CN106330273B - Precoding method and device - Google Patents

Precoding method and device Download PDF

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CN106330273B
CN106330273B CN201510388477.6A CN201510388477A CN106330273B CN 106330273 B CN106330273 B CN 106330273B CN 201510388477 A CN201510388477 A CN 201510388477A CN 106330273 B CN106330273 B CN 106330273B
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codebook
terminal
codebook vector
channel
base station
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CN106330273A (en
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任余维
苏昕
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China Academy of Telecommunications Technology CATT
Datang Mobile Communications Equipment Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0452—Multi-user MIMO systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting

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Abstract

The invention discloses a precoding method and a device, comprising the following steps: outputting an approximate channel h at the terminal; evaluating each codebook vector in a codebook according to the approximate channel h, wherein the codebook is a codebook known by the base station and the terminal; and feeding back the codebook vector to the base station according to the evaluation result. A base station side receives a codebook vector fed back by a terminal, wherein the codebook vector is obtained by the terminal after evaluating the codebook vector in a codebook according to an approximate channel h; and forming an analog pre-coding matrix according to the codebook vector, and obtaining an equivalent channel according to the analog pre-coding matrix. By adopting the invention, the terminal can dynamically adjust the number of the feedback codebook vectors, can adapt to base stations with different numbers of digital channels and fully utilizes all digital channel resources; and the precision of analog and digital precoding in the analog-digital two-stage precoding processing process can be improved, and the channel feedback overhead is reduced.

Description

Precoding method and device
Technical Field
The present invention relates to the field of wireless communication technologies, and in particular, to a precoding method and apparatus.
Background
In order to reduce the implementation cost and the device complexity of the Massive MIMO technology, and reduce the transmission rate requirement caused by a large number of transceivers and the resource overhead caused by a large number of CSI-RS (channel state information reference signals), a digital-analog hybrid precoding technology has been proposed in recent years.
Fig. 1 is a schematic diagram of a Digital-Analog hybrid precoding structure, and as shown in the figure, the Digital-Analog hybrid precoding refers to adding a first-stage Analog precoding a on an rf signal of an ABF (Analog Beam Forming) near the front end of an antenna system on the basis of a Digital domain precoding D of a conventional DBF (Digital Beam Forming). Analog precoding enables a coarser matching of the transmitted signal with the channel to be achieved in a simpler manner. The dimension of the equivalent channel formed after the Analog pre-coding is smaller than the actual number of antennas, so that the AD/DA (A: Analog; D: Digital) conversion device, the number of Digital channels and the corresponding baseband processing complexity required thereafter can be greatly reduced. The residual interference of the analog precoding part can be processed once again in the digital domain, thereby ensuring the quality of MU-MIMO (multiple users-MIMO, multi-user MIMO) transmission.
Compared with full-digital precoding, digital-analog hybrid precoding is a compromise scheme of performance and complexity, and has a high practical prospect in a system with a high frequency band and a large bandwidth or a large number of antennas.
In the prior art, the digital-analog hybrid precoding at least has the following disadvantages: in the scheme adopted in practice, the precision of precoding in the analog domain is limited, and if the precision needs to be improved, the cost of precoding feedback resources in the analog domain is high.
Disclosure of Invention
The invention provides a precoding method and a precoding device, which are used for reducing channel feedback overhead when the precision of analog and digital precoding is ensured in the process of digital-analog mixed precoding.
The embodiment of the invention provides a precoding method, which comprises the following steps:
outputting an approximate channel h at the terminal;
evaluating a codebook vector in a codebook according to the approximate channel h, wherein the codebook is a codebook known by the base station and the terminal;
and feeding back the codebook vector to the base station according to the evaluation result.
Preferably, the approximate channel h is determined based on a Los path angle, or determined based on a downlink codebook measurement manner.
Preferably, the evaluation of the codebook vectors in the codebook is based on an SNR criterion or an SINR criterion.
Preferably, the terminal feeds back a codebook vector having a maximum SNR value or SINR value to the base station.
Preferably, further comprising: when feeding back codebook vectors to the base station, the SNR values or SINR values corresponding to these vectors are fed back.
Preferably, M codebook vectors are fed back when feeding back codebook vectors to the base station, where M is the number of digital channels.
The embodiment of the invention provides a precoding method, which comprises the following steps:
receiving a codebook vector fed back by a terminal, wherein the codebook vector is obtained by the terminal after evaluating the codebook vector in a codebook according to an approximate channel h;
forming a simulation pre-coding matrix according to the codebook vector;
and obtaining an equivalent channel according to the analog precoding matrix.
Preferably, the outputting an analog precoding matrix according to the codebook vector includes:
after receiving a codebook vector fed back by a terminal, determining the number of times that the codebook vector is fed back by the terminal;
and selecting the first M codebook vectors with the most times to form an analog precoding matrix, wherein M is the number of digital channels.
Preferably, further comprising: and when the receiving terminal feeds back the codebook vector to the base station, receiving the SNR value or the SINR value corresponding to the codebook vector.
Preferably, after receiving the codebook vector fed back to the base station by the terminal and the SNR value or SINR value corresponding to the codebook vector, the capacity of the codebook vector is determined according to the number of SNR values or SINR values corresponding to the codebook vector, and the first M codebook vectors with the largest capacity are selected as the analog precoding matrix, where M is the number of digital channels.
Preferably, obtaining the equivalent channel according to the analog precoding matrix includes:
acquiring an approximate channel h of each terminal and forming the approximate channel h;
and obtaining an equivalent channel according to the analog precoding matrix and the approximate channel h.
An embodiment of the present invention provides a precoding apparatus, including:
a channel module for outputting an approximate channel h at a terminal;
the evaluation module is used for evaluating a codebook vector in a codebook according to the approximate channel h, wherein the codebook is a codebook known by the base station and the terminal;
and the feedback module is used for feeding back the codebook vector to the base station according to the evaluation result.
Preferably, the channel module is further configured to determine an approximate channel h based on the Los path angle, or determine the approximate channel h based on a downlink codebook measurement manner.
Preferably, the evaluation module is further configured to evaluate the codebook vectors in the codebook based on SNR criterion or SINR criterion.
Preferably, the feedback module is further configured to feed back the codebook vector having the largest SNR value or SINR value to the base station.
Preferably, the feedback module is further configured to feed back an SNR value or an SINR value corresponding to the codebook vector when feeding back the codebook vector to the base station.
Preferably, the feedback module is further configured to feed back M codebook vectors when feeding back codebook vectors to the base station, where M is the number of digital channels.
An embodiment of the present invention provides a precoding apparatus, including:
the receiving module is used for receiving a codebook vector fed back by the terminal, wherein the codebook vector is obtained by the terminal after evaluating the codebook vector in the codebook according to the approximate channel h;
the analog pre-coding matrix module is used for forming an analog pre-coding matrix according to the codebook vector;
and the equivalent channel module is used for obtaining an equivalent channel according to the analog precoding matrix.
Preferably, the analog precoding matrix module is further configured to determine, after receiving a codebook vector fed back by the terminal, the number of times that the codebook vector is fed back by the terminal, and select the first M codebook vectors with the largest number of times to form an analog precoding matrix, where M is the number of digital channels.
Preferably, the receiving module is further configured to receive an SNR value or an SINR value corresponding to the codebook vector when the receiving terminal feeds back the codebook vector to the base station.
Preferably, the analog precoding matrix module is further configured to, after receiving the codebook vector fed back to the base station by the terminal and the SNR value or SINR value corresponding to the codebook vector, determine the capacity of the codebook vector according to the SNR value or SINR value number corresponding to the codebook vector, and select the first M codebook vectors with the largest capacity as the analog precoding matrix, where M is the number of digital channels.
Preferably, the equivalent channel module is further configured to obtain an approximate channel h of each terminal when obtaining the equivalent channel according to the analog precoding matrix, and form the approximate channel h; and obtaining an equivalent channel according to the analog precoding matrix and the approximate channel h.
The invention has the following beneficial effects:
in the existing scheme, a codebook vector of each angle direction is evaluated by a method of analog domain based on space angle search, and a terminal feeds back evaluation information. For 3D-MIMO systems, the 3D space searched is very large, requiring 0-90 degrees in the vertical dimension and 0-180 degrees in the horizontal dimension. The feedback resource overhead and delay introduced by small steps is very large if to achieve an accurate search. For example, in a horizontal dimension range of 0-180 degree search, if the step size is 1 degree, 180 feedbacks are required, and then the codebook vector of each user can be accurate to 1 degree.
In the technical scheme provided by the embodiment of the invention, the terminal determines the codebook vector as the final analog domain precoding and directly provides the codebook vector to the base station; the base station determines an analog precoding matrix according to the information and acquires an equivalent channel. Since the terminal and the base station share the same codebook, the terminal evaluates all codebook vectors based on the approximate channel h. If the codebook of the terminal contains 180 codebook vectors, it is possible to cover the horizontal dimension of 0-180 degrees at intervals of 1 degree. Although the approximate channel h evaluation codebook may not ensure that the codebook vector is accurate to 1 degree, the terminal codebook evaluation mode and the base station terminal determination simulation precoding mode provided by the scheme can reduce the interference between codebooks as a whole and make up for the deficiency of accuracy. After all evaluations are completed, only 1 evaluation result needs to be fed back, that is, under the condition that the accuracy of the scheme is approximately equivalent to that of the existing scheme due to the reduction of interference among codebooks, compared with the existing scheme which needs to be fed back for multiple times, the feedback overhead and delay are greatly reduced. Meanwhile, the terminal adopting the technical scheme provided by the embodiment of the invention can dynamically adjust the number of the feedback analog codebook vectors, so that the terminal can adapt to the number of digital channels of different base station terminals and fully utilize all different digital channel resources.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is a diagram illustrating a digital-analog hybrid precoding structure in the prior art;
FIG. 2 is a schematic diagram of a flow chart of implementing a precoding algorithm of a finite feedback modulus architecture in an embodiment of the present invention;
fig. 3 is a schematic flowchart of an implementation of a terminal-side precoding method in an embodiment of the present invention;
FIG. 4 is a schematic flowchart of an embodiment of a method for precoding at a base station side;
FIG. 5 is a schematic structural diagram of a terminal-side precoding apparatus according to an embodiment of the present invention;
FIG. 6 is a schematic structural diagram of a base station side precoding apparatus according to an embodiment of the present invention;
fig. 7 is a schematic structural diagram of a terminal according to an embodiment of the present invention;
fig. 8 is a schematic diagram of a base station structure according to an embodiment of the present invention.
Detailed Description
The following describes embodiments of the present invention with reference to the drawings.
The inventor notices in the process of invention that:
in view of the important role of MIMO (Multiple Input Multiple Output) technology in increasing peak rate and system spectrum utilization, wireless access technology standards such as LTE (Long Term Evolution)/LTE-a (LTE-Advanced, Long Term Evolution upgrade) are constructed based on MIMO + OFDM (Orthogonal frequency division Multiplexing) technology. The performance gain of the MIMO technology comes from the space freedom degree that can be obtained by the multi-antenna system, so that one of the most important evolution directions of the MIMO technology in the standardization development process is the extension of dimension.
In order to further improve the MIMO technology, a massive antenna technology (MassiveMIMO) is introduced into the mobile communication system. Academic research and preliminary channel actual measurement results show that the Massive MIMO technology can greatly improve the utilization efficiency of the system frequency band and support a larger number of access users. Therefore, Massive MIMO technology is considered by various organizations as one of the most potential physical layer technologies in the next generation of 5G mobile communication systems.
If the Massive MIMO base station System adopts a conventional PAS (Passive Antenna System) Antenna structure, in this structure, a plurality of Antenna ports (each port corresponds to an independent rf-if-baseband channel) are horizontally arranged, and a plurality of vertical-dimension arrays corresponding to each port are connected by rf cables. At this time, the optimization of the spatial characteristics of each terminal signal in the horizontal dimension can be realized only in the horizontal dimension by adjusting the relative amplitude/phase between different ports, and only uniform sector-level precoding can be adopted in the vertical dimension. Thus, the vertical spatial resolution of the system is severely limited, which in turn restricts the overall performance enhancement of the system. Therefore, the PAS structure is not suitable for future Massive MIMO systems.
If an AAS (Active Antenna System) technology is introduced into a mobile communication System, the base station Antenna System can obtain a greater degree of freedom in the vertical dimension, and can optimize signals at the UE (user equipment) level in a three-dimensional space. Although maximum spatial resolution and optimal MU-MIMO performance can be achieved with AAS techniques, this architecture requires a large number of AD/DA converters and a large number of complete rf-baseband processing channels, which would be a huge burden both on the cost of the device and on the complexity of the baseband processing. The problem is particularly obvious in high frequency band and large bandwidth. In addition, the AAS structure corresponds to more reference signal ports on the premise of the same antenna array sub-number as compared with the PAS structure. Considering that the spatial resolution of the channel state information directly depends on the number of the ports, if the channel information of each antenna port is obtained, the AAS structure needs more CSI-RS, and at this time, a large amount of time-frequency resources are consumed. These are all challenges for the application of AAS technology.
In order to reduce the implementation cost and the device complexity of the Massive MIMO technology, and reduce the transmission rate requirement caused by a large number of transceivers and the resource overhead caused by a large number of CSI-RSs (channel state information reference signals), a digital-analog hybrid precoding technology that has been adopted in recent years is adopted. Compared with full-digital precoding, digital-analog hybrid precoding is a compromise scheme of performance and complexity, and has a high practical prospect in a system with a high frequency band and a large bandwidth or a large number of antennas. In the MIMO technology, especially for the MU-MIMO technology, the accuracy of the channel state information that can be obtained by the network side will directly determine the precoding/precoding accuracy and the efficiency of the scheduling algorithm, thereby affecting the overall system performance. Therefore, the acquisition of channel state information has been one of the most central problems in the standardization of MIMO technology.
The difficulty of channel state information and precoding in the hybrid architecture is that according to the current LTE signal structure, all the used reference signals are inserted in the baseband, so that the channel state required for digital precoding can be obtained through channel estimation. In the hybrid architecture, due to the processing of front-end analog precoding, the number of formed equivalent digital channels is less than the number of actual antennas, and the dimensionality of a channel matrix obtained through a reference signal is far lower than the dimensionality of a complete channel matrix experienced by an antenna end. Therefore, the spatial resolution achievable by digital precoding is limited by the dimension of the number of digital channels, and the interference suppression capability suffers a certain loss compared to the dimension of the complete channel matrix. In addition, for the analog precoding part, the processing procedure is closer to the physical antenna side, and compared with the digital precoding, the MIMO channel has higher degree of freedom. However, since there is no way to estimate the reference signal with the baseband inserted into the matching dimension, the analog precoding part cannot directly acquire the complete channel state information no matter FDD (Frequency Division Duplex) or TDD (Time Division Duplex).
Based on the above analysis of hybrid architectures and the corresponding difficulties, there are some feasible solutions at the present stage. The main idea is as follows: the first step is to realize the digital domain precoding, and the second step is to realize the analog domain precoding. In the first step, the initialization of the analog domain is fixed (e.g. the analog weight of the previous period is used, or the fixed angle weight is used, etc.), and since the dimension of the digital domain is low, the reference signal of the baseband can realize the accurate estimation of the channel at that time, and the digital domain precoding is performed based on the accurately estimated channel. And in the second step, the digital domain precoding is determined, the weight of the analog domain is searched in the range of vertical dimension and horizontal dimension angles based on a fixed step length, the terminal feeds back the result of each search, and finally the optimal analog domain precoding vector is selected.
However, this method has the following disadvantages: firstly, the analog domain is searched based on a certain step length, the precision of the analog domain is limited if the step length is large, and the feedback resource consumption is large if the step length is small. Second, there may be differences in the analog forming methods used for the digital domain measurement reference signal and the demodulation reference signal. For example, the reference signal for digital domain measurement is analog shaped according to an initialized fixed weight (for example, a certain fixed downward inclination angle is adopted), and the reference signal for demodulation in the final service data is the weight after the second step of analog shaping. This difference can cause inaccuracy in channel quality measurement, thereby affecting the performance of multi-user scheduling, resource allocation and link adaptation. In addition, the channel estimation required in the digital domain also causes a certain resource consumption.
Based on this, the embodiments of the present invention provide a terminal side and a base station side precoding method, and first the implementation of the terminal side is described according to the implementation sequence of the two-stage precoding, then the implementation of the base station side is described, and then the two-stage implementation is described as a whole. In the description process, the implementation description from the terminal and the base station side respectively does not mean that the terminal and the base station are necessarily implemented in cooperation, and actually, when the terminal and the base station are implemented separately, the problems at the terminal side and the base station side are solved respectively, and only when the terminal and the base station are used in combination, a better technical effect is obtained.
In the following, the terminal and the base station will be described separately, and in the description, the number of users is K, the number of digital channels is M, and the number of antenna arrays is Ntx, unless otherwise specified.
Fig. 2 is a schematic flowchart of an implementation of a precoding method at a terminal side, as shown in the figure, the implementation may include:
step 201, outputting an approximate channel h on a terminal;
step 202, evaluating a codebook vector in a codebook according to an approximate channel h, wherein the codebook is a codebook known by a base station and a terminal;
and step 203, feeding back the codebook vector to the base station according to the evaluation result.
In an implementation, the approximate channel h is determined based on a Los path angle, or determined based on a downlink codebook measurement mode.
The specific implementation of the approximate channel h acquisition method in step 201 may be as follows:
1. the LOS path (near LOS path) is directly used to obtain the approximate channel h.
Before system precoding and channel estimation, the azimuth information of each terminal can be roughly determined by some reference signals between the base station and the terminal, so that the vertical angle theta of the approximate Los path can be obtainedkAnd horizontal angle
Figure BDA0000752280180000091
An approximate channel h can be obtained by utilizing the existing Los path channel model.
For example, for user k, the approximate channel of user k is defined as hkIf the channel model of Saleh-Valebzuela is considered, the Los path propagation angle of user k is known
Figure BDA0000752280180000092
The approximate channel h of the user k can be obtained based on the Los path channel structurek：
Where m is 0. ltoreq. W, n is 0. ltoreq. H, W and H are dimensions in the horizontal direction and the vertical direction, respectively, Ntx is the total number of antennas, and Ntx is WH.
2. Based on the downlink measurement.
The system presets a common codebook corresponding to a set of codebook vectors. The specific configuration of the codebook and the numbering of the beams are known to the base station and the terminal prior to communication.
The base station analog domain transmits codebook vectors in a codebook to all users one by one (such as time division, frequency division or other modes which can enable the terminal to distinguish), y received by user kk,iCan be expressed as:
yk,i＝hkvi+nk
where v isiRepresentative i codebook vectors, one selected from the i codebook vectors and hkBest matching one codebook vector:
Figure BDA0000752280180000094
at this time, it can be approximately considered
Figure BDA0000752280180000095
Thereby obtaining an approximate channel hk。
In the implementation of step 202, the evaluation of the codebook vectors in the codebook according to the approximate channel h may be based on SNR criterion or SINR criterion.
In specific implementation, the terminal may adopt any of the following schemes in a manner of evaluating a codebook vector in a codebook according to a channel h:
1. codebook evaluation based on SNR criterion (energy criterion).
The base station and all terminals share the same codebook, and the specific composition of the codebook and the numbering mode of the beams are known by the base station and the terminals before communication.
Calculating SNR corresponding to each codebook vector under the condition that the power is the same for all codebooksk,i＝ρ|hkvi|2Where p represents a normalization factor for noise and power.
2. Codebook evaluation based on SINR criterion.
The base station and all terminals share the same codebook, and the specific composition of the codebook and the numbering mode of the beams are known by the base station and the terminals before communication.
For all codebooks, under the condition of same power, calculating the corresponding codebook vector of each codebook vector
Figure BDA0000752280180000101
Where p represents the normalization factor of noise and power.
In the implementation, the method can further comprise the following steps: when feeding back codebook vectors to the base station, the SNR values or SINR values corresponding to these vectors are fed back.
In implementation, when feeding back codebook vectors to the base station, M codebook vectors are fed back, where M is the number of digital channels.
In the implementation of step 203, the codebook vector may be fed back to the base station specifically as follows.
The terminal feedback mode can adopt any one of the following schemes. Also, it is assumed here that the terminal has an Ntx antenna, M digital channels, and K users.
a. Only the way of feeding back the M codebook vector numbers.
And each terminal selects M codebook vectors corresponding to the maximum SNR values or the SINR values based on the SNR calculation mode or the SINR calculation mode in the last step.
Each terminal feeds back the M codebook vector numbers to the base station. Correspondingly, at the base station, if the codebook vector in the codebook is fed back by the user once, the weight is +1, otherwise + 0. And selecting M codebook vectors with the largest weight in the codebook as the analog domain precoding A.
For example, consider an architecture with K-5 users, Ntx-10 antennas, and M-7 digital channels. As shown in table 1.
TABLE 1 simulation precoding example with feedback of codebook vector number only
Codebook numbering v1 v2 v3 v4 v5 v6 v7 v8 v9 v10
User1
1 1 1 0 1 1 0 1 0 1
User2 1 0 1 1 1 0 1 0 1 1
User3 1 0 1 0 1 0 1 1 1 1
User4 1 1 0 1 1 1 0 1 1 0
User5 1 0 1 1 0 1 1 0 1 1
Weighted sum 5 2 4 3 4 3 3 3 4 4
As shown in table 1, each user only feeds back M codebook vector numbers with the maximum snr (sinr) value in the codebook, and if a certain vector is fed back, it is marked as 1 in the codebook and is not fed back with a flag bit of 0. And then adding the weights corresponding to each vector in the codebook, and selecting M vectors with the maximum weight sum (bold italic labeling part) to form the analog domain precoding A.
b. The way to feed back the M codebook vector numbers and the corresponding sinr (snr) values.
Each terminal selects codebook vectors corresponding to M maximum SNR values (or SINR values) based on the SNR calculation method or SINR calculation method of the previous step.
Each terminal feeds back the M vector numbers, and corresponding snr (sinr) values, to the base station. At the base station, the corresponding capacity is calculated using the snr (sinr) value of the feedback, and the capacity that is not fed back is 0. Each codebook calculates the sum of the capacities that each user can provide, namely:
Figure BDA0000752280180000111
or
Figure BDA0000752280180000112
And selecting M codebook vectors with the maximum capacity in the codebook as the simulation domain precoding A.
For example, consider an architecture with K-5 users, Ntx-10 antennas, and M-7 digital channels. At the base station, for each vector, the corresponding capacity is calculated for the snr (sinr) values fed back by K users, as shown in the following table:
TABLE 2 example analog precoding of feedback vector number and SNR (SINR) value
Codebook numbering v1 v2 v3 v4 v5 v6 v7 v8 v9 v10
User1 51 67 15 72 0 92 78 0 40 0
User2 15 40 57 5 0 0 1 0 25 36
User3 0 2 65 95 77 60 4 0 0 69
User4 0 26 10 88 0 38 60 2 64 0
User5 16 0 56 0 54 0 11 58 23 20
Capacity and 82 135 203 260 131 190 154 60 152 125
as shown in table 2, each user feeds back only M vector numbers with the maximum SNR (SINR) value, and its SNR or SINR value. If a certain vector is fed back, the corresponding capacity (calculated by SNR/SINR in the above formula) is marked in the codebook, and the vector is not fed back and marked as 0. And then adding the capacities corresponding to each vector in the codebook, and selecting M codebook vectors with the maximum capacity sum to form an analog domain precoding A.
Fig. 3 is a schematic flowchart of an implementation of a base station side precoding method, as shown in the figure, the implementation may include:
step 301, receiving a codebook vector fed back by a terminal, wherein the codebook vector is obtained by the terminal after evaluating the codebook vector in a codebook according to an approximate channel h;
step 302, forming a simulation pre-coding matrix according to the codebook vector;
and 303, obtaining an equivalent channel according to the analog precoding matrix.
In implementation, in a specific implementation, any of the following schemes may be adopted in a manner of outputting an analog precoding matrix according to the codebook vector. Also, it is assumed here that the base station has Ntx antennas, M digital channels, and K users.
a. Only the way of feeding back the M codebook vector numbers.
In implementation, after receiving a codebook vector fed back by a terminal, determining the number of times that the codebook vector is fed back by the terminal;
and selecting the first M codebook vectors with the most times to form an analog precoding matrix, wherein M is the number of digital channels.
Specifically, each terminal selects M codebook vectors corresponding to the maximum SNR values or SINR values based on the SNR calculation mode or SINR calculation mode in the previous step.
Each terminal feeds back the M codebook vector numbers to the base station. Correspondingly, at the base station, if the codebook vector in the codebook is fed back by the user once, the weight is +1, otherwise + 0. And selecting M codebook vectors with the largest weight in the codebook as the analog domain precoding A.
For example, consider an architecture with K-5 users, Ntx-10 antennas, and M-7 digital channels. As shown in table 3.
TABLE 3 analog precoding example with feedback of codebook vector number only
Codebook numbering v1 v2 v3 v4 v5 v6 v7 v8 v9 v10
User1
1 1 1 0 1 1 0 1 0 1
User2 1 0 1 1 1 0 1 0 1 1
User3 1 0 1 0 1 0 1 1 1 1
User4 1 1 0 1 1 1 0 1 1 0
User5 1 0 1 1 0 1 1 0 1 1
Weighted sum 5 2 4 3 4 3 3 3 4 4
As shown in table 3, each user only feeds back M codebook vector numbers with the maximum snr (sinr) value in the codebook, and if a certain vector is fed back, it is marked as 1 in the codebook and is not fed back with flag bit 0. And then adding the weights corresponding to each vector in the codebook, and selecting M vectors with the maximum weight sum (bold italic labeling part) to form the analog domain precoding A.
b. The way to feed back the M codebook vector numbers and the corresponding sinr (snr) values.
In the implementation, after the codebook vectors fed back to the base station by the receiving terminal and the SNR values or SINR values corresponding to the vectors, the capacity corresponding to the codebook vectors is determined according to the number of SNR values or SINR values corresponding to the codebook vectors, and the first M codebook vectors with the largest capacity are selected as the analog precoding matrix, where M is the number of digital channels.
Since what the base station side receives is what the terminal side feeds back, the specific implementation may refer to the implementation in which the terminal side feeds back codebook vectors and SNR values or SINR values corresponding to the vectors to the base station as described above.
Specifically, each terminal selects codebook vectors corresponding to M maximum SNR values (or SINR values) based on the SNR calculation method or SINR calculation method in the previous step.
Each terminal feeds back the M vector numbers, and corresponding snr (sinr) values, to the base station. At the base station, the corresponding capacity is calculated using the snr (sinr) value of the feedback, and the capacity that is not fed back is 0. Each codebook calculates the sum of the capacities that each user can provide, namely:
Figure BDA0000752280180000141
or
Figure BDA0000752280180000142
And selecting M codebook vectors with the maximum capacity in the codebook as the simulation domain precoding A.
For example, consider an architecture with K-5 users, Ntx-10 antennas, and M-7 digital channels. At the base station, for each vector, the corresponding capacity is calculated for the snr (sinr) values fed back by K users, as shown in the following table:
TABLE 4 examples of analog precoding for feedback vector number and SNR (SINR) value
Codebook numbering v1 v2 v3 v4 v5 v6 v7 v8 v9 v10
User1 51 67 15 72 0 92 78 0 40 0
User2 15 40 57 5 0 0 1 0 25 36
User3 0 2 65 95 77 60 4 0 0 69
User4 0 26 10 88 0 38 60 2 64 0
User5 16 0 56 0 54 0 11 58 23 20
Capacity and 82 135 203 260 131 190 154 60 152 125
as shown in table 4, each user feeds back only M vector numbers with the maximum SNR (SINR) value, and its SNR or SINR value. If a certain vector is fed back, the corresponding capacity (calculated by SNR/SINR in the above formula) is marked in the codebook, and the vector is not fed back and marked as 0. And then adding the capacities corresponding to each vector in the codebook, and selecting M codebook vectors with the maximum capacity sum to form an analog domain precoding A.
In the implementation of step 303, obtaining an equivalent channel according to the analog precoding matrix may include:
acquiring an approximate channel h of each terminal and forming the approximate channel h;
and obtaining an equivalent channel according to the analog precoding matrix and the approximate channel h.
In specific implementation, in the process of digital domain precoding, considering that the analog domain precoding A is determined, H is takeneqHA, the equivalent channel model seen in the digital domain. The processing model in the digital domain can now be expressed as: y is HeqDs + N, where D denotes the digital domain precoding matrix.
Due to the processing of the analog domain A, the H at high latitude is converted into the equivalent channel H at low latitudeeq. Therefore, the precoding method in the digital domain can directly utilize the relatively complicated precoding method in the conventional.
The digital domain is for the equivalent channel HeqThe acquisition mode of (2) can be implemented by any one of the following two modes:
a. the conventional approach acquires an accurate channel.
The method can be directly referred to the previous MIMO mode, for example, in a TDD system, the downlink channel H is obtained by utilizing the uplink reference signal based on the channel reciprocityeq. In FDD system, base station end sends pilot frequency (or code book) shapeAnd (4) detecting and feeding back the user to the base station.
b. Using an approximation channel hk。
Two approximate channels h determined based on Los path angle or based on downlink codebook measurements as given in the previous terminal side implementationkAnd (4) obtaining mode. Base station obtains approximate channel h of each userkAn approximate channel H may be composed. At this time, the analog A is also known at the base station, and H can be obtainedeq＝HA。
For the digital domain precoding method, the digital domain precoding can also be directly performed in a conventional manner, and due to the low operation dimensionality, algorithms with slightly high complexity, such as ZF algorithm and MMSE algorithm, can be used.
Considering the capacity constraint of inter-user interference in MU-MIMO and the shortage of pre-coding in the analog domain in eliminating the inter-user interference, a ZF pre-coding algorithm is recommended to be adopted in the digital domain, namely:
Figure BDA0000752280180000151
a combined embodiment of a terminal and a base station will be described below.
FIG. 4 is a schematic diagram of a finite feedback modulus architecture precoding algorithm implementation flow, in the whole process, the first four blocks (step 401 and 404) represent analog domain precoding, and the last block (step 405) represents digital domain precoding. In the description, it is assumed that the number of users is K, the number of digital channels is M, and the number of antenna arrays is Ntx. As shown in the figure, the technical scheme provided by the embodiment of the invention mainly comprises the following steps:
a terminal side:
step 401, the terminal outputs an approximate channel h;
the obtaining of the approximate channel h may be performed in two ways, that is, the approximate channel h is obtained based on the Los path angle, or the approximate channel h is obtained based on the downlink codebook measurement, which has already been described in the above embodiments, and is not described here again.
Step 402, the terminal evaluates the codebook vector in the codebook, and outputs the codebook vector and an SNR (Signal-to-Noise Ratio) or SINR (Signal-to-Interference plus Noise Ratio) value;
the terminal may evaluate in two ways, and the evaluation is performed based on an SNR criterion or an SINR criterion, which has already been described in the foregoing embodiments and is not described herein again.
Step 403, the terminal selects M codebook vector codebooks from the codebook to feed back to the base station;
there may be two selection modes: selecting a codebook corresponding to the M maximum SNR values or selecting a codebook corresponding to the M maximum SINR values; the feedback mode can have two types: feeding back M codebook vector numbers or feeding back M codebook vector numbers and their snr (sinr) values. The above embodiments have been described, and are not described in detail herein.
At a terminal side, a base station and the terminal share the same codebook, approximate full-latitude channel state information is obtained by utilizing channel estimation, and each terminal evaluates all codebook vectors in the codebook and feeds back the codebook evaluation information to the base station.
A base station side:
step 404, the base station determines the analog domain precoding and outputs an analog precoding matrix A;
there are two ways to determine the analog domain precoding: and calculating the weight sum to obtain the maximum M codebook vectors or calculating the capacity sum to obtain the maximum M codebook vectors. The determination here is related to the selection of the codebook vector in the terminal-side step 403, which has already been described in the above embodiments and is not described here again.
Step 405, digital domain pre-coding;
wherein: there are two ways to obtain equivalent channels: obtaining the accurate channel Heq in a conventional manner, or obtaining the accurate channel Heq according to a by using two approximate channels h given in step 401: heq ═ HA. The above embodiments have been described, and are not described in detail herein.
Finally, the equivalent channel Heq can be used for digital domain beam forming, such as zero forcing and the like. The digital domain precoding method herein can directly utilize the existing method, and is not described herein again.
And at the base station side, after the terminal feeds back the evaluation information of the codebook of the base station, the base station selects a codebook vector as the final analog domain precoding A, the analog domain precoding is fixed, and the digital domain precoding is carried out on the basis of an equivalent channel subjected to the analog precoding. The equivalent channel may be obtained by estimating a real equivalent channel using a baseband reference signal, or by jointly processing the approximate channel h information given in step 401 and the analog precoding.
Based on the same inventive concept, the embodiment of the present invention further provides a precoding apparatus, and because the principles of solving the problems of these apparatuses are similar to the precoding method, the implementation of these apparatuses can refer to the implementation of the method, and repeated details are not repeated.
Fig. 5 is a schematic structural diagram of a terminal-side precoding apparatus, as shown in the figure, the apparatus may include:
a channel module 501, configured to output an approximate channel h on a terminal;
an evaluation module 502, configured to evaluate a codebook vector in a codebook according to the approximate channel h, where the codebook is a codebook known by the base station and the terminal;
and a feedback module 503, configured to feed back the codebook vector to the base station according to the evaluation result.
In an implementation, the channel module may be further configured to determine the approximate channel h based on the Los path angle, or determine the approximate channel h based on a downlink codebook measurement manner.
In an implementation, the evaluation module may be further configured to evaluate the codebook vectors in the codebook based on an SNR criterion or an SINR criterion.
In an implementation, the feedback module may be further configured to feed back the codebook vector having the largest SNR value or SINR value to the base station.
In an implementation, the feedback module may be further configured to feed back an SNR value or an SINR value corresponding to the codebook vector when feeding back the codebook vector to the base station.
In an implementation, the feedback module may be further configured to feed back M codebook vectors when feeding back codebook vectors to the base station, where M is the number of digital channels.
Fig. 6 is a schematic structural diagram of a base station side precoding apparatus, as shown in the figure, the apparatus may include:
a receiving module 601, configured to receive a codebook vector fed back by a terminal, where the codebook vector is obtained by the terminal after evaluating a codebook vector in a codebook according to an approximate channel h;
an analog pre-coding matrix module 602, configured to form an analog pre-coding matrix according to the codebook vector;
an equivalent channel module 603, configured to obtain an equivalent channel according to the analog precoding matrix.
In implementation, the analog precoding matrix module is further configured to determine the number of times that the codebook vector is fed back by the terminal after receiving the codebook vector fed back by the terminal, select the first M codebook vectors with the largest number of times to form an analog precoding matrix, where M is the number of digital channels.
In an implementation, the receiving module may be further configured to receive an SNR value or an SINR value corresponding to the codebook vector when the receiving terminal feeds back the codebook vector to the base station.
In implementation, the analog precoding matrix module is further configured to, after receiving a codebook vector fed back to the base station by the terminal and an SNR value or SINR value corresponding to the codebook vector, determine a capacity of the codebook vector according to the SNR value or SINR value number corresponding to the codebook vector, and select the first M codebook vectors with the largest capacity as the analog precoding matrix, where M is the number of digital channels.
In implementation, the equivalent channel module may be further configured to obtain an approximate channel h of each terminal when obtaining the equivalent channel according to the analog precoding matrix, and form the approximate channel h; and obtaining an equivalent channel according to the analog precoding matrix and the approximate channel h.
For convenience of description, each part of the above-described apparatus is separately described as being functionally divided into various modules or units. Of course, the functionality of the various modules or units may be implemented in the same one or more pieces of software or hardware in practicing the invention.
When the technical scheme provided by the embodiment of the invention is implemented, the implementation can be carried out as follows.
Fig. 7 is a schematic structural diagram of a terminal, and as shown in the figure, the user equipment includes:
the processor 700, which is used to read the program in the memory 720, executes the following processes:
outputting an approximate channel h at the terminal;
evaluating a codebook vector in a codebook according to the approximate channel h, wherein the codebook is a codebook known by the base station and the terminal;
a transceiver 710 for transmitting data under the control of the processor 700, performing the following processes:
and feeding back the codebook vector to the base station according to the evaluation result.
In an implementation, the approximate channel h is determined based on a Los path angle, or determined based on a downlink codebook measurement mode.
In an implementation, the evaluation of codebook vectors in a codebook is based on an SNR criterion or an SINR criterion.
In implementation, the terminal feeds back a codebook vector having a maximum SNR value or SINR value to the base station.
In an implementation, the method further comprises the following steps: and when the codebook vector is fed back to the base station, feeding back an SNR value or an SINR value corresponding to the codebook vector.
In implementation, when feeding back codebook vectors to the base station, M codebook vectors are fed back, where M is the number of digital channels.
Where in fig. 7, the bus architecture may include any number of interconnected buses and bridges, with various circuits being linked together, particularly one or more processors represented by processor 700 and memory represented by memory 720. The bus architecture may also link together various other circuits such as peripherals, voltage regulators, power management circuits, and the like, which are well known in the art, and therefore, will not be described any further herein. The bus interface provides an interface. The transceiver 710 may be a number of elements including a transmitter and a receiver that provide a means for communicating with various other apparatus over a transmission medium. The user interface 730 may also be an interface capable of interfacing with a desired device for different user devices, including but not limited to a keypad, display, speaker, microphone, joystick, etc.
The processor 700 is responsible for managing the bus architecture and general processing, and the memory 720 may store data used by the processor 700 in performing operations.
Fig. 8 is a schematic structural diagram of a base station, as shown in the figure, the base station includes:
the processor 800, which is used to read the program in the memory 820, executes the following processes:
forming a simulation pre-coding matrix according to the codebook vector;
obtaining an equivalent channel according to the analog precoding matrix;
a transceiver 810 for transmitting data under the control of the processor 800, performing the following processes:
and receiving a codebook vector fed back by the terminal, wherein the codebook vector is obtained by the terminal after evaluating the codebook vector in the codebook according to the approximate channel h.
In an implementation, the outputting an analog precoding matrix according to the codebook vector includes:
after receiving a codebook vector fed back by a terminal, determining the number of times that the codebook vector is fed back by the terminal;
and selecting the first M codebook vectors with the most times to form an analog precoding matrix, wherein M is the number of digital channels.
In an implementation, when a receiving terminal feeds back a codebook vector to a base station, the receiving terminal receives an SNR value or an SINR value corresponding to the codebook vector.
In the implementation, after the codebook vectors fed back to the base station by the receiving terminal and the SNR values or SINR values corresponding to the vectors, the capacity corresponding to the codebook vectors is determined according to the number of SNR values or SINR values corresponding to the codebook vectors, and the first M codebook vectors with the largest capacity are selected as the analog precoding matrix, where M is the number of digital channels.
In implementation, obtaining an equivalent channel according to the analog precoding matrix includes:
acquiring an approximate channel h of each terminal and forming the approximate channel h;
and obtaining an equivalent channel according to the analog precoding matrix and the approximate channel h.
Where in fig. 8, the bus architecture may include any number of interconnected buses and bridges, with various circuits being linked together, particularly one or more processors represented by processor 800 and memory represented by memory 820. The bus architecture may also link together various other circuits such as peripherals, voltage regulators, power management circuits, and the like, which are well known in the art, and therefore, will not be described any further herein. The bus interface provides an interface. The transceiver 810 may be a number of elements including a transmitter and a transceiver providing a means for communicating with various other apparatus over a transmission medium. The processor 800 is responsible for managing the bus architecture and general processing, and the memory 820 may store data used by the processor 800 in performing operations.
In summary, the embodiments of the present invention provide implementation schemes of analog domain channel estimation, terminal codebook estimation, analog precoding, and digital domain based on equivalent channel precoding. The scheme can improve the precision of analog and digital precoding and reduce the channel feedback overhead. Meanwhile, the terminal can also dynamically adjust the number of the fed-back analog codebook vectors, so that the terminal can adapt to the number of digital channels of different base station terminals and fully utilize all different digital channel resources.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, optical storage, and the like) having computer-usable program code embodied therein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims (22)

1. A precoding method, comprising:
outputting an approximate channel h at the terminal;
evaluating a codebook vector in a codebook according to the approximate channel h, wherein the codebook is a codebook known by the base station and the terminal;
and feeding back the codebook vector to the base station according to the evaluation result.
2. The method of claim 1, wherein the approximate channel h is determined based on a Los path angle or determined based on downlink codebook measurement.
3. The method of claim 1, wherein evaluating codebook vectors in a codebook is based on an SNR criterion or an SINR criterion.
4. Method according to claim 3, characterized in that the terminal feeds back to the base station the codebook vector having the largest SNR value or SINR value.
5. The method of claim 3 or 4, further comprising: and when the codebook vector is fed back to the base station, feeding back an SNR value or an SINR value corresponding to the codebook vector.
6. The method of any of claims 1 to 4, wherein M codebook vectors are fed back when feeding back codebook vectors to the base station, M being the number of digital channels.
7. A precoding method, comprising:
receiving a codebook vector fed back by a terminal, wherein the codebook vector is obtained by the terminal after evaluating the codebook vector in a codebook according to an approximate channel h;
forming a simulation pre-coding matrix according to the codebook vector;
and obtaining an equivalent channel according to the analog precoding matrix.
8. The method of claim 7, wherein outputting an analog precoding matrix based on the codebook vector comprises:
after receiving a codebook vector fed back by a terminal, determining the number of times that the codebook vector is fed back by the terminal;
and selecting the first M codebook vectors with the most times to form an analog precoding matrix, wherein M is the number of digital channels.
9. The method of claim 7, further comprising: and when the receiving terminal feeds back the codebook vector to the base station, receiving the SNR value or the SINR value corresponding to the codebook vector.
10. The method according to claim 9, wherein after receiving the codebook vector fed back to the base station by the terminal and the SNR or SINR value corresponding to the codebook vector, determining the capacity of the codebook vector according to the number of SNR or SINR values corresponding to the codebook vector, and selecting the first M codebook vectors with the largest capacity as the analog precoding matrix, where M is the number of digital channels.
11. The method according to any of claims 7 to 10, wherein obtaining the equivalent channel based on the analog precoding matrix comprises:
acquiring an approximate channel h of each terminal and forming the approximate channel h;
and obtaining an equivalent channel according to the analog precoding matrix and the approximate channel h.
12. A precoding apparatus, comprising:
a channel module for outputting an approximate channel h at a terminal;
the evaluation module is used for evaluating a codebook vector in a codebook according to the approximate channel h, wherein the codebook is a codebook known by the base station and the terminal;
and the feedback module is used for feeding back the codebook vector to the base station according to the evaluation result.
13. The apparatus of claim 12, wherein the channel module is further configured to determine the approximate channel h based on a Los path angle or based on downlink codebook measurements.
14. The apparatus of claim 12, wherein the evaluation module is further configured to evaluate the codebook vectors in the codebook based on an SNR criterion or an SINR criterion.
15. The apparatus of claim 14, wherein the feedback module is further configured to feed back codebook vectors with maximum SNR or SINR values to the base station.
16. The apparatus of claim 14 or 15, wherein the feedback module is further configured to feed back an SNR value or an SINR value corresponding to the codebook vector when feeding back the codebook vector to the base station.
17. The apparatus of any of claims 12 to 15, wherein the feedback module is further configured to feed back M codebook vectors when feeding back codebook vectors to the base station, where M is the number of digital channels.
18. A precoding apparatus, comprising:
the receiving module is used for receiving a codebook vector fed back by the terminal, wherein the codebook vector is obtained by the terminal after evaluating the codebook vector in the codebook according to the approximate channel h;
the analog pre-coding matrix module is used for forming an analog pre-coding matrix according to the codebook vector;
and the equivalent channel module is used for obtaining an equivalent channel according to the analog precoding matrix.
19. The apparatus of claim 18, wherein the analog precoding matrix module is further configured to determine, after receiving a codebook vector fed back by the terminal, the number of times that the codebook vector is fed back by the terminal, select the first M codebook vectors with the largest number of times to form an analog precoding matrix, where M is the number of digital channels.
20. The apparatus of claim 18, wherein the receiving module is further configured to receive an SNR value or an SINR value corresponding to the codebook vector when the receiving terminal feeds back the codebook vector to the base station.
21. The apparatus of claim 20, wherein the analog precoding matrix module is further configured to, after receiving the codebook vector fed back from the terminal to the base station and the SNR value or SINR value corresponding to the codebook vector, determine a capacity of the codebook vector according to the SNR value or SINR value number corresponding to the codebook vector, and select the first M codebook vectors with the largest capacity as the analog precoding matrix, where M is the number of digital channels.
22. The apparatus according to any of claims 18 to 21, wherein the equivalent channel module is further configured to, when obtaining the equivalent channel according to the analog precoding matrix, obtain an approximate channel h of each terminal, and form the approximate channel h; and obtaining an equivalent channel according to the analog precoding matrix and the approximate channel h.
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