Hardware Implementation And Multi User Transmission Method Of Broadband Ultra-high-speed WLAN

With the rapid development of the wireless communication technology and the popularity of smart terminals,WLAN has become more and more important in people's daily life.Through introducing new technologies and improving the channel bandwidth,the transmission rate of IEEE802.11 ac protocol can achieve gigabit per second.This greatly meets people's demand for wireless transmission speed under several scenes like work,entertainment,video games,etc.This paper mainly studies the key modules of timing synchronization,frequency synchronization and the downlink multi-user transmission method based on IEEE802.11 ac protocol.Besides,we use NI-PXI hardware platform for the actual programming test.The main work of the paper is introduced as follows:1.The IEEE802.11 ac physical layer specification is described in detail,including the improved technologies adopted by IEEE802.11ac,the physical layer transmission frame format and the baseband signal processing of the transmitter and receiver.2.Based on IEEE802.11 ac protocol and NI-PXI hardware platform,we research two key modules of the receiver which are timing synchronization and residual phase tracking.1)A robust timing synchronization scheme is proposed.All the receiver antennas judge the arrival of packet data jointly and do symbol synchronization independently.This improves the robustness under the boundary conditions.In the system which has four transmitting antennas,four receiving antennas and 40MHz bandwidth,the hardware implementation are carried out.2)In the actual system which has two transmitting antennas,two receiving antennas and 20MHz bandwidth,a new type of pilot insertion method and an improved residual phase tracking algorithm are proposed and realized.The pilot insertion method has a reset signal and is suitable to WLAN system.The residual phase tracking algorithm solves the tailing problem of constellation.Simulation results and hardware testing results show that the algorithm reduces the bit error rate of the receiver.3.Based on IEEE802.11ac protocol and NI-PXI hardware platform,we research the WLAN downlink multi-user system design and hardware implementation.In the system,the base station is equipped with four transmitting antennas.The system has two users and each user is equipped with two receiving antennas.Firstly,the performance of three precoding schemes is simulated.Then,we put forward an implementation scheme of the downlink multi-user system and prove its feasibility by making a system-level software simulation.Three kinds of matrix nullspace solving methods are introduced for the core precoding module.Hardware resource consumption analysis and algorithm latency evaluation of three solutions are calculated in the development environment of LabVIEW 2013.Finally,key modules of the transmitter and receiver are implemented and tested in the FPGA of NI-PXI hardware platform.4.The four-in four-out,40MHz bandwidth downlink hardware implementation is finished at the NI-PXI hardware platform.This paper mainly introduces the transmission architecture of data stream,the difficulty in the system design and implementation.Finally,this paper shows the constellation and video stream transmission using BPSK,QPSK and 16QAM mapping methods.