| Power Line Communication is the key to Smart Grid—one of the national strategic planning. With wide layout and convenient access, power line is favored by more smart home and smart community. Power line is built mainly for power transportation. However, problems, such as channel noise, strong interference, weaken signal and unmatched change of impedance, will show in the process of communication. Without enlarging the signal bandwidth, MIMO can accelerate the transfer rate and enhance the anti-interference ability of the communication system. Hence, the application and research of MIMO in PLC system is one direction in present studies of low-voltage bandwidth PLC. Research on space-time coding in MIMO system and selection of space-coding which fits into PLC is beneficial for enhancing effective and stable PLC.In the first part of the paper, the author introduced conditions for PLC signal channel, diversity and spatial multiplexing of MIMO, presented PLC-MIMO system model and its system capacity. Then the author theoretically analyzed the criteria for space-time coding design, and the encoding and decoding methods for space-time trellis codes, space-time block codes, differential space-time block codes, and made stimulation analysis for their performance. The results show that it is difficulty to make the complexity of space-time trellis code decoding increase exponentially with the transmission rate. The diversity increase of space-time block codes can significantly reduce the error rate. Compared to space-time block codes, although channel estimation is not used in decoding, differential space-time block codes sacrifices system SNR, so it cannot be applied to the changeable channel environment of PLC network.The paper put forward a new way of orthogonal space-time-frequency code, and presents error performance combined with theoretical analysis of power line mixed noise model and multi-path fading channel model. The results show that the coding strategy has better anti-interference ability, lower noise sensitivity, and can get greater SNR gain. On this basis, the author proposes a space-time-frequency coding strategy for PLC communication system. Under the condition of a built mixed noise and multi-path channel, the author made stimulation comparison among space-time coding, space-frequency coding, space-time-frequency coding in the MIMO-PLC-OFDM communications system. The results show that space-time-frequency codes has lower error rate than the other two codes in the power line channel. Although there may be a little loss for coding rate, it has better applicability in the PLC. |
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