Research And Implementation Of Key Transmission Modules In Ultra-High-Speed WLAN System

Wireless local network (WLAN) has become one of the standard configurations of intelligent terminals nowadays, people have put higher expectation on communication quality and transmission rate of WLAN. With the development of the new generation of very high throughput IEEE 802.11ac standard, market demand for 802.11ac devices has increased dramatically, as a result, investigations on the ultra-high-speed WLAN system and its transmission modules from an implementation point are of important application value and practical significance.This paper mainly studies and designs the key transmission modules of the ultra-high-speed WLAN based on IEEE 802.11ac standard, furthermore, the paper realizes the transmitter of the WLAN system with 4×4 antennas and 40MHz bandwidth on the NI-PXI platform. The main work can be described as follows.Firstly, the physical layer technologies of IEEE 802.11ac with high throughput performance are studied. The paper specifically describes the frame structure of 802.11ac physical layer, then uses 40MHz channel bandwidth as an example to discuss the physical layer characteristics with high transmission bandwidth such as subcarrier design and frame structure, on this basis, the paper introduces the transmitting and receiving process on physical layer of 802.11ac, which provides standard support for the hardware design and implementation.For the LDPC coding module in 802.11ac physical layer transmission, the paper introduces several common LDPC coding algorithms such as direct linear coding, Gaussian elimination coding and approximated lower triangular matrix coding, and then simplifies the approximated lower triangular coding algorithm by exploiting the special structure of parity check matrix in 802.11ac to design a coding scheme of low computation complexity. Furthermore, based on the simplified scheme, the paper takes the dual feedback shift registers structure as the core to implement LDPC coding module of high throughput and low hardware resource consumption on the NI-PXI platform, and verifies the proposed scheme.For the precoding module in ultra high-speed WLAN system, the paper discusses two SVD precoding algorithms which are suitable for hardware implementation:two-side Jacobi algorithm and the algorithm based on Hermitian matrix eigen value decomposition. Then an improved SVD algorithm based on iterative EVD by minimum sum of rows is proposed to reduce the number of iterations and therefore to reduce the computational complexity. The paper also carriers out hardware design and implementation of 4×4 SVD precoding module on the NI-PXI platform, and verifies and analyze its performance from both software simulation and hardware test.Finally, the paper introduces NI-PXI platform, and then designs WLAN transmitter of 4×4 antennas and 40MHz bandwidth on NI-PXI based on 802.11ac standard. The system architecture and data communication process are analyzed, and all the modules of the transmitter in FPGA are specifically carried out, including preamble generating, channel coding, stream parsing, constellation mapping, pilot inserting, IFFT, cyclic prefix adding and cyclic shift delay operating. The paper lastly verifies the realized system by constellation test and video stream transmitting demonstration.