Research On The Reconfigurable MIMO Detection Techniques For WiMAX

WiMAX is a wireless MAN technology base on IEEE802.16e standard, it uses a large number of B3G technologies to improve the performance, such as MIMO (Multiple-Input Multiple-Output), OFDMA (Orthogonal Frequency Division Multiplexing Access), beamforming techniques and etc. This article did some in-depth research in MIMO technology.First, the basic concept of MIMO system, channel capacity of a variety of MIMO systems and the MIMO transmission schemes are introduced in this article, and then the analysis, simulation and summary of the traditional detection methods for V-BLAST system methods.This article did in-depth research in the scenario that the terminal is equipped with only one antenna while the base station equipped with several antennae. Two receiver diversity techniques in the SIMO system are analyzed, which are MRC (Maximum Ratio ComBining) algorithm and IRC (Interference Reduced ComBing) based on different criteria, performance comparison of these two algorithms is also given. Since the covariance matrix of interference may be singular under some situation, detailed analysis of this problem as well as matrix inversion avoiding judgments criteria and schemes are given in this article.In the configuration mode with 1 transmitter antenna and 4 receiver antennae, the biggest problem in the FPGA implementation of the IRC detector is to get the inversion of a 4×4 positive definite Hermitian matrix. Five hardware implementation methods of matrix inversion are analyzed, including two direct inversion methods: blockwise inversion method and algebra cofactor method and three methods by carrying out decomposition before doing the matrix inversion: QR decomposition based on CORDIC technology, SGR algorithm and Cholesky decomposition. Cholesky decomposition is selected as the most appropriate matrix inversion method in the FPGA implementation of IRC compared with other four methods on the aspect of computation complexity, hardware implementation complexity and latency.In order to support 1T2R and 1T4R configuration mode, a design of configurable matrix inversion module is given which can be configured as a 2*2 or 4*4 matrix inversion module.Based on the analysis of algorithms and the knowledge of the WiMAX protocol, An IRC detector is successfully implemented on the FPGA, which is applied in the physical layer of BandAMC zone in the uplink of WiMAX. It can work in the mode 1 transmitter antenna 4 receiver antennae as well as 1 transmitter antenna and 2 receiver antennae by simple configuration; it also supports different modulation types. The details of FPGA implementation of this detector is described as well as the design and solution for resource multiplexing reconfigured design and pipeline operation.The on-board experiments show that working in the WiMAX TDD mode, the implemented IRC detector achieves 3.19Gbps throughput which has very high practical value.