Research On Synchronization Techniques For OFDMA System

With the development of mobile communication systems, the demanding for high-speed service is higher and higher, which cause the OFDM technology is widely used. LTE, UWB,Wimax and 4G systems and are all taking OFDM technology as their key technology.Compared with traditional single-user OFDM systems, synchronization technology for OFDMA system are more difficult. First, the received signal is the superposition of multiple users, each user's experience through the channel and the fading is different, so the timing and frequency offset is different, therefore the traditional OFDM synchronization of single-parameter problem becomes into a multi-parameter problem. Secondly, the correction of one user's time and frequency offset would misalign other initially aligned users, so the time error and frequency offset compensation has become more complex.This paper first reviews development of mobile communications, as well as OFDM, OFDMA. The second chapter describes the basic principle of the conventional OFDM and establishes a downlink OFDMA system model, which is the basis for researching synchronization technology for OFDMA system. Chapter three takes a brief introduction to the influence on system performance because of the time and frequency errors. This article gives description of synchronization for uplink and downlink separately. There are reasons for the particularity of uplink synchronization, and also in accordance with the timing order. The fourth chapter describes the downlink synchronization technology, which is divided into acquisition and tracking. Chapter five analyzes OFDMA uplink synchronization according to different sub-carrier allocation scheme, and gives a certain improvements. Chapter six describes the timing and frequency offset compensation in uplink, which is the last step of the whole process.A large number of simulations are provided for the algorithms described in the article.