Research Of Synchronization With Discrete Multi-tone Modulation

As an advanced multi-carrier modulation technique, discrete multi-tone modulation (DMT) has many advantages over traditional single-carrier modulation. Stream DMT has been widely applied in xDSL, and communication system based on burst OFDM has also been popular, but the application of burst-mode DMT has not been reported. We adopt burst DMT technology in a project which requires high-speed communication between two nodes in a cable channel.Basic principles of DMT and its synchronization technology is discussed, especially the synchronization technology suitable for burst DMT system.The introduction of cyclic prefix releases the accuracy requirements for symbol synchronization. Classic symbol synchronization algorithms include the maximum likelihood algorithm based on cyclic prefix, algorithm based on the cross correlation, the algorithm based on phase rotation and maximum channel capacity algorithm. Maximum channel capacity algorithm which takes channel characteristics into account is somehow ideal. Burst DMT systems require higher speed and accuracy for symbol synchronization. This paper proposed a suitable symbol synchronization algorithm based on training symbol for burst DMT system. The algorithm simplifies the cross correlation algorithm and improves its capacity, which achieves acceptable performance and complexity.Considering the mismatch of sampling frequency will lead to not only phase rotation but also inter-carrier interference, the requirement of DMT system for sampling frequency synchronization is quite harsh. This article describes the sampling frequency offset estimation method in frequency domain, and analyzed the three main methods of correction. Correction methods based on VCXO and interpolation are not suitable for burst DMT system because they usually take long time to stabilize the loop. In the project, we use estimate and correct phase deviations in the frequency domain, which achieve good results when high stable crystal is adopted. Also some simulation results are given.