Key Technology Research And Verification Of Time-Frequency Sychronization For 4 Channel IEEE 802.11ac Signals

In order to meet the high-bandwidth and high-quality network services,IEEE released the 802.11 ac standard in 2013.The IEEE 802.11 ac standard operates in the band of 5.170GHz~5.835 GHz.Combining MIMO technology,it supports a maximum data bandwidth of 160 MHz and a theoretical transmission rate of 1Gbps.Because the physical layer of 802.11 ac standard adopts orthogonal frequency division multiplexing technology,the receiver is very sensitive to time deviation and frequency deviation,so the synchronization problem is the primary solution to ensure high-speed and reliable transmission.This paper studies the time-frequency synchronization technology of 4 channals 802.11 ac signals,and uses the Non-HT Long Training field(L-LTF)of the 802.11 ac data frame to design a 4 channals time-frequency synchronization algorithm for centralized MIMO,which is implemented on the hardware platform.Firstly,this paper introduces the frame structure of the Very High Throughput(VHT)mode and key technology in the IEEE 802.11 ac physical layer.The multi-antenna technology of 802.11 standard is simply analyzed,and the existing time-frequency synchronization technology of 802.11 signal is studied and summarized.Then we analyze the Doppler shift and coverage,and give system performance indicators.Secondly,this paper puts forward a method of time-frequency synchronization based on the L-LTF field of 802.11 ac frame and gives the derivation of this algorithm,and the performance of the synchronization algorithm is simulated.It is showed in the result that,when SNR=35dB,the time synchronization accuracy is limited in 1% of the OFDM symbol and the frequency synchronization error is limited in 0.016% of the subcarrier spacing,and finally frequency offset estimation ranged over-156kHz~156kHz.Thirdly,the overall implementation scheme of the time-frequency synchronization algorithm is designed.The structure and processing flow of the divided sub-modules are introduced respectively.Taking the simulation link as a reference,the modules are implemented on FPGA.Then the resource consumption is given in this paper.Finally,the synchronization algorithm is tested on the 4T4R-802.11 ac hardware platform,which includes functional and performance tests.The result shows that,the functions of the time-frequency synchronization module all meet the requirements.The packet error rate of the QPSK link can limited in 10% when the SNR is 12 dB,13dB,16 dB,17dB for 1T1 R,2T2R,3T3 R,4T4R test scenarios.Furthermore,the packet error rate of the 256 QAM link can limited in 10% when the SNR is 29 dB,32dB for 1T1 R,2T2R test scenarios.This article studies the time-frequency synchronization technology of 802.11 ac signals for a 4x4 centralized MIMO model.The synchronization algorithm is successfully verified on the hardware platform.This study provides engineering reference to the application of 802.11 ac multi-antenna technology.