CN113645165B - Packet interpolation-weighting combination channel estimation method and system for 5G downlink - Google Patents

Packet interpolation-weighting combination channel estimation method and system for 5G downlink Download PDF

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CN113645165B
CN113645165B CN202111128165.3A CN202111128165A CN113645165B CN 113645165 B CN113645165 B CN 113645165B CN 202111128165 A CN202111128165 A CN 202111128165A CN 113645165 B CN113645165 B CN 113645165B
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matrix
estimation
pilot
channel response
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CN113645165A (en
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郑生华
王昕�
姚艳军
张正宇
贺超
朱峰
任伟龙
陈�田
黄永华
王文哲
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CETC 38 Research Institute
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H04L25/0226—Channel estimation using sounding signals sounding signals per se
    • 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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2602—Signal structure
    • H04L27/261—Details of reference signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2649—Demodulators
    • H04L27/265—Fourier transform demodulators, e.g. fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators

Abstract

A packet interpolation-weighting combination channel estimation method and system of a 5G downlink belongs to the technical field of 5G system channel estimation, and solves the problems of high pilot signal overhead and high channel estimation complexity in the prior technical scheme; compared with the prior art, the pilot frequency placement structure combining Frequency Division Multiplexing (FDM) and Code Division Multiplexing (CDM) reduces the overhead of pilot signals, and has better performance when the same number of time-frequency resources are used, because the multi-antenna ports adopt CDM multiplexing, the signals received by the receiving end antennas are mixed signals, the complete pilot frequency information is obtained by adopting a combination decomposition and combination synthesis method, and the complexity of the implementation of the channel estimation method of the antenna ports adopting CDM multiplexing is reduced.

Description

Packet interpolation-weighting combination channel estimation method and system for 5G downlink
Technical Field
The invention belongs to the technical field of 5G system channel estimation, and particularly relates to a method and a system for packet interpolation-weighted combination channel estimation of a 5G downlink.
Background
LTE (Long Term Evolution) only the pilot structure of Frequency division multiplexing (FDM, frequency-Division Multiplexing) is used for downlink MIMO signal transmission, so the multi-antenna channel estimation of the LTE system can be simplified to that of a single-antenna system. And the maximum supported antenna port number of the 5G downlink is twice that of the LTE system, if only the traditional FDM mode is adopted, the overhead of the pilot frequency becomes large, which seriously affects the performance of the system, so the 5G downlink adopts a pilot frequency placement structure combining frequency division multiplexing and code division multiplexing (CDM, code Division Multiplexing). This structure reduces the overhead of the pilot signal and has better performance when using an equal number of time-frequency resources. However, at the same time, the pilot structure also makes channel estimation more complex, the pilot signal using frequency division multiplexing can be easily separated in the frequency domain, the channel information corresponding to each antenna port can be directly obtained, and the channel information of each antenna port cannot be directly separated due to the change of the channel by using the pilot frequency using code division multiplexing; in this case, how to find the channel information of each antenna port is a difficult problem.
The Chinese patent application No. CN108809868A publication No. 2018, 11, 13 discloses a channel estimation method and system based on a 5G communication network, wherein the channel estimation method comprises the steps of demodulating a reference signal transmitted by a channel to obtain a demodulation reference signal; carrying out channel estimation on each subcarrier in the demodulation reference signal to obtain a channel estimation result of each subcarrier; and calculating the channel impulse response of each subcarrier according to the channel estimation results of the adjacent subcarriers with the preset number adjacent to each subcarrier. According to the embodiment of the invention, the channel impulse response of each subcarrier is calculated through calculating the channel estimation result of each subcarrier in the reference signal and the channel estimation results of the subcarriers with the adjacent preset number of subcarriers, so that the result error of the calculation of the single subcarrier is averaged, and the accuracy of channel estimation is improved. However, this document does not solve the problems of the prior art that the pilot signal overhead is large and the channel estimation complexity is high.
Disclosure of Invention
The invention aims at designing a method and a system for packet interpolation-weighted combination channel estimation of a 5G downlink so as to solve the problems of high pilot signal overhead and high channel estimation complexity in the prior art.
A method of packet interpolation-weighted combining channel estimation for a 5G downlink, comprising the steps of:
s1, in a multi-antenna system of a 5G downlink, a pilot frequency structure adopts a mode of multiplexing FDM and CDM, and a receiving end obtains a frequency domain receiving signal at a pilot frequency symbol through discrete Fourier transform;
s2, carrying out LS estimation and MMSE filtering on the frequency domain received signal; a transform domain approach is introduced that employs partially symmetric spread DFT-transformed channel estimation (PSE-DFT) to reduce the computational complexity of MMSE estimation.
S3, grouping the channel information estimated by LS according to the pilot frequency structure and the period of CDM code, so that each group of subcarrier channel parameters have the same linear combination coefficient; and decomposing the mixed channel information into a plurality of combined signal vectors, wherein T is a sampling interval by taking the first T frequency points of the mixed channel information after MMSE filtering as a starting point, and decomposing out T groups of combined signals, wherein each group of combined signals is a linear combination of frequency domain responses of all antenna ports.
S4, interpolating the channel signals of each group to obtain channel estimation values of all pilot points; the T groups of combined signals obtained by the combination and decomposition are subjected to independent interpolation, and all N can be obtained by adopting discrete Fourier transform interpolation p Estimates of T different linear combinations of multi-antenna port frequency domain responses at each frequency point.
S5, combining all the group weights to obtain channel parameters of each antenna port; and obtaining a synthesis matrix of all the linear combination coefficients according to the pilot frequency structure, and synthesizing estimated values of different linear combinations of channel parameters of all the antenna ports by using the synthesis matrix to obtain frequency domain channel response on pilot frequency symbols of each antenna port.
Compared with the prior art, the pilot frequency placement structure combining Frequency Division Multiplexing (FDM) and Code Division Multiplexing (CDM) reduces the overhead of pilot signals, and has better performance when the same number of time-frequency resources are used, because the multi-antenna ports adopt CDM multiplexing, the signals received by the receiving end antennas are mixed signals, the complete pilot frequency information is obtained by adopting a combination decomposition and combination synthesis method, and the complexity of the implementation of the channel estimation method of the antenna ports adopting CDM multiplexing is reduced.
As a further improvement of the technical scheme of the present invention, the method for performing MMSE filtering in step S2 specifically includes:
LS estimation is carried out on the frequency domain received signal to obtain:
Figure GDA0004259313370000021
performing mirror symmetry expansion on the obtained LS estimation value: let P points spread on each side, i.e. original length N p P points are spread on each mirror image on both sides to obtain a total length N p +2p sequence, the process of which is expressed by mathematical expression:
Figure GDA0004259313370000031
performing DFT conversion on the spread sequence: the P selected in the mirror symmetry expansion is such that the total length after expansion is an integer power of 2, and is implemented by using an FFT algorithm, where the expression is:
Figure GDA0004259313370000032
the sequence after DFT conversion has no correlation, namely the filter matrix Γ is approximate to a diagonal matrix, and the specific expression is:
Figure GDA0004259313370000033
the correlation matrix needs to be estimated
Figure GDA0004259313370000034
And noise power->
Figure GDA0004259313370000035
DFT-processed sequence->
Figure GDA0004259313370000036
Is completely uncorrelated, i.e. the correlation matrix of the sequence +.>
Figure GDA0004259313370000037
The correlation matrix of each time slot is only one sample point, and the correlation matrix is a statistic, so that a large number of sample points are needed; therefore, in order to increase the gain of accurate correlation matrix estimation, it is necessary to add +.>
Figure GDA0004259313370000038
Smooth, set +.>
Figure GDA0004259313370000039
Representing +.>
Figure GDA00042593133700000310
Is a smoothing factor of alpha, then +.>
Figure GDA00042593133700000311
Estimation of noise power: after DFT conversion, the energy of the channel is concentrated on a limited path, so the values of the rest paths are all noise, the estimated value of the noise power can be obtained by averaging the values on the paths, and a total of N is set σ The points are noise, so the average is:
Figure GDA00042593133700000312
performing IDFT on the filtered signals to obtain:
Figure GDA00042593133700000313
despreading the inverse transformed sequence, taking the middle N p The individual values can be obtained:
Figure GDA00042593133700000314
the MMSE filtered mixed channel vector is expressed as:
Figure GDA0004259313370000041
wherein, the liquid crystal display device comprises a liquid crystal display device,
Figure GDA0004259313370000042
represents noise after MMSE filtering, +.>
Figure GDA0004259313370000043
Representing the hybrid channel response of the antenna ports within the ith CDM code group; the mixed channel response g is the channel response g of each antenna port in the same CDM code group p And coefficient C p Multiplying and then summing to obtain; c (C) p Is formed by an orthogonal mask c p Obtained by periodic expansion, i.e. orthogonal code C p The elements in (a) have periodicity, and the periodicity is the number of OCCs in one CDM code group, and is also the number T= |W of antenna ports of one CDM code group i |。
As a further improvement of the technical solution of the present invention, the method for grouping the channel information estimated by LS according to the pilot structure and the period of the CDM code in step S3, so that each group of subcarrier channel parameters has the same linear combination coefficient is as follows: decomposing the mixed channel information into a plurality of combined signal vectors to cause
Figure GDA0004259313370000044
g p,t ＝[g p,t (1),g p,t (2),…,g p,t (M)] T 、/>
Figure GDA0004259313370000045
Respectively representing t-th combined channel response, p-th antenna port t-th combined channel response and t-th combined noise vector, wherein ∈>
Figure GDA0004259313370000046
Then:
Figure GDA0004259313370000047
wherein, the liquid crystal display device comprises a liquid crystal display device,
Figure GDA0004259313370000048
g p,t (j)＝g p (j′),j＝1,2,…,M,j′＝(j-1)×T+t；/>
Figure GDA0004259313370000049
Figure GDA00042593133700000410
as a further improvement of the technical solution of the present invention, the method for interpolating the channel signals of each group in step S4 to obtain the channel estimation values of all pilot points includes:
will be
Figure GDA00042593133700000411
Performing DFT conversion to obtain: />
Figure GDA00042593133700000412
Zero padding operation is carried out on channel response parameters of the DFT conversion domain, and the sampling number of the channel is increased to obtain the length N p Channel response of (c):
Figure GDA00042593133700000413
finally, carrying out IDFT on the zero-filled DFT domain channel response to obtain N p Channel response of point:
Figure GDA00042593133700000414
as a further improvement of the technical solution of the present invention, the method for combining all the combining weights in step S5 to obtain the channel parameters of each antenna port includes: representing estimates of T different linear combinations of channel response parameters for T antenna ports as a matrix
Figure GDA0004259313370000051
Obtaining a synthesis matrix of all linear combination coefficients according to a pilot frequency structure, synthesizing estimated values of different linear combinations of channel parameters of all antenna ports by using the synthesis matrix, and obtaining a frequency domain channel response on pilot frequency symbols of each antenna port, wherein the synthesis matrix is as follows: />
Figure GDA0004259313370000052
Wherein p is E W i The method comprises the steps of carrying out a first treatment on the surface of the Calculating T unknowns according to T linear uncorrelated equations; synthesizing the estimated values of different linear combinations of the channel parameters of the plurality of antenna ports on each pilot frequency point by utilizing the synthesis matrix to obtain the estimated value of the channel frequency domain response of each antenna, wherein the estimated value of the frequency domain response of the t antenna port is as follows: />
Figure GDA0004259313370000053
A packet interpolation-weighted combining channel estimation system for a 5G downlink, comprising: a first module, a second module, a third module, a fourth module, and a fifth module;
the first module is used for obtaining a frequency domain receiving signal at a pilot symbol by a receiving end through discrete Fourier transform in a multi-antenna system of a 5G downlink by adopting a mode of multiplexing FDM and CDM;
the second module is used for carrying out LS estimation and MMSE filtering on the frequency domain received signal;
the third module is configured to group the channel information estimated by the LS according to the pilot structure and the period of the CDM code, so that each group of subcarrier channel parameters has the same linear combination coefficient;
the fourth module is used for interpolating the channel signals of each group to obtain channel estimation values of all pilot points;
and the fifth module is used for combining all the group weights to obtain the channel parameters of each antenna port.
As a further improvement of the technical solution of the present invention, the method for performing MMSE filtering in the second module specifically includes:
LS estimation is carried out on the frequency domain received signal to obtain:
Figure GDA0004259313370000054
performing mirror symmetry expansion on the obtained LS estimation value: let P points spread on each side, i.e. original length N p P points are spread on each mirror image on both sides to obtain a total length N p +2p sequence, the process of which is expressed by mathematical expression:
Figure GDA0004259313370000055
performing DFT conversion on the spread sequence: the P selected in the mirror symmetry expansion is such that the total length after expansion is an integer power of 2, and is implemented by using an FFT algorithm, where the expression is:
Figure GDA0004259313370000061
the sequence after DFT conversion has no correlation, namely the filter matrix Γ is approximate to a diagonal matrix, and the specific expression is:
Figure GDA0004259313370000062
the correlation matrix needs to be estimated
Figure GDA0004259313370000063
And noise power->
Figure GDA0004259313370000064
DFT-processed sequence->
Figure GDA0004259313370000065
Is completely uncorrelated, i.e. the correlation matrix of the sequence +.>
Figure GDA0004259313370000066
The correlation matrix of each time slot is only one sample point, and the correlation matrix is a statistic, so that a large number of sample points are needed; therefore, in order to increase the gain of accurate correlation matrix estimation, it is necessary to add +.>
Figure GDA0004259313370000067
Smooth, set +.>
Figure GDA0004259313370000068
Representing +.>
Figure GDA0004259313370000069
Is a smoothing factor of alpha, then +.>
Figure GDA00042593133700000610
Estimation of noise power: after DFT conversion, the energy of the channel is concentrated on a limited path, so the values of the rest paths are all noise, the estimated value of the noise power can be obtained by averaging the values on the paths, and a total of N is set σ The points are noise, so the average is:
Figure GDA00042593133700000611
performing IDFT on the filtered signals to obtain:
Figure GDA00042593133700000612
despreading the inverse transformed sequence, taking the middle N p The individual values can be obtained:
Figure GDA00042593133700000613
the MMSE filtered mixed channel vector is expressed as:
Figure GDA00042593133700000614
wherein, the liquid crystal display device comprises a liquid crystal display device,
Figure GDA00042593133700000615
represents noise after MMSE filtering, +.>
Figure GDA00042593133700000616
Representing the hybrid channel response of the antenna ports within the ith CDM code group; the mixed channel response g is the channel response g of each antenna port in the same CDM code group p And coefficient C p Multiplying and then summing to obtain; c (C) p Is formed by an orthogonal mask c p Obtained by periodic expansion, i.e. orthogonal code C p The elements in (a) have periodicity, and the periodicity is the number of OCCs in one CDM code group, and is also the number T= |W of antenna ports of one CDM code group i |。
As a further improvement of the technical solution of the present invention, the method for grouping the channel information estimated by LS according to the pilot structure and the period of the CDM code in the third module so that each group of subcarrier channel parameters has the same linear combination coefficient is as follows: decomposing the mixed channel information into a plurality of combined signal vectors to cause
Figure GDA0004259313370000071
g p,t ＝[g p,t (1),d p,t (2),…,g p,t (M)] T 、/>
Figure GDA0004259313370000072
Respectively representing t-th combined channel response, p-th antenna port t-th combined channel response and t-th combined noise vector, wherein ∈>
Figure GDA0004259313370000073
Then:
Figure GDA0004259313370000074
wherein, the liquid crystal display device comprises a liquid crystal display device,
Figure GDA0004259313370000075
g p,t (j)＝g p (j′),j＝1,2,…,M,j′＝(j-1)×T+t；/>
Figure GDA0004259313370000076
Figure GDA0004259313370000077
as a further improvement of the technical solution of the present invention, the method for interpolating the channel signals of each group in the fourth module to obtain the channel estimation values of all pilot points includes:
will be
Figure GDA0004259313370000078
Performing DFT conversion to obtain: />
Figure GDA0004259313370000079
Zero padding operation is carried out on channel response parameters of the DFT conversion domain, and the sampling number of the channel is increased to obtain the length N p Channel response of (c):
Figure GDA00042593133700000710
finally, carrying out IDFT on the zero-filled DFT domain channel response to obtain N p Channel response of point:
Figure GDA00042593133700000711
as a further improvement of the technical solution of the present invention, the method for combining all the combining weights in the fifth module to obtain the channel parameters of each antenna port includes: representing estimates of T different linear combinations of channel response parameters for T antenna ports as a matrix
Figure GDA00042593133700000712
Obtaining a synthesis matrix of all linear combination coefficients according to a pilot frequency structure, synthesizing estimated values of different linear combinations of channel parameters of all antenna ports by using the synthesis matrix, and obtaining a frequency domain channel response on pilot frequency symbols of each antenna port, wherein the synthesis matrix is as follows: />
Figure GDA00042593133700000713
Wherein p is E W i The method comprises the steps of carrying out a first treatment on the surface of the Calculating T unknowns according to T linear uncorrelated equations; synthesizing the estimated values of different linear combinations of the channel parameters of the plurality of antenna ports on each pilot frequency point by utilizing the synthesis matrix to obtain the estimated value of the channel frequency domain response of each antenna, wherein the estimated value of the frequency domain response of the t antenna port is as follows: />
Figure GDA0004259313370000081
The invention has the advantages that:
compared with the prior art, the pilot frequency placement structure combining Frequency Division Multiplexing (FDM) and Code Division Multiplexing (CDM) reduces the overhead of pilot signals, and has better performance when the same number of time-frequency resources are used, because the multi-antenna ports adopt CDM multiplexing, the signals received by the receiving end antennas are mixed signals, the complete pilot frequency information is obtained by adopting a combination decomposition and combination synthesis method, and the complexity of the implementation of the channel estimation method of the antenna ports adopting CDM multiplexing is reduced.
Drawings
Fig. 1 is a flowchart of a packet interpolation-weighted combining channel estimation method for a 5G downlink according to an embodiment of the present invention;
fig. 2 is a block diagram of a 5G downlink system according to a first embodiment of the present invention;
fig. 3 is a block diagram of channel estimation using a partially symmetric-spread DFT transform according to an embodiment of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The technical scheme of the invention is further described below with reference to the attached drawings and specific embodiments:
example 1
As shown in fig. 1 and fig. 2, the processing procedure of the 5G downlink in the embodiment of the present invention is as follows:
at the base station end, the user data stream is coded, rate-matched, modulated, layer-mapped, inserted pilot frequency is mapped to the time-frequency resource grid of each antenna port, pre-coded, then modulated by IFFT (Inverse Fast Fourier Transform ) and added with CP (Cyclic Prefix), and finally transmitted.
At the user end, the channel is received, de-CPs and FFT (Fast Fourier Transform ) de-modulation, sub-carrier de-mapping, pilot extraction, channel estimation.
Assuming that there is no interference between the pre-encoded beams, the method of packet interpolation-weighted combining channel estimation for the 5G downlink of the present invention will be described below by taking detailed analysis of users within one beam as an example.
The base station is provided with N T The root transmit antenna has P (p=1, 2,4,8, where p=4) antenna ports, the reference signals occupy the same time-frequency resource block, the antenna port set distinguished by OCC is called a CDM code group, W i Index set indicating the antenna port included in the i (i=0, 1 CDM code group, e.g., W) 0 = {0,1} means that the 0 th CDM code group contains two antenna ports 0 and 1.
Let user terminal configuration N R Root receiving antenna, where N T Far greater than N R The following description will take OFDM (Orthogonal Frequency Division Multiplexing, i.e., orthogonal frequency division multiplexing) symbols containing pilots as an example. Let the number of frequency domain subcarriers of the system be N I The number of actually allocated subcarriers is N b RB number is N RB . If the first OFDM symbol in one data subframe on the p-th antenna port contains pilot frequency, making the OFDM symbol be
Figure GDA0004259313370000091
From the pilot structure, it is known that:
Figure GDA0004259313370000092
wherein, the liquid crystal display device comprises a liquid crystal display device,
Figure GDA0004259313370000093
for the length N of the first OFDM symbol in one data subframe on the p-th antenna port p ＝6N RB Is a pilot sequence of (a); />
Figure GDA0004259313370000094
Representing the orthogonal code used by the p-th antenna port; />
Figure GDA0004259313370000095
Representing the pilot sequence to OFDM symbol subcarrier mapping matrix for the p-th antenna port.
The specific transceiving flow from the base station antenna port to the user antenna is as follows: (1) Each antenna port of the base station end will be N b Point-containing pilot data symbols
Figure GDA0004259313370000096
According to the centralized mapping matrix Q, from dimension N b Mapping the signal vector of (2) to N I Vector of dimension; (2) Precoding data of the P antenna ports, and mapping the data to N through a precoding matrix W T On each physical antenna, each antenna corresponds to N I A data vector of dimensions; (3) For N on each physical antenna I Vector N I Performing IFFT operation of points, performing serial-parallel conversion on the obtained time domain signals, and adding CPs; (4) the user receives the signal, removes CP and carries on FFT transformation; (5) Will receive N I Vector inverse mapping of dimensions to N b Is used for the signal vector of (a).
Let the downlink transmission channel be a quasi-static channel with a channel length L. The different antennas and the different paths are uncorrelated, and the receiving end is ideally synchronous. Then, the frequency domain expression of the j sub-carrier signal of the first pilot-containing OFDM symbol received by the nth antenna of the user is:
Figure GDA0004259313370000097
Figure GDA0004259313370000101
wherein h is n,m (j) Representing the frequency domain channel response of the jth subcarrier from the mth transmit antenna to the nth receive antenna,
Figure GDA0004259313370000102
precoding matrix representing antenna port to physical antenna, < ->
Figure GDA0004259313370000103
Nth OFDM symbol representing the nth antenna port i Symbol of subcarrier g n,m (j) Represents the N < th i Equivalent virtual channel response of sub-carriers from the p-th transmit port to the n-th receive antenna, ">
Figure GDA0004259313370000104
Indicating that the nth receiving antenna is at the nth of the first OFDM symbol i Noise of sub-carrier, obeying the mean value 0, power +.>
Figure GDA0004259313370000105
Is a complex gaussian distribution of (c).
All antenna ports are divided into different CDM groups, pilot frequency of the same CDM group antenna port occupies the same time-frequency resource, and the formula 2 can be written as follows by adopting code division multiplexing:
Figure GDA0004259313370000106
the pilots used by the antenna ports belonging to different CDM groups are frequency division multiplexed, i.e., the sets of time-frequency resource blocks used by them are independent and do not overlap each other, and the time-frequency resource used by one CDM group will not transmit any signal in the other CDM, i.e., set to zero, so the pilot signal of the ith CDM group can be easily extracted from equation 3, expressed as:
Figure GDA0004259313370000107
therefore, the signal that the terminal nth antenna receives all subcarriers of the ith OFDM symbol of the antenna port in the ith CDM group can be expressed as:
Figure GDA0004259313370000108
Figure GDA0004259313370000111
wherein, the liquid crystal display device comprises a liquid crystal display device,
Figure GDA0004259313370000112
g n,p ＝[g n,p (1),g n,p (2),…,g n,p (N b )] T ，/>
Figure GDA0004259313370000113
is the complex Gaussian white noise vector of the ith OFDM symbol from the ith CDM code group antenna port to the nth receiving antenna, with dimension N b The mean value is zero, the variance is +.>
Figure GDA0004259313370000114
Matrix P p Is a mapping matrix, is represented by N b N occupied by pilot signal in sub-carrier p The positions of the sub-carriers. For ease of calculation we here represent only the signal of the pilot sub-carriers
Figure GDA0004259313370000115
Wherein, the liquid crystal display device comprises a liquid crystal display device,
Figure GDA0004259313370000116
representing the channel response for the subcarriers occupied by the pilot sequence. The generation of pilot sequence is known to be independent of antenna port number by the reference signal generation process, let +.>
Figure GDA0004259313370000117
Equation 6 can be written as:
Figure GDA0004259313370000118
for convenience of presentation, we remove the superscripts that do not change in the following calculations. Thus, equation 7 can be reduced to
Figure GDA0004259313370000119
From the above equation, it can be seen that the downlink system can be simplified to a plurality of simple systems with two transmitting and one receiving, and the pilot signals of the two transmitting antenna ports are processed by adopting a code division multiplexing manner.
In the LS and MMSE channel estimation method, only the average value of every two adjacent pilots is obtained, namely the length N is used p The pilot sequence only finds N p The pilot information is not fully utilized by/2 frequency domain channel parameters.
Thus, to further improve the accuracy of the channel estimation, the present invention employs a packet-interpolation-filtering (Grouping interpolation and merging, GIM) algorithm.
Formula 8 is rewritten as:
y=xg+z (formula 9)
Wherein, the liquid crystal display device comprises a liquid crystal display device,
Figure GDA00042593133700001110
representing the channel mix response of all antenna ports within a CDM of the base station to one antenna of the user.
LS estimation and MMSE filtering are performed on the channel mixed response.
Under the MMSE criterion, the MMSE estimation expression of the channel mixed response g can be obtained as follows:
Figure GDA0004259313370000121
in the MMSE channel estimation method, matrix inversion operation exists, and the invention introduces a transform domain method to reduce the computation complexity of MMSE estimation. Common one-dimensional transform domain methods are DFT channel estimation, DCT channel estimation, where partially symmetric spread DFT-transformed channel estimation (PSE-DFT) is employed.
LS estimation is carried out on the frequency domain received signal, and the obtained result is:
Figure GDA0004259313370000122
the obtained LS estimation value is subjected to mirror symmetry expansion, and each side is assumed to be expanded by P points, namely the original length is N p P points are spread on each mirror image on both sides to obtain a total length N p +2p sequence, the process of which is expressed by mathematical expression:
Figure GDA0004259313370000123
the DFT-transformed sequence after spreading can be implemented using an FFT algorithm if P chosen in the mirror-symmetric spreading is such that the total length after spreading is an integer power of 2. The expression is as follows:
Figure GDA0004259313370000124
performing MMSE filtering, and assuming that DFT conversion has good decorrelation, the sequence after DFT conversion has no correlation, namely the filter matrix Γ can be approximated to a diagonal matrix, and the specific expression is:
Figure GDA0004259313370000125
wherein the correlation matrix needs to be estimated
Figure GDA0004259313370000126
And noise power->
Figure GDA0004259313370000127
Assume that the sequence after DFT +.>
Figure GDA0004259313370000128
Is completely uncorrelated, i.e. the correlation matrix of the sequence +.>
Figure GDA0004259313370000129
Is a diagonal matrix. The correlation matrix for each slot is only one sample point, while the correlation matrix is a statistic and requires a large number of sample points. Therefore, in order to increase the gain of accurate correlation matrix estimation, it is necessary to add +.>
Figure GDA00042593133700001210
Smooth, set +.>
Figure GDA00042593133700001211
Representing +.>
Figure GDA00042593133700001212
The smoothing factor is alpha (which is typically found from simulations), then +.>
Figure GDA00042593133700001213
Figure GDA0004259313370000131
For the estimation of the noise power, it is assumed that the energy of the channel is concentrated on a limited path after DFT conversion, so that the values of the remaining paths are all noise, and the estimated value of the noise power can be obtained by averaging the values on the paths. Let a total of N σ The individual points are noise (this value is typically obtained from simulations), so the average is:
Figure GDA0004259313370000132
IDFT (Inverse Discrete Fourier Transform ) is performed on the filtered signal to obtain:
Figure GDA0004259313370000133
despreading the inverse transformed sequence and taking the middleN p The individual values can be obtained:
Figure GDA0004259313370000134
the MMSE filtered mixed channel vector may represent:
Figure GDA0004259313370000135
/>
wherein, the liquid crystal display device comprises a liquid crystal display device,
Figure GDA0004259313370000136
represents noise after MMSE filtering, +.>
Figure GDA0004259313370000137
Representing the hybrid channel response of the antenna ports within the i-th CDM code group. The mixed channel response g is the channel response g of each antenna port in the same CDM code group p And coefficient C p Multiplication and then summation. C (C) p Is formed by an orthogonal mask c p Obtained by periodic expansion, i.e. orthogonal code C p The elements in (a) have periodicity, and the periodicity is the number of OCCs in one CDM code group, and is also the number T= |W of antenna ports of one CDM code group i |。
According to the characteristic, the mixed channel information in the formula 17 is decomposed into a plurality of combined signal vectors, if the following is made
Figure GDA0004259313370000138
g p,t ＝g p,t (1), p,t (2),…, p,t (M)] T 、/>
Figure GDA0004259313370000139
Respectively representing t-th combined channel response, p-th antenna port t-th combined channel response and t-th combined noise vector, wherein
Figure GDA00042593133700001310
Then:
Figure GDA00042593133700001311
wherein, the liquid crystal display device comprises a liquid crystal display device,
Figure GDA00042593133700001312
g p,t (j)＝g p (j′),j＝1,2,…,M,j′＝(j-1)×T+t；/>
Figure GDA00042593133700001313
Figure GDA0004259313370000141
as can be seen from equation 18, the combining and decomposing refers to decomposing T groups of combined signals with the first T frequency points of the mixed channel information after MMSE filtering as the starting point, and T as the sampling interval, where each group of combined signals is a linear combination of frequency domain responses of all antenna ports.
The T groups of combined signals obtained by the combination decomposition are subjected to independent interpolation, so that all N groups of combined signals can be obtained p Estimates of T different linear combinations of multi-antenna port frequency domain responses at each frequency point. The invention adopts a discrete Fourier interpolation method to carry out
Figure GDA0004259313370000142
Performing DFT conversion to obtain: />
Figure GDA0004259313370000143
Zero padding operation is carried out on channel response parameters of DFT (Discrete Fourier Transform ) transformation domain, and the sampling number of the channel is increased to obtain a length N p Channel response of (c):
Figure GDA0004259313370000144
finally, carrying out IDFT on the zero-filled DFT domain channel response to obtain N p Channel response of point:
Figure GDA0004259313370000145
by the equation 18, it can be seen that the combined signal is an estimated value of T-group uncorrelated linear combinations of T-antenna ports, and the estimated values of T-different linear combinations of channel response parameters of T-antenna ports can be expressed as a matrix
Figure GDA0004259313370000146
And then, according to the pilot structure, obtaining a synthesis matrix of all the linear combination coefficients, and synthesizing estimated values of different linear combinations of channel parameters of all the antenna ports by using the synthesis matrix to obtain frequency domain channel response on pilot symbols of each antenna port. The synthesis matrix is:
Figure GDA0004259313370000147
wherein p is E W i 。
Obviously, we can calculate T unknowns from T linearly uncorrelated equations. Synthesizing the estimated values of different linear combinations of the channel parameters of the plurality of antenna ports on each pilot frequency point by utilizing the synthesis matrix of the formula 20 to obtain an estimated value of the channel frequency domain response of each antenna, wherein the estimated value of the frequency domain response of the t antenna port is as follows:
Figure GDA0004259313370000148
the invention researches a grouping interpolation-weighting combination channel estimation method based on pilot frequency assistance of a 5G downlink, wherein a pilot frequency placement structure combining Frequency Division Multiplexing (FDM) and Code Division Multiplexing (CDM) is adopted in a system, the algorithm utilizes the periodical change of CDM codes in a frequency domain, sub-carriers with the same coefficient combination are extracted to be used as a group, then each group is interpolated to obtain channel information of all pilot frequency points, and finally the channel information of each group is combined to obtain frequency domain channel response of all pilot frequencies of each antenna port. Compared with the prior art, the structure reduces the overhead of pilot signals, has better performance when using the same number of time-frequency resources, and can obtain complete pilot information by utilizing a combination decomposition and combination synthesis method because the signals received by the antenna of the receiving end are mixed signals by adopting CDM multiplexing of a plurality of antenna ports, and reduces the complexity of the realization of the antenna port channel estimation method which adopts CDM multiplexing.
Unlike LTE, the pilot structure of the 5G downlink adopts a combination of FDM and CDM, where the FDM multiplexing mode is based on that different antenna ports occupy different subcarrier sets, so that different antenna ports are easily separated in the frequency domain. The CDM multiplexing means that different antenna ports occupy the same time-frequency resource, and the pilot signals of different antenna ports are obtained by multiplying the sequences by an orthogonal code using the same sequence.
The invention firstly describes the reference signal of the physical downlink shared channel (Physical Downlink Shared Channel, PDSCH) link of the 5G system, and then establishes a physical downlink shared channel model of the 5G system. Since the physical downlink shared channel model of the 5G system can be simplified into a CDM multiplexing multi-antenna channel model, the invention mainly expands and researches the model. Classical channel estimation methods are mainly LS estimation and MMSE estimation, and by directly using the method in a CDM multiplexing multi-antenna channel model, channel information of subcarriers occupied by pilot frequency cannot be obtained, and the obtained frequency domain channel parameters are far smaller than the pilot frequency length, for example, two antenna ports are multiplexed by CDM, and the obtained channel parameters are half of the pilot frequency length. In order to improve the accuracy of channel estimation, the invention provides a channel estimation method of packet interpolation filtering, which separates the channel information of multiple antenna ports by a mathematical method and avoids the interference between the antenna ports. Compared with the prior art, the pilot frequency placement structure combining Frequency Division Multiplexing (FDM) and Code Division Multiplexing (CDM) reduces the overhead of pilot signals, and has better performance when using the same amount of time-frequency resources.
The above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (2)

  1. The packet interpolation-weighted combination channel estimation method of the 5G downlink is characterized by comprising the following steps:
    s1, in a multi-antenna system of a 5G downlink, a pilot frequency structure adopts a mode of multiplexing FDM and CDM, and a receiving end obtains a frequency domain receiving signal at a pilot frequency symbol through discrete Fourier transform;
    s2, carrying out LS estimation and MMSE filtering on the frequency domain received signal; the method comprises the following steps:
    LS estimation is carried out on the frequency domain received signal to obtain:
    Figure QLYQS_1
    performing mirror symmetry expansion on the obtained LS estimation value: let P points spread on each side, i.e. original length N p P points are spread on each mirror image on both sides to obtain a total length N p +2p sequence, the process of which is expressed by mathematical expression:
    Figure QLYQS_2
    performing DFT conversion on the spread sequence: the P selected in the mirror symmetry expansion is such that the total length after expansion is an integer power of 2, and is implemented by using an FFT algorithm, where the expression is:
    Figure QLYQS_3
    the sequence after DFT conversion has no correlation, namely the filter matrix Γ is approximate to a diagonal matrix, and the specific expression is:
    Figure QLYQS_4
    the correlation matrix needs to be estimated
    Figure QLYQS_7
    And noise power->
    Figure QLYQS_9
    DFT-processed sequence->
    Figure QLYQS_11
    Is completely uncorrelated, i.e. the correlation matrix of the sequence +.>
    Figure QLYQS_6
    The correlation matrix of each time slot is only one sample point, and the correlation matrix is a statistic, so that a large number of sample points are needed; therefore, in order to increase the gain of accurate correlation matrix estimation, it is necessary to add +.>
    Figure QLYQS_8
    Smooth, set +.>
    Figure QLYQS_10
    Representing +.>
    Figure QLYQS_12
    Is a smoothing factor of alpha, then
    Figure QLYQS_5
    Estimation of noise power: after DFT conversion, the energy of the channel is concentrated on a limited path, so the values of the rest paths are all noise, the estimated value of the noise power can be obtained by averaging the values on the paths, and a total of N is set σ The points are noise, so the average is:
    Figure QLYQS_13
    performing IDFT on the filtered signals to obtain:
    Figure QLYQS_14
    despreading the inverse transformed sequence, taking the middle N p The individual values can be obtained:
    Figure QLYQS_15
    the MMSE filtered mixed channel vector is expressed as:
    Figure QLYQS_16
    wherein, the liquid crystal display device comprises a liquid crystal display device,
    Figure QLYQS_17
    represents noise after MMSE filtering, +.>
    Figure QLYQS_18
    Representing the hybrid channel response of the antenna ports within the ith CDM code group; the mixed channel response g is the channel response g of each antenna port in the same CDM code group p And coefficient C p Multiplying and then summing to obtain; c (C) p Is formed by an orthogonal mask c p Obtained by periodic expansion, i.e. orthogonal code C p The elements in (a) have periodicity, and the periodicity is the number of OCCs in one CDM code group, and is also the number T= |W of antenna ports of one CDM code group i |；
    S3, grouping the channel information estimated by LS according to the pilot frequency structure and the period of CDM code, so that each group of subcarrier channel parameters have the same linear combination coefficient; the method comprises the following steps:
    decomposing the mixed channel information into a plurality of combined signal vectors to cause
    Figure QLYQS_19
    g p,t ＝[g p,t (1),g p,t (2),…,g p,t (M)] T 、/>
    Figure QLYQS_20
    Respectively representing t-th combined channel response, p-th antenna port t-th combined channel response and t-th combined noise vector, wherein ∈>
    Figure QLYQS_21
    Then:
    Figure QLYQS_22
    wherein, the liquid crystal display device comprises a liquid crystal display device,
    Figure QLYQS_23
    g p,t (j)＝g p (j′),j＝1,2,…,M,j′＝(j-1)×T+t；/>
    Figure QLYQS_24
    Figure QLYQS_25
    s4, interpolating the channel signals of each group to obtain channel estimation values of all pilot points; the method comprises the following steps: will be
    Figure QLYQS_26
    Making DFT changesAnd (3) replacing to obtain: />
    Figure QLYQS_27
    Zero padding operation is carried out on channel response parameters of the DFT conversion domain, and the sampling number of the channel is increased to obtain the length N p Channel response of (c):
    Figure QLYQS_28
    finally, carrying out IDFT on the zero-filled DFT domain channel response to obtain N p Channel response of point:
    Figure QLYQS_29
    s5, combining all the group weights to obtain channel parameters of each antenna port; the method comprises the following steps:
    representing estimates of T different linear combinations of channel response parameters for T antenna ports as a matrix
    Figure QLYQS_30
    Obtaining a synthesis matrix of all linear combination coefficients according to a pilot frequency structure, synthesizing estimated values of different linear combinations of channel parameters of all antenna ports by using the synthesis matrix, and obtaining a frequency domain channel response on pilot frequency symbols of each antenna port, wherein the synthesis matrix is as follows: />
    Figure QLYQS_31
    Wherein p is E W i The method comprises the steps of carrying out a first treatment on the surface of the Calculating T unknowns according to T linear uncorrelated equations; synthesizing the estimated values of different linear combinations of the channel parameters of the plurality of antenna ports on each pilot frequency point by utilizing a synthesis matrix to obtain an estimated value of the channel frequency domain response of each antenna, wherein the estimated value of the frequency domain response of the t-th antenna port is as follows: />
    Figure QLYQS_32
  2. A system for packet interpolation-weighted combining channel estimation for a 5G downlink, comprising: a first module, a second module, a third module, a fourth module, and a fifth module;
    the first module is used for obtaining a frequency domain receiving signal at a pilot symbol by a receiving end through discrete Fourier transform in a multi-antenna system of a 5G downlink by adopting a mode of multiplexing FDM and CDM;
    the second module is used for carrying out LS estimation and MMSE filtering on the frequency domain received signal; the method comprises the following steps:
    LS estimation is carried out on the frequency domain received signal to obtain:
    Figure QLYQS_33
    performing mirror symmetry expansion on the obtained LS estimation value: let P points spread on each side, i.e. original length N p P points are spread on each mirror image on both sides to obtain a total length N p +2p sequence, the process of which is expressed by mathematical expression:
    Figure QLYQS_34
    performing DFT conversion on the spread sequence: the P selected in the mirror symmetry expansion is such that the total length after expansion is an integer power of 2, and is implemented by using an FFT algorithm, where the expression is:
    Figure QLYQS_35
    the sequence after DFT conversion has no correlation, namely the filter matrix Γ is approximate to a diagonal matrix, and the specific expression is:
    Figure QLYQS_36
    the correlation matrix needs to be estimated
    Figure QLYQS_39
    And noise power->
    Figure QLYQS_40
    DFT-processed sequence->
    Figure QLYQS_42
    Is completely uncorrelated, i.e. the correlation matrix of the sequence +.>
    Figure QLYQS_38
    The correlation matrix of each time slot is only one sample point, and the correlation matrix is a statistic, so that a large number of sample points are needed; therefore, in order to increase the gain of accurate correlation matrix estimation, it is necessary to add +.>
    Figure QLYQS_41
    Smooth, set +.>
    Figure QLYQS_43
    Representing +.>
    Figure QLYQS_44
    Is a smoothing factor of alpha, then
    Figure QLYQS_37
    Estimation of noise power: after DFT conversion, the energy of the channel is concentrated on a limited path, so the values of the rest paths are all noise, the estimated value of the noise power can be obtained by averaging the values on the paths, and a total of N is set σ The points are noise, so the average is:
    Figure QLYQS_45
    performing IDFT on the filtered signals to obtain:
    Figure QLYQS_46
    despreading the inverse transformed sequence, taking the middle N p The individual values can be obtained:
    Figure QLYQS_47
    the MMSE filtered mixed channel vector is expressed as:
    Figure QLYQS_48
    wherein, the liquid crystal display device comprises a liquid crystal display device,
    Figure QLYQS_49
    represents noise after MMSE filtering, +.>
    Figure QLYQS_50
    Representing the hybrid channel response of the antenna ports within the ith CDM code group; the mixed channel response g is the channel response g of each antenna port in the same CDM code group p And coefficient C p Multiplying and then summing to obtain; c (C) p Is formed by an orthogonal mask c p Obtained by periodic expansion, i.e. orthogonal code C p The elements in (a) have periodicity, and the periodicity is the number of OCCs in one CDM code group, and is also the number T= |W of antenna ports of one CDM code group i |；
    The third module is configured to group the channel information estimated by the LS according to the pilot structure and the period of the CDM code, so that each group of subcarrier channel parameters has the same linear combination coefficient; the method comprises the following steps:
    decomposing the mixed channel information into a plurality of combined signal vectors to cause
    Figure QLYQS_51
    g p,t ＝[g p,t (1),g p,t (2),…,g p,t (M)] T 、/>
    Figure QLYQS_52
    Respectively representing t-th combined channel response, p-th antenna port t-th combined channel response and t-th combined noise vector, wherein ∈>
    Figure QLYQS_53
    Then:
    Figure QLYQS_54
    wherein, the liquid crystal display device comprises a liquid crystal display device,
    Figure QLYQS_55
    g p,t (j)＝g p (j′),j＝1,2,…,M,j′＝(j-1)×T+t；/>
    Figure QLYQS_56
    Figure QLYQS_57
    the fourth module is used for interpolating the channel signals of each group to obtain channel estimation values of all pilot points; the method comprises the following steps:
    will be
    Figure QLYQS_58
    Performing DFT conversion to obtain: />
    Figure QLYQS_59
    Zero padding operation is carried out on channel response parameters of the DFT conversion domain, and the sampling number of the channel is increased to obtain the length N p Channel response of (c):
    Figure QLYQS_60
    finally, the DF is zero-filledIDFT is carried out on T domain channel response to obtain N p Channel response of point:
    Figure QLYQS_61
    the fifth module is used for weighting and combining all the groups to obtain channel parameters of each antenna port; the method comprises the following steps:
    representing estimates of T different linear combinations of channel response parameters for T antenna ports as a matrix
    Figure QLYQS_62
    Obtaining a synthesis matrix of all linear combination coefficients according to a pilot frequency structure, synthesizing estimated values of different linear combinations of channel parameters of all antenna ports by using the synthesis matrix, and obtaining a frequency domain channel response on pilot frequency symbols of each antenna port, wherein the synthesis matrix is as follows: />
    Figure QLYQS_63
    Wherein p is E W i The method comprises the steps of carrying out a first treatment on the surface of the Calculating T unknowns according to T linear uncorrelated equations; synthesizing the estimated values of different linear combinations of the channel parameters of the plurality of antenna ports on each pilot frequency point by utilizing a synthesis matrix to obtain an estimated value of the channel frequency domain response of each antenna, wherein the estimated value of the frequency domain response of the t-th antenna port is as follows: />
    Figure QLYQS_64
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