High-rate full-diversity space-time block codes for three and four transmit antennas

In this paper, we deal with the design of high-rate, full-diversity, low maximum likelihood (ML) decoding complexity space-time block codes (STBCs) with code rates of 2 and 1.5 complex symbols per channel use for multiple-input multiple output (MIMO) systems employing three and four transmit antennas. We fill the empty slots of the existing STBCs from CIODs in their transmission matrices by additional symbols and use the conditional ML decoding technique which significantly reduces the ML decoding complexity of non-orthogonal STBCs while ensuring full-diversity and high coding gain. First, two new schemes with code rates of 2 and 1.5 are proposed for MIMO systems with four transmit antennas. We show that our low-complexity rate-2 STBC outperforms the corresponding best STBC recently proposed by Biglieri et al. for QPSK, due to its superior coding gain while our rate-1.5 STBC outperforms the full-diversity quasi-orthogonal STBC (QOSTBC). Then, two STBCs with code rates of 2 and 1.5 are proposed for three transmit antennas which are shown to outperform the corresponding full-diversity QOSTBC for three transmit antennas. We prove by an informationtheoretic analysis that the capacities of new rate-2 STBCs for three and four transmit antennas are much closer to the actual MIMO channel capacity than the capacities of classical OSTBCs and CIODs. Index Terms – MIMO systems, space-time block codes, decoding complexity, channel capacity. * Manuscript received on 20th June 2008, revised on 20th January 2009. This paper is a postprint of a paper submitted to and accepted for publication in IET Communications and is subject to IET copyright. The copy of record is available at IET Digital Library.