An Iterative SISO Improved Complex Sphere Detection and Decoder for Turbo-MIMO Systems

An iterative soft-input soft-output (SISO) improved complex sphere detection and decoder algorithm is proposed for signal detection in Turbo-MIMO system. It forms candidate points set Θ in terms of an accumulated cost function based on a search arc constrained by the received signals. Then, the candidate points subset, the lower cost bound of which is not smaller than upper bound, is fathomed and dropped from further consideration. Meanwhile, once a new feasible candidate point is turned up, the path closest to completion is casted upon to generate the set Θ with optimal candidate vectors, aiming to determining the extrinsic information for a Turbo coded bit with most likelihood. Bridged by de-multiplexing and multiplexing, an SISO improved complex sphere detection is concatenated with a SISO Log maximum a posteriori Turbo decoder as if a principal Turbo detection is embedded with a subordinate Turbo decoder, exchanging each other’s detection and decoding soft-decision information iteratively. As a result, the proposed algorithm converges rapidly, which results in lower computational complexity. The transfer curves that relate the input mutual information to the output mutual information is achieved through simulations. Thus, an asymptotic interval of the input SNR threshold for the proposed scheme to converge has been observed. Finally, an upper bound of the diversity has been obtained based on the intuitional deduction and theoretical analyses. The simulation results also show that the proposed scheme has a strong ability of anti-multi-stream interference, and its performance is close to that of the iterative soft-input soft-output list complex sphere detection and decoder algorithm, but with a shorter time delay.