Research And Implementation Of Bfsk Signal Demodulation Based On Time-frequency Analysis

Low-Voltage Power Line Carrier Communication (PLC) technology is a kind ofcommunication technology which uses low voltage distribution network as communicationmedium. Low voltage distribution network covers a wide range. All buildings almost haveaccess to power lines. Therefore, PLC has many advantages, such as no wiring, covering awide range, convenient connections and low cost etc. However, the original purpose of thepower line network is to transmit electrical energy. As a communication channel, there existmany disadvantages, such as high signal attenuation, strong noise intensity, big interferenceand time-varying volatility. In order to achieve reliable communication in suchcommunication channel, strong anti-jamming modulation and demodulation method arerequested.FSK signal has good performance in anti-interference, so it is a kind of signal modulationmode that is always used in PLC. But the traditional FSK signal demodulation method inpower line communication can not achieve satisfactory results. Time-frequency analysistechnique is a powerful tool for non-stationary signals, which can describe the relationshipbetween frequency and time.The feature of FSK signal is different frequency for differentsymbols, so FSK signal can be demodulated by way of Time-frequency analysis technique.Firstly the low-voltage power line channel characteristics and traditional FSK demodulationtechniques are analyzed in this paper. On this basis, FSK demodulation scheme based onTime-frequency analysis, mainly based on Discrete Short-time Fourier Transform (DSTFT)and Wigner–Will Distribution (WVD), is presented.In order to verify the feasibility of theschemes, the two schemes are simulated by MATLAB. In addition,an improved algorithm fordemodulating FSK signal based on DSTFT is presented to overcome the problem of too muchcalculation in code synchronization.This algorithm is base on DFT Iterative algorithm，cansolve the problem of too much calculation in accurate code synchronization.Finally, the scheme that demodulate FSK signal based on improved DSTFT algorithm ischosen as FPGA implementation scheme. FPGA chip is SPARTAN-3XC3S400which isproduced by XILINX. The whole system consists of two parts: FPGA design and peripheralcircuit design. FPGA design mainly includes frequency divider model design, modulation model design, register model design, synchronization model design, judgment model designand iterative algorithm model design. The peripheral circuit includes are amplifier, coupling,decoupling, AGC, ADC, etc. In the end, the corresponding test solutions are proposed to verifythe next work.