An underwater acoustic distributed cooperative parallel transmission method based on PD-NOMA

Abstract

The application provides a PD-NOMA-based underwater acoustic distributed cooperative parallel transmission method, which comprises the following steps: each node stores a full-network topology structure; a receiving end sends an RTR packet, and adjusts a reservation time until there is no interference if there is an interference risk; after the transmitting end receives the RTR packet, it is judged whether there is a signaling demand; if yes, it is judged whether there is an interference risk; if there is no interference, signaling is sent, if there is interference, the signaling time is adjusted or the transmitting end enters an avoidance state, and an SNT packet is sent; a paired communication pair sends a DATA data packet according to a specified time, and a non-paired non-interference communication pair sends local data; if not paired, the transmitting end enters an avoidance state; after the receiving end receives the DATA packet, the paired communication pair decodes according to a decoding order by using SIC, the non-paired communication pair directly decodes, valid signals are extracted, and an ACK reply packet is sent. The application has the advantages that the task demand and the underwater acoustic channel characteristics are fully combined, and efficient scheduling and parallel transmission of the communication pair are realized.

Description

Technical Field

[0001] This application belongs to the field of underwater acoustic communication networks and underwater acoustic MAC protocols, specifically relating to a distributed cooperative parallel transmission method for underwater acoustics based on PD-NOMA. Background Technology

[0002] In recent years, with the deepening of marine development, the demand for applications such as marine environmental monitoring, near-shore exploration, and disaster prevention has been increasing. Traditional single-node underwater acoustic communication equipment and point-to-point communication modes can no longer meet the diverse information exchange needs. These needs have spurred the construction of collaborative multi-user underwater acoustic communication networks to break down underwater information silos and achieve efficient information sharing.

[0003] However, the complexity and dynamics of underwater acoustic channels pose significant challenges to communication networks, especially in multi-user scenarios where efficient utilization and fair allocation of shared channels are crucial. Against this backdrop, the Medium Access Control (MAC) protocol, as a key technology for channel resource management and multi-user communication, plays a central coordinating role and is an important aspect of underwater acoustic communication network research.

[0004] Existing MAC protocols, primarily based on channel monitoring, reservation, and dynamic resource allocation, while mitigating communication conflicts to some extent, still suffer from limitations such as insufficient resource utilization and high transmission latency. Non-Orthogonal Multiple Access (NOMA), however, is gaining attention due to its potential to significantly improve spectrum utilization by multiplexing resources in the power or code domains. Nevertheless, current NOMA-based research largely focuses on central node control, lacking support for the flexibility and adaptability of dynamic underwater acoustic distributed networks. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of existing technologies, such as insufficient resource utilization and high transmission latency.

[0006] To achieve the above objectives, this application proposes a PD-NOMA-based underwater acoustic distributed cooperative parallel transmission method, comprising:

[0007] Step 1: Each node obtains the IDs and location information of surrounding nodes through broadcasting, stores the entire network topology, and constructs the transmit power matrix required for random pairing of nodes across the entire network;

[0008] Step 2: In each round of reservation, the receiving end dynamically generates an RTR packet carrying the ID, location information and transmission plan information of the communication pair according to the task requirements, and sends it without affecting the communication of other communication pairs. If there is a risk of interference, the reservation time is adjusted through a random backoff mechanism until there is no interference.

[0009] Step 3: After receiving the RTR packet destined for the local area, the transmitter first determines whether there is a transmission requirement. If so, it performs a receiver interference assessment based on the network status extracted from the previously monitored RTR packet. By analyzing the time overlap and power coverage of the channel occupancy, it determines whether there is an interference risk. If there is no interference, it transmits according to the original plan. If there is interference, it adjusts the transmission time or enters a backoff state through communication to ensure signal synchronization and achieve parallel transmission. At the same time, it sends an SNT signaling packet to inform the receiver of the pairing and decoding information.

[0010] Step 4: After the transmitter sends the SNT signaling packet, the paired communication pair sends DATA data packets at the specified time. The unpaired communication pair does not interfere with the transmission pair and sends DATA data packets directly. If pairing fails, the transmitter enters backoff mode until the end of this round of communication before entering Step 3 to try pairing again.

[0011] Step 5: After receiving the DATA packet, the receiving end decodes it according to the decoding order in the SNT signaling packet, extracts the valid signal, and sends an ACK reply packet without affecting other communication pairs that are currently occupying the channel.

[0012] As an improvement to the above method, the formula for constructing the transmit power matrix is:

[0013]

[0014] Where P(R) is the transmit power; SNR0 is the receive signal-to-noise ratio threshold; B 3dB (R) represents the 3dB bandwidth corresponding to the optimal frequency; N(f) represents the power spectral density of the ambient noise; A(R,f) represents the acoustic attenuation model; and R represents the transmission distance.

[0015] As an improvement to the above method, the method for determining the risk of interference is as follows:

[0016] There is a risk of interference when the following formula is not met:

[0017]

[0018] in, T represents the time when the RTR packet arrives at node number i; sendRTR Indicates the time when the receiving end initiates the RTR packet reservation; d i represents the distance from the receiving end to node i; c represents the data packet transmission speed; T represents the time when the receiver finishes receiving the RTR packet. control Indicates the transmission time of the RTR packet; This indicates the moment when node i receives a data packet from node j; d ji This represents the distance from node j to node i; This indicates the moment when node i begins to receive a data packet sent by node j to node i. ΔT represents the time when node j sends a data packet to node i and node i has finished receiving the data packet; ΔT is the protection time.

[0019] As an improvement to the above method, the adjustment of the reservation time through a random backoff mechanism includes:

[0020] Calculate the transmission time after random backoff: T sendRTR_1 =T sendRTR +T control ·rand, where the random number rand∈[0,1], is used to calculate whether there will be a collision when sending at this time. If there is still a collision, the sending time after backoff is recalculated until there is no more interference; during this process, the backoff waiting time t waiting (i) Updated to:

[0021] As an improvement to the above method, step 3 includes:

[0022] Assess whether a communication pair accessing the network will interfere with existing communication pairs in the network: The transmitting node determines whether the time periods of two communication pairs occupying the channel overlap by parsing the communication pairs currently communicating, the start time of channel occupation, and the power information used in the RTR packet, and determines whether the communication pair accessing later will cover the effective signal power of the communication pair accessing earlier.

[0023] If both time overlap and power coverage conditions are met, it is determined that the receiver is being interfered with. Taking into account time overlap, power difference, and number of pairs, the local transmission time is adjusted to ensure that the local signal and the signal of the paired communication pair arrive at the near-end receiver synchronously, thus achieving parallel transmission. Otherwise, it enters a backoff state until there is no interference.

[0024] If the time overlap or power coverage conditions are not met, the communication pair is considered to be interference-free and can send messages directly. Before sending messages, the transmitter will send an SNT signaling packet carrying pairing information and its local transmission time to inform the receiver of the pairing status and the decoding order.

[0025] As an improvement to the above method, the step of comprehensively considering time overlap, power difference, and pairing quantity to adjust the local transmission time, ensuring that the local signal and the signal of the paired communication pair arrive at the near-end receiver synchronously, and realizing parallel transmission, includes:

[0026] Check whether the communication meets the serial interference cancellation decoding conditions of the access network:

[0027]

[0028] Among them, Pi Ni represents the effective signal power of the i-th communication pair; N0 represents the noise power; Pi represents the effective signal power of the i-th communication pair. j The signal power of the interference signal from other communication pairs is represented by Q; the signal-to-noise ratio threshold at the receiver is represented by k; and the number of communication pairs is represented by k.

[0029] If the serial interference cancellation decoding condition is met, then continue to determine whether the number of paired pairs is less than the set maximum number of parallel pairs; otherwise, enter the backoff state until there is no interference.

[0030] If the number of paired pairs is less than the maximum number of parallel pairs set, the pairing is successful. The transmission time of the local communication pair is adjusted so that the local signal and the signal of the paired communication pair can arrive at the near-end receiver of the pairing group at the same time. An SNT packet carrying pairing information and the adjusted transmission time is sent to the successfully matched communication pair. Otherwise, the pairing enters a backoff state until there is no interference.

[0031] As an improvement to the above method, it also includes:

[0032] Each node periodically clears the channel and dynamically updates node information via broadcast, re-stores the entire network topology, and constructs the transmit power matrix required for random pairing of all network nodes, ensuring that communication pairs can adjust resource allocation in a timely manner according to changes in network load.

[0033] Compared with existing technologies, the advantages of this application are:

[0034] 1. This invention provides an underwater acoustic distributed cooperative parallel transmission MAC protocol UPNC-MAC that combines PD-NOMA and collision prediction mechanism. It realizes dynamic perception and resource scheduling of channel busy status in distributed underwater acoustic communication networks, thereby improving the adaptability and flexibility of the network.

[0035] 2. By combining dynamic interference assessment at the receiver with a communication pair pairing mechanism, the UPNC-MAC protocol ensures that multiple communication pairs can achieve efficient parallel transmission under interference-free conditions, effectively improving channel time utilization and system throughput.

[0036] 3. The protocol is designed with a signaling-based reservation and scheduling mechanism, which reduces the backoff time and control packet overhead caused by channel contention, thereby significantly reducing end-to-end latency and optimizing network performance.

[0037] 4. By combining serial interference cancellation (SIC) technology to effectively eliminate interference to the signal, interference-free transmission of multiple communication pairs is achieved in a dynamically changing underwater acoustic network, enhancing the system's adaptability to complex channel conditions and the needs of multi-user concurrent communication.

[0038] 5. The protocol incorporates dynamic reservation and power allocation strategies, which adjust the pairing conditions of communication pairs in real time according to task requirements, thus meeting the communication efficiency needs of different task scenarios. Attached Figure Description

[0039] Figure 1 The diagram shows the information transmission flow of the underwater acoustic distributed collaborative parallel transmission method that combines PD-NOMA and collision prediction mechanism.

[0040] Figure 2 The diagram shows the structure of an underwater acoustic distributed communication network.

[0041] Figure 3 The diagram shown is a timing diagram of the protocol.

[0042] Figure 4 The diagram shows the frame structure of the RTR protocol.

[0043] Figure 5 The diagram shown is a flowchart of the RTR (Reservation Time Adjustment) mechanism.

[0044] Figure 6 The diagram shown is a flowchart of the receiver interference assessment process.

[0045] Figure 7 The flowchart shown is for the pairing algorithm.

[0046] Figure 8 The diagram shows a simulation comparison of the normalized throughput of the transmission method proposed in this invention with the Slotted FAMA protocol and the RIPT protocol under different numbers of nodes.

[0047] Figure 9 The diagram shows the simulation results comparing the end-to-end delay of the transmission method proposed in this invention with the Slotted FAMA protocol and the RIPT protocol under different numbers of nodes.

[0048] Figure 10 The diagram shows the simulation results comparing the protocol overhead of the proposed transmission method with the Slotted FAMA and RIPT protocols under different numbers of nodes. Detailed Implementation

[0049] The technical solution of this application will be described in detail below with reference to the accompanying drawings.

[0050] This invention proposes a distributed, cooperative, parallel transmission method for underwater acoustics that combines PD-NOMA (Power Domain NOMA) with a collision prediction mechanism. Through dynamic resource allocation and channel state awareness, and by fully integrating task requirements with the characteristics of the underwater acoustic channel, it achieves efficient scheduling and parallel transmission of communication pairs. This invention can optimize network performance indicators, such as significantly increasing throughput, reducing end-to-end latency, and improving channel resource utilization. Furthermore, this transmission method, through a combination of prediction and scheduling, dynamically adapts to complex and changing underwater acoustic environments, making it suitable for various network scenarios.

[0051] like Figure 1 As shown, the underwater acoustic distributed cooperative parallel transmission method combining PD-NOMA and collision prediction mechanism provided in this application includes:

[0052] 1. Network initialization and maintenance:

[0053] 1.1 During the network initialization phase, each node obtains the identity and location information of surrounding nodes through broadcasting to establish the initial topology. The broadcasted information includes: node ID and location information, which are used for resource allocation in subsequent communication pairs.

[0054] 1.2 Based on the overall network topology and the received signal-to-noise ratio (SNR), construct the transmit power matrix required for random pairing of all network nodes according to the following formula, providing a basis for subsequent channel resource allocation.

[0055]

[0056] Where SNR0 is the received signal-to-noise ratio threshold, B 3dB (R) represents the 3dB bandwidth corresponding to the optimal frequency f0, N(f) represents the power spectral density of the ambient noise, A(R,f) represents the acoustic attenuation model, and R represents the transmission distance.

[0057] 1.3 During network maintenance, by periodically clearing channels and rebroadcasting management packets, node information is dynamically updated, and topology status is adjusted to ensure that communication pairs can adjust resource allocation in a timely manner according to changes in network load.

[0058] 2. The receiving end initiates a Transmission Request (RTR) reservation:

[0059] 2.1 In each round of reservation, the communication pair dynamically generates RTR packets according to the task requirements, broadcasts the communication pair's ID, location information, and transmission plan, and each node listens to and parses the RTR packets to obtain the communication pair's ID, location information, reservation initiation time, and the length of the transmitted DATA data packet.

[0060] 2.2 Ensure that the RTR reservation process does not affect other nodes' listening to the signaling or data packets being transmitted; if there is a risk of interference, trigger a random backoff mechanism to adjust the reservation time until no more interference occurs.

[0061] 3. Interference Assessment and Pairing Decision (SNT): The transmitter assesses the interference of the receiver by combining the network status extracted from the previous RTR packets. By analyzing the time overlap and power coverage of the channel occupancy, it determines whether there is an interference risk. If there is no interference, the transmitter transmits according to the original plan. If there is interference, the transmitter adjusts the transmission time of the pairing algorithm through communication or enters a backoff state to ensure signal synchronization and parallel transmission. At the same time, an SNT signaling packet is sent to inform the transmitter of the pairing and decoding information.

[0062] Upon receiving an RTR packet destined for the local network, the transmitter first determines whether there is a transmission requirement. If so, it performs a receiver interference assessment based on previously monitored network conditions, and selects an appropriate transmission strategy based on the assessment results and the communication pairing algorithm.

[0063] 3.1 Schematic diagram of receiver interference assessment as follows Figure 3 As shown. In this process, the transmitting node calculates and determines whether the time periods of the communication pairs occupying the channel overlap, the received power ratio of different communication pairs, and whether the communication pairs that are communicating in the RTR packet, the start time of the channel occupation, and the power used by parsing information such as the communication pairs that are communicating, the start time of the channel occupation, and the power used by the communication pairs. It also determines whether the communication pairs that are accessed later will cover the effective signal power of the communication pairs that are accessed earlier, resulting in decoding failure.

[0064] 3.2 Communication Pair Pairing Algorithm Figure 7 As shown in the diagram. For communication pairs with interference risks as described in 3.1, it is necessary to monitor the network status and assess the dynamic interference at the receiving end in real time. Taking into account time overlap, power differences, and the number of pairs, the transmission time of the communication pairs should be adjusted: if there is no interference, DATA should be sent directly according to the original planned time; if there is interference, the pairing conditions should be further checked. If they are met, the local transmission time should be adjusted to ensure that the local signal and the signal of the paired communication pair arrive at the near-end receiver synchronously, achieving parallel transmission; otherwise, a backoff state should be entered until there is no interference. After successful pairing, the transmitter will send an SNT signaling packet carrying pairing information and its local transmission time before transmission, informing the interfering receiver of the pairing status and the order of SIC decoding.

[0065] 4. Sending DATA: After sending the SNT packet, paired communication pairs send DATA data packets at specified intervals. Unpaired pairs do not interfere with each other and directly send local data. If pairing fails, the local transmitter enters a backoff phase until the current round of communication ends, then re-enters the SNT phase to attempt pairing again. Through the above transmission strategy, the UPNC-MAC protocol effectively reduces the risk of collisions during transmission while ensuring transmission efficiency.

[0066] 5. Receiver replies with ACK: After receiving the DATA packet, the receiver decodes it using SIC according to the decoding order in the SNT packet, extracts the valid signal, and then sends an ACK reply packet without affecting other communication pairs that are currently occupying the channel, so as to ensure the integrity of data transmission and synchronize the transmission status, and prepare for the next round of communication.

[0067] The model used in this embodiment is as follows: Figure 2 As shown in Table 1, this network model does not rely on a central node for channel resource allocation and scheduling. Each node possesses the ability to perceive network status and make autonomous decisions, enabling dynamic, collision-free network access. It is assumed that each node is randomly distributed in a three-dimensional underwater network, covering a water area of ​​3000m × 3000m × 300m. Each node dynamically acts as a transmitter or receiver based on task requirements, interacting with other nodes. Simulation parameter settings are shown in Table 1.

[0068] Table 1 Simulation parameter settings

[0069]

[0070] Network initialization and maintenance: During the network initialization phase, each node broadcasts a management packet carrying its local location and identity information to ensure that all nodes can store the identity and location information of all nodes in the network. Subsequently, based on the total network node locations and reception thresholds, a transmit power matrix required for random pairing of all network nodes is constructed.

[0071] During network maintenance, the system dynamically updates node information across the entire network by periodically clearing channels and rebroadcasting management packets. After initialization, each node can reserve channels and begin communication for data transmission. The data transmission stages are as follows: Figure 3 As shown.

[0072] RTR Reservation: The receiving end of the communication pair dynamically generates RTR packets according to task requirements before communication, with the frame structure as follows: Figure 4 As shown. Before initiating an RTR reservation, ensure that it does not affect other nodes listening to ongoing RTR, SNT, DATA, and ACK packets. If there is any impact, trigger a random backoff mechanism to adjust the reservation without causing interference. The specific adjustment process is as follows. Figure 5 As shown.

[0073] Assume the reservation time for the local receiver to initiate the RTR control packet is T. sendRTR The time when the node with number i is reached is: The moment of acceptance is Where, d i T represents the distance from the local receiver to node i. control To control packet transmission time.

[0074] Previously monitored packets such as RTR, SNT, DATA, and ACK from other nodes all contained the pairing status of the corresponding communication pairs and the data transmission schedule. Assume we know that node i receives a data packet from node j at the following time: The moment of acceptance is in, This indicates the moment when node i begins receiving a data packet sent by node j to node i.

[0075] To avoid conflicts, it is necessary to satisfy the following conditions. Right now Otherwise, a random backoff mechanism will be triggered. Calculate the transmission time after random backoff: T sendRTR_1 =T sendRTR +T control ·rand, where the random number rand∈[0,1], is used to calculate whether there will be a collision when transmitting at this time. If there is still a collision, the transmission time after backoff is recalculated until there is no more interference. During this process, the backoff waiting time t waiting (i) Updated to:

[0076] It is important to note that each communication pair can only be in one state at a time. For example, a communication pair that has already entered the sending state will not initiate a new RTR reservation to avoid state conflicts. This mechanism reduces the probability of the local receiver initiating a reservation and interfering with other nodes' listening, thereby ensuring subsequent data transmission.

[0077] Interference Assessment and Pairing Decision (SNT): Upon receiving an RTR packet destined for the local network, the transmitter first determines whether there is a transmission requirement. If so, it performs an interference assessment at the receiver based on previously monitored network conditions. Using the assessment results and the communication pairing algorithm, an appropriate transmission strategy is selected.

[0078] The receiver interference assessment process in this embodiment is as follows: Figure 6 As shown. When a channel is occupied by two or more communication pairs simultaneously, whether collision interference will occur depends on two conditions: communication time overlap; and the receiver's local valid signal being overshadowed by the interference signal power of other communication pairs. If both the time overlap and power overshadowing conditions are met, the receiver will experience non-negligible interference. The following is a detailed explanation of the principle.

[0079] The communication pairs reserved in this round are #ID1→#ID2 (near end) and #ID3→#ID4 (far end). Receivers #ID2 and #ID4 initiate channel reservations with transmitters #ID1 and #ID3 respectively, and all nodes in the network receive the corresponding information. During this process, transmitters #ID1 and #ID3 are aware of the following information:

[0080] 1) Communication pairs are formed: #ID1→#ID2, #ID3→#ID4;

[0081] 2) Time of reservation for each communication pair's channel: T sendRTR2 T sendRTR4 ;

[0082] 3) Length of data packet to be sent: T data1 T data3 ;

[0083] 4) Node distance matrix: Where d ij This represents the distance between nodes #IDi and #IDj;

[0084] 5) Transmission power: #ID1 transmission power P1, #ID4 transmission power P2.

[0085] Based on the above information, the first step is to determine whether the time periods during which the two communication pairs occupy the channel overlap:

[0086] max(T recvdata,12 ,T recvdata,34 )<min(T recvdata,12 +T data1 ,T recvdata,32 +T data3 )+ΔT

[0087] Where ΔT is the protection time. For #ID2, the start time for receiving a valid signal. This represents the start time of receiving the interference signal #ID4. If the above formula is satisfied, it indicates that the reception time of the interference signal overlaps with that of the local valid signal at the receiving end of the near-end communication pair. Based on this, each communication pair can parse other RTR packets to determine the arrival time period of the interference signal.

[0088] Secondly, power coverage refers to the situation where the power of the interfering signal at the receiving end is greater than the power of the effective signal. If the strength of the interfering signal is lower than that of the effective signal, even if there is time overlap, the effective signal can still be resolved as long as the signal-to-noise ratio meets the receiving threshold. To simplify the calculation, the communication ranges of each transmitting node can be compared to see if they overlap. Here, the communication range refers to the maximum distance at which the transmitted signal attenuates to the receiving threshold.

[0089] The pairing algorithm flow in this embodiment is as follows: Figure 7 As shown. This algorithm, based on monitoring network status and dynamic interference assessment at the receiver, comprehensively considers factors such as time overlap, power differences, and the number of pairs to achieve reasonable scheduling and resource utilization of local communication pairs. The specific steps are as follows:

[0090] Step S1: Input communication pair information;

[0091] ■Execution content: The system first inputs a list of paired communication pairs and scheduled communication pairs, and sets the upper limit value "M" for the number of pairs.

[0092] ■ Purpose: To ensure that the algorithm has complete input conditions during runtime, while avoiding network resource overload.

[0093] ■ Paired Communication Pairs: Communication pairs that have been successfully paired in the current network.

[0094] ■ Scheduled Communication Pairs: Communication pairs that are planned to be paired in this round.

[0095] ■M: The maximum allowed number of parallel communication pairs, which is a hard constraint on system capability.

[0096] Step S2: Monitor network communication status;

[0097] ■Execution content: The system monitors the communication status of the current network in real time, including existing communication pairs, interference signals, transmission power levels, etc.

[0098] ■ Purpose: To determine whether the current network environment is suitable for the access of new communication pairs, and to avoid communication failures due to network load or interference issues.

[0099] Step S3: Set the maximum number of parallel communication pairs;

[0100] ■Execution content: The system sets the maximum number of parallel communication pairs to 3, i.e., "M=3".

[0101] ■Purpose: This parameter is used to limit the number of communication pairs allowed at the same time to ensure that system resources are not overloaded.

[0102] Step S4: Traverse the communication pair list;

[0103] ■Execution content: According to the input list of communication pairs, extract the communication pair "Ci" in sequence and check it.

[0104] ■ Variable Explanation: Ci represents the currently paired or reserved communication pair.

[0105] Step S5: Check the interference of local communication on the receivers of all Ci in the network after access, i.e., whether...

[0106] There is time overlap and power coverage;

[0107] ■ Yes (Interference exists): Proceed to step S6 to further evaluate whether the interference elimination conditions are met.

[0108] ■No (No Interference): Proceed directly to the DATA phase and send DATA data packets according to the original schedule.

[0109] Step S6: SIC decoding condition check;

[0110] ■Execution content: Check whether the SIC (Successive Interference Cancellation) decoding conditions are met at the communication pair "Ci":

[0111]

[0112] Among them, P i P is the effective signal power of the i-th communication pair, N0 is the noise power, and P is the signal power of the i-th communication pair. j Let Q be the interference signal power of other communication pairs, Q be the signal-to-noise ratio threshold at the receiver, and k be the number of communication pairs. This power difference is key to SIC's ability to accurately eliminate interference and reconstruct a valid signal.

[0113] ■ Yes (condition met): Continue to step S7.

[0114] ■ No (condition not met): Marked as "needs to be avoided", enters the retreat process and waits for the next matching opportunity.

[0115] Step S7: Verify the pairing limit;

[0116] ■Execution content: The system checks whether the number of paired pairs in the communication pair list is less than the maximum number of parallel pairs "M".

[0117] ■ Yes (less than M): Proceed to step 8 and adjust the sending time.

[0118] ■ No (greater than or equal to M): Marked as "needs to be avoided", exit the configuration process of the current communication pair.

[0119] Step S8: Adjust the local sending time;

[0120] ■Execution content: Adjust the transmission time of the local communication pair so that its local signal can arrive at the near-end receiver of the pairing group simultaneously with the signal of the paired communication pair.

[0121] ■ Adjustment strategy: Calculate the adjustment range of transmission time based on the dynamic feedback from the receiver; ensure the timing consistency of signals arriving at the near-end receiver from different communication pairs through a synchronization mechanism.

[0122] Step S9: Output the pairing results;

[0123] ■Execution content: The system outputs the results of this round of pairing and sends pairing information and adjusted sending time to the successfully matched communication pairs.

[0124] ■Output content:

[0125] Pairing results: include the paired communication pairs, the identifiers of the transmitter and receiver.

[0126] Pairing signaling (SNT packet): Informs the receiver of the successful pairing status, the SIC decoding order, and the locally adjusted transmission time.

[0127] ■ Function: To ensure that all parties involved in the pairing process can correctly understand and execute the pairing scheme.

[0128] Step S10: End;

[0129] ■Execution content: After all communication pairs have been processed, the system exits the pairing process and enters the DATA preparation state.

[0130] ■Note: Communication pairs that fail to pair will continue to try in the next pairing round.

[0131] Sending DATA: After sending the SNT packet, paired communication pairs send DATA data packets at specified times. Unpaired, non-interfering communication pairs directly send local data. If pairing fails, the local transmitter enters a backoff state until the end of the current communication round, at which point it re-attempts pairing again during interference assessment and pairing decision (SNT). Through this transmission strategy, the UPNC-MAC protocol effectively reduces the risk of collisions during transmission while ensuring transmission efficiency.

[0132] After receiving the DATA packet, the receiving end extracts the valid signal according to the decoding order of the SNT packet, and sends an ACK reply packet without affecting other communication pairs that are currently occupying the channel, so as to ensure the integrity of data transmission and synchronize the transmission status, and prepare for the next round of communication.

[0133] Figure 8 This is a schematic diagram showing the simulation comparison results of the normalized throughput of the transmission method proposed in this invention with the SlottedFAMA protocol and the RIPT protocol under different numbers of nodes in the embodiment. The simulation results show that the normalized throughput of the transmission method provided in this invention is significantly better than the other two protocols.

[0134] Figure 9 This is a schematic diagram showing the simulation comparison results of the end-to-end delay of the transmission method proposed in this invention with the SlottedFAMA protocol and the RIPT protocol under different numbers of nodes in the embodiment. The simulation results show that the end-to-end delay of the transmission method provided in this invention is significantly better than the other two protocols under low load and medium packet length conditions.

[0135] Figure 10This is a schematic diagram showing the simulation comparison results of the overhead of the transmission method proposed in this invention with the SlottedFAMA protocol and the RIPT protocol under different numbers of nodes in the embodiment. The simulation results show that the overhead of the transmission method provided by this invention is between the two protocols.

[0136] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application do not depart from the spirit and scope of the technical solutions of this application, and should all be covered within the scope of the claims of this application.

Claims

1. A method for underwater acoustic distributed cooperative parallel transmission based on PD-NOMA, comprising: Step 1: Each node acquires the ID and position information of surrounding nodes through broadcasting, stores the topology of the whole network, and constructs the transmission power matrix required for random pairing of nodes in the whole network; Step 2: In each round of reservation, the receiving end dynamically generates RTR packets carrying the ID, position information and transmission plan information of the communication pair according to the task demand, and sends them without affecting the communication of other communication pairs, and adjusts the reservation time through a random backoff mechanism until there is no interference; Step 3: After the transmitting end receives the RTR packet for the local, it first judges whether there is a signaling demand; if there is, it combines the network state extracted from the previously listened RTR packet to evaluate the interference of the receiving end, judges whether there is an interference risk by analyzing the time overlap and power coverage of channel occupation, and if there is no interference, it sends signals according to the original plan, and if there is interference, it adjusts the signaling time through the communication pair pairing algorithm or enters the backoff state to ensure signal synchronization and realize parallel transmission, and sends SNT signaling packets to inform the receiving end of the pairing and decoding information; Step 4: After the transmitting end sends the SNT signaling packet, the paired communication pair sends the DATA packet at the specified time, and the non-paired non-interfering communication pair directly sends the DATA packet; if it is not successfully paired, the transmitting end enters the backoff state until the end of this round of communication to reattempt pairing in Step 3; Step 5: After the receiving end receives the DATA packet, it decodes according to the decoding order in the SNT signaling packet, extracts the valid signal, and sends the ACK reply packet without affecting other communication pairs that are occupying the channel.

2. The PD-NOMA based underwater acoustic distributed cooperative parallel transmission method according to claim 1, characterized in that, The formula for constructing the transmission power matrix is: ； wherein, is the transmit power; is the receive signal-to-noise ratio threshold; is the 3 dB bandwidth corresponding to the optimal frequency; is the power spectral density of the ambient noise; is the acoustic attenuation model; is the transmission distance; and f is the communication frequency. 3.The PD-NOMA based underwater acoustic distributed cooperative parallel transmission method according to claim 1, characterized in that, Step 3 includes: Evaluating whether the communication pair accessing the network will interfere with the communication pair already in the network: the transmitting end node judges whether the time period of the two communication pairs occupying the channel overlaps by analyzing the communication pairs in the RTR packet, the start time of the occupied channel and the use power information, and judges whether the communication pair accessing later will interfere with the effective signal power coverage of the communication pair accessing earlier; If both the time overlap and power coverage conditions are met, it is judged that the receiving end is interfered; considering the time overlap, power difference and pairing number, the transmission time of the local communication pair is adjusted to ensure that the local signal and the signal of the paired communication pair arrive at the receiving end of the interfered communication pair simultaneously, realizing parallel transmission; otherwise, it enters the backoff state until there is no interference; If the time overlap or power coverage condition is not met, it is considered as a non-interfering communication pair, which can directly send signals, and the transmitting end sends the SNT signaling packet carrying the pairing information and the transmission time of its local communication pair before signaling to inform the receiving end of the pairing situation and the decoding order.

4. The PD-NOMA based underwater acoustic distributed cooperative parallel transmission method according to claim 3, characterized in that, The adjustment of the transmission time of the local communication pair to ensure that the local signal and the signal of the paired communication pair arrive at the receiving end of the interfered communication pair simultaneously, realizing parallel transmission, includes: Checking whether the communication pair accessing the network meets the serial interference cancellation decoding condition: ； wherein, denotes the the effective signal power of a communication pair; denotes the noise power; denotes the interference signal power of other communication pairs; denotes the signal-to-noise ratio threshold of the receiving end; k denotes the number of communication pairs; If the serial interference cancellation decoding condition is met, it is judged whether the paired number is less than the set maximum parallel pairing number; otherwise, it enters the backoff state until there is no interference; If the paired number is less than the set maximum parallel pairing number, the pairing is successful, the transmission time of the local communication pair is adjusted, the local signal and the signal of the paired communication pair can reach the receiving end of the interfered communication pair of the pairing group at the same time, and the SNT signaling packet carrying the pairing information and the adjusted transmission time of the local communication pair is sent to the successfully matched communication pair; otherwise, it enters the backoff state until there is no interference. 5.The PD-NOMA based underwater acoustic distributed cooperative parallel transmission method according to claim 1, wherein, Also includes: Each node periodically clears the channel and dynamically updates the node information through broadcasting, re-stores the network topology, constructs the transmission power matrix required for random pairing of all network nodes, and ensures that the communication pair can adjust the resource allocation in time according to the change of network load.

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