| Power line communication is a technology which uses the existing medium and low voltage grid as the transmission medium to implement the transmission of the integrated service such as data, images, voice and etc. Power line carrier communication technology which uses the existing grid has many advantages such as rapid deployment, no additional wires, and wide coverage. And its prospect for application is very broad. But the power line network is designed for power transmission, which has its inherent drawback, so that a suitable modulation-demodulation technology should be adopted to overcome the interference and attenuation of the power line. Therefore the reliable transmission and communication on the power line will be realized.After comparing the advantages and disadvantages about the present power line carrier communication technologies which based on the characteristics of power line communication environment and power transmission, for this topic the orthogonal frequency division multiplexing modulation technology was chosen to implement the communication of power line carrier. OFDM technology has the advantage such as strong anti-interference ability, high spectrum efficiency and can be modulated or demodulated by IFFT or FFT, which has been more and more widely used in the field of power line carrier communication. However, OFDM technology also has some shortcomings:higher peak average power ratio (PAPR), much more stringent requirements of synchronous system performance on the receiving terminal. This paper aims to do the research of the low-voltage power line communication technology which is based on OFDM, and the using of DSP to implement an OFDM communication system which can send and receive data in the environment of low-voltage power line.First of all, the noise characteristics of low-voltage power line channel are analyzed on the account of domestic power line noise environment. This analysis is started with practical application system, the test of environment, the existing hardware conditions, and then the communication model which can satisfy the power line channel is established. And at the same time, the inherent characteristics of power line channel are analyzed to provide the theoretical basis for the affection of power line channel to the performance of communication system.Then, the two cores technology of OFDM system is introduced and studied. They are reducing the peak average power ratio and synchronization. And several common methods of reducing PAPR of OFDM system are compared in this paper. Next, the synchronism of the OFDM system is researched, and the influence of synchronism deviation on the system performance is analyzed. And a system synchronization algorithm which is suit for sending data on the power line is introduced. At the algorithm, the synchronization frame of the leading symbol is designed. The receiving terminal can use these long and short training sequences in the leading symbols to achieve fast synchronization. And this algorithm is simulated by MATLAB software.Finally, a complete OFDM system solution which fits power line communication is designed. The design of the transmission terminal’s each function module, and the receiving terminal’s function module completed by DSP are introduced. The practicability of the system is verified by the simulated analysis using MATLAB software of both each module and the whole system’s ber performance. TTs DSP chip TMS320VC5416 is adopted as the core control platform to write the program to achieve and test the design of the function modules mentioned above. The testing results show that the design of the system is accord with the expected performance. |
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