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

PLC short of power line communication is a kind of technology using the existing power line distribution network for data and multimedia signals transmission. It has many advantages, such as lower coast and wider coverage, but it also has many shortcomings, including the more noise and the large signal attenuation. OFDM short of orthogonal frequency division multiplexing has important application value in PLC, because it has high spectrum efficiency and can strongly combat multi-path and dispersive channel interface. But OFDM system is sensitive to carrier frequency offset and symbol timing error in some way, so carrier synchronization and symbol synchronization are very important in OFDM systems. Carrier frequency offset normalized by the subcarrier interval can be divided into an fractional frequency offset(FFO) and integral frequency offset(IFO). In this paper, we will research the fractional frequency offset estimation algorithms, carrier frequency offset estimation algorithms and symbol timing estimation algorithms separately, the idiographic work is as follows:Firstly, we researched the fractional frequency offset estimation algorithms, and improved the traditional Schmidl&Cox fractional frequency offset estimation algorithms. Cross-correlation method is used between the local training sequence and the received signal and then the new timing function multiplication based on cross-correlation function and the timing metric function of the traditional algorithm. This method eliminated the effect of timing metric plateau, get a more accurate timing point, and receive a more accurate fractional frequency offset.Secondly, we improved the weighted frequency offset estimation algorithms in OFDM system. This paper provide a new algorithm of using the weighted training sequence part which made of Chu sequence to the timing position, and then using the unweighted training sequence estimate fractional frequency offset. Then we use the correlation between training sequence and received signal to estimate the integral frequency offset. The algorithm can gets a more accurate result and can be against the interference caused by carrier frequency offset more effectively under frequency selective fading channels.Finally, we construct a new training sequence structure with Chu sequence. The even symmetry of Chu sequence made the timing metric has the only one peak, so that we can achieve the more accurate timing point. Meanwhile, the timing estimation performance has been definitely improved.The performance of above three methods under the power line background noise channel is all verified by the simulation in this article.