CN106549722B - A kind of double threshold energy detection method based on history perception information - Google Patents
A kind of double threshold energy detection method based on history perception information Download PDFInfo
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Abstract
The invention discloses a kind of double threshold energy detection methods based on history perception information, it is changed between adjacent perception frame with the state that energy measuring method estimation authorized user occupies authorized spectrum band and indeclinable probability, and the high threshold and low threshold of the constraint of target false-alarm probability are met according to the theoretical value of false-alarm probability and the setting of the two probability；Then frequency spectrum detection is carried out, if the energy statistic value of current perception frame is greater than high threshold, determine that authorized user occupies authorized spectrum band in current perception frame, otherwise, according to high threshold and low threshold, secondary judgement is carried out using the state that the energy statistic value of current perception frame and history perception frame occupies authorized spectrum band to authorized user；Advantage is not only to be able to satisfy the constraint of target false-alarm probability, but also can obtain higher detection probability, effectively increases frequency spectrum detection performance, while implementation complexity is low, and detection real-time is preferable, and the system bandwidth of occupancy is also small.
Description
Technical Field
The invention relates to a spectrum detection technology in a cognitive radio system, in particular to a double-threshold energy detection method based on historical sensing information.
Background
With the rapid development of wireless communication technology, the demand of people for frequency spectrum is increasing. Currently, most countries and regions still use a static spectrum allocation method, that is, a specific frequency band is divided for a specific user, and other users are not allowed to use the frequency band, so that the spectrum utilization rate of the wireless communication system is not high. For this reason, a Cognitive Radio (CR) technology is proposed, in which a Cognitive user uses an idle frequency band to improve the spectrum utilization efficiency of a wireless communication system without excessively interfering with the communication of an authorized user.
As a key technology in cognitive radio systems, spectrum detection technology has been a research hotspot. The quality of the spectrum detection performance reflects whether the cognitive user can discover and utilize the idle frequency band in time and whether the cognitive user interferes with the authorized user, so that the spectrum detection technology has very important significance in the field of cognitive radio.
Common single-user spectrum sensing methods include an Energy Detection (ED) method, a matched filter method, a cyclostationary feature Detection method, and the like. The energy detection method has the advantages of being simple in operation, low in complexity, free of need of prior information of authorized user signals and convenient to apply, but is sensitive to Noise uncertainty, and only judges whether an authorized user uses an authorized frequency band according to a sampled Signal energy statistical value of a cognitive user, so that when the Signal-to-Noise Ratio (SNR) of a sampled Signal of the cognitive user is low, the detection performance of the energy detection method is obviously reduced.
The industry personnel know that the duration of the perception frame of the cognitive user is far less than the average occupation duration or the average non-occupation duration of the authorized user to the authorized frequency band, so that the probability that the state of the authorized user in a certain perception frame is the same as the state of the previous perception frame is very high, namely, the state of the authorized user in the adjacent perception frame of the cognitive user has correlation. Therefore, the correlation of the states of authorized users between adjacent sensing frames can be utilized to improve the performance of spectrum sensing. In view of this, researchers have proposed an Improved Energy Detection (IED) method, when the Energy statistical value of the sampled signal of a certain sensing frame is lower than the threshold value, the average value of the Energy statistical values of the sampled signal of the historical sensing frame is used to perform secondary determination through a single threshold, so as to obtain the final determination result. Although the improved energy detection method only needs to additionally know the energy statistics of the sampled signals of the previous sensing frames, the calculation complexity is low, but only one threshold value is used in secondary judgment, on one hand, when an authorized user suddenly no longer occupies an authorized frequency band, the energy statistics of the sampled signals of the sensing frames of the cognitive user are suddenly reduced, and the energy statistics of the sampled signals of the previous sensing frames are relatively large, so that the average value of the energy statistics of the sampled signals of the current sensing frame and the previous sensing frames may be higher than the threshold value to cause misjudgment; on the other hand, when the authorized user does not occupy the authorized frequency band but the energy statistic value suddenly increases and is greater than the threshold value, the average value of the energy statistic value of the following sensing frame and the energy statistic values of the sampling signals of the previous sensing frames is higher than the threshold value, and misjudgment occurs, so that the improved energy detection method easily causes the false alarm probability to be too high, and the spectrum sensing performance is reduced.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a double-threshold energy detection method based on historical sensing information, which can well meet the constraint of target false alarm probability on the premise of ensuring higher detection probability, lower implementation complexity, better detection real-time property and small occupied system bandwidth, thereby effectively improving the spectrum sensing performance.
The technical scheme adopted by the invention for solving the technical problems is as follows: a double-threshold energy detection method based on historical perception information is characterized by comprising the following steps:
① in the cognitive radio system, the cognitive user samples the received signal at each sampling time of the perception time slot of each perception frame, and the signal sampled by the cognitive user at the nth sampling time of the perception time slot of the kth perception frame is marked as xk(n)，The initial value of K is 1, K is more than or equal to 1 and less than or equal to K, K represents the total number of perception frames of the cognitive user, K is more than or equal to 1, the initial value of N is 1, N is more than or equal to 1 and less than or equal to N, N represents the number of sampling points of a perception time slot of each perception frame of the cognitive user, N is more than or equal to 250, w is more than or equal tok(n) Gaussian white noise generated in a wireless channel when a cognitive user is at the nth sampling moment of a perception time slot of the kth perception frame, hk(n) represents the gain of the wireless channel when the cognitive user is at the nth sampling moment of the perception time slot of the kth perception frame, sk(n) indicates that the cognitive user authorizes the user to transmit at the nth sampling moment of the perception time slot of the kth perception frameThe output signal, dkIndicating the state of the authorized user occupying the authorized frequency band in the k-th sensing frame of the cognitive user, dk0 represents that the authorized user does not occupy the authorized frequency band in the k-th perception frame of the cognitive user, and dk1 represents that the authorized user occupies an authorized frequency band in the k-th sensing frame of the cognitive user;
②, detecting the state of authorized user occupying authorized frequency band in each sensing frame of cognitive user, the specific process is:
② _1, calculating the energy statistic value of the signal sampled by the cognitive user at all the sampling moments of the perception time slot of each perception frame, and recording the energy statistic value of the signal sampled by the cognitive user at all the sampling moments of the perception time slot of the kth perception frame as Uk，Wherein the symbol "|" is a modulo symbol;
② _2, judging the state of the authorized user occupying the authorized frequency band in each perception frame of the cognitive user according to the time of each perception frame of the cognitive user and the energy statistics of the signals sampled by the cognitive user at all the sampling moments of the perception time slot of each perception frame, and judging the state d of the authorized user occupying the authorized frequency band in the k-th perception frame of the cognitive userkThe judging process is as follows:
② _2a, when k<And when M is reached, judging by adopting an energy detection method: if U isk≥λEDIf yes, then judging that the authorized user occupies the authorized frequency band in the k-th perception frame of the cognitive user, and ordering dk1 is ═ 1; if U isk<λEDIf yes, then judge that the authorized user does not occupy the authorized frequency band in the k-th sensing frame of the cognitive user, and order dkWhen K is more than or equal to M, executing step ② _2b, where M represents the total number of sensing frames used when judging the state of authorized user occupying authorized frequency band, 1 is more than or equal to M < K, lambdaEDRepresenting a set decision threshold;
② _2b, calculating the k-th feeling of the cognitive userThe average value of the energy statistics of the signals sampled at all the sampling moments of the sensing time slots of the known frame and the first M-1 sensing frames is recorded as Wherein, Uk-M+1Represents the energy statistic value, U, of the signals sampled by the cognitive user at all the sampling moments of the perception time slot of the k-M +1 th perception framek-M+2Representing the signal energy statistical value, U, of the cognitive user sampled at all the sampling moments of the perception time slot of the k-M +2 th perception framek-1Representing the energy statistic value of the signals sampled by the cognitive user at all sampling moments of the perception time slot of the (k-1) th perception frame; then when U is turnedk≥λHThen, the authorized user in the k-th perception frame of the cognitive user is judged to occupy the authorized frequency band, and d is orderedk1 is ═ 1; when U is turnedk<λHAnd then, carrying out secondary judgment by adopting double thresholds: if λL≤Uk<λHAnd isAnd U isk-1≥λHIf yes, then judging that the authorized user occupies the authorized frequency band in the k-th perception frame of the cognitive user, and ordering dkOtherwise, judging that the authorized user does not occupy the authorized frequency band in the k-th sensing frame of the cognitive user, and making dk0; wherein λ isLIndicating a set low threshold, λHIndicating a set high threshold, λL<λH。
W in the step ①k(n) obedience mean 0 and varianceA gaussian distribution of (a).
In the step ② _2aWherein，Pf_targetIndicating a set target false alarm probability, Q-1(Pf_target) Represents Q (P)f_target) Q () represents the tail area function of the standard normal distribution probability density.
λ in said step ② _2bLAnd λHThe specific acquisition process comprises the following steps:
let PfTheoretical value of false alarm probability representing cognitive radio system, let Pf_targetRepresenting a set target false alarm probability;
if the cognitive radio system has less strict requirements on the false alarm probability, i.e. PfApproximation with Pf_targetIf the two signals are equal, a setting mode of a conservative threshold is adopted to obtainWherein Q is-1(Pf_target) Represents Q (P)f_target) Q () represents the tail area function of the standard normal distribution probability density, Q represents the adjustment factor, 1<q≤40，Q-1(q×Pf_target) Represents Q (q.times.P)f_target) The inverse function of (c);
if the requirement of the cognitive radio system on the false alarm probability is strict, the requirement P is requiredf≤Pf_targetThen, the setting mode of the radical threshold is adopted to obtainWherein Q is-1(Pf,H) Represents Q (P)f,H) Inverse function of, Q-1(q×Pf,H) Represents Q (q.times.P)f,H) Inverse function of, Pf,HIn order to introduce the intermediate variable(s), indicating that the authorized user does not occupy the cognitive user in the previous cognitive frame of the two adjacent cognitive frames of the cognitive userProbability of weight band and when authorized user does not occupy authorized band in next sensing frameIs determined by the estimated value of (c),indicating the probability that the authorized user does not occupy the authorized frequency band in the previous sensing frame and the authorized user occupies the authorized frequency band in the next sensing frame of two adjacent sensing frames of the cognitive userAn estimate of (d).
SaidAndis acquired prior to the spectrum sensing being performed,andthe acquisition process comprises the following steps:
② _2b _1, selecting K 'sensing frames as training sensing frames to form a training frame set, wherein K' is not less than 1;
② _2b _2, adopting an energy detection method to judge the state that each authorized user occupies the authorized frequency band in the training frame set, and for the k' th training frame in the training frame set, if U isk'≥λEDThen, it is determined that the authorized user occupies the authorized frequency band in the kth' training sensing frame in the training frame set, and order dk'1 is ═ 1; if U isk'<λEDThen, it is determined that the authorized user does not occupy the authorized frequency band in the kth' training sensing frame in the training frame set, and order dk'0; wherein K 'is more than or equal to 1 and less than or equal to K', Uk'Representing the energy statistics of the signals sampled at all sampling instants of the sensing slot of the kth training sensing frame in the set of training frames, dk'Representing the state that the authorized user occupies the authorized frequency band in the k' th training perception frame in the training frame set;
② _2b _3, counting event d when traversing from the 2 nd training perception frame to the Kth training perception frame in the training frame setk”＝0,dk”-1Number of occurrences of 1, denoted num (d)k”＝0,dk”-11); and counting the event d when the 2 nd training perception frame in the training frame set traverses to the K' th training perception framek”Number of occurrences of 0, denoted num (d)k”0); wherein K is more than or equal to 2 and less than or equal to K', dk”Indicating the state of the authorized user occupying the authorized frequency band in the k' th training sensing frame in the training frame set, dk”-1Representing the state that the authorized user occupies the authorized frequency band in the kth' -1 th training perception frame in the training frame set;
② _2b _4, according to num (d)k”＝0,dk”-11) and num (d)k”Not equal to 0) to obtainThen according toTo obtain
Compared with the prior art, the invention has the advantages that:
the method utilizes the property that the probability that the state of the authorized frequency band occupied by the authorized user changes between adjacent sensing frames is small, namely, the method firstly estimates the probability that the state of the authorized frequency band occupied by the authorized user changes and does not change between the adjacent sensing frames by using an energy detection method, and sets a high threshold value and a low threshold value which meet the constraint of the target false alarm probability according to the theoretical value of the false alarm probability and the estimated two probabilities; and then carrying out spectrum detection, if the energy statistical value of the current sensing frame is greater than a high threshold, directly judging that the authorized user occupies the authorized frequency band in the current sensing frame, otherwise carrying out secondary judgment on the state that the authorized user occupies the authorized frequency band by using the energy statistical values of the current sensing frame and the historical sensing frame: if the energy statistic value of the current sensing frame is larger than the low threshold value, the energy statistic value of the previous sensing frame is larger than the high threshold value, and the average value of the energy statistic values of the current sensing frame and the previous sensing frames is also larger than the high threshold value, judging that the authorized user occupies an authorized frequency band in the current sensing frame, otherwise, judging that the authorized user does not use the authorized frequency band in the current sensing frame; the method of the invention can not only meet the constraint of the target false alarm probability, but also obtain higher detection probability, and effectively improve the spectrum detection performance, thereby improving the use efficiency of the spectrum, and simultaneously realizing low complexity, better detection real-time performance and small occupied system bandwidth.
Drawings
FIG. 1 is a structural model of a sensing frame when a cognitive user performs spectrum detection;
FIG. 2 is Pf_target0.01, the detection probability P of the present invention method (conservative threshold), the present improved energy detection method (aggressive threshold), the present invention method (conservative threshold), the present invention method (aggressive threshold)dAnd false alarm probability PfA change curve along with the signal-to-noise ratio gamma of the cognitive user receiving end;
FIG. 3 is Pf_target0.1, the detection probability P of the present invention method (conservative threshold), the present improved energy detection method (aggressive threshold), the present invention method (conservative threshold), the present invention method (aggressive threshold)dAnd false alarm probability PfFollow-up cognitive user interfaceThe variation curve of the signal-to-noise ratio gamma of the receiving end;
FIG. 4a is a graph of the effect of the adjustment factor q on the detection probability of an existing energy detection method, an existing improved energy detection method (conservative threshold), an existing improved energy detection method (aggressive threshold), a method of the invention (conservative threshold), a method of the invention (aggressive threshold);
FIG. 4b is a graph of the effect of the adjustment factor q on the false alarm probability of an existing energy detection method, an existing improved energy detection method (conservative threshold), an existing improved energy detection method (aggressive threshold), a method of the invention (conservative threshold), and a method of the invention (aggressive threshold);
FIG. 5a isAndthe change of the detection probability of the existing energy detection method, the existing improved energy detection method (conservative threshold), the existing improved energy detection method (aggressive threshold), the method of the invention (conservative threshold) and the method of the invention (aggressive threshold) during the change;
FIG. 5b isAndthe change condition of the false alarm probability of the existing energy detection method, the existing improved energy detection method (conservative threshold), the existing improved energy detection method (aggressive threshold), the method (conservative threshold) and the method (aggressive threshold) during the change;
fig. 6 is a block diagram of the overall implementation of the method of the present invention.
Detailed Description
The invention is described in further detail below with reference to the accompanying examples.
Fig. 1 shows a structural model of a sensing frame when a cognitive user performs spectrum sensing, and the invention provides a double-threshold energy detection method based on historical sensing information on the basis, and a general implementation block diagram of the method is shown in fig. 6, and the method comprises the following steps:
① in the cognitive radio system, the cognitive user samples the received signal at each sampling time of the perception time slot of each perception frame, and the signal sampled by the cognitive user at the nth sampling time of the perception time slot of the kth perception frame is marked as xk(n)，Wherein, K is an initial value of 1, K is greater than or equal to 1 and less than or equal to K, K represents the total number of the perception frames of the cognitive user, K is greater than or equal to 1, and K is taken in the embodiment>10000, if K is 20000, the initial value of N is 1, N is not less than 1 and not more than N, N represents the number of sampling points of the sensing time slot of each sensing frame of the cognitive user, N is not less than 250, in order to ensure that the detection result of the sensing frame has high reliability, the sampling length of each sensing frame should be made as large as possible, in this embodiment, N is 1000, w is takenk(n) Gaussian white noise generated in a wireless channel when a cognitive user is at the nth sampling moment of a perception time slot of the kth perception frame, hk(n) represents the gain of the wireless channel when the cognitive user is at the nth sampling moment of the perception time slot of the kth perception frame, sk(n) represents the signal sent by the authorized user when the cognitive user is at the nth sampling moment of the perception time slot of the kth perception frame, dkIndicating the state of the authorized user occupying the authorized frequency band in the k-th sensing frame of the cognitive user, dk0 represents that the authorized user does not occupy the authorized frequency band in the k-th perception frame of the cognitive user, and dkAnd 1 represents that the authorized user occupies the authorized frequency band in the k-th sensing frame of the cognitive user.
In this embodiment, w in step ①k(n) obedience mean 0 and varianceIs taken in this example
②, detecting the state of authorized user occupying authorized frequency band in each sensing frame of cognitive user, the specific process is:
② _1, calculating the energy statistic value of the signal sampled by the cognitive user at all the sampling moments of the perception time slot of each perception frame, and recording the energy statistic value of the signal sampled by the cognitive user at all the sampling moments of the perception time slot of the kth perception frame as Uk，Wherein, the symbol "|" is a modulus symbol, when N is large enough (N is more than or equal to 250), U iskThe approximation follows a gaussian distribution, representing a gaussian distribution with a mean N and a variance of 2N,representing a mean value of N (1+ gamma) and a variance of 2N (1+ gamma)2Gamma represents the signal-to-noise ratio of the receiving end of the cognitive user.
② _2, judging the state of authorized user occupying authorized frequency band in each perception frame of the cognitive user according to the time of each perception frame of the cognitive user and the energy statistic value of the sampling signal of the cognitive user at all the sampling moments of the perception time slot of each perception frame, and judging the state d of authorized user occupying authorized frequency band in the kth perception frame of the cognitive userkThe judging process is as follows:
② _2a, when k<And M, judging by adopting the conventional energy detection method:if U isk≥λEDIf yes, then judging that the authorized user occupies the authorized frequency band in the k-th perception frame of the cognitive user, and ordering dk1 is ═ 1; if U isk<λEDIf yes, then judge that the authorized user does not occupy the authorized frequency band in the k-th sensing frame of the cognitive user, and order dkWhen K is greater than or equal to M, execute step ② _2b, where M represents the total number of sensing frames used when determining the state that the authorized user occupies the authorized frequency band, and 1 is greater than or equal to M and less than K, where M is 5 in this embodiment, λEDIndicating a set decision threshold.
In this embodiment, step ② _2a is takenWherein, Pf_targetThe target false alarm probability is set to be small enough to ensure that the detection result of the sensing frame has high credibility, and the general requirement P is thatf_targetNot more than 0.1, in this example P is takenf_target0.01 or Pf_target＝0.1，Q-1(Pf_target) Represents Q (P)f_target) Q () represents the tail area function of the standard normal distribution probability density,exp () represents an exponential function with a natural base e as the base, and t is an integral variable.
② _2b, calculating the average value of the energy statistics of the sampling signals of the cognitive user at all the sampling moments of the perception time slots of the k-th perception frame and the previous M-1 perception frame, and recording the average value as Wherein, Uk-M+1Representing the energy statistic value U of the sampling signals of the cognitive user at all the sampling moments of the perception time slot of the k-M +1 th perception framek-M+2Represents the energy statistic value, U, of the signals sampled by the cognitive user at all the sampling moments of the perception time slot of the k-M +2 th perception framek-1Represents the energy statistics of the signals sampled by the cognitive user at all sampling moments of the perception time slot of the (k-1) th perception frame,the approximation follows a gaussian distribution, represents the mean value of μavgAnd the variance is (sigma)avg)2The distribution of the gaussian component of (a) is,x represents the total number of sensing frames corresponding to the authorized frequency band occupied by the authorized user in the k-th sensing frame and the first M-1 sensing frames of the cognitive user; then when U is turnedk≥λHThen, the authorized user in the k-th perception frame of the cognitive user is judged to occupy the authorized frequency band, and d is orderedk1 is ═ 1; when U is turnedk<λHAnd then, carrying out secondary judgment by adopting double thresholds: if λL≤Uk<λHAnd isAnd U isk-1≥λHIf yes, then judging that the authorized user occupies the authorized frequency band in the k-th perception frame of the cognitive user, and ordering dkOtherwise, judging that the authorized user does not occupy the authorized frequency band in the k-th sensing frame of the cognitive user, and making dk0; wherein λ isLIndicating a set low threshold, λHIndicating a set high threshold, λL<λH。
In the embodiment, when k is larger than or equal to M, the cognitive radio system obtains the theoretical value P of the false alarm probability in the k-th perception frame of the cognitive userfThe expression of (c) can be described as:wherein,is shown at dkEvent U under the condition of 0k>λHThe probability of the occurrence of the event is,is shown at dk1 event λL<Uk≤λH,Uk-1>λH,The probability of occurrence; then orderOrder toOrder toLet Pf,L＝q×Pf,HTo obtainWherein,is shown at dkEvent U under the condition of 0k>λLThe probability of the occurrence of the event is,is shown at dk1 condition of event Uk>λHThe probability of the occurrence of the event is, q denotes an adjustment factor, sinceL<λHSo q is>1, set in the present embodiment 1<q is less than or equal to 40, if q is 10,indicating the probability that the authorized user does not occupy the authorized frequency band in the previous sensing frame and the authorized user does not occupy the authorized frequency band in the next sensing frame of the two adjacent sensing frames of the cognitive user,indicating the probability that the authorized user does not occupy the authorized frequency band in the previous sensing frame and the authorized user occupies the authorized frequency band in the next sensing frame of the two adjacent sensing frames of the cognitive user,and the change probability of the state of the authorized frequency band occupied by the authorized user in the adjacent perception frame of the cognitive user is very small, so thatDue to the fact thatThus, it is possible to provideCan obtain the productWhen the requirement of the cognitive radio system on the false alarm probability is not strict, the lambda can be obtained by using the setting mode of the conservative thresholdLAnd λHTo makeThat is, the probability of the state change of the authorized frequency band occupied by the authorized user in the adjacent perception frame of the cognitive user is smallerAnd the cognitive radio system generally requires a false alarm probability PfLess than or equal to 0.1, so that the product can be obtainedWhen the requirement of the cognitive radio system on the false alarm probability is strict, the lambda can be obtained by using the setting mode of the radical thresholdLAnd λHTo makeI.e. lambda in step ② _2bLAnd λHThe specific acquisition process comprises the following steps: let PfTheoretical value of false alarm probability representing cognitive radio system, let Pf_targetThe target false alarm probability is set to be small enough to ensure that the detection result of the sensing frame has high credibility, and the general requirement P is thatf_targetNot more than 0.1, in this example P is takenf_target0.01 or Pf_target0.1; if the cognitive radio system has less strict requirements on the false alarm probability, i.e. PfApproximation with Pf_targetEqual, can adopt the setting mode of the conservative threshold to obtainWherein Q is-1(Pf_target) Represents Q (P)f_target) Q () represents the tail area function of the standard normal distribution probability density,exp () represents an exponential function based on a natural base e, t is an integral variable, and q represents an adjustment factor, and is set to 1 in the present embodiment<Q is less than or equal to 40, for example, Q is 10, Q-1(q×Pf_target) Represents Q (q.times.P)f_target) The inverse function of (a) is,if the requirement of the cognitive radio system on the false alarm probability is strict, the requirement P is requiredf≤Pf_targetThen, the setting mode of the radical threshold is adopted to obtainWherein Q is-1(Pf,H) Represents Q (P)f,H) The inverse function of (a) is,Q-1(q×Pf,H) Represents Q (q.times.P)f,H) The inverse function of (a) is,Pf,Hfor introducing intermediate variables, for meeting the setting requirements of an aggressive thresholdSolving the quadratic equation of one element to obtain Indicating the probability that the authorized user does not occupy the authorized frequency band in the previous sensing frame and the authorized user does not occupy the authorized frequency band in the next sensing frame of two adjacent sensing frames of the cognitive userIs determined by the estimated value of (c),indicating the probability that the authorized user does not occupy the authorized frequency band in the previous sensing frame and the authorized user occupies the authorized frequency band in the next sensing frame of two adjacent sensing frames of the cognitive userIs determined by the estimated value of (c),andthe method comprises the steps of obtaining K ' training sensing frames before performing spectrum detection, wherein K ' and the number N of sampling points are large enough to ensure the accuracy of a result, wherein K ' is 10000 and N is 5000 in the embodiment, ② _2b _1, selecting K ' sensing frames as training sensing frames to form a training frame set, wherein K ' is not less than 1, ② _2b _2, judging the state of authorized users occupying authorized frequency bands in each training sensing frame in the training frame set by adopting an energy detection method, and judging the kth ' training sensing frame in the training frame set if U is equal to or more than 1, and if U is equal to or more than 2, judging the state of authorized frequency bands occupied by the authorized users in the K ' training sensing frames in the training framek'≥λEDThen, it is determined that the authorized user occupies the authorized frequency band in the kth' training sensing frame in the training frame set, and order dk'1 is ═ 1; if U isk'<λEDThen, it is determined that the authorized user does not occupy the authorized frequency band in the kth' training sensing frame in the training frame set, and order dk'0; wherein K 'is more than or equal to 1 and less than or equal to K', Uk'Representing the energy statistics of the sampled signals at all sampling instants of the sensing slot of the kth training sensing frame in the set of training frames, dk'② _2b _3, counting the event d when traversing from the 2 nd training perception frame to the K' th training perception frame in the training frame setk”＝0,dk”-1Number of occurrences of 1, denoted num (d)k”＝0,dk”-11); and counting the event d when the 2 nd training perception frame in the training frame set traverses to the K' th training perception framek”Number of occurrences of 0, denoted num (d)k”0); wherein K is more than or equal to 2 and less than or equal to K', dk”Indicating the state of the authorized user occupying the authorized frequency band in the k' th training sensing frame in the training frame set, dk”-1Indicating the state of authorized user occupying authorized frequency band in the k' -1 th training perception frame in the training frame set ② _2b _4 according to num (d)k”＝0,dk”-11) and num (d)k”Not equal to 0) to obtainThen according toTo obtain
The feasibility and effectiveness of the method of the invention are further illustrated by computer simulation.
The method includes the steps that Gaussian white noise generated in a wireless channel is assumed, the mean value is 0, the variance is 1, signals sent by authorized users are also the mean value is 0, the variance is 1, the amplitude obeys normal distribution, the signal-to-noise ratio gamma of a receiving end of a cognitive user does not change along with time, and meanwhile, the fact that all perception frames of the cognitive user are independent is assumed. According to the 802.22 protocol, the duration TF of the sensing frame is set to 10ms, and the authorized user occupies the average duration of the authorized frequency bandAnd average duration without occupying authorized frequency bandObey a poisson distribution.
In order to obtain a relatively stable and reliable simulation result, each false alarm probability and detection probability is obtained by detecting 50000 sensing frames. When detecting a spectrum, the number of sampling points N is 1000.
FIG. 2 shows Pf_target0.01, the detection probability P of the present invention method (conservative threshold), the present improved energy detection method (aggressive threshold), the present invention method (conservative threshold), the present invention method (aggressive threshold)dAnd false alarm probability PfThe change curve of the signal-to-noise ratio gamma of the receiving end of the cognitive user is obtained. As can be seen from fig. 2, the detection probability of each method increases with the increase of the signal-to-noise ratio γ of the receiving end of the cognitive user; the existing improved energy detection method has higher detection probability, but is used for cognitionWhen the signal-to-noise ratio γ of the receiving end of the user is large, the false alarm probability is also high, and the false alarm probability close to the target false alarm probability cannot be guaranteed under both the conservative threshold and the aggressive threshold, for example, when γ is-8 dB, the false alarm probabilities of the existing improved energy detection method (conservative threshold) and the existing improved energy detection method (aggressive threshold) are respectively as high as 0.065 and 0.049; the false alarm probability of the method (conservative threshold) and the method (aggressive threshold) of the invention is not obviously increased, no matter how large the signal-to-noise ratio gamma of the receiving end of the cognitive user, the method (conservative threshold) and the detection probability of the method (aggressive threshold) of the invention are close to the requirement of the target false alarm probability, and the method (conservative threshold) and the detection probability of the method (aggressive threshold) of the invention are only slightly lower than the existing improved energy detection method, but have obvious improvement compared with the existing energy detection method, for example, when the gamma is equal to-8 dB, the detection probability of the method (conservative threshold) of the invention is 0.92, which is 0.07 higher than the existing energy detection method.
FIG. 3 shows Pf_target0.1, the detection probability P of the present invention method (conservative threshold), the present improved energy detection method (aggressive threshold), the present invention method (conservative threshold), the present invention method (aggressive threshold)dAnd false alarm probability PfThe change curve of the signal-to-noise ratio gamma of the receiving end of the cognitive user is obtained. Comparing FIG. 2, the target false alarm probability Pf_targetWhen the signal-to-noise ratio gamma of the receiving end of the same cognitive user is increased to 0.1, the detection probability of various methods is obviously improved. As in fig. 2, the false alarm probability is increased by the existing improved energy detection method (conservative threshold) and the existing improved energy detection method (aggressive threshold) while the detection probability is increased, and the false alarm probability of the existing improved energy detection method (conservative threshold) is even significantly larger than the target false alarm probability. Under the conservative threshold setting method, the detection probability of the method is only slightly lower than that of the existing improved energy detection method (conservative threshold), and the false alarm probability of the method is far lower than that of the existing improved energy detection method (conservative threshold); the method (the aggressive threshold) of the invention can strictly meet the requirement of the target false alarm probability and has good detection probability performance.
FIG. 4a shows the effect of the adjustment factor q on the detection probability of an existing energy detection method, an existing improved energy detection method (conservative threshold), an existing improved energy detection method (aggressive threshold), a method of the invention (conservative threshold), a method of the invention (aggressive threshold); fig. 4b shows the effect of the adjustment factor q on the false alarm probability of the existing energy detection method, the existing improved energy detection method (conservative threshold), the existing improved energy detection method (aggressive threshold), the inventive method (conservative threshold), and the inventive method (aggressive threshold). Setting target false alarm probability P in simulationf_targetAnd the signal-to-noise ratio gamma of the receiving end of the cognitive user is-8 dB (0.01). As can be seen from fig. 4a and 4b, the detection probability and the false alarm probability of the existing energy detection method, the existing improved energy detection method (conservative threshold), the existing improved energy detection method (aggressive threshold) do not change with q, because these two methods are independent of q; the false alarm probability of the method (conservative threshold) is increased approximately linearly along with the increase of q, but is always obviously smaller than the false alarm probability of the existing improved energy detection method (conservative threshold), and the detection probability gradually approaches the detection probability of the existing improved energy detection method (conservative threshold) along with the increase of q, so that the method (conservative threshold) can effectively reduce the false alarm probability and simultaneously has higher detection probability; the false alarm probability of the method (the aggressive threshold) is reduced along with the increase of q and is always lower than the target false alarm probability, the detection probability of the method (the aggressive threshold) shows the trend of increasing first and then reducing, and the detection probability reaches the maximum near q-5, so the method (the aggressive threshold) can obtain higher detection probability on the premise of ensuring the target false alarm probability.
FIG. 5a showsAndexisting energy detection methods at the time of change, existing modified energy detection methods (conservative thresholds), existing modified energy detection methods (aggressive thresholds), methods of the invention (conservative thresholds), methods of the invention (aggressive thresholds)Limit) of the detection probability, fig. 5b givesAndthe change of the false alarm probability of the existing energy detection method, the existing improved energy detection method (conservative threshold), the existing improved energy detection method (aggressive threshold), the method of the invention (conservative threshold) and the method of the invention (aggressive threshold). As can be seen from FIGS. 5a and 5b, the detection probability and the false alarm probability of the conventional energy detection method are not dependent on each otherAnd(ii) a change; the false alarm probabilities of the existing improved energy detection method (conservative threshold), the existing improved energy detection method (aggressive threshold), the inventive method (conservative threshold) and the inventive method (aggressive threshold) are all reduced along with the increase of the existing improved energy detection method (conservative threshold), and the detection probabilities are all increased along with the increase of the existing improved energy detection method (conservative threshold) and the inventive method (aggressive threshold), because when the existing improved energy detection method (conservative threshold), the existing improved energy detection method (aggressive threshold) and the inventiveAndwhen the frequency spectrum detection rate is increased, the state change probability of the authorized user occupying the authorized frequency band in the adjacent sensing frame is reduced, and the energy of the signals sampled by the adjacent frames is utilized to improve the accuracy of the frequency spectrum detection. It can also be seen from fig. 5a and 5b thatAndwhen the method is changed, the false alarm probability of the method is lower than that of the existing improved energy detection method; at the same time, the bookThe detection probability of the method is slightly lower than that of the existing improved energy detection method, but is far higher than that of the existing energy detection method.
The simulation analysis fully shows that the method is feasible and effective.
Claims (4)
1. A double-threshold energy detection method based on historical perception information is characterized by comprising the following steps:
① in the cognitive radio system, the cognitive user samples the received signal at each sampling time of the perception time slot of each perception frame, and the signal sampled by the cognitive user at the nth sampling time of the perception time slot of the kth perception frame is marked as xk(n)，Wherein k isThe initial value is 1, K is more than or equal to 1 and less than or equal to K, K represents the total number of perception frames of the cognitive user, K is more than or equal to 1, the initial value of N is 1, N is more than or equal to 1 and less than or equal to N, N represents the number of sampling points of the perception time slot of each perception frame of the cognitive user, N is more than or equal to 250, wk(n) Gaussian white noise generated in a wireless channel when a cognitive user is at the nth sampling moment of a perception time slot of the kth perception frame, hk(n) represents the gain of the wireless channel when the cognitive user is at the nth sampling moment of the perception time slot of the kth perception frame, sk(n) represents the signal sent by the authorized user when the cognitive user is at the nth sampling moment of the perception time slot of the kth perception frame, dkIndicating the state of the authorized user occupying the authorized frequency band in the k-th sensing frame of the cognitive user, dk0 represents that the authorized user does not occupy the authorized frequency band in the k-th perception frame of the cognitive user, and dk1 represents that the authorized user occupies an authorized frequency band in the k-th sensing frame of the cognitive user;
②, detecting the state of authorized user occupying authorized frequency band in each sensing frame of cognitive user, the specific process is:
② _1, calculating the energy statistic value of the signal sampled by the cognitive user at all the sampling moments of the perception time slot of each perception frame, and recording the energy statistic value of the signal sampled by the cognitive user at all the sampling moments of the perception time slot of the kth perception frame as Uk，Wherein the symbol "|" is a modulo symbol;
② _2, judging the state of the authorized user occupying the authorized frequency band in each perception frame of the cognitive user according to the time of each perception frame of the cognitive user and the energy statistics of the signals sampled by the cognitive user at all the sampling moments of the perception time slot of each perception frame, and judging the state d of the authorized user occupying the authorized frequency band in the k-th perception frame of the cognitive userkThe judging process is as follows:
② _2a, when k is less than M, using energy detection method to judge if U is less than Mk≥λEDThen judging that the authorized user occupies the authorization in the k perception frame of the cognitive userFrequency band, order dk1 is ═ 1; if U isk＜λEDIf yes, then judge that the authorized user does not occupy the authorized frequency band in the k-th sensing frame of the cognitive user, and order dkWhen K is more than or equal to M, executing step ② _2b, where M represents the total number of sensing frames used when judging the state of authorized user occupying authorized frequency band, 1 is more than or equal to M < K, lambdaEDRepresenting a set decision threshold;
② _2b, calculating the average value of the energy statistics of the signals sampled by the cognitive user at all the sampling moments of the perception time slots of the k-th perception frame and the previous M-1 perception frame, and recording the average value as Wherein, Uk-M+1Represents the energy statistic value, U, of the signals sampled by the cognitive user at all the sampling moments of the perception time slot of the k-M +1 th perception framek-M+2Representing the signal energy statistical value, U, of the cognitive user sampled at all the sampling moments of the perception time slot of the k-M +2 th perception framek-1Representing the energy statistic value of the signals sampled by the cognitive user at all sampling moments of the perception time slot of the (k-1) th perception frame; then when U is turnedk≥λHThen, the authorized user in the k-th perception frame of the cognitive user is judged to occupy the authorized frequency band, and d is orderedk1 is ═ 1; when U is turnedk＜λHAnd then, carrying out secondary judgment by adopting double thresholds: if λL≤Uk＜λHAnd isAnd U isk-1≥λHIf yes, then judging that the authorized user occupies the authorized frequency band in the k-th perception frame of the cognitive user, and ordering dkOtherwise, judging that the authorized user does not occupy the authorized frequency band in the k-th sensing frame of the cognitive user, and making dk0; wherein λ isLIndicating a set low threshold, λHIndicating a set high threshold, λL＜λH；
λ in said step ② _2bLAnd λHThe specific acquisition process comprises the following steps:
let PfTheoretical value of false alarm probability representing cognitive radio system, let Pf_targetRepresenting a set target false alarm probability;
if the cognitive radio system has less strict requirements on the false alarm probability, i.e. PfApproximation with Pf_targetIf the two signals are equal, a setting mode of a conservative threshold is adopted to obtainWherein Q is-1(Pf_target) Represents Q (P)f_target) Q () represents the tail area function of the standard normal distribution probability density, Q represents the adjustment factor, Q is more than 1 and less than or equal to 40, Q-1(q×Pf_target) Represents Q (q.times.P)f_target) The inverse function of (c);
if the requirement of the cognitive radio system on the false alarm probability is strict, the requirement P is requiredf≤Pf_targetThen, the setting mode of the radical threshold is adopted to obtainWherein Q is-1(Pf,H) Represents Q (P)f,H) Inverse function of, Q-1(q×Pf,H) Represents Q (q.times.P)f,H) Inverse function of, Pf,HIn order to introduce the intermediate variable(s), indicating the probability that the authorized user does not occupy the authorized frequency band in the previous sensing frame and the authorized user does not occupy the authorized frequency band in the next sensing frame of two adjacent sensing frames of the cognitive userIs determined by the estimated value of (c),indicating the probability that the authorized user does not occupy the authorized frequency band in the previous sensing frame and the authorized user occupies the authorized frequency band in the next sensing frame of two adjacent sensing frames of the cognitive userAn estimate of (d).
2. The method according to claim 1, wherein w is the threshold energy of ①k(n) obedience mean 0 and varianceA gaussian distribution of (a).
3. The method according to claim 1 or 2, wherein the step ② _2a comprises obtaining a dual threshold energy detection based on historical perceptual informationWherein, Pf_targetIndicating a set target false alarm probability, Q-1(Pf_target) Represents Q (P)f_target) Q () represents the tail area function of the standard normal distribution probability density.
4. The method of claim 1, wherein the method comprises detecting the energy level of the sensing signal based on the historical perceptual informationAndis acquired prior to the spectrum sensing being performed,andthe acquisition process comprises the following steps:
② _2b _1, selecting K 'sensing frames as training sensing frames to form a training frame set, wherein K' is not less than 1;
② _2b _2, adopting an energy detection method to judge the state that each authorized user occupies the authorized frequency band in the training frame set, and for the k' th training frame in the training frame set, if U isk'≥λEDThen, it is determined that the authorized user occupies the authorized frequency band in the kth' training sensing frame in the training frame set, and order dk'1 is ═ 1; if U isk'＜λEDThen, it is determined that the authorized user does not occupy the authorized frequency band in the kth' training sensing frame in the training frame set, and order dk'0; wherein K 'is more than or equal to 1 and less than or equal to K', Uk'Representing the energy statistics of the signals sampled at all sampling instants of the sensing slot of the kth training sensing frame in the set of training frames, dk'Representing the state that the authorized user occupies the authorized frequency band in the k' th training perception frame in the training frame set;
② _2b _3, counting event d when traversing from the 2 nd training perception frame to the Kth training perception frame in the training frame setk”＝0,dk”-1Number of occurrences of 1, denoted num (d)k”＝0,dk”-11); and counting the event d when the 2 nd training perception frame in the training frame set traverses to the K' th training perception framek”Number of occurrences of 0, denoted num (d)k”0); wherein K is more than or equal to 2 and less than or equal to K', dk”Indicating the state of the authorized user occupying the authorized frequency band in the k' th training sensing frame in the training frame set, dk”-1Representing the state that the authorized user occupies the authorized frequency band in the kth' -1 th training perception frame in the training frame set;
② _2b _4, according to num (d)k”＝0,dk”-11) and num (d)k”Not equal to 0) to obtainThen according toTo obtain
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| CN109067483B (en) * | 2018-09-12 | 2021-06-15 | 宁波大学 | Maximum eigenvalue frequency spectrum sensing method using past sensing time slot data |
| CN111465023B (en) * | 2020-03-25 | 2022-04-19 | 山东大学 | Self-adaptive double-threshold spectrum sensing method based on historical energy information |
| CN111740795B (en) * | 2020-06-24 | 2022-05-27 | 南京邮电大学 | Double-threshold cooperative sensing method based on secondary user history judgment |
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