Research On Frequency Offset Correction Technique Based On New Pilot Pattern In Next Generation WLAN System

In recent centuries, especially since the third revolution of science and technology revolution, networked, intelligent user terminal unprecedented popularity, so that people become increasingly dependent on wireless networks, Especially the increasing demand for cheap wireless LAN of high throughput and high bandwidth. However, the limited frequency resource is a kind of precious resource, so it is very necessary to use the communication technology with high utilization rate of frequency band.Orthogonal frequency division multiple access is a derivative technology of FDMA and OFDM technology, It has a high frequency spectrum efficiency under high-speed transmission scenarios. Furthermore it has a good non-LOS effect and is more compatible with noise and multipath fading impact.It also has a flexibility on modulation and power parameters setting etc. It has been widely used in HD mobile TV and wireless local area network, and become one of the key technologies of mobile LTE system and the next generation WLAN system IEEE802.11ax.The high-performance OFDMA system is based on the orthogonality of the sub carriers, however, particularly be sensitive to the synchronization error is the natural defects of OFDMA technology, especially to the sub carrier frequency offset. Even if a small amount of CFO exists in the system, the orthogonality among different carriers can be destroyed to some extent, and resulted in inter carrier interference and inter symbol interference, the performance of the system will be severely deteriorated. In order to improve performance of OFDMA system, reduce interference and increase reliability of the OFDMA system, accurate frequency synchronization is necessary.The paper studied frequency offset synchronization algorithm with the comb type pilot. CFO estimation with pilot can effectively avoid taking up too much time and frequency resources with using training symbols, and the performance is good. However, the performance of CFO estimation with pilot is large guided by the pattern of pilot,especially in frequency selective channel, when the interval of adjacent pilot carrier is longer than reciprocal of the maximum multipath time delay, the performance will has a serious decline. The next generation WLAN system IEEE802.11ax uses technology of OFDMA, which adopt block sub carrier allocation scheme of resource unit. To 20MHz bandwidth, for example, each resource unit (RU) consist of 24 user data sub carriers and two pilot, and there is a common pilot between two adjacent resource units. Based on researching the position of the pilot sub carrier in RU, we study improve the performance of CFO estimation and channel estimation with pilot estimation,by adjusting the position of the pilot. After deduction, two design schemes of the pilot pattern are proposed, namely, pilot pattern design of equal spaced and pilot pattern design of pilot clusters. At the end of this paper, by studying the CFO estimation algorithm which in the uplink of MIMO-OFDM,extend the application range of the algorithm and the performance of CFO estimation in OFDM A system under small residual frequency offset is solved very well. Then through a number of simulation experiments of Matlab, to verify the good performance of the new designed pilot pattern with the CFO algorithm.