CN108366035A - A kind of method for precoding reducing ADMA system signal peak-to-average power ratios - Google Patents
A kind of method for precoding reducing ADMA system signal peak-to-average power ratios Download PDFInfo
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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
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- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
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Abstract
The present invention discloses a kind of method for precoding reducing ADMA system signal peak-to-average power ratios, including：Assuming that system base-station antenna, base station has obtained downlink perspective domain channel matrix, is sent to the raw data symbols vector of user；It needs to execute T iteration assuming that obtaining the transmission signal with desired low peak-to-average power ratio, obtains the transmission power factor and need to execute T2 iteration, meet the transmission assemble of symbol of low peak-to-average power ratio；Initialization；The correction matrix of MMSE estimations is calculated, the modified MMSE estimations for sending signal is calculated, and estimated result is mapped to transmission assemble of symbol, if t+1 is the integral multiple of T2, calculates the new transmission power factor, otherwise continue iteration；It calculates and introduces the transmission signal phasor that damping factor obtains；Current iteration number is updated, determines that obtained transmission signal phasor is the required transmission signal with desired low peak-to-average power ratio.There is the present invention lower complexity, preferable system errors performance system cost can be greatly reduced.
Description
Technical Field
The invention relates to a precoding method for reducing the peak-to-average power ratio of ADMA system signals, belonging to the technical field of mobile communication.
Background
The large-scale MIMO multiple access transmission technology is an important link for realizing 5G key performance indexes. Since the base station deploys a large-scale antenna array, acquisition of Channel State Information (CSI) becomes a bottleneck problem, and conventional transmission schemes, such as time division multiple access, frequency division multiple access, and code division multiple access, are no longer suitable for large-scale MIMO systems. For this reason, a multi-user transmission scheme using massive MIMO spatial dimension resources has gained wide attention, and the ADMA technique is one of them.
ADMA is a multi-user transmission technique based on angle domain channel characteristics. The ADMA technology maps the spatial CSI of the user to an angle domain to obtain the CSI of the angle domain, and then reduces the dimensionality of a channel matrix by utilizing the sparsity of the channel distribution of the angle domain of the user. By introducing an additional angle rotation factor in the angle domain, the ADMA technique can further reduce the channel matrix dimension while obtaining a more accurate estimation of the user angle of arrival or beam direction.
The ADMA system has a plurality of advantages, can fully excavate space dimension resources, improves the space resolution and the space resource utilization rate, and obviously reduces the training overhead. However, the ADMA system also has a problem of high peak-to-average power ratio, especially in the downlink data transmission process, the angular domain signals in each beam direction are mutually overlapped, and a transmission signal with a very large amplitude value variation range may be obtained, which brings a great challenge to the design of the RF device, and will greatly reduce the energy efficiency of the system and increase the hardware cost of the system. Therefore, designing a transmit signal with a low peak-to-average power ratio is advantageous for implementing a low cost ADMA system.
Disclosure of Invention
The technical problem to be solved by the present invention is to overcome the defects of the prior art, and provide a precoding method for reducing the peak-to-average power ratio of an ADMA system signal, so as to solve the problem that a transmission signal in the ADMA system has a high peak-to-average power ratio. The invention realizes obvious peak-to-average power ratio suppression effect and better system error performance with lower complexity and greatly reduces the system cost.
The invention specifically adopts the following technical scheme to solve the technical problems:
a precoding method for reducing the peak-to-average power ratio of an ADMA system signal comprises the following steps:
step (1) assuming that the antenna of the base station of the ADMA system is M, the base station already obtains a downlink angle domain channel matrix H, and the vector of an original data symbol sent to a user is s;
step (2) assumes that T iterations are required to be performed to obtain a transmit signal vector x with a desired low peak-to-average power ratio, and T iterations are required to be performed to obtain a transmit power factor β2For the second iteration, the transmit symbol set satisfying the low peak-to-average power ratio is χM；
Step (3) initializing current iteration times t and sending signal vector xttransmit power factor βtdamping factor α;
step (4) calculating a correction matrix of MMSE estimationWherein,representing an angle domain channel matrix introducing a transmission power factor, and diag ((-)) representing a diagonal matrix formed by solving diagonal elements of the matrix;
step (5) calculates a modified MMSE estimate of the transmitted signal vector x and maps the estimate to a set of transmitted symbols χMI.e. transmitting signal vectorsWherein,representing the mapping of the vector on a specified set;
step (6) judging if T +1 is T2Integer multiple of (2), then according to the optimization expressionCalculating a new transmit power factor, where K is the number of users, σ2is the noise variance of the system, otherwise, βt+1＝βt；
step (7) calculating a transmission signal vector x obtained by introducing a damping factor α according to the transmission signal vector obtained in step (5)t+1＝αxt+(1-α)xt+1；
Step (8) updating the current iteration time T to T +1, and executing step (4) if T is less than T; otherwise, determining the transmission signal vector obtained in the step (7) as the obtained transmission signal vector x with the expected low peak-to-average power ratio.
Further, as a preferred technical solution of the present invention: in the step (1), the downlink angle domain channel is obtained by using an angle reciprocity method.
Further, as a preferred technical solution of the present invention: the symbol set χ sent in the step (2) isMThe symbol set is transmitted for a constant envelope composed of individual elements, and the individual elements are evenly distributed over a unit circle.
Further, as a preferred technical solution of the present invention: the step (6) further comprises updating the angle domain channel matrix after calculating the new transmission power factorAnd a correction matrix Wu。
further, as a preferable technical solution of the present invention, in the step (7), the damping factor α is 0.95.
By adopting the technical scheme, the invention can produce the following technical effects:
the precoding method for reducing the peak-to-average power ratio of the ADMA system signal comprises the steps of firstly carrying out modified MMSE estimation on a transmitted signal, then mapping an estimation result to a transmitted symbol set with a low peak-to-average power ratio characteristic, then reducing the change degree of the transmitted signal brought by the first two operations by using a damping factor, and iteratively executing the steps until the iteration number reaches a preset value, wherein the obtained transmitted signal is the precoded output. By iteratively performing the modified MMSE estimation and symbol set mapping, a transmitted signal with low peak-to-average power ratio characteristics can be obtained. In addition, the precoding method based on the peak-to-average power ratio inhibition has lower complexity, can obtain obvious peak-to-average power ratio inhibition effect and better system error performance, and greatly reduces the system cost.
Drawings
Fig. 1 is a block diagram of an ADMA system transmission link according to the method of the present invention.
Fig. 2 is a schematic diagram of a constant envelope transmit symbol set used in the present invention.
FIG. 3 is a graph of the peak to average power ratio characteristic of the method of the present invention.
Detailed Description
The following describes embodiments of the present invention with reference to the drawings.
The invention provides a precoding method for reducing the peak-to-average power ratio of an ADMA system signal, a block diagram of a transmission link of the ADMA system adopted by the method is shown in figure 1, and the method of the invention comprises the following steps:
step (1) assuming that the antenna of the base station of the ADMA system is M, the base station already obtains a downlink angle domain channel matrix H, and the vector of an original data symbol sent to a user is s;
the base station obtains the downlink angle domain channel matrix on the premise of realizing precoding, and the ADMA system downlink angle domain channel is obtained by using an angle reciprocity method. That is, in TDD mode, the downlink channel can be directly obtained from the uplink channel estimation result due to reciprocity of the uplink and downlink, however, in FDD mode, the above channel reciprocity is no longer satisfied. Considering that the propagation path of electromagnetic wave has reciprocity, only those signal waves propagating in reverse direction along the uplink path between the user and the base station can reach the user during downlink transmission, therefore, the AOD of the signal beam expected to be transmitted to the user must be the same as the AOA of the signal beam from the user in uplink, and this characteristic is called angle reciprocity, and the present ADMA system downlink angle domain channel is obtained by using the principle of angle reciprocity.
step (2) assumes that T iterations are required to be performed to obtain a transmit signal vector x with a desired low peak-to-average power ratio, and T iterations are required to be performed to obtain a transmit power factor β2For the second iteration, the transmit symbol set satisfying the low peak-to-average power ratio is χM；
Since the peak-to-average power ratio characteristic of the transmitted signal depends on the transmitted symbol set χMPreferably, the transmission symbol set χMThe constant envelope precoding is a constant envelope transmission symbol set formed by each element, each element is uniformly distributed on a unit circle, if the x elements are distributed on the circle, the constant envelope precoding can be realized, and at the moment, the peak-to-average power ratio of a transmission signal is approximately 0 dB.
Step (3) initializing the current iteration time t as 0, and sending a signal vector xttransmission power factor beta of 0tthe damping factor α is 0.95, wherein the damping factor α can be effectively designed to avoid oscillation of the transmission signal caused by overlarge change in the iteration process.
Step (4) because the matrix W is correcteduCan realize unbiased MMSE estimation, thereby calculating a correction matrix of the MMSE estimationWherein,angle domain signaling representing introduced transmit power factorA channel matrix, diag (·) represents a diagonal matrix formed by diagonal elements of the matrix; the superscript H denotes the conjugate transpose of the matrix, and the superscript-1 denotes the inverse of the matrix.
The step (5) of mapping the modified MMSE estimation result to the designated set of transmission signals is the key to achieving low peak-to-average power ratio transmission signals. Thus, a modified MMSE estimate of the transmitted signal vector x is calculated and the estimate is mapped to the set of transmitted symbols xMI.e. transmitting signal vectorsWherein,representing the mapping of vectors onto a specified set.
Step (6) judging if T +1 is T2Integer multiple of (2), then according to the optimization expressionCalculating a new transmit power factor, where K is the number of users, σ2is the noise variance of the system, otherwise, βt+1＝βt；
and, if the current iteration process updates the transmission power factor β, the next iteration process needs to correspondingly update the angle domain channel matrixAnd a correction matrix
step (7) is to calculate a transmission signal vector x obtained by introducing a damping factor α according to the transmission signal vector obtained in the step (5)t+1＝αxt+(1-α)xt+1(ii) a And (4) enabling the transmission signal obtained in the current iteration to be the weighted sum of the transmission signal obtained in the previous iteration and the transmission signal vector obtained in the step (5).
Step (8) updating the current iteration time T to T +1, and executing step (4) if T is less than T; otherwise, determining the transmission signal vector obtained in the step (7) as the obtained transmission signal vector x with the expected low peak-to-average power ratio. That is, when the number of iterations is large enough, a transmission signal with a low peak-to-average power ratio and low inter-user interference can be obtained.
The invention is described below in connection with a massive MIMO-ADMA system example.
Considering a large-scale MIMO-ADMA downlink data transmission scenario, a base station configures a ULA antenna array with 128 antenna units, and simultaneously serves 8 single-antenna users that are randomly and uniformly distributed in a coverage area of the base station and do not overlap with each other in an angle domain, and a constant envelope transmission symbol set composed of 16 elements is adopted, where each element is uniformly distributed on a unit circle, as shown in fig. 2, that is:
order toIndicating the downlink angle domain channel estimation matrix that the base station has obtained,in order to obtain a transmission signal vector x with constant envelope characteristics, 50 iterations are required, i.e. T is 50, to prevent the transmission signal vector from oscillating during the iteration and to ensure good system error performance, 1 iteration of the transmission power factor beta is required, i.e. T is performed every 10 iterations of the transmission signal vector2＝10。
Initializing the current iteration time t as 0, and sending a signal vector x00, transmission power factor beta0first, the correction matrix for the MMSE estimate is calculated:
wherein,the channel matrix of an angle domain introducing a sending power factor is shown, diag (·) shows a diagonal matrix formed by diagonal elements of the matrix, a superscript H shows a conjugate transpose of the matrix, and a superscript-1 shows an inverse of the matrix. Next, a modified MMSE estimate of the transmit signal vector x is calculated and the estimate is mapped to the transmit symbol set χMI.e. transmit signal vector:
wherein,representing the mapping of vectors onto a specified set. If T +1 is T2Integer multiple of (d), then according to the optimized expression:
calculating a new transmit power factor, where K is the number of users, σ2is the noise variance of the system, otherwise, βt+1＝βt(ii) a Then, a transmission signal vector obtained by introducing a damping factor is calculated:
xt+1＝αxt+(1-α)xt+1
finally, updating the current iteration times:
t＝t+1
further, if T is judged to be less than T, the step (4) is switched to; otherwise, determining that the transmission signal vector obtained in the step (7) is the transmission signal with the constant envelope characteristic, namely that the peak-to-average power ratio of the transmission signal is approximately 0 dB.
The present invention can obtain a transmission signal with low peak-to-average power ratio characteristics by iteratively performing modified MMSE estimation and symbol set mapping, and the result is shown in fig. 3. As can be seen from fig. 3, with the precoding method of the present invention, the PAPR of the transmitted signal is less than 0.1dB with a 98% probability, and less than 0.2dB with a 99% probability, thereby achieving the precoding effect. Therefore, the precoding method based on peak-to-average power ratio suppression has lower complexity and better system error performance, and can greatly reduce the system cost.
The embodiments of the present invention have been described in detail with reference to the drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention.
Claims (5)
1. A precoding method for reducing the peak-to-average power ratio of an ADMA system signal is characterized by comprising the following steps:
step (1) assuming that the antenna of the base station of the ADMA system is M, the base station already obtains a downlink angle domain channel matrix H, and the vector of an original data symbol sent to a user is s;
step (2) assumes that T iterations are required to be performed to obtain a transmit signal vector x with a desired low peak-to-average power ratio, and T iterations are required to be performed to obtain a transmit power factor β2For the second iteration, the transmit symbol set satisfying the low peak-to-average power ratio is χM；
Step (3) initializing current iteration times t and sending signal vector xttransmit power factor βtdamping factor α;
step (4) calculating a correction matrix of MMSE estimationWherein,representing an angle domain channel matrix introducing a transmission power factor, and diag ((-)) representing a diagonal matrix formed by solving diagonal elements of the matrix;
step (5) calculates a modified MMSE estimate of the transmitted signal vector x and maps the estimate to a set of transmitted symbols χMI.e. transmitting signal vectorsWherein,representing the mapping of the vector on a specified set;
step (6) judging if the iteration times T +1 is T2Integer multiple of (2), then according to the optimization expressionCalculating a new transmit power factor, where K is the number of users, σ2is the noise variance of the system, otherwise, βt+1＝βt；
step (7) calculating a transmission signal vector x obtained by introducing a damping factor α according to the transmission signal vector obtained in step (5)t +1＝αxt+(1-α)xt+1；
Step (8) updating the current iteration time T to T +1, and executing step (4) if T is less than T; otherwise, determining
And (4) the transmission signal vector obtained in the step (7) is the obtained transmission signal vector x with the expected low peak-to-average power ratio.
2. The precoding method for reducing peak-to-average power ratio of an ADMA system as claimed in claim 1, wherein: in the step (1), the downlink angle domain channel is obtained by using an angle reciprocity method.
3. The precoding method for reducing peak-to-average power ratio of an ADMA system as claimed in claim 1, wherein: the symbol set χ sent in the step (2) isMThe symbol set is transmitted for a constant envelope composed of individual elements, and the individual elements are evenly distributed over a unit circle.
4. The precoding method for reducing peak-to-average power ratio of an ADMA system as claimed in claim 1, wherein: the step (6) further comprises updating the angle domain channel matrix after calculating the new transmission power factorAnd a correction matrix Wu。
5. the precoding method for reducing the peak-to-average power ratio of the ADMA system signal as claimed in claim 1, wherein the damping factor α in the step (7) is 0.95.
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