Synchronization Technologies For OFDM System

OFDM (Orthogonal Frequency Division Multiplexing) is a key technology in the 4th Generation mobile communication. The main principle of OFDM system is to split a high-rate serial data into a set of low-rate sub-streams, each of which is modulated on a separate sub-carrier, so that each sub-carrier is small enough in bandwidth to experience frequency flat fading. Moreover, OFDM uses the spectrum more efficiently by keeping the sub-carrier orthogonal to one another.However, OFDM system is far more vulnerable to symbol timing and carrier frequency synchronization errors compared to single carrier transmission system. Timing synchronization error is caused by the unknown arrival time of OFDM symbols, while frequency synchronization error is caused by the mismatch of the local oscillator in the transmitter and receiver as a result of inherent instability. Timing error results in the rotation of sub-carrier constellation, while frequency error leads to the loss of orthogonality and causes inter-carrier interference (ICI). The result is that the loss of synchronization will lead to substantial degradation of error probability performance.Under this situation, accurate timing and frequency synchronization are of great importance to OFDM system. This paper introduces the basic principle and key technologies of OFDM system, and analyzes the impact of synchronization errors, as well as some traditional solutions. Based on these work, this paper analyzes a joint synchronization estimation scheme, which includes cyclic prefix and pilots. In order to solve this scheme's ML estimation, the paper presents a reasonable estimation flow, and the simulation result shows the advantages of this flow. Furthermore, the paper also does simulation on the performance of cyclic prefix and pilot,...