CN102905321B - Admission control method in cognitive radio network - Google Patents

Abstract

The invention discloses an admission control method in a cognitive radio network, and relates to the technical field of radio communication. The invention provides a new admission control mechanism by analyzing access performances such as blocking rate and switching rate of a secondary user while a compulsive priority queuing theory is adopted. According to the current frequency spectrum resource and access capacity of the secondary users, the secondary user to be accessed is adaptively to be accepted or rejected. The following two conditions are considered mainly: one is that how to determine a reasonable secondary user access range under the condition that spectrum efficiency of a master user is constant; and the other one is that how to determine the access capacity of the secondary users according to the spectrum efficiency of the master user under the condition that the access capacity of the secondary users is constant. The admission control mechanism not only can guarantee QoS (quality of service) of a cognitive user in a network but also can reduce unnecessary overhead in the network.

Description

Admission control method in cognitive radio network

Technical Field

The invention relates to a cognitive radio network, in particular to a new mechanism for a cognitive user entering the network to obtain reliable service meeting self QoS.

Background

In a conventional radio network, a fixed spectrum allocation manner is mostly adopted, and even if a licensed spectrum is idle, an unlicensed spectrum is not occupied, thereby causing waste of spectrum resources. The cognitive radio technology is one of effective means for improving the spectrum utilization rate, and can find and utilize a spectrum hole on the premise of not influencing the communication of authorized users, so that the problem of spectrum resource shortage is solved easily.

The existing research of cognitive radio is performance analysis under a specific environment, and qualitative and quantitative research is lacked for QoS factors such as switching rate and blocking rate which can greatly affect the transmission performance of secondary users in a network. Because the cognitive radio technology can effectively utilize the spectrum holes, in order to ensure the communication quality, the cognitive radio technology is suitable for accessing secondary users only when the idle spectrum resources in the network meet certain conditions, otherwise, the access is meaningless; similarly, the network can only access a proper amount of secondary users under the fixed primary user spectrum efficiency. Therefore, it is necessary to provide a new admission control technology, which can define the access conditions and ranges qualitatively and quantitatively.

The Chinese patent with the publication number of CN102123400A discloses a QoS method based on CWAN, and the new framework provided by the invention optimizes the end-to-end QoS performance of the cognitive network and improves the feasibility of realizing the cognitive network. However, the specific detailed description of the access condition, range and blocking procedure of the user is lacked, and the self-adaption has certain defects, and the access condition and range of the secondary user are not determined quantitatively.

Disclosure of Invention

In order to solve the above technical problems, the present invention provides a new admission control method based on performance analysis of the switching rate, blocking rate, etc. of dynamic spectrum access in a cognitive radio network.

The invention adopts the technical scheme to solve the technical problems and provides an admission control method in a cognitive radio network, wherein in the cognitive radio network, the state probability p of an instant rejection system is used_k、p_mCalling a formulaDetermining the spectrum efficiency of a spectrum occupied by a main user, according to a formula:determining the access amount of the secondary user, wherein,，0≤k≤m，，rho is the access amount of the master user, m is the total channel number, k is the current channel number, and lambda₁、λ₂、μ₁、μ₂The number of the primary and secondary users arriving in unit time and the number of the primary and secondary users served in unit time are counted; determining the switching probability P of the secondary user according to the access performance relationship of eta and alpha to the switching rate and the blocking rate of the secondary user by the Markov state transition diagram_HandoffAnd the blocking probability P_BlockingAccording to the formula β = ω P_Handoff+(1-ω)P_BlockingObtaining a weighting factor beta, and determining a threshold value beta of the beta according to the QOS requirement of a user_threshold(ii) a And carrying out admission control on the secondary user. The further control is specifically as follows:

when the spectrum efficiency eta of the main user is certain, beta is less than beta_thresholdObtaining the threshold value alpha of the access amount of the secondary user_thresholdThe total amount of the access amount of the secondary users in the system after accessing the new user is alpha' = alpha_new+α_accessedIn which α is_accessedFor the amount of secondary users that have been accessed, α_newThe number of the newly accessed secondary users is; when alpha' is less than or equal to alpha_thresholdAllowing all cognitive users requesting access to enter the system by the system; when alpha' is greater than alpha_thresholdTime, system with probabilityAdmitting a secondary user into the system. When the access amount of the secondary user is certain, according to a formula beta_threshold=ωP_H-threshold+(1-ω)P_B-thresholdDetermining a threshold value beta of beta_thresholdAt β < β, depending on the QoS requirements of the user_thresholdTime-derived threshold η_threshold(ii) a When a new user is accessed, the frequency spectrum utilization rate eta' of the secondary user in the system is less than or equal to eta_thresholdWhen the system is in use, all the cognitive users requesting access are allowed to enter the system by the system; when eta' is less than or equal to eta_thresholdTime system with probabilityAdmitting a secondary user into the system.

The user can select the corresponding secondary user switching rate and the threshold value P of the blocking rate according to the actual requirement (i.e. when the user has higher requirement for the service quality, the threshold value of the blocking rate is selected to be smaller, when the user quantity needing to be accessed is increased, the threshold value of the blocking rate is selected to be larger, and the corresponding switching rate is decreased)_H-threshold、P_B-thresholdThe invention obtains the beta threshold value according to the switching rate selected by the user and the threshold value of the blocking rate, and provides an admission control method for controlling the secondary user.

Compared with the prior art, the method and the device can adaptively accept or reject the secondary user to be accessed according to the current spectrum resource condition and the service quality requirement of the secondary user, and can better guarantee the QoS requirement of the secondary user and the overall performance of the network through acceptance control. Meanwhile, the invention can qualitatively and quantitatively give the access range and conditions of the secondary user.

Drawings

FIG. 1 is a schematic diagram of forced priority queuing;

figure 2 is a markov state transition diagram;

FIG. 3 is a graph showing the relationship between the effects of eta and alpha on the switching rate and blocking rate of the secondary users;

fig. 4 is a flow chart of an admission control method.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more clear, the admission control method of the present invention is specifically described below with reference to the accompanying drawings. Fig. 1 is a schematic diagram of forced priority queuing for dynamic spectrum access of a cognitive radio network based on the forced priority queuing theory.

In the schematic diagram, a main user queue is an instant system, and the arrival obedience parameter of the main user is lambda₁Poisson distribution with a time-of-service compliance parameter of mu₁Negative exponential distribution of (c). The secondary user queue is an M/M/M/n multi-service window waiting loss queuing model, and the arrival process compliance parameter of the secondary user is lambda₂Poisson distribution with a time-of-service compliance parameter of mu₂Negative exponential distribution of (1), the length of the queue of the secondary user is n_s. Parameter lambda₁、λ₂Respectively representing the number of arriving main users and sub-users in unit time, and a parameter mu₁And mu₂Indicating the number of primary users and the number of secondary users served per unit time.

A markov state transition diagram corresponding to figure 1 is shown in figure 2.

The channel state in the system is three types: occupied by a master user, occupied by a secondary user and in an idle state. The number in the circle is identified as (i, j, k), where i represents the number of channels occupied by the current state secondary user, j represents the number occupied by the current state primary user, and k represents the queue length of the current secondary user waiting for service. The number of channels is m, the maximum queue length of the secondary user is n_s。

Obtaining the switching probability P of the secondary user according to the Markov state transition diagram_HoffAnd the blocking probability P_BAs follows: <math> <mrow> <msub> <mi>P</mi> <mi>Handoff</mi> </msub> <mo>=</mo> <munderover> <mi>&Sigma;</mi> <mrow> <mi>i</mi> <mo>=</mo> <mn>0</mn> </mrow> <mrow> <mi>m</mi> <mo>-</mo> <mn>1</mn> </mrow> </munderover> <munderover> <mi>&Sigma;</mi> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>m</mi> </munderover> <munderover> <mi>&Sigma;</mi> <mrow> <mi>k</mi> <mo>=</mo> <mn>1</mn> </mrow> <msub> <mi>n</mi> <mi>s</mi> </msub> </munderover> <msub> <mi>p</mi> <mi>Handoff</mi> </msub> <mrow> <mo>(</mo> <mi>i</mi> <mo>,</mo> <mi>j</mi> <mo>,</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow> </math>

<math> <mrow> <msub> <mi>P</mi> <mi>Blocking</mi> </msub> <mo>=</mo> <munderover> <mi>&Sigma;</mi> <mrow> <mi>i</mi> <mo>=</mo> <mn>0</mn> </mrow> <mrow> <mi>m</mi> <mo>-</mo> <mn>1</mn> </mrow> </munderover> <munderover> <mi>&Sigma;</mi> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>m</mi> </munderover> <msub> <mi>p</mi> <mi>Blocking</mi> </msub> <mrow> <mo>(</mo> <mi>i</mi> <mo>,</mo> <mi>j</mi> <mo>,</mo> <msub> <mi>n</mi> <mi>s</mi> </msub> <mo>)</mo> </mrow> <mo>+</mo> <munderover> <mi>&Sigma;</mi> <mrow> <mi>i</mi> <mo>=</mo> <mn>0</mn> </mrow> <mi>m</mi> </munderover> <munderover> <mi>&Sigma;</mi> <mrow> <mi>j</mi> <mo>=</mo> <mn>0</mn> </mrow> <mi>m</mi> </munderover> <mi>p</mi> <mrow> <mo>(</mo> <mi>i</mi> <mo>,</mo> <mi>j</mi> <mo>,</mo> <msub> <mi>n</mi> <mi>s</mi> </msub> <mo>)</mo> </mrow> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow> </math>

wherein p is_Handoff(i, j, k) represents the probability of a handover occurring, p (i, j, n)_s) Representing a steady state probability; p_HandoffThe sum of probabilities, P, representing the next user's handover in various states_BlockingThe sum of the blocking rate and the switching rate of the new secondary user when the secondary user queue is full. The access amount of the secondary user is as follows:

<math> <mrow> <mi>&alpha;</mi> <mo>=</mo> <mfrac> <msub> <mi>&lambda;</mi> <mn>2</mn> </msub> <mrow> <mi>m</mi> <msub> <mi>&mu;</mi> <mn>2</mn> </msub> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>3</mn> <mo>)</mo> </mrow> </mrow> </math>

can be based on the state probability p of the instant rejection system_k、p_mAnd (3) calling a formula (4) to determine that the spectrum efficiency of the spectrum occupied by the main user is as follows: <math> <mrow> <mi>&eta;</mi> <mo>=</mo> <munderover> <mi>&Sigma;</mi> <mrow> <mi>k</mi> <mo>=</mo> <mn>0</mn> </mrow> <mrow> <mi>m</mi> <mo>-</mo> <mn>1</mn> </mrow> </munderover> <mfrac> <mi>k</mi> <mi>m</mi> </mfrac> <msub> <mi>p</mi> <mi>k</mi> </msub> <mo>+</mo> <msub> <mi>p</mi> <mi>m</mi> </msub> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>4</mn> <mo>)</mo> </mrow> </mrow> </math>

wherein,，0≤k≤m，，. Wherein rho is the access amount of a master user, k is the current channel number, and the parameter lambda₁、λ₂、μ₁、μ₂The number of arriving primary and secondary users counted in unit time and the number of primary and secondary users served in unit time are calculated.

The Markov model is solved by using a steady-state solution method, so that the switching rate and the blocking rate of a secondary user can be obtained, when the network condition is fixed, the blocking rate is reduced along with the increase of the access amount, and the switching possibility is higher, namely the switching rate is increased; since a reduction in handover rate necessarily results in a reduction in the number of secondary users accessing the network and an increase in blocking rate, the handover probability P is determined in order to balance the two_HandoffAnd the blocking probability P_BlockingAccording to the formula: β = ω P_Handoff+(1-ω)P_Blocking(5) The QoS factor beta is determined. Where ω is a weighting coefficient. ω =0 represents the blocking probability of β paying attention only to the secondary user; ω =1 represents the handover probability of β paying attention only to the secondary user; when omega is more than 0 and less than 1, the blocking rate and the switching rate of the secondary user are considered simultaneously. The switching rate and the blocking rate of the secondary user can satisfy the following relation:

the secondary user switching probability is as follows: $P_{\mathrm{Handoff}}=\frac{N_h}{N_a+N_h}---\left(6\right)$

wherein N is_hFor the number of times of subscriber switching, N_aThe number of the second users with successful access (including the second users which are re-accessed by re-entering the queuing queue without success of switching). The secondary user blocking probability is:

$P_{\mathrm{Blocing}}=\frac{N_{\mathrm{af}}}{N_{\mathrm{SU}}}---\left(7\right)$

wherein N is_afIndicating the number of unsuccessful accesses (secondary users with unsuccessful re-entry into the queue for handover), N_SUIndicating the total number of sub-users accessed.

And further obtaining a relation graph of alpha and eta and the access performance of the secondary user, namely, the switching rate and the blocking rate, as shown in fig. 3, the relation graph of the influence of eta and alpha on the switching rate and the blocking rate of the secondary user is obtained. And as the switching rate and the blocking rate of the secondary users are increased along with the increase of alpha and eta, the blocking rate threshold value is in direct proportion to the quantity of the users needing to be accessed. Selecting threshold value P of corresponding secondary user switching rate and blocking rate according to service quality requirement of user_H-threshold、P_B-thresholdAs can be seen from fig. 3, the corresponding point at the inflection point in the graph may be selected as P_H-threshold、P_B-threshold。

An admission control scheme is proposed below for the handover rate and blocking rate of the secondary users, etc. The following is discussed in two cases:

firstly, when the spectrum efficiency of a primary user is fixed and the number of secondary users changes, how to control the amount of cognitive users to ensure the QoS of the cognitive users; and secondly, when the amount of the cognitive users is stable and the use efficiency of the primary user on the frequency spectrum resources changes, how to control the primary user to ensure the QoS of the cognitive users.

Fig. 4 is a flow chart of an admission control method according to the present invention.

1. When the primary user frequency spectrum efficiency eta is constant, according to the formula (4)Is determinedIs a fixed value, because the network resource is fixed, it inevitably causes the change of the access quantity alpha of the secondary user, along with the change of the access quantity alpha of the user, the arrival rate lambda of the secondary user₂And service rate mu₂And also varies according to the sub-user switching rate P_HandoffAnd the blocking rate P_BlocingAnd calling the formula (5) to further obtain the corresponding relation among the access quantities alpha and beta, the switching rate and the blocking rate.

1) Selecting corresponding secondary user switching rate and threshold value P of blocking rate according to actual user QoS requirement_H-threshold、P_B-threshold. Then according to the formula beta_threshold=ωP_H-threshold+(1-ω)P_B-thresholdDetermining a threshold value beta of beta_threshold. Beta < beta to ensure the QoS required by the cognitive user_thresholdSearching a threshold value of the access quantity of the secondary user according to the corresponding relation between the access quantity alpha and beta, the switching rate and the blocking rate;

2) the total amount of the access amount of the secondary users in the system after the new users are accessed is alpha' = alpha_new+α_accessedIn which α is_accessedFor the amount of secondary users that have been accessed, α_newFor the newly accessed secondary user quantity, according to the formulaAndcan be derived, wherein_accessed、λ_newThe number of users accessed to the system and the number of newly arrived users in unit time are respectively; mu.s_accessed、μ_newRespectively the number of users served by the system in unit time and the number of users to receive service;

3) when alpha' is less than or equal to alpha_thresholdAllowing all cognitive users requesting access to enter the system by the system;

4) when alpha' is greater than alpha_thresholdThe time system needs to carry out admission control on the secondary users with probabilityAdmitting a cognitive user into the system;

5) by limiting the number of the cognitive users entering the system, the access amount of the cognitive users entering the system and using the frequency spectrum resources is enabled to be as close as possible to alpha_thresholdThe level thus guarantees the QoS of the cognitive user.

2. When the access quantity alpha' of the secondary user is constant, according to the formula (3):in the knowledge that,the value of the secondary user is constant, and the spectrum efficiency of the primary user is influenced certainly when the network condition is constant and the access amount of the secondary user is constant. As η varies, the arrival rate λ of the primary user₁And service rate mu₁And the switching rate and the blocking rate of the secondary user are influenced, and the switching rate of the secondary user can be obtained according to a Markov modelAnd rate of blockingAnd then according to the formula (5), the corresponding relation among the utilization rates eta and beta of the primary user frequency spectrum, the switching rate and the blocking rate can be further obtained。

1) Selecting corresponding secondary user switching rate and threshold value P of blocking rate according to actual user QoS requirement_H-threshold、P_B-threshold. Then according to the formula beta_threshold=ωP_H-threshold+(1-ω)P_B-thresholdDetermining a threshold value beta of beta_threshold. In order to ensure the QoS required by the cognitive user, beta is less than beta according to the QoS requirement of the user_thresholdObtaining a threshold value eta of eta_threshold；

2) When a new user is accessed, the frequency spectrum utilization rate eta' of the secondary user in the system is less than or equal to eta_thresholdWhen the system is in use, all the cognitive users requesting access are allowed to enter the system by the system;

3) when eta' is greater than eta_thresholdThe time system needs to carry out admission control on the secondary users with probabilityAdmitting a cognitive user into the system; the access quantity of the cognitive users which can enter the system and use the frequency spectrum resources is as close as possible to eta_thresholdThe level thus guarantees the QoS of the cognitive user.

Claims (2)

1. An admission control method in a cognitive radio network is characterized in that in the cognitive radio network, the admission control method is based on the state probability p of an instant rejection system_k、p_mCalling a formulaDetermining the spectrum efficiency of a spectrum occupied by a main user, according to a formula:number of times of determinationThe access amount of the user; determining the switching probability P of the secondary user according to the access performance relationship of eta and alpha to the switching rate and the blocking rate of the secondary user by the state transition diagram of the Markov model_HandoffAnd the blocking probability P_BlockingAccording to the formula β ═ ω P_Handoff+(1-ω)P_BlockingObtaining a weighting factor beta, and determining a threshold value beta of the weight factor beta according to the quality of service (QOS) requirement of a user_threshlodWherein0≤k≤m，rho is the access amount of a master user, m is the total channel number, k is the current channel number, omega is a weighting coefficient, and lambda₁、λ₂、μ₁、μ₂The number of the primary and secondary users arriving in unit time and the number of the primary and secondary users served in unit time are counted; when the spectrum efficiency eta of the main user is constant, beta<β_threshlodObtaining the threshold value alpha of the access quantity of the secondary user_thresholdAfter accessing the new user, the total amount of the access amount α' of the secondary user in the system is α ═ α -_new+α_accessed(ii) a When alpha' is less than or equal to alpha_thresholdAllowing all cognitive users requesting access to enter the system by the system; when alpha'>α_thresholdTime, system with probabilityAdmitting a secondary user into the system, wherein_accessedFor the amount of secondary users that have been accessed, α_newThe number of the newly accessed secondary users is; when the access amount of the secondary user is certain, selecting the threshold value P of the switching rate of the secondary user according to the QoS requirement of the actual user_H-thresholdAnd a threshold value P of the blocking rate_B-thresholdAccording to the formula beta_threshlod＝ωP_H-threshold+(1-ω)P_B-thresholdDetermining a threshold value beta of beta_threshlod，β<β_threshlodTime-derived threshold η_threshold(ii) a When a new user is accessed, the frequency spectrum utilization rate eta' of the secondary user in the system is less than or equal to eta_thresholdWhen the system is in use, all the cognitive users requesting access are allowed to enter the system by the system; eta'>η_thresholdTime system with probabilityAdmitting a secondary user into the system.

2. The admission control method according to claim 1, wherein the secondary user switching rate is solved according to a markov modelAnd rate of blockingWherein N is_hFor the number of times of subscriber switching, N_aNumber of sub-users successfully accessed, N_afIndicates the number of unsuccessful accesses, N_SUIndicating the total number of sub-users accessed.