Research On Carrier Synchronization Technology For OFDM Systems In Power Line Communication Channels

Power line communication (PLC) is a special communication using the existingpower line distribution network for data and multimedia signals transmission. Orthogonalfrequency division multiplexing (OFDM) technology is an important modulationtechnology of PLC, but one of the main shortcomings of an OFDM system is its highsensitivity to the carrier frequency offset (CFO). Therefore, CFO synchronization is oneof the key technologies of an OFDM system. CFO normalized by the subcarrier intervalcan be divided into integral frequency offset (IFO) and fractional frequency offset (FFO).The paper will research the IFO estimation algorithms and FFO estimation algorithmsseparately.Firstly, the paper researches the IFO estimation algorithms, and proposes amaximum-a-posteriori (MAP) criterion IFO estimation algorithm which is an improvedmethod on the basis of the original cross-correlation IFO estimation algorithm with Chusequence. The proposed algorithm takes the data symbols around training sequence andthe noise into consideration on the basis of the original algorithm, and a correction termis added in the algorithm which can improve the IFO estimation accuracy.Secondly, the paper researches the FFO estimation algorithms. Aimming at theperformance’s sharp decline in frequency selective fading channels of themaximum-likelihood (ML) criterion FFO estimation algorithm of the Fourier Transformbased traditional OFDM systems, the paper puts forward the Fractional FourierTransform (FrFT) based OFDM systems ML criterion FFO estimation algorithm underthe AWGN channels. The algorithm adopts chirp basis functions replacing the sinusoidalbasis functions as the OFDM system subcarriers, and can be against the interferencecaused by FFO more effectively than the traditional OFDM algorithm under frequencyselective fading channels on the premise of no computational complexity increasing.Finally, applying the FrFT to the traditional OFDM systems ML criterion CFOestimation algorithm over frequency selective fading channels, the paper give one FrFTbased FFO estimation algorithm of frequency selective fading channels. The algorithm makes full use of the multipath delay spread information of the frequency selectivefading channels, extending the range for the cyclic prefix correlates. And comparied withthe FrFT based OFDM systems ML criterion FFO estimation algorithm in AWGNchannels, this algorithm can estimate the FFO more accurately under frequency selectivefading channels.The estimation performance of the three algorithms is verified through simulationsunder power line channels.