CN101702635A - Method for switching frequency spectrum based on cognitive radio technology and system thereof - Google Patents
Method for switching frequency spectrum based on cognitive radio technology and system thereof Download PDFInfo
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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
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 non-overlapping copies respectively for each different wireless communication system, under this spectrum allocation may system, be accompanied by the 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, and this becomes the matter of utmost importance that research, exploitation and deployment faced of many novel radios and mobile communication system.
Yet, 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 in 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 also is the rare problem of frequency spectrum is outmoded fixed frequency spectrum allocation strategy, rather than the shortage of frequency spectrum itself.
For make full use of distribute to that authoring system uses but on certain period or particular space unappropriated idle frequency spectrum resource, cognitive radio technology is subjected to paying close attention to widely and studying 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 transmission parameter to communicate.At present, extensively carried out and obtained more achievement in research about the research of the dynamic frequency spectrum deployment in the 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.Research about Dynamic Spectrum Management at present mainly is divided into frequency spectrum detection, frequency spectrum judging, frequency spectrum share and four aspects of frequency spectrum mobility.
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 insert idle frequency spectrum simultaneously, and the frequency spectrum mobility is that the frequency spectrum switching then 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 and efficiently use idle frequency spectrum that necessary base is provided, the research work of this three aspect 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 then 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 take over seamlessly other idle frequency range and continue communication when abdicate this section frequency spectrum; 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, also can carry out frequency spectrum and switch, cognitive user is switched to the idle frequency spectrum that other is more suitable for based on the consideration of system to load balancing.
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 frequency spectrum in essence, the frequency spectrum switching is a particularly important ring.Research work about frequent spectrum handoff technique at present just launches, and 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 cognitive user communication continuity and QoS.
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, may further comprise the 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 desired, 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 the 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; In the frequency spectrum detection window duration that resets, detect the frequency spectrum availability and surpass available duration via threshold value and the unappropriated usable spectrum that resets above the usable spectrum threshold value that resets, available duration via.
Further, the frequency spectrum detection window duration that resets is that frequency spectrum switches the maximum delay threshold value, and 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 finishing frequency spectrum detection,, calculate and reset the frequency spectrum detection window duration according to the frequency spectrum stability at every turn, and with this as duration of frequency spectrum detection period next time; Perhaps when the needs frequency spectrum switch but the usable spectrum set when empty, 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 the step (3), further comprising the steps of: as if do not need to switch frequency spectrum, in the duration of frequency spectrum detection period, to detect usable spectrum, and upgrade the usable spectrum set according to detected usable spectrum.
Further, upgrade the operation of usable spectrum set according to detected usable spectrum, further comprising the steps of: if the usable spectrum set less than, and detect period T in entire spectrum simultaneously
SenceIn satisfy p all the time
Candidate〉=p
Threshold+ p
Hysteresis1, and frequency spectrum available duration via τ 〉=τ
Threshold, then usable spectrum is joined the 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 detect period T in entire spectrum
SenceIn satisfy p all the time
Candidate〉=p
Worst+ p
Hysteresis2, and the frequency spectrum available duration via satisfies τ
Candidate〉=τ
Worst, then replace the poorest frequency spectrum p in the usable spectrum set with usable spectrum
Worst, p wherein
Hysteresis2Be spectrum replacement lagged value, τ
Threshold_relaxBe the available duration via of usable spectrum, τ
WorstBe the shortest frequency spectrum available duration via in the usable spectrum set; If the usable spectrum in the usable spectrum set is occupied or no longer meet the requirements, then 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 the system that frequency spectrum switches based on cognitive radio technology, comprising: the dividing time-steps module is divided into transfer of data period and frequency spectrum detection period with the communication process of cognitive user 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, judges whether to need to switch frequency spectrum, if desired, judges in the usable spectrum set whether have usable spectrum; The frequency spectrum detection module detects the frequency spectrum availability and surpasses usable spectrum threshold value, available duration via above 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 having usable spectrum, reset the frequency spectrum detection window duration, reset usable spectrum threshold value and/or available duration via threshold value, and in the frequency spectrum detection window duration that resets, detect the frequency spectrum availability above the usable spectrum threshold value that resets, available duration via above 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 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 finished frequency spectrum detection, and with this as duration of frequency spectrum detection period next time; Perhaps when the needs frequency spectrum switch but the usable spectrum set when empty, 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 in the duration of frequency spectrum detection period, upgrades the usable spectrum set according to detected usable spectrum.
Further, the system that described frequency spectrum switches also comprises: frequency spectrum is estimated 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 carry out frequency spectrum when switching in cognitive user, detect usable spectrum 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 available duration via threshold value and the unappropriated usable spectrum that resets above the usable spectrum threshold value that resets, available duration via in the frequency spectrum detection window duration that resets, and keeps the continuation communication process of cognitive user.Therefore, the present invention can guarantee cognitive user communication continuity and QoS.
Further, the present invention also can safeguard different usable spectrum set by adjusting 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 further understanding of the present invention, constitutes the application's a part, and illustrative examples of the present invention and explanation thereof are used to explain the present invention, do not constitute improper qualification 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
When the employed frequency spectrum of cognitive user is authorized to that the user recovers or link-quality variation or employed frequency spectrum 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 the service quality and the throughput of system of cognitive user.
Frequency spectrum switches and to switch on the 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 also is that frequency spectrum switches the switching in regular meeting is the sub-district; Secondly, frequency spectrum switches and has very strong randomness because the arrival of authorized user and leave, wireless channel conditions and user's business demand all has very big randomness, the generation that frequency spectrum switches also has very big randomness; Once more, 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 makes the frequency spectrum switching more complicated than the minizone switching, a lot of new theory and the processing methods of each process need, and need each process better to coordinate.
Specify frequency spectrum switching method of the present invention below in conjunction with drawings and Examples,, especially guarantee cognitive user communication continuity and QoS to coordinate switching flow.
Fig. 1 the present invention is based on cognitive radio technology to carry out the method flow diagram that frequency spectrum switches, and may further comprise the 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 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 the system, and the perhaps multiple of basic Transmission Time Interval, or the multiple of frame etc. are duration fixedly; The number of times and the transfer of data window duration of also can be according to the frequency spectrum stability, having carried out frequency spectrum detection be adjusted flexibly.
Adjust if desired, can define the frequency spectrum stability and be:
F wherein
AvailableFor certain section frequency spectrum is arranged in the number of times that usable spectrum is gathered, F continuously
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 the described set:
Wherein N is the size of usable spectrum set, the number of usable spectrum unit in promptly gathering, η
iIt is the frequency spectrum stability of i usable spectrum unit.H is big more to illustrate that then the frequency spectrum in the usable set is stable more.
H will influence the duration of frequency spectrum detection next time, and the duration of big more then next frequency spectrum detection period of H then can be short more, and vice versa.The duration of frequency spectrum detection can be defined as linear function, logarithmic function or the exponential function of H according to no business model 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 with 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:
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_thFor cognitive user letter drying compares threshold value.
Since 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 significantly 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 desired, 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, to detect current use frequency spectrum 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, in the duration of frequency spectrum detection period, detect usable spectrum, and upgrade the usable spectrum set according to detected usable spectrum.Jump to step 102 and continue to carry out the flow process of transfer of data period and frequency spectrum detection period.
Upgrade the usable spectrum set and comprise interpolation, replace and remove usable spectrum, be specially:
If usable spectrum set less than, and detect period T in entire spectrum simultaneously
SenceIn satisfy p all the time
Candidate〉=p
Threshold+ p
Hysteresis1, and frequency spectrum available duration via τ 〉=τ
Threshold, then 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 detect period T in entire spectrum
SenceIn satisfy p all the time
Candidate〉=p
Worst+ p
Hysteresis2, and the frequency spectrum available duration via satisfies τ
Candidate〉=τ
Worst, then replace the poorest frequency spectrum p 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 the shortest frequency spectrum available duration via 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 is meant, the frequency spectrum availability is no longer surpassed the usable spectrum that usable spectrum threshold value, available duration via no longer surpass the available duration via threshold value, then it is removed in the usable spectrum set.p
Hysteresis1And p
Hysteresis2When being respectively the frequency spectrum increase with spectrum replacement is the lagged value of avoiding ping-pong to introduce, 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, 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 various combination forms such as detection, energy measuring, feature detection, collaborative detection based on interference temperature.
When safeguarding the usable spectrum set, can separately or take all factors into consideration 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. according to usable spectrum.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 frequency spectrum is not had strict qualification.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 big more, and then the handoff failure probability of cognitive user is just more little, but the system-computed complexity is high more, just might satisfy the QoS of survice requirement more, obtains bigger 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 an 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.To specify the computational process of frequency spectrum availability p below.
Frequency spectrum availability p is:
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 regulate the transmittability and the shared significance level of transmission capacity of usable spectrum, wherein transmittability can be characterized by user's accessible transmission rate on this section frequency spectrum, transmission capacity is relevant with 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, the spectrum availability of the big more representative usable spectrum of p is just high more.
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, only need the usable spectrum that detected ordering is the highest to get final product as the switching target frequency 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 in the frequency spectrum detection window duration that resets, detect the frequency spectrum availability above the usable spectrum threshold value that resets, available duration via above the available duration via threshold value and the unappropriated usable spectrum that reset.
Wherein, there is not 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.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.To illustrate below.
Consider the requirement of cognitive user, can set coefficient of relaxation to reduce requirement to usable spectrum to handover delay; Also can not adopt coefficient of relaxation, directly frequency spectrum be assessed.
Coefficient of relaxation is defined as:
Wherein, T
Sence_lastFor cognitive user is switched last frequency spectrum detection duration before the requirement, T
DelayBe the handover delay threshold value, promptly the patient maximum handover delay of cognitive user is 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 with the available duration via threshold value frequency spectrum, specific as follows:
p
threshold_relax＝ω·p
threshold
τ
threshold_relax＝ω·τ
threshold
Wherein, p
Threshold_relaxAnd τ
Threshold_relaxBe respectively the 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 be carried out the frequency spectrum switching, if usable spectrum set non-NULL, then the usable spectrum in the pair set carries out fast detecting assessment (whether only detecting frequency spectrum by other CUs) in order, and the usable spectrum that detected ordering is the highest is finished switching as the switching target frequency spectrum.Described fast frequency spectrum detects and only is meant that at the detection of usable spectrum, its detection method can be simple energy measuring, because of its detect frequency spectrum relative fixed and detection method simple, the more common frequency spectrum detection process of execution speed is faster.
In step 109, cognitive user keeps the existing communication state, initiates the frequency spectrum handoff request again, process ends.
The present invention is based on cognitive radio technology and carry out the method that frequency spectrum switches, at first, need carry out frequency spectrum when switching in cognitive user, detect usable spectrum 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 available duration via threshold value and the unappropriated usable spectrum that resets above the usable spectrum threshold value that resets, available duration via in the frequency spectrum detection window duration that resets, and keeps the continuation communication process of cognitive user.Therefore, the present invention can guarantee cognitive user communication continuity and QoS.
Further, the present invention also can safeguard different usable spectrum set by adjusting 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: dividing time-steps module, data transmission module, frequency spectrum judging module, frequency spectrum detection module, frequency spectrum switching module.
The dividing time-steps module is divided into transfer of data period and frequency spectrum detection period with the communication process of cognitive user 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 frequency spectrum detection module detection usable spectrum, and to upgrade the usable spectrum set, the concrete renewal operated and will be described in the frequency spectrum detection module.Switch frequency spectrum if desired, call the frequency spectrum detection module and carry out frequency spectrum detection, judge according to testing result whether usable spectrum set exists usable spectrum, when testing result shows that when usable spectrum was arranged, the notice frequency spectrum switching module was switched.
When testing result shows when not having 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 in the frequency spectrum detection window duration that resets, detect the frequency spectrum availability above the usable spectrum threshold value that resets, available duration via above 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 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 above 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 in the duration of frequency spectrum detection period, and upgrades the usable spectrum set according to detected usable spectrum.
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 simultaneously at entire spectrum detection period T
SenceIn satisfy p all the time
Candidate〉=p
Threshold+ p
Hysteresis1, and the frequency spectrum available duration via satisfies τ 〉=τ
Threshold, then usable spectrum is joined in the usable spectrum set; Full in the usable spectrum set, and at entire spectrum detection period T
SenceIn satisfy p all the time
Candidate〉=p
Worst+ p
Hysteresis2, and the frequency spectrum available duration via satisfies τ
Candidate〉=τ
Worst, then usable spectrum is replaced frequency spectrum p the poorest in the available set
Worst, τ wherein
WorstBe the shortest frequency spectrum available duration via in the usable spectrum set; Usable spectrum in usable spectrum set detects by other CUs or no longer meets the requirement of usable spectrum assessment level, then 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 finished frequency spectrum detection, according to the frequency spectrum stability, calculate and also to 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 switch but the usable spectrum set when empty, 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: frequency spectrum is estimated 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 be carried out frequency spectrum when switching in cognitive user, detects usable spectrum 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 usable spectrum set usable spectrum be sky 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 available duration via threshold value and the unappropriated usable spectrum that resets above the usable spectrum threshold value that resets, available duration via in the frequency spectrum detection window duration that resets, and keeps the continuation communication process of cognitive user.Therefore, the present invention can guarantee cognitive user communication continuity and QoS.
Further, the present invention also can safeguard different usable spectrum set by adjusting 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:
At authorized user is the user of gsm system, the untapped frequency spectrum of cognitive user use authority user, and when authorized user is recovered frequency spectrum again, carry out the frequency spectrum switching.
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, then its probability density function is:
Call office is every obeying the negative exponent distribution that average duration is 1/ λ, and its probability density function is:
If average call duration is 1/ μ, then its probability density function is:
It is the Poisson distribution of μ that probability distribution obedience departure rate is left in conversation, and its probability density function is:
According to above-mentioned probability distribution, have only when authorized user conversation interim cognitive user just can take its frequency spectrum, then its transfer of data period continues the probability distribution of duration and is:
Suppose that frequency spectrum detection pre-estimation threshold value ρ is 0.7 in gsm system, promptly satisfy G when cognitive user must may be authorized to the probability that the user recovers behind communication time x on the usable spectrum
1O'clock (x)＞0.7, suppose that this moment, authorized user may occur, then stop transfer of data, carry out frequency spectrum detection.
In the frequency spectrum detection period, cognitive user at first determines whether to carry out frequency spectrum to be switched, and carries out frequency spectrum detection then, and the time of frequency spectrum detection will last till the time of frequency spectrum handover delay threshold value defined always for the first time.The user is if need frequency spectrum to switch, and do not have satisfactory frequency spectrum, then begins handoff request next time.
When detecting idle frequency spectrum, according to the usable spectrum assessment level:
Idle frequency spectrum is assessed, the spectrum concentration of wherein considering gsm system is in the 900MHz frequency range, carrier frequency is very little to the influence of frequency spectrum, so the value of β is less relatively, can get 0.1, α can get 0.9, and the bandwidth of frequency spectrum detection is narrower, the general value of frequency spectrum correct detection probability ε is more than 90%, then usable spectrum threshold value p
ThresholdCan value be 1.According to authorized user and the professional probability distribution that arrives and leave of cognitive user, 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 then
Threshold=λ e
-0.9 λ, when detected idle frequency spectrum satisfies simultaneously: S
Available={ s:p 〉=1, τ 〉=λ e
-0.9 λThe time, then it is joined in the usable spectrum set, in the present embodiment, setting the usable spectrum set sizes is 3, then only will satisfy three best spectrum unit of above condition and join in the set.
Next according to usable spectrum set replacement criteria usable spectrum is gathered and upgraded, wherein two lagged value p
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:
Wherein, t is the number of times of certain user's frequency spectrum detection, and the calculated value the when H in the formula is t-1 time is if t-1=1 is H=0 then.Like this, if the frequency spectrum stability that described usable spectrum is concentrated is high more, then needs short more detection time and upgrade the usable spectrum set.
When cognitive user need be carried out the frequency spectrum switching, according to the frequency spectrum switching criterion, if usable spectrum set non-NULL then carries out the fast detecting assessment again to the frequency spectrum in this set, and on detected first usable spectrum, proceed transfer of data, finish 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 the requirement of cognitive user, for usable spectrum set replacement criteria is set coefficient of relaxation to reduce the requirement to usable spectrum to handover delay.
Coefficient of relaxation wherein:
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 frequency spectrum success rate for switching.
If switch maximum delay threshold value T at the predefined frequency spectrum of system
DelayDetect usable spectrum in the=1s, cognitive user is adjusted its corresponding transmitter parameter and proceed transfer of data on this usable spectrum, finishes switching;
If do not detect usable spectrum yet in the predefined frequency spectrum of system switches the maximum delay threshold value, then cognitive user withdraws from this frequency spectrum switching flow, concurrent handoff request next time.
Embodiment two:
At authorized user is the user of wideband OFDM system, the frequency spectrum that the dynamic use authority user of cognitive user is not used, and when cognitive user proposes more high bandwidth request, carry out the frequency spectrum switching.
Because class of business is very abundant, comprise conversation class, stream class, interactive class and background classes etc., each business requires all inequality to time delay, delay variation, bandwidth etc., when the cognitive user of communicating by letter proposes new more high bandwidth requirements professional, can carry out frequency spectrum and switch to meet consumers' demand.
Present embodiment consider when cognitive user just at use authority user's frequency spectrum, and frequency spectrum pre-estimation threshold value is also during no show, because authorized user is recovered the switching that frequency spectrum triggers.
As if when this handover trigger, if this cognitive user has been safeguarded a usable spectrum set, and should gather non-NULL, the user then 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, then the user need carry out frequency spectrum detection immediately.
In the frequency spectrum detection period, at first with detected idle frequency spectrum 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:
Idle frequency spectrum is assessed, considered that the frequency spectrum of ofdm system may relatively disperse (such as the LTE system), carrier frequency is bigger to the influence 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 less relatively value, but whether available α be still decision frequency spectrum topmost factor, can get 0.7 at this α, β can get 0.3.Because 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 about 70%, then usable spectrum threshold value p
ThresholdCan value be 1.5.According to the historical information of authorized user and the professional frequency spectrum that uses of cognitive user, setting the lasting duration of frequency spectrum under 90% probability is the available duration via threshold tau
Threshold, when detected idle frequency spectrum satisfies simultaneously: S
Available={ s:p 〉=1.5, τ 〉=τ
ThresholdThe time, then it is joined in the usable spectrum set, and select to meet the highest one of ordering in the described set as the switching target frequency spectrum.
About the time of frequency spectrum detection, the time of frequency spectrum detection will last till the time of frequency spectrum handover delay threshold value defined always for the first time, because multiple business is to the diversity of delay requirement, time delay threshold value T
DelayDetermine can consider to distinguish different types of service separately, also can take all factors into consideration the ratio of each professional service class and shared offered load thereof.
If switch maximum delay threshold value T at the predefined frequency spectrum of system
DelayIn detect suitable usable spectrum, cognitive user is adjusted its corresponding transmitter parameter and proceed transfer of data on this usable spectrum, finishes switching;
If do not detect usable spectrum yet in the predefined frequency spectrum of system switches the maximum delay threshold value, then cognitive user withdraws from this frequency spectrum switching flow, concurrent handoff request next time.
Claims (13)
1. one kind is carried out the method that frequency spectrum switches based on cognitive radio technology, may further comprise the 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;
(3) in the frequency spectrum detection period, judge whether to need to switch frequency spectrum, if desired, 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.
2. the method for switching according to the described frequency spectrum of claim 1 wherein, detects the operation that whether has usable spectrum in the usable spectrum set in the step (4), and is further comprising the steps of:
If there is no usable spectrum resets the frequency spectrum detection window duration, resets usable spectrum threshold value and/or available duration via threshold value;
In the frequency spectrum detection window duration that resets, detect the frequency spectrum availability and surpass available duration via threshold value and the unappropriated usable spectrum that resets above the usable spectrum threshold value that resets, available duration via.
3. the method for switching according to the described frequency spectrum of claim 2, wherein, the frequency spectrum detection window duration that resets is that frequency spectrum switches the maximum delay threshold value, and 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.
4. according to the method for claim 2 or 3 described frequency spectrums switchings, wherein, reset the operation of frequency spectrum detection window duration, may further comprise the steps:
After finishing 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 switch but the usable spectrum set when empty, 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.
5. the method for switching according to the described frequency spectrum of claim 1 wherein, judges whether to need to switch the operation of frequency spectrum in the step (3), and is further comprising the steps of:
If do not need to switch frequency spectrum, in the duration of frequency spectrum detection period, detect usable spectrum, and upgrade the usable spectrum set according to detected usable spectrum.
6. the method for switching according to the described frequency spectrum of claim 5 wherein, is upgraded the operation that usable spectrum is gathered according to detected usable spectrum, and is further comprising the steps of:
If usable spectrum set less than, and detect period T in entire spectrum simultaneously
SenceIn satisfy p all the time
Candidate〉=p
Threshold+ p
Hysteresis1, and frequency spectrum available duration via τ 〉=τ
Threshold, then usable spectrum is joined the 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 detect period T in entire spectrum
SenceIn satisfy p all the time
Candidate〉=p
Worst+ p
Hysteresis2, and the frequency spectrum available duration via satisfies τ
Candidate〉=τ
Worst, then replace the poorest frequency spectrum p in the usable spectrum set with usable spectrum
Worst, p wherein
Hysteresis2Be spectrum replacement lagged value, τ
Threshold_relaxBe the available duration via of usable spectrum, τ
WorstBe the shortest frequency spectrum available duration via in the usable spectrum set;
If the usable spectrum in the usable spectrum set is occupied or no longer meet the requirements, then it is removed in the usable spectrum set.
7. the method for switching according to the described frequency spectrum of claim 1, wherein, 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 the probability of recovering frequency spectrum surpasses frequency spectrum detection pre-estimation threshold value ρ, start the frequency spectrum detection period.
8. one kind is carried out the system that frequency spectrum switches based on cognitive radio technology, comprising:
The dividing time-steps module is divided into transfer of data period and frequency spectrum detection period with the communication process of cognitive user 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, judges whether to need to switch frequency spectrum, if desired, judges in the usable spectrum set whether have usable spectrum;
The frequency spectrum detection module detects the frequency spectrum availability and surpasses usable spectrum threshold value, available duration via above 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.
9. the system that described according to Claim 8 frequency spectrum switches, wherein, the frequency spectrum detection module is not when having usable spectrum, reset the frequency spectrum detection window duration, reset usable spectrum threshold value and/or available duration via threshold value, and in the frequency spectrum detection window duration that resets, detect the frequency spectrum availability above the usable spectrum threshold value that resets, available duration via above the available duration via threshold value and the unappropriated usable spectrum that reset.
10. the system of switching according to the described frequency spectrum of claim 9, 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 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.
11. according to Claim 8 or the system switched of 9 described frequency spectrums, wherein, the frequency spectrum detection module is after the frequency spectrum detection module is finished frequency spectrum detection, according to the frequency spectrum stability, calculate and also to 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 switch but the usable spectrum set when empty, 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.
12. the system that described according to Claim 8 frequency spectrum switches, wherein, the frequency spectrum detection module also when not needing to switch frequency spectrum, detects usable spectrum in the duration of frequency spectrum detection period, and upgrades the usable spectrum set according to detected usable spectrum.
13. the system that described according to Claim 8 frequency spectrum switches, also comprise: frequency spectrum is estimated 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.
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