LU501337A1

LU501337A1 - Underwater Broadcast Transmission Method Based on Hierarchy and State

Info

Publication number: LU501337A1
Application number: LU501337A
Authority: LU
Inventors: Xiujuan Du; Xiaojing Tian; Duoliang Han
Original assignee: Univ Qinghai Normal
Priority date: 2021-03-12
Filing date: 2022-01-27
Publication date: 2022-09-12
Also published as: LU501337B1; CN113099392A; CN113099392B

Abstract

The present invention relates to the technical field of underwater broadcast, in particular to an underwater broadcast transmission method based on hierarchy and state, which comprises the following steps: 1) enabling a node to send data; 2) judging whether all neighbor nodes are not in a ''receiving state''; 3) judging whether an upper-layer neighbor node has an ''unknown'' state or a ''sending avoidance'' state; 4) broadcasting the first frame of data; 5) receiving a first frame ACK; 6) broadcasting the remaining N-1 frames, and starting a timeout timer; 7) receiving the last frame ACK during the timing period; 8) judging whether the data frame in a packet chain is completely received; 9) enabling the sending node to broadcast an 'end-of- transmission' control frame; 10) enabling the neighbor node to broadcast an ''end-of-reception'' control frame. According to the method, a traditional RTS/CTS handshake mechanism can be avoided to a great extent, thus improving the channel utilization rate and the network throughput and reducing unnecessary time consumption and energy consumption.

Description

BL-5386 ' LU501337 Underwater Broadcast Transmission Method Based on Hierarchy and State Technical field The present invention relates to the technical field of underwater broadcast, in particular to an underwater broadcast transmission method based on hierarchy and state. Background technique The bit error rate of the underwater acoustic channel is high, generally in the range of 107-107; the propagation delay of underwater acoustic communication is long, and the delay is close to the second level; the bandwidth is narrow, generally on the order of tens of kbps; compared with traditional modems, acoustic modems consume more energy, and underwater nodes are generally powered by batteries, and it 1s difficult to charge and replace the batteries; underwater nodes move with the movement of water currents or other underwater activities, and energy exhaustion or hardware failure easily leads to node failure, so the underwater sensor network topology changes dynamically; the distance difference between nodes and the long propagation delay bring time and space characteristics to UWSNSs, and these characteristics bring great challenges to the MAC protocol design of UWSNs.

In the hierarchical network protocol design model, each layer of the protocol provides the lower layer transmission service function for its upper layer protocol, and the MAC protocol of the underwater sensor network provides channel access control for the routing and forwarding of packets, that is, coordinating multiple nodes to use the underwater acoustic shared channel resources with limited bandwidth fairly and efficiently. In the underwater sensor network, data packets are always transmitted in the direction from the underwater sensor node to the surface Sink node. UWSNs packet routing 1s divided into two types: unicast routing and broadcast routing. When using unicast routing, the data packet is always selected by the previous hop node (or source node) to determine a single next hop node during transmission, and the data message

BL-5386 LU501337 is routed and forwarded to the selected next hop node, that is, only use the best route for data transmission.

As these unicast routes generally require a conflict-avoided underwater acoustic network MAC mechanism to provide channel access control services for them, scholars at home and abroad have proposed a variety of conflict- avoided unicast MAC protocols for UWSNs.

However, in the broadcast routing protocol, the receiving node needs to determine whether it performs routing and forwarding for the received message.

Therefore, when the broadcast routing is used, the message is redundantly forwarded along multiple paths during the transmission process.

Broadcast routing also needs the MAC mechanism of the underwater acoustic network to avoid conflicts to provide channel access control services for it.

However, when broadcast routing is used, the sending node does not clearly give the next hop routing node, so that those conflict-avoided underwater MAC protocols suitable for unicast routing (such as the MAC mechanism based on RTS/CTS handshake) cannot be applied to broadcast routing transmission, and underwater broadcast routing transmission can only choose to use random access MAC mechanisms (such as ALOHA and time slot ALOHA protocols). In the MAC protocol based on random access, the sending node sends data packets without any channel coordination process, which is suitable for networks with a small amount of relatively sporadic traffic load, but as the traffic load increases, the random access MAC protocol is easy to generate packets, which will cause low-bandwidth, long-delay UWSNs to produce a large number of collisions and retransmissions when the traffic load is large, thereby reducing channel utilization and energy efficiency.

Summary of the invention The present invention provides an underwater broadcast transmission method based on hierarchy and state, which can overcome certain or some defects of the prior art.

The underwater broadcast transmission method based on hierarchy and state according to the present invention includes the following steps:

BL-5386 ’ LU501337 1) enabling the node to send data; 2) Judging whether all neighbor nodes are not in the "receiving state"; if yes, proceed to the next step; if not, back off and re-judge the state of neighbor nodes; 3) Judging whether the upper-level neighbor node has an "unknown" or state or a "sending avoidance" state; if yes, proceed to the next step; if not, back off and re-judge the state of the neighbor node; 4) broadcasting the first frame of data; 5) receiving the first frame ACK; 6) broadcasting the remaining N-1 frames, and starting the timeout timer; 7) receiving the last frame ACK during the timing period; 8) judging whether the data frame in the packet chain is completely received; if yes, proceed to the next step; if not, retransmit the lost data frames; 9) enabling the sending node to broadcast an "end-of-transmission" control frame; 10) enabling the neighbor node to broadcast an "end-of-reception" control frame.

Preferably, a packet chain is composed of N data frames, and the numbers of the N data frames are sorted from largest to smallest, called the frame sequence number; the sequence number of the first frame 1s N, the sequence number of the second frame is N-1, ..., and the sequence number of the last frame is 1. Preferably, when the packet chain is transmitted in the channel, the first frame in the packet chain is first broadcast and sent; after each neighbor node receives the first frame, an ACK carrying the sequence number of the first frame is immediately returned to the sending node; after receiving the ACK from any upper-layer neighbor node, the sending node broadcasts the remaining N-1 frames in the packet chain successively, and after each upper layer receives the last frame in the packet chain, the neighbor node will immediately reply to the sending node with an ACK carrying the sequence number of the correctly received frame in the packet chain; the sending node judges whether the data frame in the packet chain has been completely received according to the frame sequence number, and the unsuccessfully received data frame 1s retransmitted to form a sub-packet chain and then forwarded again until the transmission is successful or fails

BL-5386 LU501337 because the number of retransmissions exceeds the limit.

Preferably, when hearing the first frame in the packet chain, every node that is heard needs to immediately reply an ACK frame to the sending node; when the sending node successfully transmits all data frames in a packet chain, that is, the sending node receives an ACK from its upper neighbor, confirming that all frames in the packet chain have been successfully received, the sending node sends a control frame with a frame type field of "10" to indicate the end of transmission and enters the transmission avoidance phase; each neighbor node that receives the control frame sends a control frame with a frame type field of "11" to indicate the end of the reception.

Preferably, the node can learn the real-time state of its neighbor nodes through listening; when a data frame with a frame type field of "00" is heard and the frame sequence number is greater than 1, the state of the neighbor node that has sent the data frame 1s "transmission"; when an ACK frame with a frame type field of "01" is heard and the confirmed frame sequence number is greater than 1, the state of the node that has sent the ACK is "reception"; when a control frame with a frame type field of "10" is heard, the state of the sending node of this frame is "sending avoidance"; when a control frame with a frame type field of "11" is heard, the state of the sending node of this frame 1s "transition from receiving to unknown".

Preferably, the LSPB-MAC protocol is used to send the packet chain; after the node sends a frame with the largest or smallest sequence number in the packet chain, the sending node starts the timeout timer, waits to receive the corresponding ACK frame before the timer expires, and judges whether a data frame is lost during the transmission process according to the received ACK.

Preferably, in the LSPB-MAC protocol, it is assumed that all nodes have the same communication range as R, and the speed of acoustic signal propagation in water is V; therefore, the maximum data propagation delay can be calculated as T= ; the maximum time required for the complete transmission process of a data frame by a node is assumed to be a transmission cycle, including the data frame transmission until the ACK confirmation from the receiving node is received; the time required for the

BL-5386 )

LU501337 sending node to broadcast the data frame includes the transmission delay 7, and propagation delay 7, of the data frame; the time required for the receiving node to reply to the ACK frame includes the transmission delay 7, and propagation delay Trop-scx Of the ACK; suppose that node S is the sending node, and node R is the upper neighbor node of the sending node; node S sends out the data frame, until the receiving node R receives the frame, and the time required is the sum of the data transmission delay and propagation delay; the sending node S broadcasts the data and starts its own timeout timer, and listen to whether the ACK frame from node R 1s received during the timing period; if the ACK frame from node R is received before its timer expires and the ACK carries the sequence numbers of all data frames transmitted by node S, it means that the data transmission 1s successful; otherwise, it needs to be retransmitted; the timeout timer should be set large enough to ensure that the sending node can successfully receive the ACK frame from the upper neighbor node, and the data propagation delay is set to the maximum propagation time delay; therefore, the timeout timer setting based on the maximum propagation delay can be expressed in mathematical expression as: Dimer = Tata + Fax + Tack + Trae > Further, the timeout timer Time can be expressed as:

Liner = Tata + Tack + 21 ax Preferably, in the hierarchical topology of the underwater sensor network, G=(V,F), where V is a set of nodes, and F is a point-to-point link set in which the transmission quality exceeds a certain threshold, namely:

F={,)d, >Adjeol.j EVY : Where, dj is the threshold constant; d, refers to the average delivery rate from node / tonode ; when the transmission quality is not interfered by the nodes,

BL-5386 LU501337 and it 1s related to the attenuation characteristics of the channel, strength of the underwater acoustic signal, etc.;

The set of neighbor nodes of the node i can be expressed by the following formula: NO ={jljeV AG DEF};

Suppose that the time 7, ; required to transmit a data frame between node /and node ; is the sum of the maximum propagation delay 7, of sending data and the data frame transmission delay 7, , namely:

Ly = loos + Towa 5 Then the state of node ; at 7, can be recorded as a binary random variable S,(T,,), and its S,(T,,) =1 indicates that the state of node j meets the conditions of node i to broadcast the data frame; otherwise, it means that the state of the node ; is not suitable for node 7 to broadcast the data; when node / needs to send a data packet, first check the real-time state of the neighbor node in the neighbor table; only when the current transmission of node 7 does not interfere with any other reception that has been performed by any neighbor node; among the expected next-hop candidate forwarding nodes, node 7 will try to send the first frame of data when there is a node that is not in the sending state; that is, when the state of all neighboring nodes meets the sending conditions of node /; that is, for any neighbor node ;, S,(7;;)=1; if there is a data frame transmission between node / and node ; at 7,, the probability of the successful delivery of the data frame can be expressed as: DT) =dys 5), (5) =01;

Obviously, D,(7;,) is a random variable related to s,(7;,); the formula reflects that the actual delivery rate of data frames in the network is the result of the joint effect of the state of the receiving node and own conditions of the channel:

In the LSPB-MAC protocol, node 7 first checks the state information of neighbor nodes from the neighbor table, and then judges whether to broadcast the data according to the corresponding mechanism; the nodes between the links are all judged to meet

BL-5386 LU501337 the forwarding conditions before broadcasting and forwarding, and finally, reach the destination node sink.

At this time, the entire transmission is completed.

The present invention solves the large conflict problem caused by the random access MAC mechanism used in underwater broadcast routing.

On the basis of not using a handshake mechanism, the present invention perceives the state of neighbor nodes, and further transmits the data based on the state of neighbor nodes, thus avoiding conflicts and improving the utilization rate of the underwater acoustic channel with scarce bandwidth resources.

The present invention can directly provide channel access control for hierarchical broadcast routes such as literature, and can also provide shared channel access control for other broadcast routes after modification.

Description of the drawings Figure 1 is a flowchart of an underwater broadcast transmission method based on hierarchy and state in Embodiment 1; Figure 2 is an underwater three-dimensional sensor network model in Embodiment 1; Figure 3 shows the structure of the package chain in Embodiment 1; Figure 4 is a time chart of data transmission in Embodiment 1; Figure 5 is a schematic diagram of receiving-receiving collision in Embodiment 1; Figure 6 is a schematic diagram of the transmission-reception collision in Embodiment 1; Figure 7 is a schematic diagram of neighbor "receiving state" collision in Embodiment 1; Figure 8 is a schematic diagram of collision of upper-layer neighbors in "transmission state" in Embodiment 1; Figure 9 is a network layout diagram in Embodiment 1.

BL-5386 ; LU501337 Specific embodiments In order to further understand the content of the present invention, the present invention will be described in detail with reference to the drawings and embodiments.

It should be understood that the embodiments are only for explaining but not limiting the present invention.

Embodiment 1 As shown in Figure 1, this embodiment provides an underwater broadcast transmission method based on hierarchy and state, which comprises the following steps: 1) enabling the node to send data; 2) Judging whether all neighbor nodes are not in the "receiving state"; if yes, proceed to the next step; if not, back off and re-judge the state of neighbor nodes; 3) Judging whether an upper-level neighbor node has an "unknown" or state or a "sending avoidance" state; if yes, proceed to the next step; if not, back off and re-judge the state of the neighbor node; 4) Broadcasting the first frame of data; 5) receiving the first frame ACK; 6) broadcasting the remaining N-1 frames, and starting the timeout timer; 7) receiving the last frame ACK during the timing period; 8) judging whether the data frame in the packet chain is completely received; if yes, proceed to the next step; if not, retransmit the lost data frames; 9) enabling the sending node to broadcast an "end-of-transmission" control frame; 10) enabling the neighbor node to broadcast an "end-of-reception" control frame.

Taking into account the mobility of nodes underwater, in order to make the simulation results more suitable for the underwater environment with dynamic changes in topology, this paper considers the three-dimensional underwater wireless sensor network model shown in Figure 2. The model is composed of sink nodes on the water surface and ordinary sensor nodes deployed underwater.

The sink node is equipped with an underwater acoustic modem and an RF modem.

The sink node uses the underwater acoustic modem to communicate with the underwater node; uses the RF

BL-5386 LU501337 modem to communicate with the nodes on the water surface and the surface relay station for radio frequency communication. This protocol only considers the communication between sink nodes and underwater sensor nodes. If a data packet sent by the source node can be successfully received by the sink node, we consider the data packet to be successfully transmitted. The underwater sensor node has data acquisition and related processing technology. The underwater node converts the acquired underwater physical, biological phenomenon and acoustic information into electrical signals, which are converted into digital signals through the A/D interface circuit and sent to the node processor. The microprocessor of the node then processes the received data, and packs the processed data according to the relevant network protocol, and then transmits it to the sink node on the water surface in a multi-hop mode of underwater sound.

In order to better study the data forwarding problem in UWSNs, the network model is set as follows: (1) the sink node is deployed on the water surface within the monitoring range, and all underwater sensor nodes are randomly deployed in the three- dimensional area. (2) underwater sensor nodes have the same initial energy, transmission power, transmission radius, etc. (3) the communication state of each underwater sensor node is equal, and it is possible to become a receiving node and a sending node.

In the LSPB-MAC protocol, in order to avoid conflicts and reduce retransmissions, while taking into account the transmission efficiency and fairness of channel occupation, channel access control is implemented based on the following rules: (1) A node is allowed to transmit at most one data packet chain in a data transmission stage, and each packet chain contains at most N data frames, thus avoiding the channel being occupied by a node for a long time.

(2) The minimum interval between two data transmission phases of the same node is 7, , that is, when the node completes the transmission of a packet chain, the node enters the sending avoidance phase, and the time period for sending avoidance is 7, where 7, should be long enough, and the backoff time is generally set as:

BL2380 LU501337 T,=2RTT (4-1) Where, RTT is the maximum round-trip delay of the data packet.

(3) Each packet chain contains multiple data frames, and LSPB-MAC will sequence the data frames in each packet chain and transmit them in descending order of sequence numbers.

The LSPB-MAC protocol adopts the packet chain transmission mechanism. When the node successfully occupies the channel, it will transmit all the frames belonging to the same packet chain. The composition of the packet chain is shown in Figure 3. A packet chain is composed of N data frames, and the numbers of the N data frames are sorted from largest to smallest, called the frame sequence number; the sequence number of the first frame is N, the sequence number of the second frame is N-1, ......, and the sequence number of the last frame is 1. Preferably, when the packet chain is transmitted in the channel, the first frame in the packet chain is first broadcast and sent; after each neighbor node receives the first frame, an ACK carrying the sequence number of the first frame is immediately returned to the sending node; after receiving the ACK from any upper-layer neighbor node, the sending node broadcasts the remaining N-1 frames in the packet chain successively, and after each upper layer receives the last frame in the packet chain, the neighbor node will immediately reply to the sending node with an ACK carrying the sequence number of the correctly received frame in the packet chain. the sending node judges whether the data frame in the packet chain has been completely received according to the frame sequence number, and the unsuccessfully received data frame is retransmitted to form a sub-packet chain and then forwarded again until the transmission is successful or fails because the number of retransmissions exceeds the limit.

The format of each data frame is shown in Table 1, where the frame sequence number is used to mark the sequence number of the data frame in the packet chain, and the immediate ACK field is used to indicate whether the receiving node immediately responds to the ACK frame; "0" means "no reply", and"1" means immediate reply. In the protocol proposed in this embodiment, there is a need to immediately reply to the

BL-5386 LU501337 first frame and the last frame in the packet chain. Bit 2 1 Variable | 16

ZA Field Frame type Confirm Source | 00: data Frame immediately | Data FCS node 01: ACK sequence ID 10: end of | number transmission 11: end of reception Position | Frame header Load Frame

PT Table 1 Format of Data Frame Nodes using the LSPB-MAC protocol decide whether to broadcast the packet chain based on the state of neighbor nodes. In UWSNs, the state of neighbor nodes will dynamically change with the transmission of data. Therefore, nodes using the LSPB- MAC protocol first need to obtain the real-time state of neighbor nodes.

In order to facilitate the neighbor nodes to obtain the real-time state, when hearing the first frame in the packet chain, each node that is heard needs to immediately reply an ACK frame to the sending node. Some information on the ACK control frame is shown in Table 4-3. It can be seen from Table 2 that the value of the ACK frame type field is "01", indicating that the node that sends the frame has entered the receiving state.

Bit 8 8 8 2 6 Field Sending Sending node Receivingnode Frametype Frame sequence node ID hierarchy ID 01: ACK number ~~ Table2ACKControlFrame When the sending node successfully transmits all data frames in a packet chain, that is, the sending node receives an ACK from its upper neighbor, confirming that all frames in the packet chain have been successfully received, the sending node sends a

BL-5386 LU501337 control frame with a frame type field of "10" to indicate the end of transmission and enters the transmission avoidance phase. Each neighbor node that receives the control frame sends a control frame with a frame type field of "11" to indicate the end of the reception.

It is not difficult to see from the above transmission mechanism that a node can learn the real-time state of its neighbor nodes through listening. For example, when a data frame with a frame type field of "00" is heard and the frame sequence number is greater than 1, the state of the neighbor node that has sent the data frame is "transmission"; when an ACK frame with a frame type field of "01" 1s heard and the confirmed frame sequence number is greater than 1, the state of the node that has sent the ACK is "reception"; when a control frame with a frame type field of "10" is heard, the state of the sending node of this frame is "sending avoidance"; when a control frame with a frame type field of "11" is heard, the state of the sending node of this frame is "transition from receiving to unknown". The pseudo code for obtaining the state of neighbor nodes is shown in Algorithm 1.

Algorithm 1 Obtain the state of neighbor nodes. Input: listen to frames from neighboring nodes Output: update the state of neighbor nodes in the neighbor table UPON Listen to a frame DO IF (the frame type field value is "00") & (frame sequence number>1) THEN Update the neighbor table and set the state field of the sending node of the frame to "0"; // Indicate that the node is about to send the remaining frames in the packet chain ELSE IF (the frame type field value is "00") & (frame sequence number =1) |THEN Update the neighbor table and set the state field of the sending node of the frame to "1"; // Indicate that the node is ready to receive data IF (the frame type field value is "01") & (frame sequence number>1) THEN

BL-5386 LU501337 Update the neighbor table and set the state of the neighbor node of the ACK frame to "1"; // Indicate that the neighbor node is ready to receive the remaining data frames ELSE IF (the frame type field value is "10") THEN Update the neighbor table and set the state of the neighbor node of the control frame to "3"; // Indicate that the neighbor node has sent an "end of transmission” control frame and entered the transmission avoidance state IF (the frame type field value 1s "11") THEN Update the neighbor table and set the state field of the sending node of the frame to "2". // Indicate that the neighbor node stops receiving the data and the node is in an unknown or idle state.

ENDIF

ENDUPON The LSPB-MAC protocol is used to send the packet chain. After the node sends a frame with the largest or smallest sequence number in the packet chain, the sending node starts the timeout timer, waits to receive the corresponding ACK frame before the timer expires, and judges whether a data frame is lost during the transmission process according to the received ACK. In this protocol, we assume that all nodes have the same communication range as R, and the propagation speed of acoustic signals in the water is V. Therefore, the maximum propagation delay of data can be calculated as T= The maximum time required for the complete transmission process of a data frame by a node is assumed to be a transmission cycle, including the transmission of the data frame until the receipt of the ACK from the receiving node, as shown in Figure 4. The time required for the sending node to broadcast the data frame includes the transmission delay 7,, and the propagation delay 7, , of the data frame; the time

BL-5386 LU501337 required for the receiving node to reply to the ACK frame includes the transmission delay 7, and the propagation delay 7, ,. of the ACK. As shown in Figure 4, assume that node S is the sending node, and node R is the upper neighbor node of the sending node. The node S sends out the data frame, and the time required until the receiving node R receives the frame is the sum of the data transmission delay and the propagation delay.

The sending node S starts its own timeout timer while broadcasting the data, and monitors whether it receives the ACK frame from the node R during the timing. If the ACK frame from the node R is received before its timer expires, and the ACK carries the sequence numbers of all the data frames transmitted by the node S, which means that the data transmission 1s successful. Otherwise, it needs to be retransmitted. The timeout timer should be set large enough to ensure that the sending node can successfully receive the ACK frame replied from the upper-layer neighbor node. Here, the data propagation delay is set to the maximum propagation delay. Therefore, the timeout timer setting based on the maximum propagation delay can be expressed in mathematical expression as: Timer = Tata + Tax + Tacx + Toa 5 Further, the timeout timer omer can be expressed as; Timer = Tata + Tacx + 21 max System model: G =, F) in the hierarchical topology of the underwater sensor network, where VW 1s the set of nodes, and F is the set of point-to-point links whose transmission quality exceeds a certain threshold, namely: F={,)d, >Adjeol.j EVY : Where, dr isathreshold constant; d, refers to the average delivery rate from node / tonode ; when the transmission quality is not interfered by nodes, and it is related to the attenuation characteristics of the channel and the strength of the underwater acoustic signal; The set of neighbor nodes of the node i can be expressed by the following

BL-5386 LU501337 formula: NO ={jljeV AG DEF};

Let the time 7, , required to transmit data frames between node / and node /

be the sum of the maximum propagation delay 7, Of sending data and the data frame transmission delay 7,,,, namely: 15 = Toax + Ta

Then the state of node ; at 7, can be recorded as a binary random variable S,(T,,), and its S,(T,,) =1 indicates that the state of node j meets the conditions of node i to broadcast the data frame; otherwise, it means that the state of node ; is not suitable for node _ to broadcast the data; in order to avoid two common "receive- receive" collisions and "send-receive" collisions, when node i needs to send a data packet, first check the real-time state of the neighbor node in the neighbor table; only when the current transmission of node 7 does not interfere with any other reception that has been performed by any neighbor node; among the expected (route-aware) next-hop candidate forwarding nodes, node 7 will try to send the first frame of data when there 1s a node that is not in the sending state; that is, when the state of all neighboring nodes meets the sending conditions of node /; that is, for any neighbor node j, S,(7;,)=1; if there is a data frame transmission between node ; and node ; at 7;,, the probability of the successful delivery of the data frame can be expressed as:

DT) =dys 5), (5) =01;

Obviously, D,(7;,) is a random variable related to s,(7;,); the formula reflects that the actual delivery rate of data frames in the network is the result of the joint effect of the state of the receiving node and own conditions of the channel;

In the LSPB-MAC protocol, node i first checks the state information of neighbor nodes from the neighbor table, and then judges whether to broadcast the data according to the corresponding mechanism; the nodes between the links are all judged to meet the forwarding conditions before broadcasting and forwarding, and finally, reach the destination node sink.

At this time, the entire transmission is completed.

Bl-2386 LU501337 "Receive-receive" collision The traditional ground sensor network uses electromagnetic waves as the communication carrier, and its propagation delay is very small and almost negligible. Therefore, only the difference in sending time is considered in the research. It is believed that as long as the sending node sends the data packet at a different time, the time of data arriving at the receiving node will also be different (it can also be considered that the time when the data packet arrives at the receiving node is only related to the time when the data packet is sent), so that the collision of these packets at the same node can be avoided by scheduling different sending nodes to send at different times. However, as shown in Figure 5, the propagation delay of acoustic signals under water is relatively long and cannot be ignored. The underwater acoustic channel is shared by multiple nodes, even if multiple neighboring nodes do not send a data pack to the same receiving node at the same time. Their different spatial locations cause data packet collisions at the receiving node, so that the receiving node cannot receive the data packet correctly. This "receive-receive" collision is caused by the two- dimensional uncertainty of time and space in the underwater environment.

The dynamic topology of the underwater environment increases the temporal and spatial uncertainty of UWSNs. Therefore, when designing the collision avoidance algorithm of the MAC protocol, the probability of data packet collisions will decrease by mastering the real-time conditions such as the node state and mobility in the network topology.

"Send-receive" collision Due to cost reasons, UWSNs nodes generally work in half-duplex mode, and a node in the sending state cannot receive data, and vice versa. As shown in Figure 6, when the sending node S sends a data packet to its neighbor node R,, its neighbor node R, sends the data packet to the node S at the same time. At this time, a "send- receive” collision will occur at the node S, resulting in The data packet sent by the node R, cannot be successfully received by the node S.

In order to ensure reliable data transmission, data packets in the underwater

BL-5386 LU501337 acoustic channel need to be retransmitted after the collision.

The retransmission process consumes additional energy.

As the number of retransmissions increases, the energy overhead is greater.

What's important, too many retransmissions will increase the burden on the network and further increase packet collisions.

Therefore, a certain collision avoidance mechanism must be adopted to reduce collisions in the channel.

In order to solve the collision problem in the channel, the most common method is to avoid the collision in the channel by adopting the RTS/CTS handshake mechanism.

According to the traditional MAC protocol based on handshake, although the transmission between nodes is dynamically coordinated through the interaction of control packets such as RTS/CTS, which reduces data collisions, the optimized data packet size transmitted in the underwater acoustic network is 100-200 bytes, and the length of the RTS/CTS control packet is dozens of bytes.

Compared with the data packet, the length of the RTS/CTS packet is not negligible.

For UWSNs with narrow bandwidth and large delay, the use of the RTS/CTS handshake mechanism increases the end-to-end delay and reduces the bandwidth utilization and network throughput.

Therefore, this embodiment proposes an underwater broadcast MAC protocol based on level and state awareness, which can largely avoid the traditional RTS/CTS handshake mechanism, improve channel utilization and network throughput, and reduce unnecessary time consumption and energy consumption.

Collision avoidance mechanism based on neighbor node state In this embodiment, in order to avoid the above two conflicts, when node i needs to send a data packet, first check the real-time state of the neighbor node in the neighbor table, only if this transmission will not interfere with other receptions already performed by any neighbor node i, And among those expected (route-aware) next-hop candidate forwarding nodes, node i will try to send a data frame when there is a node that is not in the sending state.

This will effectively avoid the aforementioned "receive- receive" collision and "send-receive" collision, and improve the efficiency of channel use.

Next, we analyze how the LSPB-MAC protocol avoids the collision of "receive-

BL-5386 LU501337 receive” and "send-receive" based on the hierarchical broadcast routing protocol. When a layer-based broadcast routing protocol is used, data packets are generally transmitted along the path from the high-level through the low-level and finally to the sink node. After the initialization phase is completed, each node maintains a dynamic neighbor table, as shown in Table 3, which includes the ID, level, and state information of the neighbor node. The state field records the real-time state of the neighbor node. The state of the neighbor node is divided into "Sending state”, "Receiving state", "Unknown" and "Sending avoidance" states. Among them, "sending state” means that the neighboring node is sending data, which is represented by "0"; "receiving state" means that the neighboring node is receiving data or is about to receive data, which is represented by "1"; and the "unknown state” is Refers to the node state is not clear, or may be idle, represented by "2"; "transmission avoidance" means that the neighbor node has just finished sending data and enters the transmission avoidance phase, which is represented by "3".

Neighbor node ID Hierarch State field value Node state y IDO 2 2 Unknown ID1 3 1 Receiving state ID2 4 2 Unknown ID3 4 0 Sending state ID4 3 2 Unknown ID5 2 3 Sending avoidance ID6 4 0 Sending state Table 3 Node Neighbor Table We use the hierarchical network topology shown in Figure 7 to analyze the impact of neighbor node status on data transmission. With the sending node S as the center, the neighbor node whose level value is less than 1 of node S is defined as the upper neighbor node of node S. In a layer-based routing protocol, a node sends data, and it is expected to be successfully received and forwarded by its upper-level neighboring

BL-5386 LU501337 nodes. As shown in Figure 7, all nodes in the topology forward data in the form of broadcast, and the data frame broadcast by node S can be received by all its neighbor nodes (NO, N1, N2, N3, N4, N5). When a neighbor node (N1 in the figure) is already in the "receiving state", that is, node N1 is receiving data frames sent by other nodes (N6), if the sending node S broadcasts the data frame at this time, the frame will be in the neighbor node N1 A collision occurs at any location, causing the neighbor node N1 to fail to correctly receive data sent by other nodes. Therefore, when the neighbor node of node S is in the "receiving state”, node S does not broadcast and send data frames, which can reduce the collision in the channel to a great extent.

The broadcast data frame of the sending node S is correctly received by the upper neighbor node and replies with all the frame sequence numbers in the transmitted packet chain. We think this transmission is successful. The above analysis shows that when all neighboring nodes are not in the "receiving state", the data frame broadcast and forwarded by the node will not collide. As shown in Figure 8, if the neighbor nodes of node S are not in the "receiving state”, but the upper neighbor nodes NO and N5 are in the "transmitting state" and are sending data, the upper neighbor nodes will not receive the data frame broadcast by S, resulting in data frame transmission failure. Therefore, except for other neighbor nodes, they cannot be in the "receiving state", and the status of the upper neighbor nodes must also be considered. When the upper neighbor is in the "sending state”, the sending node S does not broadcast the sending data, so that collisions in the channel can be avoided to a certain extent.

Therefore, based on the above analysis, when a node has a data frame to be sent, it decides whether to broadcast the data frame according to the status information of the neighbor node. Only if all neighbor nodes satisfying the sending node are not in the "receiving state", and the upper neighbor nodes are not all in the "sending state”, (that is, there is any upper-level neighbor node whose state is "unknown" or "sending avoidance"), the node will broadcast and forward the data. After multi-hop forwarding layer by layer, the data is finally transmitted to the sink node.

BL-5386 LU501337 Performance analysis Suppose the network layout is shown in Figure 9. In this figure, the sending node S has a total of N neighbor nodes, of which M are upper-level neighbor nodes, and M=2 (Ny and N; respectively) in the figure. Assume that there are X nodes among the M upper-level neighbor nodes that satisfy the status of "unknown" or "sending avoidance", and 1< kK <M . The data of all nodes are generated to obey the Poisson distribution with the parameter A.

The channel utilization is a very important parameter for evaluating the performance of the MAC protocol. The channel utilization is the ratio of the time 7, for transmitting valid data frames to the total time 7, , which can be defined as: v-L The total time 7, includes the time 7,, for data transmission failure in the channel, the backoff time 7,, for the node to complete the transmission of a packet chain and enter the transmission avoidance phase, the time 7, for successful data transmission, and the channel idle time 7, .

In the LSPB-MAC protocol, when the sending node completes the judgment of the neighbor node hierarchy and meets the forwarding conditions, that is, all neighbor nodes are not in the "receiving state", and there are any upper neighbor nodes whose status 1s "unknown" or "sending avoidance". The sending node will broadcast the first data frame to its neighbor nodes. Assume that the time it takes for the sending node S to broadcast the data frame to each neighbor node is: T=Tp +The 5 Where, 7, represents the maximum propagation delay between the node S and its neighbor nodes, and 7, represents the transmission delay of the data frame.

The success of data transmission in the LSPB-MAC protocol needs to be considered in two parts. The first part is the successful broadcast of the first dataframe; the second part is the ACK frame that any upper-layer neighbor node responds to the first frame, and the remaining N-1 frames are broadcast, and during the timing period,

BL-5386 LU501337 the upper-layer neighbor node will listen to the ACK of the last frame of reply. If there 1s no missing frame sequence number in the ACK, it indicates that the data is forwarded successfully. Assuming that node S starts to broadcast the first data frame at 7,=0, there will be the following two collision possibilities during the broadcast of the data frame: If the neighbor node of the sending node S has a "receiving state” within 7° time, that is, the neighbor node is receiving data frames sent by other nodes, and the data frames broadcast by the sending node will affect the node reception. Therefore, the probability that the neighbor node of the sending node will not switch from "unknown", "sending avoidance" or "sending state” to "receiving state” within T time is: RAD eT De aw POST a HE g—= Where, Q is the number of neighbor nodes of any neighbor node of node S (the node and node S are mutually hidden terminals).

If there is any upper-level neighbor node that switches from "unknown" or "sending avoidance" to "sending state” within 7° time, the data frame sent by this node will cause a collision in the channel with the data frame broadcast by the sending node; The probability that the upper-layer neighbor node will not switch from the "unknown" or "sending avoidance" state to the "sending state" within T time (that 1s, the probability that all upper neighbor nodes will not send the first dara frame within 7 time) is: Pv =0) =e CE ke ; Define P, as the probability that there is no collision when broadcasting the data frame in the channel, that is, the state of all neighbor nodes does not switch from "unknown", "transmission avoidance" or "transmission state” to "reception state" within 7 time, and the status of the upper neighbor node is not switched from the "unknown" or "sending avoidance" state to the "sending state". Therefore, the probability of successful data frame transmission in the channel can be expressed as:

BL-5386 LU501337 P =e. Ke, After the data frame is successfully transmitted, the node S broadcasts all the remaining N-1 frames in the packet chain and starts the timeout timer. During the timing period, it listens to whether the upper neighbor node responds to the ACK of the last frame. If it does not listen during the timing period when an upper-level neighbor node replies with an ACK frame, it means that the data collided in the channel and the transmission was not successful. In the case of a given bit error rate (BER), the probability of an error in the transmission of a data packet containing L bits can be expressed as: P,=1-(1- BER)" = L-BER ; Data transmission failure means that after node S broadcasts the data, it does not hear any upper-layer neighbor node reply ACK frame within the timing period. Therefore, the data transmission failure time during this period can be expressed as: Tut = Tier "(1-P 3 Where, 7, . isthe set timeout time (that is, the listening time).

The sending node receives the ACK of the last frame replied from the upper-layer neighbor node, and judges whether the data frame in the transmitted packet chain is correctly received by the upper-layer neighbor node according to the frame sequence number carried in the ACK, If a frame sequence number carried in the ACK is missing, it means that the data frame corresponding to the missing sequence number is lost and needs to be retransmitted. Suppose that the time for transmitting N-1 frames in the packet chain in the channel 1s 7. ,, , which includes the propagation delay and transmission delay of transmitting N-1 frames. Then the time from the time when the node starts to send the data packet chain to the time when the upper-layer neighbor node responds to the ACK frame can be defined as: Met Tr) ZN BAR) = An ck Where, N is the number of retransmissions, and 7, 1s the sum of the propagation time and the transmission delay required to listen to any upper-layer

BL-5386 LU501337 neighbor node to send an ACK. The total time from the retransmission of the data to the success of the transmission can be expressed as: Tam =T+T, x +1, =T + Tack + Lam ace - 1-F, Where, 7 1s the transmission delay and propagation delay required for broadcasting the data frame. Therefore, the time for data to be successfully transmitted in the channel is: I, =P Tam > When a node completes the transmission of a packet chain, the node enters the sending avoidance phase, and the sending avoidance time (i.e. back-off time) is set to T,, and the back-off time can be expressed as: Typ =T, =2RIT | The 1dle time in the channel is: Lge = an ; Where, each node generates a packet every 1/2 second on average.

From the formula, the channel utilization rate is:

SE Lt LT tT, Where, 7. is the time to transmit a valid data frame, that is, the time to successfully transmit a data frame in the channel; 7,,+7 + Lane +7,, 1s the total time of data transmission in the channel.

Therefore, it can be concluded that the greater the proportion of the time to successfully transmit a data frame in the entire data transmission process, the better the channel utilization rate, and the channel utilization rate is positively correlated with the effective data transmission time. The effective time of transmitting data is related to the probability of successful data transmission, that is, it is directly related to the state of the receiving node. The protocol judges the status of the receiving node, avoids the hidden terminal problem to a large extent, reduces the collision in the channel, and

BL-5386 LU501337 improves channel utilization.

The present invention and its embodiments are schematically described above, and the description is not restrictive. What is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited to this.

Therefore, if a person of ordinary skill in the art is inspired and does not deviate from the purpose of the invention, without creative design, structural methods and embodiments similar to the technical solution shall fall within the protection scope of the invention.

Claims

BL-5386 LU501337 CLAIMS

1. The underwater broadcast transmission method based on hierarchy and state is characterized in that it includes the following steps: 1) enabling a node to send data; 2) Judging whether all neighbor nodes are not in the "receiving state"; if yes, proceed to the next step; if not, back off and re-judge the state of neighbor nodes; 3) Judging whether an upper-level neighbor node has an "unknown" or state or a "sending avoidance" state; if yes, proceed to the next step; if not, back off and re-judge the state of the neighbor node; 4) Broadcasting a first frame of data; 5) receiving a first frame ACK; 6) broadcasting the remaining N-1 frames, and starting a timeout timer; 7) receiving the last frame ACK during the timing period; 8) judging whether the data frame in the packet chain is completely received; if yes, proceed to the next step; if not, retransmit the lost data frames; 9) enabling the sending node to broadcast an "end-of-transmission" control frame; 10) enabling the neighbor node to broadcast an "end-of-reception" control frame.

2. The underwater broadcast transmission method based on hierarchy and state according to Claim 1, characterized in that: a packet chain is composed of N data frames, and the numbers of the N data frames are sorted from largest to smallest, called the frame sequence number; the sequence number of the first frame 1s N, the sequence number of the second frame is N-1, ..., and the sequence number of the last frame is 1.

3. The underwater broadcast transmission method based on hierarchy and state according to Claim 2, characterized in that: when the packet chain is transmitted in the channel, the first frame in the packet chain is first broadcast and sent; after each

BL-5386 LU501337 neighbor node receives the first frame, an ACK carrying the sequence number of the first frame 1s immediately returned to the sending node; after receiving the ACK from any upper-layer neighbor node, the sending node broadcasts the remaining N-1 frames in the packet chain successively, and after each upper layer receives the last frame in the packet chain, the neighbor node will immediately reply to the sending node with an ACK carrying the sequence number of the correctly received frame in the packet chain; the sending node judges whether the data frame in the packet chain has been completely received according to the frame sequence number, and the unsuccessfully received data frame is retransmitted to form a sub-packet chain and then forwarded again until the transmission 1s successful or fails because the number of retransmissions exceeds the limit.

4. The underwater broadcast transmission method based on hierarchy and state according to Claim 3, characterized in that: when hearing the first frame in the packet chain, every node that 1s heard needs to immediately reply an ACK frame to the sending node; when the sending node successfully transmits all data frames in a packet chain, that 1s, the sending node receives an ACK from its upper neighbor, confirming that all frames in the packet chain have been successfully received, the sending node sends a control frame with a frame type field of "10" to indicate the end of transmission and enters the transmission avoidance phase; each neighbor node that receives the control frame sends a control frame with a frame type field of "11" to indicate the end of the reception.

5. The underwater broadcast transmission method based on hierarchy and state according to Claim 4, is characterized in that: the node can learn the real-time state of its neighbor nodes through listening; when a data frame with a frame type field of "00" is heard and the frame sequence number is greater than 1, the state of the neighbor node that has sent the data frame is "transmission"; when an ACK frame with a frame type field of "01" is heard and the confirmed frame sequence number is greater than 1, the

BL-5386 LU501337 state of the node that has sent the ACK is "reception"; when a control frame with a frame type field of "10" is heard, the state of the sending node of this frame 1s "sending avoidance"; when a control frame with a frame type field of "11" is heard, the state of the sending node of this frame is "transition from receiving to unknown".

6. The underwater broadcast transmission method based on hierarchy and state according to Claim 5, characterized in that the LSPB-MAC protocol is used to send the packet chain; after the node sends a frame with the largest or smallest sequence number in the packet chain, the sending node starts the timeout timer, waits to receive the corresponding ACK frame before the timer expires, and judges whether a data frame 1s lost during the transmission process according to the received ACK.

7. The underwater broadcast transmission method based on hierarchy and state according to Claim 6, characterized in that: in the LSPB-MAC protocol, it 1s assumed that all nodes have the same communication range as R, and the speed of acoustic signal propagation in water is V; therefore, the maximum data propagation delay can be calculated as =p the maximum time required for the complete transmission process of a data frame by a node is assumed to be a transmission cycle, including the data frame transmission until the ACK confirmation from the receiving node is received; the time required for the sending node to broadcast the data frame includes the transmission delay 7, and propagation delay 7,,.,, of the data frame; the time required for the receiving node to reply to the ACK frame includes the transmission delay 7, and propagation delay 7,,,, , of the ACK; suppose that node S is the sending node, and node R is the upper neighbor node of the sending node; node S sends out the data frame, until the receiving node R receives the frame, and the time required is the sum of the data transmission delay and propagation delay; the sending node S broadcasts the data and starts its own timeout timer, and listen to whether the ACK frame from node R is received during the timing period; if the ACK frame from node R is received before its timer expires and the ACK carries the sequence numbers of all

Bl-2386 LU501337 data frames transmitted by node S, it means that the data transmission 1s successful; otherwise, it needs to be retransmitted; the timeout timer should be set large enough to ensure that the sending node can successfully receive the ACK frame from the upper neighbor node, and the data propagation delay 1s set to the maximum propagation time delay; therefore, the timeout timer setting based on the maximum propagation delay can be expressed in mathematical expression as: Dimer = Tata + Toa + Tack + Tax 5 Further, the timeout timer 71... can be expressed as: Dimer = Tata + Tack + 21 ax

8. The underwater broadcast transmission method based on hierarchy and state according to Claim 7, is characterized in that: in the hierarchical topology of the underwater sensor network, G = (V,F), where V 1s a set of nodes, and / is a point-to- point link set in which the transmission quality exceeds a certain threshold, namely: F={i,pld,>d, .i.jeV| ; Where, d,,., is the threshold constant; d, refers to the average delivery rate from node / tonode ; when the transmission quality is not interfered by the nodes, and it 1s related to the attenuation characteristics of the channel, strength of the underwater acoustic signal, etc.; The set of neighbor nodes of the node / can be expressed by the following formula: No ={/ljeV AG DEF}; Suppose that the time 7, , required to transmit a data frame between node /and node ; is the sum of the maximum propagation delay 7, of sending data and the data frame transmission delay 7, , namely: 15, = To + Tha 3 Then the state of node ; at 7, can be recorded as a binary random variable S,(T,,), and its S,(T,,) =1 indicates that the state of node j meets the conditions of

BL-5386 LU501337 node i to broadcast the data frame; otherwise, it means that the state of the node ; is not suitable for node 7 to broadcast the data; when node / needs to send a data packet,

first check the real-time state of the neighbor node in the neighbor table; only when the current transmission of node i does not interfere with any other reception that has been performed by any neighbor node; among the expected next-hop candidate forwarding nodes, node 7 will try to send the first frame of data when there is a node that is not in the sending state; that is, when the state of all neighboring nodes meets the sending conditions of node /; that is, for any neighbor node ;, S,(7;;)=1; if there is a data frame transmission between node / and node ; at 7,, the probability of the successful delivery of the data frame can be expressed as:

DT) =dys 5), (5) =01;

In the LSPB-MAC protocol, node 7 first checks the state information of neighbor nodes from the neighbor table, and then judges whether to broadcast the data according to the corresponding mechanism; the nodes between the links are all judged to meet the forwarding conditions before broadcasting and forwarding, and finally, reach the destination node sink.

At this time, the entire transmission is completed.