Researches On Frequency Offset Estimation And Compensation Technique In OFDMA System

Orthogonal frequency division multiple access technique is based on OFDM technology, combined with FDMA techniques forming a multi-user access technology. It has advantages of OFDM, but it is also very sensitive to synchronization errors, especially for the carrier frequency offset (CFO:Carrier Frequency Offsets) because frequency offset causes the destruction of orthogonality between subcarriers, leading to inter-carrier interference and multi-user interference (MUI:Multi-User Interference), seriously affecting the performance of the system. Therefore, frequency offset estimation and compensation of the uplink receiver is very important for OFDMA system to reduce the multi-user interference and improve system performance. However, with respect to the downlink OFDMA system, the uplink received signal is the superposition of a plurality of user signal due to fading and delay. The channel characteristics of each user are different, so the CFO of each user are not the same, the frequency offset estimation for each user and the frequency offset compensation is very difficult. This paper mainly focus on the problem, and study the frequency offset estimation and compensation for OFDMA system uplink. The main work is as follows:First, the process of OFDM systems to send and receive signals, mathematical models, as well as the basic principles of modulation and demodulation method are briefly introduced, and then a system model of OFDMA uplink system is established. After that, the impact of carrier frequency offset for OFDMA system is analyzed. And current domestic and foreign offset estimation and compensation methods of OFDMA systems are classified and summarized.The paper studies the frequency offset estimation algorithm based on sub-band allocation OFDMA system. The CFO estimation performance under different channel environments are analyzed. Then CFO estimation method using the received signal for interleaved subcarrier allocation OFDMA system is described. Through the analysis of the limitations of the methods described above, a multi-user frequency offset estimation method which is not affected by subcarrier allocation is given. However, the algorithm is an iterative algorithm, and the paper doesn’t give any certain methods to determine the initial value of the iterative algorithm. Therefore, this paper presents a method for determining the initial value of the iterations of the algorithm, and the improved algorithm is simulated and compared with others.On this basis, the frequency-domain compensation method based on sub-band allocation, using circular convolution and iterative methods to finish multi-user frequency offset compensation and interference cancellation is studied firstly. Then the multi-user compensation and separation algorithm for OFDMA system based on interleaved subcarrier allocation under is introduced. Finally, the compensation issue for OFDMA system based on arbitrary subcarrier allocation is analysed. The frequency offset compensation and users’ information extraction is achieved by introducing interfering matrix. But the complexity of inver interference matrix is high. Without affecting system performance, an improved interference matrix via setting the bandwidth is used to reduce interference matrix computation. Simulation results show the good performance of the algorithm.