A high-rate full-diversity 2x2 space-time code with simple maximum likelihood decoding

Multiple-input multiple-output (MIMO) techniques have become an essential part of broadband wireless communications systems. For example, the recently developed IEEE 802.16e specifications for broadband mobile wireless access include three MIMO profiles employing 2x2 space-time codes (STCs) and two of those, namely, Alamouti's STC for transmit diversity, and the 2x2 spatial multiplexing (SAP scheme, are mandatory on the downlink of Mobile WiMAX systems. The first of these has full diversity but it is only half-rate, while the second is full rate but suffers from diversity loss. In this paper, we develop a full-diversity STC of size 2x2, which represents an interesting trade-off between these two schemes. More specifically, the presented code is of rate 3/4, it has full diversity, and it leads to simple maximum-likelihood (ME) detection whose complexity grows only linearly with the size of the signal constellation This makes it a suitable candidate for future evolutions of broadband wireless systems toward higher data rates and performance.