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CN119483832A - A multi-band cross-layer reliable transmission method based on real-time underwater acoustic communication system - Google Patents

A multi-band cross-layer reliable transmission method based on real-time underwater acoustic communication system Download PDF

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Publication number
CN119483832A
CN119483832A CN202510040110.9A CN202510040110A CN119483832A CN 119483832 A CN119483832 A CN 119483832A CN 202510040110 A CN202510040110 A CN 202510040110A CN 119483832 A CN119483832 A CN 119483832A
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data
frame
decoding
data frame
module
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CN119483832B (en
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瞿逢重
席杰
温昕
陆雪松
涂星滨
魏艳
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Zhejiang University ZJU
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Zhejiang University ZJU
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    • 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
    • H04L1/0057—Block codes
    • 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
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/0061—Error detection codes
    • 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
    • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
    • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
    • H04L1/1607—Details of the supervisory signal
    • 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
    • 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

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Detection And Prevention Of Errors In Transmission (AREA)

Abstract

The invention discloses a multiband cross-layer reliable transmission method based on a real-time underwater acoustic communication system, which comprises the steps that a transmitting end respectively packages and carries out LDPC-CRC coding and band modulation after dividing a complete transmitting bit stream evenly, a receiving end carries out LDPC-CRC decoding which considers random phase offset on an equalized receiving signal, calculates the signal-to-noise ratio of each band to adaptively adjust the decoding code rate, returns data packet information and code rate which are in decoding errors to the transmitting end, each band contains all data packets in decoding errors and carries out retransmission, if the data packet of any band is decoded correctly, the data packet is considered to be retransmitted successfully, otherwise, the data packet is retransmitted again until the maximum retransmission times are reached, and when all the data packets are decoded correctly, the transmitting end is instructed to carry out the transmission of data to be transmitted in the next frame. The invention reduces the retransmission request times, improves the probability of successful retransmission and improves the reliability of underwater acoustic communication.

Description

Multiband cross-layer reliable transmission method based on real-time underwater acoustic communication system
Technical Field
The invention relates to the field of underwater acoustic communication, in particular to a multiband cross-layer reliable transmission method based on a real-time underwater acoustic communication system.
Background
The reliable data transmission aims to ensure that the receiving end can correctly acquire the original data of the transmitting end, and in the field of land wireless radio frequency communication and network, a mechanism widely used for the reliable transmission is redundancy and retransmission, and along with the development of the underwater acoustic communication technology, the two means are also used in the underwater acoustic communication and network. However, reliable data transmission becomes more challenging in underwater acoustic communications than wireless radio frequency networks. The underwater acoustic channel has the characteristics of poor quality, strong time variation, large propagation delay and the like, and the wide application of a redundancy mechanism is limited, so that the performance of a retransmission mechanism is influenced.
The redundancy mechanism aims to provide error detection and error correction capability for the receiving end, and the retransmission mechanism aims to improve the probability of successful reception of the receiving end under the condition of ensuring reliable transmission. A typical redundancy mechanism is forward error control (forward error control, FEC) but it does not always guarantee transmission reliability itself, and if the error rate of the channel is too large, the receiver cannot correct all errors, and should trigger retransmission to be successfully received. A typical retransmission mechanism is automatic repeat request (automatic repeat request, ARQ) which uses a combination of acknowledgement schemes at the receiving end to update the receiving state and retransmission schemes at the transmitting end.
Although the reliability of transmission can be enhanced by using a series of equalization techniques in the physical layer, in the case of a very bad underwater acoustic channel, the situation that the data packet is wrongly decoded still cannot be avoided. FEC and ARQ can relieve the pressure of the equalization technology to a certain extent, but considering that the delay of the underwater sound propagation is longer, a great time waste is caused by repeated retransmission, and the uncertainty of the quality of the underwater sound channel also makes the redundancy of the forward error correction code not well known.
In order to realize a reliable transmission method in a real-time underwater acoustic communication system, besides the performance of the method, the problems of complexity, instantaneity and the like are also required to be considered. Therefore, the reliable transmission method with good performance is designed, and meanwhile, the reliable transmission method can be realized in an underwater sound embedded communication system, and has important value for improving the quality of real-time underwater sound communication.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a multiband cross-layer reliable transmission method based on a real-time underwater sound communication system, which can be realized in an embedded chip and a programmable logic gate array.
The specific technical scheme is as follows:
A multiband cross-layer reliable transmission method based on a real-time underwater acoustic communication system comprises the following steps:
S1, when data to be transmitted of a current frame is transmitted for the first time, a transmitting end uniformly divides a complete transmission bit stream into k parts at a data link layer, packages each part of bit stream into a corresponding transmission data structure body and inputs the corresponding transmission data structure body into a physical layer, wherein the transmission data structure body comprises a plurality of transmission data frames;
S2, after the data in the transmission data structure is subjected to channel coding with variable code rate in a physical layer, respectively modulating the data to k different frequency bands and transmitting the data to a receiving end;
S3, when data is received for the first time, the receiving end carries out channel decoding of variable code rate taking random phase offset into consideration on the equalized symbol in a physical layer, and simultaneously calculates signal-to-noise ratios of k frequency bands respectively, and adaptively adjusts the decoding code rate of the k frequency bands;
S4, the receiving end stores the data packet with correct decoding in the data link layer, encapsulates the original frequency band where the data packet with incorrect decoding is located, the original position in the transmitted data frame and the decoding code rate after self-adaptive adjustment into an ACK data packet, and returns the ACK data packet to the transmitting end;
s5, when the data is retransmitted and transmitted, the transmitting end analyzes the ACK data packet at the data link layer, updates the coding rate of the channel coding with the variable code rate by using the self-adaptive adjusted coding rate, extracts the data packet in the transmitting data structure body according to the original frequency band where the data packet with the decoding error is positioned and the original position in the transmitting data frame, copies the decoded data packet into each frequency band to form a retransmission data frame, and sends the retransmission data frame into the physical layer to perform the channel coding, the frequency band modulation and the retransmission of the variable code rate at the physical layer;
and S6, when the data retransmission is received, the receiving end executes the decoding operation described in S3, if the data packet of any frequency band is correctly decoded, the data packet is considered to be successfully retransmitted, otherwise, the retransmission is considered to be failed, the operations of S4-S6 are performed again until the maximum retransmission times are reached, and when all the data packets are correctly decoded, an ACK data packet is generated in a data link layer to indicate the transmitting end to transmit the data to be transmitted of the next frame.
Further, in the step S1, the size of the complete transmission bit stream isEach bit stream has a size of,The method comprises the steps of representing the upward rounding, wherein the transmitted data frames comprise a synchronous head, a frame head and a plurality of data packets, and the number of the data packets contained in each transmitted data frame is not more than a threshold valueOne data packet contains a bit stream of the size ofThe data frame number expression allocated in each band transmission data structure is as follows:
in the formula, Representing redundant information in each data packet, and indicating the number of effective bits in the data packet;
Before transmitting the data structure In the frame transmission data frames, the number of data packets in each transmission data frame isThe number of data packets in the data frame transmitted in the last frame is as follows:
。
further, in the step S3, the variable code rate channel decoding selects LDPC-CRC decoding, and the LDPC-CRC decoding that considers the random phase offset is performed on the equalized symbol, which is specifically implemented by the following sub-steps:
(3.1) performing likelihood ratio calculation considering random phase offset according to noise variance and phase variance, wherein the expression is as follows:
Where r represents the scalar of the equalized received signal, t represents the scalar of the transmitted symbol sequence, Representing the variance of the gaussian white noise,Representing the variance of the random phase offset; representing taking the imaginary function, representing the conjugate symbol; the first to send symbols for each A number of bits of a bit,Expressed in the modulation symbol setA set of symbols with 0 bits,Is thatElements of (a) and (b); expressed in the modulation symbol set A set of symbols with a bit of 1,Is thatElements of (a) and (b);
(3.2) calculating a check matrix, wherein the master control controls cyclic displacement and data storage according to code rate and code length information to finish the confirmation of the check matrix H;
Iterative decoding, namely performing iterative decoding by adopting an LDPC method until convergence to obtain a final bit likelihood ratio, and performing soft decision on the final bit likelihood ratio to obtain decoding bits;
And (3.4) CRC checking, namely CRC checking the decoding bits, sending the decoding bits passing the CRC checking to a data link layer of a receiving end for storage, and sending the decoding bits not passing the CRC checking to the data link layer of the receiving end at the original frequency band where the data packet is located and the original position in the transmitted data frame.
Further, in the step S3, signal-to-noise ratios of k frequency bands are calculated respectively, and the adaptive adjustment of the decoding code rates of the k frequency bands is realized specifically by the following operations:
The received signal received by the receiving end is as follows The signals obtained by respectively passing through the band-pass filters of k frequency bands areThe corresponding in-band signal energy is calculated, a section of noise signal with the same length as the received signal is taken in front of each frequency band synchronous headThe corresponding noise signal capability is calculated, and the signal-to-noise ratio expression of k frequency bands is obtained as follows:
dividing the signal-to-noise ratio into different sections, wherein each section corresponds to different decoding code rates, and the decoding code rates are reduced along with the reduction of the signal-to-noise ratio, and respectively adjusting the decoding code rates of k frequency bands according to the sections where the signal-to-noise ratios of different frequency bands are located ,And updating the decoding code rate of the variable code rate channel decoding by using the adjusted decoding code rate, and simultaneously sending the updated variable code rate channel decoding code rate to a data link layer of a receiving end.
Further, the transmitted data frame comprises a synchronous head, a frame head and a plurality of data packets, wherein the original information bit vector expression of each data packet is as follows:
Wherein i represents the frame number of the current transmitted data frame, p represents the number of data packets contained in the current data frame, b represents the frequency band number of the current data frame, s 0 represents the first original information bit, s 1 represents the second original information bit, and so on; Indicating the total number of transmission data frames allocated in the kth band transmission data structure;
The expression of the retransmission data frame is as follows:
in the formula, The original band in which the packet representing the decoding error is located,The original position of the packet representing the decoding error in the transmitted data frame, n=1, 2.
The underwater acoustic communication system is used for realizing the multiband cross-layer reliable transmission method based on the real-time underwater acoustic communication system, and comprises a physical layer and a data link layer, wherein the physical layer and the data link layer transmit data frames, instructions and code rates through an advanced extensible interface;
The data link layer comprises a data frame sending module of a sending end, a data frame receiving module of a receiving end and a retransmission frame sending module, wherein the output of the data frame sending module is a sending data frame, the output of the retransmission frame sending module is a retransmission data frame, and the data frame receiving module is used for receiving and storing a data packet with correct decoding;
The physical layer comprises a channel coding module and a multiband modulation module of a variable code rate of a transmitting end, an equalization module, a signal-to-noise ratio calculation module and a channel decoding module of the variable code rate considering random phase offset of a receiving end;
when the data frame is transmitted for the first time, the output of the data frame transmitting module is used as the input of a channel coding module with a variable code rate; when in retransmission, the output of the retransmission frame sending module is used as the input of a channel coding module with a variable code rate, the output of the channel coding module with the variable code rate is used as the input of a multiband modulation module, and the output of the multiband modulation module is output to a receiving end through a multi-channel transducer;
The receiving end receives signals through a multipath hydrophone, the input of the equalization module and the signal-to-noise ratio calculation module are both receiving signals, the equalization module outputs the signals as the input of a channel decoding module with a variable code rate considering random phase offset, the outputs of the channel decoding module with the variable code rate considering random phase offset and the signal-to-noise ratio calculation module are input into a data link layer through an advanced extensible interface, wherein a data packet with correct decoding is input into a data frame receiving module, an ACK data frame is packaged and returned to a data frame sending module, and a data packet with incorrect decoding is packaged into the ACK data frame in an original frequency band, an original position in the sent data frame and a decoding code rate after self-adaption adjustment, and is input into a retransmission frame sending module.
Further, the data link layer is an ARM chip, and the physical layer is a programmable logic gate array.
Further, the output of the data frame transmitting module is divided into a plurality of frequency bands, each frequency band corresponds to a transmitting data structure body, a plurality of transmitting data frames are established in the transmitting data structure body, and each transmitting data frame sequentially comprises a synchronous head, a frame head and at mostAnd a protection interval is arranged between the synchronous header and the frame header and between the frame header and the data packet.
Further, the frame header of the transmission data frame is encapsulated with identification information, including the data frame type and the total frame number of the transmission data frame of the current frequency bandFrame number of currently transmitted data frameNumber of data packets in currently transmitted data frameCurrent band number;
The data frame types comprise a sending data frame, an ACK frame and a retransmitting data frame.
Further, the ACK data frame sequentially comprises a synchronous head, a frame head and an ACK data packet, wherein the ACK data packet comprises a frequency band where a decoding error data packet is located, a position in a transmitted data frame and a decoding code rate;
The retransmission data frame sequentially comprises a synchronous head, a frame head and a plurality of data packets for storing effective data, wherein the identification information packaged in the frame head comprises a data frame type and the total frame number of the transmission data frame of the current frequency band Frame number of currently transmitted data frameNumber of data packets in currently transmitted data frameCurrent band numberThe original frequency band where the decoding error data packet is located, and the original position of the decoding error data packet in the transmission data frame.
The beneficial effects of the invention are as follows:
(1) The invention combines the forward error correction code mechanism adapted to the underwater sound physical layer and the multiband retransmission mechanism of the data link layer, thereby greatly improving the reliability of the underwater sound communication transmission. Considering that the channels of all the frequency bands of the underwater acoustic physical layer are different, the cross-layer transmission protocol design carries out self-adaptive retransmission of the data link layer and code rate adjustment of the physical layer through the channel information carried by the ACK data packet, and the throughput of communication is improved on the premise of ensuring the communication reliability.
(2) The invention reduces the retransmission request times by utilizing a multi-band retransmission mechanism, improves the probability of successful retransmission, and can effectively solve the problems of slow propagation of underwater sound communication and poor quality of underwater sound channels.
(3) The method can be realized on the embedded platform with lower resource consumption and calculation time delay, and has higher instantaneity.
Drawings
Fig. 1 is a schematic diagram of a frame and a data flow of an underwater acoustic communication system according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of a structure of a transmission data frame according to an embodiment of the present invention.
Fig. 3 is a schematic diagram of a frame header structure of a transmission data frame according to an embodiment of the present invention.
Fig. 4 is a schematic diagram of an ACK data frame according to an embodiment of the present invention.
Fig. 5 is a schematic diagram of a structure of a retransmission data frame header according to an embodiment of the present invention.
Fig. 6 is a flow chart of the internal part of the data frame transmitting module in the data link layer in the embodiment of the present invention.
Fig. 7 is a flowchart illustrating an LDPC-CRC decoding module considering random phase offset in a physical layer according to an embodiment of the present invention.
Fig. 8 is a flow chart of the inside of the snr calculation module in the physical layer in the embodiment of the present invention.
Fig. 9 is a flow chart of the retransmission frame transmitting module in the data link layer in the embodiment of the present invention.
Detailed Description
The objects and effects of the present invention will become more apparent from the following detailed description of the preferred embodiments and the accompanying drawings, in which the present invention is further described in detail. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
As shown in fig. 1, an underwater acoustic communication system includes a cross-layer design of a physical layer and a data link layer. The data link layer is realized by using an ARM chip suitable for data analysis, the ARM comprises a data frame sending module of a sending end, a data frame receiving module of a receiving end and a retransmission frame sending module, the output of the data frame sending module is a sending data frame, and the output of the retransmission frame sending module is a retransmission data frame. The physical layer is implemented by using a programmable logic gate array (field programmable GATE ARRAY, hereinafter referred to as FPGA) with high speed and high parallel processing capability, the FPGA includes a channel coding module and a multiband modulation module with variable code rate at a transmitting end, an equalization module, a signal-to-noise ratio calculation module at a receiving end, and a channel decoding module with variable code rate considering random phase offset, in this embodiment, the channel coding module with variable code rate selects an LDPC-CRC (low density parity check code-cyclic redundancy check, low DENSITY PARITY CHECK-cyclic redundancy check) coding module, and correspondingly, the channel decoding module with variable code rate selects an LDPC-CRC decoding module. Advanced extensible interfaces (advanced extensible interface, AXI for short) are used between ARM and FPGA to carry out high-speed transmission of data frames, instructions and code rates. The receiving end also comprises a multipath transducer for outputting a transmission signal, and a multipath hydrophone for receiving the signal.
The outputs of the data frame transmitting module and the retransmission frame transmitting module of the data link layer of the transmitting end are input into the physical layer through the AXI and are used as the input of the LDPC-CRC encoding module, the output of the LDPC-CRC encoding module is used as the input of the multiband modulating module, and the output of the multiband modulating module is output to the receiving end through the multipath transducer. The receiving end receives signals through a multipath hydrophone, the received signals are used as the input of an equalization module and a signal-to-noise ratio calculation module in a physical layer, the output of the equalization module is used as the input of an LDPC-CRC decoding module considering random phase offset, and the output of the LDPC-CRC decoding module considering random phase offset and the signal-to-noise ratio calculation module are input into a data link layer through an AXI. The data with correct decoding is input into the data frame receiving module, and the ACK data frame is packaged and returned to the data frame transmitting module, and the information of the frequency band, position, code rate and the like of the data with incorrect decoding is packaged into the ACK data frame and returned to the retransmission frame transmitting module.
The output of the data frame transmitting module is divided into a plurality of frequency bands, each frequency band corresponds to a transmitting data structure body, and a plurality of transmitting data frames are established in the transmitting data structure body. As shown in FIG. 2, each transmitted data frame comprises, in order, a synchronization header, a frame header, and at mostIndividual data packet @Set by man). And a guard interval is arranged between the synchronization head and the frame head and between the frame head and the data packet, so as to reduce intersymbol interference (Inter Symbol Interference, which is called ISI hereinafter) caused by the strong multipath effect of the underwater sound channel. As shown in FIG. 3, the frame header of the transmitted data frame is encapsulated with identification information for the receiving end to determine the receiving logic, wherein the identification information comprises the data frame type and the total frame number of the transmitted data frame of the current frequency bandFrame number of currently transmitted data frameNumber of data packets in currently transmitted data frameCurrent band number. The data frame types comprise a sending data frame, an ACK frame and a retransmitting data frame.
As shown in fig. 4, the ACK data frame sequentially includes a sync header, a frame header, and an ACK data packet. The ACK packet includes a frequency band in which the decoding error packet is located, a position in the transmission data frame, and a code rate.
As shown in fig. 5, the retransmission data frame sequentially includes a sync header, a frame header, and a plurality of data packets storing valid data. The identification information encapsulated in the frame header comprises the data frame type and the total frame number of the transmitted data frame of the current frequency bandFrame number of currently transmitted data frameNumber of data packets in currently transmitted data frameCurrent band numberThe original frequency band where the decoding error data packet is located, and the original position of the decoding error data packet in the transmission data frame.
Based on the underwater acoustic communication system, the embodiment of the invention also provides a multiband cross-layer reliable transmission method based on the real-time underwater acoustic communication system, which comprises the following steps:
S1, as shown in FIG. 6, when the data to be transmitted of the current frame is transmitted for the first time, a transmitting end uniformly divides the complete transmission bit stream corresponding to the data to be transmitted of the current frame into k parts in a data frame transmitting module of a data link layer, packages each part of transmission bit stream into corresponding transmission data structures, and inputs the k transmission data structures into a physical layer. The method comprises the following steps:
The transmitting end transmits the complete bit stream at the data link layer Dividing into k parts, putting into k transmitting data structures, each part of bit stream having the size of,Representing an upward rounding. Establishing a plurality of transmission data frames in a transmission data structure body, wherein each transmission data frame comprises a synchronous head, a frame head and at mostA data packet, a data packet containing a bit stream of the size ofThe number of data frame frames allocated in each band transmission data structure (specifically, set by human) can be expressed as:
in the formula, Representing redundant information in each data packet indicating the number of valid bits in the data packet.
Before the front partIn the frame transmission data frames, the number of data packets in each transmission data frame isThe number of data packets in the data frame transmitted in the last frame is as follows:
And packaging all the identification information into a frame header of the transmitted data frame for the receiving end to judge the receiving logic. The original information bit vector of each data packet in the transmission data frame is encapsulated into the corresponding data packet, and then sent to the physical layer for coding and modulation transmission, and the original information bit vector of each data packet in the transmission data frame can be expressed as:
Wherein i represents the frame number of the current transmitted data frame, p represents the number of data packets contained in the current data frame, b represents the frequency band number of the current data frame, s 0 represents the first original information bit, s 1 represents the second original information bit, and so on; the total number of transmission data frames allocated in the kth band transmission data structure is represented.
S2, the LDPC-CRC coding module of the transmitting end at the physical layer vectors the original information bitsAfter CRC encoding and LDPC encoding are sequentially carried out, the transmitting data structure body is subjected to multiband modulation through the multiband modulation module, and finally, the modulated k digital signals with different frequency bands are respectively subjected to signal transmission through k groups of multipath transducers.
And S3, when data is received for the first time, the receiving end carries out LDPC-CRC decoding which considers random phase offset on the symbols balanced by the balancing module at the LDPC-CRC decoding module which considers random phase offset of the physical layer, and meanwhile, the signal-to-noise ratio calculation module calculates the signal-to-noise ratio of k frequency bands respectively, and the decoding code rate of the k frequency bands is adjusted in a self-adaptive mode.
As shown in fig. 7, the LDPC-CRC decoding is specifically implemented by the following sub-steps:
(3.1) the Doppler effect of the underwater acoustic channel is considered to generate the residual frequency offset and the random phase, and the symbol equalized by the equalization module compensates the residual frequency offset, so that the equalized received signal Can be expressed as:
in the formula, In order to transmit the sequence of symbols,For random phase offset, the obeying mean is 0, and the variance isIs a gaussian distribution of (c); Is Gaussian white noise, obeys to have a mean value of 0 and a variance of Is a complex gaussian distribution of (c).
The conditional probability density function of (2) is:
Taking into account that Derived from Taylor expansion propertiesThe conditional probability density function may be modified as:
wherein, is a conjugate symbol.
Taking into account thatFor gaussian distribution, the conditional probability density function can be further reduced to:
in the formula, The representation takes the imaginary function.
Likelihood ratio calculation considering random phase offset is performed according to noise variance and phase variance: the bit log likelihood ratio of the suppressed phase noise of (a) can be expressed as:
in the formula, The first to send symbols for eachA number of bits of a bit,Is thatIs used for the observation of the (a),Expressed in the modulation symbol setA set of symbols with 0 bits,Is thatElements of (a) and (b); expressed in the modulation symbol set A set of symbols with a bit of 1,Is thatIs a component of the group.
And (3.2) calculating a check matrix, namely controlling cyclic displacement and data storage by a master control according to code rate and code length information based on the existing LDPC coding mode, and completing confirmation of the check matrix H.
And (3.3) performing iterative decoding, namely performing iterative decoding by adopting an LDPC (low density parity check) method until convergence to obtain a final bit likelihood ratio, and performing soft decision on the final bit likelihood ratio to obtain decoding bits.
And (3.4) CRC checking, namely, performing CRC checking on the decoded bits, wherein the final result is all 0, which means that the check is passed, the decoding result is correct, the check result and the valid bit information are output, the decoded bit information is sent to the data link layer of the receiving end, otherwise, the decoding result is incorrect, and the check result and the data packet related information are output to the data link layer.
The signal-to-noise ratio of k frequency bands is adaptively adjusted through a signal-to-noise ratio calculation module, and the method specifically comprises the following steps:
As shown in fig. 8, the reception signal received by the reception end is set to be The signals obtained by respectively passing through the band-pass filters of k frequency bands areThe corresponding in-band signal energy is calculated, a section of noise signal with the same length as the received signal is taken in front of each frequency band synchronous headThe corresponding noise signal capability is calculated, so that the signal to noise ratio of k frequency bands is calculated, and the expression is as follows:
the signal-to-noise ratio is divided into different intervals, each interval corresponds to different code rates, and the code rate is reduced along with the reduction of the signal-to-noise ratio, so that higher reliability is ensured. According to the interval of signal-to-noise ratio of different frequency bands Respectively adjusting the decoding code rate of k frequency bands,And setting code rate for the interval where the signal to noise ratio is. And storing the adjusted decoding code rate into an LDPC-CRC decoding module which considers random phase offset of a physical layer of a receiving end, and simultaneously sending the LDPC-CRC decoding module into a data link layer of the receiving end.
And S4, the receiving end encapsulates the data packet information with the decoding errors and the decoding code rate after self-adaptive adjustment into an ACK data frame at a data link layer and returns the ACK data frame to the transmitting end. The method comprises the following steps:
The receiving end obtains the bit data packet and the error information decoded by the physical layer in each frequency band data frame in the data link layer, sends the data packet with correct decoding into the receiving structure body of the data frame receiving module for caching, and sends the data packet with incorrect decoding into the original frequency band And the original position of the data packet in the transmitted data frameSending the data frame to a retransmission frame sending module for buffering, wherein N is the total number of error data packets in the data frame, and sending the data frame to the retransmission frame sending module、AndDecoding code rate after self-adaptive updating of individual frequency bandsAnd packaging the data packet into a data packet of the ACK data frame, and returning the data packet to the transmitting end.
S5, as shown in FIG. 9, when retransmitting and transmitting data, the transmitting end analyzes the ACK data packet at the data link layer to adaptively update the decoding code rate of k frequency bandsSending to a physical layer coding module to update the coding rate according to、Extracting the data packet in the transmitting data structure body, copying the data packet into each frequency band, so that each frequency band contains all the data packets which are decoded by mistake, and forming a retransmission data frame, wherein the retransmission data frame can be expressed as:
And finally, sending the retransmission data frame to a physical layer for coding, multiband modulation and underwater sound transmission.
S6, when the data is retransmitted and received, the receiving end executes the decoding operation in S3, if the data packet of any frequency band is decoded correctly, the data packet is considered to be retransmitted successfully, otherwise, the retransmission is considered to be failed, the operations of S4-S6 are executed again, and the original data packet of all decoding errors of a new round is processedAndAnd packaging the ACK data frame, returning to the transmitting end and indicating the transmitting end to continue retransmission until the maximum retransmission times are reached. And when the maximum retransmission times are reached and the correct transmission of all the data packets is not realized, the communication is considered to be failed.
The invention encodes and decodes the effective information bits through the forward error correction code of the physical layer, improves the successful receiving probability of the receiving end, copies the error data packet to all frequency bands for retransmission under the condition that the forward error correction code can not correct all errors through a multiband retransmission mechanism of the data link layer, improves the reliability of transmission, evaluates the channel quality of each frequency band when one frame of data is received, carries out self-adaptive adjustment on the forward error correction code rate of each frequency band, and improves the effective data throughput. On the other hand, the underwater sound channel also shows different performances in different frequency bands, the total communication frequency band is divided into a plurality of sub-frequency bands to be transmitted, and the receiving end evaluates the channel quality of each frequency band to control the coding and retransmission strategy of the transmitting end, so that the retransmission times can be effectively reduced, and the transmission throughput can be increased on the premise of ensuring successful transmission.
It will be appreciated by persons skilled in the art that the foregoing description is a preferred embodiment of the invention, and is not intended to limit the invention, but rather to limit the invention to the specific embodiments described, and that modifications may be made to the technical solutions described in the foregoing embodiments, or equivalents may be substituted for elements thereof, for the purposes of those skilled in the art. Modifications, equivalents, and alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.

Claims (10)

1.一种基于实时水声通信系统的多频带跨层可靠传输方法，其特征在于，包括以下步骤：1. A multi-band cross-layer reliable transmission method based on a real-time underwater acoustic communication system, characterized in that it includes the following steps: S1：发送端将当前帧待发送数据对应的完整的发送比特流均分为k份，将每份比特流封装至对应的发送数据结构体中，所述发送数据结构体包括多个发送数据帧；发送数据结构体中的数据进行可变码率的信道编码后，分别调制到k个不同的频带向接收端发送；S1: The transmitting end divides the complete transmission bit stream corresponding to the data to be transmitted in the current frame into k parts, and encapsulates each bit stream into a corresponding transmission data structure, wherein the transmission data structure includes multiple transmission data frames; after the data in the transmission data structure is subjected to variable code rate channel coding, it is modulated into k different frequency bands and sent to the receiving end; S2：接收端对接收信号进行均衡操作后，进行考虑了随机相位偏移的可变码率的信道译码，同时分别计算k个频带的信噪比，自适应调整k个频带的译码码率；得到译码后的比特数据包、译码正误信息、自适应调整后的译码码率；S2: After equalizing the received signal, the receiving end performs variable rate channel decoding taking into account the random phase offset, and calculates the signal-to-noise ratio of the k frequency bands respectively, and adaptively adjusts the decoding rate of the k frequency bands; obtains the decoded bit data packet, decoding error information, and adaptively adjusted decoding rate; S3：存储译码正确的数据包，并将译码错误的数据包所在的原始频带和在发送数据帧中的原始位置、自适应调整后的译码码率封装进ACK数据包中，返回给发送端；S3: Store the correctly decoded data packets, and encapsulate the original frequency band of the incorrectly decoded data packets, the original position in the transmitted data frame, and the adaptively adjusted decoding code rate into an ACK data packet, and return it to the sender; S4：发送端解析ACK数据包，将解错的数据包复制到每个频带中，形成重传数据帧，基于自适应调整后的译码码率更新编码码率后，对其进行可变码率的信道编码、频带调制与重传；S4: The sender parses the ACK data packet, copies the decoded data packet to each frequency band to form a retransmission data frame, updates the encoding code rate based on the adaptively adjusted decoding code rate, and then performs variable code rate channel coding, frequency band modulation and retransmission on it; S5：接收端执行S2所述的操作，若任意一个频带的数据包译码正确，则认为该数据包重传成功，反之则认为重传失败，再次进行S3-S5的操作，直到达到最大重传次数；当所有数据包都译码正确时，接收端生成ACK数据包指示发送端进行下一帧待发送数据的发送。S5: The receiving end performs the operation described in S2. If the data packet of any frequency band is decoded correctly, the data packet is considered to be retransmitted successfully. Otherwise, the retransmission is considered to have failed, and the operations of S3-S5 are performed again until the maximum number of retransmissions is reached. When all data packets are decoded correctly, the receiving end generates an ACK data packet to instruct the sending end to send the next frame of data to be sent. 2.根据权利要求1所述的基于实时水声通信系统的多频带跨层可靠传输方法，其特征在于，所述S1中，完整的发送比特流大小为，每份比特流的大小为，表示向上取整；所述发送数据帧包括同步头、帧头、多个数据包；每个发送数据帧中包含的数据包数量不大于阈值，一个数据包所含的比特流大小为，每个频带发送数据结构体中分配的数据帧帧数表达式如下：2. According to the multi-band cross-layer reliable transmission method based on the real-time underwater acoustic communication system of claim 1, it is characterized in that in S1, the size of the complete transmission bit stream is , the size of each bit stream is , Indicates rounding up; the transmitted data frame includes a synchronization header, a frame header, and multiple data packets; the number of data packets contained in each transmitted data frame is not greater than the threshold , the bit stream size of a data packet is , the number of data frames allocated in each frequency band sending data structure is expressed as follows: ； ; 式中，代表每个数据包中的冗余信息，用来指示该数据包中有效比特的个数；In the formula, Represents the redundant information in each data packet and is used to indicate the number of valid bits in the data packet; 在发送数据结构体的前帧发送数据帧中，每个发送数据帧中数据包的个数为，最后一帧发送数据帧中数据包的个数为：Before sending the data structure In the frame sending data frame, the number of data packets in each sending data frame is , the number of data packets in the last frame sent is: 。 . 3.根据权利要求1所述的基于实时水声通信系统的多频带跨层可靠传输方法，其特征在于，所述S2中，可变码率的信道译码选用LDPC-CRC译码，对均衡后的符号进行考虑了随机相位偏移的LDPC-CRC译码具体通过如下子步骤实现：3. According to the multi-band cross-layer reliable transmission method based on the real-time underwater acoustic communication system of claim 1, it is characterized in that in said S2, the variable code rate channel decoding uses LDPC-CRC decoding, and the LDPC-CRC decoding of the equalized symbols taking into account the random phase offset is specifically implemented by the following sub-steps: （2.1）根据噪声方差和相位方差进行考虑随机相位偏移的似然比计算，表达式如下：(2.1) The likelihood ratio considering random phase offset is calculated based on the noise variance and phase variance, and the expression is as follows: ； ; ； ; 式中，r表示均衡后的接收信号的标量，t表示发送符号序列的标量，表示高斯白噪声的方差，表示随机相位偏移的方差；表示取虚部函数，*表示共轭符号；为每个发送符号的第个比特，表示在调制符号集合中第个比特为0的符号集合，为中的元素；表示在调制符号集合中第个比特为1的符号集合，为中的元素；Where r represents the scalar of the received signal after equalization, t represents the scalar of the transmitted symbol sequence, represents the variance of Gaussian white noise, represents the variance of the random phase shift; Indicates the imaginary part function, * indicates the conjugate symbol; For each transmitted symbol bits, Indicates the first The set of symbols with bits set to 0, for Elements in Indicates the first The set of symbols with bits set to 1, for Elements in （2.2）计算校验矩阵：总控根据码率和码长信息控制循环位移与数据存储，完成校验矩阵H的确认；(2.2) Calculate the check matrix: The master control controls the cyclic shift and data storage according to the code rate and code length information to complete the confirmation of the check matrix H; （2.3）迭代译码：采用LDPC的方法进行迭代译码直至收敛，获得最终比特似然比，对其进行软判决获得译码比特；(2.3) Iterative decoding: Use the LDPC method to perform iterative decoding until convergence, obtain the final bit likelihood ratio, and make soft decisions on it to obtain the decoded bits; （2.4）CRC校验：将译码比特进行CRC校验，对校验通过的译码比特进行存储；校验不通过的数据包所在的原始频带和在发送数据帧中的原始位置送入接收端。(2.4) CRC check: The decoded bits are subjected to CRC check and the decoded bits that pass the check are stored; the original frequency band of the data packets that fail the check and the original position in the transmitted data frame are sent to the receiving end. 4.根据权利要求1所述的基于实时水声通信系统的多频带跨层可靠传输方法，其特征在于，所述S2中，分别计算k个频带的信噪比，自适应调整k个频带的译码码率具体通过如下操作实现：4. The multi-band cross-layer reliable transmission method based on a real-time underwater acoustic communication system according to claim 1 is characterized in that, in S2, respectively calculating the signal-to-noise ratios of the k frequency bands and adaptively adjusting the decoding bit rates of the k frequency bands are specifically implemented by the following operations: 所述接收端接收到的接收信号为，分别经过k个频带的带通滤波器得到的信号为，计算其对应的带内信号能量；取每个频带同步头前的一段与接收信号长度相同的噪声信号，计算其对应的噪声信号能力，得到k个频带的信噪比表达式如下：The receiving signal received by the receiving end is , the signals obtained by passing through the bandpass filters of k frequency bands are , calculate the corresponding in-band signal energy; take a noise signal with the same length as the received signal before the synchronization head of each frequency band , calculate the corresponding noise signal capability, and get the signal-to-noise ratio expression of k frequency bands as follows: ； ; 将信噪比划分为不同的区间，每个区间对应不同的译码码率，且译码码率随着信噪比的降低而降低；根据不同频带的信噪比所在的区间，分别调整k个频带的译码码率，为信噪比所在区间对应设置的译码码率；用调整后的译码码率更新可变码率的信道译码的译码码率。The signal-to-noise ratio is divided into different intervals, each interval corresponds to a different decoding rate, and the decoding rate decreases as the signal-to-noise ratio decreases; according to the intervals where the signal-to-noise ratios of different frequency bands are located, the decoding rates of k frequency bands are adjusted respectively. , The decoding code rate is set corresponding to the interval where the signal-to-noise ratio is located; and the decoding code rate of the variable code rate channel decoding is updated with the adjusted decoding code rate. 5.根据权利要求1所述的基于实时水声通信系统的多频带跨层可靠传输方法，其特征在于，所述发送数据帧包括同步头、帧头、多个数据包；每个数据包的原始信息比特向量表达式如下：5. According to the multi-band cross-layer reliable transmission method based on the real-time underwater acoustic communication system of claim 1, it is characterized in that the sent data frame includes a synchronization header, a frame header, and multiple data packets; the original information bit vector expression of each data packet is as follows: ； ; 式中，i表示当前发送数据帧帧号，p表示当前数据帧所包含的数据包个数，b表示当前数据帧所在频带编号；s0表示第一个原始信息比特，s1表示第二个原始信息比特，以此类推；表示第k个频带发送数据结构体中分配的发送数据帧总帧数；Where i represents the frame number of the currently transmitted data frame, p represents the number of data packets contained in the current data frame, b represents the frequency band number of the current data frame; s 0 represents the first original information bit, s 1 represents the second original information bit, and so on; Indicates the total number of transmission data frames allocated in the transmission data structure of the kth frequency band; 所述重传数据帧的表达式如下：The expression of the retransmission data frame is as follows: ； ; 式中，表示译码错误的数据包所在的原始频带，表示译码错误的数据包在发送数据帧中的原始位置，n=1,2,…,N。In the formula, Indicates the original frequency band where the data packet with decoding error is located, Indicates the original position of the data packet with decoding error in the transmitted data frame, n=1,2,…,N. 6.一种水声通信系统，用于实现权利要求1-5任意一项所述的基于实时水声通信系统的多频带跨层可靠传输方法，其特征在于，包括物理层和数据链路层；所述物理层和数据链路层之间通过先进可扩展接口进行数据帧、指令和码率的传输；6. An underwater acoustic communication system, used to implement the multi-band cross-layer reliable transmission method based on a real-time underwater acoustic communication system according to any one of claims 1 to 5, characterized in that it includes a physical layer and a data link layer; the physical layer and the data link layer transmit data frames, instructions and bit rates through an advanced extensible interface; 所述数据链路层包括：发送端的数据帧发送模块，以及接收端的数据帧接收模块、重传帧发送模块；所述数据帧发送模块的输出为发送数据帧，所述重传帧发送模块的输出为重传数据帧，所述数据帧接收模块用于接收并存储译码正确的数据包；The data link layer includes: a data frame sending module at the sending end, and a data frame receiving module and a retransmission frame sending module at the receiving end; the output of the data frame sending module is a sending data frame, the output of the retransmission frame sending module is a retransmission data frame, and the data frame receiving module is used to receive and store correctly decoded data packets; 所述物理层包括发送端的可变码率的信道编码模块和多频带调制模块，以及接收端的均衡模块、信噪比计算模块、考虑随机相位偏移的可变码率的信道译码模块；The physical layer includes a variable code rate channel coding module and a multi-band modulation module at the transmitting end, and an equalization module, a signal-to-noise ratio calculation module, and a variable code rate channel decoding module considering random phase offset at the receiving end; 首次发送时，所述数据帧发送模块的输出作为可变码率的信道编码模块的输入；重传发送时，所述重传帧发送模块的输出作为可变码率的信道编码模块的输入；可变码率的信道编码模块的输出作为多频带调制模块的输入，多频带调制模块的输出通过多路换能器向接收端输出；During the first transmission, the output of the data frame transmission module is used as the input of the variable code rate channel coding module; during the retransmission transmission, the output of the retransmission frame transmission module is used as the input of the variable code rate channel coding module; the output of the variable code rate channel coding module is used as the input of the multi-band modulation module, and the output of the multi-band modulation module is output to the receiving end through the multi-channel transducer; 接收端通过多路水听器接收信号，所述均衡模块和信噪比计算模块的输入均为接收信号，均衡模块输出作为考虑随机相位偏移的可变码率的信道译码模块的输入，考虑随机相位偏移的可变码率的信道译码模块和信噪比计算模块的输出通过先进可扩展接口输入数据链路层；其中，译码正确的数据包输入数据帧接收模块，并封装ACK数据帧返回数据帧发送模块；译码错误的数据包，其所在的原始频带、在发送数据帧中的原始位置、自适应调整后的译码码率封装进ACK数据帧中，输入重传帧发送模块。The receiving end receives signals through a multi-channel hydrophone, the inputs of the equalization module and the signal-to-noise ratio calculation module are both received signals, the output of the equalization module is used as the input of the variable code rate channel decoding module considering random phase offset, and the outputs of the variable code rate channel decoding module considering random phase offset and the signal-to-noise ratio calculation module are input into the data link layer through an advanced extensible interface; wherein, the correctly decoded data packet is input into the data frame receiving module, and the ACK data frame is encapsulated and returned to the data frame sending module; the incorrectly decoded data packet, its original frequency band, original position in the sent data frame, and adaptively adjusted decoding code rate are encapsulated into the ACK data frame and input into the retransmission frame sending module. 7.根据权利要求6所述的水声通信系统，其特征在于，所述数据链路层选用ARM芯片，所述物理层选用可编程逻辑门阵列。7. The underwater acoustic communication system according to claim 6 is characterized in that the data link layer uses an ARM chip and the physical layer uses a programmable logic gate array. 8.根据权利要求6所述的水声通信系统，其特征在于，所述数据帧发送模块的输出分为多个频带，每个频带对应一个发送数据结构体，发送数据结构体中建立多个发送数据帧；每个发送数据帧依次包括：一个同步头、一个帧头和至多个数据包；所述同步头和帧头之间、帧头和数据包之间设置有保护间隔。8. The underwater acoustic communication system according to claim 6, characterized in that the output of the data frame sending module is divided into multiple frequency bands, each frequency band corresponds to a sending data structure, and multiple sending data frames are established in the sending data structure; each sending data frame includes: a synchronization header, a frame header and at most A protection interval is set between the synchronization header and the frame header, and between the frame header and the data packet. 9.根据权利要求8所述的水声通信系统，其特征在于，所述发送数据帧的帧头中封装有标识信息，包括：数据帧类型、当前频带的发送数据帧总帧数、当前发送数据帧帧号、当前发送数据帧中数据包个数、当前频带编号；9. The underwater acoustic communication system according to claim 8, characterized in that the frame header of the transmitted data frame is encapsulated with identification information, including: data frame type, total number of transmitted data frames in the current frequency band , Current data frame number being sent , the number of data packets in the current sent data frame , Current frequency band number ; 所述数据帧类型包括：发送数据帧、ACK帧、重传数据帧。The data frame types include: sending data frame, ACK frame, and retransmission data frame. 10.根据权利要求6所述的水声通信系统，其特征在于，所述ACK数据帧依次包括：一个同步头、一个帧头和ACK数据包；ACK数据包中包括译码错误数据包所在的频带、在发送数据帧中的位置、译码码率；10. The underwater acoustic communication system according to claim 6, characterized in that the ACK data frame comprises: a synchronization header, a frame header and an ACK data packet in sequence; the ACK data packet includes the frequency band where the decoding error data packet is located, the position in the transmitted data frame, and the decoding code rate; 所述重传数据帧依次包括：一个同步头、一个帧头和多个储存有效数据的数据包，其中，帧头中封装的标识信息包括：数据帧类型、当前频带的发送数据帧总帧数、当前发送数据帧帧号、当前发送数据帧中数据包个数、当前频带编号、译码错误数据包所在的原始频带、译码错误数据包在发送数据帧中的原始位置。The retransmission data frame includes: a synchronization header, a frame header and multiple data packets storing valid data, wherein the identification information encapsulated in the frame header includes: data frame type, total number of data frames sent in the current frequency band , Current data frame number being sent , the number of data packets in the current sent data frame , Current frequency band number , the original frequency band where the decoding error data packet is located, and the original position of the decoding error data packet in the transmitted data frame.
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朱涛: ""水声通信中基于极化码的混合自动重传策略"", 《中国优秀硕士学位论文全文数据库（电子期刊）信息科技辑》, 15 February 2023 (2023-02-15) *
韩维；黄建国: ""LDPC码与ARQ在水声通信中的性能研究"", 《计算机工程与应用》, 16 January 2009 (2009-01-16) *

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