Research On Estimation Algorithms Of Synchronization Errors For OFDMA Uplink Link

Orthogonal frequency division multiple access (OFDMA) is a multiple accesstechnology based on the combination of OFDM with FDMA, it inherits manyadvantages from OFDM technology and has a wide range of applications. OFDMAtechnology has been one of the key technologies for the fourth generation mobilecommunication networks (4G system). Currently, OFDMA uplink synchronizationthchnology is a research focus in OFDMA system.Firstly, we describe the fundamental principles and system architectures for OFDMsystem and OFDMA system in detail.Then, the impact of synchronization errors toOFDMA system is discussed, and a mathematical model for the analysis of OFDMAuplink signal transmission is established. On this basis, we delve into several trainingsequence-based carrier frequency offset estimation algorithms, includingMaximum-Likelihood algorithm, APFE(Alternating-Projection Frequency Estimator)algorithm and asymptotically efficient algorithm which are developed from MLalgorithm. Through theoretical analysis and simulation study of asymptotically efficientfrequency offset estimation algorithm, we know that this algorithm has less complexitywhile it has a good performance, but there are several drawbacks which leads it has apoor performance when the number of sub-carriers are small or SNR is low. In order toget rid of these drawbacks, we give a proposed algorithm using MPSO algorithm andcombining carrier frequency offset range estimation algorithm. The proposed algorithmsolves the problems that asymptotically efficient algorithm is too sensitive to initialvalues and its cost function must have a perfect form. In addition, this proposedalgorithm avoids a complex computation for Hessian matrix in the iteration process andimproves the estimation performance. Through soft simulation, we find the proposedalgorithm has a better performance when the sub-carriers are limited or SNR is low.