Underwater acoustic communication parameter adaptive adjustment method

Abstract

The invention relates to a self-adaptive adjustment method for underwater acoustic communication parameters, which comprises the following steps: estimating signal-to-noise ratio and channel maximum multipath time delay, at a receiving end, counting noise and signal energy to obtain received signal-to-noise ratio estimation, and carrying out matched filtering processing on a received synchronous signal to obtain channel maximum multipath time delay estimation; performing bit error rate statistics before error correction, sequentially performing de-interleaving, error correction decoding and CRC (Cyclic Redundancy Check) on a result output by signal demodulation, if the result is correct, performing error correction coding and interleaving processing on a decoding result again, and comparing a bit output after processing with a bit output by signal demodulation through bit judgment to finish bit error rate statistics before error correction. The adaptive capacity of underwater acoustic communication to channels can be effectively improved, the method is easy to implement, a transceiver does not need to shake hands for multiple times, and the method has good practical value.

Description

Technical Field:

[0001] The present invention belongs to the technical field of underwater acoustic communication, and particularly relates to a method for adaptively adjusting underwater acoustic communication parameters. Background Art:

[0002] The underwater acoustic channel has characteristics such as severe multipath spread, time-varying, and space-varying. To adapt to the changes in the underwater acoustic channel, underwater acoustic communication devices are usually designed with multiple communication rate gears. Users with certain professional background knowledge are required to select an appropriate rate gear according to the transmission conditions of the underwater acoustic channel. Some underwater acoustic communication products have the function of automatically selecting the rate gear. Before the formal data transmission, the sender sends test data at a certain rate gear, and the receiver feeds back the test result to the sender. The sender then replaces the rate gear and resends the test data according to the test result. This process needs to be repeated multiple times to select the best rate gear. There are also some underwater acoustic communication products that use an error control technology based on the retransmission mechanism to achieve reliable communication. The receiver feeds back the sequence numbers of the packets with decoding errors to the sender. After receiving the feedback, the sender resends the packets with decoding errors. When the channel condition is good, the number of retransmissions is small, and when it is poor, multiple retransmissions are required to ensure correct data reception. The transmission conditions of the underwater acoustic channel have a large dynamic range. When the channel condition is good, generally a relatively low transmission power can achieve high-rate and low bit error rate data transmission. When the channel condition is poor, a very high transmission power is required to ensure correct data transmission at a low rate. Whether it is the rate automatic adjustment method or the error automatic retransmission method, due to the half-duplex communication mode of underwater acoustic communication and the slow sound speed, when the communication distance is far, these communication methods that require multiple handshakes and feedback between the transceiver will make the underwater transmission time of the signal occupy most of the communication time, and its equivalent communication rate is very low, which limits the application range of underwater acoustic communication. Summary of the Invention:

[0003] The technical problem to be solved by the present invention is to provide a method for adaptively adjusting underwater acoustic communication parameters. This method comprehensively utilizes information such as signal-to-noise ratio, maximum channel multipath delay, CRC check result, and pre-error correction bit error rate statistics to adaptively adjust parameters such as transmission power, training sequence length, modulation order, and coding rate, so that underwater acoustic communication can perform reliable communication at the best communication rate, and can effectively improve the adaptability of underwater acoustic communication to the channel. This method is simple to implement, does not require multiple handshakes between the transceiver, and has good practical value.

[0004] The technical solution of the present invention is to provide a method for adaptively adjusting underwater acoustic communication parameters, including the following steps,

[0005] Signal-to-noise ratio and channel maximum multipath delay estimation. At the receiving end, by statistically analyzing the noise and signal energy, the received signal-to-noise ratio estimation is obtained. By performing matched filtering on the received synchronization signal, the channel maximum multipath delay estimation is obtained.

[0006] Pre-error-correction bit error rate statistics. The results of signal demodulation output are successively deinterleaved, error-correction decoded, and CRC-checked. If the check is correct, the decoded results are re-error-coded and interleaved, and the bits output after processing are compared with the bits output by bit decision after signal demodulation to complete the pre-error-correction bit error rate statistics.

[0007] Adaptive adjustment of communication parameters. The receiving end feeds back the signal-to-noise ratio, channel maximum multipath delay estimation results, CRC check results, and pre-error-correction bit error rate-related information to the transmitting end. The transmitting end uses the above information to adjust communication parameters including transmit power, training sequence length, modulation order, and coding rate.

[0008] Underwater acoustic communication channels are characterized by time-variation and space-variation, and the transmission conditions have a very large dynamic range. It is difficult to communicate robustly "anytime" and "anywhere" with fixed communication parameters. It is necessary to dynamically adjust communication parameters to achieve an acceptable bit error rate range at an appropriate communication rate or transmit power. Common parameters of underwater acoustic communication include transmit power, modulation order, coding rate of error-correction coding, and training sequence length. Among them, transmit power directly affects the received signal-to-noise ratio and is one of the factors determining the bit error rate performance; the training sequence length affects the channel estimation accuracy. To ensure the convergence of the adaptive channel estimation algorithm, it generally needs to be greater than the channel maximum multipath delay length. The longer the training sequence length, the greater the communication overhead and the lower the effective communication rate; under the same channel transmission conditions, the higher the modulation order, the higher the communication rate, but the greater the bit error rate; the coding rate of error-correction coding affects the error-correction performance. The lower the coding rate, the stronger the error-correction performance, but the lower the communication rate. Therefore, by adaptively adjusting these parameters, underwater acoustic communication can achieve the bit error rate requirement at an appropriate rate or power. The traditional method of adjusting underwater acoustic communication parameters generally only uses the signal-to-noise ratio and channel measurement results at the receiving end to adjust communication parameters. This method often cannot ensure that subsequent communication can be controlled within an acceptable bit error rate range. The present invention further uses the CRC check results and pre-error-correction bit error rate information, adaptively adjusts communication parameters using different strategies, and leaves a certain signal-to-noise ratio margin, which can effectively ensure the correctness of subsequent underwater acoustic communication at the best rate.

[0009] Preferably, during the adaptive adjustment process of communication parameters, when CRC check fails, first, if the length of the training sequence is less than the maximum multipath delay of the channel, increase the length of the training sequence; then, according to the signal-to-noise ratio required for the current modulation order or coding rate parameter to reach the acceptable bit error rate range and the feedback signal-to-noise ratio, with a certain signal-to-noise ratio margin, increase the transmit power; finally, if the current transmit power is already the maximum, reduce the modulation order, and if the current modulation order is the minimum, reduce the coding rate.

[0010] Preferably, during the adaptive adjustment process of communication parameters, when CRC check is successful and the bit error rate before error correction is low (less than 0.01), first, increase the modulation order, and if the current modulation order is the maximum, increase the coding rate; then, according to the signal-to-noise ratio required for the adjusted modulation order or coding rate condition to reach the acceptable bit error rate range, and the signal-to-noise ratio feedback from the receiving end, with a certain signal-to-noise ratio margin, reduce the transmit power.

[0011] Preferably, when CRC check is successful and the bit error rate before error correction is high (0.01 - 0.1), first increase the transmit power; then, if the current transmit power is the maximum, reduce the modulation order, and if the current modulation order is the minimum, reduce the coding rate.

[0012] Furthermore, the communication parameters include transmit power, training sequence length, modulation order, and coding rate.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] The present invention proposes an adaptive adjustment method for underwater acoustic communication parameters, which comprehensively utilizes information such as signal-to-noise ratio, estimated value of the maximum multipath delay of the channel, CRC check result, and bit error rate before error correction to adaptively adjust parameters such as transmit power, training sequence length, modulation order, and coding rate. Compared with the traditional underwater acoustic communication parameter adjustment method, the present invention also utilizes the CRC check result and the bit error rate information before error correction, and adopts different parameter adjustment strategies respectively, which can effectively ensure the correctness of subsequent underwater acoustic communication at the best rate. During the communication parameter adjustment process of the present invention, only the receiving end needs to feedback the received decoding information once, without multiple handshakes between the transceiver and the receiver, which has good practical value. Description of the Drawings:

[0015] Figure 1 It is a block diagram for adaptive adjustment of underwater acoustic communication parameters;

[0016] Figure 2 It is a flowchart for communication parameter adjustment when CRC check fails;

[0017] Figure 3 It is a flowchart for adjusting communication parameters when CRC check is successful;

[0018] Figure 4 It is a flowchart for adjusting communication parameters when the CRC check is correct and the bit error rate before error correction is low;

[0019] Figure 5 It is a flowchart for adjusting communication parameters when the CRC check is correct but the bit error rate before error correction is high. Specific implementation manner:

[0020] The present invention will be further described in detail below in conjunction with the accompanying drawings in terms of the specific implementation manner:

[0021] Figure 1 This is a block diagram for adaptive adjustment of underwater acoustic communication parameters of the present invention. At the receiving end, first, by statistically analyzing the noise and signal energy, an estimated received signal-to-noise ratio is obtained. By performing matched filtering on the received synchronization signal, time synchronization and the channel multipath extension structure are obtained, and then the maximum multipath delay information is obtained. The signal-to-noise ratio and the maximum multipath delay will be used as important bases for adaptive adjustment of communication parameters. Then, the received signal is successively demodulated, deinterleaved, and CRC-checked to complete the receiving decoding process. If the CRC check is correct, it indicates that there are no errors after error correction, but there may be errors before error correction. The bits output by decoding are successively error-coded and interleaved to generate the bits before error correction. At the same time, the bits output by bit decision after signal demodulation are compared to complete the statistics of the bit error rate before error correction. Finally, the receiving decoding situation is fed back to the sending end. To prevent transmission errors of the feedback information, the feedback information can be sent at the lowest rate of communication parameters and the maximum power. The feedback information includes the CRC check result, the received signal-to-noise ratio, and the maximum multipath delay. When the CRC check is correct, the feedback information also includes the bit error rate before error correction.

[0022] The sending end adaptively adjusts the communication parameters according to the received feedback information. If the CRC check is incorrect, it indicates that the current channel transmission condition is poor, and high-power or low-rate communication parameters are required to improve the communication robustness. The communication parameter adjustment is as Figure 2 shown, and the specific steps are as follows:

[0023] Step 1: Adjust the length of the training sequence. If the length of the training sequence is greater than the maximum multipath delay length, increase the length of the training sequence and jump to Step 2; otherwise, directly jump to Step 2.

[0024] Step 2: Adjust the transmission power. According to the signal-to-noise ratio required to achieve an acceptable bit error rate range under the current modulation order and coding rate parameters, determine whether the signal-to-noise ratio fed back by the receiving end meets the requirements. If it meets the requirements, it indicates that although the current signal-to-noise ratio is relatively high, there are still bit errors after error correction, and other communication parameters need to be adjusted to improve the receiving correctness, then jump to Step 3; if it does not meet the requirements, then according to the signal-to-noise ratio required to achieve an acceptable bit error rate and the currently fed-back signal-to-noise ratio, with a certain signal-to-noise ratio margin, increase the transmission power. If the current is already the maximum transmission power, then jump to Step 3; otherwise, increase the transmission power. If the power has been adjusted to the maximum but the signal-to-noise ratio still does not meet the requirements, then jump to Step 3; otherwise, jump to Step 5.

[0025] Step 3: Adjust the modulation order. If the current is the minimum modulation order, then jump to Step 4; otherwise, decrease the modulation order and jump to Step 5.

[0026] Step 4: Reduce the coding rate and jump to Step 5.

[0027] Step 5: End of this process.

[0028] If the CRC check is correct, then adjust the communication parameters according to the bit error rate before error correction fed back by the receiving end, such as Figure 3 shown. If the bit error rate before error correction is relatively low, in this embodiment, less than 0.01, it indicates that the current channel transmission condition is good, and higher rate or lower power communication parameters can be adopted for subsequent communication. The communication parameter adjustment is as Figure 4 shown. If the bit error rate before error correction is relatively high, in this embodiment, in the range of 0.01 - 0.1 and at the critical value that the error correction code can correct, it indicates that the current channel transmission condition is average. Although error correction can ensure the transmission correctness with a certain probability, to ensure the robustness and reliability of subsequent communication, the transmission power, modulation order or coding rate parameters can be finely adjusted, such as Figure 5 shown. If the bit error rate before error correction is moderate, it indicates that the channel transmission condition is good, and the transmission correctness can be ensured with a high probability through error correction, then maintain the current communication parameters.

[0029] Figure 4 It is the flowchart of communication parameter adjustment when the CRC check is correct but the bit error rate before error correction is relatively low. The specific steps are as follows:

[0030] Step 1: Adjust the modulation order or coding rate. If the current is the maximum modulation order, then increase the coding rate and jump to Step 2; otherwise, increase the modulation order and jump to Step 2.

[0031] Step 2: Adjust the transmission power. Determine whether the signal-to-noise ratio (SNR) margin is large based on the SNR required to achieve an acceptable bit error rate (BER) range under the adjusted modulation order or coding rate, and compare it with the SNR fed back by the receiving end. If there is a certain margin, jump to Step 3; if there is a large margin and the current power is not the lowest, reduce the transmission power and jump to Step 3. If the current power is already the minimum, directly jump to Step 3.

[0032] Step 3: End of this process.

[0033] Figure 5 It is a flowchart for adjusting communication parameters when the CRC check is correct but the bit error rate before error correction is high. The specific steps are as follows:

[0034] Step 1: Adjust the transmission power. If the current transmission power is not the highest, increase the transmission power and jump to Step 2; otherwise, directly jump to Step 2.

[0035] Step 2: Adjust the modulation order or coding rate. If the current modulation order is the minimum, reduce the coding rate and jump to Step 3; otherwise, decrease the modulation order and jump to Step 3.

[0036] Step 3: End of this process.

[0037] In summary, the adaptive adjustment method for underwater acoustic communication parameters proposed by the present invention aims to achieve reliable communication at the best communication rate for underwater acoustic communication. It comprehensively utilizes information such as the SNR, the estimated value of the maximum channel multipath delay, the CRC check result, and the bit error rate before error correction to adaptively adjust parameters such as the transmission power, training sequence length, modulation order, and coding rate. Compared with the traditional method for adjusting underwater acoustic communication parameters, the present invention adopts different parameter adjustment strategies according to the CRC check result and the bit error information before error correction, which can effectively ensure the correctness of subsequent underwater acoustic communication transmission at the best rate.

[0038] The above is only an illustration of the preferred embodiments of the present invention and should not be construed as a limitation of the claims. All equivalent process transformations made using the specification of the present invention are included in the scope of the patent protection of the present invention.

Claims

1. A method for adaptively adjusting underwater acoustic communication parameters, characterized in that: The following steps are included: Signal-to-noise ratio and maximum multipath delay estimation of the channel. At the receiving end, the received signal-to-noise ratio estimation is obtained by performing noise and signal energy statistics, and the maximum multipath delay estimation of the channel is obtained by performing matched filtering on the received synchronization signal. The bit error rate statistics before error correction are performed. The results of signal demodulation output are deinterleaved, error-corrected and decoded, and CRC checks are performed in sequence. If the check is correct, the decoded results are re-encoded and interleaved. The bits output after processing are compared with the bits output by signal demodulation after bit judgment to complete the bit error rate statistics before error correction. The communication parameters are adaptively adjusted. The receiving end feeds back the signal-to-noise ratio, the channel maximum multipath delay estimation results, the CRC check results, and the information related to the bit error rate before error correction to the sending end. The sending end uses the above information to adjust the communication parameters.

2. The method for adaptively adjusting underwater acoustic communication parameters according to claim 1, characterized in that: During the adaptive adjustment of communication parameters, when a CRC check error occurs, first, if the training sequence length is less than the maximum multipath delay of the channel, the training sequence length is increased; then, the transmission power is increased according to the current modulation order or coding rate parameters to achieve the required signal-to-noise ratio and the feedback signal-to-noise ratio within the acceptable bit error rate range, and a certain signal-to-noise ratio margin is left; finally, if the current transmission power is the maximum, the modulation order is reduced; if the current modulation order is the minimum, the coding rate is reduced.

3. The method for adaptively adjusting underwater acoustic communication parameters according to claim 1, characterized in that: During the adaptive adjustment of communication parameters, when the CRC check is correct and the bit error rate before error correction is less than 0.01, first, the modulation order is increased. If the current modulation order is the maximum, the coding rate is increased; then, according to the signal-to-noise ratio required to achieve an acceptable bit error rate range under the adjusted modulation order or coding rate conditions, as well as the signal-to-noise ratio fed back by the receiving end, a certain signal-to-noise ratio margin is left and the transmit power is reduced.

4. The method for adaptively adjusting underwater acoustic communication parameters according to claim 1, characterized in that: When the CRC check is correct and the bit error rate before error correction is in the range of 0.01-0.1, the transmission power is first increased; then, if the current transmission power is the maximum, the modulation order is reduced; if the current modulation order is the minimum, the coding rate is reduced.

5. The method for adaptively adjusting underwater acoustic communication parameters according to claim 1, characterized in that: Communication parameters include transmit power, training sequence length, modulation order and coding rate.

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