Study On Adaptive OFDM Modulation Schemes Over Low Voltage Power Line

The advantages of power line communication including high transmitting speed, convenience and low cost, but its bad channel characteristics restrict its performance. As the development of modern digital signal processing technology, OFDM applied in extensive range especially wireless communications. OFDM developed with adaptive technology gradually. Due to the advantages of OFDM and the speed demand of broadband PLC, adaptive OFDM technology applied to PLC in order to improve its performance. The key aspect of adaptive OFDM includes accurate channel estimation and efficient adaptive modulation schemes. Firstly, the thesis discusses power line channel characteristics in detail, and then an experiment of measuring its attenuation is implement in the lab. As for channel estimation, firstly the thesis discusses the estimation methods based on training series and pilot, then a comparison of these two methods in performance and calculation complexity is given. The thesis studies on how to establish the adaptive OFDM system, emphases on how to select the suitable modulation parameters of the system. A whole model of adaptive OFDM modulation for broadband communication based on low voltage power line is introduced after a detail analysis of the system. The method of modulation parameter selecting is the key content of the thesis. Firstly, the thesis discusses the adaptive modulation system based on SNR threshold, introduces the methods of SNR threshold setting. Then based on it, an optimize scheme considering both the transmitting power and modulation mode selecting is introduced. Performance emulation shows that the optimize scheme enhances the data throughput of the system in the same BER restrict comparing to the traditional OFDM modulation system.