Design Of Blind Demodulation Circuit For Short Distance Wireless Communication Signals

With the wide application of short distance non-cooperative communication to the radio monitoring, single-point to multipoint network communication and cognitive radio. In the case of no priori information,. receiver can't get any parameter modulation signal. In order to get useful information in the case of unauthorized access, blind demodulation technology must be used. Therefore, building a short distance wireless communication signals blind demodulation system has important practical significance.A blind demodulation system is proposed in this thesis, including six different kinds of communication signals(ASK/FSK/BPSK/QPSK/MSK/QAM). The thesis improved the original application of blind demodulation based on cyclic spectrum estimation algorithm after analyzing the advantages and disadvantages of the existing blind demodulation algorithm, the Matlab simulation result shows that the cyclic spectral computation time has been reduced to 1/19 of the original one. Based on cyclic spectrum estimation algorithm improved, the thesis puts forward a kind of modulation identification scheme based on cyclic spectrum signal characteristic parameters. in the case of no priori information, the thesis uses the characteristics of the five independent parameters on six kinds of modulation signal, which is based on binary tree classifier decision process. By analyzing the characteristic parameter with experience value we can get the recognition result. When the signal-to-noise ratio is 10 dB, the recognition rate reached more than 90%. After receiving the modulation type, the thesis gives the corresponding parameter estimation methods for each kind of modulation type. Especially for QPSK and 16QAM signal, a square method is used to estimate the carrier frequency. According to the SNR, data points, sampling rate, the thesis analyzes the parameter estimation performance for six kinds of modulation type. In order to complete the blind demodulation process, the 2FSK/MSK signal demodulation were studied, using the common of two signals. Through the carrier frequency estimation and symbol rate estimation, the digital frequency conversion and bit synchronization of intermediate frequency signal and the zero frequency signal is finished, in result of the 2FSK/MSK signal blind demodulation results. The thesis design the circuit of blind demodulation scheme based on cyclic spectrum, and uses the Modelsim software to analyze the key modules.The blind demodulation circuit hardware resource consumption is analyzed by using the Quartus software.Also, the function verification and performance test are done on FPGA platform. According to the results of the validation, the blind demodulation circuit design function correctly and the resource consumption decreased by 40% than traditional solution. When the signal-to-noise ratio of is lOdB, signal modulation recognition rate can achieve above 90%, carrier estimation error is less than 10-3, symbol rate estimation error is less than 10-2, and 2FSK/MSK signal blind demodulation error rate is below 0.8%, meeting the design requirements.