CN103179578B - Frequency spectrum switching method in a kind of CR system and device - Google Patents

Abstract

The invention discloses the frequency spectrum switching method in a kind of CR system and implement device thereof, the frequency spectrum being used for realizing in CR system switches, lower switching rate and higher throughput of system can be ensured, and provide better performance guarantee on system cognizant user bearing capacity He in handoff failure amount.Wherein said frequency spectrum switching method comprises: the information of cognitive user and primary user in CR system update current time slots channel, adds up all cognitive user having access channel demands, statistics idle channel; By every bar channel combinations of pairs between two in each cognitive user for access channel and idle channel, calculate respectively according to parameters and obtain judgement matrix S; The cognitive user Su that in selection matrix S, element maximum is corresponding accesses respective channels Ch; Delete the successful user of access and channel, repeat the operation of above-mentioned combinations of pairs, until cognitive user or idle channel are empty.

Description

Frequency spectrum switching method in a kind of CR system and device

Technical field

The present invention relates to wireless communication field, be specifically related to the condition of multi-system coexistence time-frequency spectrum changing method in LTE-CR system.

Background information

Cognitive radio is the hot technology solving current spectral scarcity of resources, it is by cognitive radio environment, seek available spectrum resources, carry out intelligence, dynamically frequency spectrum to select, break traditional in the mode of wireless communication system fixed partition frequency spectrum resource, thus improve the utilance of frequency spectrum resource.

In cognitive radio networks, user comprises authorized user (primary user (PR)) and cognitive user (secondary user (SR)): the former enjoys the preferential right of frequency spectrum, latter dynamically follows the tracks of the former spectrum occupancy, and its untapped idle frequency spectrum communicates.When authorized user reuses frequency spectrum, frequency spectrum need be returned to it and use by cognitive user.In order to ensure the continuation that cognitive user communicates and QoS, it smoothly can transfer to other idle frequency ranges and continue communication while abdicating frequency spectrum; In addition, when frequency spectrum shared by cognitive user can not meet its business demand, also can transfer to other more suitably idle frequency spectrums, be frequency spectrum and switch.

It is a kind of novel switching that frequency spectrum switches, and is one of cognitive radio key technology, carries out frequency range conversion where necessary for cognitive user.Frequency spectrum switches in and determines the utilance of frequency spectrum and the throughput of system to a great extent, therefore, explores and sets up efficient frequency spectrum switching model and switching channels selection algorithm has important theory and using value.

Traditional frequency spectrum handoff technique is to the information of cognitive user SU itself, and the Information Pull of channel CH is abundant all not in system, only adopt even the mode of Stochastic accessing, also namely when cognitive user is forced to exit channel, random choose channel access from remaining idle channel.

The problem of conventional method may have: the channel possibility primary user arrival rate of new access is very high, after cognitive user access, secondary will occur again because primary user arrives again soon even switch for three times, the impact repeatedly switching the handover delay brought will make cognitive user communication performance deteriorate significantly; The factor such as signal to noise ratio, bandwidth of new access channel determines channel capacity, and channel capacity deficiency will cause cognitive user transmission rate greatly to reduce, and this also can affect its communication performance; Give a domestic consumer by certain " outstanding " channel allocation, cause waist performance, and make the cognitive user total throughout of whole system can not get problem improved etc.

So we need one can make full use of user profile, channel information, many-sided performance index such as time delay, speed can be taken into account, the method of most suitable channel access is selected for each user, entire system performance is improved, and is not only the frequency spectrum switching method that some cognitive user performances improve.

Summary of the invention

The invention provides a kind of frequency spectrum switching method accurately, in effective CR system and implement device, guarantee the cognitive user greatly reduced in CR system be hide primary user arrive needs generation switching times, improve the throughput of system to cognitive user, the final object realizing guarantee cognitive user communication quality simultaneously.

The present invention takes full advantage of the effective information in channel, does not have the low switching rate of simple pursuit, the throughput that also simple pursuit is high, but utilizes the method for weighting to consider the two as final channel pairs foundation, has taken into account the superiority of two kinds of performances; Consider all cognitive user in system, selected optimum in whole combinatorial matrix, instead of only consider the match condition of some users and a certain bar channel, ensure that the optimal switching of whole system is selected.

Specific implementation process

As figure (1), for realizing the basic procedure of frequency spectrum switching device shifter in each time slot of CR system.

This flow process comprises the following steps:

1. in current time slots channel, the information of cognitive user upgrades, and comprises the time T transmitted _trans, the data volume D that is transmitted _transdeng, wherein transmitted data amount increase is not carried out for the cognitive user being extruded channel and being still in " detection state ", only carry out the increase of respective transmissions time delay VT, finally its channel taken is discharged for the cognitive user completing transmission, by its effective data rate R _effectivecarry out record.

2. in current time slots channel, the information of primary user upgrades, if now primary user's end of transmission, discharges the channel that it occupies; If primary user occurs, and present channel does not exist cognitive user, then normally access this channel; If when primary user occurs, have cognitive user to exist, then primary user also normally accesses, but will hang up cognitive user, makes it enter " detection state ", and puts it into switching user S set U _handoverin, in propagation delay time VT afterwards, do not transmit data.

3. new user produces at random, is recorded in new access set SU by unified for the user of these new generations _newin, in order to follow-up access channel.

4. add up the idle channel in current all channels, be recorded in idle channel set CH _idle, in order to follow-up access operation.

5., according to the information of channel and the information of each switching cognitive user, calculate the matrix PH of minimum switching probability.Suppose SU _handoverlength is M, CH _idlelength is N, and so PH is the matrix of M × N, and wherein each is all the combinations of pairs of a cognitive user and a channel.Suppose when switching user Su1 and needing selective channel Ch1, channel has idled the X0 time, and cognitive user has transmitted the Y0 time, so under this condition, wish cognitive user continue to need the transmission time be less than channel continue can be idle time, namely the probable value of this situation is

$P{H}_{\mathrm{ij}}=P(Y_j-Y0<X_i-X0|Y_j>Y0,X_i>X0)$

$=\frac{P(Y_j-Y0<X_i-X0,Y_j>Y0,X_i>X0)}{P(X_i>X0)P(Y_j>Y0)}$

$=\frac{{{\mathrm{\&mu;}}_S}_j}{{{\mathrm{\&mu;}}_S}_j+{{\mathrm{\&lambda;}}_P}_i}$

Wherein for S set U _handoverthe data length distributed constant of a middle jth cognitive user, λ _pifor set CH _idlein the ON distributions parameter of i-th channel.

If because a cognitive user there occurs switching, so impact of handover delay, makes its total transmission time lengthening, so wish to reduce switching times as far as possible, also namely we wish a kind of SU that selection switching probability is as far as possible little _handover(i) and CH _idlej the combination of (), make this probable value larger, the probability so switched is also less.When prediction, this distributed constant value is utilized to calculate pH value.

6., according to each channel information and each cognitive user information, calculate matrix t remaining time _left.The same with PH matrix, if SU _handoverlength is M, CH _idlelength is N, so t _leftfor the matrix of M × N, wherein each is all the combinations of pairs of a cognitive user and a channel.So hypothesis is at switching user Su _jneed selective channel Ch _itime, cognitive user remaining data M _j, the signal to noise ratio of selective channel is SNR _i, bandwidth is B _i, then channel capacity is

C _i＝B _ilog ₂(1+SNR _i)

Then remaining time is:

${t_{\mathrm{left}}}^{\mathrm{ij}}=\frac{M_j}{C_i}$

Because every bar channel has the attributes such as different signal to noise ratios, bandwidth, the capacity which results in channel is different, and based on the principle that cognitive user is transmitted with Shannon capacity, we wish that the channel that selection capacity is high as far as possible transmits, to improve the throughput of system, that is we desirably remaining time less, so final effective data rate Re _ffectivealso just can be higher.

In order to unified with PH, here by t _leftget inverse, namely

${T_{\mathrm{left}}}^{\mathrm{ij}}=\frac{1}{{t_{\mathrm{left}}}^{\mathrm{ij}}}$

That we finally will select like this is T _lefta pair combination that middle element maximum is corresponding, consistent with PH.

7. be dimensionless pattern by two matrix disposals, namely two matrixes be normalized respectively, for PH matrix, each element in PH ' after process

${{\mathrm{PH}}^{\&prime;}}_{\mathrm{ij}}=\frac{P{H}_{\mathrm{ij}}}{\sqrt{\underset{i}{\mathrm{\&Sigma;}}\underset{j}{\mathrm{\&Sigma;}}P{H}_{\mathrm{ij}}^2}}$

In like manner obtain T _leftbe normalized to T ' _left

${T^{\&prime;}}_{\mathrm{Left}}=\frac{T_{\mathrm{ij}}}{\sqrt{\underset{i}{\mathrm{\&Sigma;}}\underset{j}{\mathrm{\&Sigma;}}{T}_{\mathrm{ij}}^2}}$

8. comprehensive two attribute, configuration weighting parameters α and β, α and β employing empirical value here, generally all gets 0.5, and obtains conclusive judgement matrix S

S＝αPH′+βT′ _Left

9. select the corresponding cognitive user Su and channel Ch of the maximum in s-matrix to combine, and by this cognitive user access respective channels, delete new access user S set U afterwards _handoverwith idle channel CH _idlein each self-corresponding element, jump to the 5th step continue, until SU _handoveror CH _idlefor sky.

10. couple SU _newprocess with to SU _handoverprocess consistent, but priority treatment switches user SU _handoverset, repeats no more.After being disposed, statistical system relevant information, terminates current time slots.

Here is the design parameter of emulation:

Simulation result as Fig. 3,4,5,6 visible, therefore can find out that the frequency spectrum handoff algorithms of weighted comprehensive of the present invention compares traditional random access algorithm, greatly can reduce switching rate, and significantly improve throughput of system, the traffic carrying capacity increasing system bearing with cognitive user arrival rate gradually is also improved largely, handoff failure amount is but relatively less simultaneously, so above-mentioned simulating, verifying the present invention is successful, believable.

Accompanying drawing explanation

Fig. 1 is the workflow of CR system spectrum switching device shifter

Fig. 2 is the cooperation relation figure in frequency spectrum switching device shifter between each module

Fig. 3 is the detailed operation flow process of data processing module

Fig. 4 is the advantage on inventive method contrast conventional method switching rate

Fig. 5 is the advantage in inventive method contrast conventional method throughput

Fig. 6 is the advantage in inventive method contrast conventional method service bearer amount

Fig. 7 is the advantage in inventive method contrast conventional method handoff failure amount.

Claims (5)

1. the frequency spectrum switching method in CR system, is characterized in that, comprising:

The information of cognitive user and primary user in CR system update current time slots channel, adds up all cognitive user having access channel demands, statistics idle channel;

By every bar channel combinations of pairs between two in each cognitive user for access channel and idle channel, obtain parameters, comprise the data volume D that cognitive user has been transmitted _trans, the data length distributed constant μ of cognitive user, the bandwidth B of channel, the quantum condition entropy parameter lambda that the signal to noise ratio snr of channel and channel clear meet, calculate a decision value for every a pair combination respectively, this value is by maximum rate T _leftthe most very much not switching probability PH two weighting compositions, final acquisition adjudicates matrix S;

Select the corresponding cognitive user Su and channel Ch of the maximum in s-matrix element to combine, and by this cognitive user access respective channels, upgrade channel information;

Delete the successful user of access and channel, repeat the operation of above-mentioned combinations of pairs, until cognitive user or idle channel are empty.

2. method according to claim 1, is characterized in that, the information of cognitive user and primary user in CR system update current time slots channel, adds up all cognitive user having access channel demands, and statistics idle channel, specifically comprises:

The information of cognitive user in current time slots channel is upgraded, comprises the time T transmitted _trans, the data volume D that is transmitted _transdeng, its channel occupied is discharged for the user completing transmission;

The information of primary user in current time slots channel is upgraded, if now primary user's end of transmission, discharges the channel that it occupies; If when primary user occurs, there is the situation that cognitive user is extruded channel, then cognitive user is recorded to and switches user S set U _handoverin;

New user produces at random, is recorded in new access set SU by unified for the user of these new generations _newin, in order to follow-up access channel; Add up the idle channel in current all channels, be recorded in idle channel set CH _idlein.

3. method according to claim 1, is characterized in that, by every bar channel combinations of pairs between two in each cognitive user for access channel and idle channel, after obtaining parameters, calculates respectively, finally obtains judgement matrix S, specifically comprise:

SU _handoveruser and SU _newuser's priority and each idle channel combinations of pairs between two, calculate the matrix PH of minimum switching probability, suppose when cognitive user Su1 needs selective channel Ch1, channel has idled the X0 time, cognitive user has transmitted the Y0 time, so under this condition, wish cognitive user continue to need transmission time Y-Y0 be less than channel continue can be idle time X-X0, the probability that this situation occurs is the element of PH;

SU _handoveruser and SU _newuser's priority and each idle channel combinations of pairs between two, calculate matrix T remaining time _left, suppose at switching user Su _jneed selective channel Ch _itime, cognitive user remaining data M _j, the signal to noise ratio of selective channel is SNR _i, bandwidth is B _i, then can calculate channel capacity is C _i, and then can obtain remaining transmission time T _left;

Be dimensionless pattern by two matrix disposals, be namely normalized respectively two matrixes, and be added after two normalization matrixes are multiplied by coefficient, coefficient respectively gets 0.5, obtains adjudicating matrix S.

4. method according to claim 3, is characterized in that, SU _handoveruser priority is in SU _newcarry out and idle channel CH _idlepairing and selection.

5. the frequency spectrum switching device shifter in CR system, is characterized in that, comprising:

System information acquisition module, for upgrading the information of cognitive user and primary user in CR system current time slots channel, adds up all cognitive user having access channel demands, statistics idle channel;

Data processing module, for by every bar channel combinations of pairs between two in each cognitive user for access channel and idle channel, obtains parameters, comprises the data volume D that cognitive user has been transmitted _trans, the data length distributed constant μ of cognitive user, the bandwidth B of channel, the quantum condition entropy parameter lambda that the signal to noise ratio snr of channel and channel clear meet, calculate a decision value for every a pair combination respectively, this value is by maximum rate T _leftthe most very much not switching probability PH two weighting compositions, final acquisition adjudicates matrix S;

Spectrum allocation may module, carries out cognitive user spectrum allocation may for the result according to data processing in accordance with the method for claim 1, cognitive user is accessed channel;

Scheduler module, for coordinating the ordinal relation between first three module, and ensures that Data processing can realize the recursive call of spectrum allocation may module.