Method for sensing OFDM spectrum under conditions of time asynchronization and unknown cyclic prefix length

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 [0001] The invention relates to a spectrum sensing technology in a cognitive radio system, in particular to an OFDM spectrum sensing method under the condition of time asynchronous and unknown cyclic prefix length. Background technique [0002] Broadband wireless communication services require the support of a large number of spectrum resources. The existing static spectrum allocation method results in a very low utilization rate of spectrum resources, which leads to the phenomenon of lack of spectrum resources. The proposal of cognitive radio provides a feasible idea for improving spectrum utilization. In order to avoid interference to the existing wireless communication system, the cognitive radio system must be able to determine whether the channel is idle or not. Spectrum sensing can be used to determine whether the channel is idle, so spectrum sensing is one of the key technologies in cognitive radio. [0003] Orthogonal frequency division multiplexin...

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Problems solved by technology

In "Autocorrelation-Based Decentralized Sequential Detection of OFDM Signals in Cognitive Radios" in 2009, Chaudhari et al. proposed the use of the correlation feature of the cyclic prefix, through Calculate the autocorrelation function of the received signal to achieve spectrum sensing, but this method does not take into account the non-stationary characteristics of the autocorrelation function

In response to this problem, Axell et al. in 2011 in "Optimal and Sub-Optimal Spectrum Sensing of OFDM Signals in Known and Unknown Noise Variance (OFDM Optimal and Suboptimal Spectrum Sensing Method when Known and Unknown Noise Variance)" A new spectrum sensing method based on the autocorrelation function of the cyclic prefix is ​​proposed, which has better detection performance compared with the method proposed by Chaudhari et al. Asynchronous deviation is searched to achieve time synchronization, so the amount of calculation is large; on the other hand, this method needs to know the length of the cyclic prefix of the OFDM signal, so when the length of the cyclic prefix of the OFDM signal is unknown, the proposed by Axell et al. method will fail

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