CN114938252B - Bidirectional interference suppression method applied to multi-user filtering multitone underwater acoustic communication - Google Patents

Bidirectional interference suppression method applied to multi-user filtering multitone underwater acoustic communication Download PDF

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CN114938252B
CN114938252B CN202210551936.8A CN202210551936A CN114938252B CN 114938252 B CN114938252 B CN 114938252B CN 202210551936 A CN202210551936 A CN 202210551936A CN 114938252 B CN114938252 B CN 114938252B
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CN114938252A (en
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李海森
孙琳
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Harbin Engineering University
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    • 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
    • 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
    • H04L25/03012—Arrangements for removing intersymbol interference operating in the time domain
    • H04L25/03019—Arrangements for removing intersymbol interference operating in the time domain adaptive, i.e. capable of adjustment during data reception
    • H04L25/03082—Theoretical aspects of adaptive time domain methods
    • 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
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2689—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
    • H04L27/2691—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation involving interference determination or cancellation
    • 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
    • H04L2025/03649—Algorithms using recursive least square [RLS]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

Abstract

The invention discloses a bidirectional interference suppression method applied to multi-user filtering multitone underwater acoustic communication, which comprises the following steps: the bidirectional parallel interference suppression structure is adopted to process co-channel interference and intersymbol interference in multi-user filtering multi-tone underwater acoustic communication, the forward structure is used for processing the sub-band signals after filtering multi-tone demodulation, and the reverse structure is used for processing the time reversal form of the sub-band signals. The forward and reverse structures of the method are preprocessed by adopting a time reversal technology, the post-processing is performed by adopting continuous interference cancellation and decision feedback equalization, and the final decision value of the user sequence can be obtained by combining the results of the two-way processing. The invention has the beneficial effects that: the additional diversity gain is obtained through the bidirectional processing, so that error propagation can be avoided, and the error rate and the output mean square error which are lower than those of the traditional unidirectional interference suppression method can be obtained, and the reliability is higher.

Description

Bidirectional interference suppression method applied to multi-user filtering multitone underwater acoustic communication
Technical Field
The invention relates to the technical field of multi-user underwater acoustic communication, in particular to a method for improving the co-channel interference and intersymbol interference suppression performance in multi-user filtering multi-sound underwater acoustic communication by avoiding error propagation and obtaining additional diversity gain through bidirectional processing.
Background
The multi-carrier modulation is used in multi-user underwater acoustic communication, so that the code element range influenced by intersymbol interference (intersymbol interference, ISI) caused by multi-path expansion of an underwater acoustic channel and co-channel interference (co-channel interference, CCI) caused by channel correlation can be reduced, the communication performance is improved, and the complexity of interference suppression is reduced. Orthogonal frequency division multiplexing (orthogonal frequency division multiplexing, OFDM) is the most widely studied and used multi-carrier technology in the field of underwater acoustic communications. However, the OFDM sub-bands overlap each other, are relatively sensitive to frequency offset, and require complex frequency offset estimation and compensation techniques. Compared with OFDM, multi-user filtering multitone (filtered multitoned, FMT) can be implemented not only by dividing symbol ranges of sub-bands to reduce CCI and ISI effects and by fast fourier transform, but also in recent years, has been applied to multi-user underwater acoustic communications because the pass bands of FMT sub-bands do not overlap each other and have strong spectrum suppression and are insensitive to frequency offset. In multi-user FMT underwater acoustic communication, dividing the sub-band reduces the symbol range affected by CCI and ISI, but because the bandwidth of the sub-band is still greater than the relevant bandwidth of the channel, the signal after FMT demodulation at the receiving end still has shortened CCI and ISI, which needs to be suppressed. Document [1] (Li H S, sun L, du W D, et al multiple-input multiple-output passive time reversal acoustic communication using filtered multitone modulation [ J ]. Applied Acoustics,2017,119 (4): 29-38.) proposes an interference suppression method combining successive interference cancellation and adaptive equalization, which achieves a good effect, but has limited interference suppression performance because the equalizer used is a linear equalizer. Theoretically, if the decision value that the equalizer has output is accurate, better performance will be obtained by replacing the linear equalization in the approach of document [1] with a decision feedback equalizer (decision feedback equalizer, DFE). However, when the error rate of the decided value is high, the DFE is prone to error propagation problems.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a bidirectional interference suppression method applied to multi-user filtering multitone underwater acoustic communication.
In order to achieve the above object, the present invention adopts the following technical scheme:
a bi-directional interference suppression method applied to multi-user filtering multitone underwater acoustic communications, comprising:
at the receiving end of the multi-user FMT underwater acoustic communication, a bidirectional interference suppression method is used for processing the sub-band signals after FMT demodulation. The forward structure is used to process the FMT demodulated sub-band signal and the reverse structure is used to process the time-reversed version of the sub-band signal. The forward and reverse structures of the method are preprocessed by Time Reversal (TR) technology, the post-processing is performed by continuous interference cancellation and DFE, and the final decision value of the user sequence is obtained by combining the results of the two-way processing.
Further, the bidirectional interference suppression method comprises the following steps:
s1: in the forward interference suppression, firstly, preprocessing is carried out on sub-band signals after FMT demodulation by utilizing a TR technology to realize precompression of CCI and ISI, and then, interference cancellation and DFE are adopted to carry out post-processing on residual CCI and ISI after TR;
s2: in reverse interference suppression, firstly, storing a received signal of an FMT demodulated sub-band signal by using a buffer, outputting the signal which enters the buffer at first, and performing time reversal processing in a mode that the signal which enters the buffer at last is output at first, then preprocessing the reversed FMT sub-band signal by using a TR technology, and performing post-processing by adopting interference cancellation and DFE;
s3: storing the estimated value of the DFE output sub-band signal in the inversion processing according to the signal output by the DFE in the inversion structure by using a buffer, outputting the signal which enters the buffer at first and outputting the signal which enters the buffer at last, performing time inversion processing in a mode of outputting the signal which enters the buffer at last, and performing equal gain combination on the processed signal and the sub-band signal output by the forward processing DFE;
s4: and judging the signals output by the equivalent gain combination, wherein the judgment value is used for interference estimation in next interference cancellation of other user sub-band signals.
Further, interference cancellation and adaptive equalization in forward and reverse interference suppression are performed sequentially, iteratively, and stopped when system performance has stabilized.
Further, S1 is specifically:
the TR processed signal in forward interference rejection is:
Figure BDA0003650388780000031
in the above, alpha is the user sequence number, m is the sub-band sequence number, q (α,γ),(m,m) (lT, nT) represents the mth subband sequence d of the gamma user at the transmitting end γ,m (lT) and mth TR output signal y in the alpha-th receiver forward structure α,m Combined channel response between (nT), d α,m (lT) represents the symbol sequence transmitted by the alpha user on the m-th sub-band, d α,m (nT) represents d when l=n α,m The value of (lT), T represents the symbol interval and N represents the number of users.
The estimated value of CCI in the forward structure is:
Figure BDA0003650388780000032
in the above
Figure BDA0003650388780000033
Representing a subband sequence d after two-way interference suppression processing α,m (nT) decision value.
The signal after interference cancellation is:
Figure BDA0003650388780000034
q (α,α),(m,m) (lT, nT) represents q when γ=α (α,γ),(m,m) Values of (lT, nT), q (α,α),(m,m) (nT, nT) represents q when l=n (α,α),(m,m) Values of (lT, nT).
The residual ISI is suppressed by adopting a DFE, and the estimated value of the DFE output is as follows:
Figure BDA0003650388780000041
where a (nT) and b (nT) represent the coefficients of the DFE feedforward and feedback filters, respectively, N 1 And N 2 N is the number of non-causal and causal taps of the feedforward filter f For the number of taps of the feedback filter,
Figure BDA0003650388780000042
representing the decision value, z, of the forward DFE α,m (nT) represents a signal of interference cancellation output in the forward structure.
Further, S2 is specifically:
the TR processed signal in reverse interference suppression is expressed as:
Figure BDA0003650388780000043
in the above
Figure BDA0003650388780000044
An mth sub-band sequence d representing a gamma user at a transmitting end γ,m (lT) and mth TR output signal in the structure opposite to the alpha-th receiver>
Figure BDA0003650388780000045
Combined channel response between->
Figure BDA0003650388780000046
Representing the transmission of sequence d by the gamma user on the m th sub-band γ,m Time reversed version of (lT),>
Figure BDA0003650388780000047
representing the transmission of sequence d by the alpha user on the m th sub-band α,m Time reversed version of (lT),>
Figure BDA0003650388780000048
represents +.>
Figure BDA0003650388780000049
Is a value of (2).
The signal after reverse interference cancellation is:
Figure BDA00036503887800000410
in the above
Figure BDA00036503887800000411
Represents +.>
Figure BDA00036503887800000412
Value of->
Figure BDA00036503887800000413
Represents +.>
Figure BDA00036503887800000414
Value of->
Figure BDA00036503887800000415
Decision value +.>
Figure BDA00036503887800000416
Is a time-reversed version of (a).
The DFE output estimate is:
Figure BDA0003650388780000051
in the above
Figure BDA0003650388780000052
And->
Figure BDA0003650388780000053
Representing the coefficients of the DFE feedforward and feedback filters, respectively, in the inverse process, +.>
Figure BDA0003650388780000054
Decision value representing DFE in inverse structure, +.>
Figure BDA0003650388780000055
Representing the interference canceled output signal in the inverse configuration.
Further, the gain combination in S4 is specifically:
Figure BDA0003650388780000056
wherein ρ represents a merging coefficient having a value ranging from 0 to 1,
Figure BDA0003650388780000057
representing the estimated value of the output after the forward structure processing, < >>
Figure BDA0003650388780000058
Representing DFE output estimate in inverse structure +.>
Figure BDA0003650388780000059
Is a time-reversed version of (a).
Compared with the prior art, the invention has the advantages that:
the additional diversity gain is obtained through the bidirectional processing, so that the problem that the DFE is easy to generate error propagation when the communication performance is poor can be avoided, the error rate and the output mean square error which are lower than those of the traditional unidirectional interference suppression method can be obtained, and the reliability is higher.
Drawings
FIG. 1 is a schematic block diagram of a multi-user FMT underwater acoustic communication with two-way interference suppression in accordance with an embodiment of the present invention;
FIG. 2 is a schematic block diagram of FMT modulation and demodulation in accordance with an embodiment of the present invention;
FIG. 3 is a schematic block diagram of two-way interference suppression in accordance with an embodiment of the present invention;
FIG. 4 is a graph of combined channel response after TR processing in accordance with an embodiment of the present invention;
fig. 5 is a signal-to-interference ratio diagram after TR processing in the embodiment of the present invention;
FIG. 6 is a graph of performance after TR processing in accordance with an embodiment of the present invention;
FIG. 7 is a graph showing the sub-band performance of the two-way interference suppression method and the two-way interference suppression method according to the embodiment of the present invention;
fig. 8 is a graph showing the overall performance of the two-way interference suppression method and the two-way interference suppression method according to the embodiment of the present invention.
Detailed Description
The invention will be described in further detail below with reference to the accompanying drawings and by way of examples in order to make the objects, technical solutions and advantages of the invention more apparent.
Architecture of communication system
In order to facilitate analysis, the principle of the proposed method is analyzed by taking a communication system with 2 array elements transmitting 2 paths of user signals and 2 array elements receiving as an example, and in practical application, the proposed method is suitable for the situation of multi-array element transmitting and multi-array element receiving. Fig. 1 shows a schematic block diagram of the system, and the schematic block diagram of FMT modulation and demodulation in fig. 1 is shown in fig. 2.
As can be seen from fig. 1 and 2, the mth subband signal outputted by the beta-th FMT demodulation can be expressed as
Figure BDA0003650388780000061
D in formula (1) α,i (nT) represents the signal transmitted by the alpha element in the ith sub-band, T represents the symbol interval, g t (nT c ) And g r (nT c ) Representing the discrete time response of the transmit and receive filters respectively,
Figure BDA0003650388780000062
discrete time form, w, representing the response of the underwater acoustic channel between the alpha-th transmitting element and the beta-th receiving element β (kT c ) Representing noise received by the beta-th receiving array element, T c =t/K represents the symbol interval after interpolation, and K represents a multiple of interpolation.
The signal after the demodulation of the right end FMT of the formula (1) includes a signal transmitted on the m-th subband, inter-carrier interference generated by other subband signals on the m-th subband signal, and a noise 3 part. The subcarriers of the FMT are not overlapped with each other and have strong spectrum rejection, are insensitive to frequency offset, and under the condition that the receiving and transmitting sides are fixed, the influence of the inter-carrier interference on the communication performance is very slight and can be ignored. When the power of the transmission signal is high, the influence of noise on the communication performance is also small. The method mainly focuses on CCI and ISI suppression, and the communication structure in question is based on the fixed condition of both transceivers, thus ignoring the effects of noise and inter-carrier interference, equation (1) may be expressed as
Figure BDA0003650388780000071
From equation (2), it can be seen that the discrete time response of the ith sub-channel between the alpha th transmitting element and the beta th receiving element is
Figure BDA0003650388780000072
As shown in equation (3), the channel response is different for each sub-band, so the receiving end needs to process the signal output by FMT demodulation separately.
Forward interference suppression
Fig. 3 is a schematic block diagram of two-way interference suppression, taking the mth subband sequence of the alpha user as an example. As can be seen from fig. 3, the method comprises 2 parallel interference suppression structures, wherein the upper half of fig. 3 is a forward structure for demodulating the output sub-signals of the FMT
Figure BDA0003650388780000073
Processing is performed, the lower half is of an inverse structure for demodulating the FMT to output a time-reversed version of the sub-signal +.>
Figure BDA0003650388780000074
And (5) processing.
As can be seen from fig. 3, the TR processed signal in the forward structure can be expressed as
Figure BDA0003650388780000075
Q in formula (4) (α,γ),(m,m) (lT, nT) represents the combined channel response after TR processing expressed as
Figure BDA0003650388780000076
The expression in the formula (5)
Figure BDA0003650388780000077
Is an underwater sound channel->
Figure BDA0003650388780000078
Is a time-reversed version of (a).
Formula (4) may be further represented by
Figure BDA0003650388780000079
The right-hand side of equation (6), item 1, is the desired signal and items 2 and 3 represent residual CCI and ISI, respectively, after TR processing, requiring post-processing.
The proposed method employs interference cancellation to suppress residual CCI. For interference cancellation, CCI needs to be estimated first. The estimated value of CCI in the forward structure is that
Figure BDA0003650388780000081
In (7)
Figure BDA0003650388780000082
And the decision value of the subband sequence after the bidirectional interference suppression processing is represented.
The signal after interference cancellation is
Figure BDA0003650388780000083
The method adopts DFE to inhibit residual ISI, and the DFE output estimated value is
Figure BDA0003650388780000084
In the formula (9), a (nT) and b (nT) respectively represent coefficients of the DFE feedforward and feedback filters, N 1 And N 2 N is the number of non-causal and causal taps of the feedforward filter f For the number of taps of the feedback filter,
Figure BDA0003650388780000085
representing the decision value of the forward DFE.
Reverse interference suppression
The TR processed signal in reverse interference rejection can be expressed as
Figure BDA0003650388780000086
In (10)
Figure BDA0003650388780000087
Representing a time-reversed version of the sequence transmitted by the gamma user on the ith sub-band,
Figure BDA0003650388780000088
representing the combined channel response after TR processing in the reverse structure, expressed as
Figure BDA0003650388780000089
Due to the matched filter characteristics of TR technology and the matching of the transmit and receive filters of FMT, when α=γ
Figure BDA0003650388780000091
Thus, formula (10) may be further represented as
Figure BDA0003650388780000092
In the reverse configuration, the proposed method still uses interference cancellation and DFE to handle CCI and ISI represented by items 2 and 3, respectively, at the right end of equation (12). The signal after reverse interference cancellation is
Figure BDA0003650388780000093
The DFE output estimate in the inverse structure is
Figure BDA0003650388780000094
In the formula (14)
Figure BDA0003650388780000095
And->
Figure BDA0003650388780000096
Representing the coefficients of the DFE feedforward and feedback filters in the inverse process respectively,
Figure BDA0003650388780000097
representing the decision value of the DFE in the reverse structure.
Combining decisions
The output signal of the DFE in the reverse structure is time-reversed and combined with the output signal of the DFE in the forward structure
Figure BDA0003650388780000098
ρ in the formula (15) represents a merging coefficient whose value ranges from 0 to 1. Since the TR processed combined channel response has symmetry, the proposed method sets the value of ρ to 0.5.
In the method, interference cancellation in a forward structure and a reverse structure and DFE processing are sequentially and iteratively carried out until the performance of the whole system is stable.
Specific underwater acoustic communication computing example
The underwater acoustic communication method provided by the invention has been verified in the experiment of a channel pool of the Harbin engineering university, and a specific calculation example is given below to illustrate the effectiveness of the invention.
The channel pool is 45m long, 5m deep and 6m wide, sound absorbing wedges are distributed around the pool, and the bottom of the pool is a sand bottom. 2 transmitting array elements are 1.5m and 2m from the water surface, 2 receiving array elements are 0.7m and 0.9m from the water surface, and the communication distance between the transmitting and receiving array elements is 15m.
In the test, the signals transmitted by 2 array elements consist of a hamming windowed chirp signal of 8-16kHz, a guard interval and an information signal. The communication band of the information signal is 8-16kHz, and is divided into 4 sub-bands based on the FMT principle. The roll-off coefficient of the transmit and receive filters on each band is set to 0.5, the number of transmitted symbols is 1600, and BPSK mapping is used, with the first 250 and the last 250 symbols used for training of DFE in bi-directional interference suppression. In the experiment, the filter coefficient used for channel estimation of each sub-band is 61, the causal and non-causal taps of the DFE feedforward filter are 23, the taps of the feedback filter are 8, the adaptive algorithm used for channel estimation and DFE is a recursive least squares (recursive least squares, RLS) algorithm, and the forgetting factor is set to 0.999.
First, the performance after TR treatment was analyzed as represented by TR treatment in the forward structure. To quantitatively analyze the effect of CCI and ISI after TR processing, a signal-to-interference ratio is defined
Figure BDA0003650388780000101
In (16)
Figure BDA0003650388780000102
And SIR α,m Respectively representing the power ratio, sigma, of the TR processed signal with respect to ISI, CCI and total interference α,m Sum sigma γ,m The average power of the transmission sequence of the mth sub-band for the alpha and gamma users is shown, respectively.
Figure BDA0003650388780000103
And SIR α,m Higher means better interference immunity and less residual interference.
Figure 4 shows a continuous time version of the combined channel response after TR processing. In FIG. 4, q (1,1),(m,m) (t) and q (2 ,2),(m,m) The waveforms of (t) are normalized with respect to their maximum values, q (1,2),(m,m) (t) relative to q (1,1),(m,m) The maximum value of (t) is normalized, q (2,1),(m,m) (t) relative to q (2,2),(m,m) The maximum value of (t) is normalized. Fig. 5 shows the calculated signal-to-interference ratio based on equation (16).
By performing a joint analysis of fig. 4 and 5, the following three points can be found. First, q in FIG. 4 (1,2),(m,m) The amplitude of (t) is significantly greater than q (2,1),(m,m) (t), which illustrates that user 2 has a significantly greater CCI for user 1 than user 1 has for user 2, as in FIG. 5
Figure BDA0003650388780000111
The results of (2) are consistent. Second, in FIG. 4, except for the 4 th sub-band, and q (1,1),(m,m) (t) compared with q (2 ,2),(m,m) Side lobe compression of (t) is more pronounced, as compared to +.>
Figure BDA0003650388780000112
Is consistent. Third, except for the 1 st sub-band of user 1,/in FIG. 5>
Figure BDA0003650388780000113
And->
Figure BDA0003650388780000114
That is, the effect of residual ISI after TR processing is greater than the residual CCI.
Fig. 6 shows the performance of each subband after TR processing, with the error rate and the output mean square error as performance indicators. As can be seen from fig. 6, for sub-bands 1-3, the error rate and output mean square error for user 1 are both higher than for user 2, because the residual CCI and ISI in the user 1 signal are more, which is comparable to the SIR in fig. 5 1,m ＜SIR 2,m M=1, 2,3 are identical; for the 4 th sub-band, the error rate and output mean square error for user 1 is lower than for user 2, which is comparable to the SIR in fig. 5 1,m ＞SIR 2,m M=4 is also consistent.
Fig. 7 and 8 show the performance of each sub-band after the proposed method bi-directional interference cancellation and DFE and the total performance after serial-to-parallel conversion, respectively. For comparison, the performance of 2 one-way interference suppression methods is presented simultaneously in fig. 7 and 8. The 2 comparison methods are respectively as follows: first, the LE-based one-way interference suppression method employed in document [1 ]; second, a method of unidirectional interference suppression based on DFE.
As can be seen from fig. 7 and 8, reference [1]]Compared with the LE-based one-way interference suppression method, the error rate and the output mean square error of the method are obviously reduced, and the performance is obviously improved; compared with the one-way interference suppression method based on the DFE, the error rate is reduced to 10 after the interference suppression processing of the two methods -3 Even if the error rate of some sub-bands is reduced to 0, the error rate of the method is lower, but the difference is not obvious, and the output mean square error of the method is obviously lower from the perspective of analyzing the output mean square error, so that the performance improvement is obvious. Furthermore, as can be seen from the constellation diagram of fig. 8, compared with 2 comparison methods, the estimated value of the symbol processed by the proposed method is more intensively distributed near the expected values-1 and 1, and the performance is better.
Those of ordinary skill in the art will appreciate that the embodiments described herein are intended to aid the reader in understanding the practice of the invention and that the scope of the invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific modifications and combinations from the teachings of the present disclosure without departing from the spirit thereof, and such modifications and combinations remain within the scope of the present disclosure.

Claims (5)

1. A bi-directional interference suppression method applied to multi-user filtering multitone underwater acoustic communication, comprising:
processing the sub-band signals after FMT demodulation by using a bidirectional interference suppression method at a receiving end of multi-user filtering multitone (filtered multitoned, FMT) underwater acoustic communication; the forward structure is used for processing the FMT demodulated sub-band signals, and the reverse structure is used for processing the time reversal form of the sub-band signals; the forward and reverse structures of the method are preprocessed by Time Reversal (TR) technology, post-processed by continuous interference cancellation and decision feedback equalizer (decision feedback equalizer, DFE), and the final decision value of the user sequence is obtained by combining the results of the bidirectional processing;
the bidirectional interference suppression method comprises the following steps:
s1: in forward interference suppression, firstly, preprocessing sub-band signals after FMT demodulation by using a TR technology to realize precompression of co-channel interference (co-channel interference, CCI) and intersymbol interference (intersymbol interference, ISI), and then, adopting interference cancellation and DFE to post-process residual CCI and ISI after TR;
s2: in reverse interference suppression, firstly, storing a received signal of an FMT demodulated sub-band signal by using a buffer, outputting the signal which enters the buffer at first, and performing time reversal processing in a mode that the signal which enters the buffer at last is output at first, then preprocessing the reversed FMT sub-band signal by using a TR technology, and performing post-processing by adopting interference cancellation and DFE;
s3: storing the estimated value of the DFE output sub-band signal in the reverse processing according to the signal output by the DFE in the reverse structure by using the buffer, outputting the signal which enters the buffer at first, performing time reversal processing in a mode that the signal which enters the buffer at last is output at first, and performing equal gain combination on the processed signal and the sub-band signal output by the forward processing DFE;
s4: and judging the signals output by the equivalent gain combination, wherein the judgment value is used for interference estimation in next interference cancellation of other user sub-band signals.
2. The method for two-way interference suppression applied to multi-user filtering multitone underwater acoustic communication according to claim 1, wherein the method comprises the following steps: interference cancellation and adaptive equalization in forward and reverse interference suppression are performed sequentially, iteratively, and stopped when system performance has stabilized.
3. The method for two-way interference suppression applied to multi-user filtering multitone underwater acoustic communication according to claim 1, wherein the method comprises the following steps: s1 specifically comprises the following steps:
the TR processed signal in forward interference rejection is:
Figure FDA0004195748250000021
in the above, alpha is the user sequence number, m is the sub-band sequence number, q (α,γ),(m,m) (lT, nT) represents the mth subband sequence d of the gamma user at the transmitting end γ,m (lT) and mth TR output signal y in forward structure of alpha-th user receiving end α,m Combined channel response between (nT), d α,m (lT) represents the symbol sequence transmitted by the alpha user on the m-th sub-band, d α,m (nT) represents d when l=n α,m A value of (lT), T representing symbol intervals, N representing the number of users;
the estimated value of CCI in the forward structure is:
Figure FDA0004195748250000022
in the above
Figure FDA0004195748250000023
Representing a subband sequence d after two-way interference suppression processing α,m A decision value of (nT);
the signal after interference cancellation is:
Figure FDA0004195748250000024
q (α,α),(m,m) (lT, nT) represents q when γ=α (α,γ),(m,m) Values of (lT, nT), q (α,α),(m,m) (nT, nT) represents q when l=n (α,α),(m,m) A value of (lT, nT);
the residual ISI is suppressed by adopting a DFE, and the estimated value of the DFE output is as follows:
Figure FDA0004195748250000031
in the abovea (nT) and b (nT) represent coefficients of the DFE feedforward and feedback filters, respectively, N 1 And N 2 N is the number of non-causal and causal taps of the feedforward filter f For the number of taps of the feedback filter,
Figure FDA0004195748250000032
representing the decision value, z, of the forward DFE α,m (nT) represents a signal of interference cancellation output in the forward structure.
4. The method for two-way interference suppression applied to multi-user filtering multitone underwater acoustic communication according to claim 1, wherein the method comprises the following steps: s2 specifically comprises the following steps:
the TR processed signal in reverse interference suppression is expressed as:
Figure FDA0004195748250000033
in the above
Figure FDA0004195748250000034
An mth sub-band sequence d representing a gamma user at a transmitting end γ,m (lT) and mth TR output signal in the structure opposite to the alpha-th receiver>
Figure FDA0004195748250000035
Combined channel response between->
Figure FDA0004195748250000036
Representing the transmission of sequence d by the gamma user on the m th sub-band γ,m Time reversed version of (lT),>
Figure FDA0004195748250000037
representing the transmission of sequence d by the alpha user on the m th sub-band α,m Time reversed version of (lT),>
Figure FDA0004195748250000038
represents +.>
Figure FDA0004195748250000039
Is a value of (2);
the signal after reverse interference cancellation is:
Figure FDA00041957482500000310
in the above
Figure FDA00041957482500000311
Represents +.>
Figure FDA00041957482500000312
Value of->
Figure FDA00041957482500000313
Indicating when l=n
Figure FDA00041957482500000314
Value of->
Figure FDA00041957482500000315
Decision value +.>
Figure FDA00041957482500000316
Is a time reversed version of (a);
the DFE output estimate is:
Figure FDA0004195748250000041
in the above
Figure FDA0004195748250000042
And->
Figure FDA0004195748250000043
Representing the coefficients of the DFE feedforward and feedback filters, respectively, in the inverse process, +.>
Figure FDA0004195748250000044
Decision value representing DFE in inverse structure, +.>
Figure FDA0004195748250000045
Representing the interference canceled output signal in the inverse configuration.
5. The method for two-way interference suppression applied to multi-user filtering multitone underwater acoustic communication according to claim 1, wherein the method comprises the following steps: the gain combination in S4 is specifically:
Figure FDA0004195748250000046
wherein ρ represents a merging coefficient having a value ranging from 0 to 1,
Figure FDA0004195748250000047
representing the estimated value of the output after the forward structure processing, < >>
Figure FDA0004195748250000048
Representing DFE output estimate in inverse structure +.>
Figure FDA0004195748250000049
Is a time-reversed version of (a).
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