Flex-Sphere: An FPGA Configurable Sort-Free Sphere Detector For Multi-user MIMO Wireless Systems
Cavallaro, Joseph R.
Spatial division multiplexing (SDM) in MIMO technology significantly increases the spectral efficiency, and hence capacity, of a wireless communication system: it is a core component of the next generation wireless systems, e.g. WiMAX, 3GPP LTE and other OFDM-based communication schemes. Moreover, spatial division multiple access (SDMA) is one of the widely used techniques for sharing the wireless medium between different mobile devices. Sphere detection is a prominent method of simplifying the detection complexity in both SDM and SDMA systems while maintaining BER performance comparable with the optimum maximum-likelihood (ML) detection. There are several approaches for realizing sphere detectors, and the algorithmic landscape is rich with methods that enable the designer to make various tradeoffs between performance, e.g. throughput of the wireless channel, BER, and implementation complexity, e.g. silicon area for an ASIC implementation or FPGA resource envelope for an FPGA implementation. This paper describes the FPGA realization of a configurable and flexible sort-free sphere detector, Flex-Sphere, that supports 4;16;64-QAM modulations as well as a combination of 2;3 and 4 antenna/user configuration for uplink transmission. The detector provides a data rate of up to 849:9 Mbps. The algorithmic optimizations employed to produce an FPGA friendly realization are discussed.