Theoretical And Experimental Study Of The Low-Voltage Powerline Communication System Based On OFDM

Powerline Communication (PLC) as a new connection measure for family wide-band network is becoming more attractive in the recent years. The low-voltage Powerline Communication attracts increasing attention due to its resplendent perspective involving home automation and home Internet. But the noises, the frequency selective attenuation and the multi-path propagation inherently existed in the powerline make it very difficult to realize. To overcome these problems, a technique called Orthogonal Frequency Division Multiplexing (OFDM) was proposed as a new and efficient method for high-bit-rate communications. Therefore, it is valuable to be engaged with the PLC research based on the OFDM. Based on the analysis of the basic theory, the state of application of Low Voltage Powerline Communication, as well as the whole schemes of designing an OFDM based experimental PLC system are presented. Finally, the powerline OFDM communication system model is built in an experiment environment. The thesis consists of the following three main parts: In chapter 3, the design scheme for a prototype powerline OFDM communication system is discussed. The system structure of the software module and the functions of each part of the developed system are given in detail. The design of the overall hardware wide-band coupling device including the power amplifier and the carrier source are explained. The experiment testing of this powerline OFDM communication system shows that the OFDM based high-bit-rate communication over 220V powerline network is definitely feasible. In chapter 4, a nonlinear equalization method based on the multi-layer perceptron for OFDM Powerline Communication is proposed to compensate the influence of the time-varying frequency selective fading characteristics in the powerline channel. Using this scheme, a nonlinear equalizer is realized. The realized equalizer is successfully used in the developed system as a research platform. The best step size for the training of the MLP is obtained by the experiments. In order to verify the effectiveness of the proposed equalizer, the proposed equalizer as well as the linear equalizer is used in the experimental PLC system. Test results show that the nonlinear equalizer is more effective in tracking the variation of the powerline communication channel. Chapter 5 deals with the OFDM symbol timing. As the performance of the OFDM based communication system is sensitive to the error of synchronization, this problem is investigated in detail in the thesis. A new metric rule was proposed for timing synchronization. The delay and correlation algorithms as well as the new synchronization algorithm proposed were used in a realistic low voltage power line. The performances of three kinds of timing synchronization algorithms, including the proposed algorithm, were compared on the developed system. Test results show that the proposed approach was independent from the frequency offset and robust to the multi-path fading channels. Therefore. It provides a well suitable synchronization scheme for OFDM based PLC system.