A High Throughput Configurable SDR Detector for Multi-user MIMO Wireless Systems

Abstract

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. On the other hand, with different standards supporting different system parameters, it is crucial for both base station and handset devices to be configurable and seamlessly switch between different modes without the need for separate dedicated hardware units. This challenge emphasizes the need for SDR designs that target the handset devices. In this paper, we propose the architecture and FPGA realization of a configurable sort-free sphere detector, Flex-Sphere, that supports 4, 16, 64-QAM modulations as well as a combination The detector provides a data rate of up to 857.1 Mbps that fits well within the requirements of any of the next generation wireless standards. The algorithmic optimizations employed to produce an FPGA friendly realization are discussed.

Flexible N-Way MIMO Detector on GPU

“…We permutate the channel matrix such that the in-phase and the quadrature parts of the same complex symbol are adjacent neighbors [10]:…”

Low complexity scalable MIMO sphere detection through antenna detection reordering

“…We then permute the real-value decomposed channel matrix such that the in-phase and the quadrature parts of the same complex symbol are adjacent neighbors [5]: In the real-value model, the number of elements in each vector is doubled and both dimensions of the matrixH are doubled. Furthermore, each element of the equivalent transmit vector,s i ; is an element drawn from a finite alphabet X 0 with cardinality Q ¼ ffiffiffiffi ffi M p :For example, the real value decomposed constellation alphabet for QPSK is {-1,1} and Q = 2.…”

“…However, this approximation reduces the BER performance of the detector. To recover some of the performance loss, authors in [5] present a hard decision detector called Flexsphere. While the search process is still SSFE, Flexsphere perform V-BLAST-like antenna reordering and modified real-value decomposition (RVD) to improve BER performance.…”

“…Since a typical wireless system usually combines a softoutput detector and a soft-input decoder to maximize performance, we aim to design a soft output MIMO detector by extending the design outlined in [5]. An existing implementation of the Flexsphere detector [6] for WiMAX shows that the V-BLAST-like preprocessing block uses significant amount of FPGA resources due to matrix inversions, while the QR decomposition and detection blocks combined use significantly less FPGA resources.…”

Reconfigurable real-time MIMO detector on GPU

“…The typical suboptimal MIMO detectors are ASIC designs [2][3][4]. In addition, researchers have investigated many other ways of hardware implementation such as FPGA [5,6] and application-specific instruction set processor (ASIP) [7]. To the best of our knowledge, there are no existing implementations of soft MIMO detector on GPU.…”