Research On Key Technology Of Power Line Communication System Based On OFDM And Its FPGA Implementation

Power line communication is a communication method which use power line for information transmission.There are noise,multipath interference and frequency selective fading in the power line channel.Information transmitted in this environment will be greatly disturbed.OFDM has good anti-interference characteristics and can be quickly implemented by Fourier transform,so it is the preferred modulation method in broadband PLC technology development.This thesis studies on the key technologies of power line communication system based on OFDM and implements it with FPGA.The major contents are summarized as follows:Firstly,this thesis briefly introduces the background,significance and development status of power line communication at home and abroad.Then,according to the physical layer protocol of the interconnection technical specification on the low-voltage power line broadband carrier communication,the physical layer system architecture of OFDM and the physical layer data structure are introduced,and then the principle of OFDM system's submodule at transmitter are introduced,such as scrambling code,channel coding,diversity copy,adding cyclic prefix and adding window.Secondly,having a research on frame synchronization,symbol synchronization,sampling synchronization and channel estimation techniques of system receiver:Comparing the performance of three frame synchronization techniques which includes energy detection of received signal,energy detection of double sliding window and packet detection based on preamble.Then choosing the best performing packet detection method as the system's frame synchronization scheme.Analyzing the effect of symbol synchronization bias and presenting the receiver's constellation of OFDM symbol.Making a simulation comparison of S&C and H.Minn algorithm with delay correlation,cross-correlation and its three improved algorithm based on local sequence in MATLAB and then choose one algorithm suitable for this thesis.In order to reduce the complexity of hardware implementation,the algorithm is improved again and finally a new symbol synchronization algorithm is obtained.Analyzing the influence of the sampling frequency offset and presenting the receiver's constellation of OFDM symbol with the fractional frequency offset.The system that this thesis studied only exits fractional frequency offset,so we choose the simple delay correlation algorithm to estimate the frequency offset.Through MATLAB simulation,we found that the algorithm has a large estimation error at low SNR,so we improved the algorithm.Then we simulated the mean square error of the actual and estimated frequency offset between original algorithm and improved algorithm.Giving priority to the complexity of hardware implementation,this thesis uses LS algorithm to implement channel estimation.Since the LS algorithm ignores the noise and has poor performance at low SNR,we have improved the algorithm.Then,we not only simulated the mean square error of the channel estimation value and actual value between original algorithm and improved algorithm,but also simulated the receiver's symbol error rate of OFDM symbols that was compensated by channel estimation value.Finally,according to the principle in the physical layer protocol and the improved synchronization and channel estimation algorithm,we implemented the key technology of the OFDM system by FPGA.