Research And Application On Carrier Frequency Offset Estimation Of IEEE 802.11ac RF Conformance Test

IEEE 802.11ac system is very sensitive to carrier frequency offset which results in serious inter-carrier interference(ICI) and severe performance degradation in RF conformance test system. This paper focuses on the study of carrier frequency offset estimation algorithms in IEEE 802.11ac RF conformance test system, the main contents are organized as follows:Firstly, the key techniques applied in IEEE 802.11ac physical layer(PHY) is introduced in detail, including the principle and features of OFDM, MIMO and MIMO-OFDM technology. Then, the frame structure of the preamble and head of PLCP are studied and the models and workflow of IEEE 802.11ac PHY transceiver are given.Secondly, the influence of carrier frequency offset on OFDM receiver is analyzed and the importance of frequency offset estimation is demonstrated. This paper studies several classic carrier frequency offset estimation algorithms for OFDM systems including data-aided and non-data-aided algorithms, and expands the algorithms based on SISO systems to MIMO. Then, the paper gives the simulation and performance comparison results of the time-domain and frequency-domain correlation frequency offset estimation algorithm based on training sequence, the maximum likelihood algorithm based on cyclic prefix, as well as the blind estimation algorithm based on virtual carriers.Thirdly, a brief introduction of main types of measurements including spectrum, transmit power and IQ imbalance is given. Then the main modules of the receiver baseband signal processing including synchronization, channel estimation and equalization, data analysis and EVM calculation are analyzed in this paper. Special attention is given to the analysis and implementation of the timing algorithm as it also belongs to IEEE 802.11ac synchronization technology.Finally, the IEEE 802.11ac RF conformance test platform is implemented and a symbol synchronization algorithm is given in this paper based on the features of IEEE 802.11ac MIMO system. In addition, an improved frequency offset estimation algorithm that gets the frequency offset estimation by the joint linear operation of several estimated values calculated from the time-domain correlation based on the training sequence in IEEE 802.11ac preamble is proposed. Then, the proposed algorithm in this paper is simulated and results prove that the improved coarse algorithm has high stability and it improves the MSE performance at least 3dB compared to the classic method. The proposed fine algorithm makes full use of the cyclic prefix and has high accuracy. The test results show that the synchronization scheme in this paper works better in RF test system.And then a summary of this thesis and a future research prospect are respectively given.