Research On Pilot Synchronization For Millimeter-Wave WLAN

With the development of all kinds of wireless business requirements and the popularity of intelligent terminals, low frequency bands are more crowded, not only does the next generation of wireless local area network (WLAN) system needs to provide wider network services, but it needs to support the real-time business at a higher rate. The current WLAN systems can not fully meet these requirements, so in 2012, the institute of electrical and electronics engineers (IEEE) 802.11 standardization organization, according to the millimeter-wave bands submitted by China, founded the working group of IEEE 802.11 aj. In order to support Gbps implementation in less crowded bands and provide a better network performance, the group is working hard on the next generation of WLAN standard in millimeter-wave bands in China. Due to its higer carrier frequency, millimeter-wave makes the carrier frequency offset bigger. Compared to low frequency bands, millimeter-wave bands are more susceptible to nonlinear and the limitation of device manufacture craft, which brings about that millimeter is seriously influenced by phase noise in the high modulation. All of these factors result in that the synchronization of millimeter-wave is more difficult. Based on the latest IEEE 802.11 aj orthogonal frequency division multiplexing (OFDM) system, this thesis studies how to use pilot to improve the performance of WLAN OFDM system in the millimeter-wave bands, from the angle of how to use pilot to remove frequency offset and phase noise. The main works are as follows:First, this thesis states the basic principle of OFDM system and its structure model in detail, and analyses the influence of the carrier offset, sampling clock frequency offset and phase noise on the performance of OFDM receiver. Based on the study of the relevant frame structure of the physical layer and the physical simulation model of IEEE 802.11 aj, a solid theoretical basis is provided for the analysis and simulation of pilot synchronization algorithm.Secondly, this thesis proposes a new algorithm to optimize the pilot position. From the angle of how to use pilot to do sampling frequency synchronization and the residual phase tracking, the algorithm makes use of pilot frequency interval to optimize pilot position. On the basis of the IEEE 802.11 aj frame format, this thesis uses the method of numerical simulation to make performance analysis of the proposed algorithm. Numerical simulation results show that, under the condition of without increasing system complexity, the proposed algorithm can significantly improve the system performance.Finally, on the basis of discuss of the existing phase noise generation model, this thesis proposes a phase noise model, which conforms to the characteristics of 45 GHz millimeter-wave, and simulates how this model affects OFDM system. Then this thesis studies phase noise suppression algorithms in the WLAN OFDM system, and concludes the compromise between the accuracy and complexity of existing phase noise suppression algorithms in WLAN OFDM system. Therefore, this thesis proposes an algorithm, which makes use of the phase noise’s low pass character in frequency domain. Compared with the iteration algorithm, which makes use of pilot and data, the proposed algorithm reduces the computational complexity under the condition of keeping system performance.