CN101702635B - Method for switching frequency spectrum based on cognitive radio technology and system thereof - Google Patents

Abstract

The invention provides a method for switching a frequency spectrum based on a cognitive radio technology and a system thereof. The system comprises: a time diving module for dividing the communication process of a cognitive user into a data transmission time and a frequency spectrum detection time according to time dimension; a data transmitting module for performing communication and data transmission on the frequency spectrum currently utilized by the cognitive user at the time transmission time; a frequency spectrum judging module for judging whether the frequency spectrum is needed to be switched at the frequency spectrum detection time, wherein if the frequency spectrum is needed to be switched, judging whether an available frequency spectrum is existed in an available frequency spectrum set; a frequency spectrum detecting module for detecting that the availability of the frequency spectrum exceeds the threshold value of the available frequency spectrum, the available time exceeds the threshold value of the available time, and the unoccupied available frequency spectrum; and a frequency spectrum switching module for switching the frequency spectrum which is currently utilized by the cognitive user into the available frequency spectrum. The invention can guarantee the continuity of the communication of the cognitive user and the service quality.

Description

A kind of method and system that carries out the frequency spectrum switching based on cognitive radio technology

Technical field

The present invention relates to radio communication and moving communicating field, relate in particular to based on cognitive radio technology and carry out the method and system that frequency spectrum switches.

Background technology

The special-purpose frequency range that traditional fixed frequency spectrum allocative decision is distributed respectively non-overlapping copies for each different wireless communication system, under this spectrum allocation may system, be accompanied by fast development and the widespread deployment of wireless and mobile communication system, become more and more rare as frequency spectrum resource wireless and the important carrying of mobile communication, the following most of frequency range of 2GHz that particularly is suitable for mobile communication has been distributed totally, the matter of utmost importance that this research, exploitation and deployment that becomes many novel radios and mobile communication system faces.

Yet, the many radio management departments of process and communication enterprise, R﹠D institution use present situation to measure discovery to frequency spectrum, the special-purpose frequency spectrum of distributing to wireless and mobile communication system is within the most of the time and be underutilized, in certain period and certain segment space scope, there is a large amount of frequency spectrum cavity-pockets that is not used on the dedicated frequency band of having distributed.The root that is also the rare problem of frequency spectrum is outmoded fixed frequency spectrum allocation strategy, rather than the shortage of frequency spectrum itself.

For take full advantage of distribute to that authoring system uses but on certain period or particular space unappropriated idle frequency spectrum resource, cognitive radio technology is paid close attention to widely and is studied as a kind of effective solution.It can detect, follow the tracks of, adapt to the variation of wireless environment dynamically, dynamically utilizes the untapped frequency spectrum of authoring system, selects suitable transformation parameter to communicate.At present, extensively carried out and obtained more achievement in research about the research of the dynamic frequency spectrum deployment in cognitive radio technology and management strategy, mechanism and algorithm, wherein as the WINNER system in Europe can the dynamically adapting frequency spectrum behaviour in service, and then regulate, change system parameters to realize real-time reliable communication; The IEEE 802.22 radio area network standards of the U.S. are based on cognitive radio technology, and research is carried out mobile communication to the radio and television frequency range of fully not used.

During idle frequency spectrum empty the different QoS of variation characteristic and miscellaneous service require be present cognitive radio research with use in two subject matters facing, and Dynamic Spectrum Management is to address these problems most crucial technology.At present mainly be divided into frequency spectrum detection, frequency spectrum judging, frequency spectrum share and frequency spectrum mobility four aspects about the research of Dynamic Spectrum Management.

Frequency spectrum detection is carried out the real-time excavation of idle frequency spectrum, frequency spectrum judging is selected suitable idle frequency spectrum for cognitive user foundation is provided, frequency spectrum share solves the problem that a plurality of users access idle frequency spectrum simultaneously, and the frequency spectrum mobility is that the frequency spectrum switching can make the user keep well being connected with the lasting of network by upgrading frequency spectrums of operation.Frequency spectrum detection, adjudicate and be shared as cognitive user effective use idle frequency spectrum necessary basis is provided, the research work of this three aspects: is carried out early.

After adopting cognitive radio technology, usually the user is divided into authorized user and cognitive user, authorized user is enjoyed the first priority right to use to frequency spectrum distribution, and the cognitive user frequency spectrum of detection of dynamic, tracking authorized user takies situation, communicates on its untapped idle frequency spectrum.When authorized user was reused the frequency spectrum that cognitive user using, cognitive user need stop at the communication on this section frequency spectrum at once, this section frequency spectrum is returned authorized user use.In order to guarantee continuation, QoS of survice and the throughput of cognitive user communication, it can when abdicate this section frequency spectrum, take over seamlessly other idle frequency range and continue communication; In addition, when the link-quality of the shared frequency spectrum of cognitive user becomes very poor or it is can not satisfy user's current business or Added Business demand the time, perhaps based on the consideration of system to load balancing, also can carry out frequency spectrum and switch, cognitive user is switched to the idle frequency spectrum that other is more suitable for.

The user is seamless in order to satisfy, the demand of ubiquitous communication, keeps the qos requirement that continues to be connected and to ensure various application of user and network, and from dynamic management and the use that realizes in essence frequency spectrum, the frequency spectrum switching is a particularly important ring.Research work about frequent spectrum handoff technique at present just launches, and the aspects such as frequency spectrum switching criterion, mechanism are demanded research urgently.

Summary of the invention

The object of the present invention is to provide based on cognitive radio technology and carry out the method and system that frequency spectrum switches, to guarantee continuity and the QoS of cognitive user communication.

According to an aspect of the present invention, propose a kind of method of carrying out the frequency spectrum switching based on cognitive radio technology, comprise the following steps: (1) is divided into transfer of data period and frequency spectrum detection period with the communication process of cognitive user by the time dimension; (2) in the transfer of data period, cognitive user communicates and transfer of data on the frequency spectrum of current use; (3) in the frequency spectrum detection period, judge whether to need to switch frequency spectrum, if necessary, execution in step (4); (4) detect in the usable spectrum set whether have usable spectrum, if exist, execution in step (5), the frequency spectrum availability of described usable spectrum surpass the usable spectrum threshold value, available duration via surpasses available duration via threshold value and unoccupied; (5) frequency spectrum with the current use of cognitive user switches to described usable spectrum.

Further, detect the operation that whether has usable spectrum in the usable spectrum set in step (4), further comprising the steps of: if there is no usable spectrum, reset the frequency spectrum detection window duration, reset usable spectrum threshold value and/or available duration via threshold value; Detect the frequency spectrum availability and surpass over the usable spectrum threshold value that resets, available duration via available duration via threshold value and the unappropriated usable spectrum that resets in the frequency spectrum detection window duration that resets.

Further, the frequency spectrum detection window duration that resets is that frequency spectrum switches the maximum delay threshold value, and the usable spectrum threshold value that resets and available duration via threshold value are to obtain after former usable spectrum threshold value and available duration via threshold value are weighted respectively.

Further, after completing frequency spectrum detection, according to the frequency spectrum stability, calculate and reset the frequency spectrum detection window duration at every turn, and with this as duration of frequency spectrum detection period next time; Perhaps switch but usable spectrum set when be sky when the needs frequency spectrum, resetting the frequency spectrum detection duration before the frequency spectrum detection that will carry out begins is frequency spectrum handover delay threshold value, as the duration of the frequency spectrum detection that will carry out.

Further, judge whether to need to switch the operation of frequency spectrum in step (3), further comprising the steps of: as if do not need to switch frequency spectrum, to detect usable spectrum within the duration of frequency spectrum detection period, and upgrade the usable spectrum set according to the usable spectrum that detects.

Further, upgrade the operation of usable spectrum set according to the usable spectrum that detects, further comprising the steps of: if the usable spectrum set less than, and simultaneously at whole frequency spectrum detection period T _SenceIn satisfy all the time p _Candidate〉=p _Threshold+ p _Hysteresis1, and frequency spectrum available duration via τ 〉=τ _Threshold, usable spectrum is joined usable spectrum set, wherein p _CandidateBe the frequency spectrum availability of usable spectrum, p _ThresholdBe usable spectrum threshold value, p _Hysteresis1For frequency spectrum adds lagged value, τ _ThresholdBe frequency spectrum available duration via threshold value; If the usable spectrum set is full, and at whole frequency spectrum detection period T _SenceIn satisfy all the time p _Candidate〉=p _Worst+ p _Hysteresis2, and the frequency spectrum available duration via satisfies τ _Candidate〉=τ _Worst, replace frequency spectrum p the poorest in the usable spectrum set with usable spectrum _Worst, p wherein _Hysteresis2Be spectrum replacement lagged value, τ _{Threshold_relax}Be the available duration via of usable spectrum, τ _WorstBe frequency spectrum available duration via the shortest in the usable spectrum set; If the usable spectrum in the usable spectrum set is occupied or no longer meet the requirements, it is removed in the usable spectrum set.

Further, step (2) is also carried out following operation in the transfer of data period: definition frequency spectrum detection pre-estimation threshold value ρ; Estimate to be authorized to the probability that the user recovers frequency spectrum after cognitive user communicates in the communication time of setting; When calculating the probability of recovering frequency spectrum and surpass frequency spectrum detection pre-estimation threshold value ρ, start the frequency spectrum detection stage.

According to a further aspect of the invention, also propose a kind ofly to carry out based on cognitive radio technology the system that frequency spectrum switches, comprising: the period is divided module, and the communication process of cognitive user is divided into transfer of data period and frequency spectrum detection period by the time dimension; Data transmission module, in the transfer of data period, cognitive user communicates and transfer of data on the frequency spectrum of current use; Frequency spectrum judging module, in the frequency spectrum detection period, judging whether needs to switch frequency spectrum, if necessary, judges whether there is usable spectrum in the usable spectrum set; The frequency spectrum detection module detects the frequency spectrum availability and surpasses usable spectrum threshold value, available duration via over available duration via threshold value and unappropriated usable spectrum; Frequency spectrum switching module switches to described usable spectrum with the frequency spectrum of the current use of cognitive user.

Further, the frequency spectrum detection module is not when there is no usable spectrum, reset the frequency spectrum detection window duration, reset usable spectrum threshold value and/or available duration via threshold value, and detect the frequency spectrum availability over the usable spectrum threshold value that resets, available duration via in the frequency spectrum detection window duration that resets over the available duration via threshold value and the unappropriated usable spectrum that reset.

Further, the frequency spectrum detection window duration that resets is that frequency spectrum switches the maximum delay threshold value, and the usable spectrum threshold value that resets and available duration via threshold value are to obtain after former usable spectrum threshold value and available duration via threshold value are weighted respectively.

Further, the frequency spectrum detection window duration is calculated and reset to the frequency spectrum detection module according to the frequency spectrum stability, after the frequency spectrum detection module is completed frequency spectrum detection, and with this as duration of frequency spectrum detection period next time; Perhaps switch but usable spectrum set when be sky when the needs frequency spectrum, resetting the frequency spectrum detection duration before the frequency spectrum detection that will carry out begins is frequency spectrum handover delay threshold value, as the duration of the frequency spectrum detection that will carry out.

Further, the frequency spectrum detection module also when not needing to switch frequency spectrum, detects usable spectrum within the duration of frequency spectrum detection period, upgrades the usable spectrum set according to the usable spectrum that detects.

Further, the system that described frequency spectrum switches also comprises: the spectrum prediction module, definition frequency spectrum detection pre-estimation threshold value ρ, estimate to be authorized to the probability that the user recovers frequency spectrum after cognitive user communicates in the communication time of setting, when the probability of recovering frequency spectrum surpasses frequency spectrum detection pre-estimation threshold value ρ, start the frequency spectrum detection period.

The present invention is based on cognitive radio technology and carry out the method that frequency spectrum switches, at first, need to carry out frequency spectrum when switching in cognitive user, usable spectrum be detected and the frequency spectrum of the current use of cognitive user is switched to described usable spectrum, in order to guarantee the communication process of cognitive user.Secondly, usable spectrum is empty or occupied in the usable spectrum set, reset the frequency spectrum detection window duration, reset usable spectrum threshold value and/or available duration via threshold value, and detection frequency spectrum availability surpasses over the usable spectrum threshold value that resets, available duration via available duration via threshold value and the unappropriated usable spectrum that resets in the frequency spectrum detection window duration that resets, and keeps the continuation communication process of cognitive user.Therefore, the present invention can guarantee continuity and the QoS of cognitive user communication.

Further, the present invention also can safeguard different usable spectrum set by adjusting the parameters such as frequency spectrum detection period density, usable spectrum set sizes, detection pre-estimation threshold value, handover delay threshold value, and the frequency spectrum that adapts to different business switches demand.

Description of drawings

Accompanying drawing described herein is used to provide a further understanding of the present invention, consists of the application's a part, and illustrative examples of the present invention and explanation thereof are used for explaining the present invention, do not consist of improper restriction of the present invention.In the accompanying drawings:

Fig. 1 the present invention is based on cognitive radio technology to carry out the method flow diagram that frequency spectrum switches.

Fig. 2 the present invention is based on cognitive radio technology to carry out the system construction drawing that frequency spectrum switches.

Embodiment

The frequency spectrum that uses when cognitive user is authorized to that the user recovers or link-quality variation or the frequency spectrum that uses can not satisfy its current business or new business demand or for the load between equalizing system, can adopt frequency spectrum to switch to improve service quality and the throughput of system of cognitive user.

Frequency spectrum switches and to switch on switching flow with the minizone that some is similar, and still, frequency spectrum switches and is different from traditional minizone and switches.At first, frequency spectrum switches might not need adjacent base station to participate in, and is also that the frequency spectrum switching can be often the switching in the residential quarter; Secondly, frequency spectrum switches and has very strong randomness, due to the arrival of authorized user and leave, wireless channel conditions and user's business demand all has very large randomness, the generation that frequency spectrum switches also has very large randomness; Again, because the bandwidth of different authoring systems, carrier-frequency range are all different, make frequency spectrum switch to need and more consider the factor that frequency spectrum is relevant and be not only the signal to noise ratio of link.So frequency spectrum switches more new features and makes the frequency spectrum switching more complicated than the minizone switching, a lot of new principles of each process need and processing method, and need each process better to coordinate.

Illustrate frequency spectrum switching method of the present invention below in conjunction with drawings and Examples, to coordinate switching flow, especially guarantee continuity and the QoS of cognitive user communication.

Fig. 1 the present invention is based on cognitive radio technology to carry out the method flow diagram that frequency spectrum switches, and comprises the following steps:

In step 101, the communication process of cognitive user is divided into transfer of data period and frequency spectrum detection period by the time dimension.

The time long correlation of the service distribution of the zero hour of frequency spectrum detection period and the shared frequency spectrum of cognitive user and its ongoing transfer of data period.The time-domain position of frequency spectrum detection period can be even distribution, also can be defined as the non-uniform Distribution such as Poisson distribution, exponential distribution according to the arrival situation of business; The duration of frequency spectrum detection period can be changeless, can be set to the multiple of time slot in system, and the perhaps multiple of basic Transmission Time Interval, or the multiple of frame etc. are duration fixedly; Also can adjust flexibly according to frequency spectrum stability, the number of times that carries out frequency spectrum detection and transfer of data window duration.

If need to adjust, can define the frequency spectrum stability and be:

$\mathrm{\η}=\frac{F_{\mathrm{available}}}{F_{\mathrm{sence}}}$

F wherein _AvailableBe arranged in continuously the number of times of usable spectrum set for certain section frequency spectrum, F _SenceFor system in certain period carries out the number of times of frequency spectrum detection.

The overall frequency spectrum stability of usable spectrum set is defined as the normalization frequency spectrum stability of all frequency spectrum elements in described set:

$H=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}\frac{{\mathrm{\η}}_i}{N}$

Wherein N is the size of usable spectrum set, the number of usable spectrum unit in namely gathering, η _iIt is the frequency spectrum stability of i usable spectrum unit.H is larger illustrates that the frequency spectrum in usable set is more stable.

H will affect the duration of frequency spectrum detection next time, and the duration of larger next frequency spectrum detection period of H can be shorter, and vice versa.The duration of frequency spectrum detection can be defined as according to no business model linear function, logarithmic function or the exponential function of H next time.

In step 102, in the transfer of data period, cognitive user communicates and transfer of data on the frequency spectrum of current use.

Can also carry out frequency spectrum in the transfer of data period and switch pre-estimation, concrete operations are: definition frequency spectrum detection pre-estimation threshold value ρ, estimate to be authorized to the probability that the user recovers frequency spectrum after cognitive user communicates in the communication time of setting, when the probability of recovering frequency spectrum surpasses frequency spectrum detection pre-estimation threshold value ρ, cognitive user need stop transfer of data, begins to carry out frequency spectrum detection.The probability that authorized user is recovered frequency spectrum is relevant to the historical information that frequency spectrum uses with its service distribution model.

Considering that authorized user is reused when frequency spectrum that cognitive user takies transmits can make the channel quality variation of cognitive user, thereby needs to open the situation of frequency spectrum detection period, and we are defined as follows frequency spectrum detection pre-estimation threshold value:

$\mathrm{\&rho;}=\left\{\begin{array}{cc}{\mathrm{\&rho;}}_{\mathrm{th}}& {\mathrm{SU}}_{\mathrm{SINR}}>{\mathrm{SU}}_{\mathrm{SINR}\_\mathrm{th}}\\ 0& {\mathrm{SU}}_{\mathrm{SINR}}<{\mathrm{SU}}_{\mathrm{SINR}\_\mathrm{th}}\end{array}\right.$

Wherein, ρ _thBe frequency spectrum detection pre-estimation initial threshold, SU _SINRBe the dry ratio of letter that cognitive user obtains by pilot tone, reference signal etc., SU _{SINR_th}For cognitive user letter drying compares threshold value.

Due to just when the frequency spectrum of cognitive user may be recovered or primary user carry out frequency spectrum detection when occurring suddenly, the method than periodically detecting has greatly reduced unnecessary detection number of times, and then improves the throughput of system.

In step 103, in the frequency spectrum detection period, judge whether to need to switch frequency spectrum, if necessary, execution in step 105, otherwise execution in step 104.

When cognitive user by corresponding pilot channel or under it pilot frequency information, reference signal etc. of system obtain frequency spectrum handover trigger information, or the user initiatively trigger switching the time, such as, higher business demand is arranged, current use frequency spectrum to be detected occupied, being judged as needs to switch frequency spectrum.The triggering that frequency spectrum switches can occur in transfer of data and frequency spectrum detection stage.

In step 104, detect usable spectrum within the duration of frequency spectrum detection period, and upgrade the usable spectrum set according to the usable spectrum that detects.Jump to the flow process that step 102 continues performing data transmission period and frequency spectrum detection period.

Upgrade the usable spectrum set and comprise interpolation, replace and remove usable spectrum, be specially:

If the usable spectrum set less than, and simultaneously at whole frequency spectrum detection period T _SenceIn satisfy all the time p _Candidate〉=p _Threshold+ p _Hysteresis1, and frequency spectrum available duration via τ 〉=τ _Threshold, usable spectrum is joined in the usable spectrum set, wherein p _CandidateBe the frequency spectrum availability of usable spectrum, p _Hysteresis1For frequency spectrum adds lagged value; If the usable spectrum set is full, and at whole frequency spectrum detection period T _SenceIn satisfy all the time p _Candidate〉=p _Worst+ p _Hysteresis2, and the frequency spectrum available duration via satisfies τ _Candidate〉=τ _Worst, replace frequency spectrum p the poorest in the usable spectrum set with usable spectrum _Worst, p wherein _Hysteresis2Be spectrum replacement lagged value, τ _CandidateBe the available duration via of usable spectrum, τ _WorstBe frequency spectrum available duration via the shortest in the usable spectrum set; If the usable spectrum in the usable spectrum set is by other CUs or no longer meet the requirements, here said meeting the requirements refers to, the frequency spectrum availability is no longer surpassed usable spectrum threshold value, available duration via no longer surpass the usable spectrum of available duration via threshold value, it is removed in the usable spectrum set.p _Hysteresis1And p _Hysteresis2Be the lagged value of avoiding ping-pong to introduce when being respectively the frequency spectrum increase with spectrum replacement, can set flexibly according to factors such as heavy traffic situations.

In step 105, detect in the usable spectrum set whether have usable spectrum, if so, execution in step 108, otherwise execution in step 106.The frequency spectrum availability of described usable spectrum surpasses the usable spectrum threshold value, available duration via surpasses available duration via threshold value and unoccupied.

The frequency spectrum detecting method that cognitive user is used can be based on the detection of transmitter, based on the detection of receiver, method or their the various combination forms such as detection, energy measuring, feature detection, collaborative detection based on interference temperature.

When safeguarding the usable spectrum set according to usable spectrum, can separately or consider following factor: the historical information that carrier frequency, bandwidth, link-quality, frequency spectrum detection reliability, frequency spectrum use, the available duration via of frequency spectrum, described usable spectrum set sizes etc.Wherein, frequency spectrum in the usable spectrum set is called spectrum unit, spectrum unit adaptive-bandwidth, the frequency spectrum transmittability before and after the present invention is switched the frequency spectrum QoS by bandwidth, carrier frequency, SNR and user etc. makes total evaluation, and the bandwidth of switching target spectrum is not had strict restriction.Wherein, the size of usable spectrum set and system to cognitive user outage probability, blocking probability, QoS of survice and throughput and usable spectrum to be authorized to the probability that the user recovers relevant.The usable set of system maintenance is larger, and the handoff failure probability of cognitive user is just less, but the system-computed complexity is higher, just more might satisfy the QoS of survice requirement, obtains larger throughput, and vice versa.

In the present embodiment, the usable spectrum that satisfies frequency spectrum availability, frequency spectrum available duration via is joined usable spectrum set, i.e. S _Available={ s:p 〉=p _Threshold, τ 〉=τ _Threshold.Wherein, S _AvailableBe the usable spectrum set, s represents to add the spectrum unit in the usable spectrum set, and p is the frequency spectrum availability, p _ThresholdFor adding the usable spectrum threshold value in the usable spectrum set, its size is determined jointly by user's qos requirement and usable spectrum set sizes.τ is available duration via, and the available duration via τ that distributes to frequency spectrum according to the service probability of authorized user carries out pre-estimation, τ _ThresholdBe frequency spectrum available duration via threshold value.The below will illustrate the computational process of frequency spectrum availability p.

Frequency spectrum availability p is:

$p=[\mathrm{\&alpha;}\&CenterDot;\frac{B_T\log (1+{\mathrm{\&gamma;}}_T)}{B_S\log (1+{\mathrm{\&gamma;}}_S)}+\mathrm{\&beta;}\&CenterDot;{\left(\frac{f_S}{f_T}\right)}^2]\&CenterDot;\exp (\mathrm{\&epsiv;}-1)$

B wherein _S, γ _S, f _SRepresent that respectively cognitive user using the bandwidth of frequency spectrum, signal to noise ratio (SNR) and carrier frequency; B _T, γ _T, f _TRepresent that respectively cognitive user detects the bandwidth of unappropriated usable spectrum unit, SNR and carrier frequency; α, β are respectively regulatory factor (alpha+beta=1), in order to the transmittability of regulating usable spectrum and the shared significance level of transmission capacity, wherein transmittability can be characterized by user's accessible transmission rate on this section frequency spectrum, transmission capacity is relevant to spectral characteristic, characterize the space transmission large scale loss situation of this frequency spectrum, α, β can adjust respectively according to factors such as system's usable spectrum span and service distribution; ε is the probability that usable spectrum is correctly detected.In following formula, p is larger represents that the spectrum availability of usable spectrum is just higher.

Further, usable spectrum in the usable spectrum set is sorted according to frequency spectrum availability order from big to small.Like this, after when switching frequency spectrum, a highest usable spectrum of sequence that only needs to detect gets final product as switching target spectrum, can realize detecting fast usable spectrum.

In step 106, reset the frequency spectrum detection window duration, reset usable spectrum threshold value and/or available duration via threshold value, and detect the frequency spectrum availability over the usable spectrum threshold value that resets, available duration via in the frequency spectrum detection window duration that resets over the available duration via threshold value and the unappropriated usable spectrum that reset.

Wherein, there is no usable spectrum in the usable spectrum set, such as, the usable spectrum set is that sky or usable spectrum are occupied.The frequency spectrum detection window duration that resets is that frequency spectrum switches the maximum delay threshold value, and frequency spectrum switches the maximum delay threshold value and determined by combined factors such as cognitive user business demand, service quality, detection errors.The usable spectrum threshold value that resets and available duration via threshold value are to obtain after former usable spectrum threshold value and available duration via threshold value are weighted respectively.The below will illustrate.

Consider cognitive user to the requirement of handover delay, can set coefficient of relaxation to reduce the requirement to usable spectrum; Also can not adopt coefficient of relaxation, directly frequency spectrum be assessed.

Coefficient of relaxation is defined as:

$\mathrm{\&omega;}=\frac{T_{\mathrm{sence}\_\mathrm{last}}}{T_{\mathrm{Delay}}}$

Wherein, T _{Sence_last}For cognitive user is switched last frequency spectrum detection duration before requirement, T _DelayBe the handover delay threshold value, namely the patient maximum handover delay of cognitive user, determined by combined factors such as cognitive user business demand, service quality, detection errors.Use described coefficient of relaxation to usable spectrum threshold value P _ThresholdBe weighted with the assessment requirement of further reduction to frequency spectrum with the available duration via threshold value, specific as follows:

p _{threshold_relax}＝ω·p _threshold

τ _{threshold_relax}＝ω·τ _threshold

Wherein, p _{Threshold_relax}And τ _{Threshold_relax}Be respectively usable spectrum threshold value and the available duration via threshold value of carrying out after the coefficient of relaxation weighting.

In step 107, judge whether to detect usable spectrum, if detect, execution in step 108, otherwise execution in step 109.

In step 108, the frequency spectrum of the current use of cognitive user is switched to described usable spectrum.

When cognitive user need to be carried out the frequency spectrum switching, if usable spectrum set non-NULL, the usable spectrum in pair set carries out fast detecting assessment (whether only detecting frequency spectrum by other CUs) in order, and the usable spectrum that detected sequence is the highest is completed switching as switching target spectrum.Described fast frequency spectrum detects and only refers to that for the detection of usable spectrum, its detection method can be simple energy measuring, and frequency spectrum is relatively fixing and detection method is simple because it detects, and the more common frequency spectrum detection process of execution speed is faster.

In step 109, cognitive user keeps the existing communication state, again initiates the frequency spectrum handover request, process ends.

The present invention is based on cognitive radio technology and carry out the method that frequency spectrum switches, at first, need to carry out frequency spectrum when switching in cognitive user, usable spectrum be detected and the frequency spectrum of the current use of cognitive user is switched to described usable spectrum, in order to guarantee the communication process of cognitive user.Secondly, usable spectrum is empty or occupied in the usable spectrum set, reset the frequency spectrum detection window duration, reset usable spectrum threshold value and/or available duration via threshold value, and detection frequency spectrum availability surpasses over the usable spectrum threshold value that resets, available duration via available duration via threshold value and the unappropriated usable spectrum that resets in the frequency spectrum detection window duration that resets, and keeps the continuation communication process of cognitive user.Therefore, the present invention can guarantee continuity and the QoS of cognitive user communication.

Further, the present invention also can safeguard different usable spectrum set by adjusting the parameters such as frequency spectrum detection period density, usable spectrum set sizes, detection pre-estimation threshold value, handover delay threshold value, and the frequency spectrum that adapts to different business switches demand.

Fig. 2 the present invention is based on cognitive radio technology to carry out the system construction drawing that frequency spectrum switches, and comprising: the period is divided module, data transmission module, frequency spectrum judging module, frequency spectrum detection module, frequency spectrum switching module.

Period is divided module, and the communication process of cognitive user is divided into transfer of data period and frequency spectrum detection period by the time dimension.

Data transmission module, in the transfer of data period, cognitive user communicates and transfer of data on the frequency spectrum of current use.

Frequency spectrum judging module, in the frequency spectrum detection period, judging whether needs to switch frequency spectrum, if do not need to switch frequency spectrum, also calls the frequency spectrum detection module and detects usable spectrum, and to upgrade the usable spectrum set, specifically upgrading operation will describe in the frequency spectrum detection module.If need to switch frequency spectrum, call the frequency spectrum detection module and carry out frequency spectrum detection, judge according to testing result whether the usable spectrum set exists usable spectrum, when showing, testing result notify frequency spectrum switching module to switch when usable spectrum is arranged.

When testing result shows when there is no usable spectrum, such as, the usable spectrum set is that sky or usable spectrum are occupied, also calling the frequency spectrum detection module continues to detect, this moment, the frequency spectrum detection module reset the frequency spectrum detection window duration, reset usable spectrum threshold value and/or available duration via threshold value, and detect the frequency spectrum availability over the usable spectrum threshold value that resets, available duration via in the frequency spectrum detection window duration that resets over the available duration via threshold value and the unappropriated usable spectrum that reset.Wherein, the frequency spectrum detection window duration that resets is that frequency spectrum switches the maximum delay threshold value, and the usable spectrum threshold value that resets and available duration via threshold value are to obtain after former usable spectrum threshold value and available duration via threshold value are weighted respectively.

Frequency spectrum switching module switches to described usable spectrum with the frequency spectrum of the current use of cognitive user.

The frequency spectrum detection module detects the frequency spectrum availability and surpasses usable spectrum threshold value, available duration via over available duration via threshold value and unappropriated usable spectrum.

Wherein, the frequency spectrum detection module also when not needing to switch frequency spectrum, detects usable spectrum within the duration of frequency spectrum detection period, and upgrades the usable spectrum set according to the usable spectrum that detects.

The operation of the renewal usable spectrum set that the frequency spectrum detection module is carried out comprises interpolations, deletion and replaces usable spectrum, and is specific as follows: the usable spectrum set less than, and the while is at whole frequency spectrum detection period T _SenceIn satisfy all the time p _Candidate〉=p _Threshold+ p _Hysteresis1, and the frequency spectrum available duration via satisfies τ 〉=τ _Threshold, usable spectrum is joined in the usable spectrum set; Full in the usable spectrum set, and at whole frequency spectrum detection period T _SenceIn satisfy all the time p _Candidate〉=p _Worst+ p _Hysteresis2, and the frequency spectrum available duration via satisfies τ _Candidate〉=τ _Worst, usable spectrum is replaced frequency spectrum p the poorest in available set _Worstτ wherein _WorstBe frequency spectrum available duration via the shortest in the usable spectrum set; Usable spectrum in the usable spectrum set detects by other CUs or no longer meets the requirement of usable spectrum assessment level, it is removed p in the usable spectrum set _Hysteresis1And p _Hysteresis2Be respectively frequency spectrum and add lagged value and spectrum replacement lagged value.

The frequency spectrum detection module resets the frequency spectrum detection window duration, specifically comprise following dual mode: after the frequency spectrum detection module is completed frequency spectrum detection, according to the frequency spectrum stability, calculate and reset the frequency spectrum detection window duration, and with this as duration of frequency spectrum detection period next time; Perhaps switch but usable spectrum set when be sky when the needs frequency spectrum, resetting the frequency spectrum detection duration before the frequency spectrum detection that will carry out begins is frequency spectrum handover delay threshold value, as the duration of the frequency spectrum detection that will carry out.

In addition, system of the present invention also comprises: the spectrum prediction module, definition frequency spectrum detection pre-estimation threshold value ρ, estimate to be authorized to the probability that the user recovers frequency spectrum after cognitive user communicates in the communication time of setting, when calculating the probability of recovering frequency spectrum and surpass frequency spectrum detection pre-estimation threshold value ρ, start the frequency spectrum detection period.

The present invention is based on cognitive radio technology and carry out the system that frequency spectrum switches, at first, the frequency spectrum detection module need to be carried out frequency spectrum when switching in cognitive user, usable spectrum detected and the frequency spectrum of the current use of cognitive user is switched to described usable spectrum, in order to guarantee the communication process of cognitive user.Secondly, the frequency spectrum detection module also in the usable spectrum set usable spectrum be empty or occupied, reset the frequency spectrum detection window duration, reset usable spectrum threshold value and/or available duration via threshold value, and detection frequency spectrum availability surpasses over the usable spectrum threshold value that resets, available duration via available duration via threshold value and the unappropriated usable spectrum that resets in the frequency spectrum detection window duration that resets, and keeps the continuation communication process of cognitive user.Therefore, the present invention can guarantee continuity and the QoS of cognitive user communication.

Further, the present invention also can safeguard different usable spectrum set by adjusting the parameters such as frequency spectrum detection period density, usable spectrum set sizes, detection pre-estimation threshold value, handover delay threshold value, and the frequency spectrum that adapts to different business switches demand.

Below by drawings and Examples, technical scheme of the present invention is described in further detail.

Embodiment one:

Be the user of gsm system for authorized user, the untapped frequency spectrum of cognitive user use authority user, and carry out the frequency spectrum switching when authorized user is recovered frequency spectrum again.

The frequency spectrum handover mechanism and the criterion that propose according to the present invention, its frequency spectrum switching flow is as follows:

Because the gsm system business is mainly speech business, the probability distribution that the authorized user conversation arrives is obeyed Poisson distribution, and call office distributes every obeying negative exponent; Conversation continues the probability distribution of duration and obeys the negative exponent distribution, and conversation is left probability and obeyed Poisson distribution.

If the conversation arrival rate is λ, its probability density function is:

$P_1\left(k\right)=\frac{e^{-\mathrm{\&lambda;}}{\mathrm{\&lambda;}}^k}{k!}$

Call office is every obeying the negative exponent distribution that average duration is 1/ λ, and its probability density function is:

$G_1\left(x\right)=\left\{\begin{array}{cc}\mathrm{\&lambda;}{e}^{-\mathrm{\&lambda;x}}& x\&GreaterEqual;0\\ 0& x<0\end{array}\right.$

If average call duration is 1/ μ, its probability density function is:

$G_2\left(x\right)=\left\{\begin{array}{cc}\mathrm{\&mu;}{e}^{-\mathrm{\&mu;x}}& x\&GreaterEqual;0\\ 0& x<0\end{array}\right.$

It is the Poisson distribution of μ that probability distribution obedience departure rate is left in conversation, and its probability density function is:

$P_2\left(k\right)=\frac{e^{-\mathrm{\&mu;}}{\mathrm{\&lambda;}}^k}{k!}$

According to above-mentioned probability distribution, only have just can take its frequency spectrum when authorized user conversation interim cognitive user, its transfer of data period continues the probability distribution of duration and is:

$G_1\left(x\right)=\left\{\begin{array}{cc}\mathrm{\&lambda;}{e}^{-\mathrm{\&lambda;x}}& x\&GreaterEqual;0\\ 0& x<0\end{array}\right.$

Suppose that frequency spectrum detection pre-estimation threshold value ρ is 0.7 in gsm system, namely satisfy G when cognitive user must may be authorized to the probability that the user recovers after communication time x on usable spectrum ₁(x)＞0.7 o'clock, suppose that this moment, authorized user may occur, stop transfer of data, carry out frequency spectrum detection.

In the frequency spectrum detection period, at first cognitive user determines whether to carry out frequency spectrum switches, and then carries out frequency spectrum detection, and the time of frequency spectrum detection will be continued until the time of frequency spectrum handover delay threshold value defined for the first time.If the user needs frequency spectrum to switch, and there is no satisfactory frequency spectrum, begin handover request next time.

When idle frequency spectrum being detected, according to the usable spectrum assessment level:

$p=[\mathrm{\&alpha;}\&CenterDot;\frac{B_T\log (1+{\mathrm{\&gamma;}}_T)}{B_S\log (1+{\mathrm{\&gamma;}}_S)}+\mathrm{\&beta;}\&CenterDot;{\left(\frac{f_S}{f_T}\right)}^2]\&CenterDot;\exp (\mathrm{\&epsiv;}-1)$

Idle frequency spectrum is assessed, consider that wherein the spectrum concentration of gsm system is in the 900MHz frequency range, carrier frequency is very little on the impact of frequency spectrum, so value less of β, can get 0.1, α and can get 0.9, the bandwidth of frequency spectrum detection is narrower, the general value of frequency spectrum correct detection probability ε is more than 90%, usable spectrum threshold value p _ThresholdCan value be 1.According to the probability distribution that authorized user and cognitive user business arrive and leave, frequency spectrum available duration via probability distribution satisfies G ₁(x), its average available duration via is 1/ λ, and the available duration via of setting under frequency spectrum 90% probability is the available duration via threshold tau _Threshold, τ _Threshold=λ e- ^{0.9 λ}, when the idle frequency spectrum that detects satisfies simultaneously: S _Available={ s:p 〉=1, τ 〉=λ e ^{-0.9 λ}The time, it is joined in the usable spectrum set, in the present embodiment, setting the usable spectrum set sizes is 3, only will satisfy three best spectrum unit of above condition and join in set.

Next according to usable spectrum set replacement criteria to usable spectrum set upgrade, two lagged value p wherein _Hysteresis1And p _Hysteresis2Value is 0.1 and 0.2 respectively.

The frequency spectrum detection window duration is the handover delay threshold value for the first time, and later each frequency spectrum detection window duration can be adjusted according to the frequency spectrum stability for the first time, has defined the linear function of a H at this:

$T_{\mathrm{sence}}=\left\{\begin{array}{cc}{T}_{\mathrm{Delay}}& t=1\\ T_{\mathrm{Delay}}(1-H)& t>1\end{array}\right.$

Wherein, t is the number of times of certain user's frequency spectrum detection, and the calculated value the when H in formula is t-1 time is if t-1=1 is H=0.Like this, if the frequency spectrum stability that described usable spectrum is concentrated is higher, needs shorter detection time and upgrade the usable spectrum set.

When cognitive user need to be carried out the frequency spectrum switching, according to the frequency spectrum switching criterion, if usable spectrum set non-NULL carries out the fast detecting assessment again to the frequency spectrum in this set, and proceed transfer of data on detected first usable spectrum, complete switching;

If the frequency spectrum in usable spectrum set this moment is all occupied, cognitive user begins the frequency spectrum of certain scope is detected.Consider cognitive user to the requirement of handover delay, for usable spectrum set replacement criteria is set coefficient of relaxation to reduce the requirement to usable spectrum.

Coefficient of relaxation wherein:

$\mathrm{\&omega;}=\frac{T_{\mathrm{sence}\_\mathrm{last}}}{T_{\mathrm{Delay}}}$

Usable spectrum threshold value p in this moment usable spectrum assessment level _Threshold=1 ω=ω by this coefficient of relaxation, has an opportunity to search the more frequency spectrum of multiple coincidence requirement, thereby has improved the success rate that frequency spectrum switches.

If switch maximum delay threshold value T at the predefined frequency spectrum of system _DelayUsable spectrum detected in=1s, cognitive user is adjusted its corresponding transmitter parameter and proceed transfer of data on this usable spectrum, completes switching;

If usable spectrum do not detected yet in the predefined frequency spectrum of system switches the maximum delay threshold value, cognitive user withdraws from this frequency spectrum switching flow, concurrent handover request next time.

Embodiment two:

Be the user of wideband OFDM system for authorized user, the frequency spectrum that the dynamic use authority user of cognitive user is not used, and carry out the frequency spectrum switching when cognitive user proposes more high bandwidth request.

Because class of business is very abundant, comprise conversation class, stream class, interactive class and background classes etc., each business requires not identical to time delay, delay variation, bandwidth etc., when the cognitive user of communicating by letter proposes the business of new more high bandwidth requirements, can carry out frequency spectrum and switch to meet consumers' demand.

The present embodiment considers when cognitive user just at use authority user's frequency spectrum, and spectrum prediction meter threshold value is not when also arriving, because authorized user is recovered the switching that frequency spectrum triggers.

If when this handover trigger, if this cognitive user has been safeguarded a usable spectrum set, and should gather non-NULL, the user can directly select a suitable frequency spectrum that satisfies the requirement of cognitive user new business to switch in described set; If the usable spectrum set is frequency spectrum empty or that do not meet the demands, the user need to carry out frequency spectrum detection immediately.

In the frequency spectrum detection period, at first with the idle frequency spectrum that detects as switching usable spectrum, according to the usable spectrum assessment level, usable spectrum is assessed, and satisfactory frequency spectrum is put into the usable spectrum set as usable spectrum.

Usable spectrum assessment level expression formula is as follows:

$p=[\mathrm{\&alpha;}\&CenterDot;\frac{B_T\log (1+{\mathrm{\&gamma;}}_T)}{B_S\log (1+{\mathrm{\&gamma;}}_S)}+\mathrm{\&beta;}\&CenterDot;{\left(\frac{f_S}{f_T}\right)}^2]\&CenterDot;\exp (\mathrm{\&epsiv;}-1)$

Idle frequency spectrum is assessed, considered that the frequency spectrum of ofdm system may relatively disperse (such as the LTE system), carrier frequency is larger on the impact of frequency spectrum, so β can get relatively large value; Because ofdm system is a broadband system, the frequency spectrum that authorized user is vacateed generally can satisfy the basic communication demand of cognitive user, so α can get the value of less, but α is still the whether available topmost factor of frequency spectrum that determines, can get 0.7, β at this α and can get 0.3.Due to the broader bandwidth of frequency spectrum detection and may cross over multistage discrete spectrum (such as the LTE system), the general value of frequency spectrum correct detection probability ε is 70% left and right, usable spectrum threshold value p _ThresholdCan value be 1.5.According to the historical information of authorized user and cognitive user frequency spectrum that business is used, setting the lasting duration of frequency spectrum under 90% probability is the available duration via threshold tau _Threshold, when the idle frequency spectrum that detects satisfies simultaneously: S _Available={ s:p 〉=1.5, τ 〉=τ _ThresholdThe time, it is joined in the usable spectrum set, and select to meet a highest conduct switching target spectrum of sequence in described set.

About the time of frequency spectrum detection, the time of frequency spectrum detection will be continued until the time of frequency spectrum handover delay threshold value defined for the first time, due to the diversity of multiple business to delay requirement, and time delay threshold value T _DelayDetermine can consider separately to distinguish different types of service also can consider the service class of each business and the ratio of shared offered load thereof.

If switch maximum delay threshold value T at the predefined frequency spectrum of system _DelayIn suitable usable spectrum detected, cognitive user is adjusted its corresponding transmitter parameter and proceed transfer of data on this usable spectrum, completes switching;

If usable spectrum do not detected yet in the predefined frequency spectrum of system switches the maximum delay threshold value, cognitive user withdraws from this frequency spectrum switching flow, concurrent handover request next time.

Claims (7)

1. one kind is carried out based on cognitive radio technology the method that frequency spectrum switches, and comprises the following steps:

(1) communication process with cognitive user is divided into transfer of data period and frequency spectrum detection period by the time dimension;

(2) in the transfer of data period, cognitive user communicates and transfer of data on the frequency spectrum of current use; Wherein, also carry out following operation in the transfer of data period: definition frequency spectrum detection pre-estimation threshold value ρ, estimate to be authorized to the probability that the user recovers frequency spectrum after cognitive user communicates in the communication time of setting, when the probability of recovering frequency spectrum surpasses frequency spectrum detection pre-estimation threshold value ρ, execution in step (3);

(3) in the frequency spectrum detection period, judging whether needs to switch frequency spectrum, if do not need to switch frequency spectrum, and execution in step (4); If need to switch frequency spectrum, execution in step (5);

(4) detect usable spectrum within the duration of frequency spectrum detection period, and upgrade the usable spectrum set according to the usable spectrum that detects, return to afterwards step (2);

(5) detect in the usable spectrum set whether have usable spectrum, if there is usable spectrum, execution in step (8), if there is no usable spectrum, execution in step (6), the frequency spectrum availability of wherein said usable spectrum surpass the usable spectrum threshold value, available duration via surpasses available duration via threshold value and unoccupied;

(6) reset the frequency spectrum detection window duration, reset usable spectrum threshold value and/or available duration via threshold value, and detect the frequency spectrum availability over the usable spectrum threshold value that resets, available duration via in the frequency spectrum detection window duration that resets over the available duration via threshold value and the unappropriated usable spectrum that reset;

(7) judge whether to detect usable spectrum, if usable spectrum detected, execution in step (8);

(8) frequency spectrum with the current use of cognitive user switches to described usable spectrum.

2. the method switched of frequency spectrum according to claim 1, wherein, the frequency spectrum detection window duration that resets is that frequency spectrum switches the maximum delay threshold value, and the usable spectrum threshold value that resets and available duration via threshold value are to obtain after former usable spectrum threshold value and available duration via threshold value are weighted respectively.

3. the method switched of described frequency spectrum according to claim 1 and 2, wherein, reset the operation of frequency spectrum detection window duration, comprises the following steps:

After completing frequency spectrum detection at every turn, according to the frequency spectrum stability, calculate and reset the frequency spectrum detection window duration, and with this as duration of frequency spectrum detection period next time; Perhaps

When the needs frequency spectrum switches but usable spectrum set when be sky, resetting the frequency spectrum detection duration before the frequency spectrum detection that will carry out begins is frequency spectrum handover delay threshold value, as the duration of the frequency spectrum detection that will carry out.

4. the method switched of frequency spectrum according to claim 1, wherein, upgrade the operation of usable spectrum set according to the usable spectrum that detects, and is further comprising the steps of:

If the usable spectrum set less than, and simultaneously at whole frequency spectrum detection period T _SenceIn satisfy all the time p _Candidate〉=p _Threshold+ p _Hysteresis1, and frequency spectrum available duration via τ 〉=τ _Threshold, usable spectrum is joined usable spectrum set, wherein p _CandidateBe the frequency spectrum availability of usable spectrum, p _ThresholdBe usable spectrum threshold value, p _Hysteresis1For frequency spectrum adds lagged value, τ _ThresholdBe frequency spectrum available duration via threshold value;

If the usable spectrum set is full, and at whole frequency spectrum detection period T _SenceIn satisfy all the time p _Candidate〉=p _Worst+ p _Hysteresis2, and the frequency spectrum available duration via satisfies τ _Candidate〉=τ _Worst, replace frequency spectrum p the poorest in the usable spectrum set with usable spectrum _Worst, p wherein _Hysteresis2Be spectrum replacement lagged value, τ _CandidateBe the available duration via of usable spectrum, τ _WorstBe frequency spectrum available duration via the shortest in the usable spectrum set;

If the usable spectrum in the usable spectrum set is occupied or no longer meet the requirements, it is removed in the usable spectrum set.

5. one kind is carried out based on cognitive radio technology the system that frequency spectrum switches, and comprising:

Period is divided module, and the communication process of cognitive user is divided into transfer of data period and frequency spectrum detection period by the time dimension;

Data transmission module, in the transfer of data period, cognitive user communicates and transfer of data on the frequency spectrum of current use;

The spectrum prediction module, definition frequency spectrum detection pre-estimation threshold value ρ, estimate to be authorized to the probability that the user recovers frequency spectrum after cognitive user communicates in the communication time of setting, when the probability of recovering frequency spectrum surpassed frequency spectrum detection pre-estimation threshold value ρ, the indication frequency spectrum judging module judged whether to need to switch frequency spectrum;

Frequency spectrum judging module, in the frequency spectrum detection period, judging whether needs to switch frequency spectrum, if need to switch frequency spectrum, judges whether there is usable spectrum in the usable spectrum set;

The frequency spectrum detection module is used for detecting usable spectrum within the duration of frequency spectrum detection period when not needing to switch frequency spectrum, and upgrades the usable spectrum set according to the usable spectrum that detects; Detect the frequency spectrum availability and surpass usable spectrum threshold value, available duration via over available duration via threshold value and unappropriated usable spectrum; When there is no usable spectrum, reset the frequency spectrum detection window duration, reset usable spectrum threshold value and/or available duration via threshold value, and detect the frequency spectrum availability over the usable spectrum threshold value that resets, available duration via in the frequency spectrum detection window duration that resets over the available duration via threshold value and the unappropriated usable spectrum that reset;

Frequency spectrum switching module switches to described usable spectrum with the frequency spectrum of the current use of cognitive user.

6. the frequency spectrum system switched according to claim 5, wherein, the frequency spectrum detection window duration that the frequency spectrum detection module resets is that frequency spectrum switches the maximum delay threshold value, and the usable spectrum threshold value that resets and available duration via threshold value are to obtain after former usable spectrum threshold value and available duration via threshold value are weighted respectively.

7. the frequency spectrum system switched according to claim 5, wherein, the frequency spectrum detection module is after the frequency spectrum detection module is completed frequency spectrum detection, according to the frequency spectrum stability, calculate and reset the frequency spectrum detection window duration, and with this as duration of frequency spectrum detection period next time; Perhaps switch but usable spectrum set when be sky when the needs frequency spectrum, resetting the frequency spectrum detection duration before the frequency spectrum detection that will carry out begins is frequency spectrum handover delay threshold value, as the duration of the frequency spectrum detection that will carry out.

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