A method for underwater acoustic node adaptive retransmission based on distance measurement

Abstract

The application discloses a kind of underwater acoustic node adaptive retransmission methods based on distance measurement, comprising the following steps: sending node transmits data to target node and starts timer;Target node receives data, and transmits to sending node after processing;Judge whether the data transmitted by target node is successfully received by sending node, if the data transmitted by target node is not received or cannot be completely correctly received by sending node within retransmission timeout time, then retransmit according to retransmission rule;Sending node and target node complete two-way communication, and input and update other node information table stored in sending node during communication process.The application carries out distance measurement while node communication, improves the utilization efficiency of data;Node characteristic information is included in the selection standard of retransmission rule, and is constantly updated, improves the data transmission throughput between nodes, and improves the adaptability of node under different underwater acoustic channel conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of underwater acoustic communication method, and particularly relates to a self-adaptive retransmission method of underwater acoustic node based on distance measurement. BACKGROUND

[0002] Data transmission by using acoustic wave as carrier is one of the most effective methods of underwater long-distance wireless communication, and is also the main form of underwater long-distance communication, which is widely used in ocean observation, sea condition early warning monitoring and other fields. In order to improve the stability of underwater acoustic node communication, ensure reliable communication and reduce the energy consumption of underwater acoustic node, in view of the data loss caused by time-varying characteristics of channel, multipath interference and Doppler spread in underwater acoustic communication process, a suitable retransmission scheme needs to be designed to ensure reliable transmission of data between nodes.

[0003] In the existing adaptive transmission method, some methods establish and train underwater acoustic communication model based on deep neural network, so as to realize adaptive selection of underwater acoustic communication system and data transmission. In this kind of method, signal-to-noise ratio, time delay, Doppler and other characteristics are artificially established to divide the performance by using a quantitative score table, a large number of samples are sent into the network for training, and the trained model is used for selection of communication system. However, due to the variability of underwater environment, the effective period of input sample of the model is not long, and the adaptability of the model is greatly different in different sea areas. Moreover, the deployment of deep neural network requires high-power hardware support, and the energy of underwater node is limited. Therefore, most of the energy should be used for data transmission to improve the efficiency of data transmission. In some methods, underwater nodes synchronize the clock by broadcasting signals, and reasonably allocate time slots for data retransmission of each node to avoid collision of arriving data. However, a large amount of data transmission is needed before data transmission to correct the state of the node, which reduces the overall channel utilization efficiency, and is not suitable for underwater nodes with position deviation. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a self-adaptive retransmission method of underwater acoustic node based on distance measurement.

[0005] The specific technical scheme is as follows:

[0006] A self-adaptive retransmission method of underwater acoustic node based on distance measurement, comprising the following steps:

[0007] Step 1: the sending node transmits data to the target node and starts a timer;

[0008] Step 2: the target node receives data, processes and transmits to the sending node;

[0009] Step three: judging whether the sending node successfully receives the data transmitted by the target node, if the sending node does not receive or fails to completely correctly receive the data transmitted by the target node within the retransmission timeout, retransmission is performed according to the retransmission rule;

[0010] Step four: the sending node and the target node complete bidirectional communication, and each feature in the communication process is input and the other node information table stored in the sending node is updated;

[0011] The retransmission rule is: setting the maximum retransmission number upper limit L total , and different transmission rates R0, …, R n in ascending order from small to large; i = 0, …, n, L total and The relationship between them is:

[0012]

[0013] If the sending node fails to receive the data fed back by the target node, the sending node maintains the current rate R i , retransmits to the target node, but does not exceed the retransmission upper limit number of the current rate If the data fed back by the target node is still not received when the retransmission number upper limit L is reached, the transmission rate is reduced to R i-1 , and retransmission is continued; when the data fed back by the target node is correctly received after multiple retransmissions, or the maximum retransmission upper limit number L total is reached, transmission is stopped.

[0014] If the sending node can synchronize the data fed back by the target node, the content recorded in the other node information table stored in the sending node after the last successful transmission with the target node is compared with the current transmission, if there is no record of the last successful transmission, the default mode information is compared with the current transmission, and the calculated distance of the current transmission is taken as the parameter selection basis for the next retransmission.

[0015] If the sending node only obtains the signal-to-noise ratio of the target node without the distance information between the sending node and the target node, the optimal data frame length under the signal-to-noise ratio is selected for retransmission; if it still fails to completely correctly transmit, the speed is reduced for retransmission according to the case that the sending node fails to receive the data fed back by the target node, until the data is correctly received or the maximum retransmission upper limit number L total is reached, and transmission is stopped.

[0016] Further, the step one is specifically: when the sending node transmits data to the target node, the sending node retrieves the other node information table stored in the sending node, if the sending node has transmitted data to the target node, the characteristic information of the last communication with the target node is retrieved, the volume and modulation mode of the last successful transmission are selected for data transmission; if the sending node has not transmitted data to the target node, the data transmission is performed according to the artificial set node transmission mode; the sending node starts the internal timer when transmitting the first point of LFM, and performs ranging timing.

[0017] Further, the characteristic information includes: target node serial number, estimated distance between the target node and the current node, last transmission sound volume, sending node signal-to-noise ratio, target node signal-to-noise ratio.

[0018] Further, the step two is specifically: the target node starts the internal timer while receiving data, and takes the total processing time of the target node as the communication data, which is packaged into the ACK frame together with the signal-to-noise ratio of the target node, and after the total processing time arrives, the packaged ACK frame is transmitted to the sending node.

[0019] Further, in the step three, the adaptive threshold detection algorithm is used to judge whether the sending node receives the data feedback by the target node, and the specific operation is as follows:

[0020] (1) The node completes autocorrelation synchronization detection on the received LFM signal r(t) and the local LFM sequence, and the expression is:

[0021]

[0022] In the formula, L is the length of the LFM signal under a certain sampling rate, c(m) represents the discrete expression form of the LFM signal cached locally by the node; r(m) is the discrete expression form of r(t); the expression of the LFM signal cached locally by the node is as follows:

[0023]

[0024] In the formula, c(t) is the LFM signal cached locally by the node, which is a continuous signal, a(t) is the envelope of the linear frequency modulation pulse, f s is the starting frequency of the LFM signal; τ is the pulse width, i.e. the duration of the LFM signal; B is the frequency variation range; t is time;

[0025] The received LFM signal of the node is r(t), and the expression is:

[0026] r(t) = c(t) * h(t) + n(t)

[0027] Wherein, h(t) is the equivalent channel in the whole underwater acoustic signal transmission link, n(t) is Gaussian white noise;

[0028] (2) Normalizing the R r (z) after completing the autocorrelation synchronization detection, and the expression is as follows:

[0029]

[0030] Wherein, U(z) represents the energy of the autocorrelation synchronization detection of the LFM signal received by the node, R(z) is the average value of the total energy of the autocorrelation synchronization detection, and Q(z) is the ratio of U(z) and R(z);

[0031] (3) Comparing Q(z) with the synchronization threshold value set by the node, if Q(z) is greater than the set threshold value, it represents that the LFM signal is detected, and the data synchronization is completed.

[0032] Further, in the case that the retransmission rule sending node can synchronize to the data feedback of the target node, the measured distance this time is taken as the parameter selection basis for the next retransmission, specifically: when the measured distance this time is greater than the last time, and the signal-to-noise ratio of the target node this time is less than the last time, the sound volume is increased for data frame transmission; in other cases, the sound volume of the last time is maintained for transmission.

[0033] Further, the distance D u The calculation expression is as follows:

[0034]

[0035] Wherein, T total is the total time recorded by the sending node, and the timing starts from the data transmission of the sending node to the target node, and the timing is stopped immediately after the sending node synchronizes to the data of the target node; T reply is the total processing time of the receiving node, and T lfm is the time length of the LFM synchronization used by the sending node and the target node.

[0036] The beneficial effects of the present application are:

[0037] (1) The present application calculates the distance while communicating in the node, reduces the feedback redundancy, and improves the utilization efficiency of data.

[0038] (2) The present application takes the node characteristic information into the selection standard of the retransmission rule, and through the update iteration of the other node information table stored in the node in the multiple transmission process, the most suitable retransmission scheme is adaptively selected, the data transmission throughput between nodes is improved, and the adaptability of the node under different underwater acoustic channel conditions is improved. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 is a flow chart of the method of the present application.

[0040] Figure 2 is a flow chart of the retransmission rule of the present application.

[0041] Figure 3 is a curve chart of the relationship between the length of the data frame and the throughput under different signal-to-noise ratios.

[0042] Figure 4 is a result chart of the LFM autocorrelation synchronization detection in the embodiment of the present application.

[0043] Figure 5 is a schematic diagram of the asynchronous ranging principle between the sending node and the target node. DETAILED DESCRIPTION

[0044] The present application will be described in detail below with reference to the accompanying drawings and preferred embodiments, and the purposes and effects of the present application will become more apparent. The present application will be further described in detail below in combination with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0045] As shown in Figure 1 , the steps of the underwater acoustic node adaptive retransmission method based on distance measurement are as follows:

[0046] Step 1: The sending node transmits data to the target node and starts a timer.

[0047] When any node acts as a sending node and needs to transmit data to a target node, the other node information table stored in the sending node is retrieved.

[0048] Table 1: Other node information table stored in the sending node

[0049] Node number Calculated distance Sound volume (power consumption) SNR of sending node SNR of target node Modulation mode [N0] [do] [P0] Rec SNR0 ]] send SNR0 ]] Mod0 [N1] [D1] [P1] Rec SNR1 ]] send SNR1 ]] Mod1 …… …… …… …… …… …… <![CDATA[N self ]]> / / / / / …… …… …… …… …… …… <![CDATA[N i ]]> D i ]]> P i ]]> Rec SNRi ]] send SNRi ]] mod i ]]>

[0050] The rules for the sending node to transmit data to the target node are as follows:

[0051] (1) If the sending node has transmitted data to the target node, the characteristic information at the last communication with the target node is retrieved, and the volume and modulation mode of the last successful transmission are selected for data transmission. The characteristic information includes: target node serial number, measured distance between the target node and the current node, last transmission sound volume, sending node signal-to-noise ratio, and target node signal-to-noise ratio.

[0052] (2) If the sending node has not transmitted data to the target node, the node default transmission mode is used for data transmission, which is set by human.

[0053] The sending node encapsulates data, adjusts the sending volume according to the transmission rule, and starts an internal timer when sending the first point of LFM (Linear Frequency Modulation), to perform ranging timing.

[0054] Step two: The target node receives data, encapsulates ACK frames, and transmits them to the sending node.

[0055] After successfully synchronizing and demodulating the physical layer information of the sending node, the target node receives data while starting an internal timer, and the total processing time T of the target node is calculated. reply As communication data, the signal-to-noise ratio of the target node is encapsulated into ACK (Acknowledge character) frames, and the timing time T is calculated. reply After arrival, the encapsulated ACK frames are transmitted to the sending node.

[0056] Step three: Determine whether the sending node successfully receives the data transmitted by the target node.

[0057] If the sending node does not receive or cannot correctly receive the ACK frame information of the target node within the retransmission timeout time, retransmission is performed according to the retransmission rule. Here, the retransmission timeout time refers to the time value obtained by dividing the maximum communication distance of the underwater acoustic node by the sound speed, which can be adjusted according to actual needs. For example, as shown in the following table, the retransmission rule is as follows: Figure 2

[0058] Set the maximum retransmission limit L total and different transmission rates R0, …, R n (R0, …, R n are arranged in ascending order), and the corresponding retransmission limit and The relationship between them is:

[0059]

[0060] Case one: If the sending node cannot obtain the distance information D i of the target node and the signal-to-noise ratio of the target node , i.e., it cannot synchronize to the ACK frame feedback by the target node, the sending node maintains the current rate R i for retransmission to the target node, but does not exceed the retransmission limit number of the current rate If the retransmission limit number is reached , the current transmission rate is reduced to R i-1 ​And continue to retransmit according to the retransmission rule in case one above. When the data returned by the target node is correctly received after multiple retransmissions, or the maximum retransmission limit L is reached... total When the transmission stops, the transmission will cease.

[0061] Scenario 2: If the sending node can obtain the distance information D of the target node. i Signal-to-noise ratio with the target node If the system can synchronize with the ACK frame returned by the target node, confirming that the data is transmitted from the target node and obtaining the received signal-to-noise ratio (SNR) information, then it compares the transmission rate, voice volume, transmitted data frame length, calculated distance, and SNR of the previous successful transmission with the current transmission (if there is no record of the previous successful transmission, the default method is used for comparison). Based on the current calculated distance D... i Then select the parameters for the next retransmission to the target node. When the calculated distance D... i The signal-to-noise ratio of the target node is greater than the previous one, and the signal-to-noise ratio of the target node this time is greater. If the volume is less than the previous volume, the volume is increased for data frame transmission; otherwise, the previous volume is maintained for transmission.

[0062] Scenario 3: If the sending node only obtains the signal-to-noise ratio of the target node. And without distance information D i In this case, the optimal data frame length for that signal-to-noise ratio is selected for retransmission. For example... Figure 3 As shown in the figure, the optimal data frame length for transmission is selected within a certain signal-to-noise ratio range to maximize the data throughput between the sending and receiving nodes. It can be seen from the figure that within a signal-to-noise ratio range of 5.5 dB to 6.5 dB, the data throughput between nodes increases with the length of the transmitted data frame within a certain range. If transmission still fails to be completely correct, retransmission is performed at a reduced speed according to retransmission rule case one until it is correctly received or the maximum number of retransmissions L is reached. total Transmission stops when the target node sends data packets. Completely correct transmission here means that all data packets transmitted by the sending node are acknowledged by the ACK frame returned by the target node, thus completing the correct transmission of communication data from the sending node to the target node.

[0063] In the above retransmission rules, the detection process involves checking whether the sending node has obtained the distance information D of the target node. i Signal-to-noise ratio with the target node Before, need judge sending node whether detects target node's LFM signal, or target node whether detects sending node's LFM signal, through sending node or target node received LFM signal and local LFM sequence self correlation completes synchronization. Considering the multipath effect of underwater acoustic channel, if using fixed threshold decision method will not effectively detect direct path, or sending node and target node distance is far, make LFM amplitude too small and can not synchronize detection, if detect non direct path, then ranging error will greatly increase, therefore adopt adaptive threshold detection algorithm, for removing above-mentioned influence. The process of adaptive threshold detection algorithm is as follows:

[0064] (1) the expression of LFM signal cached locally by node is as follows:

[0065]

[0066] In the formula, c (t) is the LFM signal cached locally by node, and is continuous signal, a (t) is the envelope of linear frequency modulation pulse, f s is the starting frequency of LFM signal, τ is pulse width, which can be understood as the duration of LFM signal, and B is the frequency variation range.

[0067] The received LFM signal of node is denoted as r (t), and its expression is as follows:

[0068] r (t) = c (t) * h (t) + n (t)

[0069] In the formula, h (t) is the equivalent channel in the whole underwater acoustic signal transmission link, and n (t) is Gaussian white noise.

[0070] The received LFM signal r (t) of node is synchronized, that is, the received LFM signal r (t) and the local LFM sequence are self-correlated and synchronized for detection. In actual verification process, self-correlation synchronization detection is carried out in digital domain, and the expression is as follows:

[0071]

[0072] In the formula, L is the length of LFM signal under a certain sampling rate, c (m) represents the discrete expression form of LFM signal cached locally by node, and r (m) is the discrete expression form of r (t).

[0073] (2) in order to achieve the effect of adaptive threshold detection, the R r (z) after self-correlation synchronization detection is normalized, and its expression is as follows:

[0074]

[0075] In the formula, U(z) represents the energy of the LFM signal autocorrelation synchronization detection received by the node, R(z) is the average value of the total energy of the autocorrelation synchronization detection in this segment, and Q(z) is the ratio of U(z) to R(z).

[0076] (3) U(z) represents the energy of autocorrelation synchronization detection of the LFM signal received by the transmitting or receiving node, because LFM synchronization is required for all receptions, whether the transmitting node sends a data frame to the target node or the target node sends an ACK frame back to the transmitting node. Compare Q(z) with the synchronization threshold set by the node. If Q(z) is greater than the set threshold, it means that the LFM signal has been detected and synchronization is completed.

[0077] like Figure 4 The figure shows the LFM synchronization detection results in sea trial data from a certain sea area. The LFM signal parameters were set as follows: frequency sweep range of 13–18 kHz, duration of 200 ms, constant amplitude, and sampling rate of 96 kHz for both the transmitting and target nodes. As can be seen from the figure, the synchronization peak is still very significant even with the presence of multipath effects, indicating effective signal synchronization.

[0078] Step 4: After completing bidirectional communication with the target node, the sending node inputs the various characteristics of the communication process and updates the other node information table stored internally by the sending node, which serves as the basis for selecting the retransmission scheme.

[0079] like Figure 5 As shown, the sending node stops timing immediately after receiving the LFM signal of the ACK frame synchronized with the target node, thus obtaining the total duration T. total And obtain the current speed of sound V from the sound velocity meter. s The distance D between the sending node and the target node. i The expression is as follows:

[0080]

[0081] In the formula, T total T is the total duration of the record sent by the node. reply T represents the total processing time of the receiving node. lfm The duration for which the sending node and the target node use LFM for synchronization.

[0082] The method of this invention realizes the distance calculation between the sending node and the target node, and uses distance, signal-to-noise ratio, and sound volume as reference standards. With the goal of improving throughput, it reallocates the transmission rate, sound volume, and data frame length to achieve adaptive retransmission between the sending node and the target node, thereby improving the overall communication efficiency of the underwater acoustic communication system and enhancing the adaptability of the node under different channel conditions.

[0083] Those skilled in the art can understand that the above description is only the preferred examples of the present application and is not used to limit the present application, and although the present application is described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacements for part of the technical features. Any modification, equivalent replacement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An adaptive retransmission method for underwater acoustic nodes based on distance measurement, characterized in that, Includes the following steps: Step 1: The sending node transmits data to the target node and starts a timer; Step 2: The target node receives the data, processes it, and then transmits it to the sending node; Step 3: Determine whether the sending node has successfully received the data transmitted by the target node. If the sending node does not receive or fails to fully and correctly receive the data transmitted by the target node within the retransmission timeout period, then retransmit according to the retransmission rules. Step 4: The sending node and the target node complete bidirectional communication, inputting various characteristics during the communication process and updating the other node information table stored internally by the sending node; In step three, an adaptive threshold detection algorithm is used to determine whether the sending node has received the data fed back by the target node. The specific operation is as follows: (1) The node receives the LFM signal Autocorrelation synchronization detection with the local LFM sequence is performed, expressed as: ； In the formula, The length of the LFM signal at a certain sampling rate. The discrete representation of the LFM signal cached locally by the node; yes The discrete representation of the LFM signal; the expression for the LFM signal locally buffered by the node is as follows: ； In the formula, The LFM signal is cached locally on the node and is a continuous signal. It is the envelope of a linear frequency modulated pulse. It is the starting frequency of the LFM signal; B is the pulse width, i.e., the duration of the LFM signal; B is the frequency range; t is time. The LFM signal received by the node is Its expression is: ； In the formula, h(t) is the equivalent channel in the entire underwater acoustic signal transmission link, and n(t) is Gaussian white noise; (2) After completing the autocorrelation synchronization detection The normalization process is performed, and the expression is as follows: ； ； ； In the formula, This represents the energy detected by the autocorrelation synchronization of the LFM signal received by the node. This represents the average total energy of the autocorrelation synchronous detection in this segment; for and The ratio; (3) Compared with the synchronization threshold set by the node, if If the value is greater than the set threshold, it means that an LFM signal has been detected and data synchronization has been completed. The retransmission rule is as follows: a maximum limit is set for the number of retransmissions. And the different transmission rates R0, ..., R arranged in ascending order of size. n Below is the corresponding maximum number of retransmissions. , i=0,…,n, and The relationship between them is: ； If the sending node fails to receive data from the target node, the sending node maintains its current rate. Retransmit to the target node, but not exceeding the retransmission limit for the current rate. If the maximum number of retransmissions is reached... If no data is received from the target node by then, the transmission rate will be reduced to [a lower value]. And continue to retransmit; when the data returned by the target node can be correctly received after multiple retransmissions, or when the maximum number of retransmissions is reached. When the transmission stops, the transmission will cease. If the sending node can synchronize the data fed back by the target node, it compares the contents of the other node information table stored internally by the sending node after the last successful transmission with the target node with the current data. If there is no record of the last successful transmission, it compares the default mode information with the current data and uses the current measured distance as the basis for selecting parameters for the next retransmission. Specifically: if the current measured distance is greater than the previous one, and the current target node's signal-to-noise ratio is less than the previous one, the transmission volume is increased for data frame transmission; otherwise, the transmission volume of the previous one is maintained. If the sending node only obtains the signal-to-noise ratio (SNR) of the target node but lacks distance information between them, it selects the optimal data frame length at that SNR for retransmission. If the transmission still fails to be completely correct, it retransmits at a reduced speed as if the sending node had not received data from the target node, until the data is correctly received or the maximum number of retransmissions is reached. Transmission will stop at this time; The distance between the sending node and the target node The calculation expression is as follows: ； In the formula, The total duration recorded by the sending node starts timing from the time the data is transmitted from the sending node to the target node, and stops timing immediately after the sending node synchronizes the data with the target node. This represents the total processing time of the receiving node. The duration for which the sending node and the target node use LFM for synchronization.

2. The adaptive retransmission method for underwater acoustic nodes based on distance measurement according to claim 1, characterized in that, Step one specifically involves: when the sending node transmits data to the target node, it searches the other node information table stored internally. If the sending node has transmitted data with the target node before, it retrieves the feature information from the last communication with the target node and selects the volume and modulation method from the last successful transmission for data transmission. If the sending node has not transmitted data with the target node before, it transmits data according to the manually set node transmission method. The sending node starts its internal timer when transmitting the first point of LFM to perform ranging timing.

3. The adaptive retransmission method for underwater acoustic nodes based on distance measurement according to claim 2, characterized in that, The feature information includes: target node number, the calculated distance between the target node and the current node, the volume of the last transmitted sound, the signal-to-noise ratio of the sending node, and the signal-to-noise ratio of the target node.

4. The adaptive retransmission method for underwater acoustic nodes based on distance measurement according to claim 1, characterized in that, The second step is as follows: while receiving data, the target node starts its internal timer and uses the target node's total processing time as communication data. This data is then combined with the target node's signal-to-noise ratio and encapsulated in the ACK frame. After the total processing time is reached, the encapsulated ACK frame is transmitted to the sending node.

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