weight matrix, the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports, the determining module 702 is specifically configured to: determine an m-column matrix in the second weight matrix, and concatenate the first weight matrix and the m-column matrix in the second weight matrix, to obtain the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports, where m is an integer greater than 0 and less than a quantity of columns of the second weight matrix.

[0129] Before the receiving a first pilot signal sent by user equipment by using N first antenna ports, the receiving module 701 may be further configured to receive the first pilot signal sent by the user equipment by using the M second antenna ports. The determining module 702 may be further configured to: determine, based on the first pilot signal received by the receiving module 701, a downlink channel gain matrix corresponding to the M second antenna ports, and determine, based on the downlink channel gain matrix corresponding to the M second antenna ports, a third weight matrix corresponding to the M second antenna ports. The third weight matrix is used to represent the downlink channel information corresponding to the M second antenna ports. When determining the m-column matrix in the second weight matrix, the determining module 702 may specifically be configured to determine the m-column matrix in the second weight matrix, where a rank of the m-column matrix is equal to a rank of the third weight matrix.

[0130] If the PMI is determined by the user equipment based on the second pilot signal received by using the M second antenna ports and the N first antenna ports, after the receiving a first pilot signal sent by user equipment by using N first antenna ports, the receiving module 701 may be further configured to receive the first pilot signal sent by the user equipment by using the M second antenna ports. The determining module 702 may be further configured to: determine, based on the first pilot signal received by the receiving module 701, a downlink channel gain matrix corresponding to the M second antenna ports, and determine, based on the downlink channel gain matrix corresponding to the M second antenna ports, a fourth weight matrix corresponding to the M second antenna ports. The fourth weight matrix is used to represent the downlink channel information corresponding to the M second antenna ports. When determining, based on the first weight matrix and the second weight matrix, the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports, the determining module 702 may specifically be configured to: concatenate the first weight matrix and the fourth weight matrix to obtain a fifth weight matrix, and adjust the fifth weight matrix based on the second weight matrix, to obtain the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports.

[0131] In a possible implementation, when adjusting the fifth weight matrix based on the second weight matrix, the determining module 702 may specifically be configured to multiply the second weight matrix by the fifth weight matrix.

[0132] In a possible implementation, when adjusting the fifth weight matrix based on the second weight matrix, the determining module 702 may specifically be configured to: adjust a size of a matrix element in the second weight matrix and / or the fifth weight matrix and multiply the adjusted second weight matrix by the adjusted fifth weight matrix.

[0133] When determining, based on the downlink channel gain matrix corresponding to the N first antenna ports, the first weight matrix corresponding to the N first antenna ports, the determining module 702 may specifically be configured to: determine an H*H-order orthogonal matrix of the downlink channel gain matrix corresponding to the N first antenna ports, and a rank of the downlink channel gain matrix corresponding to the N first antenna ports. H is a quantity of receiving ports of the network side device. Then the determining module 702 determines first n columns of the H*H-order orthogonal matrix as the first weight matrix. n is equal to the rank of the downlink channel gain matrix corresponding to the N first antenna ports.

[0134] The apparatus further includes an encoding module 704, configured to perform precoding weighting on the second pilot signal based on a preset weight matrix. When sending the second pilot signal to the user equipment, the sending module 703 may specifically be configured to send the weighted second pilot signal to the user equipment. When determining the second weight matrix based on the PMI, the determining module 702 is specifically configured to multiply the preset weight matrix by the PMI to obtain the second weight matrix.

[0135] Division of the modules in the embodiments of this application is only an example, and is merely logical function division. There may be other division manners during actual implementation. In addition, the functional modules in the embodiments of this application may be integrated into one processor, or each of the modules may exist alone physically, or two or more modules may be integrated into one module. The integrated module may be implemented in a form of hardware, or may be implemented in a form of a software functional module.

[0136] When the integrated module may be implemented in a form of hardware, as shown in FIG. 8, the apparatus for obtaining downlink channel information may include a processor 802. The hardware of the entity corresponding to the module may be the processor 802. The processor 802 may be a central processing unit (English: central processing unit, CPU for short), a digital processing module, or the like. The apparatus for obtaining downlink channel information may further include a communications interface 801, and the processor 802 receives and sends data by using the communications interface 801. The apparatus further includes a memory 803, configured to store a program executed by the processor 802. The memory 803 may be a non-volatile memory such as a hard disk (English: hard disk drive, HDD for short) or a solid-state drive (English: solid-state drive, SSD for short), or may be a volatile memory (English: volatile memory), for example, a random-access memory (English: random-access memory, RAM for short). The memory 803 is any other medium that can be configured to carry or store expected program code in a form of an instruction or a data structure and that can be accessed by a computer, but is not limited thereto.

[0137] The processor 802 is configured to execute the program code stored in the memory 803, and is specifically configured to perform the method described in the embodiment shown in FIG. 2 or FIG. 6. Reference may be made to the method described in the embodiment shown in FIG. 2 or FIG. 6, and details are not described herein again in this application.

[0138] A specific connection medium among the communications interface 801, the processor 802, and the memory 803 is not limited in the embodiments of this application. In the embodiments of this application, in FIG. 8, the memory 803, the processor 802, and the communications interface 801 are connected to each other by using a bus 804. The bus is represented by using a bold line in FIG. 8. A manner of connection between other components is only for schematic description, but is not used as a limitation. The bus may be classified into an address bus, a data bus, a control bus, or the like. For ease of representation, only one thick line is used to represent the bus in FIG. 8, but this does not mean that there is only one bus or only one type of bus.

[0139] An embodiment of this application further provides a computer-readable storage medium, configured to store a computer software instruction that needs to be executed for execution of the foregoing processor, and the computer software instruction includes a program that needs to be executed for execution of the foregoing processor.

[0140] An embodiment of the present invention further provides a chip. The chip includes the foregoing communications interface and the foregoing processor, and is configured to support a network side device in implementing any one of the methods described in the embodiments shown in FIG. 2 to FIG. 6.

[0141] A person skilled in the art should understand that the embodiments of this application may be provided as a method, a system, or a computer program product. Therefore, this application may use a form of hardware only embodiments, software only embodiments, or embodiments with a combination of software and hardware. Moreover, this application may use a form of a computer program product that is implemented on one or more computer-usable storage media (including but not limited to a disk memory, a CD-ROM, an optical memory, and the like) that include computer usable program code.

[0142] This application is described with reference to the flowcharts and / or block diagrams of the method, the device (system), and the computer program product according to this application. It should be understood that computer program instructions may be used to implement each process and / or each block in the flowcharts and / or the block diagrams and a combination of a process and / or a block in the flowcharts and / or the block diagrams. These computer program instructions may be provided for a general-purpose computer, a dedicated computer, an embedded processor, or a processor of any other programmable data processing device to generate a machine, so that the instructions executed by a computer or a processor of any other programmable data processing device generate an apparatus for implementing a specific function in one or more processes in the flowcharts and / or in one or more blocks in the block diagrams.

[0143] These computer program instructions may be stored in a computer-readable memory that can instruct the computer or any other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory generate an artifact that includes an instruction apparatus. The instruction apparatus implements a specific function in one or more processes in the flowcharts and / or in one or more blocks in the block diagrams.

[0144] These computer program instructions may be loaded onto a computer or another programmable data processing device, so that a series of operations and steps are performed on the computer or the another programmable device, thereby generating computer-implemented processing. Therefore, the instructions executed on the computer or the another programmable device provide steps for implementing a specific function in one or more processes in the flowcharts and / or in one or more blocks in the block diagrams.

[0145] Obviously, a person skilled in the art can make various modifications and variations to this application without departing from the scope of this application. This application is intended to cover these modifications and variations of this application provided that they fall within the scope of protection defined by the following claims.

Claims

1. A method for obtaining downlink channel information, comprising: receiving (S201), by a network side device, a first pilot signal sent by user equipment by using N first antenna ports, and determining, based on the received first pilot signal, a downlink channel gain matrix corresponding to the N first antenna ports, wherein N is an integer greater than 0; determining (S202, S203), by the network side device based on the downlink channel gain matrix corresponding to the N first antenna ports, a first weight matrix corresponding to the N first antenna ports, wherein the first weight matrix is used to represent downlink channel information corresponding to the N first antenna ports; sending (S204), by the network side device, a second pilot signal to the user equipment; receiving (S205) a precoding matrix indicator, PMI, fed back by the user equipment, wherein the PMI is determined by the user equipment based on the second pilot signal received by using P antenna ports, wherein the PMI is determined by the user equipment based on the second pilot signal received by using the M second antenna ports and the at least one first antenna port; and the P antenna ports comprise M second antenna ports and at least one first antenna port; determining (S206), by the network side device, a second weight matrix based on the PMI, wherein the second weight matrix is used to represent downlink channel information corresponding to P receiving ports; and determining (S207), by the network side device based on the first weight matrix and the second weight matrix, downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports, wherein the determining (207), by the network side device based on the first weight matrix and the second weight matrix, downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports comprises: determining, by the network side device, an m-column matrix in the second weight matrix, and concatenating the first weight matrix and the m-column matrix in the second weight matrix, to obtain the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports, wherein m is an integer greater than 0 and less than a quantity of columns of the second weight matrix.

2. The method according to claim 1, wherein before the receiving (S201), by a network side device, a first pilot signal sent by user equipment by using N first antenna ports, the method further comprises: receiving, by the network side device, the first pilot signal sent by the user equipment by using the M second antenna ports, and determining, based on the received first pilot signal, a downlink channel gain matrix corresponding to the M second antenna ports; and determining, by the network side device based on the downlink channel gain matrix corresponding to the M second antenna ports, a third weight matrix corresponding to the M second antenna ports, wherein the third weight matrix is used to represent the downlink channel information corresponding to the M second antenna ports; and the determining, by the network side device, an m-column matrix in the second weight matrix comprises: determining, by the network side device, the m-column matrix in the second weight matrix based on the third weight matrix, wherein a rank of the m-column matrix is equal to a rank of the third weight matrix.

3. The method according to any one of claims 1 to 2, wherein the determining (S202), by the network side device based on the downlink channel gain matrix corresponding to the N first antenna ports, a first weight matrix corresponding to the N first antenna ports comprises: determining, by the network side device, an H*H-order orthogonal matrix of the downlink channel gain matrix corresponding to the N first antenna ports, and a rank of the downlink channel gain matrix corresponding to the N first antenna ports, wherein H is a quantity of receiving ports of the network side device; and determining, by the network side device, first n columns of the H*H-order orthogonal matrix as the first weight matrix, wherein n is equal to the rank of the downlink channel gain matrix corresponding to the N first antenna ports.

4. The method according to any one of claims 1 to 3, wherein the sending (S204), by the network side device, a second pilot signal to the user equipment comprises: performing, by the network side device, precoding weighting on the second pilot signal based on a preset weight matrix; and sending, by the network side device, the weighted second pilot signal to the user equipment; and the determining, by the network side device, a second weight matrix based on the PMI comprises: multiplying, by the network side device, the preset weight matrix by the PMI to obtain the second weight matrix.

5. An apparatus (70) for obtaining downlink channel information, comprising: a receiving module (701), configured to receive a first pilot signal sent by user equipment by using N first antenna ports, wherein N is an integer greater than 0; a determining module (702), configured to: determine, based on the first pilot signal received by the transceiver, a downlink channel gain matrix corresponding to the N first antenna ports; and determine, based on the downlink channel gain matrix corresponding to the N first antenna ports, a first weight matrix corresponding to the N first antenna ports, wherein the first weight matrix is used to represent downlink channel information corresponding to the N first antenna ports; a sending module (703), configured to: send a second pilot signal to the user equipment, and receive a precoding matrix indicator, PMI, fed back by the user equipment, wherein the PMI is determined by the user equipment based on the second pilot signal received by using P antenna ports, wherein the PMI is determined by the user equipment based on the second pilot signal received by using the M second antenna ports and the at least one first antenna port; and the P antenna ports comprise M second antenna ports and at least one first antenna port; and the determining module (702) is further configured to: determine a second weight matrix based on the PMI received by the transceiver, wherein the second weight matrix is used to represent downlink channel information corresponding to the P receiving ports; and determine, based on the first weight matrix and the second weight matrix, downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports, wherein when determining, based on the first weight matrix and the second weight matrix, the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports, the determining module (702) is specifically configured to: determine an m-column matrix in the second weight matrix, and concatenate the first weight matrix and the m-column matrix in the second weight matrix, to obtain the downlink channel information that corresponds to the N first antenna ports and that corresponds to the M second antenna ports, wherein m is an integer greater than 0 and less than a quantity of columns of the second weight matrix.

6. The apparatus (70) of claim 5, wherein before the receiving a first pilot signal sent by user equipment by using N first antenna ports, the receiving module (701) is further configured to: receive the first pilot signal sent by the user equipment by using the M second antenna ports; and the determining module (702) is further configured to: determine, based on the first pilot signal received by the transceiver, a downlink channel gain matrix corresponding to the M second antenna ports; and determine, based on the downlink channel gain matrix corresponding to the M second antenna ports, a third weight matrix corresponding to the M second antenna ports, wherein the third weight matrix is used to represent the downlink channel information corresponding to the M second antenna ports; and when determining the m-column matrix in the second weight matrix, the determining module (702) is specifically configured to: determine the m-column matrix in the second weight matrix based on the third weight matrix, wherein a rank of the m-column matrix is equal to a rank of the third weight matrix.

7. The apparatus (70) according to any one of claims 5 to 6, wherein when determining, based on the downlink channel gain matrix corresponding to the N first antenna ports, the first weight matrix corresponding to the N first antenna ports, the determining module (702) is specifically configured to: determine an H*H-order orthogonal matrix of the downlink channel gain matrix corresponding to the N first antenna ports, and a rank of the downlink channel gain matrix corresponding to the N first antenna ports, wherein H is a quantity of receiving ports of the network side device; and determine first n columns of the H*H-order orthogonal matrix as the first weight matrix, wherein n is equal to the rank of the downlink channel gain matrix corresponding to the N first antenna ports.

8. The apparatus (70) according to any one of claims 5 to 7, further comprising an encoding module (704), configured to perform precoding weighting on the second pilot signal based on a preset weight matrix; when sending the second pilot signal to the user equipment, the sending module (703) is specifically configured to send the weighted second pilot signal to the user equipment; and when determining the second weight matrix based on the PMI, the determining module (702) is specifically configured to multiply the preset weight matrix by the PMI to obtain the second weight matrix.

9. A computer-readable storage medium, wherein the computer-readable storage medium stores a program, and when the program is read and executed by one or more processors, the method according to any one of claims 1 to 4 can be implemented.