CN102571241A - Improved double-threshold cooperative spectrum sensing method - Google Patents

Abstract

The invention relates to an improved double-threshold cooperative spectrum sensing method, which comprises the following steps that: a cognitive user in a cognitive radio system senses a local spectrum, compares and classifies sensed main user energy values, if the energy values are beyond two thresholds, can directly perform local judgment to obtain a hard judgment result whether a main user exists and send the result to a fusion center, if the energy values are between the two thresholds, the cognitive user needs to send the sensed main user energy values and signal to noise ratios to the fusion center, and the fusion center calculates a weight factor of each cognitive user according to the received signal to noise ratios and performs fusion judgment according to the received energy values to obtain a soft judgment result whether the main user exists; and the fusion center comprehensively processes the hard judgment result and the soft judgment result, and makes a final judgment whether the main user exists by using an 'or' rule. According to the method, the advantage of double-threshold cooperative spectrum sensing can be fully realized; and the spectrum sensing performance is improved.

Description

A kind of improved double threshold cooperative frequency spectrum sensing method

Technical field

The present invention is a kind of improved double threshold cooperative frequency spectrum sensing method, is mainly used in the not high problem of perceptual performance that solves in the cognitive radio system, belongs to cognitive radio system perceptual performance field.

Background technology

Along with the expansion of broadband multimedia services, radio spectrum resources is more and more in short supply, and the imbalance between supply and demand of frequency spectrum is more and more sharp-pointed.But radio spectrum resources is a kind of non-renewable resources, can only utilize frequency spectrum resource again, and therefore how research improves the utilance of frequency spectrum, could alleviate the rare difficult problem of frequency spectrum resource.Cognitive radio technology has arisen at the historic moment under this background.The basic point of departure of cognitive radio is exactly not influence under the situation of authorizing the frequency range proper communication; Have the Wireless Telecom Equipment of cognitive function can the idle frequency range of insertion authority in; And dynamically to utilize frequency spectrum, its core concept be exactly Wireless Telecom Equipment to be had find idle frequency spectrum and the ability of rationally utilizing.The cognition wireless electric energy fundamentally solves at present the unreasonable application to frequency spectrum resource that the fixed allocation policy because of frequency spectrum causes.

Along with the development of cognitive radio technology, the frequency spectrum perception technology has become the basis and the prerequisite of cognitive radio technology development.An important prerequisite that realizes cognitive radio is not influence to authorize main user's communications in the frequency range; In order main user not to be caused interference; Cognitive radio can only be found the frequency spectrum hole through frequency spectrum is constantly detected; And utilize the frequency spectrum hole to communicate, and this frequency range will in time discovered and withdraw to cognitive radio when main user's restoring communication.The effect of frequency spectrum perception is to confirm unappropriated frequency range as quickly as possible and accurately, and frequency spectrum perception result inaccurate or time-delay brings interference can for main user, and therefore, the speed of frequency spectrum perception and accuracy are extremely important.Frequency spectrum sensing method has single user's frequency spectrum perception and collaborative spectrum sensing.

1. single user's frequency spectrum perception

The energy perception is a most widely used cognitive method in single user's frequency spectrum perception.The energy perception is proposed in 1967 by H.urkowitz the earliest, and core concept is to judge according to the energy that receives signal or the size of power whether signal exists.The basic principle of energy measuring can be described as: cognitive user at first will receive signal through band pass filter, obtain the signal of the target frequency bands of the perception of wanting; Then the target frequency bands signal is passed through the square law device, obtain this signal power and estimate; Then the power to this signal is estimated integration in certain fixing cycle, obtains the statistic of the signal energy in the target frequency bands; At last the energy statistics amount and the decision threshold that obtain are compared; Be higher than this thresholding and represent that then there is main user's transmission signals in current this frequency range; Explain that main user is using this frequency range; Be lower than this thresholding and then represent not main user's transmission signals in current this frequency range, explain that this frequency range is by main user's use.

2. collaborative spectrum sensing

Collaborative spectrum sensing proposes on single user's frequency spectrum perception basis; Purpose is in order to solve the concealed terminal in single user's frequency spectrum perception; Sensitivity required problems such as high, obtained bigger perceptual performance gain with less relatively communication overhead. and the collaborative spectrum sensing structure chart is as shown in Figure 1 in the cognitive radio.The collaborative spectrum sensing process generally includes local perception, and perception information transmission and perception information merge three phases.Local perception and single user's frequency spectrum perception process are in full accord; Control channel is adopted in the transmission of perception information usually, between cognitive user and control centre, transmits; Because perception information can be the court verdict of 1 bit, also can be local detection statistic, so exist hard decision to merge and soft fusion perception information amalgamation mode.

People such as Jiang Zhu are at document Jiang Zhu; Zhengguang Xu; Furong; Wang, Benxiong Huang and Bo Zhang.Double Threshold Energy Detection of Cooperative Spectrum Sensing in cognitive radio.3rd International Conference on Cognitive Radio Oriented Wireless Networks and Communications, CrownCom 2008; The double threshold cooperation perception method that proposes among the May2008 is a kind of mixing judgement cooperation algorithm, combines hard decision and soft fusion dual mode.The cognitive user of subparticipation cooperation adopts soft fusion that detected a series of energy values are sent to fusion center in this algorithm; The cognitive user that remainder is participated in cooperation adopts hard decision that court verdict is sent to fusion center; Fusion center is made the soft-decision result according to these energy values earlier, and the hard decision result who comprehensively receives again makes the final decision whether main user exists.

Though traditional double threshold cooperative frequency spectrum sensing method can overcome the influence of decline to sensing results to a certain extent.But this method does not consider in the actual environment that the residing wireless environment of cognitive user is also inequality, and their perception information is also just different to the percentage contribution of Centroid.If the sensing results of each cognitive user of being impartial to without distinction, so final court verdict will have bigger discrepancy with actual conditions, can reduce the perceptual performance of system.

Summary of the invention

Technical problem: the objective of the invention is to propose a kind of improved method, solve the not high problem of frequency spectrum perception performance to traditional double threshold cooperative frequency spectrum sensing method.

Technical scheme: the present invention proposes a kind of improved double threshold cooperative frequency spectrum sensing method; Recently calculate their CF according to the noise of each cognitive user, take into full account different cognitive users the contribution degree difference of Centroid is improved overall detection performance.

One, architecture

1. Fig. 2 has provided the model of double threshold frequency spectrum perception; The double threshold method is a kind of method that combines hard decision criterion and soft-decision criterion; Two different threshold values are arranged; The observation information that falls into outside reaching between two threshold values is handled with different cooperative detection algorithms respectively, both overcome the large scale decline, reduced the influence of small scale decline again to a certain extent testing result to the information dropout that system causes.

Two energy threshold values that exist in the double threshold algorithm are respectively λ ₁And λ ₂, as shown in Figure 2, as the energy detection value Y of i cognitive user _iGreater than λ ₂The time, the frequency spectrum state that cognitive user can be adjudicated this moment is H ₁, promptly have main subscriber signal to exist; Work as Y _iLess than λ ₁The time, this cognitive user judgement state this moment is H ₀, promptly not main subscriber signal exists.And as energy value Y _iBetween λ ₁And λ ₂Between the time, this cognitive user is not made judgement, but all are fallen into this interval cognitive user detected energy value Y _iSend the information fusion center to and do further judgement.Therefore, in double threshold detection method, the information fusion center will receive two category informations, and the one, hard decision is H as a result ₀Or H ₁The 2nd, energy value is with between λ ₁And λ ₂Between the detection information of cognitive user, this part energy value generates a court verdict after fusion center carries out equal gain combining, can be referred to as the soft-decision result.Last fusion center utilizes certain fusion criterion to carry out integrated treatment to soft-decision result and hard decision result, finally obtains the court verdict whether main user exists.

2. Fig. 3 has provided improved double threshold frequency spectrum perception system model; It is compared with the model of traditional double threshold frequency spectrum detection; Those can not directly make the cognitive user of local judgement, not only will send the energy value that perceives, but also need they signal to noise ratios separately be sent to Centroid.In cognitive radio system, cognitive user utilize the double threshold collaborative spectrum sensing to send out method to accomplish the complete model of entire spectrum perception as shown in Figure 4.

Here to accomplish two things at fusion center, the first, through the CF of main user to each cognitive user of snr value calculating of these cognitive user; The second, with " or " criterion (as long as there is a cognitive user to think that main user exists, just judging that main user exists) analyzes and make conclusive judgement to the information of receiving.

Two, method flow

Improved double threshold cooperative frequency spectrum sensing method is specially: in the cognitive radio system; Cognitive user is carried out frequency spectrum perception to main user respectively; And the main user energy value that perceives carried out classification processing; Send to fusion center then, make the judgement whether main user exists by fusion center according to received information at last.Concrete flow process is following:

1. each cognitive user in the cognitive radio system is carried out frequency spectrum perception to main user respectively, obtains the main user energy value that it perceives.

2. judge main user energy value that each cognitive user perceives be between two thresholdings or outside.

3. if the energy value that perceives of cognitive user is in outside two thresholdings, then independently carry out local frequency spectrum perception, draw the court verdict whether main user exists, can be described as the hard decision result, send to fusion center then respectively.

4. if the energy value that perceives of cognitive user is between two thresholdings; Cognitive user can not independently be carried out local frequency spectrum perception so; Need send to fusion center to main user energy value and the signal to noise ratio that it perceived, further handle by fusion center.

5. fusion center goes out the detection confidence of each cognitive user earlier according to the snr computation that receives.Then energy value and confidence level are carried out the weighting fusion judgement, obtain the court verdict whether main user exists, can be described as the soft-decision result.

6. fusion center main user that the front is received hard decision result who sends over and the soft-decision result who oneself obtains carries out integrated treatment, finally obtains the court verdict whether main user exists.

Beneficial effect

The present invention is directed to the not high problem of perceptual performance of double threshold frequency spectrum perception in the cognitive radio networks, proposed a solution.For each cognitive user that is operated in the different signal to noise ratio environment, give different weights, promptly after each cognitive user is delivered to the data fusion center with perception information, comprehensive judgement is done after to the different in addition weight of the perception information of each cognitive user again in the center.Because it is different to the influence of global decision at fusion center to have the cognitive user of different signal to noise ratios; So through giving each cognitive user different weights; The component that each cognitive user is occupied in global decision is also different, can obtain more satisfactory result thus.Thereby improve the perceptual performance of whole sensory perceptual system.

Description of drawings

Collaborative spectrum sensing model in Fig. 1 cognitive radio.

The double threshold frequency spectrum perception model that Fig. 2 is traditional.

The improved double threshold frequency spectrum perception of Fig. 3 model.

Improved double threshold collaborative spectrum sensing complete model figure in Fig. 4 cognitive radio system.

The perception flow chart of the whole cognitive radio system of Fig. 5.

Embodiment

Suppose total total N cognitive user in the frequency spectrum perception system, they participate in the work that cooperation frequency spectrum detects together, and the perception that provides whole cognitive radio system in conjunction with Fig. 5 is following:

1. hypothesis has N cognitive user to carry out the collaboration frequency spectrum detection, and each cognitive user is at first independently carried out single user's frequency spectrum perception, and obtaining the detected energy value is Y _i, 1=1 ... N, and each user's two-door limit value is λ ₁And λ ₂If the statistic Y of i cognitive user _iSatisfy λ ₁＜Y _i＜λ ₂, this cognitive user is just its main user energy value Y that perceives so _iAnd main user sends to fusion center to the signal to noise ratio between the cognitive user, otherwise, if the statistic Y of i cognitive user _iSatisfy Y _i＜λ ₁Or Y _i＞λ ₂, this cognitive user just can oneself be judged court verdict L _i, and hard decision L as a result _iSend to fusion center.If R _iThe detection information of i the cognitive user of receiving for fusion center, then R _iCan be expressed as:

Wherein,

$L_i=\left\{\begin{array}{cc}0& 0\≤Y_i\≤{\mathrm{\λ}}_1\\ 1& Y_i\≥{\mathrm{\λ}}_2\end{array}\right.---\left(2\right)$

γ _iThe signal to noise ratio of representing i cognitive user.

2. each cognitive user is court verdict R _iSend to fusion center, fusion center is earlier court verdict R _iClassification; Suppose to have in N the cognitive user K to send the hard decision result to fusion center; N-K cognitive user sent main user energy value and the snr value separately that perceives, and fusion center at first goes out the weights factor of each cognitive user according to snr computation, respectively the energy that each user collects carried out weighted sum according to the certain weight factor then; And compare with weighted energy with the energy threshold value, draw the court verdict D whether main user exists.Its decision rule is following:

$D=\left\{\begin{array}{ccc}0& 0\≤\underset{i=1}{\overset{N-K}{\mathrm{\Σ}}}{W}_i{Y}_i\≤\mathrm{\λ}& H_0\\ 1& \underset{i=1}{\overset{N-K}{\mathrm{\Σ}}}{W}_i{Y}_i\≥\mathrm{\λ}& H_1\end{array}\right.---\left(3\right)$

In the formula,

$W_i=\frac{(N-K){\mathrm{\γ}}_i}{\underset{i=1}{\overset{N-K}{\mathrm{\Σ}}}{\mathrm{\γ}}_i}---\left(4\right)$

3. to sum up, the discriminative information of fusion center integrating step 1,2 gained provides conclusive judgement:

Claims (2)

1. improved double threshold cooperative frequency spectrum sensing method, its characteristics are to comprise following steps:

Each cognitive user in a, the cognitive radio system is carried out frequency spectrum perception to main user respectively, obtains the main user energy value that it perceives;

B, judge main user energy value that each cognitive user perceives be between two thresholdings or outside, if energy value drops on outside two thresholdings, then can directly carry out this locality judgement, obtain the hard decision result whether main user exists;

If the c energy value drops between two thresholdings, so just can not directly carry out this locality judgement, these cognitive user not only need send to fusion center to the main user energy value that perceives, and also need also send a fusion center to their signal to noise ratio simultaneously;

D, fusion center carry out calculation process according to the signal to noise ratio of these cognitive user that receive, and calculate the corresponding CF of each cognitive user;

E, fusion center combine energy value that receives and the CF that calculates to carry out amalgamation judging; Obtain the soft-decision result whether main user exists; Through giving each cognitive user different weights; Reduce of the influence of the cognitive user of detection poor performance with expectation, improve and detect the good cognitive user of performance, treat the observation information of each sensing node at the fusion center place distinctively the comprehensively influence of judgement of data fusion center to the comprehensive judgement of data fusion center;

F, fusion center carry out integrated treatment to soft-decision result and the hard decision result who obtains at last again, utilize " or " criterion makes the final judging result whether a main user exists.

2. frequency spectrum sensing method as claimed in claim 1, its characteristics are that described CF is relevant with the signal to noise ratio of cognitive user, and the cognitive user CF that signal to noise ratio is big is just big, and the cognitive user CF that signal to noise ratio is little is just little.

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