CN110943945A - Underwater sound OFDM superposition coding receiving method - Google Patents

Underwater sound OFDM superposition coding receiving method Download PDF

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CN110943945A
CN110943945A CN201911084673.9A CN201911084673A CN110943945A CN 110943945 A CN110943945 A CN 110943945A CN 201911084673 A CN201911084673 A CN 201911084673A CN 110943945 A CN110943945 A CN 110943945A
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information
mmse
equalizer
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马璐
刘新宇
乔钢
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Harbin Engineering University
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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
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B11/00—Transmission systems employing sonic, ultrasonic or infrasonic waves
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B13/00—Transmission systems characterised by the medium used for transmission, not provided for in groups H04B3/00 - H04B11/00
    • H04B13/02—Transmission systems in which the medium consists of the earth or a large mass of water thereon, e.g. earth telegraphy
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0045—Arrangements at the receiver end
    • H04L1/0047—Decoding adapted to other signal detection operation
    • H04L1/0048—Decoding adapted to other signal detection operation in conjunction with detection of multiuser or interfering signals, e.g. iteration between CDMA or MIMO detector and FEC decoder
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0045—Arrangements at the receiver end
    • H04L1/0047—Decoding adapted to other signal detection operation
    • H04L1/005—Iterative decoding, including iteration between signal detection and decoding operation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0045—Arrangements at the receiver end
    • H04L1/0054—Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056—Systems characterized by the type of code used
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/0071—Use of interleaving
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
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    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • 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
    • 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
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L2025/0335—Arrangements for removing intersymbol interference characterised by the type of transmission
    • H04L2025/03375—Passband transmission
    • H04L2025/03414—Multicarrier
    • 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
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L2025/03592—Adaptation methods
    • H04L2025/03598—Algorithms
    • H04L2025/03611—Iterative algorithms
    • H04L2025/03636—Algorithms using least mean square [LMS]

Abstract

The invention provides an underwater sound OFDM superposition coding receiving method. The method comprises the following steps: multi-user information detection of an MMSE superposition equalizer; step two: calculating external log-likelihood ratio information of different users; step three: reconstructing the far-end information and eliminating continuous interference; step four: and performing Turbo equalization on the residual near-end user information components by using a near-end MMSE equalizer. The invention combines Turbo equalization means, can effectively reduce the bit error rate and improve the communication quality, and compared with the traditional one-time equalization, the Turbo equalization has stronger detection capability due to the iterative external soft information exchange between the soft decision feedback equalizer and the soft decision channel decoder. The method can eliminate the information interference between users and the intersymbol interference of single user information, greatly improve the robustness of the system and effectively reduce the influence of the underwater acoustic channel on the communication quality.

Description

Underwater sound OFDM superposition coding receiving method
Technical Field
The invention relates to an underwater acoustic downlink communication multiple access method, in particular to an underwater acoustic OFDM superposition coding receiving method combining Turbo equalization and continuous interference elimination.
Background
Traditional underwater acoustic communication is mainly based on a point-to-point communication mode, and with the enlargement of underwater communication scale, research on underwater acoustic communication networks is gradually increased. Research on underwater acoustic communication is gradually moving from point-to-point underwater acoustic communication technology to underwater network communication technology with multiple users. However, in actual underwater acoustic communication, the serious limitation of the communication bandwidth is one of the main bottlenecks in improving the data transmission rate of the underwater network, and how to improve the frequency spectrum utilization rate of physical layer multi-user communication within the limited bandwidth is a key problem to be solved urgently in underwater acoustic communication. The current orthogonal multiple access technology applied to underwater communication networking mainly comprises: TDMA, FDMA, OFDMA, etc. The non-orthogonal multiple access includes: CDMA, etc. A CDMA scheme can achieve higher capacity than TDMA/FDMA when the signal-to-interference ratio (SNIR) is below a certain threshold, and can achieve higher capacity under the same conditions when the required received signal quality is above the threshold. If the receiving end does not introduce a complex demodulation algorithm, the CDMA spectrum efficiency is lower than that of the orthogonal multiple access method. Therefore, the superposition coding transmission mode in the 5G technology theory is produced, and the technology can also be named as a downlink non-orthogonal multiple access technology (NOMA).
Since the superposition coding scheme is equivalent to actively introducing information interference at the transmitting end, the design of the receiving end algorithm is particularly important for information demodulation of downlink users and improvement of the overall system performance. According to the design principle of NOMA, the successive interference cancellation method is theoretically adopted at the receiving end, and the receiving algorithm can be divided into a symbol-level SIC receiver and a codeword-level SIC receiver according to the "reconstruction degree" of the remote user information, for example, the successive interference cancellation algorithm based on symbol level and codeword level is proposed in "Non-orthogonal multiple access (NOMA) for future downlink access of 5G" published by China Communications journal in 2015. On this basis, in view of the superiority of soft decision over hard decision, the Maximum Likelihood Detection (MLD) method can be used to calculate soft information and combine with SIC to demodulate user information, such as "Multi User Superior Transmission (MUST) for LTE-a systems" published in IEEE International Conference on Computer and communications (ICCC) Conference held in 2016.
Disclosure of Invention
The invention aims to provide a method for receiving underwater sound OFDM superposition coding by combining Turbo equalization and continuous interference elimination.
The purpose of the invention is realized as follows:
the method comprises the following steps: multi-user information detection of an MMSE superposition equalizer;
step two: calculating external log-likelihood ratio information of different users;
step three: reconstructing the far-end information and eliminating continuous interference;
step four: and performing Turbo equalization on the residual near-end user information components by using a near-end MMSE equalizer.
The present invention may further comprise:
1. the MMSE superposition equalizer multi-user information detection specifically includes:
(1) the data of the downlink near-end user N and the data of the downlink far-end user F are overlapped
Figure BDA0002265023690000021
Represents a constellation set of different users, where i ═ N, F, SC represent near end, far end and superposition users, respectively, [ Q ═ Ni]Represents the number of bits contained in the constellation point of the ith user,
Figure BDA0002265023690000022
represents the j bit carried by the k sub-carrier of the ith user in the information sequence
Figure BDA0002265023690000023
And
Figure BDA0002265023690000024
after respective coding, interleaving and digital modulation, the information symbols of two users are superposed
Figure BDA0002265023690000025
Wherein
Figure BDA0002265023690000026
And
Figure BDA0002265023690000027
respectively representing information symbols on the k sub-carrier of users N and F, s k]Representing the superimposed information symbols;
(2) detection of superimposed information using MMSE superimposed equalizer
When s [ k ]]After the signal reaches a receiving end through an underwater acoustic channel, an observation vector z is obtained through the preprocessing of a receiver, and the prior likelihood ratio of an MMSE superposition equalizer is set
Figure BDA0002265023690000028
Is 0, the observation vector z is subjected to linear operation to obtain s [ k ]]An estimated value of (2), the estimated value
Figure BDA0002265023690000029
By minimizing a cost function
Figure BDA00022650236900000210
The expression is obtained as:
Figure BDA00022650236900000211
wherein Cov represents covariance, if only information on data subcarriers is concerned, the following is obtained:
Figure BDA00022650236900000212
wherein s isk,j∈[0,1]，
Figure BDA00022650236900000213
A priori information representative of the detector; tanh represents the hyperbolic tangent function. s [ k ]]Mean value of
Figure BDA00022650236900000214
And variance
Figure BDA00022650236900000215
Obtained by:
Figure BDA00022650236900000216
Figure BDA00022650236900000217
wherein P represents probability βkRepresenting constellation points on the k-th subcarrier. Collecting the mean of all data symbols into a vector
Figure BDA00022650236900000314
In (1), the variance of all symbols is collected into a diagonal matrix sigmasIn the method, the following steps are obtained:
Figure BDA0002265023690000031
Figure BDA0002265023690000032
where diag stands for diagonalization and the mean value Ez of the received vector observations z is obtained by
Figure BDA0002265023690000033
So the expression for the autocovariance of z, Cov (z, z), and the cross-covariance of s [ k ] and z, Cov (s [ k ], z), is:
Figure BDA0002265023690000034
Figure BDA0002265023690000035
MMSE estimation formula
Figure BDA0002265023690000036
Is unfolded into
Figure BDA0002265023690000037
Wherein the linear filter fkIs defined as
Figure BDA0002265023690000038
2. The calculating of the external log-likelihood ratio information of different users specifically includes:
order to
Figure BDA0002265023690000039
Obtaining:
Figure BDA00022650236900000310
wherein
Figure BDA00022650236900000311
According to the matrix inversion theorem, fk' conversion to related fkExpression (2)
Figure BDA00022650236900000312
The MMSE estimate is reformulated as
Figure BDA00022650236900000313
Wherein
Figure BDA0002265023690000041
Is provided with
Figure BDA0002265023690000042
Obey mean value of muk,jVariance is
Figure BDA0002265023690000043
A Gaussian distribution of wherein
Figure BDA0002265023690000044
Figure BDA0002265023690000045
Thereby generating
Figure BDA0002265023690000046
The calculation expression of likelihood ratio information is
Figure BDA0002265023690000047
Obtaining external likelihood ratio information
Figure BDA0002265023690000048
Comprises the following steps:
Figure BDA0002265023690000049
wherein
Figure BDA00022650236900000410
To pair
Figure BDA00022650236900000411
The information of the remote users is distinguished by
Figure BDA00022650236900000412
Figure BDA00022650236900000413
Wherein j is 1.., Q in the first equation aboveFIn the second equation, j is QF+1，...，QSC。
3. The reconstructing the far-end information and the performing the continuous interference cancellation specifically include:
will be provided with
Figure BDA00022650236900000414
Through far-end de-interleaving, the information is used as initialization information of a far-end BP decoding algorithm
Figure BDA00022650236900000415
And input into a far-end decoder to realize the demodulation of the far-end user information to obtain
Figure BDA00022650236900000416
To pair
Figure BDA00022650236900000417
Performing reconstruction to obtain
Figure BDA00022650236900000418
Then, interference elimination is carried out to obtain a near-end user observation vector zN。
4. The Turbo equalizing the remaining near-end user information components by using the near-end MMSE equalizer specifically includes:
will be provided with
Figure BDA0002265023690000051
By near-end de-interleaving, near-end decoder and interleaver to obtain
Figure BDA0002265023690000052
As prior information of MMSE near-end equalizer, finally
Figure BDA0002265023690000053
Is obtained from the formula
Figure BDA0002265023690000054
External likelihood ratio information
Figure BDA0002265023690000055
Is composed of
Figure BDA0002265023690000056
Will be provided with
Figure BDA0002265023690000057
As initialization information for near-end decoding
Figure BDA0002265023690000058
After BP algorithm updating, obtaining
Figure BDA0002265023690000059
Re-interleaving it and updating prior information
Figure BDA00022650236900000510
And then, balancing again, and continuously updating the external likelihood ratio to finally realize the whole Turbo receiving algorithm.
Aiming at the problem of correct demodulation of superposition coding downlink multi-users, the invention combines OFDM modulation and superposition coding to design a practical usable underwater acoustic communication system in view of the superiority of superposition coding in improving communication rate. Mainly aiming at an OFDM underwater fixed-point communication scene, due to the fact that Doppler influence of the OFDM underwater fixed-point communication scene is weak, factors influencing underwater sound communication quality are mainly caused by multipath and environmental noise. In order to enable downlink users to correctly demodulate respective information and improve communication quality, the invention designs an superposition coding MMSE-LDPC iterative processing algorithm suitable for an underwater environment on the basis of an SIC algorithm by utilizing the idea of a Turbo equalization algorithm so as to eliminate Inter-user information interference (Inter-user interference) and Inter-symbol interference (Inter-symbol interference) of single user information.
The invention has the beneficial effects that:
in the underwater sound OFDM superposition coding receiving method based on the combined Turbo equalization and the continuous interference elimination, the Turbo equalization method is combined on the basis of the continuous interference elimination technology, the bit error rate can be effectively reduced, and the communication quality is improved. The method can eliminate the information interference between users and the intersymbol interference of single user information, greatly improve the robustness of the system and effectively reduce the influence of the underwater acoustic channel on the communication quality.
Drawings
Fig. 1 is a schematic diagram of an information superposition process of downlink near-end user QPSK modulation and far-end user BPSK modulation;
FIG. 2 is a schematic diagram of an OFDM-based superposition coding overall receiving end;
fig. 3 is a schematic diagram of a Turbo equalization-based superposition coding demodulation process.
Detailed Description
The invention is described in more detail below by way of example.
The underwater sound OFDM superposition coding receiving method combining Turbo equalization and continuous interference elimination specifically comprises the following steps:
1. the data of the downlink near-end user N and the data of the downlink far-end user F are overlapped
Use of
Figure BDA0002265023690000061
Represents constellation sets of different users, where i ═ N, F, and SC represent near-end users, far-end users, and superimposed users, respectively. [ Q ]i]Representing the number of bits contained in the constellation point of the ith user.
Figure BDA0002265023690000062
Representing the jth bit carried on the kth subcarrier of the ith user. User N is closer to the sound source node and user F is closer to the sound source nodeThe point is farther away and thus the channel condition for user N is better than for user F. In the information sequence
Figure BDA0002265023690000063
And
Figure BDA0002265023690000064
after respective coding, interleaving and digital modulation, the information symbols of two users are superposed
Figure BDA0002265023690000065
Wherein
Figure BDA0002265023690000066
And
Figure BDA0002265023690000067
representing the information symbols on the k-th sub-carrier for users N and F, respectively.
2. Detection of superimposed information using MMSE superimposed equalizer
When s [ k ]]And after the underwater sound channel reaches a receiving end, an observation vector z is obtained through the preprocessing of a receiver. Assuming MMSE superposition equalizer prior likelihood ratio
Figure BDA0002265023690000068
Under the condition of 0, s [ k ] can be obtained by specific linear operation on the observation vector z]An estimated value of (2), the estimated value
Figure BDA0002265023690000069
By minimizing a cost function
Figure BDA00022650236900000610
The expression is obtained as follows:
Figure BDA00022650236900000611
since we only focus on the information on the data subcarrier in the actual demodulation, the following k belongs to the data subcarrier without special explanation, and we can obtain
Figure BDA00022650236900000612
Wherein s isk,j∈[0,1]。s[k]The mean and variance of (c) can be obtained as follows:
Figure BDA00022650236900000613
Figure BDA00022650236900000614
collecting the mean of all data symbols into a vector
Figure BDA0002265023690000071
In (1), the variance of all symbols is collected into a diagonal matrix sigmasThus, it is possible to obtain:
Figure BDA0002265023690000072
Figure BDA0002265023690000073
the mean of the received vector observations z can be obtained by
Figure BDA0002265023690000074
The expression for the autocovariance of z and the cross-covariance of s [ k ] and z is therefore:
Figure BDA0002265023690000075
Figure BDA0002265023690000076
the MMSE estimation formula can be expanded into
Figure BDA0002265023690000077
Wherein the linear filter fkIs defined as
Figure BDA0002265023690000078
3. Computing external log-likelihood ratio information for different users
MMSE estimation when computing extrinsic information required by a channel decoder
Figure BDA0002265023690000079
Independent of s k]A priori information of. For this purpose force
Figure BDA00022650236900000710
It is possible to obtain:
Figure BDA00022650236900000711
wherein
Figure BDA00022650236900000712
According to the matrix inversion theorem, fk' can be converted intokExpression (2)
Figure BDA00022650236900000713
The MMSE estimate can now be reformulated as
Figure BDA00022650236900000714
Wherein
Figure BDA0002265023690000081
The key for simplifying the calculation of the external likelihood ratio information is to assume according to the characteristics of the MMSE detection mode
Figure BDA0002265023690000082
Obey mean value of muk,jVariance is
Figure BDA0002265023690000083
A Gaussian distribution of wherein
Figure BDA0002265023690000084
Figure BDA0002265023690000085
Thereby generating
Figure BDA0002265023690000086
The calculation expression of likelihood ratio information is
Figure BDA0002265023690000087
From this, external likelihood ratio information can be obtained
Figure BDA0002265023690000088
Comprises the following steps:
Figure BDA0002265023690000089
wherein
Figure BDA00022650236900000810
Need to do afterwards
Figure BDA00022650236900000811
To distinguish the remote user information, it is necessaryDepending on the actual modulation situation of the superposition coding at the transmitting end, there is therefore
Figure BDA00022650236900000812
Figure BDA00022650236900000813
Wherein j is 1.., Q in the first equation aboveFIn the second equation, j is QF+1，...，QSC。
4. Reconstructing far-end information and eliminating continuous interference
Will be provided with
Figure BDA0002265023690000091
Through far-end de-interleaving, the bit sequence is used as the prior initialization information of the far-end BP decoding algorithm
Figure BDA0002265023690000092
And input into a far-end decoder to realize the demodulation of the far-end user information to obtain
Figure BDA0002265023690000093
To pair
Figure BDA0002265023690000094
Performing reconstruction to obtain
Figure BDA0002265023690000095
Then, interference elimination is carried out to obtain a near-end user observation vector zN。
5. Turbo equalization of remaining near-end user information components using a near-end MMSE equalizer
Will be provided with
Figure BDA0002265023690000096
By near-end de-interleaving, near-end decoder and interleaver to obtain
Figure BDA0002265023690000097
As the prior information of MMSE near-end equalizer, the likelihood ratio is finally updated through the operation of the previous section
Figure BDA0002265023690000098
Can be obtained from the following formula
Figure BDA0002265023690000099
External likelihood ratio information
Figure BDA00022650236900000910
Is composed of
Figure BDA00022650236900000911
Will be provided with
Figure BDA00022650236900000912
As initialization information for near-end decoding
Figure BDA00022650236900000913
After BP algorithm updating, obtaining
Figure BDA00022650236900000914
Re-interleaving it and updating prior information
Figure BDA00022650236900000915
And then, balancing again, and continuously updating the external likelihood ratio to finally realize the whole Turbo receiving algorithm.
The invention discloses an underwater sound OFDM superposition coding receiving method combining Turbo equalization and continuous interference elimination. The invention provides a novel superposition coding demodulation scheme, namely an underwater sound OFDM superposition coding receiving method combining Turbo equalization and continuous interference elimination under a downlink underwater sound OFDM system, and the method can effectively improve the system robustness and the communication quality by utilizing the continuous interference elimination and Turbo equalization technology under different underwater sound channels.
The underwater sound OFDM superposition coding receiving method combining Turbo equalization and continuous interference elimination comprises the following steps:
step 1: multi-user information detection of an MMSE superposition equalizer;
step 2: calculating external log-likelihood ratio information of different users;
and step 3: reconstructing the far-end information and eliminating continuous interference;
and 4, step 4: performing Turbo equalization on the residual near-end user information components by using a near-end MMSE equalizer;
in the underwater sound OFDM superposition coding system, because the transmitting end actively introduces the information interference among users and the multipath influence is very serious under an underwater sound channel, in order to ensure that the downlink users can correctly demodulate the respective information and improve the communication quality, the Turbo equalization is introduced on the basis of the SIC algorithm to improve the system performance.
Step 1: multi-user information detection of an MMSE superposition equalizer;
the present invention designs MMSE superposition equalizer of specific superposed signal according to the constitution of superposed signal at transmitting end and the practical modulation mode of each user at far end and near end, and obtains s [ m ] by using observation vector z]Is estimated value of
Figure BDA0002265023690000101
S m under the constraint of linear operation only]The equalizer estimate is formed by minimizing a cost function
Figure BDA0002265023690000102
The expression is obtained as follows:
Figure BDA0002265023690000103
step 2: calculating external log-likelihood ratio information of different users;
MMSE estimation when computing extrinsic information required by a channel decoder
Figure BDA0002265023690000104
Independent of s k]A priori information of. For this purpose force
Figure BDA0002265023690000105
The key for simplifying the calculation of the external likelihood ratio information is to assume according to the characteristics of the MMSE detection mode
Figure BDA0002265023690000106
Obey mean value of muk,jVariance is
Figure BDA0002265023690000107
Is gaussian distribution of, thereby generating
Figure BDA0002265023690000108
The calculation expression of likelihood ratio information is
Figure BDA0002265023690000109
The external likelihood ratio information thus obtained is:
Figure BDA00022650236900001010
need to do afterwards
Figure BDA00022650236900001011
The distinction of the far-end user information is needed according to the actual modulation condition of the superposition coding of the transmitting end, so that
Figure BDA00022650236900001012
Figure BDA00022650236900001013
Wherein j is 1.., Q in the first equation aboveFIn the second equation, j is QF+1，...，QSC。
And step 3: reconstructing the far-end information and eliminating continuous interference;
will be provided with
Figure BDA00022650236900001014
Through far-end de-interleaving, the information is used as initialization information of a far-end BP decoding algorithm
Figure BDA00022650236900001015
And input into a far-end decoder to realize the demodulation of the far-end user information to obtain
Figure BDA00022650236900001016
To pair
Figure BDA00022650236900001017
Performing reconstruction to obtain
Figure BDA00022650236900001018
Then, interference elimination is carried out to obtain a near-end user observation vector zN。
And 4, step 4: performing Turbo equalization on the residual near-end user information components by using a near-end MMSE equalizer;
will be provided with
Figure BDA0002265023690000111
By near-end de-interleaving, near-end decoder and interleaver to obtain
Figure BDA0002265023690000112
And performing Turbo equalization as the prior information of the MMSE near-end equalizer.
Through the operation of step 2, the m-th iteration process can be obtained
Figure BDA0002265023690000113
Is composed of
Figure BDA0002265023690000114
External likelihood ratio information
Figure BDA0002265023690000115
Is composed of
Figure BDA0002265023690000116
Will be provided with
Figure BDA0002265023690000117
As initialization information for near-end decoding
Figure BDA0002265023690000118
After BP algorithm updating, obtaining
Figure BDA0002265023690000119
Re-interleaving it and updating prior information
Figure BDA00022650236900001110
And then, carrying out the next iteration so as to realize the whole Turbo balance.

Claims (5)

1. An underwater sound OFDM superposition coding receiving method is characterized in that:
the method comprises the following steps: multi-user information detection of an MMSE superposition equalizer;
step two: calculating external log-likelihood ratio information of different users;
step three: reconstructing the far-end information and eliminating continuous interference;
step four: and performing Turbo equalization on the residual near-end user information components by using a near-end MMSE equalizer.
2. The underwater acoustic OFDM superposition coding receiving method according to claim 1, wherein the MMSE superposition equalizer multi-user information detection specifically comprises:
(1) the data of the downlink near-end user N and the data of the downlink far-end user F are overlapped
Figure FDA0002265023680000011
Represents a constellation set of different users, where i ═ N, F, SC represent near end, far end and superposition users, respectively, [ Q ═ Ni]Represents the number of bits contained in the constellation point of the ith user,
Figure FDA0002265023680000012
represents the j bit carried by the k sub-carrier of the ith user in the information sequence
Figure FDA0002265023680000013
And
Figure FDA0002265023680000014
after respective coding, interleaving and digital modulation, the information symbols of two users are superposed
Figure FDA0002265023680000015
Wherein
Figure FDA0002265023680000016
And
Figure FDA0002265023680000017
respectively representing information symbols on the k sub-carrier of users N and F, s k]Representing the superimposed information symbols;
(2) detection of superimposed information using MMSE superimposed equalizer
When s [ k ]]After the signal reaches a receiving end through an underwater acoustic channel, an observation vector z is obtained through the preprocessing of a receiver, and the prior likelihood ratio of an MMSE superposition equalizer is set
Figure FDA0002265023680000018
Is 0, the observation vector z is subjected to linear operation to obtain s [ k ]]An estimated value of (2), the estimated value
Figure FDA0002265023680000019
By minimizing a cost functionNumber of
Figure FDA00022650236800000110
The expression is obtained as:
Figure FDA00022650236800000111
focusing only on the information on the data subcarriers, we can:
Figure FDA00022650236800000112
wherein s isk,j∈[0,1]，
Figure FDA00022650236800000113
A priori information representative of the detector; tanh represents the hyperbolic tangent function, s [ k ]]Mean value of
Figure FDA00022650236800000114
And variance
Figure FDA00022650236800000115
Obtained by:
Figure FDA0002265023680000021
Figure FDA0002265023680000022
wherein P represents probability βkRepresenting constellation points on the k sub-carrier, collecting the mean of all data symbols into a vector
Figure FDA00022650236800000215
In (1), the variance of all symbols is collected into a diagonal matrix sigmasIn the method, the following steps are obtained:
Figure FDA0002265023680000023
Figure FDA0002265023680000024
where diag stands for diagonalization and the mean value Ez of the received vector observations z is obtained by
Figure FDA0002265023680000025
So the expression for the autocovariance of z, Cov (z, z), and the cross-covariance of s [ k ] and z, Cov (s [ k ], z), is:
Figure FDA0002265023680000026
Figure FDA0002265023680000027
MMSE estimation formula
Figure FDA0002265023680000028
Is unfolded into
Figure FDA0002265023680000029
Wherein the linear filter fkIs defined as
Figure FDA00022650236800000210
3. The underwater acoustic OFDM superposition coding receiving method according to claim 2, wherein said calculating the external log-likelihood ratio information of different users specifically comprises:
order to
Figure FDA00022650236800000211
Obtaining:
Figure FDA00022650236800000212
wherein
Figure FDA00022650236800000213
Obtaining inverse theorem according to matrix, f'kIs converted intokExpression (2)
Figure FDA00022650236800000214
The MMSE estimate is reformulated as
Figure FDA0002265023680000031
Wherein
Figure FDA0002265023680000032
Is provided with
Figure FDA0002265023680000033
Obey mean value of muk,jVariance is
Figure FDA0002265023680000034
A Gaussian distribution of wherein
Figure FDA0002265023680000035
Figure FDA0002265023680000036
Thereby generating
Figure FDA0002265023680000037
The calculation expression of likelihood ratio information is
Figure FDA0002265023680000038
Figure FDA0002265023680000039
Obtaining external likelihood ratio information
Figure FDA00022650236800000310
Comprises the following steps:
Figure FDA00022650236800000311
wherein
Figure FDA00022650236800000312
To pair
Figure FDA00022650236800000313
The information of the remote users is distinguished by
Figure FDA00022650236800000314
Figure FDA00022650236800000315
Wherein j is 1.., Q in the first equation aboveFIn the second equation, j is QF+1，...，QSC。
4. The underwater acoustic OFDM superposition coding receiving method according to claim 3, wherein the reconstructing the far-end information and performing successive interference cancellation specifically comprises:
will be provided with
Figure FDA0002265023680000041
Through far-end de-interleaving, the information is used as initialization information of a far-end BP decoding algorithm
Figure FDA0002265023680000042
And input into a far-end decoder to realize the demodulation of the far-end user information to obtain
Figure FDA0002265023680000043
To pair
Figure FDA0002265023680000044
Performing reconstruction to obtain
Figure FDA0002265023680000045
Then, interference elimination is carried out to obtain a near-end user observation vector zN。
5. The underwater acoustic OFDM superposition coding receiving method according to claim 4, wherein said Turbo equalizing the remaining near-end user information components using a near-end MMSE equalizer specifically comprises:
will be provided with
Figure FDA0002265023680000046
By near-end de-interleaving, near-end decoder and interleaver to obtain
Figure FDA0002265023680000047
As prior information of MMSE near-end equalizer, finally
Figure FDA0002265023680000048
Is obtained from the formula
Figure FDA0002265023680000049
External likelihood ratio information
Figure FDA00022650236800000410
Is composed of
Figure FDA00022650236800000411
Will be provided with
Figure FDA00022650236800000412
As initialization information for near-end decoding
Figure FDA00022650236800000413
After BP algorithm updating, obtaining
Figure FDA00022650236800000414
Re-interleaving it and updating prior information
Figure FDA00022650236800000415
And then, balancing again, and continuously updating the external likelihood ratio to finally realize the whole Turbo receiving algorithm.
CN201911084673.9A 2019-11-08 2019-11-08 Underwater sound OFDM superposition coding receiving method Pending CN110943945A (en)

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