CN114039634B - Modified vector disturbance soft demodulation method - Google Patents

Modified vector disturbance soft demodulation method Download PDF

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CN114039634B
CN114039634B CN202111485808.XA CN202111485808A CN114039634B CN 114039634 B CN114039634 B CN 114039634B CN 202111485808 A CN202111485808 A CN 202111485808A CN 114039634 B CN114039634 B CN 114039634B
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llr
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CN114039634A (en
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谭佳滨
肖悦
吴朝武
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University of Electronic Science and Technology of China
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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
    • 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
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/06—Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection
    • H04L25/067—Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection providing soft decisions, i.e. decisions together with an estimate of reliability

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Abstract

The invention belongs to the technical field of wireless communication, and particularly relates to a modified vector disturbance soft demodulation method. In the method provided by the invention, the original LLR function is corrected, and the modulus part is considered in the function, so that the corrected function can meet the probability distribution requirement of the data after the modulus is taken by a VP receiving end, and the output soft information is corrected. Compared with the method for directly carrying out hard decision on the VP, the method provided by the invention can provide good performance gain; at the same time, if the original LLRs are used, the performance is even worse than for hard decisions.

Description

Modified vector disturbance soft demodulation method
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a modified vector disturbance soft demodulation method.
Background
Recently, a new non-linear precoding technique, Vector Perturbation (VP) precoding, has been proposed, and the key idea is to select an additive Perturbation Vector to shape the transmitted symbols, and obtain the optimal Perturbation Vector through a search algorithm such as LRA. By the vector perturbation technology, the coding technology can achieve the performance close to the total capacity. On the other hand, soft information such as Log-Likelihood Ratio (LLR) is used in the soft decision technology, and the soft information is output in combination with the related channel coding technology, so that the overall error code performance of the system is greatly improved compared with that of hard decision and soft decision.
However, the VP technique uses a modulo operation so that the data at the receiving end does not follow a gaussian distribution.
Disclosure of Invention
Aiming at the problems, the invention provides a new LLR function for the soft decision of the VP to improve the overall error code performance of the VP system by repairing the original LLR.
For ease of understanding, the modified soft decision scheme employed by the present invention is illustrated as follows:
the VP technique uses a perturbation vector to perturb the original data, i.e., v ═ s + τ l, where v denotes the perturbed data, s denotes the sign vector, l denotes the perturbation vector, whose dimension is the same as s,
Figure GDA0003437847340000011
τ is a positive real number, usually chosen as τ 2| c- max And + delta, wherein, the modulus of the constellation point symbol with the maximum amplitude in the QAM constellation set represents the minimum Euclidean distance between the constellation point symbols. Assuming ZF precoding is used, i.e. the precoding matrix is
Figure GDA0003437847340000012
The transmitted power is normalized to 1, then the transmitted signal is
Figure GDA0003437847340000013
Wherein the content of the first and second substances,
Figure GDA0003437847340000014
then the received data is
Figure GDA0003437847340000015
The received data is multiplied by a power normalization factor, and then the disturbance vector is removed through the modular transportation to obtain
Figure GDA0003437847340000016
The modulo operation is defined as
Figure GDA0003437847340000017
This makes it possible to find that the distribution to which the noise is subjected at this time is a non-gaussian distribution, and LLRs cannot be used as soft information directly.
The technical scheme of the invention is as follows:
a modified vector perturbation soft demodulation method comprises the following steps:
s1, defining the vector of the sending symbols as S, one symbol corresponding to n bits b n ...b 2 ，b 1 ，b 0 }；
S2, for vectorThe kth element s of s k For s, for k Ith bit b i Without loss of generality, assume b i Corresponding value probability and s k Is related to the in-phase component of, i.e.
Figure GDA0003437847340000021
m is b i Symbol s corresponding to 0 k The value of the in-phase component of (a);
s3, calculation b i LLR of (a):
Figure GDA0003437847340000022
wherein M is 0 And M 1 Are respectively b i When equal to 0 and 1
Figure GDA0003437847340000023
X is all values of
Figure GDA0003437847340000024
Is a positive real number, tau,
Figure GDA0003437847340000025
is a mean of 0 and a variance of σ 2 Of a Gaussian variable, n i The ith element of n is expressed, and the modulus operation is defined as
Figure GDA0003437847340000026
To L (b) i ) The terms of numerator and denominator are weighted:
Figure GDA0003437847340000027
wherein l is the disturbance amount;
to M 0 And M 1 Value addition limits are such that M 1 . + -. T and M 0 ±τ∈[-τ,τ]The final log-likelihood ratio (LLR) is obtained as:
Figure GDA0003437847340000031
s4, respectively obtaining b by adopting the method of the step S3 k And k is not equal to the soft information of i, and after the soft information of the whole code word is obtained, a decoder is used for decoding to obtain the estimation of the code word.
The method has the advantages that the original LLR function is corrected, the modulus part is considered in the function, so that the corrected function can meet the probability distribution requirement of data after the modulus of a VP receiving end is acquired, and the output soft information is corrected. Compared with the method for directly carrying out hard decision and original soft decision on VP, the scheme provided by the invention can provide good performance gain
Drawings
FIG. 1 is a block diagram of a VP soft decision system;
fig. 2 is a schematic diagram showing the bit error rate performance comparison of the hard decision, the original soft decision and the modified soft decision scheme when the number of the transmitting antennas is 4 and the number of users is 4, when BPSK modulation is adopted and 1/3-rate LDPC coding is used;
fig. 3 is a schematic diagram showing the error rate performance comparison of the hard decision, the original soft decision and the modified soft decision scheme when the number of the transmitting antennas is 4 and the number of users is 4, QPSK modulation is adopted, and 1/3-rate LDPC coding is used;
Detailed Description
The technical scheme of the invention is described in detail in the following with reference to the accompanying drawings and embodiments:
the technical scheme of the invention mainly provides a new LLR function, and the specific derivation process is as follows:
for a transmitted symbol vector s, only one symbol s of s is considered k Representing the kth element in the vector s while taking into account the corresponding ith bit b i 。b i Corresponding value probability and s k Is related to the in-phase or quadrature component of (1), provided that it is related to the in-phase component
Figure GDA0003437847340000032
m is b i Symbol s when equal to 0 k More specifically, b i The probability of a value of 0 being equal to s k The probability that the corresponding component is m.
Assuming that the disturbance value probability P (l) is equal probability, then
Figure GDA0003437847340000041
Without loss of generality, LLR molecular fraction is considered
Figure GDA0003437847340000042
Figure GDA0003437847340000043
Representing a set of integers, wherein x is
Figure GDA0003437847340000044
Real part of the kth element of (1), M 0 And M 1 Are respectively b i When equal to 0 and 1
Figure GDA0003437847340000045
All values of (a).
Will s k Is substituted into the whole formula and the formula is divided into two parts, namely a part with k equal to 0 and the rest. Namely the above type
Figure GDA0003437847340000046
Order to
Figure GDA0003437847340000047
By
Figure GDA0003437847340000048
Taking logarithm of the original formula to obtain the formula
Figure GDA0003437847340000049
The reduction of the second term of the second and the term ln of the above formula is done by the following methods:
a) take all the terms of the first summation operationThe largest term in (i.e. the molecule equals
Figure GDA00034378473400000410
k is an integer, k is not equal to 0, and the formula can be simplified to account for monotonicity of the exponential operation
Figure GDA00034378473400000411
b) Taking the maximum sum of two of all the terms of the first summation operation, taking into account that the monotonicity numerator of the exponential operation is equal to
Figure GDA00034378473400000412
c) The sum of the largest finite term of all the terms of the first summation operation is taken.
Scheme b) used in the present invention gives the formula
Figure GDA0003437847340000051
Further consider that
Figure GDA0003437847340000052
Wherein l is the disturbance amount; therefore, can be applied to P { x | b i 0 corresponding part is weighted to get a more accurate LLR, in fact for P { x | b i 0 is equivalent to a pair
Figure GDA0003437847340000053
Corresponding partial weights, thus obtained using the same scheme
Figure GDA0003437847340000054
The resulting LLRs are then:
Figure GDA0003437847340000055
to reduce complexity, M needs to be paired 0 And M 1 Value addition limits are such that M 1 . + -. tau and M 0 ±τ∈[-τ,τ]The final log-likelihood ratio (LLR) is obtained as:
Figure GDA0003437847340000056
s.t.M 0 ±τ,M 1 ±τ∈[-τ,τ]
using the above functions, respectively, b is obtained k And k is not equal to the soft information of i, and after the soft information of the whole code word is obtained, a decoder is used for decoding to obtain the estimation of the code word.
Examples
In this example, the number of transmitting antennas is 4, the number of users is 4, each user is configured with one receiving antenna, the modulation mode uses the normalized 16QAM modulation using gray codes, one symbol of which corresponds to 4 bits { b } 3 ，b 2 ，b 1 ，b 0 }，
Figure GDA0003437847340000057
The channel coding uses convolutional codes and the decoding uses viterbi decoding.
S1, calculating b first 0 Probability of 0, b 0 Corresponds to s i In phase component of
Figure GDA0003437847340000058
That is to say M 0 ＝{-d,-3d}。
S2, calculating
Figure GDA0003437847340000061
Weighting each item of the probability to obtain the final LLR b i Moiety 0
Figure GDA0003437847340000062
Consider M 0 Limiting the value to obtain b in the final LLR i Moiety 0
Figure GDA0003437847340000063
Same principle for b 0 The probability of 1 is given as the probability of,
Figure GDA0003437847340000064
that is M 1 Obtained as { d,3d }, yield
Figure GDA0003437847340000065
S3, calculation b 0 Soft information of
Figure GDA0003437847340000066
S4, obtaining b 3 ，b 2 ，b 1 After the soft information of the whole code word is obtained, a decoder is used for decoding to obtain the estimation of the code word.

Claims (1)

1. A modified vector perturbation soft demodulation method, comprising the steps of:
s1, defining the vector of the sending symbols as S, one symbol corresponding to n bits b n ...b 2 ，b 1 ，b 0 }；
S2, for the k-th element S in the vector S k For s, for k Ith bit b i Let b be i Corresponding value probability and s k Is related to the in-phase component of, i.e.
Figure FDA0003764341800000011
m is b i Symbol s corresponding to 0 k The value of the in-phase component of (a);
s3, calculation b i Log Likelihood Ratio (LLR):
Figure FDA0003764341800000012
wherein, M 0 And M 1 Are respectively b i When equal to 0 and 1
Figure FDA0003764341800000013
X is all values of
Figure FDA0003764341800000014
Is a positive real number, tau,
Figure FDA0003764341800000015
is a mean of 0 and a variance of σ 2 A Gaussian variable of (1), defining a precoding matrix as
Figure FDA0003764341800000016
Then
Figure FDA0003764341800000017
v denotes the perturbed data, n i The ith element of n is expressed, and the modulus operation is defined as
Figure FDA0003764341800000018
To L (b) i ) The terms of numerator and denominator are weighted:
Figure FDA0003764341800000019
wherein l is the disturbance amount;
to M 0 And M 1 Value addition limits are such that M 1 . + -. T and M 0 ±τ∈[-τ,τ]The final LLR is obtained as:
Figure FDA00037643418000000110
s.t.M 0 ±τ,M 1 ±τ∈[-τ,τ]
s4, respectively obtaining b by adopting the method of the step S3 k And k is not equal to the soft information of i, and after the soft information of the whole code word is obtained, a decoder is used for decoding to obtain the code wordIs estimated.
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