FSK Demodulation Based On Time-frequency Distribution Theory And Its Implementation By DSP

Power Line Carrier Communication technology is a unique Communication mode, ituses the ready-made solid and reliable Power grids as Carrier signal transmission channel,therefore it has a transmission characteristics such as reliable, routing, and reasonable withoutthe transmission channel and it is the only cable Communication mode of investment. Thispaper mainly involves the low voltage power lines。Since the late20th century, along with thedevelopment of communication modulation technology and adaptive technology, the lowvoltage electric communication has developed rapidly and toward practical direction. Itprovide convenient data transmission platform for long-distance meter reading, with electricalautomation, intelligent family and digital communities. So far it has the extremely broadprospect for researching the low-pressure electric communication.Compared with high voltage power line carrier-current communication, it outstandingperforms in characteristic of line impedance conditions, low circuit impedance, high signalattenuation and strong noise intensity for signal transmission in380/220v low voltage powerlines. Therefore it is impossible to demodulate the signal effectively using the traditionalmethod from time domain.The PLCC technology which mentioned is applied in thefollowing main environmental consideration: non-strict demand for delaying, low carrierfrequency, low transmission rate,high demand in anti-jamming and using time-frequencyanalysis of Discrete short-time Fourier Transform to demodulate the FSK signal. Differentfrom the traditional methods, time-frequency analysis is the non-stationary signal analysis ofpowerful tools. This method put signal from the time domain innuendo to two-dimensionaltime-frequency plane, demodulating the FSK signal by analyzing the frequency and timingrelationship, thus realize reliable low-voltage power line carrier-current communication.This paper adopts the dsPIC33FJ256GP710of Microchip company to realize the mainalgorithm parts of FSK modulation and demodulation. It is a high-performance16digitalsignal processor, modified harvard structure, internal hardware on time-multiplier,accumulators, use line structure, has the very high parallel characteristics, and a digital signalprocessing design specifically for the command system, can achieve high complexity of digital signal processing algorithm. And the price is low, it is more practical. Chip system isdivided into three parts including modulation, demodulation and asynchronouscommunication. buffer circuit are mainly for sending power amplifier, coupled circuits andresonant filter circuits, etc.It can still demodulate the signal through estimating the spectrum although thewaveform is interfered seriously in time domain in the system online test of laboratoryenvironment.It is visible that the demodulation system based on DSTFT perform goodanti-disturbance capacity and it can overcome serious channel environment in power linecommunication.