Research Of Low Voltage Power Line Communication System Based On Adaptive OFDM

Power Line Carrier(Power Line Carrier,PLC)communication technology is based on the existing distribution network as a communication medium.This kind of technology has its advantages,such as no additional wiring,low construction cost and wide coverage.However,The environment of power line communication has the characteristics of large attenuation,many burdens and complicated interference.Therefore,it is significant to achieve an efficient and reliable power line communication.It could be done according to the characteristics of the power line channel environment,and by researching on available means of communication.Orthogonal Frequency Division Multiplexing(OFDM)technology can suppress inter-symbol interferences effectively,and its spectrum utilization rate is high.Adaptive modulation technology makes full use of the spectrum resource,and improves system performance significantly.This paper aims at studying the low voltage power line communication system based on adaptive OFDM,which intending to develop a adaptive communication system with high availability and reliability in accordance with the characteristics of the power line channel.(1)Exploring the OFDM system which is suitable for low voltage power line communication:First,we analysis and compare the single-carrier with multi-carriers transmission system.Multi-carriers system is superior to single-carrier systems if the sub-carrier stays orthogonal.Then we analyzes the main modules of OFDM system,including modulation and demodulation,orthogonal sub-carriers and cyclic prefix.Finally,we set up the basic framework of the OFDM communication system in power line carrier channel.(2)Studying on the channel estimation algorithm which is based on pilot:the paper discusses on the design and structural characteristics of block,comb and lattice pilot in detail,while taking advantage of the multi-path channel model,to simulate the bit error rate performance based on the east square(LS)algorithm,the Least Mean square error(MMSE)algorithm and discrete Fourier transform(DFT)algorithm.The results show that,the anti-noise performance of LS algorithm is poor;the complexity of MMSE algorithm is high;the complexity of the DFT algorithm is much lower than the MMSE algorithm,and the performance is better than the LS algorithm.(3)Studying on the adaptive bit and power allocation algorithm:First,according to the three adaptive bit power allocation criteria based on minimum transmit power,minimum bit error rate and maximum transmission rate,this paper takes use of Lagrange multipliers optimized separately obtained the bit and power allocation of Fischer algorithm,the Hughes-Hartos algorithm and the traditional water-filling algorithm.The three adaptive modulation algorithms are simulated in the multipath channel then.Among them,the improvement of traditional water-filling algorithm is adding the power redistribution module and the power fine adjustment module to achieve a higher performance of the water-filling algorithm.Finally,with choosing the appropriate parameters of the system and the improved water-filling algorithm,this paper sets up a low voltage power line communication system based on adaptive OFDM,and simulates the BER performance of the system and the root mean square(RMS)performance.The results show that,compared with the traditional water filling algorithm,the root mean square(RMS)performance of improved algorithm is improving;Compared with the Fischer algorithm,bit error rate(BER)performance of improved algorithm is better;Compared with the Hughes-Hartos algorithm,the improved algorithm's complexity is lower even their error rate performance are almost quite.