Coded-OFDM based PLC Channel for SISO and MIMO Smart Grid Systems

Abstract

The electricity demand is increasing due to the people’s living standards is in the increase. Many countries began to shift their attention to Smart Grid (SG) systems instead of the traditional Gird. Communication technology in the SG has gradually become the most popular core issue in recent years.The PLC, which uses the existing power grid to propagation medium in grid communication system with the low cost and easy to set up, can replace the wireless SG communication system – like optical Fiber. In this thesis, new receiver technology in Single Input and Single Output (SISO) PLC system and new channel estimation method in the MIMO PLC system has been investigated to optimize the Bit Error-Rate (BER) performance of the PLC system with real-valued Orthogonal Frequency-Division Multiplexing (OFDM) input. The novel contributions in this thesis are presented in three sections. First of all, we consider PLC for the SG in the presence of impulse noise modelled using the Symmetric α-stable (SαS) distribution. The proposed system utilizes coded OFDM with a real-valued output signal implemented using Hermitian symmetry of the modulated symbols in the frequency domain. In this part, we compare the BER performance of both Low-Density Parity-Check (LDPC) code and Polar code in the PLC channel to choose the better error correction method about PLC system. In the receiver part, we introduce a novel Maximal Ratio Combining (MRC) technique that exploits the Hermitian symmetry inherent in the real-valued OFDM symbol and compare its performance to the Zero Forcing (ZF) equalizer and Minimum Mean Square Error (MMSE) equalizer that are used to remove the effect of the Intersymbol interference (ISI). The presented simulation results included in the investigation demonstrate that in the PLC channel, the performance of the proposed MRC approach using LDPC codes outperforms the polar codes consis- tently for Quadrature Amplitude Modulation (QAM) of orders M = 16 and M = 256. Secondly, to investigate the channel estimation method utilised in the MIMO-PLC system, the comb pilot and the block pilot design methods are presented to estimate the ideal PLC channel and compared the BER performance of the two estimate pilot methods. As both pilot methods’ performance is affected by Additive White Gaussian Noise (AWGN), an averaging process method is introduced to reduce the effects of AWGN and Mean Square Error (MSE) metric is used to assess the quality of the channel estimation. The value of the estimated PLC channel in each averaging time (frame) is different. Meanwhile, they are affected by the value of the previous averaging times. The BER performance in the estimated channel system becomes better after the averaging procession. Moreover, the performance of the averaging approach in pilot design method is affected by the different weight factors and the averaging times, In this part, the thesis focuses on analysing the averaging pilot design and provides the best choice of the value of the weight factors and the averaging times. Finally, We investigate a 2 × 2 MIMO-OFDM system and propose a novel Nonzero-comb Pilot (NZCP) design for channel estimation that can cope with pilot contamination without the zero data insertion in adjacent channels. The BER performance vs. Eb/N0 is demonstrated using numerical simulations for uncoded and coded systems using LDPC error correcting codes. The performance is compared with conventional comb and the block pilot methods through the frequency-selective multipath PLC channels and in the presence of AWGN. The numerical results presented demonstrate that the NZCP approach using averaging outperforms all the methods considered, e.g. for the uncoded system at a BER of 10−5 an improvement in Eb/N0 of 3.6 and 4 dB against block and comb approaches, respectively. In contrast, in the coded system, the coding gain is of the order of 20 dB compared to the uncoded cases with the NZCP proposed method outperforming all the other considered approaches by at least 0.5 dB. In conclusion, the work presented in this thesis provides the MRC detector to optimize the performance of the SISO-PLC system. Furthermore, it also introduces and compares different types of channel estimation pilot technology. The averaging approach and NZCP method have been utilized in MIMO-PLC to optimize the BER performance based on the traditional pilot design.