Multi-mode Signal Modulation Recognition And Demodulation Engineering

Communication signal modulation classification and demodulation is one of essential technologies realizing non-cooperative communication task. It is the important technological basis of building SDR(software defined radio)-based general receiver and smart modulator/demodulator, as it can conduct modulation classification and demodulation of unknown signal. In recent years, high-speed digital signal processing technology and high-speed special-purpose devices have developed rapidly, which ensures engineering implementation of modulation classification and demodulation technology.In this context, this paper addresses the fundamental theory and engineering implementation of multi-mode signal modulation classification and demodulation, based on a specific research project.First, modulation automatic classification algorithm of SDR is introduced. According to the requirement of the research project, an improved hierarchical judgment classification method based on statistical characteristics parameter extraction is put forth. Then, a general-purpose coherent demodulation module based on digital orthogonal transformation is introduced and the demodulation algorithm of specific signal is given. Also, carrier synchronization and bit synchronization problems involved in demodulation are analyzed. Considering the requirement of this research work, synchronization adopts baseband processing COSTAS loop and early- late gate synchronizer, and the design and parameter calculation of synchronization loop is detailed.The paper also describes the general-purpose digital signal processing platform selected for the system. The hardware implementation of classification and demodulation functions in DSP and FPGA is described and analyzed in details. Specification test for classification and demodulation functions was conducted under system test environment. In the end, the paper summarizes the research work described above and gives the future research direction.