Time Ofdm System, Frequency Synchronization And Peak-to Reduce The Problem Study

Orthogonal frequency division multiplexing(OFDM) is a high-speed information transmis- sion. It has higher spectrum efficiency, a strong anti-frequency-selective fading and anti-jamming capability. However OFDM and MIMO-OFDM systems are very sensitive to time and frequeney synehronization errors, espceially the frequency synehronization errors. Correct time and Precise frequency synchronization are necessary for OFDM and MIMO-OFDM systems. On the other hand, OFDM signal is a synthesis of multi-path signals.Therefore,it has relatively high average peak power, which will bring many unfavorable factors in the course of transmission.Some kind of important techniques, that being closely related to the OFDM, were discussed in the thesis. These key techniques of an OFDM system consists of the synchronization of time domain and frequency domain, the channel and the noise estimation, the peak-to-average power ratio(PAPR) of an OFDM system. Firstly, the origins, the development and the application of the OFDM techniques were mentioned in the thesis, and the basic concepts of an OFDM system was also provided in the following words. Then, the synchronization technique of OFDM was introduced in to the thesis, include the frame synchronization, the frequency synchronization and reference clock signal synchronization. The unfavourable effects of the unsynchronization in an OFDM systems, including inter channel interference (ICI) and inter symbol interference (ISI), were also analysed. Subsequently, some way to reduce PAPR of an OFDM system were discussed in the thesis, such as predistortion (Include clipping, clipping and filtering, companding, etc.), Encodeing (Iinclude, Golay code, Complementary Golay code, Reed-Muller code, etc.), Probabilistic algorithm (Iinclude partial transimit sequence, selected Mapping, pulse shaping, tone Reservation, tone injection, etc.). Some algorithm were simulated using Matlab software. Finally, a complete OFDM system was proposed and simulated by the Matlab partially.