Reduced complexity two-stage approximate sorting Fixed Complexity Sphere Decoder with real-valued lattice formulation for MIMO system

This paper presents a multiple-input multiple-output (MIMO) decoder which combines fixed complexity sphere decoder (FSD) algorithm with a new real-valued lattice formulation to simultaneously improve the throughput, bit error rate (BER), complexity and power. A pair-wise sorted QR decomposition (P-SQRD) approach is also introduced to enhance the lattice searching efficiency and BER while preserving important characteristics of the real-valued lattice structure. Two-stage approximate sorting scheme with minimum data swapping is adopted to intelligently trade-off the number of paths to be visited at each lattice level and further reduce complexity and power. The proposed MIMO decoding algorithm achieves 20% reduction in the overall complexity compared to the other constant throughput SDs [3]-[4] for a 4times4 MIMO system with only minor BER degradation.