Research On Detection Method Of Weak Signal In Spectrum Monitoring System

In the field of the wireless communication, both the raising of a theory and the implementation of a technology see spectrum resources as foundation. However, the resources are relatively limited, which make it quite essential to make use of them efficiently. In such context, monitoring the spectrum resources effectively becomes a most crucial issue.This paper mainly studies the method of effective detection of weak signals in multi-node spectrum monitoring system, which is largely elaborated on two aspects:the research on the detection scheme of weak signals using single node, and the design and improvement of the multi-node joint detection algorithm.As with the detection scheme of single-node, the research focuses on the detection of the signals with the same frequency using the Chaos theory. The Chaos system is a nonlinear system, and is able to restrain the interference of the noise effectively without weakening the signals. The study applies the Chaos theory in the detection of communication signals, and detects the phase modulation signals using the characteristics of chaotic system. After the theoretical analysis of the detection and demodulation of QPSK signals, the paper puts forward a demodulation method using double Duffing oscillators, and then simulates the demodulator and proves that the method can demodulate weak QPSK signal under -7dB SNR of which the SER is 1%. At last, the paper raises a scheme of detection and demodulation of general MPSK signals using a row of Duffing oscillators, as well as carries out a summary and analysis of the regularity of the oscillator number selection, the oscillator phase position design and the detection decision criterion.When the Signal to Noise Ratio becomes extremely low, or under circumstances where signals encounter large-scale fading, the reliability of weak signal detection using single node drops considerably. On the basis of the multi-node and multi-sensor characteristics of the monitoring system, the research approach of cooperative sensing in the Cognitive Radio theory can be taken as reference, and the multi-node joint detection can be used to detect weak signals, thus to improve the validity and the reliability of the detection. Based on the essential requirements of the monitoring system in the joint decision, this paper brings up a sequential detection algorithm of two-dimension information-based weighted reliability, which evaluates the node reliability using two-dimension information of the Duffing oscillator row state sets and the historical state sets, and at the same time optimizes the selection of weighting coefficients. As to the selection and judgement of the node, the sequential detection algorithm is adopted in order to keep the balance between the reliability and the validity of the system. Taking advantage of this algorithm, this paper studies the multi-node detection scheme based on Chaos theory, and realizes the detection and demodulation of MPSK signals.