CN103248441B - Method for sensing OFDM spectrum under conditions of time asynchronization and unknown cyclic prefix length - Google Patents
Method for sensing OFDM spectrum under conditions of time asynchronization and unknown cyclic prefix length Download PDFInfo
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Abstract
The invention discloses a method for sensing an OFDM (Orthogonal Frequency Division Multiplexing) spectrum under conditions of time asynchronization and unknown cyclic prefix length. The processing procedure of the method comprises the following steps: at first, sampling a receipt signal from a monitoring channel to obtain a sampled signal; then, computing an autocorrelation function of the sampled signal according to the sampled value in the sampled signal; next, computing test statistic according to an autocorrelation coefficient in the autocorrelation function of the sampled signal under the condition of time asynchronization; and at last, judging whether the monitoring channel is in the idle state or not according to the test statistic and the judgment threshold. The method has the advantages that the spectrum sensing can be carried out by directly using the sampled signal, without the need of time synchronization, so that the computation complexity is reduced effectively. When the cyclic prefix length of an OFDM signal is unknown, the method can still realize the spectrum sensing of the OFDM signal, and further improves the spectrum sensing performance of the OFDM signal.
Description
Technical field
The present invention relates to the frequency spectrum perception technology in a kind of cognitive radio system, especially relate to asynchronous and OFDM frequency spectrum sensing method under circulating prefix-length unknown situation of a kind of time.
Background technology
The support of a large amount of frequency spectrum resource of broadband wireless communications service needed.The existing static spectral method of salary distribution causes the low-down result of frequency spectrum resource utilization rate, thus causes the phenomenon of frequency spectrum resource shortage.The proposition of cognitive radio is improve the availability of frequency spectrum to provide a feasible thinking.In order to avoid causing interference to existing wireless communication system, cognitive radio system must can judge whether channel is in idle condition.Frequency spectrum perception can be used for judging whether channel is in idle condition, and therefore frequency spectrum perception is one of key technology in cognitive radio.
OFDM (Orthogonal frequency division multiplexing, OFDM) technology has availability of frequency spectrum high, and this technology is current and that future, wireless communication standard was widely adopted technology.Therefore the frequency spectrum perception (namely judging whether there is ofdm signal in channel) of ofdm signal is had very important significance.The existing frequency spectrum sensing method for ofdm signal mainly can be divided into frequency domain detection method and tim e-domain detection method two class.Wherein, frequency domain detection method needs the frequency spectrum calculating collection signal, therefore has larger amount of calculation; Tim e-domain detection method utilizes the autocorrelation performance of Cyclic Prefix in collection signal to realize frequency spectrum perception.The people such as Chaudhari proposed the correlation properties utilizing Cyclic Prefix in 2009 in " based on the distributed Sequential Detection of autocorrelative ofdm signal in Autocorrelation-Based Decentralized Sequential Detection of OFDM Signals in Cognitive Radios(cognitive radio) ", realize frequency spectrum perception by the auto-correlation function calculating Received signal strength, but the method does not consider the non-stationary property of auto-correlation function.For this problem, the people such as Axell proposed a kind of frequency spectrum sensing method of the auto-correlation function based on Cyclic Prefix newly in " OFDM during the known and unknown noise variance of Optimal and Sub-Optimal Spectrum Sensing of OFDM Signals in Known and Unknown Noise Variance(optimum and suboptimum frequency spectrum sensing method) " in 2011, compared with the method that the method and the people such as Chaudhari propose, there is more excellent detection perform, but because the method needs asynchronous departure of all possible time to received signal to carry out searching for realize time synchronized, therefore amount of calculation is larger, on the other hand, the method needs the length of the Cyclic Prefix of known ofdm signal, and therefore when the length of the Cyclic Prefix of ofdm signal is unknown, the method that the people such as Axell propose will lose efficacy.
Summary of the invention
Technical problem to be solved by this invention is to provide asynchronous and OFDM frequency spectrum sensing method under circulating prefix-length unknown situation of a kind of time, its amount of calculation is little, and under the length unknown condition of the Cyclic Prefix of ofdm signal, can improve the frequency spectrum perception performance of ofdm signal further.
The present invention solves the problems of the technologies described above adopted technical scheme: asynchronous and OFDM frequency spectrum sensing method under circulating prefix-length unknown situation of a kind of time, it is characterized in that its processing procedure is: first, Received signal strength from supervisory channel is sampled, obtains sampled signal; Then, according to the sampled value in sampled signal, the auto-correlation function of calculating sampling signal; Then, under time asynchronous condition, according to the auto-correlation coefficient in the auto-correlation function of sampled signal, test statistics is calculated; Finally, according to the size of test statistics and decision threshold, judge whether supervisory channel is in idle condition.
It specifically comprises the following steps:
1. utilize the sampling module in cognitive radio system to carry out M sampling to the Received signal strength from supervisory channel, obtain the sampled signal be made up of the sampled value of M sampled point, wherein, M is positive integer, and M>N
d, N
drepresent the number of the subcarrier of ofdm signal;
2. according to the sampled value in sampled signal, the auto-correlation function of calculating sampling signal, is designated as ρ (t) by t auto-correlation coefficient in the auto-correlation function of sampled signal,
wherein, the number of the auto-correlation coefficient in the auto-correlation function of sampled signal is M-N
d, t is positive integer, and 1≤t≤M-N
d, x (t) represents t sampled value in sampled signal, x (N
d+ t) represent N in sampled signal
d+ t sampled value, m is positive integer, and 1≤m≤M, x (m) represents m sampled value in sampled signal;
3. under time asynchronous condition, according to the auto-correlation coefficient in the auto-correlation function of sampled signal, calculate test statistics, be designated as T,
wherein, symbol " " is the symbol that takes absolute value;
4. test statistics T and decision threshold λ is compared, if T is greater than λ, then judge that supervisory channel is in busy condition, if T is less than or equal to λ, then judge that supervisory channel is in idle condition, wherein, λ=F
-1(P
f), P
frepresent false alarm probability, span is 0<P
f<0.5, F
-1() is the inverse function of F (),
e is nature radix, and e=2.71828..., y are variable.
Compared with prior art, the invention has the advantages that:
1) the inventive method does not need time synchronized just can directly utilize sampled signal to carry out frequency spectrum perception, therefore significantly reduces computation complexity.
2) the inventive method is when the length of the Cyclic Prefix of ofdm signal is unknown, still can realize the frequency spectrum perception to ofdm signal, and can improve the frequency spectrum perception performance of ofdm signal further.
Accompanying drawing explanation
Fig. 1 is the FB(flow block) of frequency spectrum sensing method of the present invention;
The frequency spectrum sensing method that the people such as Fig. 2 is under different state of signal-to-noise, Axell propose compares schematic diagram with the detection probability of the inventive method.
Embodiment
Below in conjunction with accompanying drawing embodiment, the present invention is described in further detail.
Asynchronous and OFDM frequency spectrum sensing method under circulating prefix-length unknown situation of a kind of time that the present invention proposes, as shown in Figure 1, its main processes is its FB(flow block): first, samples, obtain sampled signal to the Received signal strength from supervisory channel; Then, according to the sampled value in sampled signal, the auto-correlation function of calculating sampling signal; Then, under time asynchronous condition, according to the auto-correlation coefficient in the auto-correlation function of sampled signal, test statistics is calculated; Finally, according to the size of test statistics and decision threshold, judge whether supervisory channel is in idle condition.
Ofdm signal frequency spectrum sensing method of the present invention, it specifically comprises the following steps:
1. utilize the sampling module in cognitive radio system to carry out M sampling to the Received signal strength from supervisory channel, obtain the sampled signal be made up of the sampled value of M sampled point, wherein, M is positive integer, and M>N
d, N
drepresent the number of the subcarrier of ofdm signal, as N
ddesirable M=432 when=32.
2. according to the sampled value in sampled signal, the auto-correlation function of calculating sampling signal, is designated as ρ (t) by t auto-correlation coefficient in the auto-correlation function of sampled signal,
wherein, the number of the auto-correlation coefficient in the auto-correlation function of sampled signal is M-N
d, t is positive integer, and 1≤t≤M-N
d, x (t) represents t sampled value in sampled signal, x (N
d+ t) represent N in sampled signal
d+ t sampled value, m is positive integer, and 1≤m≤M, x (m) represents m sampled value in sampled signal.
3. under time asynchronous condition, according to the auto-correlation coefficient in the auto-correlation function of sampled signal, calculate test statistics, be designated as T,
wherein, symbol " || " is the symbol that takes absolute value.
4. test statistics T and decision threshold λ is compared, if T is greater than λ, then judge that supervisory channel is in busy condition, if T is less than or equal to λ, then judge that supervisory channel is in idle condition, wherein, λ=F
-1(P
f), P
frepresent false alarm probability, span is 0<P
f<0.5, F
-1() is the inverse function of F (),
e is nature radix, and e=2.71828..., y are variable.
By following emulation to further illustrate feasibility and the validity of frequency spectrum sensing method of the present invention.
Suppose that the number of the subcarrier of ofdm signal is N
d=32, the length of the Cyclic Prefix of ofdm signal is N
c=8, sampling number is M=432, sets the value of false alarm probability as P according to the requirement of IEEE802.22 standard
f=0.1.The method that the people such as Fig. 2 gives signal to noise ratio when changing from-20dB to 5dB, Axell propose and the inventive method pass through comparing of the detection probability that 100000 Monte Carlo simulations obtain.Frequency spectrum sensing method due to people's propositions such as Axell needs the length of the Cyclic Prefix of known ofdm signal, so suppose N when calculating the test statistics of the frequency spectrum sensing method that the people such as Axell propose
c=8 is known, and suppose N when calculating the test statistics of the inventive method
c=8 is unknown.As can be seen from Figure 2, when signal to noise ratio is less, the detection probability of the inventive method is greater than the detection probability of the frequency spectrum sensing method that the people such as Axell propose, but all cannot reach the requirement that in IEEE802.22 standard, detection probability is greater than 0.9; When signal to noise ratio is greater than 0.5dB, the detection probability of the inventive method is a bit larger tham the detection probability of the frequency spectrum sensing method that the people such as Axell propose, and both reaches the requirement that in IEEE802.22 standard, detection probability is greater than 0.9.Analysis chart 2, although what the detection probability of the frequency spectrum sensing method that the detection probability of the inventive method proposes than people such as Axell was high is not a lot, but consider that the frequency spectrum sensing method that the people such as Axell propose needs the length of the Cyclic Prefix of ofdm signal known, and the inventive method does not need the length of the Cyclic Prefix of ofdm signal known, this is enough to feasibility and validity that the inventive method is described.
Claims (1)
1. a time asynchronous and OFDM frequency spectrum sensing method under circulating prefix-length unknown situation, is characterized in that its processing procedure is: first, sample, obtain sampled signal to the Received signal strength from supervisory channel; Then, according to the sampled value in sampled signal, the auto-correlation function of calculating sampling signal; Then, under time asynchronous condition, according to the auto-correlation coefficient in the auto-correlation function of sampled signal, test statistics is calculated; Finally, according to the size of test statistics and decision threshold, judge whether supervisory channel is in idle condition;
This OFDM frequency spectrum sensing method specifically comprises the following steps:
1. utilize the sampling module in cognitive radio system to carry out M sampling to the Received signal strength from supervisory channel, obtain the sampled signal be made up of the sampled value of M sampled point, wherein, M is positive integer, and M>N
d, N
drepresent the number of the subcarrier of ofdm signal;
2. according to the sampled value in sampled signal, the auto-correlation function of calculating sampling signal, is designated as ρ (t) by t auto-correlation coefficient in the auto-correlation function of sampled signal,
wherein, the number of the auto-correlation coefficient in the auto-correlation function of sampled signal is M-N
d, t is positive integer, and 1≤t≤M-N
d, x (t) represents t sampled value in sampled signal, x (N
d+ t) represent N in sampled signal
d+ t sampled value, m is positive integer, and 1≤m≤M, x (m) represents m sampled value in sampled signal;
3. under time asynchronous condition, according to the auto-correlation coefficient in the auto-correlation function of sampled signal, calculate test statistics, be designated as T,
wherein, symbol " || " is the symbol that takes absolute value;
4. test statistics T and decision threshold λ is compared, if T is greater than λ, then judge that supervisory channel is in busy condition, if T is less than or equal to λ, then judge that supervisory channel is in idle condition, wherein, λ=F
-1(P
f), P
frepresent false alarm probability, span is 0<P
f<0.5, F
-1() is the inverse function of F (),
e is nature radix, e=2.71828 ..., y is variable.
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| CN103873163B (en) * | 2013-11-05 | 2016-03-23 | 南京航空航天大学 | A kind of degree of rarefication self-adapting compressing frequency spectrum sensing method based on asymptotic step-length |
| GB2560040B (en) * | 2017-02-28 | 2019-12-25 | Imagination Tech Ltd | OFDM signal presence detection |
| CN107222870B (en) * | 2017-06-21 | 2019-09-03 | 宁波大学 | Ofdm signal frequency spectrum sensing method asynchronous for the time and being not present under offset frequency situation |
| CN107465473B (en) * | 2017-06-21 | 2020-07-03 | 宁波大学 | OFDM signal spectrum sensing method under time synchronization and frequency offset condition |
| CN109600754B (en) * | 2018-12-24 | 2021-09-10 | 南京工业大学 | Sequential spectrum sensing method based on space-time correlation in WCSN (wideband coherent combining) |
| CN110856181B (en) * | 2019-11-20 | 2021-07-20 | 长江师范学院 | Distributed service matching sequential spectrum access decision method |
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| US6628735B1 (en) * | 1999-12-22 | 2003-09-30 | Thomson Licensing S.A. | Correction of a sampling frequency offset in an orthogonal frequency division multiplexing system |
| CN101630983B (en) * | 2009-07-30 | 2013-01-16 | 哈尔滨工业大学 | Idle frequency spectrum detecting method by using cyclic spectrum statistic value in cognitive radio |
| CN101848046B (en) * | 2010-06-22 | 2012-11-28 | 上海交通大学 | Method for increasing detection probability of frequency spectrum perception |
| CN102404063B (en) * | 2011-12-26 | 2013-09-25 | 电子科技大学 | GLRT (General Likelihood Ratio Test) detection method based on oversampling |
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