Research On Low Voltage Power Line Carrier Communication System Based On OFDM

Low-voltage power line communication uses the existing power line as the communication medium to couple the signal of transmitter to the low-voltage power line for data transmission.This technology has incomparable advantages such as synchronization with power grid construction,avoidance of re-wiring,easy access and so on.It has become the physical network with the highest household rate.However,the actual power line channel environment is complex,the signal transmission process will be affected by the power line multipath effect,noise interference and other factors.Orthogonal frequency division multiplexing(OFDM)has become the best solution to these problems because of its high spectrum utilization and anti-multipath interference.In this paper,based on OFDM technology,low-voltage power line communication is studied in depth.The research contents are as follows:(1)In-depth study of the low-voltage power line channel environment.Firstly,the basic principle of low-voltage power line carrier communication is explained in detail,and the system framework model is constructed.Then,the characteristics of the power line channel are analyzed,including impedance characteristics,attenuation characteristics,noise characteristics,time-varying characteristics,and multipath transmission effects.Finally,the low-voltage power line channel model is established according to the multipath effect of power line channel,which lays a theoretical foundation for the subsequent system design.(2)Research and analysis of OFDM technology,from the basic principles to the realization of key technologies such as modulation and demodulation.For the complex channel environment of low-voltage power lines,OFDM technology utilizes guard interval,signal synchronization technology and channel estimation technology to make the signal have strong anti-attenuation and robustness in the transmission process.Combined with the channel characteristics of power lines,a low-voltage power line OFDM system is established and simulated by MATLAB,which lays a foundation for the research of subsequent channel estimation techniques.(3)Analyze the sparse characteristics of low-voltage power line channel,apply compressed sensing reconstruction algorithm to channel estimation of OFDM system,and propose an improved Generalized Orthogonal Matching Pursuit(GOMP)algorithm.The algorithm improves the atomic selection by using the conjugate symmetry of Fourier transform,which reduces the computational complexity.In the iteration process,there is no need to compare with the K value of channel sparsity,which solves the problem that other algorithms such as GOMP need to know the channel sparsity in advance.The simulation results show that the mean square error of the improved GOMP algorithm is smaller than other greedy algorithms as the signal-to-noise ratio increases.It is verified that the improved algorithm can be applied to the low-voltage power line channel estimation field.(4)This topic selects Atheros OFDM chip to complete the design of carrier communication system,including core function module,analog front end module,coupling module and power module.The hardware test platform is built,and the network test of the carrier communication system,the test of the physical layer communication rate,and the error rate test are completed.The experimental results show that the physical layer rate of the carrier communication system designed by this subject can reach 197 Mbps or more.And the feasibility of the improved algorithm is verified.Compared with the traditional channel estimation algorithm,the improved algorithm can compensate the channel attenuation well and reduce the mean square error and bit error rate.