Transmission performance analysis method for opportunistic access of cognitive users in cognitive radio systems

Abstract

A method for analyzing the transmission performance of opportunistic access of cognitive users in a cognitive radio system, comprising the following steps: 1) modeling and analyzing the dynamics of a single channel in the system and the state of the cognitive radio system; 2) analyzing the probability of successful switching, blocking probability, and re-access probability of a single channel switch of a cognitive user in the next sensing cycle; 3) analyzing the average transmission probability and average blocking probability of a cognitive user when the cognitive user experiences no more than Q switching blocking-re-access times; 4) analyzing the average switching delay and average number of blocking times when the cognitive user experiences no more than Q switching blocking-re-access times. The present invention proposes a method for evaluating the transmission performance of opportunistic access under the switching blocking-re-access mechanism by establishing a calculation model for parameters such as the average transmission probability, average blocking probability, average switching delay, and average number of blocking times of cognitive users, thereby laying a theoretical foundation for optimizing the design of the transmission performance of opportunistic spectrum access in cognitive radio systems.

Description

Technical Field

[0001] The invention relates to a cognitive radio system (CRS), and in particular to an evaluation and analysis method for opportunistic spectrum access transmission performance of cognitive users in a multi-channel cognitive radio system. Background Art

[0002] Cognitive radio technology has become a research hotspot and important topic in the field of wireless communications in recent years due to its great advantages in improving wireless spectrum efficiency. As a technical solution that is most compatible with the static spectrum management system, opportunistic spectrum access based on cognitive radio has attracted widespread attention from researchers. Its basic idea is that cognitive users (secondary users) can access communications by opportunistically using idle frequency bands not occupied by authorized users by sensing spectrum occupancy without excessively affecting the normal communication of authorized users (primary users), that is, "opportunistically accessing and transmitting" by "taking advantage of every opportunity" to use authorized frequency bands. Wireless regional area network (WRAN) based on 802.22 protocol is a typical application example of opportunistic spectrum access.

[0003] Since the occupancy of wireless spectrum changes dynamically with the spectrum access and exit of users, periodic perception of spectrum status and timely execution of channel switching to avoid authorized users becoming cognitive users is an effective solution to guarantee the access priority of authorized users and resolve the access conflict between primary and secondary users. The so-called channel switching refers to the strategy of cognitive users exiting the current channel and looking for another idle channel to continue transmission when they perceive that an authorized user appears on their working channel. The channel switching of cognitive users is affected by factors such as the activities of authorized users and the number of available channels. In addition, there are two situations in channel switching: success and failure. After the switching fails, whether to exit the system directly or try to access the transmission again after temporary blocking, and how many times cognitive users perform switching blocking-re-access are important issues that affect the transmission performance of cognitive users. They are also difficult issues that are worth exploring in the opportunistic spectrum access of cognitive radio systems and are still blank at present.

[0004] Judging from the current research status at home and abroad, most opportunistic spectrum access studies discuss the transmission performance of cognitive users when a single channel switch occurs, and lack research on multiple switching blocking-reaccess mechanisms; for example, document CN113836491A only analyzes the reaccess transmission performance of cognitive users after a single channel switch-blocking, and does not study the average transmission performance and blocking performance of cognitive users after multiple switching blocking-reaccess. In short, existing work has not yet analyzed the multiple switching blocking-reaccess mechanism of cognitive users, nor has there been a complete evaluation method for opportunistic spectrum access transmission performance, which has brought difficulties to the in-depth analysis of cognitive system performance and the optimization of opportunistic transmission schemes. Therefore, it is of great theoretical and practical significance to study the multiple switching blocking-reaccess mechanism of cognitive users and then establish a cognitive user opportunistic access transmission performance analysis and evaluation model. Summary of the invention

[0005] In order to solve the above technical problems, the present invention is based on the analysis of the single switching performance of cognitive users, studies and establishes a performance analysis model for multiple switching blocking-reaccess of cognitive users, and proposes a complete opportunistic access transmission performance evaluation method, which is suitable for cognitive radio systems with multiple parallel channels, wherein cognitive users adopt a periodic sensing-access scheme to perform opportunistic spectrum access transmission, and adopt channel switching and multiple switching blocking-reaccess mechanisms to avoid conflicts between primary and secondary users and improve the efficiency of opportunistic transmission.

[0006] The method for analyzing transmission performance of cognitive user opportunistic access in a cognitive radio system of the present invention comprises the following steps:

[0007] Step 1: A cognitive radio system has N parallel channels and carries a number of authorized users and cognitive users. For the cognitive radio system, a system model and access protocol are constructed; a single channel dynamics and cognitive radio system status in the cognitive radio system are modeled and analyzed;

[0008] Step 2: Analyze the success switching probability, blocking probability and re-access probability of the cognitive user during a single channel switching.

[0009] Step 3: Analyze the average transmission probability and average blocking probability of cognitive users when they experience no more than Q handover blocking-re-access times;

[0010] Step 4: Analyze the average switching delay and average number of blocking times when the cognitive user experiences no more than Q switching blocking-re-access times.

[0011] Furthermore, in step 1, the system model is constructed as follows:

[0012] The authorized user has the priority of channel access, and is also called the primary user; the cognitive user opportunistically utilizes the idle channel through spectrum sensing, and its spectrum access priority is lower than that of the primary user, and is also called the secondary user; the authorized user is based on the rate λ p,t The Poisson process arrives at the system, and the average service time in the system follows the mean 1 / μ p,t The exponential distribution of cognitive users is s,t The Poisson process arrives at the system, and the average service time in the system follows the mean 1 / μ s,t exponential distribution of

[0013] The cognitive radio system has a total of N channels, all channels have equal status, and each channel has an equal opportunity to carry authorized user services and cognitive user services; the arrival rate and departure rate of authorized users relative to a single channel are calculated as λ p,i =λ p,t / N,μ p,i =μ p,t / N; the arrival rate and departure rate of cognitive users relative to a single channel are calculated as λ p,i =λ p,t / N,μ p,i =μ p,t / N.

[0014] Furthermore, in step 1, the access protocol designed is specifically:

[0015] The primary user adopts centralized access control, and the central access point (such as a base station) uniformly manages and coordinates the allocation of access channels for the primary user; the central access point of the authorized user does not perform channel sensing, and cannot know the occupation of the channel by the cognitive user, and only records the channel allocation of the authorized user; the newly arrived authorized user is randomly assigned a channel that is not occupied by other primary users by the central access point, but it may be occupied by the cognitive user, in which case the cognitive user needs to retreat; if there is no channel available for allocation, the access request of the authorized user is directly rejected;

[0016] Cognitive users use distributed access management and start to execute periodic spectrum sensing-transmission scheme when data needs to be transmitted. Each sensing period T includes sensing time slot τ and transmission time slot T t =T-τ; Once a new cognitive user successfully accesses, it becomes an active user, and the sensing period of the first access is called the initial access period; the active cognitive user broadcasts the channel currently occupied by itself in the transmission time slot of its initial access period to avoid access conflicts with other cognitive users; the active cognitive user continues to sense and transmit periodically until its data transmission ends or it is forced to exit the system due to excessive switching blocking times;

[0017] Cognitive users use channel switching to avoid access collisions between primary and secondary users. Once an active cognitive user senses that an authorized user appears on its working channel, it will immediately search for an idle channel to perform channel switching. If the cognitive user finds a new idle channel, the switching is successful, and the corresponding switching time overhead is T h If it cannot find an idle channel, the handover fails, and the cognitive user will be temporarily blocked and queue up to wait for the next sensing time slot to arrive before trying to access the transmission again. This strategy is called the blocking-reaccess mechanism, and the time overhead of a single blocking is T t ; If the re-access fails, the cognitive user will be forcibly blocked and exit the system; if the re-access is successful, the cognitive user continues to perform opportunistic access transmission; in order to ensure the transmission continuity of cognitive users and reduce the total switching delay, each cognitive user is allowed to perform no more than Q times of switching blocking-re-access; in addition, it is stipulated that the cognitive user's service data transmission time each time shall not exceed M perception cycles, M≥2Q+1;

[0018] Only one user is allowed to access any channel at any time; the access priority of different users to the channel is specified as follows:

[0019] Main user > cognitive user that needs to switch in the current time slot > cognitive user that was blocked in the previous time slot and needs to access again in the current time slot > newly arrived cognitive user.

[0020] Furthermore, in step 1, the single channel dynamics modeling analysis is as follows:

[0021] For any channel i, i∈I={1,2,...,N}, depending on whether it is occupied and which type of user is occupying it, channel i has three states: idle (not occupied), that is, state 0; occupied by an authorized user, that is, state 1; occupied by a cognitive user, that is, state 2; the state set of a single channel is defined as S={0,1,2}.

[0022] Let X i (t) represents the instantaneous state of channel i at time t, X i (t) is modeled as a 0-1-2 three-state Markov process, whose state transition rate matrix Q i And the state transition probability matrix P i (t) are expressed as

[0023]

[0024] in, Unified Characterization, represents the rate at which channel i transitions from state m to state n, m,n∈S={0,1,2}, calculated as

[0025]

[0026] Unified Characterization, represents the probability that channel i transitions from state m to state n after time t, m,n∈S={0,1,2}, which is obtained by solving the Kolmogorov forward equation P i ′(t)=P i (t)Q i Get, that is

[0027]

[0028]

[0029]

[0030]

[0031]

[0032]

[0033]

[0034]

[0035]

[0036] Among them, P i ′(t) represents the transition probability matrix P i The first-order derivative of (t); coefficients D1~D6 and E1~E6 are

[0037]

[0038]

[0039] In the formula, Represents X i (t) is the steady-state distribution, that is, channel i is in state s i The probability of is calculated by formula (8), that is,

[0040]

[0041] Among them, λ p,i ,μ p,i They represent the arrival rate and departure rate of authorized users on channel i respectively; s,i ,μ s,i denote the arrival rate and departure rate of cognitive users on channel i respectively;

[0042] Considering the load balancing of each channel, let λ p,i =λ p ,μ p,i =μ p ,λ s,i =λ s ,μ s,i =μ s , the steady-state distributions of all channels will be the same, i.e. At this time, all the labels i in formula (8) can be removed.

[0043] Further, in step 1, the cognitive radio system status analysis is as follows:

[0044] For a cognitive radio system with N indifferent channels, its system state A(t) is jointly characterized by the states of the N channels, that is,

[0045] A(t)=[X1(t),X2(t),...X, N (t)],t≥0,X i ∈S (9)

[0046] Among them, X i (t) represents the instantaneous state of channel i at time t, i∈I={1,2,...,N}, X i (t)∈S={0,1,2}; the state space of cognitive radio system is A(t)∈S N .

[0047] Cognitive radio systems are in a stable state The probability of

[0048]

[0049] Among them, s i represents the stable state of channel i, s i ∈S={0,1,2}; Indicates that channel i is in stable state s i The probability of is calculated by formula (8).

[0050] Furthermore, in step 2, the success switching probability, blocking probability, and re-access probability of the cognitive user when experiencing a single channel switching are analyzed as follows:

[0051] Step 2-1, calculating the success switching probability and blocking probability of a cognitive user when experiencing a single channel switching;

[0052] Let the success switching probability and blocking probability of a cognitive user undergoing a single channel switching be P h and P b , calculated by formula (11)

[0053]

[0054] Where u=[s1,s2,...,s N ] represents the state of cognitive radio system (CRS), s i represents the state of channel i; Π(u) represents the probability that CRS is in state u, which is calculated by formula (10); Pr(n) represents the probability that n primary users arrive in CRS, which is calculated by formula (12):

[0055]

[0056] Among them, λ t represents the arrival rate of authorized users relative to the system, T represents the duration of the perception cycle;

[0057] p h (u,n) and p b (u,n) respectively represent the conditional successful switching probability and conditional blocking probability of the cognitive user when the system state is u and n authorized users arrive, which are calculated by equation (13) and equation (14) respectively:

[0058]

[0059]

[0060] Among them, N s and N i Respectively represent the CRS state as u=[s1,s2,...,s N ], the number of active cognitive users and the number of idle channels are calculated by formula (15):

[0061]

[0062] Among them, 1 [x] is an indicator function, the function value is 1 when x = 1, otherwise it is 0; j represents the number of cognitive users that may switch in the current perception cycle when the system state is u, j∈[j1,j2], j1=max(0,nN i ),j2=min(N s ,n);j h represents the number of cognitive users who successfully switched, j b represents the number of cognitive users temporarily blocked due to handover failure, j h and j b Calculated as

[0063] j h =j-max(0,nNi ),j b =max(0,nN i )=j1 (16)

[0064] Step 2-2, calculating the re-access probability of the cognitive user in the next sensing period after experiencing a single switching blockage;

[0065] Considering that blocking-reaccess involves two sensing cycles, let the CRS states of the current sensing cycle and its adjacent previous sensing cycle be u, u′ respectively. The conditional reaccess probability p of the cognitive user under the given system state u, u′ is re (u,u′) is calculated as

[0066]

[0067] Where n represents the number of newly arrived authorized users in the current sensing cycle, n′ represents the number of newly arrived primary authorized users in the previous sensing cycle; λ t represents the arrival rate of authorized users relative to the system, N s ′ and N i ′ respectively represent the number of active cognitive users and the number of idle channels in the system in the previous sensing cycle (when the CRS system state is u′), which can be calculated by formula (15) (let u = u′); N i represents the number of idle channels in the system in the current sensing period (when the CRN system state is u), which is calculated by formula (15);

[0068] The condition described in formula (17) is then connected to the probability p re (u,u′) takes the average of u′,u, and obtains the re-access probability of the cognitive user after a single handover blocking (i.e., blocking-re-access probability) P re , calculated as

[0069]

[0070] Where Π(u′) represents the steady-state distribution of CRS, which is calculated by formula (10); T represents the duration of the sensing cycle; Pr(u′→u|T) represents the probability of CRS transitioning from state u′ to state u after time T, which is calculated by formula (19):

[0071]

[0072] in, Indicates that channel i in CRS changes from state s after time T i 'Transfer state s i The probability of is calculated by equations (3)-(5).

[0073] Furthermore, in step 3, the average transmission probability and average blocking probability of the cognitive user when experiencing no more than Q handover blocking-re-access times are analyzed as follows:

[0074] Step 3-1, calculate the average transmission probability when the cognitive user experiences no more than Q handover blocking-re-access times;

[0075] The probability of successful transmission when a cognitive user experiences q handover blocking-re-access is 0≤q≤Q,q∈N + , where H1 represents the hypothetical event that the cognitive user successfully completes the transmission, N + represents a set of non-negative integers. Since a cognitive user needs to go through two consecutive sensing cycles to experience a handover blocking-re-access, the number of sensing cycles j that may be experienced when q handover blocking-re-access occurs q Should satisfy 2q+1≤j q ≤M, where the first sensing period is the initial access period, and the initial successful access probability of the cognitive user is According to the location where the switching blocking time slot occurs, a single cognitive user q The number of transmission patterns that have q switching blocking-re-access in a sensing cycle is The probability of each transmission pattern appearing is calculated as 2q+1≤j q ≤M; Supplementary provisions, when j q >M or j q <2q+1,

[0076] Therefore, cognitive user experience j q The conditional transmission probability of q handover blocking-re-access in a sensing period Calculated as

[0077]

[0078] in, Represents cognitive user experience j q The transmission pattern when q switching blockages and re-accesses occur in a sensing period (i.e., the transmission frame arrangement pattern determined by different switching blockage positions); represents the initial access probability of the cognitive user in the first sensing cycle; and Calculated as

[0079]

[0080]

[0081] Among them, π1 represents the probability that a single channel is occupied by an authorized user; pd represents the probability that an authorized user occupies the channel and is correctly detected, i.e., the detection probability; p f It represents the probability that an idle channel is misjudged as occupied, i.e., the false alarm probability; usually 0≤p f <<p d ≤1;

[0082] Consider q Discrete uniform distribution on the interval [2q+1,M], that is, j q The probability distribution function of

[0083]

[0084] For equation (20), q Take the average and get the transmission probability when the cognitive user experiences q switching blocking-re-access for

[0085]

[0086] Among them, Pr(j q ) represents j q The distribution function of is obtained by formula (23); Represents cognitive user experience j q The conditional transmission probability of q switching blocking-re-access occurring in a sensing period is calculated by formula (20); Represents cognitive user experience j q The transmission pattern when q switching blockages and re-accesses occur in a sensing period (i.e., the transmission frame arrangement pattern determined by different switching blockage positions) is calculated by formula (21); represents the initial access probability of the cognitive user in the first sensing cycle, which is calculated by formula (22); M represents the maximum number of sensing cycles that the cognitive user may experience, M ≥ 2Q + 1;

[0087] Summing (24) with respect to q, we obtain the transmission probability when the cognitive user experiences no more than Q handover blocking-re-access times: for

[0088]

[0089] Among them, Pr(j q ) represents j q The distribution function of is obtained by formula (23); and Calculated by formula (22) and formula (21) respectively; P b and P re Calculated by formula (11) and formula (18) respectively; M represents the maximum number of perception cycles experienced by the cognitive user, M ≥ 2Q + 1;

[0090] Step 3-2, calculate the average blocking probability when the cognitive user experiences no more than Q handover blocking-re-access times;

[0091] The average blocking probability when a cognitive user experiences no more than Q handover blocking-re-access times is It is calculated by formula (26) as

[0092]

[0093] in, represents the initial access probability of cognitive users, which is calculated by formula (22); Represents cognitive user experience j q The number of transmission patterns when there are q sensing cycles and q blocking-reaccess times is calculated by formula (21); P b and P re They represent the single handover blocking probability and blocking-reaccess probability of cognitive users, respectively, and are calculated by equations (11) and (18), respectively.

[0094] Furthermore, in step 4, the average switching delay and average number of blocking times when the cognitive user experiences no more than Q switching blocking-re-access times are analyzed as follows:

[0095] Step 4-1, calculate the average switching delay when the cognitive user experiences no more than Q switching blocking-re-access times;

[0096] The average switching delay is defined as the average total time overhead incurred by the cognitive user in performing channel switching to avoid the primary user in a complete data transmission (i.e., the process from the cognitive user activating the transmission to the completion of the transmission or being forced to exit the system due to the switching number exceeding the upper limit).

[0097] Consider cognitive user experience q After q sensing cycles and q handover blocking occurs, all data transmission is completed after re-access, 2q+1≤j q ≤M, 0≤q≤Q, then there are q groups of switching blocking-re-access perception cycles, and the average switching delay of each group is P b (T t +P tr τ); Remaining(j q -2q-1) sensing cycles without switching or successful switching, the average switching delay of each sensing cycle is P h T h ; Considering the cognitive user experience q The conditional transmission probability of q handover blocking-re-access occurs in a sensing period is Cognitive User Experience qAverage switching delay when q switching blocking-re-access occur in a sensing period Calculated as

[0098]

[0099] in, Represents cognitive user experience j q The conditional transmission probability of q switching blocking-re-access occurring in a sensing period is calculated by formula (20); P h , P b , P re They represent the success switching probability, blocking probability, and blocking-reaccess probability of a single channel switching of a cognitive user, respectively, and are calculated by equations (11) and (18); T h , T t , τ represent the single channel switching overhead, transmission time slot duration, and perception time of the cognitive user, respectively; M represents the maximum number of perception cycles that the cognitive user may experience, M≥2Q+1;

[0100] Consider q Discrete uniform distribution on the interval [2q+1,M], for equation (27) with respect to j q Calculate the average switching delay when the cognitive user experiences q switching blockages and re-access Calculated as

[0101]

[0102] Among them, Pr(j q ) represents j q The distribution function of is calculated by formula (23); Calculated by formula (20); P h , P b , P re Calculated by formula (11) and formula (18) respectively; T h , T t , τ represent the single channel switching overhead, transmission time slot duration, and perception time of the cognitive user, respectively; M represents the maximum number of perception cycles that the cognitive user may experience, M≥2Q+1;

[0103] Summing equation (28), we get the average switching delay when the cognitive user experiences no more than Q switching blocking-re-access times: for

[0104]

[0105] Among them, Pr(j q ) is calculated by formula (23); Calculated by formula (20); represents the average switching delay of the cognitive user after q switching blocking-re-access, which is calculated by formula (28); M represents the maximum number of perception cycles experienced by the cognitive user, M≥2Q+1;

[0106] Step 4-2, calculate the average number of blocking times when the cognitive user experiences no more than Q handover blocking-re-access times;

[0107] The average number of blocking times when cognitive users experience no more than Q switching blocking-re-access is It is calculated by formula (30) as

[0108]

[0109] in, represents the average transmission probability of a cognitive user when it experiences q handover blocking-reaccess, which is calculated by formula (24); represents the initial access probability of cognitive users, which is calculated by formula (22); Represents cognitive user experience j q The number of transmission patterns when q blocking-reaccess occurs in a sensing cycle is calculated by formula (21); P b and P re They represent the single handover blocking probability and blocking-reaccess probability of cognitive users, which are calculated by equations (11) and (18) respectively; M represents the maximum number of sensing cycles that a cognitive user can experience, M≥2Q+1.

[0110] The beneficial effects of the present invention are as follows: (1) an evaluation model and analysis method for the opportunistic access transmission performance of cognitive users in a multi-channel cognitive radio system under a multiple switching blocking-reaccess mechanism is established. Based on this method, the relationship between the opportunistic transmission performance of cognitive users and the user arrival rate and user departure rate can be studied, and an optimization scheme for opportunistic access transmission performance based on service rate regulation can be studied accordingly; the impact of the number of blocking-reaccess times on transmission performance can also be analyzed, and an optimization scheme for opportunistic access transmission performance based on the number of blocking-reaccess times can be studied accordingly; these schemes provide a theoretical basis and technical tools for the subsequent design of optimizing opportunistic spectrum access performance;

[0111] (2) The cognitive user opportunistic access transmission performance analysis method proposed in the present invention is the first to analyze the transmission performance under the multiple switching blocking-reaccess mechanism, filling the technical gap in the field of cognitive user opportunistic access transmission performance analysis in multi-channel cognitive radio systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0112] Figure 1 It is a flow chart of the analysis of transmission performance of cognitive user opportunity access in the present invention;

[0113] Figure 2 is a scene diagram of the cognitive radio system in the present invention;

[0114] Figure 3 is the state transition relationship diagram of channel i;

[0115] Figure 4 is a transmission time slot structure diagram of a cognitive user in the present invention;

[0116] FIG5( a ) is a schematic diagram of the relationship curve between the average transmission probability and the departure rate of cognitive users;

[0117] FIG5( b ) is a schematic diagram of the relationship curve between the average blocking probability and the leaving rate of cognitive users;

[0118] FIG5( c ) is a schematic diagram of the average switching delay-leaving rate relationship curve of cognitive users;

[0119] FIG5(d) is a schematic diagram of the relationship curve between the average number of re-access times and the departure rate of cognitive users. DETAILED DESCRIPTION

[0120] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments in conjunction with the accompanying drawings.

[0121] like Figure 1 As shown, a flow chart of a method for analyzing transmission performance of cognitive user opportunistic access in a multi-channel cognitive wireless system is provided. The method can be implemented by the following steps:

[0122] Step 1: Design system model, switching scheme and access protocol for multi-channel multi-user cognitive radio system, and model and analyze the dynamics of single channel and the state of cognitive radio system in the system;

[0123] Step 1-1, design system model, switching scheme and access protocol;

[0124] The cognitive radio system has N parallel channels and carries multiple authorized users and cognitive users; the authorized users (primary users) and cognitive users (secondary users) are respectively p,t and λ s,t The Poisson process arrives at the system; the average service time of primary and secondary users in the system follows the mean of 1 / μ p,t and 1 / μ s,t The arrival rate and departure rate of authorized users relative to a single channel are λ p,i =λ p,t / N,μ p,i =μ p,t / N, the arrival rate and departure rate of cognitive users relative to a single channel are λ p,i =λ p,t / N,μp,i =μ p,t / N.

[0125] The access process of authorized users is centrally managed by the base station; the base station only records the channel allocation of authorized users and cannot know the channel occupancy of cognitive users; the base station randomly assigns a channel that is not occupied by other authorized users to the newly arrived authorized users; if there is currently no channel available for allocation, the authorized user's access request is directly rejected.

[0126] Cognitive users use a periodic sensing-transmission time slot structure for opportunistic access transmission. Each sensing period T contains a sensing time slot τ and a transmission time slot T d =T-τ; cognitive users use channel switching and blocking-re-access mechanism to avoid collision between primary and secondary users, and the single channel switching time overhead is T h From the transmission time slot T d ; The number of switching blocking-reaccess times allowed for each secondary user shall not exceed Q times, and the time for each service data transmission shall not exceed M perception cycles, M≥2Q+1.

[0127] Only one user is allowed to occupy any channel at any time, and the access priorities of different users are: main user > cognitive user that needs to switch in the current time slot > cognitive user that was blocked in the previous time slot and needs to access again in the current time slot > newly arrived cognitive user.

[0128] It should be noted that the number of channels N, the user (service) rate λ p,t , s,t , μ p,t , μ s,t , maximum number of re-access times Q, maximum number of sensing cycles M, sensing cycle T, sensing time τ, switching time overhead T h , the above system parameters are all known parameters.

[0129] Step 1-2: Model and analyze the dynamics of a single channel in a cognitive radio system;

[0130] Let X i (t) represents the instantaneous state of channel i at time t, which can be modeled as a 0-1-2 three-state Markov process with a state transition rate m,n∈S={0,1,2},i∈I={1,2,...,N},calculated as

[0131]

[0132] Its state transition probability Calculated as

[0133]

[0134]

[0135]

[0136]

[0137]

[0138]

[0139]

[0140]

[0141]

[0142] Among them, coefficients D1~D6 and E1~E6 are calculated as follows:

[0143]

[0144]

[0145] In the formula, Indicates that channel i is in state s i The average probability is calculated by formula (7):

[0146]

[0147] Among them, λ p,i ,μ p,i They represent the arrival rate and departure rate of authorized users on channel i respectively; s,i ,μ s,i denote the arrival rate and departure rate of cognitive users on channel i respectively.

[0148] Considering the load balancing of each channel, let λ p,i =λ p ,μ p,i =μ p ,λ s,i =λ s ,μ s,i =μ s , the steady-state distribution of all channels will be consistent, that is, At this time, all the labels i in formula (7) can be removed.

[0149] Step 1-3: Model and analyze the cognitive radio system state and its steady-state distribution;

[0150] The cognitive radio system state A(t) is represented by the joint state of N channels:

[0151] A(t)=[X1(t),X2(t),...X, N (t)],t≥0,X i ∈S (8)

[0152] Among them, X i (t) represents the state of channel i; the state space of cognitive radio system is

[0153] Cognitive radio systems are in a stable state The probability of

[0154]

[0155] Among them, s i represents the stable state of channel i, s i ∈S={0,1,2}; Indicates that channel i is in stable state s i The probability of is calculated by formula (7).

[0156] Step 2: The successful switching probability, blocking probability and re-access probability of the cognitive user during a single channel switching are analyzed as follows:

[0157] Step 2-1, calculating the success switching probability and blocking probability of a cognitive user when experiencing a single channel switching;

[0158] The probability of successful switching when a cognitive user experiences a single channel switch is P h , blocking probability P b Calculated as

[0159]

[0160] Where Pr(n) is calculated by formula (11):

[0161]

[0162] p h (u,n) and p b (u,n) respectively represent the conditional successful switching probability and conditional blocking probability of the cognitive user when the system state is u and n authorized users arrive, which are calculated by equation (12) and equation (13) respectively:

[0163]

[0164]

[0165] Among them, N s and N iThey represent the CRN system state as u=[s1,s2,...,s N ], the number of active cognitive users and idle channels in the system are calculated by formula (14):

[0166]

[0167] Among them, j∈[j1,j2], j1=max(0,nN i ),j2=min(N s ,n);j h and j b Calculated as

[0168] j h =j-max(0,nN i ),j b =max(0,nN i )=j1 (15)

[0169] Step 2-2, calculating the re-access probability of the cognitive user in the next sensing period after experiencing switching blocking;

[0170] Given two consecutive system states u,u′, the conditional blocking-reaccess probability p of a cognitive user is re (u,u′) is calculated as

[0171]

[0172] Among them, λ t represents the arrival rate of authorized users relative to the system, N i represents the number of idle channels in the system when the current state is u, which is calculated by formula (14); N s ′ and N i ′ represents the number of active cognitive users and idle channels in the system when the current state is u′, which is calculated by formula (14);

[0173] The p re (u,u′) Take the average of u′,u to get the single handover blocking-reaccess probability P of the cognitive user re for

[0174]

[0175] Where Π(u′) represents the steady-state distribution of the CRN system, which is calculated by formula (9); T is the sensing period; Pr(u′→u|T) is calculated by formula (18):

[0176]

[0177] Step 3: Analyze the average transmission probability and average blocking probability of cognitive users when they experience no more than Q handover blocking-re-access times;

[0178] Step 3-1, calculate the average transmission probability when the cognitive user experiences no more than Q handover blocking-re-access times;

[0179] The probability of successful transmission when a cognitive user experiences q handover blocking-re-access Calculated as

[0180]

[0181]

[0182]

[0183] in, Represents cognitive user experience j q The transmission pattern when q switching blocking-re-access occurs in a sensing period is calculated by formula (20); represents the initial access probability of the cognitive user, which is calculated by formula (21); M represents the maximum number of sensing cycles that the cognitive user may experience, M ≥ 2Q + 1; π1 represents the probability that a single channel is occupied by the primary user; p d represents the detection probability; p f Indicates the false alarm probability; usually p d >>p f .

[0184] Transmission probability of a cognitive user experiencing no more than Q handover blocking-reaccess times Calculated as

[0185]

[0186] in, and Calculated by formula (21) and formula (20) respectively; P b and P re They are calculated by equation (10) and equation (17) respectively; M represents the maximum number of perception cycles experienced by the cognitive user, M ≥ 2Q + 1.

[0187] Step 3-2, calculate the average blocking probability when the cognitive user experiences no more than Q handover blocking-re-access times;

[0188] Average blocking probability when cognitive users experience no more than Q handover blocking-re-access times Calculated as

[0189]

[0190] in, Calculated by formula (21); Calculated by formula (20); P b and P re They are calculated by equation (10) and equation (17) respectively; M represents the maximum number of perception cycles experienced by the cognitive user, M ≥ 2Q + 1.

[0191] Step 4: Analyze the average handover delay and average number of blocking times when the cognitive user experiences no more than Q handover blocking-re-access times;

[0192] Step 4-1, calculate the average switching delay when the cognitive user experiences no more than Q switching blocking-re-access times;

[0193] Average handover delay of cognitive users after q handover blocking-re-access and complete transmission Calculated as

[0194]

[0195]

[0196] in, Represents cognitive user experience j q The conditional transmission probability of q switching blocking-re-access occurs in a sensing period; P h , P b , P re They represent the success switching probability, blocking probability, and blocking-reaccess probability of a single channel switching of a cognitive user, respectively, and are calculated by equations (10) and (17); T h , T d , τ represent the single channel switching overhead, transmission slot duration, and perception time of the cognitive user, respectively; M represents the maximum number of perception cycles experienced by the cognitive user, M≥2Q+1.

[0197] Average handover delay when cognitive users experience no more than Q handover blocking-reconnection times Calculated as

[0198]

[0199] in, From formula (25), we get: Calculated by formula (24); P b , P h and P re They are calculated by equation (10) and equation (17) respectively; M represents the maximum number of perception cycles experienced by the cognitive user, M ≥ 2Q + 1.

[0200] Step 4-2, calculate the average number of blocking times when the cognitive user experiences no more than Q handover blocking-re-access times;

[0201] Cognitive users experience no more than Q handover blocking times - average number of blocking times when reconnecting Calculated as

[0202]

[0203] in, Calculated by formula (21); Calculated by formula (20); P b and P re They are calculated by equation (10) and equation (17) respectively; M represents the maximum number of perception cycles experienced by the cognitive user, M ≥ 2Q + 1.

[0204] Let the number of channels N = 5, and the sensing time slot T in each sensing cycle s =0.1s, transmission time slot T t =0.3s, sensing period T = T s +T d =0.4s, the single switching time overhead is T h =0.05s; primary user arrival rate λ p,t =2 / s, primary user departure rate μ p,t =2 / s; Cognitive user arrival rate λ s,t ∈{5,10,15,20} / s, cognitive user leaving rate μ s,t ∈[0,10] / s; each cognitive user experiences at most Q=3 blocking-reaccess times, and each transmission time of the cognitive user does not exceed M=8 sensing cycles.

[0205] Based on the above assumptions, the simulation results of the cognitive user opportunistic access transmission performance of the present invention are as follows: Figure 5(a)-Figure 5(d) As shown, where:

[0206] FIG5( a ) shows the average transmission probability-departure rate relationship curve of cognitive users, which shows that the average transmission probability of cognitive users gradually increases with the increase of cognitive user departure rate, and gradually decreases with the increase of cognitive user arrival rate.

[0207] FIG5( b ) shows the average blocking probability-leaving rate curve of cognitive users, which shows that the average blocking probability of cognitive users gradually decreases with the increase of cognitive user leaving rate, and gradually increases with the increase of cognitive user arrival rate.

[0208] FIG5(c) shows the average switching delay-departure rate relationship curve of cognitive users, which shows that the average switching delay of cognitive users gradually decreases with the increase of cognitive user departure rate; and also gradually decreases with the increase of cognitive user arrival rate.

[0209] Figure 5(d) shows the relationship curve between the average blocking times and the leaving rate of cognitive users. It shows that when the arrival rate of cognitive users is less than the leaving rate, the average blocking times of cognitive users gradually decreases with the increase of the leaving rate of cognitive users; when the arrival rate of cognitive users is greater than the leaving rate, the average blocking times of cognitive users first increases and then gradually decreases with the increase of the leaving rate of cognitive users.

[0210] Based on the above observations, the average transmission probability of cognitive users can be maximized or the switching delay of cognitive users can be minimized under the condition of constraining the switching delay of cognitive users to meet the transmission performance requirements of opportunistic access.

[0211] The present invention is applicable to cognitive users adopting periodic spectrum sensing and opportunistic spectrum access transmission mode, wherein cognitive users adopt channel switching to avoid authorized users, and adopt a restricted switching blocking-reaccess mechanism to improve the opportunistic transmission performance. By establishing a calculation model of parameters such as the average transmission probability, average blocking probability, average switching delay, and average blocking times of cognitive users, a method for evaluating the transmission performance of opportunistic access under the switching blocking-reaccess mechanism is proposed, which lays a theoretical foundation for optimizing the design of the transmission performance of opportunistic spectrum access in cognitive radio systems.

[0212] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for analyzing transmission performance of cognitive user opportunistic access in a cognitive radio system, characterized in that: The method comprises the following steps: Step 1: A cognitive radio system has N parallel channels and carries a number of authorized users and cognitive users. For the cognitive radio system, a system model and access protocol are constructed; a single channel dynamics and cognitive radio system status in the cognitive radio system are modeled and analyzed; Step 2: Analyze the success switching probability, blocking probability, and re-access probability in the next sensing cycle of the cognitive user when experiencing a single channel switching; specifically: Step 2-1, calculating the success switching probability and blocking probability of a cognitive user when experiencing a single channel switching; Step 2-2, calculating the re-access probability of the cognitive user in the next sensing period after experiencing a single switching blockage; Considering that blocking-reaccess involves two sensing cycles, let the CRS states of the current sensing cycle and its adjacent previous sensing cycle be u, u′ respectively. The conditional reaccess probability p of the cognitive user under the given system state u, u′ is re (u,u′) is calculated as Where n represents the number of newly arrived authorized users in the current sensing cycle, n′ represents the number of newly arrived authorized users in the previous sensing cycle; λ t represents the arrival rate of authorized users relative to the system, N s ′ and N i ′ respectively represent the number of active cognitive users and idle channels in the system in the previous sensing cycle, that is, when the CRS system state is u′; N i Indicates the number of idle channels in the system when the current sensing period, i.e. the CRN system state is u; The condition described in formula (17) is then connected to the probability p re (u,u′) Take the average of u′,u to get the re-access probability of the cognitive user after a single switching blockage, that is, the blocking-re-access probability P re , calculated as Where Π(u′) represents the steady-state distribution of CRS, T represents the duration of the sensing cycle; Pr(u′→u|T) represents the probability that the CRS transitions from state u′ to state u after a period of time T, which is calculated by formula (19): in, Indicates that channel i in CRS changes from state s after time T i 'Transfer state s i probability; Step 3: Analyze the average transmission probability and average blocking probability of cognitive users when they experience no more than Q handover blocking-re-access times; Step 4: Analyze the average switching delay and average number of blocking times when the cognitive user experiences no more than Q switching blocking-re-access times.

2. The method for analyzing transmission performance of cognitive user opportunistic access in a cognitive radio system according to claim 1, characterized in that: In step 1, the system model is constructed as follows: The authorized user has the priority of channel access, and is also called the primary user; the cognitive user opportunistically utilizes the idle channel through spectrum sensing, and its spectrum access priority is lower than that of the primary user, and is also called the secondary user; the authorized user is based on the rate λ p,t The Poisson process arrives at the system, and the average service time in the system follows the mean 1 / μ p,t The exponential distribution of cognitive users is s,t The Poisson process arrives at the system, and the average service time in the system follows the mean 1 / μ s,t exponential distribution of The cognitive radio system has a total of N channels, all of which have equal status, and each channel has an equal opportunity to carry authorized user services and cognitive user services; The arrival rate and departure rate of authorized users relative to a single channel are calculated as λ p,i =λ p,t / N,μ p,i =μ p,t / N; the arrival rate and departure rate of cognitive users relative to a single channel are calculated as λ p,i =λ p,t / N,μ p,i =μ p,t / N.

3. The method for analyzing transmission performance of cognitive user opportunistic access in a cognitive radio system according to claim 1, characterized in that: In step 1, the access protocol is specifically: Authorized users use centralized access control, and the central access point uniformly manages and coordinates the allocation of access channels for authorized users; the central access point of authorized users does not perform channel sensing, and cannot know the occupation of channels by cognitive users, and only records the channel allocation of authorized users; the central access point randomly allocates a channel that is not occupied by other authorized users to newly arrived authorized users, but it may be a channel occupied by cognitive users, in which case cognitive users need to retreat; if there is no channel available for allocation, the access request of the authorized user is directly rejected; Cognitive users use distributed access management and start to execute periodic spectrum sensing-transmission scheme when data needs to be transmitted. Each sensing period T includes sensing time slot τ and transmission time slot T t =T-τ; Once a new cognitive user successfully accesses, it becomes an active user, and the sensing period of the first access is called the initial access period; the active cognitive user broadcasts the channel currently occupied by itself in the transmission time slot of its initial access period to avoid access conflicts with other cognitive users; the active cognitive user continues to sense and transmit periodically until its data transmission ends or it is forced to exit the system due to excessive switching blocking times; Cognitive users use channel switching to avoid access collisions between primary and secondary users. Once an active cognitive user senses that an authorized user appears on its working channel, it will immediately search for an idle channel to perform channel switching. If the cognitive user finds a new idle channel, the switching is successful, and the corresponding switching time overhead is T h If it cannot find an idle channel, the handover fails, and the cognitive user will be temporarily blocked and queue up to wait for the next sensing time slot to arrive before trying to access the transmission again. This strategy is called the blocking-reaccess mechanism, and the time overhead of a single blocking is T t ; If the re-access fails, the cognitive user will be forcibly blocked and exit the system; if the re-access is successful, the cognitive user continues to perform opportunistic access transmission; in order to ensure the transmission continuity of cognitive users and reduce the total switching delay, each cognitive user is allowed to perform no more than Q times of switching blocking-re-access; in addition, it is stipulated that the cognitive user's service data transmission time each time shall not exceed M perception cycles, M≥2Q+1; Only one user is allowed to access any channel at any time; the access priority of different users to the channel is specified as follows: Main user > cognitive user that needs to switch in the current time slot > cognitive user that was blocked in the previous time slot and needs to access again in the current time slot > newly arrived cognitive user.

4. The method for analyzing transmission performance of cognitive user opportunistic access in a cognitive radio system according to claim 1, characterized in that: In step 1, the single channel dynamics modeling analysis is as follows: For any channel i, i∈I={1,2,...,N}, depending on whether it is occupied and which type of user is occupied, channel i has three states: idle, i.e. state 0; occupied by authorized users, i.e. state 1; occupied by cognitive users, i.e. state 2; the state set of a single channel is defined as S={0,1,2}; Let X i (t) represents the instantaneous state of channel i at time t, X i (t) is modeled as a 0-1-2 three-state Markov process, whose state transition rate matrix Q i And the state transition probability matrix P i (t) are expressed as in, Unified Characterization, represents the rate at which channel i transitions from state m to state n, m,n∈S={0,1,2}, calculated as Unified Characterization, represents the probability that channel i transitions from state m to state n after time t, m,n∈S={0,1,2}, which is obtained by solving the Kolmogorov forward equation P i ′(t)=P i (t)Q i Get, that is Among them, P′ i (t) represents the transition probability matrix P i The first-order derivative of (t); coefficients D1~D6 and E1~E6 are In the formula, Represents X i (t) is the steady-state distribution, that is, channel i is in state s i The probability of is calculated by formula (8), that is, Among them, λ p,i ,μ p,i They represent the arrival rate and departure rate of authorized users on channel i respectively; s,i ,μ s,i denote the arrival rate and departure rate of cognitive users on channel i respectively; Considering the load balancing of each channel, let λ p,i =λ p ,μ p,i =μ p ,λ s,i =λ s ,μ s,i =μ s , the steady-state distributions of all channels will be the same, i.e. At this time, all the labels i in formula (8) can be removed.

5. The method for analyzing transmission performance of cognitive user opportunistic access in a cognitive radio system according to claim 4, characterized in that: In step 1, the cognitive radio system status is analyzed as follows: For a cognitive radio system with N indifferent channels, its system state A(t) is jointly characterized by the states of the N channels, that is, A(t)=[X1(t),X2(t),...,X N (t)],t≥0,X i ∈S (9) Among them, X i (t) represents the instantaneous state of channel i at time t, i∈I={1,2,...,N}, X i (t)∈S={0,1,2}; the state space U of the cognitive radio system (CRS) is defined as Where S N Represents the N-dimensional {0,1,2} state space; Cognitive radio systems are in a stable state The probability of Among them, s i represents the stable state of channel i, s i ∈S={0,1,2}; Indicates that channel i is in stable state s i probability.

6. The method for analyzing transmission performance of cognitive user opportunistic access in a cognitive radio system according to claim 5, characterized in that: Step 2-1: Calculate the success switching probability and blocking probability of a cognitive user when experiencing a single channel switching; specifically: Let the success switching probability and blocking probability of a cognitive user undergoing a single channel switching be P h and P b , calculated by formula (11) Where u=[s1,s2,...,s N ] represents the CRS state of cognitive radio system, s i represents the state of channel i; Π(u) represents the probability that CRS is in state u, and Pr(n) represents the probability that n authorized users arrive in CRS, which is calculated by formula (12): Among them, λ t represents the arrival rate of authorized users relative to the system, T represents the duration of the perception cycle; p h (u,n) and p b (u,n) respectively represent the conditional successful switching probability and conditional blocking probability of the cognitive user when the CRS state is u and n authorized users arrive, which are calculated by equation (13) and equation (14) respectively: Among them, N s and N i Respectively represent the CRS state as u=[s1,s2,...,s N ], the number of active cognitive users and the number of idle channels are calculated by formula (15): Among them, 1 [x] is an indicator function, the function value is 1 when x = 1, otherwise it is 0; j represents the number of cognitive users that may switch in the current perception cycle when the system state is u, j∈[j1,j2], j1=max(0,nN i ),j2=min(N s ,n);j h represents the number of cognitive users who successfully switched, j b represents the number of cognitive users temporarily blocked due to handover failure, j h and j b Calculated as I h =j-max(0,nN i ), j b =max(0,nN i )=j1 (16)。 7. The method for analyzing transmission performance of cognitive user opportunistic access in a cognitive radio system according to claim 6, characterized in that: In step 3, the average transmission probability and average blocking probability of the cognitive user when experiencing no more than Q handover blocking-re-access times are analyzed as follows: Step 3-1, calculate the average transmission probability when the cognitive user experiences no more than Q handover blocking-re-access times; The probability of successful transmission when a cognitive user experiences q handover blocking-re-access is 0≤q≤Q,q∈Ν + , where H1 represents the hypothetical event that the cognitive user successfully completes the transmission, Ν + represents a set of non-negative integers; since a cognitive user needs to go through two consecutive perception cycles to experience a switching blockage-reaccess, the number of perception cycles j that may be experienced when q switching blockages-reaccess occur q Should satisfy 2q+1≤j q ≤M, where the first sensing period is the initial access period, and the initial successful access probability of the cognitive user is According to the location where the switching blocking time slot occurs, a single cognitive user q The number of transmission patterns that have q switching blocking-re-access in a sensing cycle is The probability of each transmission pattern appearing is calculated as Supplementary provisions: q >M or j q When <2q+1, Therefore, cognitive user experience j q The conditional transmission probability of q handover blocking-re-access in a sensing period Calculated as in, Represents cognitive user experience j q The transmission pattern when q switching blocking-re-access occur in a sensing period, that is, the transmission frame arrangement pattern determined by different switching blocking positions; represents the initial access probability of the cognitive user in the first sensing cycle; and Calculated as Among them, π1 represents the probability that a single channel is occupied by an authorized user; p d represents the probability that an authorized user occupies the channel and is correctly detected, i.e., the detection probability; p f It represents the probability that an idle channel is misjudged as occupied, i.e., the false alarm probability, 0≤p f <<p d ≤1; Consider q Discrete uniform distribution on the interval [2q+1,M], that is, j q The probability distribution function of For equation (20), q Take the average and get the transmission probability when the cognitive user experiences q switching blocking-re-access for Among them, Pr(j q ) represents j q The distribution function of Represents cognitive user experience j q The conditional transmission probability of q handover blocking-re-access occurs in a sensing period, Represents cognitive user experience j q The transmission pattern when q switching blocking-re-access occurs in a sensing cycle is: represents the initial access probability of the cognitive user in the first sensing cycle, M represents the maximum number of sensing cycles that the cognitive user may experience, M≥2Q+1; Furthermore, summing equation (24) with respect to q, we obtain the transmission probability when the cognitive user experiences no more than Q handover blocking-reaccess times: for Where M represents the maximum number of perception cycles experienced by the cognitive user, M ≥ 2Q + 1; Step 3-2, calculate the average blocking probability when the cognitive user experiences no more than Q handover blocking-re-access times; The average blocking probability when a cognitive user experiences no more than Q handover blocking-re-access times is It is calculated by formula (26) as in, represents the initial access probability of cognitive users, Represents cognitive user experience j q The number of transmission patterns when there are q sensing cycles and q blocking-reaccess times, P b and P re They represent the single handover blocking probability and blocking-reaccess probability of cognitive users respectively.

8. The method for analyzing transmission performance of cognitive user opportunistic access in a cognitive radio system according to claim 7, characterized in that: In step 4, the average handover delay and average number of blocking times when the user experiences no more than Q handover blocking-re-access times are analyzed as follows: Step 4-1, calculate the average switching delay when the cognitive user experiences no more than Q switching blocking-re-access times; The average switching delay is defined as the average total time overhead incurred by the cognitive user in performing channel switching to avoid authorized users during a complete data transmission, that is, from the time the cognitive user activates the transmission to the completion of the transmission or the switching number exceeds the upper limit and is forced to exit the system; Consider cognitive user experience q After q sensing cycles and q handover blocking occurs, all data transmission is completed after re-access, 2q+1≤j q ≤M, 0≤q≤Q, then there are q groups of switching blocking-re-access perception cycles, and the average switching delay of each group is P b (T t +P tr τ); Remaining(j q -2q-1) sensing cycles without switching or successful switching, the average switching delay of each sensing cycle is P h T h ; Considering the cognitive user experience q The conditional transmission probability of q handover blocking-re-access occurs in a sensing period is Cognitive User Experience q Average switching delay when q switching blocking-re-access occur in a sensing period Calculated as in, Represents cognitive user experience j q The conditional transmission probability of q handover blocking-re-access in a sensing period, P h , P b , P re They represent the success switching probability, blocking probability, and blocking-reaccess probability of a single channel switching of a cognitive user, respectively, and T h 、T t , τ represent the single channel switching overhead, transmission time slot duration, and perception time of cognitive users, respectively; M represents the maximum number of perception cycles that cognitive users may experience, M ≥ 2Q + 1; Consider q Discrete uniform distribution on the interval [2q+1,M], for equation (27) with respect to j q Calculate the average switching delay when the cognitive user experiences q switching blockages and re-access Calculated as Among them, Pr(j q ) represents j q The distribution function, T h 、T t , τ represent the single channel switching overhead, transmission time slot duration, and perception time of the cognitive user, respectively; M represents the maximum number of perception cycles that the cognitive user may experience, M≥2Q+1; Furthermore, by summing equation (28) with respect to q, we can obtain the average switching delay when the cognitive user experiences no more than Q switching blocking-re-access times: for Where M represents the maximum number of perception cycles experienced by the cognitive user, M ≥ 2Q + 1; Step 4-2, calculate the average number of blocking times when the cognitive user experiences no more than Q handover blocking-re-access times; The average number of blocking times when cognitive users experience no more than Q switching blocking-re-access is It is calculated by formula (30) as in, represents the average transmission probability of a cognitive user when it experiences q handover blocking-reaccess times, represents the initial access probability of cognitive users, Represents cognitive user experience j q The number of transmission patterns when q blocking-reaccess occurs in a sensing cycle, P b and P re They represent the single handover blocking probability and blocking-reaccess probability of the cognitive user respectively, M represents the maximum number of sensing cycles that the cognitive user can experience, M≥2Q+1.

Images