High performance on the fly reconfigurable MIMO detector

Abstract

Upcoming wireless communication standards such as 802.11n, WiMax etc require support for multiple modulation schemes. These standards all have multiple transmit and receive antennas(MIMO). Hence, the MIMO detector hardware should be able to accommodate different modulation schemes preferably on a single reconfigurable architecture. This paper presents an high performance FPGA implementation of a novel MIMO detector architecture that is able to reconfigure on the fly and provides quasi-optimal Bit Error Rate(BER). The design is implemented in Xilinx Virtex-4, and achieves a sustained throughput of 1.72Gbps for QPSK, 860Mbps for 16-QAM, and 430Mbps for 64-QAM. The total area is approximately 140.26KGates equivalent.Index Terms-MIMO systems, Fixed Sphere Decoding (FSD) Algorithm, On-the-fly Reconfigurability,802.11n. I. EXTENDED SUMMARY A. IntroductionTill date very few dynamically reconfigurable MIMO detectors have been reported in open literature. One implementation that supports reconfiguration is given in [6]. However, the authors in [6] use VBLAST based detection scheme that incurs significant BER degradation and an expensive processor based control unit to manage reconfigurability. Moreover, the design in [6] incurs significant reconfiguration latency which results in interruptions while switching between different modulation schemes. Authors in [7] present a design that is not dynamically reconfigurable. Our detector supports on the fly reconfigurability for QPSK, 16-QAM and 64-QAM modulation schemes. It delivers quasi-ML BER performance with no reconfiguration latency, leading to uninterrupted detection of MIMO symbols. B. MIMO DetectionThe baseband system model for a MIMO system with M T transmit and M R receive antennas can be expressed as follows [1].where s is M T × 1 transmitted vector or vector symbol, n is M R × 1 zero mean complex Gaussian noise vector, and H is a M R × M T -dimensional complex matrix. The (i, j) th element, h ij , of the matrix H denotes the complex channel gain from the j th transmit antenna to the i th receive antenna. In this paper we will assume M T = M R = 4, unless specified otherwise.The objective of the MIMO detection algorithm is to compute an estimateŝ of s such that:where Ω is set of complex entries from the QAM constellation and η is the cardinality of the set Ω.where, R is an upper triangular matrix, and Q H is the Hermitian of a unitary matrix Q[5]. Note that (3) can now be rewritten to form summation across each transmit antenna.