Research On Timing And Frequency Synchronization In OFDM System

The modern communication technologies have got rapid development since the 21st century. The commercial development and large scale deployment of the third generation mobile communication systems as TD-SCDMA, WCDMA, and CDMA2000 have been fully carried out. At the same time 3GPP starts the standardization process for 4G mobile communication systems as LTE and LTE-Advance. Next generation mobile communication systems can provide higher transmission rate, larger system throughput, better coverage and more flexible bandwidth allocation. LTE and LTE-Advance adopt many new technologies, such as MIMO, OFDM, CoMP, Relay, etc.As a special multi-carrier transmission technology, OFDM system transports data efficiently on a high-speed by dividing a high-rate data stream into many low-rate data streams and mapping onto orthogonal subcarriers. OFDM technology can also improve the spectral efficiency. Just a few subcarriers suffer deep fading within the same time, which guarantees good performance against frequency selective fading and narrowband interference. OFDM technology is considered as a core transmission technology of next generation wireless communication system.However, there are some disadvantages in OFDM system. One of these disadvantages is the sensitivity of frequency offset between subcarriers. OFDM systems need strict requirement on the orthogonality between subcarrier, and are sensitive to carrier frequency offset. Frequency offset caused by crystal oscillator and Doppler Effect destroys the orthogonality between subcarriers, introduces ICI and leads to the deterioration of system performance. So designing a fast timing synchronization algorithm and an accurate frequency synchronization algorithm becomes an important aspect for OFDM system.This paper researches the timing and frequency synchronization algorithm for OFDM system and proposes a fast timing synchronization algorithm based on LTE-TDD system, which can reduce the complexity of traditional correlation algorithm. Besides the paper find a frequency tracking algorithm based on reference signal design of LTE-TDD and a joint detection algorithm for integral frequency offset and timing based on the character of CAZAC sequence, which can improve the accuracy of frequency and timing synchronization. Computer simulation results validate the system performance of these algorithms.