Adaptive competition probability optimization method

Abstract

The invention discloses a self-adaptive competition probability optimization method, which is characterized in that user pairs are divided into effective competition user pairs and invalid competition user pairs on the basis of expected benefits of the user pairs, so that the invalid competition user pairs are kept silent in a competition stage, and invalid competition overhead is avoided; for effective competition user pairs, an approximate analytic expression of the optimal competition probability is deduced, the time overhead of successful competition of a channel is reduced, the calculation complexity is extremely low, invalid / effective competition and the trust relationship of the user pairs are decoupled, and when the invalid competition user pairs are kept silent in the competition stage, the transmission of other user pairs can still be assisted, and the transmission performance is improved. If the network is dynamically changed, the user pair is switched between the valid state and the invalid state, and the method is still applicable.

Description

Technical Field

[0001] The present invention relates to the field of network protocol and physical layer security technology in wireless communication technology, and in particular to an adaptive competition probability optimization method based on user profit prediction. Background Art

[0002] The shared channel competitive access method in the distributed network in the prior art usually adopts multi-user channel access in homogeneous and heterogeneous networks to realize relay selective detection and optimal channel access with a two-level pure threshold structure to maximize the average throughput of the system. Among them, both levels of thresholds can be calculated offline through the statistical information of the network channel, but this method is only for the scenario where the relay is trusted, and only considers the auxiliary transmission of the dedicated relay. For the scenario where the relay is untrustworthy, the existing research work is still in the early stage.

[0003] In the existing published papers, for the scenario with an untrusted relay, the sink-assisted collaborative interference was combined with the cooperative channel opportunity scheduling of multiple user pairs for the first time, and a secure channel opportunity scheduling method was proposed. However, it did not explain the scenario of multiple untrusted relays, and did not consider the trust relationship between user pairs, lacking effective utilization of trusted cooperative transmission of multiple user pairs.

[0004] In addition, similar studies mentioned above all adopted the CSMA / CA mechanism for channel competition. However, they only optimized the access decision method of users after successful competition under the assumption that all users compete for the channel with the same probability. There was a lack of optimization of the competition itself, resulting in a large number of invalid competitions, large channel competition overhead, and limited overall system performance.

[0005] It can be seen that the shared channel contention access method in the distributed network in the prior art has the following three defects:

[0006] 1. It does not take into account the potential social relationships within the network. Based on the access trust, there may be further collaborative trust relationships between user pairs.

[0007] 2. The individual benefits of users in a fair competition network are not analyzed, resulting in some users with poor transmission performance wasting channel resources.

[0008] 3. Failure to consider the optimization of contention probability results in excessive competition overhead for too many users, and some users with poor channel conditions give up access after successfully competing, resulting in ineffective contention not being effectively controlled. Summary of the invention

[0009] In view of the above problems, the present invention provides an adaptive contention probability optimization method for overcoming the above problems or at least partially solving the above problems. The method is used for probability optimization of random contention in a heterogeneous wireless cooperative network composed of multiple source-destination pairs and multiple untrusted relays.

[0010] The present invention provides the following scheme:

[0011] An adaptive competition probability optimization method, comprising:

[0012] For multiple source-destination pairs (user pair set ) and multiple untrusted relays (untrusted relay collection ), when the social trust relationship between the user pairs is The initial competition probability is, including the set of user pairs Untrusted Relay Collection And the sending probability p 0 , calculate all user pairs included in the user pair set with the sending probability p 0 When competing for access to the channel, the expected benefit Y provided to the system transmission throughput k / T,k=1,2,...,K;The expected return Y k / T,k=1,2,...,K includes the expected transmission amount Y of the user k The ratio of time cost T;

[0013] Using the expected return Y k / T, k = 1, 2, ..., K and the effective revenue threshold ζ divide the user pairs into a set of effective competing user pairs and a set of invalid competing user pairs;

[0014] Calculate the optimal competition probability p of all the valid competing user pairs * , and calculate the first-level decision threshold vector for all the valid competing users to compete for the channel and make access decisions The optimal system security throughput of all the valid competing users on the competing channel and a user pair classification set of only all the valid competing user pairs Then compete and access the channel using the following channel contention-three-level decision access method:

[0015] At the beginning of each mini-slot δ, the signal sources s of all the valid competing user pairs are k With the optimal competition probability p * Send a competing RTS data packet, and all the invalid competing user pairs remain silent; when there is only one source sending RTS, the source wins the channel transmission opportunity.

[0016] For the nth successful channel contention, the source s k Win, Xinsu k Get the instantaneous signal-to-noise ratio γ of the direct channel k (n) = γ, making first-level decisions;

[0017] Determine the user if Then the destination k Select the direct connection mechanism and send a CTS packet. k Then at the maximum achievable rate Access direct channel, duration τ d ; Otherwise, the destination k Give up access and send a CTS packet, and compete again in the next time slot;

[0018] Determine the user if Then the destination k Give up access and send CTS data packet, compete again in the next time slot. Then the destination k Select the direct connection mechanism and send a CTS packet. k At the maximum achievable rate Access direct channel, duration τ d ;

[0019] Otherwise, the destination d k Select to detect all untrusted relays and send CTS packets. L untrusted relays then reply with RTS packets in turn. The detection time is τ L =τ C +L·τ R After that, the destination k Get the signal-to-noise ratio of the cooperative two-hop link of the untrusted relay, Calculate the safe transmission rate for direct access The secure transmission rate of relay-assisted and cooperative interference access mechanisms under the assistance of untrusted relays make Make second-level decisions;

[0020] Determine the user calculate If the user or if Destination k Stop and send CTS packets, select between direct connection, relay assistance and cooperative interference, and access the channel with a higher security transmission rate. Duration Otherwise, the destination kGive up access and send a CTS packet, and compete again in the next time slot;

[0021] Destination k Select Probe J * Collaborative trusted relays and send CTS packets, trusted relay set The trusted relays in the network reply to the RTS packets in turn to detect the time After that, the destination k Obtaining the signal-to-noise ratio of a cooperative two-hop link with a trusted relay Calculate the secure transmission rate of relay-assisted and cooperative interference access mechanisms under the assistance of trusted relays Make third-level decisions;

[0022] Sure Destination k Choose to stop and send CTS packets, and select a method with a higher secure transmission rate to access among direct connection, relay-assisted empty cooperative interference under untrusted relay assistance, and relay-assisted and cooperative interference under cooperative trusted relay assistance. Duration

[0023] Otherwise, the destination d k Give up access and send a CTS packet, and compete again in the next time slot;

[0024] After a single access is completed, the n+1th successful channel contention continues.

[0025] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0026] An adaptive competition probability optimization method provided by an embodiment of the present invention takes into account the multi-level trust relationship between user pairs and between user pairs and relays, and further optimizes performance based on the current optimal three-level decision access method. An algorithm for predicting the expected benefits of user pairs under a given access equal probability-three-level access decision is proposed. Based on the access decision parameters, channel random samples can be generated according to the statistical characteristics of the network, and the expected benefits of user pairs can be calculated offline by Monte Carlo. Based on the expected benefits of user pairs, user pairs are divided into effective competition user pairs and invalid competition user pairs, so that invalid competition user pairs remain silent during the competition stage, avoiding invalid competition overhead; for effective competition user pairs, an approximate analytical expression of the optimal competition probability is derived, which reduces the time overhead of successful channel competition, and has extremely low computational complexity. The invalid / effective competition is decoupled from the trust relationship of user pairs. When the invalid competition user pairs remain silent during the competition stage, they can still assist other user pairs in transmission and improve transmission performance. If the network changes dynamically and the user pairs switch between effective and invalid, the proposed method can still be applied.

[0027] 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

[0028] 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.

[0029] Figure 1 is a flowchart of calculating expected benefits for users provided by an embodiment of the present invention;

[0030] Figure 2 is a schematic diagram of a three-level social trust network model provided by an embodiment of the present invention;

[0031] Figure 3 It is a comparison diagram of the primary decision-making benefit function relationship provided by an embodiment of the present invention;

[0032] Figure 4 It is a schematic diagram of user pairs and relay location distribution and collaborative trust network provided by an embodiment of the present invention;

[0033] Figure 5 is a curve diagram showing a change in the average security throughput of the system as a function of the SNR of the direct channel provided by an embodiment of the present invention;

[0034] Figure 6 It is a curve diagram showing the variation of the average security throughput of the system with the SNR of the relay channel provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0035] 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.

[0036] An embodiment of the present invention provides an adaptive contention probability optimization method, which may include:

[0037] Identifying social trust networks Included user pairs collection Untrusted Relay Collection And the sending probability p 0 , the social trust network It includes establishing a heterogeneous wireless collaborative network consisting of multiple information source and information sink pairs with three-level trust relationships;

[0038] Calculate all user pairs included in the user pair set with the sending probability p 0 When competing for access to the channel, the expected benefit Y provided to the system transmission throughput k / T,k=1,2,...,K;The expected return Y k / T,k=1,2,...,K includes the expected transmission amount Y of the user k The ratio of time cost T;

[0039] For specific implementation, see Figure 1 The embodiment of the present invention can provide a method for predicting the expected revenue, including:

[0040] Based on a given collaborative trust network According to the statistical characteristic parameters of the distributed wireless network channel, N is generated for each channel. e random SNR samples, calculate the first-level decision threshold vector for all users to compete for the channel and make access decisions Optimal system security throughput for all users on the contention channel and the user pair classification set of all user pairs competing for the channel Go to step 2;

[0041] Step 2: Initialize the number of accesses n = 1, the user pair sequence number k = 1, and the user pair expected transmission volume Y k =0 and time cost T=0;

[0042] Step 3: For user pair k, take the nth group of channel signal-to-noise ratios. If user pair Then go to step 4; otherwise Go to step 5;

[0043] Step 4: If Then the destination k The direct connection mechanism will be selected and CTS packets will be sent. The expected transmission volume is Update T=T+τ 0 +τ d ; Otherwise, the destination k Will choose to give up access and send CTS data packet, Y k No change, update T = T + τ 0 , go to step 10;

[0044] Step 5: If Then the destination k Will choose to give up access and send CTS data packet, Y k No change, update T = T + τ 0 , go to step 10; if Then the destinationk The direct connection mechanism will be selected and a CTS packet will be sent to update T=T+τ 0 +τ d , go to step 10; otherwise, the destination d k Select Detect untrusted relays and go to step 6;

[0045] Step 6: If the user Go to step 7, otherwise the user Go to step 8;

[0046] Step 7: OK if Then the destination k Select access and send CTS data packets. The expected transmission volume is renew T=T+τ 0 +τ d ; Otherwise, the destination k Will choose to give up access and send CTS data packet, Y k No change, update T = T + τ 0 +τ L ; Go to step 10;

[0047] Step 8: Calculate the benefit of detecting cooperative trust relays if Return to step 7; otherwise, k Select Detect Collaborative Trusted Relay and go to step 9;

[0048] Step 9: Compare The size of Then the destination k Select access and send CTS data packets. The expected transmission volume is renew T=T+τ 0 +τ d ; Otherwise, the destination k Choose to give up access and send CTS data packet, Y k Unchanged, updated Go to step 10;

[0049] Step 10: If k=K, go to step 11; otherwise, k=k+1, return to step 3;

[0050] Step 11: If n = N e , then output the user's benefit Y k / T, k=1,2,...,K; otherwise, n=n+1, k=1, return to step 3.

[0051] The optimal system average security throughput of all users competing for the channel It is defined as the unique solution that satisfies the following equation:

[0052]

[0053] Where: K represents the number of source and sink pairs, τ d represents the channel coherence time, represents the safe transmission rate under direct channel transmission, n represents the number of observations, represents the expected revenue function of all untrusted relays, γ represents the signal-to-noise ratio, and τ 0 Represents the average time of a single observation.

[0054] The optimal decision-level threshold vector for all users to compete for the channel and make access decisions Defined as:

[0055] Distribution as equation and The only solution of There is no solution with γ>0, so let

[0056] The user pair classification set of all user pairs competing for the channel Defined as:

[0057] For a given set of users Untrusted Relay Collection and social trust networks The user classifies k as follows:

[0058] If |A k |=0, Then the user has a first-level decision structure for k, which belongs to the classification set

[0059]

[0060] If |A k |=0, Then the user has a secondary decision structure for k, belonging to the classification set

[0061]

[0062] If |A k |>0, Then the user has a first-level decision structure for k, which belongs to the classification set

[0063]

[0064] If |A k|>0, Then the user has a three-level decision structure for k, which belongs to the classification set

[0065]

[0066] Using the expected return Y k / T, k = 1, 2, ..., K and the effective revenue threshold ζ divide the user pairs into a set of effective competing user pairs and a set of invalid competing user pairs;

[0067] Calculate the optimal competition probability p of all the valid competing user pairs * , and calculate the first-level decision threshold vector for all the valid competing users to compete for the channel and make access decisions The optimal system security throughput of all the valid competing users on the competing channel and a user pair classification set of only all the valid competing user pairs

[0068] At the beginning of each mini-slot δ, the signal sources s of all the valid competing user pairs are k With the optimal competition probability p * Send a contention RTS data packet, and all the invalid contention users remain silent;

[0069] For the nth successful channel contention, the source s k Win, Xinsu k Get the instantaneous signal-to-noise ratio γ of the direct channel k (n) = γ, making first-level decisions;

[0070] Determine the user if Then the destination k Select the direct connection mechanism and send a CTS packet. k Then at the maximum achievable rate Access direct channel, duration τ d ; Otherwise, the destination k Give up access and send CTS data packets, and compete again in the next time slot; in specific implementation, the embodiment of the present invention can provide a source s k Maximum achievable rate It is expressed by the following formula:

[0071]

[0072] Where: γ k represents the signal-to-noise ratio of the direct channel, D k Indicates k and d kThe straight-line distance between them, α represents the channel fading depth, h k represents the small-scale fading parameter and its mean is A negative exponential random distribution.

[0073] Determine the user if Then the destination k Give up access and send CTS data packet, compete again in the next time slot. Then the destination k Select the direct connection mechanism and send a CTS packet. k At the maximum achievable rate Access direct channel, duration τ d ;

[0074] Otherwise, the destination d k Select to detect all untrusted relays and send CTS packets. L untrusted relays then reply with RTS packets in turn. The detection time is τ L =τ C +L·τ R After that, the destination k Get the signal-to-noise ratio s of the cooperative two-hop link of the untrusted relay, Calculate the safe transmission rate for direct access The secure transmission rate of relay-assisted and cooperative interference access mechanisms under the assistance of untrusted relays make Perform the second level decision; in specific implementation, the embodiment of the present invention can provide the secure transmission rate of the direct connection input It is expressed by the following formula:

[0075]

[0076] Where: Indicates the source k The maximum achievable rate, Indicates the maximum eavesdropping rate.

[0077] Secure transmission rate of relay-assisted and cooperative interference access mechanisms under untrusted relay assistance It is expressed by the following formula:

[0078]

[0079] Where: Indicates the maximum achievable transmission rate of an untrusted relay link. Indicates the eavesdropping rate of the relay link.

[0080] Determine the user calculate If the user or if Destination k Stop and send CTS packets, select between direct connection, relay assistance and cooperative interference, and access the channel with a higher security transmission rate. Duration Otherwise, the destination k Give up access and send a CTS packet, and compete again in the next time slot;

[0081] Destination k Select Probe J * Collaborative trusted relays and send CTS packets, trusted relay set The trusted relays in the network reply to the RTS packets in turn to detect the time After that, the destination k Obtaining the signal-to-noise ratio of a cooperative two-hop link with a trusted relay Calculate the secure transmission rate of relay-assisted and cooperative interference access mechanisms under the assistance of trusted relays Make third-level decisions;

[0082] Sure Destination k Choose to stop and send CTS packets, and select a method with a higher secure transmission rate to access among direct connection, relay-assisted empty cooperative interference under untrusted relay assistance, and relay-assisted and cooperative interference under cooperative trusted relay assistance. Duration

[0083] Otherwise, the destination d k Give up access and send a CTS packet, and compete again in the next time slot;

[0084] After a single access is completed, the n+1th successful channel contention continues.

[0085] Duration It is expressed by the following formula:

[0086]

[0087] Where: τ d represents the channel coherence time, τ J =Jτ R +τ C represents the time to detect J relays;

[0088] Detection time It is expressed by the following formula:

[0089]

[0090] Where: τ C Indicates the time of transmitting CTS data packet, J* represents the optimal number of detection relays, τ R Indicates the time when the RTS packet is transmitted.

[0091] Duration It is expressed by the following formula:

[0092]

[0093] The adaptive competition probability optimization method provided by the embodiment of the present invention is based on the collaborative trust relationship between user pairs, the access trust relationship and the untrusted relationship between the user pairs and the relay. The user pairs compete for the same shared channel with the same probability using the CSMA / CA protocol. When considering the maximization of the system transmission throughput, the user pairs need to determine whether their access can provide positive benefits for the system transmission throughput, and select the access method with the largest expected transmission data volume among different access paths. If the expected transmission data volume is lower than the average transmission throughput of the system, the access should be abandoned, and the access opportunity should be left to other user pairs with good channel conditions.

[0094] Based on this access principle, the access decision of user pairs is divided into three levels. Combined with the sink-assisted cooperative interference technology in physical layer security, the transmission rate is guaranteed while suppressing untrusted relay eavesdropping to achieve the optimal system average security throughput. Since the relevant functions and thresholds in this three-level decision can be calculated, when the network topology and channel distribution are given, the user pair can predict the expected benefits of access transmission before competing for the channel based on statistical information. If the expected benefits are extremely small, it means that the user pair will always choose to give up access after successfully competing, which is invalid competition. Therefore, based on the benefit prediction of user pairs, a targeted competition probability optimization method is provided, which only allows user pairs with predicted benefits greater than a certain threshold to compete for channels with the optimal competition probability, thereby minimizing the competition overhead and improving the average security throughput of the system.

[0095] The adaptive competition probability optimization method provided by the embodiment of the present invention is introduced in detail below and its effect is verified.

[0096] In view of the problem of shared channel competition access under multi-level trust of user pairs, the present invention provides an adaptive competition probability optimization method based on user pair benefit prediction. Under this method, for a social network with a three-level trust relationship established, the nodes follow the three-level detection-decision-access equal probability fair competition access method according to their own topology, which can predict the expected benefits of user pairs, and further optimize the competition probability of user pairs based on this benefit, so as to achieve the optimal secure channel competition access without changing the fairness of user pair access, and achieve the optimal average security throughput of the system.

[0097] The social trust relationship network model considered by the present invention is as follows: Figure 2As shown, a multi-user network with three-level trust relationships is described.

[0098] The system contains multiple source nodes (i.e., information sources s 1 ,s 2 ,...,s K ), destination node (i.e., sink d 1 ,d 2 ,...,d K )), and relay node r 1 ,r 2 ,...,r L The source to sink pair satisfies the mapping relationship, and the information sent by the source sk is transmitted to the sink d via the direct / relay channel k For each user pair k, there may be three levels of trust relationships:

[0099] Collaborative trust relationship, access trust relationship and untrusted relationship. Among them, for all communicating user pairs, assuming that they have been authenticated by network security and have the qualifications to access the channel, all user pairs have access trust relationship; for some user pairs with further collaborative relationship, for example, nodes that perform the same task, nodes that collaborate in content distribution, etc., they have further collaborative trust relationship and are willing to relay data packets for each other when the other party accesses the channel. In other words, they are potential relays for each other; for relay nodes other than user pairs that have not been authenticated by the network, they are untrusted nodes for all user pairs. Untrusted nodes can serve as auxiliary relay nodes for other user pairs, but are not allowed to access the channel alone because they may leak information, and untrusted nodes continue to eavesdrop on the information of the source during the transmission of the user pair's source. In the present invention, they are referred to as untrusted relays. Therefore, in order to suppress the eavesdropping of untrusted relays, the destination is assisted in sending artificial noise to interfere with the untrusted relay in the first hop channel of the relay link to reduce its eavesdropping rate. Therefore, for user pair k, the set of user pairs willing to cooperate is called s k .

[0100] Based on a given social trust relationship network, different source-destination pairs can choose different access methods. The specific situations are divided into three types: direct connection (DT) channel access; relay-assisted-cooperative interference (CJ) channel access (untrusted relay); relay-assisted-cooperative interference (CJ) channel access (cooperative trusted relay) or give up the access opportunity and re-compete for the channel. The source-destination pair set is Contains K communication pairs, where the source index is s 1 ,...,s k ,...,s K , the destination index is d 1 ,...,d k ,...,d K, the number of untrusted relays is L, which is represented by the untrusted relay set The jth untrusted relay index is r j The set of cooperative trust user pairs (potential relays) of communication pair k is S k , then the collaborative trust network of all user pairs is expressed as

[0101] 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 For non-direct links, the node The channel SNR between u≠v is expressed as Where 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. Assume that all wireless channels are symmetric, that is, γ u,v =γ v,u .

[0102] In such a network, all source-destination pairs share the channel using a distributed CSMA / CA mechanism, and channel contention and access control are performed through request to send (RTS) packets and clear to send (CTS) packets. Assume that the time required for the transmission of RTS packets and CTS packets is τ R and τ C , the channel coherence time during which the channel state remains unchanged is τ d The specific channel contention process is described as follows. The time is divided into several micro-time slots with a duration of δ. At the beginning of each δ micro-time slot, all sources transmit with the same probability p 0 There are three possible situations in which an RTS signaling packet is sent to independently contend for a channel.

[0103] 1. No source sends RTS packets (duration is δ, probability is (1-p 0 ) K), all sources compete for the channel in the next mini-time slot.

[0104] 2. If there are two or more sources sending RTS packets (duration is τ R , with probability 1-(1-p 0 ) K )

[0105] -Kp 0 (1-p 0 ) K-1 , then an RTS transmission conflict occurs between the information sources, and all information sources continue to compete in the next mini-time slot.

[0106] 3. If there is only one source s k Send RTS packet (duration is τ R , the time cost of competing for RTS and replying CTS is τ R +τ C , with probability Kp 0 (1-p 0 ) K-1 ), then the source gets the channel access opportunity and is called the winning source s in the channel competition. k . Then, the winning destination d k Make channel access decisions and reply the decision results to the source s via CTS packets k .

[0107] Therefore, the average time for a single channel contention success is:

[0108]

[0109] Once a winning source wins the channel, the winning source s k The RTS of the competing channel, all other nodes (source, sink and untrusted relay) can obtain the RTS from s through channel estimation. k to its own channel SNR, that is, the node Get the first jump Destination k Get the direct channel SNRγ k .d k The first level decision can be made: access. k Send a CTS packet, so that the source s k At rate Access direct channel. Give up. d k Send a CTS packet to make all sources compete for the channel again.

[0110] Detect untrusted relays. kWe choose to further detect all untrusted relays to obtain the SNR of the relay and eavesdropping channels, and make further decisions based on the information after detection. k Send a CTS packet, and let L untrusted relay nodes reply RTS in turn. The RTS of the reply contains By receiving the node RTS,d k The second hop can be estimated Detection time τ L =τ C +L·τ R After all L RTSs are received, d k That is, get the two hops of all untrusted relay links And calculate the maximum safe transmission rate of the relay link d k Second level decision can be made: access, for the set of selectable relays d k The method with a higher security transmission rate is preferred in the direct link and the cooperative interference link, and a CTS packet is sent to the source s k Transmit on the preferred link at the corresponding rate, and the transmission time is Give up. k Send a CTS packet to make all sources compete for the channel again.

[0111] Detect cooperative trust relays. k Select potential relays to further explore for establishing collaborative trust relationships, represented as a set And make further decisions based on the information after detection, J * is the optimal number of detection relays. Similar to untrusted relay detection, d k Send a CTS packet to collect The nodes in the The RTS of the reply contains By receiving the node RTS,d k The second hop can be estimated Detection time After that, all J * RTS received, d k Get the collection All nodes in the two-hop relay link And calculate the maximum safe transmission rate of the relay link d k A third level decision can be made: access. For the set of selectable relays d kThe method with a higher security transmission rate is preferred in the direct link and the cooperative interference link, and a CTS packet is sent to the source s k Transmit on the preferred link at the corresponding rate, and the transmission time is Give up. k Send a CTS packet to make all sources compete for the channel again.

[0112] After a single access transmission ends, all signal sources restart the next round of channel contention, and each channel contention-access process is independent of each other.

[0113] In the above three-level access decision, if the winning source s k Select direct channel access, the achievable transmission rate of the direct link is

[0114] The maximum eavesdropping rate is

[0115] The secure transmission rate under direct channel transmission can be expressed as

[0116] make Indicates the maximum eavesdropping SNR of an untrusted relay.

[0117] If the winning source k Select the relay channel access under cooperative interference, then for a given cooperative trust network and the set of relays to be selected Sources k In the relay Equal-length two-stage data transmission is performed with the assistance of the

[0118] The maximum achievable transmission rate of the relay link is:

[0119]

[0120] The eavesdropping rate is:

[0121]

[0122] Relay The safe transmission rate of the assisted cooperative interference mechanism can be expressed as:

[0123]

[0124] For optional relay collections That is, the set of relay nodes that have obtained the link SNR, the maximum safe transmission rate and its corresponding achievable transmission rate and Can be expressed as:

[0125]

[0126] in, Indicates a set of optional relays The best relay index number within.

[0127] Based on the above equal probability competition and three-level access decision, the expected access benefits of different decisions at each level can be analyzed. Assuming that the average optimal throughput of the system is , the benefit function in the three-level decision is as follows.

[0128] a. In the third-level decision, the benefits of access and abandonment are:

[0129] and

[0130] b. In the second-level decision, the expected benefit function of detecting J collaborative trust relays is:

[0131]

[0132] in, Then the optimal number of detection relays J for detecting cooperative trust relays is * And the corresponding profit function for:

[0133]

[0134] The payoffs of stopping and giving up in the second-level decision are and

[0135] c. Expected benefit function of detecting all untrusted relays in the first-level decision There are two cases:

[0136] For satisfying |A k |>0 cooperative user pair k:

[0137]

[0138] For satisfying |A k |=0 for non-cooperative user pair k:

[0139]

[0140] The benefits of stopping and abandoning are and 0.

[0141] Optimal system average safety throughput is the unique solution that satisfies the following equation:

[0142]

[0143] By analyzing the increasing and decreasing relationship between the benefit functions in the first-level decision, three situations can be obtained, such as Figure 3 Therefore, the first-level decision threshold can be defined as And the user classification set is as follows:

[0144] First-level decision threshold vector Defined as, For equation U k (λ * ,γ)=0, and The only solution of There is no solution with γ>0, so let

[0145] User Classification Collection It is defined as, for a given set of user pairs Untrusted Relay Collection and social trust networks For user pair k:

[0146] If |A k |=0, Then the user has a first-level decision structure for k, which belongs to the classification set

[0147]

[0148] If |A k |=0, Then the user has a secondary decision structure for k, belonging to the classification set

[0149]

[0150] If |A k |>0, the user has a three-level decision structure for k, which belongs to the classification set

[0151] Based on the above equal probability competition-three-level access decision protocol and the profit function analysis, for each user pair, its access profit can be predicted. The present invention provides the following user pair expected profit prediction algorithm, the process is as follows: Figure 3 As shown, the specific steps include the following.

[0152] Step 1: Based on a given collaborative trust network According to the statistical characteristic parameters of the distributed wireless network channel, N is generated for each channel. e random SNR samples, calculate the first-level decision threshold vector Optimal system safety throughput and user pair classification set Go to step 2;

[0153] Step 2: Initialize the number of accesses n = 1, the user pair sequence number k = 1, and the user pair expected transmission volume Y k =0 and time cost T=0;

[0154] Step 3: For user pair k, take the nth group of channel SNR. If user pair Then go to step 4; otherwise Go to step 5;

[0155] Step 4: If Then the destination k The DT access mechanism will be selected and CTS will be sent. The expected transmission volume is Update T=T+τ 0 +τ d ; Otherwise, the destination k Will choose to give up access and send CTS, Y k No change, update T = T + τ 0 , go to step 10;

[0156] Step 5: If Then the destination k Will choose to give up access and send CTS, Y k No change, update T = T + τ 0 , go to step 10; if Then the destination k Will select DT access mechanism and send CTS to update T=T+τ 0 +τ d , go to step 10; otherwise, the destination d k It will choose to detect untrusted relays and go to step 6;

[0157] Step 6: If the user Go to step 7, otherwise the user Go to step 8;

[0158] Step 7: For if Then the destination k Will choose to access and send CTS, the expected transmission volume is Update T=T+τ 0 +τ d ; Otherwise, the destination k Will choose to give up access and send CTS, Y k No change, update T = T + τ 0 +τ L; Go to step 10;

[0159] Step 8: Calculate the benefit of detecting cooperative trust relays if Return to step 7; otherwise, k It will select the detection cooperative trusted relay and go to step 9;

[0160] Step 9: Compare The size of Then the destination k Will choose to access and send CTS, the expected transmission volume is Update T=T+τ 0 +τ d ; Otherwise, the destination d k Will choose to give up access and send CTS, Y k Unchanged, updated Go to step 10;

[0161] Step 10: If k=K, go to step 11; otherwise, k=k+1, return to step 3;

[0162] Step 11: If n = N e , then output the user's benefit Y k / T, k=1,2,...,K; otherwise, n=n+1, k=1, return to step 3.

[0163] By predicting the expected access benefits of user pairs, we find that there may be user pairs k that satisfy Y k / T<ζ, ζ represents the effective revenue threshold, which is a value very close to 0. For these user pairs, if the access decision is made in the way of equal probability competition-three-level decision, due to the poor transmission conditions, the probability of access channel transmission is very small. Most of the time, even if the user pair wins the channel, its destination still chooses to give up transmission. At this time, the channel competition is equivalent to invalid competition. Therefore, it is necessary to divide effective competition and invalid competition, and select the optimal competition probability according to the number of effective competing user pairs, so as to further improve the average security throughput of the system.

[0164] Define valid competing user pairs and invalid competing user pairs. The valid competing user pair k satisfies Y k / T≥ζ, otherwise it is an invalid competing user pair. Among all K users, the number of valid competing user pairs is K e , then when all valid user pairs compete for the channel with the same probability p, the cost of a single successful channel competition is:

[0165]

[0166] To obtain the optimal competition probability p * , so that τ 0 ' is the smallest, and the following derivation is obtained:

[0167] For τ 0 ′ Performing a first-order Taylor approximation yields:

[0168]

[0169] Taking the derivative, we get:

[0170]

[0171] make Solve equation K e 2 (K e -1)(τ R -δ)p 2 +2K e (K e -1)δp-K e δ=0, the optimal channel contention probability p can be obtained * as follows:

[0172]

[0173] Therefore, by predicting the benefits of user pairs under the equal probability access mechanism, dividing the user pairs into effective and invalid competing ones, and selecting the optimal channel competition probability for the effective competing user pairs, the optimal secure channel competition-decision access method based on user pair benefit prediction can be obtained as follows.

[0174] The optimal secure channel competition-decision access method based on user revenue prediction includes:

[0175] Input: User pair set Untrusted Relay Collection Social Trust Network Sending probability p 0 .

[0176] Calculate the probability p of all users sending in equal order 0 Expected benefit of contending for access to the channel:

[0177] Y k / T,k=1,2,...,K

[0178] And divide the user pairs into a set of effective competing user pairs and invalid competing user pair sets

[0179] Calculate the optimal competition probability p of the effective competing user pair * ;

[0180] Calculate the first-level decision threshold vector for only valid competing users to compete for the channel and make access decisions Optimal system security throughput for contention channels with only valid competing users and the classification set of user pairs of only valid competing users competing for the channel

[0181] At the beginning of each mini-slot δ, the signal sources s of all valid competing user pairs are k With probability p * Send a contention RTS, and invalid contention users remain silent.

[0182] For the nth successful channel contention, the source s k Win, Xinsu k Get the instantaneous SNRγ of the direct channel k (n) = γ, making first-level decisions;

[0183] If the user Then further judge; if Then the destination k Select DT access mechanism and send CTS, source s k Then at the maximum achievable rate Access direct channel, duration τ d Otherwise, the destination k Give up access and send CTS, and compete again in the next time slot.

[0184] Determine the user Then further judge; if Then the destination k Give up access and send CTS, and compete again in the next time slot. Then the destination k Select DT access mechanism and send CTS, source s k Then at the maximum achievable rate Access direct channel, duration τ d .

[0185] Otherwise, the destination d k Select Detect all untrusted relays and send CTS.

[0186] L untrusted relays then reply to RTS in turn, and the detection time τ L =τ C +L·τ R After that, the destination k Get the SNRs of the cooperative two-hop link of the untrusted relay, 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:

[0187] If the user calculate If the user or if Then the destination k Decide to stop and send CTS, select a method with a higher security transmission rate between DT and CJ to access the channel, duration

[0188] Otherwise, the destination k Give up access and send CTS, and compete again in the next time slot.

[0189] Otherwise, the destination k Select Probe J * Collaborative trust relays and sends CTS, collection The trusted relays in the network then reply to RTS in turn, detecting the time After that, the destination k Obtaining SNRs of the cooperative two-hop link of the trusted relay Calculation of secure transmission rate of CJ access mechanism assisted by trusted relay Make third-level decisions.

[0190] if Then the destination k Choose to stop and send CTS, and choose a method with a higher secure transmission rate among DT, CJ assisted by an untrusted relay, and CJ assisted by a cooperative trusted relay for access. Duration

[0191] Otherwise, the destination d k Give up access and send CTS, and compete again in the next time slot.

[0192] After a single access is completed, the n+1th successful channel contention continues.

[0193] The present invention has been rigorously simulated and tested, and the effectiveness and process feasibility of the method proposed in the present invention have been verified by computer simulation. A simulated wireless network communication scenario is constructed in MATLAB. Consider a 5km×5km square map in which 12 source-destination communication pairs and three untrusted relays are randomly deployed. The node positions and the collaborative trust relationships between user pairs are as follows: Figure 4 shown.

[0194] Referring to commonly used wireless communication scenarios, the channel fading depth is set to α=2.5.

[0195] For nodes u≠v, 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, making the SNR of the relay channel higher than that of the direct channel by ρdB is conducive to the establishment of collaborative relationships between users and promotes the formation of alliances, so that the simulation analysis results can more intuitively reflect the performance of the proposed method.

[0196] 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. Initially, the channel contention probability is p 0 =0.3.

[0197] Table 1. Expected returns of users under different parameters

[0198]

[0199]

[0200] Table 1 gives τ d =3ms, The benefits of each user under equal probability competition and optimal probability competition. It can be seen from the table that in the method proposed in the present invention, by dividing the effective competition and invalid competition user pairs and optimizing the competition probability of the effective competition user pairs, the benefits of the invalid competition user pairs are not affected, and the benefits of the effective competition user pairs are greatly improved, thereby maximizing the transmission performance of the user pairs without breaking the fairness of network access.

[0201] Figure 5 and Figure 6 The performance comparison of equal probability competition and optimal probability competition under different coherence times, direct channel SNRs and relay channel SNRs is given. Figure 5 The system average security throughput performance curves under different coherence times are given when the channel SNR changes. When the relay / direct connection SNR changes from 4dB to 20dB, the other channel SNR is fixed at 8dB.

[0202] Figure 5 and Figure 6 In the figure, the dotted line indicates that each user pair is p 0 is the performance curve of the probability competition channel; the solid line indicates that only valid competing users with individual utility greater than 0.001 compete with the optimal probability p * is the performance curve of the contention channel.

[0203] from Figure 5 and Figure 6 It can be seen that under equal probability competition, the average security throughput of the system increases with the increase of the direct channel SNR, showing a monotonically increasing trend. This is because the increase of the direct channel SNR will lead to an overall increase in the transmission rate; with the increase of the relay channel SNR, the average security throughput of the system shows a trend of first increasing and then decreasing. This is because the increase of the relay channel SNR will lead to an increase in the eavesdropping rate of untrusted relays, which has a negative impact on the effective channel security transmission, but this negative impact is limited because the secure transmission rate is always greater than or equal to 0; at the same time, the increase of the relay channel SNR will increase the cooperative transmission rate. When the increase of the relay channel SNR is small, the probability of users choosing a cooperative link is small, but the eavesdropping rate increases linearly. At this time, the increment of the average transmission rate is less than the increment of the eavesdropping rate, and the average security throughput of the system shows a downward trend.

[0204] When the SNR of the relay channel increases significantly, the probability of users choosing cooperative links increases significantly. Although the eavesdropping rate increases linearly, it can be effectively suppressed through cooperative interference, and the cooperative transmission rate also increases accordingly. At this time, the increase in the average transmission rate is greater than the increase in the eavesdropping rate, and the average security throughput of the system shows an upward trend.

[0205] Under the same channel SNR conditions, the average security throughput of the system increases with the channel coherence time τ d However, compared with the increase from 1ms to 2ms, the increase from 2ms to 3ms is smaller, which is in line with the channel transmission rules. Under the same network parameter settings, the performance of the optimal competition probability strategy is always better than that of the equal probability competition strategy, and its performance curve shows an irregular change trend with more steep increase or drop points. This is because compared with the equal probability competition strategy, the performance improvement of the optimal competition probability strategy depends on the number of invalid competition user pairs. The more invalid competition user pairs there are, the greater the performance improvement. The number of invalid competition user pairs is determined by the overall performance of the network itself and the network, and does not have a linear change relationship with the coherence time and SNR, resulting in uncertainty in the performance change trend of the improved algorithm.

[0206] Through the above simulation, the rationality and effectiveness of the proposed method are verified.

[0207] It can be seen that the adaptive competition probability optimization method provided by the embodiment of the present invention is:

[0208] 1. For a distributed wireless collaborative network with three-level social trust relationships, a three-level competition-decision channel security access method based on equal probability competition is proposed. The user benefit functions of different decision levels are analyzed, and the user access decisions and the SNR information obtained are connected. The user can make three-level access decisions based on the real-time SNR.

[0209] 2. Based on the three-level access decision method, since all decision thresholds and functions are obtained based on channel statistical information, a user pair benefit prediction algorithm that can be calculated offline is proposed. By randomly generating channel SNR samples and combining benefit comparison analysis, the expected benefit of the user pair is quantified as the ratio of the expected transmission data volume and the time cost. Based on this benefit prediction algorithm, the expected benefit of the user pair under the equal probability competition-three-level decision access method can be predicted before the competition.

[0210] 3. Based on the expected benefits of user pairs, user pairs are divided into effective competition user pairs and invalid competition user pairs. Invalid competition user pairs are user pairs with expected benefits close to 0. If the equal probability competition-three-level decision access method is followed, invalid user pairs always choose to give up access after successfully competing, and their competition is invalid competition.

[0211] 4. For valid competing user pairs, in order to minimize the average time of successful channel competition, the analytical expression of the average time is approximated by first-order Taylor. By taking derivations and solving equations, the approximate analytical expression of the optimal competition probability is derived, which has extremely low computational complexity.

[0212] 5. Based on the optimal competition probability and the related calculations of effective competing user pairs and invalid competing user pairs, combined with the original equal probability competition-three-level decision access method, an optimal secure channel competition-decision access method based on user pair benefit prediction is proposed. In the proposed method, only the expected benefits of user pairs are calculated first, and effective competing user pairs and invalid competing user pairs are divided. Then, the optimal competition probability of effective competing user pairs is calculated. Subsequently, the effective competing user pairs compete for channels with the optimal competition probability and refer to the CSMA / CA mechanism. After the competition is successful, access decisions are made in a method similar to the three-level decision.

[0213] 6. In the proposed optimal secure channel competition-decision access method based on user pair revenue prediction, although the invalid competing user pairs do not participate in the channel competition, they can still serve as cooperative trust relay nodes for other user pairs, that is, the cooperative trust relationship remains unchanged. Under this mechanism, the cooperative trust relationship and the competitive relationship are decoupled, and when the channel of the user pair changes, the trust relationship still exists. For example, if the channel conditions of an invalid competing user pair improve in the subsequent period of time, it will be transformed from an invalid competing user pair to a valid competing user pair, and its cooperatively trusted user pair will always be willing to provide relay assistance for it.

[0214] In summary, the adaptive competition probability optimization method provided by the present invention takes into account the multi-level trust relationship between user pairs and between user pairs and relays, and further optimizes the performance based on the current optimal three-level decision access method. An algorithm for predicting the expected benefits of user pairs under a given access equal probability-three-level access decision is proposed. Based on the access decision parameters, channel random samples can be generated according to the statistical characteristics of the network, and the expected benefits of user pairs can be calculated offline by Monte Carlo. Based on the expected benefits of user pairs, user pairs are divided into effective competition user pairs and invalid competition user pairs, so that invalid competition user pairs remain silent during the competition stage, avoiding invalid competition overhead; for effective competition user pairs, an approximate analytical expression of the optimal competition probability is derived, which reduces the time overhead of successful channel competition, and has extremely low computational complexity. The invalid / effective competition is decoupled from the trust relationship of user pairs. When the invalid competition user pairs remain silent during the competition stage, they can still assist other user pairs in transmission and improve transmission performance. If the network changes dynamically and user pairs switch between effective and invalid, the proposed method can still be applied.

[0215] 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.

[0216] It can be seen from the above description of the implementation mode that those skilled in the art can clearly understand that the present invention can be implemented by means of software plus a necessary general hardware platform. Based on such an understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a storage medium, such as ROM / RAM, a magnetic disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment of the present invention or some parts of the embodiments.

[0217] 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.

[0218] 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. An adaptive competition probability optimization method, characterized in that: include: Identifying social trust networks Included user pairs collection Untrusted Relay Collection And the sending probability p0, the social trust network It includes establishing a heterogeneous wireless collaborative network consisting of multiple information source and information sink pairs with three-level trust relationships; Calculate the expected benefit Y provided to the system transmission throughput when all user pairs included in the user pair set compete for access to the channel with the transmission probability p0 k / T,k=1,2,...,K;The expected return Y k / T,k=1,2,...,K includes the expected transmission amount Y of the user k The ratio of time cost T; Using the expected return Y k / T, k = 1, 2, ..., K and the effective revenue threshold ζ divide the user pairs into a set of effective competing user pairs and a set of invalid competing user pairs; Calculate the optimal competition probability p of all the valid competing user pairs * , and calculate the first-level decision threshold vector for all the valid competing users to compete for the channel and make access decisions The optimal system security throughput of all the valid competing users on the competing channel and a user pair classification set of only all the valid competing user pairs At the beginning of each mini-slot δ, the information sources s of all the valid competing user pairs are k With the optimal competition probability p * Send a contention RTS data packet, and all the invalid contention users remain silent; For the nth successful channel contention, the source s k Win, Xinsu k Get the instantaneous signal-to-noise ratio γ of the direct channel k (n) = γ, making first-level decisions; Determine the user if Then the destination k Select the direct connection mechanism and send a CTS packet. k Then at the maximum achievable rate Access direct channel, duration τ d ; Otherwise, the destination k Give up access and send a CTS packet, and compete again in the next time slot; Determine the user if Then the destination k Give up access and send CTS data packet, compete again in the next time slot. Then the destination k Select the direct connection mechanism and send a CTS packet. k At the maximum achievable rate Access direct channel, duration τ d ; Otherwise, the destination d k Select to detect all untrusted relays and send CTS packets. L untrusted relays then reply with RTS packets in turn. The detection time is τ L =τ C +L·τ R After that, the destination k Get the signal-to-noise ratio of the cooperative two-hop link of the untrusted relay, Calculate the safe transmission rate for direct access The secure transmission rate of relay-assisted and cooperative interference access mechanisms under the assistance of untrusted relays make Make second-level decisions; Determine the user calculate If the user or if Destination k Stop and send CTS packets, select between direct connection, relay assistance and cooperative interference, and access the channel with a higher security transmission rate. Duration Otherwise, the destination k Give up access and send a CTS packet, and compete again in the next time slot; Destination k Select Probe J * Collaborative trusted relays and send CTS packets, trusted relay set The trusted relays in the network reply to the RTS packets in turn to detect the time After that, the destination k Obtaining the signal-to-noise ratio of a cooperative two-hop link with a trusted relay Calculate the secure transmission rate of relay-assisted and cooperative interference access mechanisms under the assistance of trusted relays Make third-level decisions; Sure Destination k Choose to stop and send CTS packets, and select a method with a higher secure transmission rate to access among direct connection, relay-assisted empty cooperative interference under untrusted relay assistance, and relay-assisted and cooperative interference under cooperative trusted relay assistance. Duration Otherwise, the destination d k Give up access and send a CTS packet, and compete again in the next time slot; After a single access is completed, the n+1th successful channel contention continues.

2. The adaptive competition probability optimization method according to claim 1, characterized in that: The forecasting methods of the expected benefits include: Based on a given collaborative trust network According to the statistical characteristic parameters of the distributed wireless network channel, N is generated for each channel. e random SNR samples, calculate the first-level decision threshold vector for all users to compete for the channel and make access decisions Optimal system security throughput for all users on the contention channel and the user pair classification set of all user pairs competing for the channel Go to step 2; Step 2: Initialize the number of accesses n = 1, the user pair sequence number k = 1, and the user pair expected transmission volume Y k =0 and time cost T=0; Step 3: For user pair k, take the nth group of channel signal-to-noise ratios. If user pair Then go to step 4; otherwise Go to step 5; Step 4: If Then the destination k The direct connection mechanism will be selected and CTS packets will be sent. The expected transmission volume is Update T=T+τ0+τ d ; Otherwise, the destination k Will choose to give up access and send CTS data packet, Y k No change, update T = T + τ0, and go to step 10; Step 5: If Then the destination k Will choose to give up access and send CTS data packet, Y k unchanged, update T = T + τ0, and go to step 10; if Then the destination k The direct connection mechanism will be selected and a CTS packet will be sent to update T=T+τ0+τ d , go to step 10; otherwise, the destination d k Select Detect untrusted relays and go to step 6; Step 6: If the user Go to step 7, otherwise the user Go to step 8; Step 7: OK if Then the destination k Select access and send CTS data packets. The expected transmission volume is renew T=T+τ0+τ d ; Otherwise, the destination k Will choose to give up access and send CTS data packet, Y k No change, update T = T + τ0 + τ L ; Go to step 10; Step 8: Calculate the benefit of detecting cooperative trust relays if Return to step 7; otherwise, k Select Detect Collaborative Trusted Relay and go to step 9; Step 9: Compare The size of Then the destination k Select access and send CTS data packets. The expected transmission volume is renew T=T+τ0+τ d ; Otherwise, the destination k Choose to give up access and send CTS data packet, Y k Unchanged, updated Go to step 10; Step 10: If k=K, go to step 11; otherwise, k=k+1, return to step 3; Step 11: If n = N e , then output the user's benefit Y k / T, k=1,2,...,K; otherwise, n=n+1, k=1, return to step 3.

3. The adaptive competition probability optimization method according to claim 2, characterized in that: The optimal system average security throughput of all users competing for the channel It is defined as the unique solution that satisfies the following equation: Where: K represents the number of source and sink pairs, τ d represents the channel coherence time, represents the safe transmission rate under direct channel transmission, n represents the number of observations, represents the expected revenue function of all untrusted relays, γ represents the signal-to-noise ratio, and τ0 represents the average time of a single observation.

4. The adaptive competition probability optimization method according to claim 2, characterized in that: The optimal decision-level threshold vector for all users to compete for the channel and make access decisions Defined as: Distribution as equation and The only solution of There is no solution with γ>0, so let 5. The adaptive competition probability optimization method according to claim 2, characterized in that: The user pair classification set of all user pairs competing for the channel Defined as: For a given set of users Untrusted Relay Collection and social trust networks The user classifies k as follows: If |A k |=0, Then the user has a first-level decision structure for k, which belongs to the classification set If |A k |=0, Then the user has a secondary decision structure for k, belonging to the classification set If |A k |>0, Then the user has a first-level decision structure for k, which belongs to the classification set If |A k |>0, Then the user has a three-level decision structure for k, belonging to the classification set 6. The adaptive competition probability optimization method according to claim 1, characterized in that: Sources k Maximum achievable rate and secure transmission rate It is expressed by the following two formulas: Where: γ k represents the signal-to-noise ratio of the direct channel, D k Indicates k and d k The straight-line distance between them, α represents the channel fading depth, h k represents the small-scale fading parameter and its mean is Negative exponential random distribution, Indicates the source k The maximum achievable rate, Indicates the maximum eavesdropping rate.

7. The adaptive competition probability optimization method according to claim 1, characterized in that: Secure transmission rate of relay-assisted and cooperative interference access mechanisms under untrusted relay assistance It is expressed by the following formula: Where: Indicates the maximum achievable transmission rate of an untrusted relay link. Indicates the eavesdropping rate of the relay link.

8. The adaptive competition probability optimization method according to claim 1, characterized in that: Duration It is expressed by the following formula: Where: τ d represents the channel coherence time, τ J =Jτ R +τ C represents the time to detect J relays; Detection time It is expressed by the following formula: Where: τ C Indicates the time of transmitting CTS data packet, J * represents the optimal number of detection relays, τ R Indicates the time when the RTS packet is transmitted.

9. The adaptive competition probability optimization method according to claim 9, characterized in that: Transmission duration It is expressed by the following formula:

10. The adaptive competition probability optimization method according to claim 9, characterized in that: The optimal competition probability p * The derivation and calculation process is as follows: Define valid competing user pairs and invalid competing user pairs. The valid competing user pair k satisfies Y k / T≥ζ, otherwise it is an invalid competing user pair; among all K users, the number of valid competing user pairs is K e , then when all valid user pairs compete for the channel with the same probability p, the cost of a single successful channel competition is: To obtain the optimal competition probability p * , so that τ0′ is the smallest, the following derivation is obtained: Performing the first-order Taylor approximation on τ0′ yields: Taking the derivative, we get: make Solve equation K e 2 (K e -1)(τ R -δ)p 2 +2K e (K e -1)δp-K e δ=0, the optimal channel contention probability p can be obtained * as follows:

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