CN111064500B - Precoding codebook design method based on channel coding in large-scale MIMO system - Google Patents
Precoding codebook design method based on channel coding in large-scale MIMO system Download PDFInfo
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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
- H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
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- H04L1/00—Arrangements for detecting or preventing errors in the information received
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- H04L1/0009—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the channel coding
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Abstract
The invention belongs to the technical field of wireless communication, and particularly relates to a precoding codebook design method based on channel coding in a large-scale MIMO system in the large-scale MIMO system, which comprises the following steps: designing a sending signal and processing a receiving signal; channel coding; constructing a precoding codebook; the precoding codebook is determined by maximizing the channel utilization as an optimization objective. Compared with the traditional precoding design method based on the codebook, the precoding codebook design method based on the channel coding can realize the construction of a high-dimensional codebook, obtain higher channel utilization rate and improve channel estimation so as to further improve the system performance.
Description
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a precoding codebook design method based on channel coding in a large-scale MIMO system.
Background
In a large-scale MIMO system, a base station needs to perform precoding using downlink channel information to obtain better transmission performance. In a frequency division duplex system, downlink channel information can be obtained by using feedback of a user terminal, but the practical application is limited, so that a limited set of precoding codebooks need to be designed in advance, namely, codebooks known by both a receiver and a transmitter. The receiver selects an optimal precoding codebook from the codebook according to Channel State Information (CSI), and transmits a precoding codebook sequence number (PMI) to the transmitter through a limited feedback channel. By this mechanism, the system can obtain performance improvements by using well-designed codebooks.
The design of the codebook is crucial due to the limitations of the feedback channel. Codebook design is a quantization problem in which we should balance the precision and overhead of bits. However, the current codebook design mainly focuses on the lower dimensionality, limits the number of access users of the system to a certain extent, and along with the increase of the number of antennas, the dimensionality of the codebook is increased, and the search complexity of the codebook is not small and varied. In summary, it is significant to study the design scheme of the high-dimensional codebook and the performance of the high-dimensional codebook in terms of system performance and decoding complexity.
Disclosure of Invention
The invention provides a precoding codebook design method based on channel coding in a large-scale MIMO system, and solves the problems that the design complexity is high and the design is difficult to realize based on a high-dimensional codebook.
In order to achieve the purpose, the invention adopts the following technical scheme:
a precoding codebook design method based on channel coding in a large-scale MIMO system is used for FDD downlink single users and comprises the following steps:
s1, designing a sending signal and processing a receiving signal;
s2, channel coding;
s3, constructing a precoding codebook;
and S4, determining the optimal precoding codebook according to the maximum channel utilization rate as the optimization target.
As one of the preferred schemes of the invention, the massive MIMO system comprises L feedback bits, NtRoot transmitting antenna and NrThe root receives the antenna.
As one of the preferable embodiments of the present invention, step S1 specifically includes:
s1.1: for data vector s ═ s1，s2，...，sM]TPre-coding to obtain length NtVector x of (i)
x＝f·s
Wherein f is a precoding codeword selected from
A given codebook;
S1.2：Nta signal is transmitted via a transmitting antenna, via a channel H, the signal being transmitted by NrReceived at the receiving antennas, the corresponding received signal y having dimension Nr×1；
S1.3: according to the downlink communication model of the MIMO system and the signal transmission process, the received signal vector y is expressed as:
where ρ represents the received SNR, w represents the obedient mean 0, and the variance σ2Of complex Gaussian distribution of white noise of dimension NrX 1; dimension of channel H being Nr×NtThe matrix structure is expressed as:
wherein h isijIndicating the channel coefficient between the ith receiving antenna and the jth transmitting antenna.
As one of the preferable embodiments of the present invention, step S2 specifically includes:
let m be [ m ]1，m2，...，mL]Is composed of
A vector in (1) is channel coded to obtain a code word c, that is
c＝mG
Wherein G is a generating matrix of channel coding, and the size is L multiplied by N;
let the set of all codewords be
Namely, it is
Taking s as a positive integer, each codeword ciMapping using binary to decimal conversion method
To obtain 1 XN1Dimension positive integer vector cdiWherein q is 2s，N1＝N/s；
All vectors are taken together as
Then
The upper code book is
It has a size of 2L×N1。
As one of the preferable embodiments of the present invention, step S3 specifically includes:
for any codeword, a pre-coded codeword, denoted as f, can be generated by the following methodiGenerating a precoding codebook
Namely, it is
Wherein u is0＝(1，1，...，1)TIs N1A dimension column vector; thetaiFor constructed rotation matrices, i.e.
Wherein,
as one of the preferable embodiments of the present invention, step S4 specifically includes:
s4.1: from precoding codebooks
Solving the channel utilization rate:
record its maximum as gammamWherein h isjIs the jth column of channel H;
s4.2: under different channels, the channel and precoding codebook is obtained according to steps S2 and S3
And taking the average value of the highest efficiency set;
s4.3: repeating the step S4.2 under different precoding codebooks, storing all average efficiencies into a set, and respectively recording the average and maximum values as gamma1And gamma2(ii) a Taking the maximum average efficiency gamma2And the time precoding codebook is the optimal precoding codebook.
Compared with the prior art, the invention has the beneficial effects that:
compared with the traditional precoding design method based on the codebook, the precoding codebook design method based on the channel coding can construct a high-dimensional codebook, realize higher channel utilization rate and improve channel estimation so as to further improve the system performance.
Detailed Description
The technical solution of the present invention will be further explained below.
The precoding codebook design method based on the channel coding is improved aiming at the defect of low dimension of the existing codebook. The precoding codebook design method based on the channel coding is used for a codebook design method of a downlink single-user large-scale MIMO system and provides an optimal codebook selection scheme. The specific technical scheme is divided into the following four parts:
designing a transmit signal and processing a receive signal
For data vector s ═ s1，s2，...，sM]TPre-coding to obtain vector x with length of Nt
x＝f·s
Wherein f is a precoding codeword selected from
A given codebook.
Define Nt(Nt≧ M) mapping between the root transmit antenna and the modulation coincidence vector s. Obviously, the size of the codebook is limited by the number of bits L per feedback.
NtA signal is transmitted via a transmitting antenna, via a channel H, by NrReceived by the receiving antennas, the corresponding received signal y having dimension NrX 1, according to the downlink communication model and the signaling process of the MIMO system, the reception vector y can be expressed as:
where ρ represents a received SNR (Signal to Noise Ratio), w represents a obedient mean of 0 and a variance σ2Of complex Gaussian distribution of white noise of dimension NrX 1. Dimension of channel H being Nr×NtThe matrix structure is expressed as:
wherein h isijIndicating the channel coefficient between the ith receiving antenna and the jth transmitting antenna.
Two, channel coding
Let m be [ m ]1，m2，...，mL]Is composed of
A vector in the code block is subjected to channel coding to obtain a code word c
c＝mG
Where G is a generator matrix of channel coding, and the size is L × N. Let the set of all codewords be
Namely, it is
In this way it is possible to obtain,
has a size of 2LIs denoted as M, i.e. M is 2L。
Taking s as a positive integer, each codeword ciMapping using binary to decimal conversion method
To obtain 1 XN1Dimension positive integer vector cdiWherein q is 2s，N1N/s. All vectors are taken together as
Then
The upper code book is
It has a size of 2L×N1。
Third, precoding codebook design
Code book
The following design method is adopted:
fi＝θiu0
wherein u is0＝(1，1，...，1)TIs N1Vector of dimension, θiIs a rotation matrix of the construction and,
selection method of optimal precoding codebook
Determining an optimal precoding codebook by maximizing a channel utilization ratio as an optimization objective, specifically:
the first step is as follows: from precoding codebooks
Solving the channel utilization rate:
record its maximum as gammamWherein h isjIs column j of channel H. Under different channels, the channel and precoding codebook are obtained according to the process
And taking the average of the highest efficiency sets.
The second step is that: repeating the above process under different precoding codebooks, storing all average efficiencies into a set, and respectively recording the average and maximum values as gamma1And gamma2. Thus, the maximum average efficiency γ is taken2The temporal precoding codebook is the optimal precoding codebook.
The specific application case of the precoding codebook design method based on channel coding is as follows:
the feedback bit number L is 10; the channel is a randomly generated gaussian channel with dimensions of 8 x 1.
Designing a transmit signal and processing a receive signal
For data vector s ═ s1，s2，...，s8]TPrecoding to obtain a vector x of length 8, i.e.
x＝f·s
Wherein f is a precoding codeword selected from
Given a codebook, the dimension is 1 × 8. Obviously, the size of the codebook is limited by the number of bits L per feedback.
The received signal is transmitted through the transmitting antenna, after passing through the channel h, the dimension of the corresponding received signal y is 8 × 1, and according to the downlink communication model of the MIMO system and the signal transmission process, the received vector y can be expressed as:
where ρ represents a received SNR (Signal to Noise Ratio), w represents white Noise subject to a complex gaussian distribution with a mean value of 0 and a variance of 1, and dimension is 8 × 1. The channel h has dimensions of 8 × 1, and its matrix structure is denoted by h ═ h1，h2，...，h8]T。
Two, channel coding
(1) LDPC codes
The information sequence m is an information group consisting of 10 information symbols, which can be expressed as:
m＝((m1，m2，...，m10)|mi∈GF(2)，1≤i≤10)
a check matrix H of the LDPC code, which has a size of 30 × 40, is randomly constructed using the 1A method of Mackay.
The check matrix H is converted into a generator matrix G with a size of 10 × 40 using gaussian elimination. The information sequence m is channel coded to obtain a code word c, i.e.
c＝mG
The size is 1 × 40. Let the set of all codewords be
Namely, it is
In this way it is possible to obtain,
has a size of 210X 40. Taking s to 5, each code word c is converted by binary to decimal conversion methodiMapping to
To obtain a 1 × 8-dimensional positive integer vector cd1iWherein q is 2s＝32，N1N/s 8. All vectors are taken together as
Then
It has a size of 210×8。
(2) Multiple RA code
Randomly fetch the 4-bit input sequence k ═ k in GF (13)1，k2，k3，k4]The 4-bit output obtained by 1 time of the repeater is x ═ x1，x2，x3，x4](ii) a x is output y after passing through the weighting device, having
yi＝βi·xi，i＝1，2，3，4
Wherein, betaie.GF (13) is the weight value. Interweaver pi ═ pi1，π2，π3，π4]Rearranging the order of the input information y, whichOutput is as
Combining every 1 bit of the output sequence d after interleaving to obtain 4 bits of information z, then
Because of the systematic code, the final output codeword is c ═ k, z]＝[k1，k2，k3，k4，z1，z2，z3，z4]Length of 8, which is denoted as c ═ ci}1×8。
Thirdly, designing precoding codebook
For any one codeword ci＝[ci1，ci2，...，ci8]A precoding word, denoted as f, may be generated by the following methodi. Thus, a precoding codebook can be generated
Wherein, thetaiFor constructed rotation matrices, i.e.
Wherein u is0＝(1，1，...，1)TIs an 8-dimensional column vector; (u)i1，ui2，...，ui8)＝cdiIs an LDPC codeword or an RA code codeword.
Precoding codebook determination based on channel utilization
From precoding codebooks
Solving the channel utilization rate:
(1) first, GF (2) is obtained according to the method of the second item (1)5) LDPC codebook of (2)
Precoding the LDPC precoding codebook by a rotating codebook construction method based on three to obtain the LDPC precoding codebook
Randomly generating a Gaussian channel h8×1Go through the codebook
Each code word f1iCalculating the efficiency between the channel and the channel h, and comparing to obtain the highest efficiency gamma1(ii) a Second, fix the codebook
Randomly generating 1000 Gaussian channels, repeating the above process, averaging all the obtained highest efficiencies, and recording as gamma2(ii) a Thirdly, randomly generating 100 binary LDPC codebooks and mapping each code word of the kth codebook to a decimal system by using a binary conversion method
To obtain a positive integer vector c of 1 × 8 dimensionsdkiRecording all the vectors as
Then
It has a size of 210X 8. Repeating the first and second steps, and respectively recording the average value and the maximum value of all obtained efficiencies as gamma3And gamma4Recording efficiency of gamma4Time-of-day LDPC check matrix. Can be obtained through simulation
γ3＝0.6376
γ4＝0.6588
(2) Similar to the procedure of (1), except that the LDPC codebook is replaced with an RA code codebook over GF (13), the recording efficiency is γ4A temporal RA codebook. Can be obtained through simulation
γ3＝0.6007
γ4＝0.6239
Compared with the traditional precoding design method based on the codebook, the method provided by the invention can construct the high-dimensional codebook and can further improve the performance.
It should be noted that the above embodiments can be freely combined as necessary. The foregoing has outlined rather broadly the preferred embodiments and principles of the present invention and it will be appreciated that those skilled in the art may devise variations of the present invention that are within the spirit and scope of the appended claims.
Claims (2)
1. A precoding codebook design method based on channel coding in a large-scale MIMO system is used for FDD downlink single users, and is characterized by comprising the following steps:
s1, designing a sending signal and processing a receiving signal;
s2, channel coding;
s3, constructing a precoding codebook;
s4, determining an optimal precoding codebook according to the maximum channel utilization rate as an optimization target;
the massive MIMO system comprises L feedback bits, NtRoot transmitting antenna and NrA root receiving antenna;
step S1 specifically includes:
s1.1: for data vector s ═ s1,s2,...,sM]TPre-coding to obtain length NtVector x of (i)
x＝f·s
Wherein f is a precoding codeword selected from
A given codebook;
S1.2：Nta signal is transmitted via a transmitting antenna, via a channel H, the signal being transmitted by NrReceived at the receiving antennas, the corresponding received signal y having dimension Nr×1；
S1.3: according to the downlink communication model of the MIMO system and the signal transmission process, the received signal vector y is expressed as:
where ρ represents the received SNR, w represents the obedient mean 0, and the variance σ2Of complex Gaussian distribution of white noise of dimension NrX 1; dimension of channel H being Nr×NtThe matrix structure is expressed as:
wherein h isijIndicating a channel coefficient between the ith receiving antenna and the jth transmitting antenna;
step S2 specifically includes:
let m be [ m ]1,m2,...,mL]Is composed of
A vector in the code block is subjected to channel coding to obtain a code word
Namely, it is
Wherein G is a generating matrix of channel coding, and the size is L multiplied by N;
let the set of all codewords be
Namely, it is
Taking s as a positive integer, each code word
Mapping using binary to decimal conversion method
To obtain 1 XN1Vector of dimension positive integer
Wherein q is 2s，N1＝N/s；
All vectors are taken together as
Then
The upper code book is
It has a size of 2L×N1；
Step S3 specifically includes:
for any codeword, a pre-coded codeword, denoted as f, can be generated by the following methodiGenerating a precoding codebook
Namely, it is
Wherein u is0＝(1,1,...,1)TIs N1A dimension column vector; thetaiFor constructed rotation matrices, i.e.
Wherein,
2. the method according to claim 1, wherein step S4 is specifically:
s4.1: from precoding codebooks
Solving the channel utilization rate:
record its maximum as gammamWherein h isjIs the jth column of channel H;
s4.2: under different channels, the channel and precoding codebook is obtained according to steps S2 and S3
And taking the average value of the highest efficiency set;
s4.3: repeating the step S4.2 under different precoding codebooks, storing all average efficiencies into a set, and respectively recording the average and maximum values as gamma1And gamma2(ii) a Taking the maximum average efficiency gamma2And the time precoding codebook is the optimal precoding codebook.
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