Simulation And Modulation Recognition For Communication Signals

commercial and military systems. Modulation recognition is to decide the modulation mode and estimate the parameters of given signals in the absence of prior knowledge. With modulation recognition occupying an increasingly important position in the field of electronic warfare and communication confrontation, research work in this area has become more active.This thesis at first presents the time domain character and frequency domain character of common used signals, including digital modulation signals and analogue modulation signals, which is verified by simulations. Then, the definition of high order cumulants and the value of digital modulation signals'high order cumulants are presented. According to calculate the value of base band signals'high order cumulants, 2ASK, 4ASK, 2FSK, 4FSK, 2PSK, 4PSK and 8PSK can be distinguished. Compared with the former modulation recognition methods based on higher order statisties, a new method based on the fourth and sixth order cumulants of received signal for classifying digital modulation signals is proposed. Since Gaussian white noise has no influence on higher ordere umulants of received signal but does on the second cumulants,we do not use second cumulants here. Therefore, the influence of gaussian white noise on the recognition parameters presented in this paper is wiped off in the theory aspect. Feasibility of the proposed method is verified by large amount of experiment results presented in this paper. It can be implemented in lower SNR condition. The basic characteristics of MQAM signals have been analyzed based on the constellation diagram. Substraction clustering which are often used in modulation classification techniques based on constellation diagram have been simulated. Then the signals are processed by fuzzy C-means clustering. The recovered constellations are then matched with standard constellations and classified using an improved cost function. Thus, MQAM signals can be classified when match them with standard constellation patterns. The experimental results are satisfying, which are gained in different SNR condition. Those results reflect the capability and performance of different methods.