Automatic Modulation Recognition In The Software Defined Radio Technology

The traditional communication radio is designed for a single system with given modulation and bandwidth. Its application fields are too limited to adapt to the multi-modulation, multi-service system at present. And because of multi-modulation, the precondition of signal reception and demodulation is to decide the specific type of modulation. Therefore, automatic recognition of modulation signal has become a requirement of software radio receivers. Additionally, since direct spread spectrum sequence (DSSS) signal has an ultra-low power spectrum density, finding approaches to detect it and estimate its parameters in the non-cooperative communication system is a great challenge for applications.First, the paper studies the general platform of analog and digital communication signal modulation and demodulation based on software radio and verifies it with simulation by MATLAB. Secondly, the paper researches blind estimation of signals parameters, including the carrier frequency, signal to noise ratio and symbol rate of digital modulations. Thirdly, with the combination of parameters from early studies on the decision theory, a set of robust feature parameters are extracted from signal power spectrum and the power spectrum of the second and fourth power of signal. Based on these parameters, the proposed scheme is able to recognize 12 types of common used modulations, namely ASK,2FSK,MSK,4FSK,PSK,QPSK,π/4QPSK,8PSK,AM,DSB,SSB,FM. Finally, the paper studies the DSSS signal detection and its parameter estimation in non-cooperative communication using the strong self-correlation of spread spectrum sequence. These parameters are the carrier frequency, baud period, chip period and chip sequence.The automatic recognition scheme and parameters estimation have been verified with MATLAB simulation, which have made a foundation for further research of non-cooperative communication and software defined radio.