| With the rapid development of Wireless Local Area Network(WLAN)technique,the related standardizations are carrying out in full swing.The overall performance in terms of the data rate has always been improved in the evolution of the standards,such as IEEE 802.11a,802.11b and 802.11g,to the widely used standard 802.11n or 802.11ac.However,it’s necessary to find a new frequency band to satisfy the ever increasing demand by users,in particular when the lower band frequency at 2.4/5GHz becomes more and more crowded.So the WLAN in 60GHz band is arising at the historic moment.As an important standard in higher band WLAN,IEEE 802.11ad standard is devised to provide us a broadband Wi-Fi solution.And the enhanced 802.11ad standard aims at satisfying the demand of users with long time delay,MIMO or channel bonding technologies.In this paper,we will study the synchronization and channel estimation techniques in the context of the enhanced 802.11ad standard.Firstly,we review 3 kinds of physical layers and the associated applicable scenarios to highlight the differences between the single carrier(SC)systems and the multi-carrier OFDM systems.Next,we discuss the time synchronization based on the short training field(STF)in preamble by using Schmidle&Cox,Minn and the algorithms based on the Golay sequence.Then we introduce the frequency offset estimation and compensation methods on the basis of time synchronization.We verify and compare the achieved frequency estimation performance by using the L&W,Kay,L&R and Fitz algorithms.For the enhanced 802.11ad standard,we propose a synchronization realization based on the Golay complementary sequence.And it is shown that the proposed training sequence is well suited for the long delay,MIMO and channel bonding application requirements.As for the channel estimation,we focus on the Channel estimation based on the channel estimate field(CE)in 802.11ad preamble.More specifically,we concentrate on the Least Square based channel estimation in frequency domain and the Golay sequence correlation based estimate in time domain.It is shown by simulation result that,the correlation based estimate in time domain can achieve a reasonable channel estimate performance with lower realization complexity.Two equalization algorithm in frequency domain are validated to show the effectiveness of the channel estimation algorithms over the link level simulation platform.It is shown that the MMSE algorithm outperforms the ZF algorithm,as expected.At last,a ZCZ sequence construction based on the Golay complementary sequence is presented to realize synchronization and channel estimation for MIMO system.Due to the zero correlation property,now complicated MIMO channel estimation problem can be transformed into simple SISO channel estimate one,which can effectively reduce the complexity,and meet the requirement on reasonable estimate performance and realization simplicity in 802.11 ad system.All the related analysis in this thesis may provide a useful reference for the low complexity synchronization and channel estimate solution for the future millimeter wave communications. |
