阅读说明：本技术 一种基于改进融合算法的三阈值协作频谱感知方法 (Three-threshold cooperative spectrum sensing method based on improved fusion algorithm ) 是由 齐丽娜 李承原 于 2019-08-28 设计创作，主要内容包括：本发明公开了一种基于改进融合算法的三阈值协作频谱感知方法,包括以下步骤：S01,计算多个次用户对应的检测统计量；S02,将每个次用户各自的检测统计量与三阈值进行比较和本地判决,每个次用户根据判决规则将各自判决结果数据上传至融合中心；S03,融合中心接收到来自次用户的判决结果后,使用估计方法对次用户的感知的检测统计量进行数据恢复估计；S04,融合中心将合并后的检测统计量的估计值与预设的全局判决阈值进行比较后作出最终判决；S05,进行次用户的感知带宽分析。本发明提供的一种基于改进融合算法的三阈值协作频谱感知方法,能够减小感知环境中噪声不确定性和低信噪比对感知性能的影响,同时在大大降低感知开销的同时保持着较高的检测性能。(The invention discloses a three-threshold cooperative spectrum sensing method based on an improved fusion algorithm, which comprises the following steps of: s01, calculating the detection statistics corresponding to a plurality of secondary users; s02, comparing the respective detection statistic of each secondary user with the three threshold values and carrying out local judgment, and uploading the respective judgment result data to the fusion center by each secondary user according to the judgment rule; s03, after receiving the judgment result from the secondary user, the fusion center carries out data recovery estimation on the detection statistic of the perception of the secondary user by using an estimation method; s04, the fusion center compares the combined estimated value of the detection statistics with a preset global decision threshold value and then makes a final decision; and S05, performing perceptual bandwidth analysis of the secondary user. The three-threshold cooperative spectrum sensing method based on the improved fusion algorithm can reduce the influence of noise uncertainty and low signal-to-noise ratio on sensing performance in a sensing environment, and simultaneously keeps higher detection performance while greatly reducing sensing overhead.)

1. A three-threshold cooperative spectrum sensing method based on an improved fusion algorithm is characterized in that: the method comprises the following steps:

s01, calculating the detection statistics corresponding to a plurality of secondary users;

s02, comparing the respective detection statistic of each secondary user with the three threshold values and carrying out local judgment, and uploading the respective judgment result data to the fusion center by each secondary user according to the judgment rule;

s03, after receiving the judgment result from the secondary user, the fusion center carries out data recovery estimation on the detection statistic of the perception of the secondary user by using an estimation method;

s04, the fusion center compares the combined estimated value of the detection statistics with a preset global decision threshold value and then makes a final decision;

and S05, performing perceptual bandwidth analysis of the secondary user.

2. The improved fusion algorithm-based three-threshold cooperative spectrum sensing method according to claim 1, wherein: in S01, assume N timesThe user carries out cooperative spectrum sensing to judge whether a primary user exists in a section of spectrum, each secondary user collects L samples within a given time, and the nth sample value can be represented as y_i(n) the detection statistic Y thus corresponding_iIs represented as follows:

where i is 1, 2,., N, sample value y_i(n) different forms of expression exist under two hypotheses,

H₀：y_i(n)＝ω_i(n)

H₁：y_i(n)＝ω_i(n)+h_i(n)*s(n) (2)

wherein H₀And H₁Respectively indicating the assumption that the primary user is not using the spectrum and that the primary user is using the spectrum, h_i(n) represents the Rayleigh distributed channel fading coefficient, and s (n) represents the primary user signal. Omega_i(n) represents a variance ofWhite additive gaussian noise.

3. The improved fusion algorithm-based three-threshold cooperative spectrum sensing method according to claim 2, wherein: in S02, the single threshold λ is obtained according to the nemann-pearson theorem:

wherein the content of the first and second substances,representing the variance of Gaussian noise, Q^-1(. h) is the inverse of the full distribution function Q (-),wherein x is the lower limit of anomalous integration and t is the integrandIntegral variable of (P)_fRepresenting the expected false alarm probability, and L representing the number of sampling samples in the energy detection;

then the other two thresholds are set:

λ₁＝(1-α)λ

λ₂＝(1+α)λ (4)

wherein α represents a noise uncertainty factor;

the specific decision rule is as follows:

wherein L is_iIndicating the results of local decisions made based on threshold comparisons, 0, 10, 11, 1 being different results of the secondary user local decisions, respectively.

4. The improved fusion algorithm-based three-threshold cooperative spectrum sensing method according to claim 3, wherein: at S03, pair (λ)₁λ) and (λ, λ)₂) Detection statistic Y between regions_iUsing the uniform estimation method, the data distribution in these two intervals is assumed to be uniform, and thus is at (λ)₁λ), the estimated reduction value is:at (lambda )₂) Region, estimated reduction value is:

according to the detection statistic Y_iRegions far from λ (— infinity, λ)₁) And (lambda)₂, + ∞) region obeys a truncated normal distribution, assuming a set of data obeys such a normal distribution: n (mu, sigma)²)，μ，σ²Representing the mean and variance, respectively, then its corresponding truncated normal distribution can be expressed as: TN (μ, σ)²(ii) a a, b), a and b represent the limits of the truncated normal distribution, and their probability density functions can be expressed as:

where Φ (-) represents the cumulative distribution function of a standard normal distribution, if a ≦ y ≦ b, then the exponential function I_[a，b](y) 1, otherwise, I_[a，b](y) 0, the mathematical desired value e (y) is calculated as follows:

is provided with

Then it is determined that,

therefore, the temperature of the molten metal is controlled,

the last term in the integration of equation (7) is obeyed by N (μ, σ)²) Is normally distributed, on the assumption thatThen it is determined that,thus:

it is obtained that,

thus, at (- ∞, λ)₁) Region, a ═ infinity, b ═ λ₁Then the expected value for that region is:

at (lambda)₂A +∞) region, a ═ λ₂And b ∞, then the expected value for this region is:

wherein mu₁、σ₁And mu₂、σ₂The detection statistics of the signals received by the secondary users are respectively in H₀And H₁Expectation and variance under conditions, H₁Indicating that a primary user is using the spectrum, H₀Indicating a situation where the primary user is not using the spectrum,phi (x) is a standard normal distribution; phi (x) is a cumulative function of phi (x),

the expected values of the two regions were used as the estimated reduction values of the regions, respectively, to obtain estimated reduction values Y 'of all the regions'_iExpressed as follows:

5. the improved fusion algorithm-based three-threshold cooperative spectrum sensing method according to claim 4, wherein: in S04, it is assumed that each secondary user is a distance d from the primary user_iBased on the distance d_iIntroducing a weighting factor omega_i，∑ω_iThe weighting factor is defined as 1:based on this weighting factor, the final estimated detection statistic is found:

the global decision threshold is given by:

the final estimated detection statistic Y obtained_fAnd the solved global decision threshold lambda_fAnd comparing to judge whether a master user exists: if Y is_f≥λ_fThen, it can be determined that a primary user exists and the secondary user should immediately end the use of the frequency band; if Y is_f＜λ_fThen, it can be determined that the primary user does not exist, and the secondary user can obtain the usage right of the frequency band.

6. The improved fusion algorithm-based three-threshold cooperative spectrum sensing method according to claim 5, wherein: in S04, assume that the probability P that the transmission bandwidth of the ith secondary user sending data is 2 bits₂Comprises the following steps:

P₂＝P(H₀)P(λ₁＜Y_i＜λ₂|H₀)+P(H₁)P(λ₁＜Y_i＜λ₂|H₁) (14)

wherein, P (H)₀) Indicating the probability that the primary user is not using the spectrum, P (H)₁) The probability that a primary user is using the spectrum,

where γ represents the signal-to-noise ratio of the received signal, Q (-) is a complete distribution function,

obtaining the probability that the transmission bandwidth of the data sent by the ith secondary user is 1bit as follows:

P₁＝1-P₂ (17)

thus, the average bandwidth required to achieve perception by the proposed algorithm is:

Technical Field

The invention relates to a three-threshold cooperative spectrum sensing method based on an improved fusion algorithm, and belongs to the technical field of cognitive radio networks.

Background

In recent years, cooperative spectrum sensing technology has been widely used in cognitive radio networks, mainly because the method of sensing by multi-user cooperation has strong robustness, and the accuracy of sensing results can be reliably ensured while the spectrum detection performance of the system is improved, so that much favor is given. In the cognitive radio network, users of cooperative sensing jointly participate in spectrum detection, the users independently sense the spectrum and respectively upload respective sensing results to a fusion center, and the fusion center can use different fusion algorithms to judge received information so as to obtain judgment results. According to different types of information sent by each user, cooperative spectrum sensing can be divided into two types: soft fusion decision combining and hard fusion decision combining. The hard fusion judgment AND combination means that each user carries out local judgment according to respective perception data, judgment results are uploaded to a fusion center in a 1-bit data form of '1' OR '0', AND the fusion center receives the data AND then carries out information combination according to a certain fusion criterion (an AND criterion, an OR criterion OR a Majority criterion) so as to obtain a final judgment result; the soft fusion judgment combining method is different from the hard fusion judgment combining method, all secondary users do not make local judgment, but directly upload the perception data to the fusion center, and perform data fusion in the fusion center so as to make judgment.

Compared with soft fusion judgment combination, in the aspect of performance, hard fusion judgment combination is far better than soft fusion judgment combination, but in the aspect of system perception overhead, hard fusion judgment combination is better than soft fusion, because hard fusion only needs to upload a plurality of 1-bit judgment information, while soft fusion has to upload data with huge data volume, and the transmission bandwidth cost is higher.

In addition, in the conventional dual-threshold energy detection method, due to the fact that noise uncertainty and low signal-to-noise ratio exist in a sensing environment, detection statistics of signals received by a secondary user sometimes fall into a fuzzy region between two thresholds, and the conventional dual-threshold energy detection method does not make a decision on the part of sensing data, so that the part of sensing data information is wasted.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a three-threshold cooperative spectrum sensing method based on an improved fusion algorithm, which can reduce the influence of noise uncertainty and low signal-to-noise ratio on sensing performance in a sensing environment, and simultaneously greatly reduce sensing overhead and keep higher detection performance.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

a three-threshold cooperative spectrum sensing method based on an improved fusion algorithm comprises the following steps:

s01, calculating the detection statistics corresponding to a plurality of secondary users;

s02, comparing the respective detection statistic of each secondary user with the three threshold values and carrying out local judgment, and uploading the respective judgment result data to the fusion center by each secondary user according to the judgment rule;

s03, after receiving the judgment result from the secondary user, the fusion center carries out data recovery estimation on the detection statistic of the perception of the secondary user by using an estimation method;

s04, the fusion center compares the combined estimated value of the detection statistics with a preset global decision threshold value and then makes a final decision;

and S05, performing perceptual bandwidth analysis of the secondary user.

2. The improved fusion algorithm-based three-threshold cooperative spectrum sensing method according to claim 1, wherein: in S01, assuming that N secondary users perform cooperative spectrum sensing to determine whether a primary user exists in a segment of spectrum, each secondary user collects L samples within a given time period, and the nth sample value may be represented as y_i(n) the detection statistic Y thus corresponding_iIs represented as follows:

where i is 1, 2,., N, sample value y_i(n) different forms of expression exist under two hypotheses,

H₀∶y_i(n)＝ω_i(n)

H₁∶y_i(n)＝ω_i(n)+h_i(n)*s(n) (2)

wherein H₀And H₁Respectively indicating that the primary user does not use the frequency spectrum and the primary userAssumption that the spectrum is being used, h_i(n) represents the Rayleigh distributed channel fading coefficient, and s (n) represents the primary user signal. Omega_i(n) represents a variance ofWhite additive gaussian noise.

In S02, the single threshold λ is obtained according to the nemann-pearson theorem:

wherein the content of the first and second substances,representing the variance of Gaussian noise, Q^-1(. h) is the inverse of the full distribution function Q (-),wherein x is the lower limit of anomalous integration and t is the integrandIntegral variable of (P)_fRepresenting the expected false alarm probability, and L representing the number of sampling samples in the energy detection;

then the other two thresholds are set:

λ₁＝(1-α)λ

λ₂＝(1+α)λ (4)

wherein α represents a noise uncertainty factor;

the specific decision rule is as follows:

wherein L is_iIndicating the results of local decisions made based on threshold comparisons, 0, 10, 11, 1 being different results of the secondary user local decisions, respectively.

At S03, pair (λ)₁λ) and (λ, λ)₂) Between the regionsIs detected as a statistic Y_iUsing the uniform estimation method, the data distribution in these two intervals is assumed to be uniform, and thus is at (λ)₁λ), the estimated reduction value is:at (lambda )₂) Region, estimated reduction value is:

according to the detection statistic Y_iRegions far from λ (— infinity, λ)₁) And (lambda)₂, + ∞) region obeys a truncated normal distribution, assuming a set of data obeys such a normal distribution: n (mu, sigma)²)，μ，σ²Representing the mean and variance, respectively, then its corresponding truncated normal distribution can be expressed as: TN (μ, σ)²(ii) a a, b), a and b represent the limits of the truncated normal distribution, and their probability density functions can be expressed as:

where Φ (-) represents the cumulative distribution function of a standard normal distribution, if a ≦ y ≦ b, then the exponential function I_[a，b](y) 1, otherwise, I_[a，b](y) 0, the mathematical desired value e (y) is calculated as follows:

is provided with

Then it is determined that,

therefore, the temperature of the molten metal is controlled,

the last term in the integration of equation (7) is obeyed by N (μ, σ)²) Normal distribution ofSuppose thatThen it is determined that,thus:

it is obtained that,thus, at (- ∞, λ)₁) Region, a ═ infinity, b ═ λ₁Then the expected value for that region is:

at (lambda)₂A +∞) region, a ═ λ₂And b ∞, then the expected value for this region is:

wherein mu₁、σ₁And mu₂、σ₂The detection statistics of the signals received by the secondary users are respectively in H₀And H₁Expectation and variance under conditions, H₁Indicating that a primary user is using the spectrum, H₀Indicating a situation where the primary user is not using the spectrum,phi (x) is a standard normal distribution; phi (x) is a cumulative function of phi (x),

the expected values of the two regions are used as the estimated reduction values of the regions respectively, and the estimated reduction values Y of all the regions are obtained_i', denotes the following:

in S04, it is assumed that each secondary user is a distance d from the primary user_iBased on the distance d_iIntroducing a weighting factor omega_i，∑ω_iThe weighting factor is defined as 1:based on this weighting factor, the final estimated detection statistic is found:

the global decision threshold is given by:

the final estimated detection statistic Y obtained_fAnd the solved global decision threshold lambda_fAnd comparing to judge whether a master user exists: if Y is_f≥λ_fThen, it can be determined that a primary user exists and the secondary user should immediately end the use of the frequency band; if Y is_f＜λ_fThen, it can be determined that the primary user does not exist, and the secondary user can obtain the usage right of the frequency band.

In S04, assume that the probability P that the transmission bandwidth of the ith secondary user sending data is 2 bits₂Comprises the following steps:

P₂＝P(H₀)P(λ₁＜Y_i＜λ₂|H₀)+P(H₁)P(λ₁＜Y_i＜λ₂|H₁) (14)

wherein, P (H)₀) Probability that the primary user does not use the spectrum, P: (H₁) The probability that a primary user is using the spectrum,

where γ represents the signal-to-noise ratio of the received signal, Q (-) is a complete distribution function,

obtaining the probability that the transmission bandwidth of the data sent by the ith secondary user is 1bit as follows:

P₁＝1-P₂ (17)

thus, the average bandwidth required to achieve perception by the proposed algorithm is:

the invention has the beneficial effects that: the invention provides a three-threshold cooperative spectrum sensing method based on an improved fusion algorithm, the improved algorithm combines the advantages of hard fusion judgment combination and soft fusion judgment combination, a secondary user uses a three-threshold energy detection method to carry out local judgment, then the local judgment result uploaded by the secondary user is subjected to the calculation of an estimated reduction value in a fusion center, and then the fusion judgment is carried out by using the soft fusion combination algorithm, so that the system overhead in the sensing process is greatly reduced, and meanwhile, the soft fusion combination algorithm is used in the fusion center, so the sensing performance of the algorithm provided by the invention is close to the performance of the soft fusion combination algorithm; two thresholds are added on the basis of the traditional single energy detection threshold to form a three-threshold, so that the influence of noise uncertainty and low signal-to-noise ratio on sensing performance in a sensing environment can be reduced.

Drawings

FIG. 1 is a multi-user cooperative spectrum sensing model in the present invention;

FIG. 2 illustrates three threshold energy detection in accordance with the present invention;

fig. 3 is a flowchart of a three-threshold cooperative spectrum sensing method based on an improved fusion algorithm according to the present invention.

Detailed Description

The present invention is further described with reference to the accompanying drawings, and the following examples are only for clearly illustrating the technical solutions of the present invention, and should not be taken as limiting the scope of the present invention.

The invention provides a hard fusion merging decision algorithm and a soft fusion merging decision algorithm based on traditional cooperative spectrum sensing, which can recover the estimated value of the detection statistic of a secondary user by adopting a proposed data recovery mode at a fusion center according to the decision result uploaded by the secondary user, thereby executing soft fusion on the basis, greatly reducing the sensing overhead and simultaneously obtaining higher detection performance, and specifically comprises the following steps:

step one, each secondary user makes a local decision based on three-threshold energy detection: a system model is shown in FIG. 1. Suppose that N secondary users perform Cooperative Spectrum Sensing (CSS) to sense whether a primary user exists in a section of spectrum. In order to simplify the analysis difficulty, the N secondary users are considered to be the same and have different spatial positions from the primary user, so that the perceptual channels of each secondary user can be considered to be independent. Each secondary user collects a number L of samples over a given time, and the sample value may be represented as y_i(n) of (a). The corresponding detection statistics are thus represented as follows:

where i is 1, 2,., N, the nth sample value y_i(n) different forms of expression exist under two hypotheses,

H₀∶y_i(n)＝ω_i(n)

H₁∶y_i(n)＝ω_i(n)+h_i(n)*s(n) (2)

wherein H₀And H₁Respectively indicating the assumption that the primary user is not using the spectrum and that the primary user is using the spectrum, h_i(n) represents a rayleigh distributed channel fading coefficient; s (n) represents a primary user signal; omega_i(n) represents a variance ofAdditive White Gaussian Noise (AWGN).

And step two, comparing the respective detection statistic of each secondary user with the three thresholds and carrying out local judgment, and uploading the respective judgment result data to the fusion center by each secondary user according to a judgment rule. Fig. 2 shows the case of the decision threshold setting of the present invention. In order to fully utilize the perception information of the fuzzy area, the invention introduces a noise uncertainty factor alpha, two thresholds are added on the basis of the traditional single energy detection threshold to form three thresholds, and the specific thresholds are set as follows:

according to a given false alarm probability P_fFirst, according to the neman-pearson theorem, a single threshold λ is found:

wherein the content of the first and second substances,representing the variance of Gaussian noise, Q^-1(. h) is the inverse of the full distribution function Q (-),P_frepresenting the probability of false alarm in the expectation and L representing the number of sample samples in the energy detection.

Then the other two thresholds are set:

λ₁＝(1-α)λ

λ₂＝(1+α)λ (4)

if the threshold is set, then a local decision is made. Each secondary user compares the respective detection statistic with the three threshold values to make a decision, and the specific decision rule is as follows:

wherein L is_iIndicating the results of local decisions made based on threshold comparisons, 0, 10, 11, 1 being different results of the secondary user local decisions, respectively.

And each secondary user uploads the 1bit data or 2bit data of the respective judgment result to the fusion center according to the judgment rule, and the fusion center performs fusion judgment on the assumption that an uploading channel is perfect.

And step three, after receiving the judgment result from the secondary user, the fusion center carries out data recovery estimation on the detection statistic of the perception of the secondary user by using an estimation method.

In the invention, the reliability of the sensing result near the threshold lambda is poor due to the existence of noise uncertainty, and error judgment is easy to generate, so that under the condition of a certain fault tolerance rate, the method is used for (lambda)₁λ) and (λ, λ)₂) A uniform estimation method is adopted between the areas, and the data distribution of the two intervals is assumed to be uniform.

Thus, is in (lambda)₁λ), the estimated reduction value is:at (lambda )₂) Region, estimated reduction value is:

it is known that in conventional energy detection, when the number of samples sampled by a secondary user is large enough, its detection statistics obey a normal distribution; after the three-threshold energy detection is introduced, the region far away from λ is (— infinity, λ)₁) And (lambda)₂, + ∞) region is no longer normally distributed, but rather follows a truncated normal distribution, so we can find this from this distributionThe mathematical expectation of two regions is taken as the estimated value of that region.

We assume that a set of data follows such a normal distribution: n (mu, sigma)²)，μ，σ²Representing the mean and variance, respectively, then its corresponding truncated normal distribution can be expressed as: TN (μ, σ)²(ii) a a, b), a, b represent the limit of the truncated normal distribution. Their probability density function can be expressed as:

where Φ (-) represents the cumulative distribution function of a standard normal distribution. If a ≦ y ≦ b, then the exponential function I_[a，b](y) 1, otherwise, I_[a，b](y) is 0. The mathematical expectation is calculated as follows:

is provided with

Then it is determined that,

therefore, the temperature of the molten metal is controlled,

note that the last term in the integration is obeying N (μ, σ)²) Is normally distributed. Let us assume thatThen it is determined that,thus:

it is not difficult to obtain the product,

thus, at (- ∞, λ)₁) Region, a ═ infinity, b ═ λ₁Then the expected value for that region is:

at (lambda)₂A +∞) region, a ═ λ₂And b ∞, then the expected value for this region is:

wherein mu₁、σ₁And mu₂、σ₂The detection statistics of the signals received by the secondary users are respectively in H₀And H₁The expectation and the variance under the conditions are,phi (x) is a standard normal distribution; phi (x) is a cumulative function of phi (x),

the expected values of the two regions are used as the estimated reduction values of the region, so that the estimated reduction values of all the regions are obtained, and are expressed as follows:

step four, the fusion center combines the estimated value Y of the detection statistics_fAnd a preset global decision threshold lambda_fMaking a final decision after the comparison:

assuming that each secondary user is at a distance d from the primary user_iBased on the distance d_iHere we introduce a weighting factor ω_i，∑ω_i1. The weighting factor is defined as:based on this weighting factor, we can find the final estimated detection statistic:

the global decision threshold is given by:

the final estimated detection statistic Y obtained_fAnd the solved global decision threshold lambda_fBy comparison, we can judge whether a master user exists: if Y is_f≥λ_fThen, it can be determined that a primary user exists and the secondary user should immediately end the use of the frequency band; if Y is_f＜λ_fThen, it can be determined that the primary user does not exist, and the secondary user can obtain the usage right of the frequency band.

Step five, perceptual bandwidth analysis:

the probability that the transmission bandwidth of the data sent by the ith secondary user is 2 bits is assumed as follows:

P₂＝P(H₀)P(λ₁＜Y_i＜λ₂|H₀)

+P(H₁)P(λ₁＜Y_i＜λ₂|H₁) (14)

wherein, P (H)₀) Indicating the probability that the primary user is not using the spectrum, P (H)₁) Probability that a primary user is using the spectrum.

Where γ represents the signal-to-noise ratio of the received signal and Q (-) isThe function is fully distributed over the entire length of the spectrum,

it is easy to obtain that the probability that the transmission bandwidth of the ith secondary user sending data is 1bit is as follows:

P₁＝1-P₂ (17)

thus, the average bandwidth required to achieve perception by the proposed algorithm is:

the above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.