CN117134817A - Performance analysis method of double-frequency cooperative MAC protocol for unmanned aerial vehicle networking - Google Patents

Abstract

The application relates to a performance analysis method of a double-frequency cooperation MAC protocol for an unmanned aerial vehicle networking. The method comprises the following steps: respectively configuring a transceiver of an omnidirectional antenna and a transceiver of a directional antenna for nodes in an unmanned aerial vehicle network, wherein the transceiver of the omnidirectional antenna works on a low-frequency channel, and the transceiver of the directional antenna works on a high-frequency channel; the source node and the destination node perform data transmission according to a double-frequency cooperative MAC protocol, the successful reservation time of a control channel in the data transmission process is compared with the data transmission time of the data channel, and if the successful reservation time is not less than the data transmission time, the saturated throughput is calculated according to a two-dimensional Markov model; if the successful reservation time length is smaller than the data transmission time length, modeling the number of the concurrent links as a spatial multiplexing coefficient, and calculating to obtain the saturated throughput according to the solved spatial multiplexing coefficient. By adopting the method, the performance analysis can be carried out on the double-frequency cooperative MAC protocol.

Description

Performance analysis method of dual-band cooperative MAC protocol for UAV networking

Technical field

This application relates to the technical field of unmanned aerial vehicle self-organizing network, and in particular to a performance analysis method of a dual-frequency cooperative MAC protocol for unmanned aerial vehicle networking.

Background technique

The dual-frequency cooperative MAC protocol combines the advantages of high-frequency band in high transmission rate and strong anti-interference ability with low-frequency band in network maintenance and control to improve the communication reliability and transmission efficiency of the entire UAV network. Most of the existing UAV networks are MAC protocols designed based on a single operating frequency (high frequency or low frequency). The traditional low-frequency microwave band (sub-6GHz) is heavily occupied, spectrum resources are increasingly scarce, and congestion is serious. This frequency band has been unable to meet the high-throughput transmission requirements of emerging services and application scenarios. High-frequency bands (30-300GHz) such as millimeter waves have received more attention in recent years due to their rich spectrum resources and strong anti-interference capabilities. However, the attenuation of millimeter waves is serious, and beamforming technology is usually used to form directional beams to increase the transmission distance. Facing high-speed moving UAV networks, the directionality of beams causes the communication network to spend a lot of time on beam training, which is expensive.

Therefore, it is currently necessary to propose a performance analysis of the dual-frequency cooperative MAC protocol to guide the improvement of the dual-frequency cooperative MAC protocol to improve network throughput and reduce overhead. The performance analysis of the MAC protocol can effectively evaluate the impact of each parameter on the protocol performance. , which has guiding significance.

Contents of the invention

Based on this, it is necessary to address the above technical issues and provide a performance analysis method for the dual-frequency cooperative MAC protocol for UAV networking that can perform performance analysis on the dual-frequency cooperative MAC protocol.

A performance analysis method for dual-frequency cooperative MAC protocol for UAV networking, the method includes:

The nodes in the UAV network are respectively configured with omnidirectional antenna transceivers and directional antenna transceivers. The omnidirectional antenna transceiver works on the low-frequency channel, and the directional antenna transceiver works on the high-frequency channel; the low-frequency channel is the control channel. ; The high-frequency channel is a data channel; the UAV network includes a pair of source nodes and destination nodes;

Data transmission is carried out between the source node and the destination node according to the dual-frequency cooperative MAC protocol. During the data transmission process, the successful reservation time of the control channel and the data transmission time of the data channel are compared. If the successful reservation time is not less than the data transmission time, use The binary exponential backoff mechanism competes for the control channel, and the saturation throughput is calculated according to the two-dimensional Markov model;

If the successful reservation time is less than the data transmission time, the number of concurrent links is modeled as a spatial reuse coefficient, and then the spatial reuse coefficient is solved according to the location relationship of the nodes and the link relationship determination criteria, and the spatial reuse coefficient is solved based on the solved spatial reuse coefficient. The saturation throughput is calculated using coefficients; the saturation throughput is the performance analysis result of the dual-frequency cooperative MAC protocol.

In one embodiment, the process of data transmission between the source node and the destination node according to the dual-frequency cooperative MAC protocol includes:

The source node competes for the control channel through the binary exponential backoff mechanism. After the channel competition is successful, the destination node ID and the local location information of the source node are written into the RTS frame and sent to the destination node;

The destination node calculates the direction of the receiving beam based on the local location information of the source node and checks the multi-beam network allocation vector of the corresponding beam in the neighbor information list to obtain the channel flag of the destination node; it combines the source node ID, the local location information of the destination node and the channel The flag is written into the CTS frame and sent to the source node;

The source node calculates the receiving beam direction based on the local location information of the destination node and checks the multi-beam network allocation vector of the corresponding beam in the neighbor information list to obtain the channel flag of the source node; combine the local location information of the source node and the local location of the destination node The information, data transmission time, and channel flag of the source node are written into the RES frame and broadcast to all other nodes in the UAV network;

After receiving the RES frame, the destination node adjusts the receiving beam direction to receive the data frame, calculates the receiving power and interference power of the destination node during the reception process, and calculates the signal-to-interference-noise ratio at the destination node based on the received power and interference power; The noise ratio is written into the ACK frame and sent to the source node;

The source node compares the signal-to-interference-to-noise ratio with the preset signal-to-interference-to-noise ratio threshold, adjusts the direction of the receiving beam based on the comparison result and the location information provided by the previous ACK, and constructs a beam set based on the adjacent beams of the receiving beam, and assembles the beams Add it to the transmit beam training unit, and then attach the transmit beam training unit to the data frame and send it to the destination node;

After receiving the data frame, the destination node writes the signal-to-interference-to-noise ratio measurement results of the beams in each direction into the BRP frame, and sends the BRP frame after the ACK frame to the source node;

After receiving the BRP frame, the source node compares the signal-to-interference-to-noise ratio measurement results of the beams in each direction, selects the communication beam to transmit the data packet based on the comparison results, and exits beam tracking.

In one embodiment, the preset signal-to-interference-to-noise ratio threshold includes a first link threshold and a second link threshold; the source node compares the signal-to-interference-to-noise ratio with the preset signal-to-interference-to-noise ratio threshold, and based on the comparison result Adjust the direction of the receiving beam with the location information provided by the previous ACK and construct a beam set based on the adjacent beams of the receiving beam, including:

The source node compares the signal-to-interference-to-noise ratio with the pre-set signal-to-interference-to-noise ratio threshold. If the signal-to-interference and noise ratio is less than the first link threshold, it adjusts the direction of the receiving beam based on the location information provided by the previous ACK and adjusts the direction of the receiving beam according to the location information provided by the previous ACK. Adjacent beams construct a beam set.

In one embodiment, after receiving the BRP frame, the source node compares the signal-to-interference-to-noise ratio measurement results of beams in various directions, selects communication beams to transmit data packets based on the comparison results, and exits beam tracking, including:

After receiving the BRP frame, the source node compares the signal-to-interference-to-noise ratio measurement results of the beams in each direction. If the signal-to-interference-to-noise ratio measurement results in one or more beam directions are greater than the second link threshold, the source node selects the signal-to-interference-to-noise ratio. The maximum beam direction in the measurement results is used as the communication beam, continue to transmit data packets and exit beam tracking; if the signal-to-interference-noise ratio measurement result is greater than the signal-to-interference-noise ratio and all signal-to-interference-noise ratio measurement results are less than the second link threshold, it is considered that there is no choice. When reaching the required beam, continue this step; if all signal-to-interference-noise ratio measurement results are less than the signal-to-interference-noise ratio, it is considered that the UAV communication link will be disconnected and the drone will compete and reserve on the public control channel again.

In one embodiment, a binary exponential backoff mechanism is used to compete for the control channel, and the saturation throughput is calculated according to the two-dimensional Markov model, including:

Set the competition window of the competition control channel in the UAV network to _Wi = 2 ⁱ W ₀ ,i≤m, where _Wi represents the size of the i-th order competition window, m represents the maximum backoff order, and W ₀ represents the backoff process. The minimum contention window used;

During the backoff process, if the channel is idle for each time slot, the counter is decremented by 1; if the channel is detected to be busy, the counter stops and saves the remaining number of backoff time slots; when the control channel is idle again for DIFS, the counter is decreased by 1 for each idle time slot. , the counter continues to decrease by 1 from the last remaining number of time slots; when the counter value decreases to 0, the node sends the control frame RTS, assuming that the conditional probability of conflict between the control frame RTS is p, in the two-dimensional state (i, k) i represents the number of backoff levels, k represents the current value in the backoff counter, then the state transition probability is

According to the state transition probability, the steady-state probability of the two-dimensional Markov chain is set to

The steady-state probability is normalized, and based on the normalized steady-state probability, the node's sending probability at each moment is calculated as

Among them, p can be expressed as

p＝1-(1-τ) ^n-1

Then the total number of nodes is

Set the channel idle probability, successful transmission probability and transmission collision probability according to the node's transmission probability at each moment and the total number of nodes;

The mechanism of the dual-frequency cooperative MAC protocol is used to set the success time and conflict time of the control frame RTS transmission. The saturation throughput is calculated based on the channel idle probability, successful transmission probability and transmission collision probability, as well as the success time and conflict time of the control frame RTS transmission.

In one embodiment, the channel idle probability, successful transmission probability and transmission collision probability are set according to the transmission probability of the node at each moment and the total number of nodes, including:

The channel idle probability is set according to the node's transmission probability at each moment and the total number of nodes. The successful transmission probability and transmission collision probability are

p _idle = (1-τ) ⁿ

p _s =nτ(1-τ) ^n-1

p _c =1-p _idle -p _s

Among them, p _idle is the channel idle probability; p _s is the probability of successful transmission; p _c is the transmission collision probability.

In one embodiment, the mechanism of the dual-frequency cooperative MAC protocol is used to set the success time and collision time of the control frame RTS transmission, according to the channel idle probability, the successful transmission probability and the transmission collision probability, and the success time and collision time of the control frame RTS transmission. The calculated saturation throughput includes:

The mechanism of the dual-frequency cooperative MAC protocol is used to set the success time and conflict time of the control frame RTS transmission as

Among them, T _s represents the success time of control frame RTS transmission, T _c represents the collision time of control frame RTS transmission, r _c is the transmission rate of the control channel, L _RTS , L _CTS and L _RES are RTS frame, CTS frame and RES respectively. The length of the frame, T _SIFS , T _DIFS and T _EIFS are the short frame time interval, distributed coordination inter-frame interval and error inter-frame interval respectively;

Based on the channel idle probability, successful transmission probability and transmission collision probability, as well as the success time and collision time of the control frame RTS transmission, the saturation throughput is calculated as

Among them, L _d is the total amount of data transmitted, T _switch represents the time to switch from an omnidirectional antenna transceiver to a directional antenna transceiver, and σ represents the length of one time slot.

In one embodiment, the spatial reuse coefficient represents the number of links that can transmit concurrently under the current network conditions; the number of concurrent links is modeled as the spatial reuse coefficient, and is then determined based on the location relationship of the nodes and the link relationship. The criterion solves the spatial reuse coefficient, and calculates the saturated throughput based on the solved spatial reuse coefficient, including:

Analyze the link relationships in the UAV network and obtain all links in the current network;

Determine the concurrency relationship between any two links according to the link relationship determination criteria, and solve all concurrent link sets based on the concurrency relationship of the links;

Traverse all concurrent link sets c _i and determine whether the length of c _i is equal to r. If equal, then c _i is the largest concurrent link set; if the length of c _i is less than r, determine whether each link l _j can be matched with c _i is concurrent; if all links are concurrent with c _i , then c _i is the maximum concurrent link set, which is saved to the set C of all maximum concurrent link sets; where r is the number of successful negotiations within a data transmission time; the maximum The length of each subset in the concurrent link set is the spatial multiplexing coefficient;

The concurrent link throughput is calculated based on the spatial reuse coefficient, and the saturated throughput of the UAV network is calculated using the throughput of all concurrent links.

In one embodiment, the concurrent link throughput is calculated based on the spatial reuse coefficient, including:

According to the spatial reuse coefficient, the concurrent link throughput is calculated as

Among them, ε _i represents the spatial multiplexing coefficient, i represents the link sequence number, L _d is the total amount of data transmitted, T = T _d + (ε _i -1)·T _neg , T _d is the spatial multiplexing capability and data The transmission time and T _neg are the successful negotiation times, and r _d represents the data channel transmission rate.

In one embodiment, the saturation throughput of the UAV network is calculated using the throughput of all concurrent links, including:

Using the throughput of all concurrent links, the saturated throughput of the UAV network is calculated as

Among them, ε _i represents the spatial reuse coefficient, i represents the link sequence number, C = {c ₁ , c ₂ ,..., c _C } represents the set of all maximum concurrent link sets, r _d represents the data channel transmission rate, p (ε _i ) represents the probability that the maximum concurrent link set with length ε _i appears.

The performance analysis method of the above-mentioned dual-frequency cooperative MAC protocol for UAV networking first configures the nodes in the UAV network with omnidirectional antenna transceivers and directional antenna transceivers. The omnidirectional antenna transceiver works at low frequency. Channel, the transceiver of the directional antenna works on the high-frequency channel; the low-frequency channel is the control channel; the high-frequency channel is the data channel. Data transmission is performed between the source node and the destination node according to the dual-frequency cooperative MAC protocol, and the control channel is used during the data transmission process. The successful reservation duration is compared with the data transmission duration of the data channel. Based on the relationship between the negotiation duration and the transmission duration, the throughput evaluation is divided into two situations for discussion. When the negotiation time is longer than the transmission time, the throughput is analyzed based on the two-dimensional Markov model; when the negotiation time is less than the transmission time, this application models the number of concurrent links as a spatial reuse coefficient, and then based on the location relationship of the nodes and link relationship determination criteria to solve it, and finally derived the closed-form expression of saturated throughput, effectively analyzing the saturated throughput of the protocol. By performing performance analysis on the dual-frequency cooperative MAC protocol, we can effectively evaluate the impact of each parameter on the protocol performance. The impact will help guide the improvement of the dual-frequency cooperative MAC protocol, thereby improving the throughput of the communication system in UAV networking and reducing communication overhead.

Description of the drawings

Figure 1 is an application scenario diagram of a performance analysis method for a dual-band cooperative MAC protocol for drone networking in one embodiment;

Figure 2 is a schematic diagram of the transmission process in which the successful reservation time is not less than the data transmission time in one embodiment;

Figure 3 is a schematic diagram of the transmission process when the successful reservation time is less than the data transmission time in one embodiment;

Figure 4 is a schematic flowchart of finding the maximum concurrent link set in another embodiment;

Figure 5 is a schematic diagram of concurrent transmission in one embodiment.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present application more clear, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

In one embodiment, as shown in Figure 1, a performance analysis method of a dual-frequency cooperative MAC protocol for UAV networking is provided, including the following steps:

Step 102: Configure the nodes in the UAV network with omnidirectional antenna transceivers and directional antenna transceivers respectively. The omnidirectional antenna transceiver works on the low-frequency channel, and the directional antenna transceiver works on the high-frequency channel; the low-frequency channel is the control channel; the high-frequency channel is the data channel; the UAV network includes a pair of source nodes and destination nodes.

Assume that the network has n drones, which can be expressed as u = {u ₁ , u ₂ ,..., u _n }. Each node has a transceiver equipped with an omnidirectional antenna and a directional antenna respectively, which can be expressed as R _o , R _d . Among them, R _o works on a low-frequency channel (such as the Sub-6 GHz frequency band) and is used for control frame interaction of nodes throughout the network. This channel is called the control channel CCH; R _d works on a high-frequency channel (such as the millimeter wave frequency band) and is used For the transmission of data services across network nodes, this channel is called the data channel DCH.

Step 104, the source node and the destination node perform data transmission according to the dual-frequency cooperative MAC protocol, and compare the successful reservation time of the control channel and the data transmission time of the data channel during the data transmission process. If the successful reservation time is not less than the data transmission time, , then a binary exponential backoff mechanism is used to compete for the control channel, and the saturated throughput is calculated according to the two-dimensional Markov model.

Through the process of data transmission between the source node and the destination node according to the dual-frequency cooperative MAC protocol, it can be seen that the nodes work on the control channel and the data channel at the same time for frame interaction. For a certain data packet, the node needs to complete the RTS-CTS-RES control frame interaction on the control channel before it can send the data frame on the data channel. For the entire network, at a certain moment, there can be nodes sending control frames on the control channel and nodes transmitting data frames on the data channel. Therefore, the saturation throughput of the network is related to both the control channel reservation capability and the data channel data transmission capability, and there is also a mutually restrictive relationship between them. Throughput is an important indicator for evaluating the UAV network transmission capability. , The saturation throughput of high- and low-frequency cooperation is dually restricted by the control channel and the data channel, and is related to the number of successful negotiations on the control channel and the amount of link concurrency on the data channel in unit time. In order to accurately analyze the saturated throughput caused by spatial multiplexing, this application will analyze the saturated throughput of the network through the successful reservation time T _neg of the control channel and the data transmission time T _d . When T _neg ≥ T _d , The situation is shown in Figure 2. The negotiation time of the control channel is greater than or equal to the data transmission time. There is no spatial multiplexing in the network, and there is no link conflict problem in the data transmission process. At this time, the network throughput depends on the reservation capability of the control channel. At this time, the network throughput S is the control channel saturated throughput, that is

S＝S _c

This application uses a binary exponential backoff mechanism to compete for the control channel. Therefore, the control channel saturation throughput of the dual-frequency cooperative MAC protocol can be analyzed based on the two-dimensional Markov model.

Step 106, if the successful reservation time is less than the data transmission time, then the number of concurrent links is modeled as a spatial reuse coefficient, and then the spatial reuse coefficient is solved according to the location relationship of the node and the link relationship determination criteria, and based on the solution The spatial reuse coefficient is calculated to obtain the saturated throughput; the saturated throughput is the performance analysis result of the dual-frequency cooperative MAC protocol.

When T _neg <T _d , the situation is as shown in Figure 3. The negotiation time of the control channel is less than the data transmission time. The space generates multiplexing and can accommodate multiple links for concurrent transmission. At this time, the network throughput depends on the transmission capability of the data channel. At this time, the network throughput is the sum of the throughput of all concurrent links, that is

It can be seen that the saturation throughput of the data channel is related to the number of concurrent links. This application defines the spatial reuse coefficient ε, which is used to measure the degree of spatial reuse by the UAV network and represents the number of links that can be transmitted concurrently under current network conditions.

However, the degree of spatial multiplexing by network nodes is not a simple issue and depends on multiple factors, including node density ρ, node distribution D, and the number of beams M, which can be expressed as:

ε=f(ρ,D,M).

In order to solve ε, this application analyzes the link relationships of different node pairs and provides a solution method. It is assumed that the nodes are randomly distributed in the network and each node has an equal number of beams. In order to obtain the maximum concurrent transmission link in the network, it is necessary to first analyze the relationship between links. There are L links in the network, which can be expressed as L={l ₁ ,l ₂ ,…,l _L }. Where l _i ={u _s , _ur } represents the communication link between _us and _ur . For any two links l _i and l _j (i,j∈[1,L]), there is a concurrent or non-concurrent relationship, which can be expressed as l _i ||l _j respectively, Under certain conditions, all concurrent links are called maximum concurrent link set (MCLS) c={l ₁ , l ₂ ,..., l _c }. Any two links in c satisfy the following relationship

In order to describe the relationship between links and concurrent link sets, the present invention defines that if a link _la can be concurrent with all links in the set c, it can be expressed as _la ||c.

In addition, due to the different concurrency relationships between different links, the maximum concurrent link set c is not a unique set. Therefore, the set of all maximum concurrent link sets can be expressed as C={c ₁ , c ₂ ,..., c _C }. Within a limited time, the ability of spatial multiplexing is related to the relative size of the data transmission time T _d and the successful negotiation time T _neg . This application defines T _d /T _neg =r, where r is the number of successful negotiations within a data transmission time. Obviously, the maximum concurrent links in the network must be less than or equal to r.

In a random scenario, solving the maximum set of concurrent links is an NP problem. This means that ε does not have a closed form solution. Therefore, based on the above relationship, this application designs a method to solve the maximum concurrent link set c _i . The specific process is shown in Figure 4:

(1) First enter all links in the current network;

(2) Determine the concurrency relationship between any two links according to the link relationship criterion;

(3) According to the concurrency relationship of the links, solve the set of all concurrent links;

(4) Traverse all concurrent link sets c _i and determine whether the length of c _i is equal to r. If equal, then c _i is the maximum concurrent link set; if the length of c _i is less than r, then determine whether each link l _j can be concurrent with c _i ;

(5) If all links are concurrent with c _i , then c _i is the maximum concurrent link set, save it to C, and find the length of each subset in C = {c ₁ , c ₂ ,..., c _C }, that is is the maximum number of concurrent transmission links ε _i , which is the spatial reuse coefficient. As shown in Figure 5, when the maximum number of concurrent transmission links is ε _i , the total transmission time of the concurrent link set is T=T _d + (ε _i -1)·T _neg . The concurrent link throughput is calculated based on the spatial reuse coefficient and the total transmission time of the concurrent link set, and the saturated throughput of the UAV network is calculated using the throughput of all concurrent links.

In the above performance analysis method of the dual-band cooperative MAC protocol for UAV networking, the nodes in the UAV network are first configured with omnidirectional antenna transceivers and directional antenna transceivers. The omnidirectional antenna transceiver works in In the low-frequency channel, the transceiver of the directional antenna works in the high-frequency channel; the low-frequency channel is the control channel; the high-frequency channel is the data channel. Data transmission is carried out between the source node and the destination node according to the dual-frequency cooperative MAC protocol to control the data transmission process. The successful reservation time of the channel is compared with the data transmission time of the data channel. Based on the relationship between the negotiation time and the transmission time, the throughput evaluation is divided into two situations for discussion. When the negotiation time is longer than the transmission time, the throughput is analyzed based on the two-dimensional Markov model; when the negotiation time is less than the transmission time, this application models the number of concurrent links as a spatial reuse coefficient, and then based on the location relationship of the nodes and link relationship determination criteria to solve it, and finally derived the closed-form expression of saturated throughput, effectively analyzing the saturated throughput of the protocol. By performing performance analysis on the dual-frequency cooperative MAC protocol, we can effectively evaluate the impact of each parameter on the protocol performance. The impact will help guide the improvement of the dual-frequency cooperative MAC protocol, thereby improving the throughput of the communication system in UAV networking and reducing communication overhead.

In one embodiment, the process of data transmission between the source node and the destination node according to the dual-frequency cooperative MAC protocol includes:

The source node competes for the control channel through the binary exponential backoff mechanism. After the channel competition is successful, the destination node ID and the local location information of the source node are written into the RTS frame and sent to the destination node;

The destination node calculates the direction of the receiving beam based on the local location information of the source node and checks the multi-beam network allocation vector of the corresponding beam in the neighbor information list to obtain the channel flag of the destination node; it combines the source node ID, the local location information of the destination node and the channel The flag is written into the CTS frame and sent to the source node;

The source node calculates the receiving beam direction based on the local location information of the destination node and checks the multi-beam network allocation vector of the corresponding beam in the neighbor information list to obtain the channel flag of the source node; combine the local location information of the source node and the local location of the destination node The information, data transmission time, and channel flag of the source node are written into the RES frame and broadcast to all other nodes in the UAV network;

After receiving the RES frame, the destination node adjusts the receiving beam direction to receive the data frame, calculates the receiving power and interference power of the destination node during the reception process, and calculates the signal-to-interference-noise ratio at the destination node based on the received power and interference power; The noise ratio is written into the ACK frame and sent to the source node;

The source node compares the signal-to-interference-to-noise ratio with the preset signal-to-interference-to-noise ratio threshold, adjusts the direction of the receiving beam based on the comparison result and the location information provided by the previous ACK, and constructs a beam set based on the adjacent beams of the receiving beam, and assembles the beams Add it to the transmit beam training unit, and then attach the transmit beam training unit to the data frame and send it to the destination node;

After receiving the data frame, the destination node writes the signal-to-interference-to-noise ratio measurement results of the beams in each direction into the BRP frame, and sends the BRP frame after the ACK frame to the source node;

After receiving the BRP frame, the source node compares the signal-to-interference-to-noise ratio measurement results of the beams in each direction, selects the communication beam to transmit the data packet based on the comparison results, and exits beam tracking.

In a specific embodiment, the source node u _a first competes for the control channel through the binary exponential backoff mechanism. After the channel competition is successful, the destination node ID and local location information (x _a , y _a ) are written into the RTS frame and sent to the destination. Node u _b .

After u _b receives the RTS, the receiving beam direction b _b,a can be calculated based on the position information of u _a . Determine whether the channel in this direction is available by checking the value of the multi-beam network allocation vector (MNAV) corresponding to the beam direction in the neighbor information list. When MNAV=0, it means that the current channel is available, and the corresponding flag position 0 means that the channel is idle. Then write the source node ID, local location information (x _b , y _b ), and channel flag bits into the CTS frame and send it to u _a . The neighbor information list is shown in Table 1:

Table 1

Neighbor ID location information Beam ID MNAV 1 (x ₁ ,y ₁ ) 2 0 2 (x ₂ ,y ₂ ) 3 0 ··· ··· ··· ··· n (x _n ,y _n ) 0 0

Any node in the UAV network except the source node and destination node calculates the beam direction of the source node and destination node relative to the local node based on the source node position and destination node position, and updates the corresponding beam direction in the neighbor information list according to the link relationship criterion. Multibeam network allocation vectors. The link relationship criterion is

Among them, b _{a, b} represents the direction of the beam sent by the source node to the destination node, a represents the source node's logo, b represents the destination node's logo, x and y represent any node in the UAV network except the source node and the destination node respectively. to communication nodes.

The neighbor information list can reduce the probability of link interference in data transmission. Specifically, by exchanging location information, neighbor nodes can learn the location and communication beam of the communication node, and then broadcast the transmission time to neighbor nodes throughout the network. Determine communication time. Then other nodes can use a priori information to determine whether the local node can communicate at the node exchanging control packets.

When u _a receives the CTS, it determines the transmit beam direction b _a,b based on the relative position of u _b . Similarly, u _a also checks whether the MNAV in the direction b _{a and b} is 0 in the local neighbor information list. If MNAV=0, u _a writes the transmission period of the sent data frame into the Duration field and sets the channel flag position to 0. Write the local location information of the source node, the local location information of the destination node, data transmission time, and channel flag bits into the RES and broadcast them to the entire network nodes.

After receiving the RES frame, the destination node adjusts the receiving beam direction to receive the data frame, calculates the receiving power and interference power of the destination node during the reception process, and calculates the signal-to-interference-noise ratio at the destination node based on the received power and interference power; The noise ratio is written into the ACK frame and sent to the source node. Among them, the receiving power and interference power of the destination node are calculated during the reception process, including:

During the reception process, the receiving power of the destination node is calculated as

in, is the received power of source node u _a , N _t (θ ^a ,φ ^a,b ) is the transmit gain of u _a , θ ^a is the beam width of u _a , φ ^a,b is the offset angle of u _b relative to u _a , N _r (θ ^b ,φ ^b,a ) is the receiving gain of u _b , θ ^b is the beam width of u _b , φ ^b,a is the offset angle of u _a relative to u _b , d _b,a is u _b The distance from u _a , u _b represents the destination node.

During the reception process, the interference power of the destination node is calculated as

Among them, i represents the node serial number, and U represents the UAV node set.

The signal-to-interference-to-noise ratio at the destination node is calculated based on the received power and interference power, including:

According to the received power and interference power, the signal-to-interference-to-noise ratio at the destination node is calculated as

Among them, n ₀ is the noise power spectral density, and B is the channel bandwidth.

Due to the mobility of nodes, the link may be interfered with during data transmission or the communication node may exceed the communication range. When u _b receives the data frame, it needs to demodulate the received signal first. When the signal-to-interference-to-noise ratio is less than the receiver sensitivity, U _B will not be able to parse any data normally. At this time, the link is considered disconnected and the communication link needs to be re-established. Traditional methods can re-establish connections through random scanning or wide and narrow beam alignment. This method is relatively expensive, so this application proposes a fast beam tracking algorithm based on location information. The specific process is as follows:

Every time data is transmitted, u _b writes the location information into the ACK frame and sends it to u _a . After u _a is received, the beam direction can be adjusted in real time based on the location information to reduce the probability of link interruption due to node movement. Moreover, in order to solve the problem of link quality degradation caused by interference to the destination node, the destination node writes the signal-to-interference-to-noise ratio γ _a,b of the received signal into the ACK frame each time. The source node will compare γ _a,b with the signal-to-interference-to-noise ratio threshold. Let Γ _L be represented as the first threshold, that is, the threshold at which the link is about to be disconnected, and Γ _H be represented as the second threshold, that is, the threshold with good enough link quality. When γ _a,b <Γ _L , it means that the link quality is very low and the link is about to be disconnected. At this time, u _a first adjusts the direction of beams b _{a and b} based on the location information provided by the previous ACK, and constructs a beam set from the adjacent beams of b _{a and b.} and added to TRN-T. Among them, TRN-T is a transmit beam training unit, which can be used to train transmit beams in different directions. Then TRN-T is appended to the data frame and sent to u _b . After u _b receives the data frame, it writes the signal-to-interference-to-noise ratio (SINR) measurement results in each direction into the BRP frame. The BRP frame is sent to u _a after the ACK frame. If there are one or more beam directions with SINR greater than Γ _H , then u _a selects the beam direction with the maximum SINR/> As a communications beam, continue transmitting data packets and exit beam tracking. If there is a beam pair whose SINR is greater than γ _a,b and all SINRs are less than Γ _H , it is considered that no better beam has been selected and this step continues. If all SINR values are less than γ _a,b , it is considered that the UAV communication link is about to be disconnected, and competition and reservation on the CCH will be resumed.

In one embodiment, the preset signal-to-interference-to-noise ratio threshold includes a first link threshold and a second link threshold; the source node compares the signal-to-interference-to-noise ratio with the preset signal-to-interference-to-noise ratio threshold, and based on the comparison result Adjust the direction of the receiving beam with the location information provided by the previous ACK and construct a beam set based on the adjacent beams of the receiving beam, including:

The source node compares the signal-to-interference-to-noise ratio with the pre-set signal-to-interference-to-noise ratio threshold. If the signal-to-interference and noise ratio is less than the first link threshold, it adjusts the direction of the receiving beam based on the location information provided by the previous ACK and adjusts the direction of the receiving beam according to the location information provided by the previous ACK. Adjacent beams construct a beam set.

In one embodiment, after receiving the BRP frame, the source node compares the signal-to-interference-to-noise ratio measurement results of beams in various directions, selects communication beams to transmit data packets based on the comparison results, and exits beam tracking, including:

After receiving the BRP frame, the source node compares the signal-to-interference-to-noise ratio measurement results of the beams in each direction. If the signal-to-interference-to-noise ratio measurement results in one or more beam directions are greater than the second link threshold, the source node selects the signal-to-interference-to-noise ratio. The maximum beam direction in the measurement results is used as the communication beam, continue to transmit data packets and exit beam tracking; if the signal-to-interference-noise ratio measurement result is greater than the signal-to-interference-noise ratio and all signal-to-interference-noise ratio measurement results are less than the second link threshold, it is considered that there is no choice. When reaching the required beam, continue this step; if all signal-to-interference-noise ratio measurement results are less than the signal-to-interference-noise ratio, it is considered that the UAV communication link will be disconnected and the drone will compete and reserve on the public control channel again.

In one embodiment, a binary exponential backoff mechanism is used to compete for the control channel, and the saturation throughput is calculated according to the two-dimensional Markov model, including:

Set the competition window of the competition control channel in the UAV network to _Wi = 2 ⁱ W ₀ ,i≤m, where _Wi represents the size of the i-th order competition window, m represents the maximum backoff order, and W ₀ represents the backoff process. The minimum contention window used;

During the backoff process, if the channel is idle for each time slot, the counter is decremented by 1; if the channel is detected to be busy, the counter stops and saves the remaining number of backoff time slots; when the control channel is idle again for DIFS, the counter is decreased by 1 for each idle time slot. , the counter continues to decrease by 1 from the last remaining number of time slots; when the counter value decreases to 0, the node sends the control frame RTS, assuming that the conditional probability of conflict between the control frame RTS is p, in the two-dimensional state (i, k) i represents the number of backoff levels, k represents the current value in the backoff counter, then the state transition probability is

According to the state transition probability, the steady-state probability of the two-dimensional Markov chain is set to

The steady-state probability is normalized, and based on the normalized steady-state probability, the node's sending probability at each moment is calculated as

Among them, p can be expressed as

p＝1-(1-τ) ^n-1

Then the total number of nodes is

Set the channel idle probability, successful transmission probability and transmission collision probability according to the node's transmission probability at each moment and the total number of nodes;

The mechanism of the dual-frequency cooperative MAC protocol is used to set the success time and conflict time of the control frame RTS transmission. The saturation throughput is calculated based on the channel idle probability, successful transmission probability and transmission collision probability, as well as the success time and conflict time of the control frame RTS transmission.

In one embodiment, the channel idle probability, successful transmission probability and transmission collision probability are set according to the transmission probability of the node at each moment and the total number of nodes, including:

The channel idle probability is set according to the node's transmission probability at each moment and the total number of nodes. The successful transmission probability and transmission collision probability are

p _idle = (1-τ) ⁿ

p _s =nτ(1-τ) ^n-1

p _c =1-p _idle -p _s

Among them, p _idle is the channel idle probability; p _s is the probability of successful transmission; p _c is the transmission collision probability.

In a specific embodiment, in a certain time slot of the control channel, the following three situations may occur: no node sends a packet, one and only one node sends a packet, and two or more nodes send a packet. For the three states of a time slot channel, p _idle is the channel idle probability; p _s is the probability of successful transmission; p _c is the transmission collision probability.

In one embodiment, the mechanism of the dual-frequency cooperative MAC protocol is used to set the success time and collision time of the control frame RTS transmission, according to the channel idle probability, the successful transmission probability and the transmission collision probability, and the success time and collision time of the control frame RTS transmission. The calculated saturation throughput includes:

The mechanism of the dual-frequency cooperative MAC protocol is used to set the success time and conflict time of the control frame RTS transmission as

Among them, T _s represents the success time of control frame RTS transmission, T _c represents the collision time of control frame RTS transmission, r _c is the transmission rate of the control channel, L _RTS , L _CTS and L _RES are RTS frame, CTS frame and RES respectively. The length of the frame, T _SIFS , T _DIFS and T _EIFS are the short frame time interval, distributed coordination inter-frame interval and error inter-frame interval respectively;

Based on the channel idle probability, successful transmission probability and transmission collision probability, as well as the success time and collision time of the control frame RTS transmission, the saturation throughput is calculated as

Among them, L _d is the total amount of data transmitted, T _switch represents the time to switch from an omnidirectional antenna transceiver to a directional antenna transceiver, and σ represents the length of one time slot.

In one embodiment, the spatial multiplexing coefficient represents the number of links that can be transmitted concurrently under the current network conditions; the number of concurrent links is modeled as the spatial multiplexing coefficient, and is then determined based on the location relationship of the nodes and the link relationship. The criterion solves the spatial reuse coefficient, and calculates the saturated throughput based on the solved spatial reuse coefficient, including:

Analyze the link relationships in the UAV network and obtain all links in the current network;

Determine the concurrency relationship between any two links according to the link relationship determination criteria, and solve all concurrent link sets based on the concurrency relationship of the links;

Traverse all concurrent link sets c _i and determine whether the length of c _i is equal to r. If equal, then c _i is the largest concurrent link set; if the length of c _i is less than r, determine whether each link l _j can be matched with c _i is concurrent; if all links are concurrent with c _i , then c _i is the maximum concurrent link set, which is saved to the set C of all maximum concurrent link sets; where r is the number of successful negotiations within a data transmission time; the maximum The length of each subset in the concurrent link set is the spatial multiplexing coefficient;

The concurrent link throughput is calculated based on the spatial reuse coefficient, and the saturated throughput of the UAV network is calculated using the throughput of all concurrent links.

In one embodiment, the concurrent link throughput is calculated based on the spatial reuse coefficient, including:

According to the spatial reuse coefficient, the concurrent link throughput is calculated as

Among them, ε _i represents the spatial multiplexing coefficient, i represents the link sequence number, L _d is the total amount of data transmitted, T = T _d + (ε _i -1)·T _neg , T _d is the spatial multiplexing capability and data The transmission time and T _neg are the successful negotiation times, and r _d represents the data channel transmission rate.

In one embodiment, the saturation throughput of the UAV network is calculated using the throughput of all concurrent links, including:

Using the throughput of all concurrent links, the saturated throughput of the UAV network is calculated as

Among them, ε _i represents the spatial reuse coefficient, i represents the link sequence number, C = {c ₁ , c ₂ ,..., c _C } represents the set of all maximum concurrent link sets, r _d represents the data channel transmission rate, p (ε _i ) represents the probability that the maximum concurrent link set with length ε _i appears.

It should be understood that although various steps in the flowchart of FIG. 1 are shown in sequence as indicated by arrows, these steps are not necessarily executed in the order indicated by arrows. Unless explicitly stated in this article, there is no strict order restriction on the execution of these steps, and these steps can be executed in other orders. Moreover, at least some of the steps in Figure 1 may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but may be executed at different times. The execution of these sub-steps or stages The sequence is not necessarily sequential, but may be performed in turn or alternately with other steps or sub-steps of other steps or at least part of the stages.

The technical features of the above embodiments can be combined in any way. To simplify the description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, all possible combinations should be used. It is considered to be within the scope of this manual.

The above-mentioned embodiments only express several implementation modes of the present application, and their descriptions are relatively specific and detailed, but they should not be understood as limiting the scope of the invention patent. It should be noted that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all fall within the protection scope of the present application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims (10)

1. A performance analysis method for dual-frequency cooperative MAC protocol for UAV networking, characterized in that the method includes: The nodes in the UAV network are respectively configured with omnidirectional antenna transceivers and directional antenna transceivers. The omnidirectional antenna transceiver works on a low-frequency channel, and the directional antenna transceiver works on a high-frequency channel; the low-frequency The channel is a control channel; the high-frequency channel is a data channel; the UAV network includes a pair of source nodes and destination nodes; The source node and the destination node perform data transmission according to the dual-frequency cooperative MAC protocol, and compare the successful reservation time of the control channel and the data transmission time of the data channel during the data transmission process. If the successful reservation time is not less than the data transmission time, duration, a binary exponential backoff mechanism is used to compete for the control channel, and the saturation throughput is calculated based on the two-dimensional Markov model; If the successful reservation duration is less than the data transmission duration, the number of concurrent links is modeled as a spatial multiplexing coefficient, and then the spatial multiplexing coefficient is solved according to the location relationship of the nodes and the link relationship determination criteria, and the spatial multiplexing coefficient is solved according to the solved The spatial reuse coefficient is calculated to obtain the saturated throughput; the saturated throughput is the performance analysis result of the dual-frequency cooperative MAC protocol. 2. The method according to claim 1, characterized in that the process of data transmission between the source node and the destination node according to the dual-frequency cooperative MAC protocol includes: The source node competes for the control channel through the binary exponential backoff mechanism. After the channel competition is successful, the destination node ID and the local location information of the source node are written into the RTS frame and sent to the destination node; The destination node calculates the receiving beam direction based on the local location information of the source node and checks the multi-beam network allocation vector of the corresponding beam in the neighbor information list to obtain the channel flag of the destination node; the source node ID, the local location information of the destination node and the channel flag is written into the CTS frame and sent to the source node; The source node calculates the receiving beam direction based on the local location information of the destination node and checks the multi-beam network allocation vector of the corresponding beam in the neighbor information list to obtain the channel flag of the source node; combine the local location information of the source node and the destination node's The local location information, data transmission time, and channel flag of the source node are written into the RES frame and broadcast to all other nodes in the UAV network; After receiving the RES frame, the destination node adjusts the receiving beam direction to receive the data frame, calculates the receiving power and interference power of the destination node during the reception process, and calculates the signal-to-interference-to-noise ratio at the destination node based on the receiving power and interference power. ;Write the signal-to-interference-to-noise ratio into the ACK frame and send it to the source node; The source node compares the signal-to-interference-to-noise ratio with the preset signal-to-interference-to-noise ratio threshold, adjusts the direction of the receiving beam based on the comparison result and the location information provided by the previous ACK, and constructs a beam set based on the adjacent beams of the receiving beam. The beam set is added to the transmit beam training unit, and then the transmit beam training unit is appended to the data frame and sent to the destination node; After receiving the data frame, the destination node writes the signal-to-interference-to-noise ratio measurement results of the beams in each direction into the BRP frame, and sends the BRP frame after the ACK frame to the source node; After receiving the BRP frame, the source node compares the signal-to-interference-to-noise ratio measurement results of the beams in each direction, selects the communication beam to transmit the data packet based on the comparison results, and exits beam tracking. 3. The method according to claim 2, wherein the preset signal-to-interference-to-noise ratio threshold includes a first link threshold and a second link threshold; the source node compares the signal-to-interference-to-noise ratio with the preset link threshold. Compare the signal-to-interference-to-noise ratio threshold, adjust the direction of the receiving beam based on the comparison result and the location information provided by the previous ACK, and construct a beam set based on the adjacent beams of the receiving beam, including: The source node compares the signal-to-interference-to-noise ratio with the preset signal-to-interference-to-noise ratio threshold. If the signal-to-interference and noise ratio is less than the first link threshold, it adjusts the direction of the receiving beam based on the location information provided by the previous ACK and adjusts the direction of the receiving beam according to the received signal. Adjacent beams of a beam construct a beam set. 4. The method according to claim 3, characterized in that, after receiving the BRP frame, the source node compares the signal-to-interference-noise ratio measurement results of the beams in each direction, selects the communication beam to transmit the data packet according to the comparison result and exits the beam tracking, include: After receiving the BRP frame, the source node compares the signal-to-interference-to-noise ratio measurement results of the beams in each direction. If the signal-to-interference-to-noise ratio measurement results in one or more beam directions are greater than the second link threshold, the source node selects the signal-to-interference-to-noise ratio. The maximum beam direction in the measurement results is used as the communication beam, continue to transmit data packets and exit beam tracking; if the signal-to-interference-noise ratio measurement result is greater than the signal-to-interference-noise ratio and all signal-to-interference-noise ratio measurement results are less than the second link threshold, it is considered that there is no choice. When reaching the required beam, continue this step; if all signal-to-interference-noise ratio measurement results are less than the signal-to-interference-noise ratio, it is considered that the UAV communication link will be disconnected and the drone will compete and reserve on the public control channel again. 5. The method according to claim 1, characterized in that a binary exponential backoff mechanism is used to compete for the control channel, and the saturation throughput is calculated according to the two-dimensional Markov model, including: Set the competition window of the competition control channel in the UAV network to _Wi = 2 ⁱ W ₀ ,i≤m, where _Wi represents the size of the i-th order competition window, m represents the maximum backoff order, and W ₀ represents the backoff process. The minimum contention window used; During the backoff process, if the channel is idle for each time slot, the counter is decremented by 1; if the channel is detected to be busy, the counter stops and saves the remaining number of backoff time slots; when the control channel is idle again for DIFS, the counter is decreased by 1 for each idle time slot. , the counter continues to decrease by 1 from the last remaining number of time slots; when the counter value decreases to 0, the node sends the control frame RTS, assuming that the conditional probability of conflict between the control frame RTS is p, in the two-dimensional state (i, k) i represents the number of backoff levels, k represents the current value in the backoff counter, then the state transition probability is According to the state transition probability, the steady-state probability of the two-dimensional Markov chain is set to The steady-state probability is normalized, and the sending probability of the node at each moment is calculated based on the normalized steady-state probability. Among them, p can be expressed as p＝1-(1-τ) ^n-1 Then the total number of nodes is Set the channel idle probability, successful transmission probability and transmission collision probability according to the node's transmission probability at each moment and the total number of nodes; The mechanism of the dual-frequency cooperative MAC protocol is used to set the success time and conflict time of the control frame RTS transmission. The saturation throughput is calculated based on the channel idle probability, successful transmission probability and transmission collision probability, as well as the success time and conflict time of the control frame RTS transmission. . 6. The method according to claim 5, wherein the channel idle probability, successful transmission probability and transmission collision probability are set according to the transmission probability of the node at each moment and the total number of nodes, including: The channel idle probability is set according to the transmission probability of the node at each moment and the total number of nodes. The successful transmission probability and transmission collision probability are p _idle = (1-τ) ⁿ p _s =nτ(1-τ) ^n-1 p _c =1-p _idle -p _s Among them, p _idle is the channel idle probability; p _s is the probability of successful transmission; p _c is the transmission collision probability. 7. The method according to claim 6, characterized in that, the mechanism of the dual-frequency cooperative MAC protocol is used to set the success time and collision time of the control frame RTS transmission, according to the channel idle probability, the successful transmission probability and the transmission collision probability and The saturation throughput is calculated from the success time and collision time of the control frame RTS transmission, including: The mechanism of the dual-frequency cooperative MAC protocol is used to set the success time and conflict time of the control frame RTS transmission as Among them, T _s represents the success time of control frame RTS transmission, T _c represents the collision time of control frame RTS transmission, r _c is the transmission rate of the control channel, L _RTS , L _CTS and L _RES are RTS frame, CTS frame and RES respectively. The length of the frame, T _SIFS , T _DIFS and T _EIFS are the short frame time interval, distributed coordination inter-frame interval and error inter-frame interval respectively; According to the channel idle probability, successful transmission probability and transmission collision probability, as well as the success time and collision time of the control frame RTS transmission, the saturation throughput is calculated as Among them, L _d is the total amount of data transmitted, T _switch represents the time to switch from an omnidirectional antenna transceiver to a directional antenna transceiver, and σ represents the length of one time slot. 8. The method according to claim 1, wherein the spatial multiplexing coefficient represents the number of links that can be transmitted concurrently under current network conditions; the number of concurrent links is modeled as a spatial multiplexing coefficient, and then The spatial reuse coefficient is solved according to the node position relationship and link relationship determination criteria, and the saturated throughput is calculated based on the solved spatial reuse coefficient, including: Analyze the link relationships in the UAV network and obtain all links in the current network; Determine the concurrency relationship between any two links according to the link relationship determination criteria, and solve all concurrent link sets based on the concurrency relationship of the links; Traverse all concurrent link sets c _i and determine whether the length of c _i is equal to r. If equal, then c _i is the largest concurrent link set; if the length of c _i is less than r, determine whether each link l _j can be matched with c _i is concurrent; if all links are concurrent with c _i , then c _i is the maximum concurrent link set, which is saved to the set C of all maximum concurrent link sets; where r is the number of successful negotiations within a data transmission time; so The length of each subset in the maximum concurrent link set is the spatial multiplexing coefficient; The concurrent link throughput is calculated based on the spatial reuse coefficient, and the saturated throughput of the UAV network is calculated using the throughput of all concurrent links. 9. The method according to claim 8, characterized in that calculating the concurrent link throughput according to the spatial multiplexing coefficient includes: According to the spatial reuse coefficient, the concurrent link throughput is calculated as Among them, ε _i represents the spatial multiplexing coefficient, i represents the link sequence number, L _d is the total amount of data transmitted, T = T _d + (ε _i -1)·T _neg , T _d is the spatial multiplexing capability and data The transmission time and T _neg are the successful negotiation times, and r _d represents the data channel transmission rate. 10. The method according to claim 8, characterized in that the saturation throughput of the UAV network is calculated using the throughput of all concurrent links, including: Using the throughput of all concurrent links, the saturated throughput of the UAV network is calculated as Among them, ε _i represents the spatial reuse coefficient, i represents the link sequence number, C = {c ₁ , c ₂ ,..., c _C } represents the set of all maximum concurrent link sets, r _d represents the data channel transmission rate, p (ε _i ) represents the probability that the maximum concurrent link set with length ε _i appears.