CN107181510A - Method for precoding based on decorrelation in a kind of extensive mimo system - Google Patents
Method for precoding based on decorrelation in a kind of extensive mimo system Download PDFInfo
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- H—ELECTRICITY
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- 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
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- 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
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Abstract
The invention discloses the method for precoding based on decorrelation in a kind of extensive mimo system, belong to signal processing technology field.The inventive method comprises the following steps：(1) spatial correlation matrix of transmitting terminal is obtained；(2) signal after equilibrium obtains independent channel matrix (3) combination independent channel matrix and modulated is carried out to channel matrix and calculates a stage precoded signal using iterative algorithm；(4) two-stage precoded signal is calculated using de-correlation-matrix and a stage precoded signal, completes precoding.By performing the method for precoding based on decorrelation in a kind of extensive mimo system of the present invention, result in than the conventional extensive faster iterative convergence speed of MIMO method for precoding.In addition, design method of the present invention has in higher practicality, the inversion operation that can be applied to any matrix with correlation.
Description
Technical Field
The invention belongs to the technical field of signal processing, and particularly relates to a precoding method based on decorrelation in a large-scale MIMO system.
Background
Massive MIMO (Multiple-Input Multiple-Output) systems have received a lot of attention because of their excellent spectral efficiency and link reliability. By arranging a large number of antennas at the base station end, the large-scale MIMO system can simultaneously serve more users in the same frequency band, and meanwhile, the large-scale MIMO system can enable communication to be more stable, safer and more effective. Therefore, the massive MIMO system is regarded as a very promising technology for the fifth generation wireless communication system.
For a massive MIMO system, mutual interference between multiple users is more serious than that of the MIMO system, and the impact on system performance is larger. By using the precoding technology, the channel state information is fully utilized to preprocess the transmitted signals, so that each user receives 'pure' signals which are not interfered by other users, the multi-user interference can be effectively eliminated, the system capacity is greatly improved, and the system performance is optimized. Precoding techniques in massive MIMO systems have become a research focus in recent years.
In a massive MIMO system, the dimensionality of the channel matrix becomes very large due to the large number of antennas. ZF precoding and MMSE precoding which are commonly used in a traditional MIMO transmitter cause abnormally large calculation complexity in a large-scale MIMO system due to large matrix inversion operation in the calculation process of precoding matrixes; among the large-scale MIMO precoding methods which are already available at present, the precoding method based on the super-relaxation iteration method and the precoding method based on the conjugate gradient method greatly reduce the computational complexity. However, the convergence speed of these low complexity algorithms is closely related to the spatial correlation between antennas. The algorithm converges quickly when the number of base station antennas occupied by each user is large on average. However, since the degree of freedom of the system is greatly reduced due to the correlation between antennas, this is equivalent to a reduction in the number of base station antennas occupied on average per user to some extent. At this time, the super-relaxation iterative precoding method and the conjugate gradient precoding method may have a case where convergence is difficult.
Disclosure of Invention
In view of the above drawbacks or needs of the prior art, the present invention provides a precoding method based on decorrelation in a massive MIMO system, which aims to decorrelate a channel by a decorrelation matrix; then, one-stage pre-coding with lower calculation complexity is realized through an iterative algorithm; and finally, two-stage pre-coded signals are calculated by combining with the decorrelation matrix, so that the iterative convergence speed of an inversion step in the pre-coded signal calculation process is increased, and the technical problem that the conventional iterative pre-coding method in a large-scale MIMO system is difficult to converge is solved.
To achieve the above object, according to an aspect of the present invention, there is provided a decorrelation-based precoding method in a massive MIMO system, the method comprising the steps of:
(1) obtaining a spatial correlation matrix R of a transmitting endt；
(2) According to the spatial correlation matrix R of the transmitting endtCalculating a decorrelation matrix B, and performing decorrelation on the channel matrix H by using the decorrelation matrix B to obtain an independent channel matrix Hiid；
(3) Using the decorrelated channel matrix HiidComputing a one-stage precoded signal x from the modulated signal s1；
(4) Signal x is precoded using decorrelation matrix B and a stage1And calculating to obtain a two-stage pre-coding signal x to finish pre-coding.
Further, the step (1) is specifically: spatial correlation matrix R of the transmitting endtThe receiving end obtains the statistical information according to the communication channel and then feeds back the statistical information to the transmitting end.
Further, the step (2) includes:
(21) firstly, the spatial correlation matrix R of the transmitting endtPerforming evolution decomposition, and then solving generalized inverse of the matrix after evolution to obtain decorrelation matrixWherein,represents a generalized inverse;
(22) according to the formulaObtaining a channel matrix H, and obtaining an independent channel matrix H after right-multiplying the channel matrix H by a decorrelation matrix Biid。
Further, the step (3) comprises
(31) Preset variablePreset variableByDerive a system of linear equationsSolving the system of equations by using an iterative algorithm to obtain
(32) According to the ZF precoding rule, a stage of precoding signals are expressed asByIs pushed toBonding ofTo obtain
Further, the step (4) is specifically as follows: the two-stage precoded signal x is calculated by the following equation,
wherein, | Bx1I represents the matrix Bx1Is used to normalize the power of the precoded signal.
Generally, compared with the prior art, the technical scheme of the invention has the following technical characteristics and beneficial effects:
(1) compared with a general ultra-relaxation iteration precoding algorithm and a conjugate gradient method precoding algorithm, the design method has higher precoding iteration convergence speed;
(2) the precoding method provided by the invention is convenient to control, and has certain implementability and practical popularization value, so that the method can be applied to inversion of any matrix with correlation.
Drawings
FIG. 1 is a flow chart of a decorrelation-based precoding algorithm in a massive MIMO system according to the present invention;
FIG. 2 is a graph showing a relationship between the number of iterations required for implementing precoding by using a conventional ultra-relaxed iterative precoding algorithm and a conjugate gradient precoding algorithm in a large-scale MIMO system according to an embodiment of the present invention and the number of users;
fig. 3 is a graph showing a relationship between the number of iterations required for implementing precoding by the conventional ultra-relaxed iterative precoding algorithm and the conjugate gradient precoding algorithm in the large-scale MIMO system and the number of base station antennas in accordance with the embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Fig. 1 is a flowchart of a precoding method based on decorrelation in a massive MIMO system according to the present invention, which specifically includes the following steps:
(1) obtaining a spatial correlation matrix R of a transmitting endt；
The spatial correlation matrix of the transmitting end is a statistical matrix of the receiving end according to the communication channelThe information is obtained and then fed back to the sending end; it should be noted that the spatial correlation matrix R of the transmitting end is usedtStatistical information of the communication channel is utilized and thus need not be calculated separately at each time slot.
(2) According to the spatial correlation matrix R of the transmitting endtCalculating a decorrelation matrix B and decorrelating a channel matrix H by using the decorrelation matrix B to obtain an independent channel matrix Hiid；
The channel matrix can be expressed as in a massive MIMO systemHiidRepresenting independent channel matrices, RtA spatial correlation matrix representing a transmitting end; according to ZF equilibrium criteria, the decorrelation matrix is calculated by performing evolution decomposition on the spatial correlation matrix of the transmitting end and then solving generalized inverse of the matrix after evolution, namely Represents a generalized inverse; the independent channel matrix H can be obtained by right-multiplying the channel matrix H by the decorrelation matrix Biid。
(3) Unlike other methods that directly use the channel matrix H and the modulated signal s to compute the precoded signal, we use the decorrelated channel matrix HiidComputing a one-stage precoded signal x from the modulated signal s1；
According to the ZF precoding criterion, a stage of precoding signal in the present invention can be expressed asOne-stage precoded signal x is easily discovered1Involving a decorrelated channel matrix HiidInversion of (1); however, in massive MIMO systems, the dimensionality of the channel matrix becomes very large relative to conventional MIMO systems, and the channel matrix becomes very largeThe complexity of the inversion of the matrix will also become very large; to reduce computational complexity, a stage of precoding the signal x may be used1The calculation of the medium matrix inversion part is converted into the solution of a linear equation set, and the equation set is solved by using a conventional iterative algorithm, so that the solution of the pre-coded signal at one stage can be completed; the method specifically comprises the following steps: preset variableVariables ofLinear system of equations can be obtainedBy solving the system of equations with an iterative algorithmExpression in conjunction with a one-stage precoded signal andthe expression (2) shows that a stage pre-coded signal can be calculated with low complexityIn the invention, because the channel matrix after decorrelation is used by the one-stage precoding matrix, the loss of degree of freedom caused by the spatial correlation of the antenna is avoided, and thus, a faster convergence speed can be obtained when the iterative algorithm is used for calculating the one-stage precoding matrix.
(4) Signal x is precoded using decorrelation matrix B and a stage1Calculating to obtain a two-stage pre-coding signal x to complete pre-coding;
the specific calculation of the two-stage pre-coded signal isWherein | | Bx1I represents the matrix Bx1Is used for pre-programmingThe power of the coded signal is normalized.
Fig. 2 is a graph showing a relationship between the number of iterations required for implementing precoding and the number of users in the embodiment of the present invention and a conventional ultra-relaxed iterative precoding algorithm and a conventional conjugate gradient precoding algorithm when the number of base stations N of a fixed antenna is 100, and as shown in fig. 2, the iterative convergence rate for implementing precoding by the design method of the present invention is significantly increased compared with other two iterative precoding algorithms;
fig. 3 is a graph showing a relationship between the number of iterations required for implementing precoding and the number of base station antennas in the case where the number K of users fixed by the embodiment of the present invention and the conventional ultra-relaxed iterative precoding algorithm and the conjugate gradient method precoding algorithm is 50, respectively, as shown in fig. 3, the iterative convergence rate for implementing precoding by the design method of the present invention is significantly increased compared with the other two iterative precoding algorithms.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (5)
1. A pre-coding method based on decorrelation in a massive MIMO system is characterized in that the method comprises the following steps:
(1) obtaining a spatial correlation matrix R of a transmitting endt；
(2) According to the spatial correlation matrix R of the transmitting endtCalculating a decorrelation matrix B, and performing decorrelation on the channel matrix H by using the decorrelation matrix B to obtain an independent channel matrix Hiid；
(3) Using the decorrelated channel matrix HiidComputing a one-stage precoded signal x from the modulated signal s1；
(4) Signal x is precoded using decorrelation matrix B and a stage1And calculating to obtain a two-stage pre-coding signal x to finish pre-coding.
2. The pre-coding method based on decorrelation in the massive MIMO system according to claim 1, wherein the step (1) specifically comprises: spatial correlation matrix R of the transmitting endtThe receiving end obtains the statistical information according to the communication channel and then feeds back the statistical information to the transmitting end.
3. The pre-coding method based on decorrelation in the massive MIMO system according to claim 1, wherein the step (2) includes:
(21) firstly, the spatial correlation matrix R of the transmitting endtPerforming evolution decomposition, and then solving generalized inverse of the matrix after evolution to obtain decorrelation matrixWherein,represents a generalized inverse;
(22) according to the formulaObtaining a channel matrix H, and obtaining an independent channel matrix H after right-multiplying the channel matrix H by a decorrelation matrix Biid。
4. The pre-coding method based on decorrelation in massive MIMO system according to claim 1, wherein the step (3) comprises
(31) Preset variablePreset variableByDerive a system of linear equationsSolving the system of equations by using an iterative algorithm to obtain
(32) According to the ZF precoding rule, a stage of precoding signals are expressed asByIs pushed toBonding ofTo obtain
5. The pre-coding method based on decorrelation in the massive MIMO system according to claim 1, wherein the step (4) specifically comprises: the two-stage precoded signal x is calculated by the following equation,
<mrow> <mi>x</mi> <mo>=</mo> <mfrac> <mn>1</mn> <mrow> <mo>|</mo> <mo>|</mo> <msub> <mi>Bx</mi> <mn>1</mn> </msub> <mo>|</mo> <mo>|</mo> </mrow> </mfrac> <msub> <mi>Bx</mi> <mn>1</mn> </msub> <mo>,</mo> </mrow>
wherein, | Bx1I represents the matrix Bx1Is used to normalize the power of the precoded signal.
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| CN113783592A (en) * | 2021-08-27 | 2021-12-10 | 华中科技大学 | Hybrid precoding method and system for beam offset compensation |
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Application publication date: 20170919 |