Research Of Modulation Recognition For Communication Signals In Software Radio

Modulation recognition of communication signals is one of the most importanttechnologies in Software Radio (SR). On the premise that any modulation information isunknown, it can analyze the modulation types and estimate the modulation parameters of thecommunication signals from the received signals, which is helpful for subsequent signalprocessing. Modulation recognition is composed of pre-processing of received signals,extracting of signal character parameters and classification.Polyphase filter is employed in pre-processing of modulation recognition to extractinphase and quadrature components. Not only orthogonal transform is implemented, but alsosample rate is decreased. An algorithm based on maximum peak of power spectrum ofsignal's delay product is used in estimating of data period, and simulation results are given.In character parameters extracting and classification of modulation signals, an algorithmbased on the instantaneous information and its selection of judge thresholds are studied. Theresult has shown that recognition performance seriously relies on the selection of judgethresholds. In order to solve this problem, a new algorithm based on cyclic variance ofnormalized-centered absolute value is proposed. With this new algorithm, digital modulationtypes higher than four orders can be recognized without thresholds and parameter training. Atthe same time, recognition performance in different signals to noise ratio (SNR) andinfluence of different data numbers on recognition rate are all analyzed by computersimulation. Simulation results demonstrate that, the proposed method has higher recognitionrate for 4ASK, 8ASK, 16ASK, 4PSK, 8PSK, 16PSK, 8QAM and 32QAM signals inmoderate SNR.On the other hand, Not only recognition of MPSK signals based on higher-ordercumulants (HOC) is researched, but also the characters of MPSK signals are analyzed indetail, and the performance are analyzed in different SNR. Because SNR decreases seriouslyby using four step-down orders algorithm for recognition of the MPSK signals with not lessthan 8 orders, an algorithm based on two step-up orders power of signals is proposed. Thesimulation results show that higher recognition performance is obtained.