Research Of PLC Channel Frequency Spectrum Monitoring And Multi-frequency Communication System

In the beginning,the power line channel was not designed for communication,therefore,comparing with other transmission media,its environment is more severe,with more noise interference.Traditional power line communication system uses fixed and single frequency,which may result in serious co-frequency interference while different system users adopt the same frequency for transmission.In this case,this paper proposes a method of multi-frequency communication manner,to flexibly choose the frequency point with lower interference,so as to improve the reliability of power line carrier communication.Firstly,the paper describes the basic knowledge of transmission characteristics of the power line channel,modem technology,error control technology and other knowledge related.The demodulation of 2FSK signal uses high-performance digital spectrum estimation method.Then,the paper analyzes the design ideas of PLC channel frequency spectrum monitoring and multi-frequency communication system.The system can choose the frequency point with lower interference to communicate by two methods.One method is to monitor some optional channels' frequency spectrum,in order to exclude the channel which is used for other users,which can avoid the channel communicating in serious co-frequency interference before communication.The other method is to change the working channels to keep communicate during its working.This method solves the problem that the system can't communicate normally when the current working channel is disturbed.System in normal communication and idle time all can determine whether to switch the channel through the retransmission numbers of a frame of data,so as to ensure the quality of communication of real-time monitoring,at the same time,ensuring the synchronization of channel switching between the transceiver through the time control of switching channels.Next,in multi-frequency communication system of PLC,it needs the band pass filter which can change center frequency is designed by switched capacitor filter chip LTC1068-25,it changes center frequency of the band pass filter by changing the clock frequency of the chip.Paper describes the part of software,the process of software and communication protocol.It adopts a high-performance,32-bit,fixed-point DSP chip,TMS320F2812 of the TI company as the core of the system,to implement multi-frequency modem module,the encoding and decoding module and serial transceiver module and so on.Each module is designed to each independent API functions,which can be called by system's main function.Finally,setting up and testing a low-voltage PLC experiment system.The experimental results show that multi-frequency communication system designed for PLC can communicate in low interference,which improves the reliability in the harsh environment of power line channel.