Study On Timing And Frequency Synchronization Technology For OFDM System

Due to its high spectrum efficiency and good ability in coping with multi-path fading, orthogonal frequency division multiplexing (OFDM) technology has attracted considerable attention from researchers. However, OFDM system is very sensitive to symbol timing offset and carrier frequency offset, so accurate timing synchronization and frequency synchronization are necessary to OFDM system. This paper discusses on OFDM synchronization technology based on training symbol.First, the basic principle, system model and the advantage and disadvantage of OFDM system are briefly introduced. Then the signal model is derived, and the influence of synchronization errors to OFDM system performance is analyzed quantitatively. This paper comprehensively investigates the influence of symbol timing offset, carrier frequency offset and sampling clock offset on OFDM demodulated signals and bit error ratio under AWGN channel and multi-path fading channel. Several classic symbol timing synchronization and carrier frequency offset estimation algorithms are deeply studied. The algorithms are simulated, and the simulation results are analyzed.OFDM synchronization algorithms based on training symbol are investigated, and two algorithms are proposed. An improved algorithm is proposed aimed at resolving training symbol redundancy and timing metric plateau in Schmidl algorithm. The training symbol in this algorithm is conjugated symmetrical and repeated. The timing metric has a sharp peak and eliminates the plateau. Both integral and fractional frequency offset estimation employ the same training symbol, and therefore the system overhead is saved and the complexity is degraded. The second algorithm proposed in this paper does not just improve symbol timing method or frequency offset estimation method. It is a complete set of solution project of OFDM synchronization. A new training symbol with special structure is designed, and a new joint symbol timing and frequency synchronization algorithm is presented based on this symbol.New frequency offset estimation algorithms are characteristic of large estimation range and high accuracy. At the same time, timing synchronization can produce a sharp peak, through which we can find where the OFDM symbol starts. The simulation results show that the performance of the synchronization algorithms proposed here is better than that of conventional methods.