Cooperative channel access method

Abstract

The invention discloses a cooperative channel access method, which considers the conditions that a plurality of untrusted relay nodes exist at the same time and a non-collusion mode is adopted to eavesdrop an information source channel, and combines a cooperative interference mechanism to design a secure channel access method in a targeted manner. Based on the rational cooperation principle between the user pairs, the communication nodes located in the same alliance body can serve as relay nodes of the opposite side at the same time, the role diversity is increased, the same user pair can join multiple alliance bodies at the same time, and the space-time diversity and the relay diversity gain are fully utilized. For an overlapping alliance structure, in addition to detection of untrusted relays, further detection of alliance trusted relays is added, and by comparing and detecting expected revenue functions of different numbers of relay nodes, an optimal detection node and an optimal detection set are selected, so that unnecessary detection overhead is avoided to the greatest extent.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a collaborative channel access method of a mobile ad-hoc network based on dynamic alliance collaborative grouping. Background Art

[0002] For cooperative channel opportunistic scheduling in distributed networks, the research team has studied the channel perception access modeling and statistical optimization methods under the two relay point working modes of controlled and autonomous relay points. Among them, mathematical modeling is carried out based on the stopping optimization theory, and a method for full perception and access statistical decision of relay channels under the relay resource controlled mode is proposed. In view of the linear increase of the relay channel perception overhead in the controlled mode with the number of relay points, a study on the fully distributed channel perception access method under the relay resource autonomous mode is carried out, and a mathematical modeling method based on the double-order stopping optimization method is proposed. A fully distributed statistical decision optimization method of user channel competition perception and front-hop broadcast-multi-relay point distribution perception and back-hop forwarding is established, which has the statistical optimality of network throughput. However, for the scenario of untrusted relays, the existing research work is still in the primary stage. In the published papers, for the scenario with an untrusted relay, the cooperative interference assisted by the sink is combined with the cooperative channel opportunistic scheduling of multiple user pairs for the first time, and a secure channel opportunistic scheduling method is proposed, but it does not explain the scenario of multiple untrusted relays, and does not consider the mutual cooperation between user pairs, and the utilization of the cooperative gain of multiple relays is not sufficient.

[0003] It can be seen that the coordinated channel access opportunity scheduling method in the prior art has the following five defects:

[0004] 1. The cooperation willingness of user pairs is not taken into consideration. Studies that consider mutual collaboration are all conducted under the assumption that all user pairs are willing to cooperate. Studies that do not consider collaboration assume that all user pairs are uncooperative. There is a lack of analysis of user pairs’ motivations for collaboration, and the collaboration mechanism is inflexible and lacks adaptability to scenarios.

[0005] 2. The secure transmission under multiple untrusted relays is not considered. When multiple untrusted relays eavesdrop on the channel in a non-collusive manner, other physical layer security transmission methods need to be adopted to prevent untrusted relays from eavesdropping on the network.

[0006] 3. The impact of network mobility on the cooperative relationship between user pairs is not considered. When the cooperative benefits of user pairs are linked to the access transmission benefits, the cooperative relationship between user pairs is highly correlated with the network topology location. The cooperative relationship of mobile networks should take into account dynamic characteristics.

[0007] 4. The situation where a user pair can participate in multiple collaboration groups is not considered. When a user pair is limited to participating in only one alliance, the improvement of network benefits from collaboration is also limited, and the diversity gain of collaborative relay cannot be maximized.

[0008] 5. The formation rules of the distributed alliance structure are complex and require multiple iterations to achieve stability. The calculation complexity is high and the iterative calculation time is long. Summary of the invention

[0009] In view of the above problems, the present invention provides a cooperative channel access method for overcoming the above problems or at least partially solving the above problems.

[0010] The present invention provides the following scheme:

[0011] A collaborative channel access method, comprising:

[0012] For the t-th position synchronization period, determine a set K of user pairs sharing the current channel and a set L of untrusted relays;

[0013] All nodes set backoff time windows according to node IDs and broadcast location data packets in sequence according to the adaptive mechanism;

[0014] Initialize the overlapping alliance structure A cur ;

[0015] Calculate the average security throughput of the system And the individual utility of each user pair {v(A k ,A cur )} k＝1,...,K ;

[0016] For every user pair k∈K, every user pair j∈K and like Then calculate v(A k ,A c (k,j)) and v(A j ,A c (k,j)), update H→H∪(j,k)∪(k,j); H represents the set of all user pairs that have evaluated whether to establish a cooperative link;

[0017] Use the alliance formation rules to determine that the conditions for establishing cooperation are met, then update A c (k,j)→A cur Until all user pairs have no intention to cooperate and reach a stable overlapping alliance structure A cur =Aa f ;

[0018] According to the given stable alliance structure A f , calculate and obtain the first-level decision threshold vector System average security throughput And classification collection

[0019] All users compete, make decisions, and access according to the distributed optimal channel security opportunity access method;

[0020] After this round of synchronization cycle ends, if the network changes dynamically, the user pair set is updated and the next round of distance perception continues.

[0021] Preferably: the adaptive mechanism includes:

[0022] According to the node ID, set the backoff time window length of the node competing for the channel;

[0023] The user determines that the channel is idle within a δ time slot, and then sends a data packet with probability p1=1 after its backoff time ends;

[0024] If a collision occurs, the backoff time is reset after the collision ends, and a data packet is sent with probability p1=p1 / 2 after the second round of backoff time ends until the location information data packets of all nodes are sent.

[0025] Preferably, the setting of the backoff time window length for nodes competing for the channel includes: if there are K user pairs, that is, 2K nodes, then the backoff time of the i-th node is δ·i / (2K).

[0026] Preferably: Initialize the overlapping alliance structure A cur Including: At the beginning of the alliance formation, assuming that all user pairs do not cooperate, then

[0027] Preferably: Calculate the individual utility {v(A k ,A cur )} k＝1,...,K include:

[0028] For user pair i∈S l , given an overlapping alliance structure A cur =A, based on the optimal channel opportunity access method, the user's expectation of the amount of securely transmitted data for access benefits is E[Y k ], the expected time cost is E[T]; then its individual utility function is:

[0029]

[0030] Where: P0 represents the probability of the user successfully competing for the channel, and Respectively indicate that the corresponding channels belong to the classification set after successful competition User's expectation of revenue, represents the average security throughput of the optimal system, P1 represents the average probability that the winning user in the network chooses not to access the channel after successfully competing for the channel, I[τ] represents the condition, τ drepresents the channel coherence time, τ0 represents the average time of a single observation, τ J* Indicates the detection time, represents the number of the best trusted relay detection nodes J * And the corresponding profit function, Indicates the maximum eavesdropping rate.

[0031] Preferably, the average probability P1 of a winning user pair in the network choosing not to access the channel after successfully competing for the channel is expressed as:

[0032]

[0033] Where: represents the probability of giving up access in the secondary decision, is the probability of detecting a trusted relay in the alliance in the secondary decision, represents the probability of giving up access in the three-level decision, represents the direct channel SNRγ k The probability distribution function of .

[0034] Preferably: the first-level decision threshold vector It is expressed as:

[0035] For user pairs k=1,…,K, define the optimal decision-level threshold vector in Representation equation and The only solution of .

[0036] Preferably, the alliance formation rules include:

[0037] Given a coalition structure A b (k,j), we have If for alliance structure A c (k,j)=A b (k,j)? k ,A j}∪{A k ∪{s j ,d j},A j ∪{s k ,d k}}, the following conditions are met:

[0038] Condition 1: v(A k ,A c (k,j))≥v(A k ,A b (k,j)), v(A j ,A c (k,j))≥v(A j,A b (k,j))

[0039] Condition 2: v(A k ,A c (k,j))+v(A j ,A c (k,j))>v(A k ,A b (k,j))+v(A k ,A b (k,j)).

[0040] Then user pair k establishes a cooperative relationship with user pair j, and user pair k joins alliance A j , user j joins alliance A k ;

[0041] Given a coalition structure A c (k,j), there are {s k ,d k}∈A j ,{s j ,d j}∈A k , if for alliance structure A b (k,j)=A c (k,j)? k ,A j}∪{A k \{s j ,d j},A j \{s k ,d k}}, the following conditions are met:

[0042] Condition 1: v(A k ,A b (k,j))≥v(A k ,A c (k,j)), v(A j ,A b (k,j))≥v(A j ,A c (k,j));

[0043] Condition 2: v(A k ,A b (k,j))+v(A j ,A b (k,j))≥v(A k ,A c (k,j))+v(A k ,A c (k,j));.

[0044] Then user pair k breaks the cooperative relationship with user pair j, and user pair k leaves alliance A. j , user pair j leaves alliance A k .

[0045] Preferably: for a given set of user pairs K and a set of untrusted relays L, when the topological structure of all nodes remains unchanged, the operation of establishing or breaking cooperation is irreversible.

[0046] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0047] A collaborative channel access method provided in an embodiment of the present application takes into account the situation where multiple untrusted relay nodes exist at the same time and eavesdrop on the source channel in a non-collusive manner, and combines the collaborative interference mechanism to design a secure channel access method. Based on the principle of rational cooperation between user pairs, communication nodes in the same alliance can simultaneously serve as each other's relay nodes, increasing role diversity, and the same user pair can join multiple alliances at the same time, making full use of spatiotemporal diversity and relay diversity gain. For overlapping alliance structures, in addition to detecting untrusted relays, further detection of alliance trusted relays is added, and by comparing the expected benefit functions of detecting different numbers of relay nodes, the optimal detection nodes and detection sets are selected to avoid unnecessary detection overhead to the greatest extent. For a given network topology, in order to achieve a stable overlapping alliance structure, a rule for establishing / breaking cooperation is proposed, which has an irreversible property. When the topological structure remains unchanged, two user pairs that have established a cooperative relationship will no longer break the cooperative relationship, and vice versa, avoiding repeated calculations and iterations. Based on the alliance formation rule, a single-convergence dynamic alliance formation method is designed. All user pairs start from a single alliance that does not cooperate. After a round of evaluation on whether to establish a cooperative relationship, they can converge to a stable overlapping alliance structure. Taking the user pair's mobile cycle as the unit, a dynamic distributed optimal cooperative channel security access method with three stages is proposed, which includes node distance perception, dynamic overlapping alliance formation, and optimal channel security opportunity access. It can continuously maintain the optimal security access performance when the network changes dynamically.

[0048] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0050] Figure 1 is a flow chart of a collaborative channel access method provided by an embodiment of the present invention;

[0051] Figure 2 This is a diagram of an overlapping alliance collaboration network model for untrusted relay eavesdropping provided by an embodiment of the present invention;

[0052] Figure 3 is a schematic diagram of a stable alliance structure under an initial topology provided by an embodiment of the present invention;

[0053] Figure 4 is a schematic diagram of changes in a stable alliance structure after node movement provided by an embodiment of the present invention;

[0054] Figure 5 This is a comparison diagram of the impact of dynamic alliance formation on network performance provided by an embodiment of the present invention;

[0055] Figure 6 It is a comparison chart of gaming strategy performance under different coherence times provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0056] The technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all of the embodiments. Based on the embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0057] See also Figure 1 , a collaborative channel access method provided by an embodiment of the present invention, such as Figure 1 As shown, the method may include:

[0058] For the t-th position synchronization period, determine a set K of user pairs sharing the current channel and a set L of untrusted relays;

[0059] All nodes set a backoff time window according to the node ID, and broadcast the position data packet in sequence according to the adaptive mechanism; in specific implementation, the embodiment of the present application can provide a backoff time window length for setting the node contention channel according to the node ID;

[0060] The user determines that the channel is idle within a δ time slot, and then sends a data packet with probability p1=1 after its backoff time ends;

[0061] If a collision occurs, the backoff time is reset after the collision ends, and a data packet is sent with probability p1=p1 / 2 after the second round of backoff time ends until the location information data packets of all nodes are sent.

[0062] The setting of the backoff time window length for nodes competing for a channel includes: if there are K user pairs, that is, 2K nodes, then the backoff time of the i-th node is δ·i / (2K).

[0063] Initialize the overlapping alliance structure A cur ; When implementing, initialize the overlapping alliance structure A cur Including: At the beginning of the alliance formation, assuming that all user pairs do not cooperate, then H represents the set of all user pairs that have evaluated whether to establish a cooperative link.

[0064] Calculate the average security throughput of the system And the individual utility of each user pair {v(A k ,A cur )} k＝1,...,K ;

[0065] For every user pair j∈K and like Then calculate v(A k ,A c (k,j)) and v(A j ,A c (k,j)), update H→H∪(j,k)∪(k,j);

[0066] In specific implementation, the embodiment of the present application can provide a method for calculating the individual utility of each user pair.

[0067] {v(A k ,A cur )} k＝1,...,K include:

[0068] For user pair i∈S l , given an overlapping alliance structure A cur =A, based on the optimal channel opportunity access method, the user's expectation of the amount of securely transmitted data for access benefits is E[Y k ], the expected time cost is E[T]; then its individual utility function is:

[0069]

[0070] Where: P0 represents the probability of the user successfully competing for the channel, and Respectively indicate that the corresponding channels belong to the classification set after successful competition User's expectation of revenue, represents the average security throughput of the optimal system, P1 represents the average probability that the winning user in the network chooses not to access the channel after successfully competing for the channel, I[·] represents the condition, τ drepresents the channel coherence time, τ0 represents the average time of a single observation, Indicates the detection time, represents the number of the best trusted relay detection nodes J * And the corresponding profit function, Indicates the maximum eavesdropping rate.

[0071] , the average probability P1 of the winning user pair in the network choosing not to access the channel after successfully competing for the channel is expressed as:

[0072]

[0073] Where: represents the probability of giving up access in the secondary decision, is the probability of detecting a trusted relay in the alliance in the secondary decision, represents the probability of giving up access in the three-level decision, represents the direct channel SNRγ k The probability distribution function of .

[0074] Use the alliance formation rules to determine that the conditions for establishing cooperation are met, then update A c (k,j)→A cur Until all user pairs have no intention to cooperate and reach a stable overlapping alliance structure A cur =Aa f In specific implementation, the alliance formation rules provided by the embodiment of the present application include:

[0075] Given a coalition structure A b (k,j), we have If for alliance structure A c (k,j)=A b (k,j)? k ,A j}∪{A k ∪{s j ,d j},A j ∪{s k ,d k}}, the following conditions are met:

[0076] Condition 1: v(A k ,A c (k,j))≥v(A k ,A b (k,j)), v(A j ,A c (k,j))≥v(A j ,A b (k,j))

[0077] Condition 2: v(A k ,A c (k,j))+v(A j ,A c (k,j))>v(A k ,A b (k,j))+v(A k ,A b (k,j)).

[0078] Then user pair k establishes a cooperative relationship with user pair j, and user pair k joins alliance A j , user j joins alliance A k ;

[0079] Given a coalition structure A c (k,j), there are {s k ,d k}∈A j ,{s j ,d j}∈A k , if for alliance structure A b (k,j)=A c (k,j)? k ,A j}∪{A k \{s j ,d j},A j \{s k ,d k}}, the following conditions are met:

[0080] Condition 1: v(A k ,A b (k,j))≥v(A k ,A c (k,j)), v(A j ,A b (k,j))≥v(A j ,A c (k,j));

[0081] Condition 2: v(A k ,A b (k,j))+v(A j ,A b (k,j))≥v(A k ,A c (k,j))+v(A k ,A c (k,j));.

[0082] Then user pair k breaks the cooperative relationship with user pair j, and user pair k leaves alliance A.j , user pair j leaves alliance A k .

[0083] According to the given stable alliance structure A f , calculate and obtain the first-level decision threshold vector System average security throughput And classification collection In specific implementation, the embodiment of the present application can provide a first-level decision threshold vector It is expressed as:

[0084] For user pairs k=1,…,K, define the optimal decision-level threshold vector in Representation equation and The only solution of .

[0085] All users compete, make decisions, and access according to the distributed optimal channel security opportunity access method;

[0086] After this round of synchronization cycle ends, if the network changes dynamically, the user pair set is updated and the next round of distance perception continues.

[0087] The collaborative channel access method provided in the embodiment of the present application is aimed at the secure collaborative transmission communication scenario with multiple untrusted relays. In order to further improve the flexibility and efficiency of collaborative transmission, as a full combination, optimization and improvement of existing research technologies, the present invention is based on the theory of overlapping alliance formation. On the basis that a user pair can participate in multiple alliances, a mobile ad-hoc network collaborative channel access method based on dynamic alliance collaborative grouping is proposed in a multi-untrusted relay scenario. The specific technical route is to first design a distributed optimal channel security opportunity access multi-level decision method under a static overlapping alliance structure; then analyze the mapping relationship between the individual benefit function of each user pair and the average network security throughput under the multi-level decision method; then propose a distributed overlapping alliance game algorithm based on maximizing the individual benefits of user pairs and the overall network benefits, so as to obtain a stable overlapping alliance structure; finally, based on the overlapping alliance structure, the optimal distributed channel security opportunity access method suitable for the current network topology is obtained. Compared with the existing security access algorithm, the system average security throughput performance of the proposed method is verified by simulation.

[0088] The method provided in the embodiment of the present invention is described in detail below and its effect is verified.

[0089] Aiming at the scenario of secure cooperative transmission communication with multiple untrusted relays, a cooperative channel access method for mobile ad-hoc networks based on dynamic alliance cooperative grouping is proposed. Firstly, a distributed optimal channel security opportunity access multi-level decision method under a static overlapping alliance structure is designed; then, the mapping relationship between the individual benefit function of each user pair and the average network security throughput under the multi-level decision method is analyzed; then, a distributed overlapping alliance game algorithm based on maximizing the individual benefits of user pairs and the overall benefits of the network is proposed to obtain a stable overlapping alliance structure; finally, based on the overlapping alliance structure, the optimal distributed channel security opportunity access method suitable for the current network topology is obtained.

[0090] The overlapping alliance cooperation network model of untrusted relay eavesdropping considered by the present invention is as follows: Figure 2 As shown in Figure 1, a multi-user network with multiple untrusted relays is described. Consider a wireless cooperative communication network consisting of K source-destination user communication pairs and L untrusted relays, each of which is represented by the set K == {s1, d1, …, s K ,d K} and collection Indicates that s k and d k They represent the source and destination of the kth communication pair respectively.

[0091] To avoid ambiguity, in the subsequent description of the present invention, the communication pair k is equivalent to {s k ,d k}. All nodes are equipped with a single antenna and work in half-duplex mode, and the relay uses half-duplex AF mode. All user pairs share the same channel in a competitive manner. User pairs can form overlapping alliances to conduct collaborative communication, that is, they are mutually trusted relays. Dedicated untrusted relays are shared by all users and do not participate in the formation of alliances, but their continuous passive eavesdropping on the information of the winning source is one of the factors that cannot be ignored in the design of alliance formation and secure access methods. For the user pair set K =, the overlapping alliance structure is represented by S = {S1, S2, …, S |S|},S i Represents a single alliance. Users between alliances may overlap, that is, the same user pair can join multiple alliances. Considering the complexity of the overlapping alliance structure, in order to clearly represent the available relay set for each user pair, another representation of the overlapping alliance structure is defined, namely A={A1,…,A K}, where A k represents the set of all trusted relay nodes of user k, expressed as:

[0092]

[0093] Rayleigh fading is used to model the wireless channel.k To its destination k The direct channel SNR is expressed as Where D k Indicates k and d k The straight-line distance between them, α is the channel fading depth, h k is a small-scale fading parameter and its mean is Negative exponential random distribution, then γ k The mean is Negative exponential random distribution. For non-direct links, node u, The channel SNR between u≠v is expressed as:

[0094]

[0095] Among them, D u,v represents the distance between node u and node v, h u,v is a small-scale fading parameter and its mean is Negative exponential random distribution, then γ u,v The mean is Negative exponential random distribution, γ k The probability distribution function of γ u,v The probability distribution function of The method proposed in this invention is applicable to typical wireless channels such as Rice channel and Nakagami channel. Assume that all wireless channels are symmetric, that is, γ u,v =γ v,u . The channel coherence time is τ d .

[0096] based on Figure 2 The network model shown in the figure has a given overlapping alliance structure A = {A1,…,A K}, multiple users follow the following algorithm 1 to perform distributed channel security access.

[0097] Algorithm 1: Distributed Optimal Channel Security Opportunistic Access Method

[0098] Input: K, L, A,

[0099] At the beginning of each mini-slot δ, all sources send competing RTSs with probability p0;

[0100] For the nth successful channel contention, s k Win, D k Get the instantaneous SNRγ of the direct channel k (n) = γ, making first-level decisions;

[0101] If the user Then further judge; if Then d k Select DT access mechanism and send CTS, s k Then at the maximum achievable rate Access direct channel, duration τ d .

[0102] Otherwise, the user Then further judge, if Then d k Give up access and send CTS, and compete again in the next time slot.

[0103] if Then d k Select DT access mechanism and send CTS, s k Then at the maximum achievable rate Access direct channel, duration τ d .

[0104] Otherwise, d k Select to detect all untrusted relays and send CTS. L untrusted relays then reply RTS in turn. The detection time τ1 = τ C +L·τ R After that, k Get the SNRs of the cooperative two-hop link of the untrusted relay:

[0105]

[0106] Calculate the secure transmission rate of DT access and the secure transmission rate of the CJ access mechanism assisted by an untrusted relay make Make second-level decisions;

[0107] If the user Then, if Then d k Decide to stop and send CTS;

[0108] if Then d k Select DT access mechanism, s k After receiving CTS, the maximum achievable rate Access direct channel, duration τ d1 =τ d -τ1.

[0109] Otherwise, d k Select CJ access mechanism, s k After receiving CTS, the maximum achievable rate Access channel, duration τ d1 . First 1 / 2τ d1 In time, s k and d k Broadcast data and interference signals separately, and then 1 / 2τ d1 Time, untrusted relay Towards d k Amplifies and forwards the packets it receives.

[0110] Otherwise k Give up access and send CTS, and compete again in the next time slot. Then calculate the optimal number of trusted relay detection nodes J * , traverse J=1,…,|A k |, calculate the difference function like Then J * =J, end the traversal.

[0111] Otherwise, J * =|A k |. Calculation

[0112] if Then d k Select Stop and send CTS;

[0113] if Then d k Select DT access mechanism, s k After receiving CTS, the maximum achievable rate Access direct channel, duration τ d1 .

[0114] Otherwise, d k Select CJ access mechanism, s k After receiving CTS, the maximum achievable rate Access channel, duration τ d1 . First 1 / 2τ d1 In time, s k and d k Broadcast data and interference signals separately, and then 1 / 2τ d1 Time, untrusted relay Towards d k Amplifies and forwards the packets it receives.

[0115] if Then d k Give up access and send CTS, and compete again in the next time slot.

[0116] Otherwise k Select Probe J* Alliance trusted relays and send CTS, collection The trusted relays in the network then reply to RTS in turn, and the detection time τ J* =τ C +J * ·τ R After that, k Get the SNRs of the cooperative two-hop link of the trusted relay:

[0117]

[0118] Calculation of secure transmission rate of CJ access mechanism assisted by trusted relay Make third-level decisions.

[0119] if Then d k Select Stop and send CTS;

[0120] if Then d k Select DT access, k After receiving CTS, the maximum achievable rate Access direct channel, duration

[0121] Otherwise, d k Select CJ access mechanism, s k After receiving CTS, the maximum achievable rate Access channel, duration forward In time, s k and d k Broadcast data packets and interference respectively, then Time, untrusted / trusted relay Towards d k Amplifies and forwards the packets it receives.

[0122] Otherwise, d k Give up access and send CTS, and compete again in the next time slot.

[0123] After a single access is completed, the n+1th successful channel contention continues.

[0124] The successful channel competition described in Algorithm 1 is specifically described as follows: At the beginning of each competition mini-time slot, all sources independently send channel competition RTS packets with the same probability p0. If and only if there is only one source sending an RTS packet in the same mini-time slot, the source is the winning source and the channel competition is a successful channel competition. Each channel competition is independent, so the average time until a source succeeds in each channel competition is:

[0125]

[0126] where τ R Indicates the time to transmit the RTS packet, τ C represents the time for transmitting CTS packets, K represents the number of source-destination pairs, δ represents the duration of idle time slots, and the time when a conflict occurs can be τ R express.

[0127] The DT (direct connection) access mechanism described in Algorithm 1 is specifically described as follows. For the information source s k , which transmits the signal to the destination d via a direct link k , the secure transmission rate under direct channel transmission is:

[0128]

[0129] in is the achievable transmission rate of the direct link, is the maximum eavesdropping rate, let Indicates the maximum eavesdropping SNR of an untrusted relay.

[0130] The CJ (cooperative interference) access mechanism described in step 14 of Algorithm 1 is specifically described as follows: k Choose to use cooperative interference to k} to perform equal-length two-stage data transmission with the assistance of the cooperative interference transmission, and the safe transmission rate is:

[0131]

[0132] in, is the relay transmission rate.

[0133] is the maximum eavesdropping rate.

[0134] For optional relay collections Select relay node As the best relay, the maximum safe transmission rate and its corresponding achievable transmission rate and Can be expressed as:

[0135]

[0136] As described in Algorithm 1, calculate the optimal number of trusted relay detection nodes J * , specifically described as. For selecting the number of detection relays J≤|A k |, the corresponding detection relay set A is the trusted relay set of the alliance kMean SNR of intra-relay links The largest set of J federated trusted relays.

[0137] The difference function between detecting J trusted relays of the alliance and detecting J+1 trusted relays of the alliance, the profit function of detecting J relays is:

[0138]

[0139] in, Then the optimal number of trusted relay detection nodes J * And the corresponding profit function for:

[0140]

[0141] Input parameters described in Algorithm 1 The specific description is as follows. For a given user pair set K, an untrusted relay set L and an overlapping alliance structure A = {A1, A2, …, A K＝}=, the average safety throughput of the optimal system is the only solution that satisfies the following equation.

[0142]

[0143] in, The profit function for detecting all untrusted relays is For |A k |>0 non-single user pairs k, For |A k |=0 for single user pairs k,

[0144] Input parameters described in Algorithm 1 The specific description is as follows. For user pair k=1,…,K, define the optimal decision-making first-level threshold vector in Representation equation and The only solution of . Note that if There is no solution with γ>0, so let is the revenue function of direct channel access.

[0145] Input parameters described in Algorithm 1 The specific description is as follows. For a given user pair set K, an untrusted relay set L and an overlapping alliance structure A = {A1, A2, …, A K＝}}, users can classify k as follows.

[0146] For |A k |=0 single user pair, if

[0147] Then the user pair k belongs to the classification set

[0148] Otherwise, user k belongs to the classification set

[0149] For |A k |>0 alliance user pair k, belongs to the classification set

[0150] Based on the above optimal secure channel opportunity access method under a given overlapping alliance structure, and taking into account node mobility, the present invention proposes the following distributed optimal channel secure channel opportunity access method based on dynamic overlapping formation game.

[0151] Algorithm 2: Distributed optimal channel security opportunistic access method based on dynamic overlapping coalition formation game.

[0152] For the t-th position synchronization period, input the user pair set K and the untrusted relay set L that share the current channel;

[0153] In the distance perception phase, all nodes set backoff time windows according to their IDs and broadcast location data packets in sequence according to the adaptive mechanism.

[0154] Alliance formation phase, initialization

[0155] Calculate the average security throughput of the system Calculate the individual utility of each user pair {v(A k ,A cur )} k＝1,...,K ;

[0156] For each user pair k∈K, for each user pair j∈K and like Then calculate v(A k ,A c (k,j)), v(A j ,A c (k,j)), update H→H∪(j,k)∪(k,j);

[0157] If the conditions for establishing cooperation are met, update A c (k,j)→A cur Until all user pairs have no intention to cooperate. A stable overlapping alliance structure A is reached. cur =Aa f .

[0158] The optimal DCOS phase based on alliance, given a stable alliance structure A f , calculate the first-level decision threshold vector and the average safety throughput of the system Determine the classification set

[0159] All users compete, decide and access according to the distributed optimal channel security opportunity access method shown in Algorithm 1.

[0160] After this round of synchronization cycle ends, if the network changes dynamically, the user pair set is updated and the next round of distance perception continues.

[0161] The adaptive mechanism described in Algorithm 2 is specifically described as follows. First, according to the node ID, the length of the backoff time window for the node to compete for the channel is set. For example, if there are K user pairs, that is, 2K nodes, the backoff time of the i-th node is δ·i / (2K). Once the user detects that the channel is idle within a δ time slot, it will send a data packet with probability p1=1 after its backoff time ends. If a collision occurs, the backoff time will be reset after the collision ends, and the data packet will be sent with probability p1=p1 / 2 after the second round of backoff time ends, and so on, until the location information data packets of all nodes are sent.

[0162] Initialization described in Algorithm 2 The specific description is: At the beginning of the alliance formation, it is assumed that all user pairs are non-cooperative, and H represents the set of all user pairs that have evaluated whether to establish cooperative links.

[0163] The calculation of the individual utility {v(A k ,A cur )} k＝1,...,K , specifically described as. For user i∈S l , given an overlapping alliance structure A cur =A, based on the optimal channel opportunity access method of Algorithm 1, the user's expectation of the amount of securely transmitted data for access benefit is E[Y k ], the expected time cost is E[T]. Since only one user pair accesses the channel at a time, the time cost E[T] of all user pairs is the same. Then their individual utility function is:

[0164]

[0165] P0 represents the probability of the user successfully competing for the channel, expressed as:

[0166] P0=p0(1-p0) K-1 / K

[0167] and After the corresponding channel competition is successful, it belongs to the classification set The user's expectation of benefit, that is, the amount of securely transmitted data, can be expressed as:

[0168]

[0169] P1 is the average probability that the winning user pair in the network chooses not to access the channel after successfully competing for the channel, expressed as:

[0170]

[0171] in, is the probability of giving up access in the secondary decision, event It can be expressed as:

[0172]

[0173] is the probability of detecting a trusted relay in the alliance in the secondary decision, event It can be expressed as:

[0174]

[0175] is the probability of giving up access in the three-level decision, event It can be expressed as:

[0176]

[0177] The alliance formation rules in the alliance formation phase described in Algorithm 2 include two types: establishment and breaking. The specific description is as follows

[0178] Establishment: Given a coalition structure A b (k,j), we have If for alliance structure A c (k,j)=A b (k,j)? k ,A j}∪{A k ∪{s j ,d j},A j ∪{s k ,d k}}, the following conditions are met.

[0179] Condition 1: v(A k ,A c (k,j))≥v(A k ,A b (k,j)), v(A j,A c (k,j))≥v(A j ,A b (k,j))

[0180] Condition 2: v(A k ,A c (k,j))+v(A j ,A c (k,j))>v(A k ,A b (k,j))+v(A k ,A b (k,j)).

[0181] Then user pair k establishes a cooperative relationship with user pair j, that is, user pair k joins alliance A j , user j joins alliance A k .

[0182] Break: Given a coalition structure A c (k,j), there are {s k ,d k}∈A j ,{s j ,d j}∈A k , if for alliance structure A b (k,j)=A c (k,j)? k ,A j}∪{A k \{s j ,d j},A j \{s k ,d k}}, the following conditions are met:

[0183] Condition 1: v(A k ,A b (k,j))≥v(A k ,A c (k,j)), v(A j ,A b (k,j))≥v(A j ,A c (k,j));

[0184] Condition 2: v(A k ,A b (k,j))+v(A j ,A b (k,j))≥v(A k ,A c (k,j))+v(Ak ,A c (k,j));.

[0185] Then user pair k breaks the cooperative relationship with user pair j, that is, user pair k leaves alliance A j , user pair j leaves alliance A k .

[0186] The alliance formation rule has the following properties: for a given set of user pairs K and a set of untrusted relays L, when the topological structure of all nodes remains unchanged, the establishment / breaking of cooperation operations is irreversible, that is, once two nodes establish cooperation, they will not break it again, and vice versa.

[0187] Proof: According to the user's individual utility {v(A k ,A cur )} k＝1,...,K By definition, we can get that for individual average throughput, all user pairs share the same T. The revenue improvement of user pair k that establishes / breaks cooperation comes from Y k , that is, the improvement of its own transmission quality; at this time, the benefits of user pair i that does not participate in establishing / breaking cooperation are reduced, which is caused by the nature of channel competition. The increase in the access probability of individual user pairs leads to a decrease in the competition-access probability of other user pairs in the same time, and the time cost of a single access increases, which is equivalent to Y i If T increases, the benefits will decrease. Therefore, in the process of alliance formation, each change in the alliance structure will lead to an increase in benefits for users involved in the change of cooperative relationship, while other users will see a decrease in benefits at the same rate.

[0188] First, we analyze the reversibility of establishing cooperation. For user pair k, j, once they establish cooperation, the alliance structure A at this time b (k,j) and A c (k,j),A c (k, j) makes the individual average security throughput benefits of user k, j not decrease and at least one party's benefits increase. Obviously, when the other alliance structures remain unchanged, the establishment of cooperation is irreversible; when the cooperation relationship of other nodes except user k, j changes, the alliance structure becomes A', the individual average security throughput of user k, j decreases proportionally, but the Y brought by user k, j k and Y j The increment still exists, and no matter how the alliance structure is iterated, the average security throughput of the system will not decrease. b ′(k,j) and cooperative alliance structure A c′(k,j), the user can still obtain greater individual utility by cooperating with k and j, and the three conditions in Definition 6.4 are still satisfied, and the user will not break the cooperative relationship between k and j. Therefore, in the scenario of secure opportunistic access to distributed cooperative channels based on overlapping alliances mentioned in this chapter, the establishment of cooperative operation is irreversible. Similarly, the breaking of cooperative operation is also irreversible. The proof is complete.

[0189] The present invention has been rigorously simulated and tested, and relevant numerical simulations have been performed in MATLAB to analyze and evaluate the performance of the network. Consider a 5km×5km square map, in which 12 source-destination communication pairs are randomly deployed. Referring to the commonly used wireless communication scenarios, the channel fading depth is set to α=2.5.

[0190] For node u, u≠v,k∈K, the statistical parameters of the relay channel and the direct channel are set as The unit is dB, that is, for the same wireless transmission distance, the SNR of the relay channel is ρdB higher than that of the direct channel, which is conducive to the establishment of cooperative relationships between users and the formation of alliances, so that the simulation analysis results can more intuitively reflect the performance of the proposed method. Referring to the simulation parameter settings in 3.5, the coherence time for the channel state to remain unchanged under quasi-static fading is τ d =2ms, the length of an idle mini-slot is δ=25μs, and the transmission duration of RTS and CTS is τ R =τ C =50μs. In the alliance formation phase, the channel contention probability is p0=0.3.

[0191] First, the stability and reliability of the proposed distributed overlapping coalition game algorithm are verified. d =2ms, hour, Figure 3 The randomly generated node position topology and the corresponding stable alliance structure are given. The structure converges to stability after only one round of establishing cooperation, which verifies the irreversibility of the proposed establishment / breaking rules and makes the overlapping alliance formation algorithm easier to converge. Figure 3It can be seen that the formation of alliance cooperation relationship basically follows the principle of close distance, such as {3,7}, {6,8,10}, {1,2,9}. Some user pairs only form one alliance, such as user pairs 3,4,6,8,9,10,11, and some user pairs participate in multiple alliances, such as user pairs 1,2,7, and the remaining user pairs choose not to cooperate, such as user pairs 5,12. Specifically, user pairs 3 and 4 establish cooperation with user pair 7 at the same time, but they do not cooperate with each other; user pairs 1 and 2 form alliances {1,2,9} and {1,2,11} at the same time, but user pairs 9 and 11 do not cooperate with each other, which reflects the flexible reuse characteristics of overlapping alliances compared to non-overlapping alliances, and can make full use of the cooperation between user pairs to improve the overall transmission performance of the network.

[0192] Further considering the mobility characteristics of network nodes, Figure 3 The node topology shown is the initial position (the 0th move), and 8 random node moves are performed. The distance of each move is a random value between 0 and 0.5 m above and below the horizontal and vertical coordinates. The random value is generated by the rand function and obeys a uniform distribution. Once the node position exceeds the map range, its coordinates are taken as the maximum / minimum value of the map minus / plus 0.1. For example, for the updated coordinate points (2.7, 5.3) and (-0.2, 3.5), they are set to be equal to (2.7, 4.9) and (0.1, 3.5) respectively to adapt to the simulated map area.

[0193] Figure 4 The stable alliance structure after the 1st to 4th node movement is given. Figure 4 It can be seen that when the position of a node changes, its alliance cooperation relationship may change. For example, from the first move to the second move, the alliance relationship of user pairs 1, 2, 9, 11, and 12 remains unchanged, while the alliance cooperation relationship of other user pairs changes, and user pair 8 changes from a single alliance to a non-single alliance.

[0194] In addition, to further verify the adaptability of the proposed alliance formation algorithm to dynamic mobile network topology changes, Figure 5A line chart comparing the network performance under the single alliance and stable alliance structure after each node movement starting from the initial state is given. Since the node movement is random, the network channel state changes randomly, and the network throughput performance presents an irregular line with the increase in the number of movements. Specifically, for each iteration, the initial alliance structure is a full single alliance. After the alliance converges to stability, as described in Algorithm 1, the performance of all users competing for the channel with probability p0 = 0.3 corresponds to the "stable alliance structure" curve. It can be seen from the figure that compared with the full single alliance structure, the stable alliance structure formed by establishing a cooperative relationship operation can increase the average security throughput of the system by 45%-85%, verifying the effectiveness of the proposed method.

[0195] Table 1 Stable alliance structure under different network parameter settings

[0196]

[0197]

[0198] Finally, to further verify the performance of the proposed method and other game strategies, the average security throughput of the system under the proposed overlapping alliance strategy and other alliance game strategies is compared. Figure 6 The performance comparison curves of four strategies under two configurations are given. The proposed strategy refers to the situation where all user pairs compete with equal probability under a stable alliance, and perform channel security access according to Algorithm 1; non-overlapping alliance means that a user pair can only join one alliance, converge to stability under the alliance switching rule, and then perform the three-level optimal channel security access shown in Algorithm 1 based on the stable alliance structure; single alliance means that all user pairs do not cooperate and can only access the channel through direct connection or untrusted relay; large alliance means that all user pairs form a large alliance and can serve as relays for each other.

[0199] Figure 5 Given when τ d When the bandwidth changes from 1ms to 5ms, the average security throughput curves of the proposed original strategy and the four comparison strategies are shown in Figure 1. The solid line indicates the case of ρ = 5dB, and the dotted line indicates the case of ρ = 8dB. Figure 5It can be seen that the greater the difference ρ between the relay channel SNR and the direct channel SNR, the greater the performance difference between different comparison strategies. When ρ = 5dB, the performance of the proposed strategy, the large alliance strategy and the non-overlapping alliance strategy are very close. At this time, the security transmission performance gap between the relay link and the direct link is small, and the performance gain brought by the alliance collaboration is not obvious, resulting in a small performance gap between different collaboration methods. However, compared with the single alliance strategy, the improvement of the average security throughput of the system by the collaborative alliance strategy cannot be ignored. When ρ = 8dB, compared with the single alliance strategy, the collaborative alliance strategy can significantly improve the security transmission performance of the system. Among them, the performance improvement of the non-overlapping alliance strategy comes from the improvement of alliance collaboration from 0 to 1; compared with the non-overlapping alliance strategy, the performance improvement of the proposed strategy comes from the reusability of the node alliance, which further improves the relay diversity gain.

[0200] When ρ = 5dB, the average security throughput performance of the proposed strategy is basically the same as that of the grand coalition strategy. d When τ is smaller, the performance of the proposed strategy is slightly higher. d When ρ is larger, the performance of the grand coalition strategy is slightly higher. When ρ = 8dB, the performance of the two strategies is basically the same. It can be concluded that the proposed optimal channel security opportunity access method based on overlapping coalition formation takes the rational cooperation between user pairs as the starting point, maximizes the multi-relay diversity gain of user pairs as mutual relays, maximizes the average security throughput of the system, and can achieve network performance close to the ideal grand coalition strategy, achieving a win-win situation for individual user benefits and overall network benefits.

[0201] It can be seen that the cooperative channel access method provided in the embodiment of the present application studies the distributed channel security opportunity scheduling problem for the reuse of alliance user nodes for a wireless cooperative transmission network with multiple user pairs and untrusted relays. The rational cooperative security access between user pairs is modeled as an optimal channel security opportunity access problem based on the overlapping alliance formation game.

[0202] For a given overlapping alliance structure, with the goal of maximizing the average security throughput of the system, a distributed optimal channel security opportunistic access algorithm with three-level stop based on the alliance structure is designed; the eavesdropping-transmission duality of untrusted relays and the rational cooperation gain of alliance trusted relays are fully utilized;

[0203] Based on the distributed optimal channel secure opportunistic access algorithm, the individual utility function of each user pair under this method is defined as the expected average secure access throughput of the user pair, and the expression of the individual utility function is derived to quantify the rational collaboration motivation of the user pairs.

[0204] Combined with the individual utility functions of user pairs, an irreversible alliance cooperation establishment / breaking rule is proposed. When the topological structure remains unchanged, two user pairs that have established a cooperative relationship will no longer break the cooperative relationship, and vice versa. Based on the alliance formation rule, a dynamic overlapping alliance formation algorithm is designed, which allows user pairs to form alliances in a distributed manner and converge to a stable alliance structure after one round of iteration without multiple repeated iterations.

[0205] For the proposed dynamic overlapping alliance formation algorithm, a historical set is defined. After each user pair evaluates whether to establish a cooperative relationship with another user pair, the link between the two user pairs is added to the historical set regardless of whether the cooperative relationship is established. For the subsequent alliance establishment of user pairs, it is first determined whether it belongs to the historical set. If it does, it means that the evaluation of establishing a cooperative relationship has been carried out and there is no need to repeat the calculation.

[0206] For dynamic mobile networks, an adaptive backoff broadcast algorithm based on node ID is designed. The backoff time is associated with the channel conditions of the user pair, so that users with good channel conditions can access the channel first. User pairs with different channel conditions have different backoff times, so there will be no collision of broadcast data packets. For very few user pairs with basically equal channel conditions, when a broadcast data packet conflict occurs, the user pair dynamically adjusts the contention probability to reduce the conflict probability of the next competition. Under this method, all user pairs can achieve full network synchronization of location information with a shorter time overhead.

[0207] Combining the overlapping coalition game, optimal access theory and the sink-assisted collaborative interference mechanism, a dynamic distributed optimal collaborative channel security access method with three stages, namely node distance perception - dynamic overlapping coalition formation - optimal channel security opportunity access, is proposed. It has good adaptability to mobile networks and can always maintain the optimal overlapping coalition structure under dynamic changes in network topology, thereby achieving the optimal system security transmission throughput.

[0208] In summary, the collaborative channel access method provided by the present application takes into account the situation where multiple untrusted relay nodes exist at the same time and eavesdrop on the source channel in a non-collusive manner, and combines the collaborative interference mechanism to design a secure channel access method. Based on the principle of rational cooperation between user pairs, communication nodes in the same alliance can simultaneously serve as each other's relay nodes, increasing role diversity, and the same user pair can join multiple alliances at the same time, making full use of spatiotemporal diversity and relay diversity gain. For overlapping alliance structures, in addition to detecting untrusted relays, further detection of alliance trusted relays is added, and by comparing the expected benefit functions of detecting different numbers of relay nodes, the optimal detection nodes and detection sets are selected to avoid unnecessary detection overhead to the greatest extent. For a given network topology, in order to achieve a stable overlapping alliance structure, a rule for establishing / breaking cooperation is proposed, which has an irreversible property. When the topological structure remains unchanged, two user pairs that have established a cooperative relationship will no longer break the cooperative relationship, and vice versa, avoiding repeated calculations and iterations. Based on the alliance formation rule, a single-convergence dynamic alliance formation method is designed. All user pairs start from a single alliance that does not cooperate. After a round of evaluation on whether to establish a cooperative relationship, they can converge to a stable overlapping alliance structure. Taking the user pair's mobile cycle as the unit, a dynamic distributed optimal cooperative channel security access method with three stages is proposed, which includes node distance perception, dynamic overlapping alliance formation, and optimal channel security opportunity access. It can continuously maintain the optimal security access performance when the network changes dynamically.

[0209] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0210] It can be known from the description of the above implementation methods that those skilled in the art can clearly understand that the present application can be implemented by means of software plus a necessary general hardware platform. Based on such an understanding, the technical solution of the present application can be essentially or partly embodied in the form of a software product that contributes to the prior art. The computer software product can be stored in a storage medium such as ROM / RAM, a magnetic disk, an optical disk, etc., and includes several instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in the various embodiments of the present application or certain parts of the embodiments.

[0211] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can refer to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment. The system and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without creative work.

[0212] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A collaborative channel access method, characterized in that: include: For the t-th position synchronization period, determine a set K of user pairs sharing the current channel and a set L of untrusted relays; All nodes set backoff time windows according to node IDs and broadcast location data packets in sequence according to the adaptive mechanism; Initialize the overlapping alliance structure A cur ; Calculate the average security throughput of the system And the individual utility of each user pair {v(A k ,A cur )} k＝1,...,K ; For every user pair k∈K, every user pair j∈K and like Then calculate v(A k ,A c (k,j)) and v(A j ,A c (k,j)), update H→H∪(j,k)∪(k,j); H represents the set of all user pairs that have evaluated whether to establish a cooperative link; Use the alliance formation rules to determine that the conditions for establishing cooperation are met, then update A c (k,j)→A cur Until all user pairs have no intention to cooperate and reach a stable overlapping alliance structure A cur =Aa f ; According to the given stable alliance structure A f , calculate and obtain the first-level decision threshold vector System average security throughput And classification collection All users compete, make decisions, and access according to the distributed optimal channel security opportunity access method; After this round of synchronization cycle ends, if the network changes dynamically, the user pair set is updated and the next round of distance perception continues.

2. The collaborative channel access method according to claim 1, characterized in that: The adaptive mechanism includes: According to the node ID, set the backoff time window length of the node competing for the channel; The user determines that the channel is idle within a δ time slot, and then sends a data packet with probability p1=1 after its backoff time ends; If a collision occurs, the backoff time is reset after the collision ends, and a data packet is sent with probability p1=p1 / 2 after the second round of backoff time ends until the location information data packets of all nodes are sent.

3. The collaborative channel access method according to claim 2, characterized in that: The setting of the backoff time window length for nodes competing for a channel includes: if there are K user pairs, that is, 2K nodes, then the backoff time of the i-th node is δ·i / (2K).

4. The collaborative channel access method according to claim 1, characterized in that: Initialize the overlapping alliance structure A cur Including: At the beginning of the alliance formation, assuming that all user pairs do not cooperate, then 5. The collaborative channel access method according to claim 1, characterized in that: Calculate the individual utility of each user pair {v(A k ,A cur )} k＝1,...,K include: For user pair i∈S l , given an overlapping alliance structure A cur =A, based on the optimal channel opportunity access method, the user's expectation of the amount of securely transmitted data for access benefits is E[Y k ], the expected time cost is E[T]; then its individual utility function is: Where: P0 represents the probability of the user successfully competing for the channel, and Respectively indicate that the corresponding channels belong to the classification set after successful competition User's expectation of revenue, represents the average security throughput of the optimal system, P1 represents the average probability that the winning user in the network chooses not to access the channel after successfully competing for the channel, I[τ] represents the condition, τ d represents the channel coherence time, τ0 represents the average time of a single observation, Indicates the detection time, represents the number of the best trusted relay detection nodes J * And the corresponding profit function, Indicates the maximum eavesdropping rate.

6. The collaborative channel access method according to claim 5, characterized in that: The average probability P1 of the winning user pair in the network choosing not to access the channel after successfully competing for the channel is expressed as: Where: represents the probability of giving up access in the secondary decision, is the probability of detecting a trusted relay in the alliance in the secondary decision, represents the probability of giving up access in the three-level decision, represents the direct channel SNRγ k The probability distribution function of .

7. The collaborative channel access method according to claim 1, characterized in that: First-level decision threshold vector It is expressed as: For user pairs k=1,…,K, define the optimal decision-level threshold vector in Representation equation and The only solution of .

8. The collaborative channel access method according to claim 1, characterized in that: The alliance formation rules include: Given a coalition structure A b (k,j), we have If for alliance structure A c (k,j)=A b (k,j)? k ,A j }∪{A k ∪{s j ,d j },A j ∪{s k ,d k }}, the following conditions are met: Condition 1: v(A k ,A c (k,j)) ≥ v(A k ,A b (k,j)), v(A j ,A c (k,j)) ≥ v(A j ,A b (k,j)); Condition 2: v(A k ,A c (k,j)) + v(A j ,A c (k,j)) > v(A k ,A b (k,j)) + v(A k ,A b (k,j)); Then user pair k establishes a cooperative relationship with user pair j, and user pair k joins alliance A j , user j joins alliance A k ; Given a coalition structure A c (k,j), there are {s k ,d k }∈A j ,{s j ,d j }∈A k ; If for alliance structure A b (k,j)=A c (k,j)? k ,A j }∪{A k \{s j ,d j },A j \{s k ,d k }}, the following conditions are met: Condition 1: v(A k ,A b (k,j)) ≥ v(A k ,A c (k,j)), v(A j ,A b (k,j)) ≥ v(A j ,A c (k,j)); Condition 2: v(A k ,A b (k,j)) + v(A j ,A b (k,j)) ≥ v(A k ,A c (k,j)) + v(A k ,A c (k,j)); Then user pair k breaks the cooperative relationship with user pair j, and user pair k leaves alliance A. j , user pair j leaves alliance A k .

9. The collaborative channel access method according to claim 8, characterized in that: For a given set of user pairs K and a set of untrusted relays L, when the topology of all nodes remains unchanged, the operation of establishing or breaking cooperation is irreversible.

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