Design of Closed-Loop Space-Time Codes with MMSE Receivers

In recent years, research on closed-loop STCs show that with the help of feedback, the achievable rate and/or the diversity order can further be improved in space-time coded systems. In this paper, we study on the optimal closed-loop STCs with low-complexity receivers and any amount of feedback. A unified framework for designing closed-loop STCs is firstly proposed by extending the conventional linear dispersion codes to the cases with feedback. Then a new design method is proposed, where the stochastic gradient descent algorithm is employed to obtain optimal set of LDC candidates particularly for space-time coded systems with linear minimum mean square error (MMSE) receiver. The proposed method allows for flexible system parameters such as the number of transmit/receive antennas, modulated symbols and the length of codewords thus include most of the existing closed-loop STCs. Simulation results confirm the advantages of the newly-proposed design method of closed-loop STCs.