CN103596220B - A kind of flow control methods combined optimal call access control and reject control - Google Patents

Abstract

The present invention relates to the quality of service guarantee in cognitive radio networks and performance optimization, propose and a kind of combine optimal call access control and reject the QoS guarantee mechanism controlled, including system initialization, calculate optimal admission probability and reject probability and each performance indications of cognitive user.Present invention QoS guarantee based on dynamic accommodation probability and rejecting probability mechanism, in the case of making system throughput maximized, can strictly ensure the qos requirement of cognitive user simultaneously；Described method can be achieved in centralized network.

Description

A kind of flow control methods combined optimal call access control and reject control

Technical field

The present invention relates to the method for flow-control in cognitive radio networks, particularly relate to a kind of associating and most preferably receive and pick Except the strategy controlled.

Technical background

Cognitive radio technology can make cognitive user have the ability in perception cognition network and be not authorized to what user used Spectrum interposition, so chance go to utilize these spectrum interposition to reach to improve the purpose of the availability of frequency spectrum.But, owing to authorizing The uncertainty of user makes the service quality (QoS) of cognitive user often can not be guaranteed, and therefore, ensures in cognition network The qos requirement of cognitive user becomes the emphasis of people's research.

Call Admission Control is to ensure that an important method of cognitive user qos requirement.It is that base station is worked as according to system Time loading condition, and consider newly to decide whether to receive to cognitive user on the impact of other QoS of customer newly to arrive simultaneously Cognitive user.The most traditional admission control scheme is all based on channel reservation mechanism and switching relief area mechanism, Yi Jiji In admission probability mechanism.For channel reservation mechanism, it is simply that base station reserves a part of channel in advance, is served only for service priority Higher switching user (user tied up due to the arrival of authorized user), when in system, only channel reservation can use, Cognitive user access system will be refused, to ensure that the drop rate (being i.e. forced to interrupt the probability of service) of cognitive user is maintained at a certain Below threshold value；And for switching relief area mechanism, be then that switching user will be suspended (or entering in virtual buffering region) wait Until there being available channel to occur, during switching user is suspended, all for refusal cognitive user newly arrived are accessed system System；In the mechanism of admission probability, all new all will be with Probability p access system (i.e. static call access control) to user, to control Flow system flow, reaches to ensure the purpose of cognitive user QoS.

These methods, while the qos requirement of cognitive user can be ensured, but still come with some shortcomings so that gulping down of system The rate of telling does not reaches optimum.First, even if giving optimal channel reservation, the drop rate of cognitive user the most not necessarily just at At given threshold value (likely much lower than given threshold value), system throughput degradation so will be made a lot；Secondly, place If the user waited in relief area can not get available channel for a long time, handover delay the most now will be very big, equally can not Meet the qos requirement of user；Finally, if to all users all with Probability p access system, then when system load is the lightest when, Control now is unnecessary, this also reduces the throughput of system.

Summary of the invention

For the deficiencies in the prior art, it is an object of the invention to provide and most preferably connect a kind of associating in cognitive radio networks Receive and reject the strategy of control, this strategy based on dynamic accommodation probability, i.e. base station to the admission probability of cognitive user be with The change of system load and change, it can make system throughput in the case of arriving maximum, ensures that cognition is used simultaneously Drop rate and the average handover delay at family are maintained at below given thresholding.

For realizing above goal of the invention, the present invention by the following technical solutions:

A kind of flow control methods combined optimal call access control and reject control, is applied in cognitive radio networks, Comprise the following steps:

Step (a), system initialization；

Step (b), cognitive user carry out channel-aware, and sensing results is sent to base station；

Step (c), base station according to sensing results search corresponding optimal admission probability vector table or optimal reject probability to Scale, where it is assumed that system current state be (i, j, k), base station will take a random number t in interval [0,1], described i, j, The number of users waited in authorized user's number, active cognitive user number and relief area active in k expression system respectively；

(c.1) for new to user, if this random number t is less than corresponding admission probabilityThen this user will by with Machine one idle channel of distribution accepts service；Otherwise this user will be blocked；

(c.2) for switching user, if the current available free channel of system, i.e. i+j < M, M is total authorization channel number, then Any control will not be done directly to one idle channel of this switching user's random assortment in base station；If otherwise random number t is less than correspondence Rejecting probabilityTill then this switching user will wait until available free channel in entrance relief area；Otherwise it will be by Interrupt service directly to go offline.

Compared with prior art, the technique effect of the present invention is: the throughput of system can be made to maximize, simultaneously can be tight Lattice ground ensures the drop rate of cognitive user and average handover delay；Can realize in centralized network.

Accompanying drawing explanation

Fig. 1 is systematic state transfer figure；

Fig. 2 is the flow chart based on dynamic accommodation probability and the QoS guarantee mechanism rejecting probability；

Fig. 3 is the blocking rate comparison diagram of cognitive user in performance simulation；

Fig. 4 is the drop rate comparison diagram of cognitive user in performance simulation；

Fig. 5 is the average handover delay comparison diagram of cognitive user in performance simulation；

Fig. 6 is the throughput comparison diagram of cognitive user in performance simulation.

Detailed description of the invention

In order to make the purpose of the present invention, technical scheme and advantage clearer, below in conjunction with accompanying drawing and exemplary reality Execute example, the present invention is further elaborated.Should be appreciated that exemplary embodiment described herein is only in order to explain this Invention, the scope of application being not intended to limit the present invention.

Consider such a centralized cognitive radio networks: authorized user has absolute priority to go to account for compared with cognitive user The priority of the cognitive user arrived with the user Bi Xin in authorization channel, and relief area is high, when i.e. and if only if relief area be sky, The cognitive user newly arrived its is possible to entrance system and accepts service.

In the present invention, cognitive user is controlled by base station by real-time status according to system accordingly, to realize Dynamic call access control and rejecting control.Based on dynamic accommodation probability and the flow chart such as Fig. 2 of the QoS guarantee mechanism rejecting probability Shown in, comprise the following steps:

Step (a), system initialization:

(a.1) given systematic parameter.Consider such a centralized cognitive system with switching relief area: include total Authorization channel number M, authorized user and arrival rate λ of cognitive user_pAnd λ_sAnd service rate μ_pAnd μ_s(assume that user is with Poisson Process arrives and departs from system).

(a.2) optimal admission probability vector table Ρ is determined_adWith rejecting probability vector table Ρ_ev, it is by under different system state Optimal admission probabilityMost preferably reject probabilityComposition, i.e. In the present invention, in order to obtain GoodWithWill be by three-dimensional equine husband's model, (i, j k) represent a shape of system to its state State, wherein i, the use waited in authorized user's number, active cognitive user number and relief area active in j, k expression system respectively Amount.Its state transition diagram is as shown in Figure 1.

(a.2.1) probability of stability of system is calculated.

According to state transition diagram, obtain an equilibrium equation:

Wherein θ₁=1_i+j<M；θ₂=1_k=0；θ₃=1_i+j=M&j>0；Represent current state (i, j, k) under new use to cognition The optimal admission probability at family；Represent that (i, j, k) incision is used the optimal switching probability at family instead and (i.e. entered in current state The probability waited in relief area)；p_i,j,kRepresent current state (i, j, k) under the probability of stability of system.Associating equilibrium equation And normalization equation (1)Probability of stability p of each state will be obtained_i,j,k.Note, due to Ρ_ad And Ρ_evIt is unknown vector to be asked, so probability of stability p herein_i,j,kSimply unknown vector Ρ_adAnd Ρ_evFunction.

(a.2.2) according to the probability of stability of system, the performance indications of system are calculated.Obviously, the performance indications now tried to achieve Also it is unknown vector Ρ_adAnd Ρ_evFunction.

I) blocking rate of cognitive user: due to system is saturated or call access control and cause newly arriving what cognitive user was blocked Probability.

Ii) the drop rate of cognitive user: be not detected by idle channel when newly arriving the cognitive user that authorized user ties up Time, cause this user to be forced to interrupt the probability of service owing to rejecting control.

Iii) the average handover delay of cognitive user: switching user's average waiting delay in the buffer.

WhereinRepresent every authorized user, be switched to relief area The average of the cognitive user of middle wait；Represent that every one authorizes use Family, the average of the cognitive user collided with it；When expression system reaches stable Average user number in relief area；Represent that cognitive user is switched Mean Speed in relief area.

Iv) the throughput of cognitive user: complete the cognitive user number of service in the unit interval.

R_th(Ρ_ad,Ρ_ev)=λ_s·(1-P_block)·(1-P_drop) (5)

(a.2.3) optimization problem providing system describes, in the hope of optimal admission probability and rejecting probability.

max R_th(Ρ_ad,Ρ_ev)

WhereinWithIt is respectively drop rate and the threshold value of average handover delay of cognitive user.

Step (b): cognitive user carries out channel-aware, in practice, due to hardware or the restriction of efficiency, cognitive user can Can all of channel of perception, even there is certain perception mistake, for simplicity analysis, the present invention will not consider these feelings Condition, but it should be understood by those skilled in the art that the present invention being applied to also is very easy in these practical situations.For newly To cognitive user and switching user all will carry out continuous print channel-aware, until perceive available free channel or perception complete own Till channel, subsequently, sensing results information is sent to base station by cognitive user, by base station decide whether agree to access system or Enter relief area.

Step (c): base station carries out corresponding decision-making according to sensing results.Base station is receiving the letter that cognitive user transmission comes After road information, by the optimal admission probability vector table corresponding according to this information searching (for new to user) or most preferably reject probability Vector table (for switching user).

(c.1) for new to user, it is assumed that system current state is that (i, j, k), base station will take one in interval [0,1] Random number t, if this random number t is less than corresponding admission probabilityThen this user will be probabilistically assigned an idle channel Acceptance service；Otherwise this user will be blocked.

(c.2) for switching user, it is also assumed that system current state be (i, j, k), if the current available free letter of system Road, i.e. i+j < M, then any control will not be done directly to one idle channel of this switching user's random assortment in base station；If otherwise with Machine number t is less than corresponding rejecting probabilityThen this switching user will wait until in entrance relief area that available free channel is Only；Otherwise it will be interrupted to service and directly go offline.

A large amount of l-G simulation tests show, compared to channel reservation mechanism and static call access control, the tool of institute of the present invention extracting method There is bigger system throughput, and can strictly ensure the qos requirement of cognitive user.

The foregoing is only presently preferred embodiments of the present invention, not in order to limit the present invention, all essences in the present invention Any amendment, equivalent and the improvement etc. made within god and principle, should be included within the scope of the present invention.

Claims (1)

1. combine optimal call access control and reject the flow control methods controlled, being applied in cognitive radio networks, bag Include following steps:

Step (a), system initialization；

Step (b), cognitive user carry out channel-aware, and sensing results is sent to base station；

Corresponding optimal admission probability vector table or optimal rejecting probability vector table are searched according to sensing results in step (c), base station, Where it is assumed that system current state is that (i, j, k), base station will take a random number t, described i in interval [0,1], and j, k are respectively The number of users waited in authorized user's number, active cognitive user number and relief area active in expression system；

(c.1) for new to user, if this random number t is less than corresponding admission probabilityThen this user will be divided at random Join an idle channel and accept service；Otherwise this user will be blocked；

(c.2) for switching user, if the current available free channel of system, i.e. i+j < M, M is total authorization channel number, then base station Any control will not be done directly to one idle channel of this switching user's random assortment；If otherwise random number t picks less than corresponding Except probabilityTill then this switching user will wait until available free channel in entrance relief area；Otherwise it will be interrupted Service directly goes offline；

Wherein, described step (a) including:

(a.1) given systematic parameter: total authorization channel number M, authorized user and arrival rate λ of cognitive user_pAnd λ_sAnd service Rate μ_pAnd μ_s；

(a.2) optimal admission probability vector table Ρ is determined_adWith rejecting probability vector table Ρ_ev, it is by most preferably connecing under different system state Receive probabilityMost preferably reject probabilityComposition, i.e.

Described step (a.2) including:

(a.2.1) calculate the probability of stability of system, obtain probability of stability p of each state of system_i,j,k；

(a.2.2) probability of stability according to system calculates the performance indications of system；

(a.2.3) optimization problem providing system describes, in the hope of optimal admission probability and rejecting probability；

Described step (a.2.1) including:

It is balanced equation according to state transition diagram:

$\begin{array}{c}({\mathrm{\&lambda;}}_p{\mathrm{\&theta;}}_1+{\mathrm{\&lambda;}}_p{\mathrm{\&theta;}}_3+{\mathrm{\&lambda;}}_s{\mathrm{\&theta;}}_1{p}_{ad}^{(i,j,k)}+{\mathrm{i\&mu;}}_p+{\mathrm{j\&mu;}}_s)p_{i,j,k}\\ =(i+1){\mathrm{\&mu;}}_p{\mathrm{\&theta;}}_2{p}_{i+1,j,k}+(i+1){\mathrm{\&mu;}}_p{\mathrm{\&theta;}}_2{p}_{i+1,j-1,k+1}+(j+1){\mathrm{\&mu;}}_s{\mathrm{\&theta;}}_2{p}_{i,j+1,k}\\ +{\mathrm{\&lambda;}}_p{\mathrm{\&theta;}}_3(1-p_{ev}^{(i,j,k)})p_{i-1,j+1,k}+{\mathrm{\&lambda;}}_p{\mathrm{\&theta;}}_1{p}_{i-1,j,k}+{\mathrm{\&lambda;}}_p{\mathrm{\&theta;}}_3{p}_{ev}^{(i,j,k-1)}{p}_{i-1,j+1,k-1}\\ +{\mathrm{j\&mu;}}_s(1-{\mathrm{\&theta;}}_2)p_{i,j,k+1}+{\mathrm{\&lambda;}}_s{\mathrm{\&theta;}}_1{p}_{ad}^{(i,j-1,k)}{p}_{i,j-1,k}\end{array}$

Wherein θ₁=1_{I+j ＜ M}；θ₂=1_K=0；θ₃=1_{I+j=M&j ＞ 0}；Represent current state (i, j, k) under new use to cognition The optimal admission probability at family；Represent that (i, j, k) incision is used the optimal switching probability at family instead and (i.e. entered slow in current state Rush the probability waited in district)；p_i,j,kRepresent current state (i, j, k) under the probability of stability of system；

Combine above-mentioned equilibrium equation and normalization equationSolve that to obtain the stable state of each state general Rate p_i,j,k；

Described performance indications include:

I) blocking rate of cognitive user:

$P_{block}(P_{ad},P_{ev})=\underset{\&ForAll;i,j,k}{\&Sigma;}(1-p_{ad}^{(i,j,k)})\&CenterDot;p_{i,j,k}$

Ii) drop rate of cognitive user:

$P_{drop}(P_{ad},P_{ev})=\frac{{\mathrm{\&lambda;}}_p\underset{i+j=M,j>0}{\mathrm{\&Delta;}}(1-p_{ev}^{(i,j,k)})\&CenterDot;p_{i,j,k}}{{\mathrm{\&lambda;}}_s(1-P_{block})}$

Iii) the average handover delay of cognitive user:

$D_{ho}(P_{ad},P_{ev})=\frac{\stackrel{\&OverBar;}{N_{hdof}}}{\stackrel{\&OverBar;}{N_{colision}}}\&CenterDot;\frac{\stackrel{\&OverBar;}{N_{buffer}}}{\stackrel{\&OverBar;}{R_{hdof}}}$

WhereinRepresent every authorized user, be switched to relief area medium The average of the cognitive user treated；Represent every authorized user, with The average of its cognitive user collided；Relief area when expression system reaches stable In average user number；Represent that cognitive user is switched to relief area In Mean Speed；

Iv) throughput of cognitive user:

R_th(Ρ_ad,Ρ_ev)=λ_s·(1-P_block)·(1-P_drop)；

Described optimization problem is described as:

max R_th(Ρ_ad,Ρ_ev)

$s.t.\left\{\begin{array}{c}{P}_{drop}(P_{ad},P_{ev})\&le;P_d^{*}\\ D_{ho}(P_{ad},P_{ev})\&le;D_h^{*}\\ 0\&le;P_{ad}\&le;1\\ 0\&le;P_{ev}\&le;1\end{array}\right.,$

Wherein,WithIt is respectively drop rate and the threshold value of average handover delay of cognitive user.