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An asymmetric 2×2 space-time code with linear maximum-likelihood decoder complexity

Multiple-input multiple-output (MIMO) techniques have been incorporated in all of the recently developed wireless communications systems standards including the IEEE 802.11 n standard for local area networks and the IEEE 802.16 e standard on which mobile WiMAX systems are based. The main criteria in conventional space-time code (STC) design for MIMO systems are the code rate, diversity order, and coding gain. Recently, the optimum decoder complexity was added to this list of criteria and the attention was turned to the design of STCs with low decoder complexity. Specifically, the effort in full-rate 2times2 STC design focused on designing codes whose optimum decoder complexity grows only quadratically with the size of the signal constellation, and such a design was proposed by the present authors. Proceeding further, a related STC of rate-3/4 and whose optimum decoder complexity grows only linearly with the constellation size was also proposed. In the present paper, we introduce another interesting high-rate and low complexity 2times2 STC design. The new code has a linear optimum decoding complexity and its rate is higher than 3/4.