Research On Synchronization Technology Of PHY Layer In Next Generation WLAN

ABSTRACT:The rapid growth of mobile Internet and the mobile terminals, promote the development of wireless communication. Many researches work to improve the performance of the wireless local area network (WLAN), since it is one of the most important branches of wireless communication. To increase the throughput of WLAN, the next generation of WLAN standard, i.e., IEEE802.11ax has been researched and formulated based on the latest WLAN standard, i.e., IEEE802.11ac in April2014,, which is first to take the technology of OFDMA to implement MU-MIMO.802.11ax the inheritance and development of802.11ac, and it is not simply to improve the whole network throughput, but will focus on the throughput of each user and equipment intensive distribution user experience. Since OFDMA is development of OFDM, meanwhile, OFDM-MIMO system synchronization research is very popular. In order to realize the UL MU-MIMO synchronization, which includes time synchronization and frequency synchronization, the time synchronization include frame synchronization and symbol synchronization, the research of the IEEE802.11ac would be centralized in this paper.The synchronization algorithms used in802.11ac standard and the existing ones, are all power algorithm, which calculate square on correlation vectors. Here we use threshold remove noising method. For each value of correlation vector, if it is smaller than the threshold, we set it to0. This algorithm reduces the square calculation with good performances.For time synchronization, we use VHT-LTF to calculate precise synchronization, at the same time, we use the Zadoff-Chu sequences as frequency domain generation sequences, which is due to this sequences have good auto-correlation and low cross-correlation. In addition, ZC sequences have low PAPR, which is good for OFDM system. We use ZC sequences to generate an initial sequence, and then distribute different users with different numbers of cyclic shift on the initial sequence, this way can accurately distinguish each user at receiver.For frequency synchronization, this paper uses OFDMA method, the distribution of different subcarriers to different users, which can increase the spectrum utilization rate. For initial frequency synchronization, we use the previous standard method, which use L-STF, for precise frequency synchronization, we estimate it with VHT-LTF, which can reduce the complexity. At the same time, we increase one VHT-LTF to estimate frequency offset, which can make the frequency offset estimation more accurate and reliable. According to the result of simulation in single user1×1system, the PER can have a gain of1dB, gain of2-3dB2×4and4×8MIMO scenarios.