CN107222870A - For the ofdm signal frequency spectrum sensing method that the time is asynchronous and is not present under offset frequency situation - Google Patents
For the ofdm signal frequency spectrum sensing method that the time is asynchronous and is not present under offset frequency situation Download PDFInfo
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- H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
- H04W16/14—Spectrum sharing arrangements between different networks
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Abstract
The invention discloses a kind of for the ofdm signal frequency spectrum sensing method that the time is asynchronous and is not present under offset frequency situation, it samples to the reception signal from monitoring channel, obtains sampled signal；Then, the sampled value of all sampled points in sampled signal, and it is asynchronous and in the absence of under offset frequency situation in the time, and using the autocorrelation of the cyclic prefix of the ofdm signal received in signal, estimation obtains noise power；And the sampled value of the sampled point in sampled signal, calculate the covariance matrix of sampled signal；Then, according to the covariance matrix of noise power and sampled signal, test statistics is calculated；Finally, by comparing check statistic and the size of the decision threshold obtained, judge whether there is authorization user signal in monitoring channel, to realize frequency spectrum perception；Advantage is can to effectively improve the frequency spectrum perception performance of ofdm signal, and computation complexity is low.
Description
Technical field
The present invention relates to the frequency spectrum sensing method in a kind of cognitive radio system, noise work(is based on more particularly, to one kind
What rate was estimated is directed to the ofdm signal frequency spectrum sensing method that the time is asynchronous and is not present under offset frequency situation.
Background technology
Requirement with the fast development and people of the communication technology to communication data rate and quality is increasingly improved, and is caused
Being substantially improved of bandwidth demand.However, the fixed frequency spectrum distribution mechanism that there is currently is so that the availability of frequency spectrum is very low.2009
Year, wireless technology research institute of research institute of China Mobile authorizes the utilization power of frequency spectrum to be surveyed China, measured result table
The utilization rate of bright most of frequency spectrum less than 5%, have even close to 0%.In order to improve frequency spectrum resource utilization rate, there has been proposed
The technology such as dynamic spectrum access (Dynamic spectrum access, DSA) and frequency spectrum share is rare to alleviate frequency spectrum resource
Problem.Such technology allows wireless devices to interact with residing communication environment and changes self transmission according to interaction results
Parameter, so as to realize that can its key also resides in user steady with dynamic, the adaptive potential idle frequency spectrum of mode flexible utilization
Detect that frequency spectrum is idle strongly.In order to prevent producing interference to authorized user's communication, cognitive radio system is allowed for effectively
Reliably identify idle channel, therefore frequency spectrum perception is one of key technology in cognitive radio.
OFDM (Orthogonal frequency division multiplexing, OFDM) technology has
The characteristics of availability of frequency spectrum is high, and be by one of widely used technology of current and future wireless communication standard, it is therefore right
The frequency spectrum perception of ofdm signal (judges to whether there is ofdm signal in channel) that research has very important significance.It is existing
It can be divided into frequency domain detection and the class of tim e- domain detection two for the frequency spectrum sensing method of ofdm signal.Wherein, frequency domain detection needs meter
The frequency spectrum of sampled signal is calculated, therefore with larger amount of calculation；Tim e- domain detection mainly utilize ofdm signal in cyclic prefix from
Correlation properties realize frequency spectrum perception, and amount of calculation is relatively low.Zeng et al. in 2009《Spectrum sensing
Algorithms for cognitive radio based on statistical covariance (bases in cognitive radio
In the frequency spectrum sensing method of statistics covariance)》Middle proposition based on covariance matrix frequency spectrum sensing method, it can utilize OFDM
Correlation in signal realizes frequency spectrum perception, with amount of calculation it is low the characteristics of, but not account for the time asynchronous and not for this method
There is the concrete condition of frequency deviation, so the cyclic prefix autocorrelation performance of ofdm signal can not be utilized effectively.
The content of the invention
The technical problems to be solved by the invention are to provide a kind of asynchronous and not for the time based on noise power estimation
There is the ofdm signal frequency spectrum sensing method under offset frequency situation, it can effectively improve the frequency spectrum perception performance of ofdm signal,
And computation complexity is low.
The present invention solve the technical scheme that is used of above-mentioned technical problem for：One kind is asynchronous and in the absence of frequency deviation for the time
In the case of ofdm signal frequency spectrum sensing method, it is characterised in that its processing procedure is：First, to being connect from monitoring channel
The collection of letters number is sampled, and obtains sampled signal；Then, the sampled value of all sampled points in sampled signal, and in the time
Asynchronous and in the absence of under offset frequency situation, using the autocorrelation of the cyclic prefix of the ofdm signal received in signal, estimation is obtained
Noise power；Further according to the sampled value of the sampled point in sampled signal, the covariance matrix of sampled signal is calculated；Then, according to
The covariance matrix of noise power and sampled signal, calculates test statistics；Finally, comparing check statistic and acquisition are passed through
The size of decision threshold, judges whether there is authorization user signal in monitoring channel, to realize frequency spectrum perception.
The ofdm signal frequency spectrum sensing method specifically includes following steps：
Step one：The reception signal from monitoring channel is carried out M times using the sampling module in cognitive radio system
Sampling, obtains the sampled signal being made up of the sampled value of M sampled point, wherein, M=K × N, K represents to receive the OFDM in signal
The total number of the OFDM symbol included in signal, K >=1, N represents to receive any one OFDM symbols in the ofdm signal in signal
The total number of subcarrier in number, N=Nc+Nd, NcExpression receives the length of the cyclic prefix of the ofdm signal in signal, NdTable
Show receive signal in ofdm signal in any one OFDM symbol in valid data subcarrier total number, Nd≥Nc>
1, and set NcAnd NdAll it is even number；
Step 2：The sampled value of all sampled points in sampled signal, and it is asynchronous and in the absence of frequency deviation feelings in the time
Under condition, using the autocorrelation of the cyclic prefix of the ofdm signal received in signal, estimation obtains noise power, is designated as Wherein, ρηThe estimate of the coefficient correlation of reception signal is represented,Represent the power of reception signal
Estimate；
Step 3：The sampled value of sampled point in sampled signal, calculates the covariance matrix of sampled signal, is designated as
Rx, RxThe matrix tieed up for a L × L, by RxIn the i-th row jth arrange element be designated as Rx(i, j),Wherein, L ∈ [2, M-1], 1≤i≤L, 1≤j≤L, x (p) represents sampling
The sampled value of p-th of sampled point in signal, x*(p-j+i) gripping altogether for x (p-j+i), x (p-j+i) is represented in sampled signal
Pth-j+i sampled points sampled value；
Step 4：According toAnd Rx, test statistics is calculated, T is designated as,
Step 5：Decision threshold is obtained, λ is designated as；Then comparing check statistic T and decision threshold λ size, if T>
λ, then judge there is authorization user signal in monitoring channel；If T≤λ, judge in monitoring channel without authorization user signal,
Monitor channel and be in idle condition, so as to realize frequency spectrum perception.
In described step two,Wherein, 1≤n≤M-Nd, x (n) expressions
The sampled value of n-th of sampled point in sampled signal, x* (n+Nd) it is x (n+Nd) conjugation, x (n+Nd) represent in sampled signal
The n-th+NdThe sampled value of individual sampled point.
In described step two,Wherein, 1≤m≤M, x (m) represent to adopt for m-th in sampled signal
The sampled value of sampling point, symbol " | | " it is the symbol that takes absolute value.
Compared with prior art, the advantage of the invention is that：
1) compared with traditional noise power estimator is only in noise sample effectively, the inventive method estimating noise power
Process take full advantage of ofdm signal cyclic prefix autocorrelation, current perceive time slot so as to estimate exactly
Interior noise power, is effectively improved the frequency spectrum perception performance of ofdm signal.
2) the inventive method need not calculate the characteristic value of covariance matrix and the frequency spectrum of sampled signal, therefore it has meter
Complexity is calculated low, the characteristics of simple to operate.
Brief description of the drawings
Fig. 1 is the FB(flow block) of the inventive method；
Fig. 2 is, as N=64 and when received signal to noise ratio is -12 decibels, to be utilized respectively the inventive method and Zeng et al. and carry
The comparison schematic diagram for the ROC curve that the covariance method gone out is obtained；
Fig. 3 is, as N=64 and when received signal to noise ratio is -10 decibels, to be utilized respectively the inventive method and Zeng et al. and carry
The comparison schematic diagram for the ROC curve that the covariance method gone out is obtained.
Embodiment
The present invention is described in further detail below in conjunction with accompanying drawing embodiment.
It is proposed by the present invention a kind of for the ofdm signal frequency spectrum sensing method that the time is asynchronous and is not present under offset frequency situation,
Its FB(flow block) is as shown in figure 1, its processing procedure is：First, the reception signal from monitoring channel is sampled, adopted
Sample signal；Then, the sampled value of all sampled points in sampled signal, and it is asynchronous and in the absence of offset frequency situation in the time
Under, using the autocorrelation of the cyclic prefix of the ofdm signal received in signal, estimation obtains noise power；Further according to sampling letter
The sampled value of sampled point in number, calculates the covariance matrix of sampled signal；Then, according to the association of noise power and sampled signal
Variance matrix, calculates test statistics；Finally, by comparing check statistic and the size of the decision threshold obtained, judge
Authorization user signal (i.e. ofdm signal) is whether there is in monitoring channel, to realize frequency spectrum perception.
The present invention's is directed to the ofdm signal frequency spectrum sensing method that the time is asynchronous and is not present under offset frequency situation, its specific bag
Include following steps：
Step one：The reception signal from monitoring channel is carried out M times using the sampling module in cognitive radio system
Sampling, obtains the sampled signal being made up of the sampled value of M sampled point, wherein, M=K × N, K represents to receive the OFDM in signal
The total number of the OFDM symbol included in signal, K >=1, N represents to receive any one OFDM symbols in the ofdm signal in signal
The total number of subcarrier in number, N=Nc+Nd, NcExpression receives the length of the cyclic prefix of the ofdm signal in signal, NdTable
Show receive signal in ofdm signal in any one OFDM symbol in valid data subcarrier total number, Nd≥Nc>
1, and set NcAnd NdAll it is even number.
Step 2：The sampled value of all sampled points in sampled signal, and it is asynchronous and in the absence of frequency deviation feelings in the time
Under condition, using the autocorrelation of the cyclic prefix of the ofdm signal received in signal, estimation obtains noise power, is designated as Wherein, ρηThe estimate of the coefficient correlation of reception signal is represented,Represent the power of reception signal
Estimate.
In this particular embodiment, in step 2,Wherein, 1≤n≤M-
Nd, x (n) represent sampled signal in n-th of sampled point sampled value, x* (n+Nd) it is x (n+Nd) conjugation, x (n+Nd) represent
The n-th+N in sampled signaldThe sampled value of individual sampled point.
In this particular embodiment, in step 2,Wherein, 1≤m≤M, x (m) represent sampled signal
In m-th of sampled point sampled value, symbol " | | " is the symbol that takes absolute value.
Step 3：The sampled value of sampled point in sampled signal, calculates the covariance matrix of sampled signal, is designated as
Rx, RxThe matrix tieed up for a L × L, by RxIn the i-th row jth arrange element be designated as Rx(i, j),Wherein, L ∈ [2, M-1], such as take1≤i≤L, 1≤j≤L, x
(p) sampled value of p-th of sampled point in sampled signal, x are represented*(p-j+i) gripping altogether for x (p-j+i), x (p-j+i) is represented
The sampled value of-j+i sampled points of pth in sampled signal.
Step 4：According toAnd Rx, test statistics is calculated, T is designated as,
Step 5：Decision threshold is obtained using prior art, λ is designated as；Then comparing check statistic T and decision threshold λ
Size, if T>λ, then judge there is authorization user signal in monitoring channel；If T≤λ, the nothing in monitoring channel is judged
Authorization user signal, monitoring channel is in idle condition, so as to realize frequency spectrum perception.
Emulated by following to further illustrate the feasibility and validity of the inventive method.
Assuming that the ofdm signal time received in signal from monitoring channel is asynchronous and in the absence of frequency deviation, receive in signal
Ofdm signal in any one OFDM symbol valid data in subcarrier total number Nd=48, receive in signal
The length N of the cyclic prefix of ofdm signalc=16, receive the son in any one OFDM symbol in the ofdm signal in signal
The total number N=N of carrier wavec+Nd=16+48=64, takes K=14, then sampled signal is by M=K × N=14 × 64=896 sampling
The sampled value of point is constituted.If taking L=5.
Fig. 2 is given as N=64 and when received signal to noise ratio is -12 decibels, is utilized respectively the inventive method and Zeng etc.
The ROC curve that the covariance method that people proposes is obtained.From figure 2 it can be seen that the ROC curve obtained using the inventive method is far high
In the ROC curve obtained using Zeng et al. covariance methods proposed, the frequency spectrum perception performance of the inventive method is fully indicated
The covariance method proposed better than Zeng et al..
Fig. 3 is given as N=64 and when received signal to noise ratio is -10 decibels, is utilized respectively the inventive method and Zeng etc.
The ROC curve that the covariance method that people proposes is obtained.From figure 3, it can be seen that the ROC curve obtained using the inventive method is far high
In the ROC curve obtained using Zeng et al. covariance methods proposed, the frequency spectrum perception performance of the inventive method is fully indicated
The covariance method proposed better than Zeng et al..
In addition, the ROC curve shown in Fig. 2 and Fig. 3 is referred to as experiencing linearity curve, abscissa is false-alarm probability, and ordinate is inspection
Survey probability；Area below curve is bigger, then it represents that the detection performance of the frequency spectrum sensing method corresponding to the curve is better.
Claims (4)
1. a kind of be directed to the ofdm signal frequency spectrum sensing method that the time is asynchronous and is not present under offset frequency situation, it is characterised in that it
Processing procedure is：First, the reception signal from monitoring channel is sampled, obtains sampled signal；Then, believed according to sampling
The sampled value of all sampled points in number, and it is asynchronous and in the absence of under offset frequency situation in the time, utilize the OFDM received in signal
The autocorrelation of the cyclic prefix of signal, estimation obtains noise power；Further according to the sampled value of the sampled point in sampled signal, meter
Calculate the covariance matrix of sampled signal；Then, according to the covariance matrix of noise power and sampled signal, inspection statistics are calculated
Amount；Finally, by comparing check statistic and the size of the decision threshold obtained, judge whether there is authorized user in monitoring channel
Signal, to realize frequency spectrum perception.
2. according to claim 1 be directed to the ofdm signal frequency spectrum perception side that the time is asynchronous and is not present under offset frequency situation
Method, it is characterised in that it specifically includes following steps：
Step one：M sampling is carried out to the reception signal from monitoring channel using the sampling module in cognitive radio system,
The sampled signal being made up of the sampled value of M sampled point is obtained, wherein, M=K × N, K represents to receive the ofdm signal in signal
In the total number of OFDM symbol that includes, K >=1, N represents to receive in any one OFDM symbol in the ofdm signal in signal
Subcarrier total number, N=Nc+Nd, NcExpression receives the length of the cyclic prefix of the ofdm signal in signal, NdExpression connects
The total number of the subcarrier of the valid data in any one OFDM symbol in ofdm signal in the collection of letters number, Nd≥Nc>1, and
If NcAnd NdAll it is even number；
Step 2：The sampled value of all sampled points in sampled signal, and it is asynchronous and in the absence of under offset frequency situation in the time,
Using the autocorrelation of the cyclic prefix of the ofdm signal received in signal, estimation obtains noise power, is designated as Wherein, ρηThe estimate of the coefficient correlation of reception signal is represented,Represent the power of reception signal
Estimate；
Step 3：The sampled value of sampled point in sampled signal, calculates the covariance matrix of sampled signal, is designated as Rx, RxFor one
The matrix of individual L × L dimensions, by RxIn the i-th row jth arrange element be designated as Rx(i, j),
Wherein, L ∈ [2, M-1], 1≤i≤L, 1≤j≤L, x (p) represents the sampled value of p-th of sampled point in sampled signal, x*(p-
J+i) gripping altogether for x (p-j+i), x (p-j+i) represents the sampled value of-j+i sampled points of pth in sampled signal；
Step 4：According toAnd Rx, test statistics is calculated, T is designated as,
Step 5：Decision threshold is obtained, λ is designated as；Then comparing check statistic T and decision threshold λ size, if T>λ, then
Judge there is authorization user signal in monitoring channel；If T≤λ, judge in monitoring channel without authorization user signal, monitoring
Channel is in idle condition, so as to realize frequency spectrum perception.
3. according to claim 2 be directed to the ofdm signal frequency spectrum perception side that the time is asynchronous and is not present under offset frequency situation
Method, it is characterised in that in described step two,Wherein, 1≤n≤M-Nd, x
(n) sampled value of n-th of sampled point in sampled signal is represented,Conjugation, x (n+Nd) represent to adopt
The n-th+N in sample signaldThe sampled value of individual sampled point.
4. the ofdm signal frequency spectrum perception that the time is asynchronous and is not present under offset frequency situation of being directed to according to Claims 2 or 3
Method, it is characterised in that in described step two,Wherein, 1≤m≤M, x (m) are represented in sampled signal
The sampled value of m-th of sampled point, symbol " | | " it is the symbol that takes absolute value.
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