Study On Channel Estimation And Equalization Techniques For IEEE802.11ac Standard

IEEE802.11 series of standard wireless local area network has been widely popular for providing a convenient way of information access and release.Due to requirements of the virtual reality and household streaming media techniques,IEEE802.11 ac standard comes into being,which has the transmission rate up to 7Gbps and supports downlink multi-user data transmission.However,the wireless channels of WLAN systems become very complicated,resulting in the more and more difficulty of channel estimation and equalization in the receiver,with the increaseof the transmission rate and number of antennas,and also the expansion of the system bandwidth.,In this dissertation,the channel estimation and equalization techniques for the IEEE802.11 ac standard are focused on,and the channel estimation and equalization schemes s are proposed.The main contents are as follows:(1)The physical-layer frame structure,signal architecture and TGac channel model for the IEEE802.11 ac are studied.The basic principle and structure of the MIMO-OFDM systemsare also repesented.(2)A general receiver scheme for the IEEE802.11 ac is proposed,which includes multi-antenna reception processing,synchronization,channel estimation and equalization,data demodulation,and so on.Then,the channel estimation technique of training sequence is studied,and an integrated channel estimation scheme is proposed,based on the traditional long training sequence and very high throughput long training sequence.The simulation results show that the channel estimation scheme can be applied to IEEE802.11 ac receiver.(3)The applicability of the pilot-based channel tracking algorithm in the IEEE802.11 ac is studied,where pilots exist in all periods of each OFDM symbol.However,there are some flaws for the algorithm,such as,the number of pilots is smaller than the total number of subcarriers,the pilot pollution between the antennas is serious,and the channel interpolation algorithm is greatly affected by noise.The simulation results show that the channel estimation based on the preamble training sequence is not optimized the pilot-based channel tracking scheme,what is more,the performance of the system receiver is even degraded.Therefore,the conclusion is that the IEEE802.11 ac standard through the preamble channel estimation is appropriate,but that through the pilot channel for tracking is not suitable.(4)The zero-forcing ordered successive interference cancellation(ZF-OSIC)equalization scheme is proposed for the IEEE802.11 ac,since the performances of traditional MIMO channel equalization schemes are easily influenced by the noise.The simulation results show that the proposed scheme outperforms the ZF,especially for the system with large numbers of transmitting antennas.(5)The simulation model of system transceiver link is established.Based on the IEEE802.11 ac standard and TGac channel,the performance of channel estimation and equalization scheme are verified by simulation,which shows that the integration of the LS channel estimation and MMSE channel equalization scheme is suitable.Finally,by comparing the performance of different MCS and different channels,the applicability of channel estimation and equalization scheme to different modulation and different schemes is verified.