Research On Implementation Of FSK Receiver Based On Spectral Analysis Theory

On the FSK (Frequency Shift Keying) digital receiver, the signal is demodulated mainly by frequency discrimination. Except electronic reconnaissance receiver, MFSK (M-ary Frequency Shift Keying) receiver, OFDM (Orthogonal Frequency Division Multiplexing) receiver, spectrum analysis method of receiver scheme is rarely used in conventional receiver. This paper is mainly on the problem of the FSK demodulation algorithms and implementation of receiver based on the spectrum analysis principle.A new algorithm of demodulate 2FSK signal based on periodogram is proposed. It combines the periodogram method of power spectrum estimation and the DSTFT to get the time-frequency relationship of the receiving signal, and the 2FSK signal is detected by analyzing the time-frequency relationship, then the purpose of the demodulation is reached. In this paper, the principle of periodogram demodulation algorithm is researched deeply, and in order to implement the FSK receiver, the mathematical model and the theoretical deduction of the critical parameters is done based on periodogram method. The theoretical formulas have been given, including power spectrum computation expressions of two carrier frequency points in the sliding window, the signal noise ratio computation expressions of two carrier frequency points under additive gaussian white noise environment, the signal detection threshold computation expression and the relationship between signal noise ratio and symbol error rate. Due to the rounding operation and spectrum leakage when seeking the digital frequency points of two carriers, the spectrum peak values are hard to be found accurately in practical application. The method of searching the maximum values of spectrum peaks around the frequency points are used in this paper. The performance of algorithm researched is analysised by experimental simulation., the results indicate that our algorithm is much better than traditional demodulation methods. In addition, the effect of the demodulation performance of different window functions is also researched, the conclusion is given that the demodulation performance of rectangular window is poorest and the demodulation performance of hanning window is best by simulation experiment.In addition, the bit synchronization technology is researched. And the bit synchronism circuit based on digital phase-locked loop is implemented under SystemView environment.Finally, a simulation system of spectrum receiver is built under SystemView environment, and this system includes some key structures such as radio frequency, demodulation, synchronization, sample decision. The simulation results indicate that the demodulation algorithm proposed in this paper is feasible and reasonable.