Research And Application Of Sampling Frequency Estima-Tion On IEEE 802.11ac Protocol RF Conformance Test

Sampling Frequency Offset(SFO) is the sampling frequency deviation due to crystal frequency mismatch between receiver and transmitter, which causes the signal amplitude distortion, phase rotation, and inter-carrier interference(ICI). This paper focuses on the sampling frequency offset estimation algorithm for IEEE 802.11ac RF Conformance Test System. The main contributions of this work are given as follows:This paper introduces the key technology of IEEE 802.11ac. Including the basic principles and key technologies of OFDM. Detailed analysis of the IEEE 802.11ac physical layer protocols is given, including frame format, long training sequence, short training sequence, pilots, as well as IEEE 802.11ac system transceiver model.The existing sampling frequency offset estimation techniques are studied and simulated. A the-oretical model of sampling frequency offset estimation is established to analyze the effects of sampling frequency offset and carrier frequency offset on the system. A variety of joint estimation algorithms of sampling frequency offset and carrier frequency offset are simulated, including fre-quency offset estimation algorithm based on cyclic prefix, frequency offset estimation algorithm based on training sequence, comprehensive frequency offset estimation algorithm and MIMO fre-quency offset estimation algorithm.The technologies of radio frequency conformance testing are introduced. This paper briefly de-scribes the PXI modular RF conformance testing system, including the hardware architecture and software implementation. The main radio frequency test metrics are analyzed. The whole base-band processing system and algorithm realization of each module are introduced.In this paper, the frequency offset estimation algorithms are applied to IEEE 802.11ac system, and some improvements are proposed. Accurate timing synchronization is the premise of good frequency offset estimation. Due to the problem of pseudo multipath effect of the traditional fine synchronization algorithm in MIMO system, this paper proposes an improved fine synchroniza-tion algorithm in MIMO system, which is based on the penalty factor and local integration strategy. Simulation results show that the proposed algorithm can effectively resist the pseudo multipath effect, and the timing synchronization error is much less than that of the traditional algorithm. We propose a maximum likelihood estimation algorithm based on long training sequence, and derive the closed form expression of the carrier frequency offset. Simulation results show that the pro-posed algorithm is better than the existing algorithms and has a low time complexity. The maxi-mum likelihood estimation algorithm is extended to MIMO, and the frequency offset estimation error is also much smaller than that of the existing MIMO joint frequency offset estimation algo-rithm. Recursive least square(RLS) algorithm is applied to the frequency offset tracking of IEEE 802.11ac, and the frequency offset estimation error is very small. Finally, the overall implementa-tion scheme of the joint frequency offset estimation is simulated. The joint frequency offset esti-mation scheme has small estimation error, fast convergence speed and low computation complex-ity.Finally, the research work of this thesis is summarized and prospected.