Research On Low-voltage Power Line Channel Characteristics And Transmission Performance Optimization Method For AMI

Building the high-speed, bidirectional and real-time communication system is the basis of Smart Grid, using the existing electricity grid as medi. The solution can saving the national resources, and protect ecological and environmental well. The metering and Home LAN, mainly depend on the low voltage power line and indoor line. How to make high-speed communication technology adapted to the low voltage power grid, is the research emphasis of power line communication(PLC). Low voltage power channel limits the high-speed data communication,with large signal attenuation, time-varying and strong noise.The Orthogonal Frequency Division Multiplexing(OFDM) modulation technique splits a high-rate datastream into a number of lower rate streams that are transmitted simulataneously over a number of subcarriers. Because the symbol duration increases for the lower rate parallel subcarriers, the relative amount of dispersion in time caused by multipath delay spread is decreased. Intersymbol interference is eliminated almost completely by introducing a guard time in every OFDM symbol. It is developing rapidly in the electric power communication.At present, PLC technology mainly focused on the narrow band. For meeting the transmission rate and bit error rate, the existing technology switched among different modes, At the same time all subchannels use same mapping method and equal transmit power. The anti-interference method is closing some interference serious subcarrier. The parameters design such as modulation and coding are based on the worst channel condition, so the data frame redundancy, spectrum efficiency is reduced, when the channel with large disturbances, the communication speed is fall steeply. In this thesis, based on the study of the channel and noise model, by suppressing power line noise and dynamic allocation subcarrier bits, we achieved the goal of optimal channel capacity, and improved the frequency efficiency and communication speed. We also constructed automatic meter reading system based on the OFDM power carrier communication technology, which realized the network access layer and the online link quality detection method. The main work includes:(1) Through the measurement about narrow band power channel(9-95 k Hz) multipath transmission characteristics and the noise distribution, we got the statistical distribution of parameters such as attenuation, multipath, noise power and pulse rate, then we constructed the random model described by these parameters to simulate the real power environment. Based on this model, we designed and evaluated the optimal channel capacity method.(2) We selected G3- PLC protocol in physical layer to constructe OFDM communication up/down link using MATLAB. We designed downlink synchronization detection algorithm, improved the uplink baseband mapping method, make it suitable for mapping and decoding soft decision, that improved the performance of OFDM system anti-interference.(3) Power line noises include the stationary distribution of background noise and non-stationary distribution of impulse noise. We used the improved time-domain nonlinear Clipping/Blanking method to suppress Impulse noise; For the background noise, because of its stable Gaussianity, the OFDM signals conform to the linear distribution model. Based on the principal component analysis(PCA), we decomposed the clean signal and power noise feature vector, using VRE(Variance of the Recontruction Error) minimum variance criterion, we determined the optimal signal rank, under the constraint of signal distortion minimum condition, linear estimates of the signal is derived by Lagrange optimum extreme method.(4) Based on power channel model, noise suppression scheme and the existing OFDM physical frame structure, we researched aminimum-complexity bit-loading algorithm that maximizes the data rate given BER and power level constraints. Results show that this bit-loading algorithm achieves almost identical performance as the incremental algorithm but with much lower complexity.(5) Based on the research technique on the physical layer, the existed MAC layer and the routing protocol, we build the AMI system based on OFDM power carrier communication. The solution include G3 module and intelligent terminal network layer. We completed the joining network test, online link quality test, reliability and stability test.