| The rapid development of wireless mobile communication puts forward higherrequirements on mobility of communication, data transmission rate andcommunication coverage. Orthogonal Frequency Division Multiple Access (OFDMA)technology as a multi-carrier modulation technique can provides multiple accessmethod which has been adopted by the fourth generation mobile communicationsystem. In OFDMA system, timing synchronization is one of the key issues to besolved, it directly affects the integrity and accuracy of information in communicationprocess, and is crucial to the quality and performance of the communication system.When multi-user access in uplink simultaneously, timing synchronization is facingmany difficulties, such as multi-parameter estimation, difficulties of compensationand multi-access interference. Therefore, an effective timing synchronizationalgorithm to achieve multi-user synchronization is needed in uplink of communicationsystem. In this paper, timing synchronization in uplink of OFDMA system is studied:Firstly, the Orthogonal Frequency Division Multiplexing (OFDM) technologyand OFDMA technology, their basic principles, advantages and disadvantages areresearched, besides, the structure of uplink in OFDMA system is described in detail.Since wireless channel is also an important part of communication system, multipathfading channel is introduced in this paper, including the channel’s characteristics,models and parameters.Secondly, synchronization and ranging technology in OFDMA system areresearched. For synchronization problem, mainly including affect and significance oftiming synchronization, and studying about timing synchronization in multi-useruplink. For ranging, focusing on ranging process, structure and relevant characteristicof ranging code.Finally, timing synchronization algorithms are studied and analyzed. In the first,traditional timing synchronization algorithms based on cyclic prefix and trainingsequence in OFDM system are researched, mainly, including introduction, detailedanalysis and simulation results for some classic algorithms. Because of theshortcoming of traditional algorithm, ranging algorithm in uplink of OFDMA systemis referenced, then time domain and frequency domain algorithms are studied. Analgorithm, combined with a multi-user interference cancellation and channel estimation, is proposed based on frequency domain. Through the algorithm simulationin the case of different number of users, the experiment result shows that theperformance of the proposed algorithm is the best, especially in multi-userenvironment.This paper focuses on realizing multi-user detection and timing estimation byranging and timing synchronization algorithm. Thus the improved algorithm based onfrequency domain can effectively eliminate the interference between multiple users,get better performance of detection and timing estimation. |
