Two complex orthogonal space-time codes for eight transmit antennas

Two complex orthogonal space-time codes for eight transmit antennas" (2004). Two new constructions of complex orthogonal space-time block codes of order 8 based on the theory of amicable orthogonal designs are presented and their performance compared with that of the standard code of order 8. These new codes are suitable for multi-modulation schemes where the performance can be sacrificed for a higher throughput. Introduction: Transmit antenna diversity can be accomplished with the use of space-time codes (STCs) [1]. Out of the STCs, space-time block codes (STBCs) developed from the amicable orthogonal designs [2] lead to the simplest receiver structures and minimum processing delays if combined with modulation schemes having complex signal constellations, such as in the case of quaternary phase shift keying (QPSK) or quadrature amplitude modulation (QAM). The simplest STBC based on amicable orthogonal designs is an Alamouti code [1] providing a transmission rate of 1 for the two transmit antenna system. STBCs based on amicable orthogonal designs, usually referred to as complex orthogonal STBCs, for a larger number of transmit antennas cannot provide the transmission rate of 1 but they are attractive nevertheless since they can provide a full diversity for the given number of transmit antennas and are usually simple to decode. There exist some complex orthogonal STBCs designs for four transmit antennas and eight transmit antennas , e.g. [3], providing the rates of 3=4 and 1=2, respectively. They are usually based on those amicable orthogonal designs where each variable is represented just once in a design. Hence, the code matrices have many zeros (50% for eight transmit antennas) resulting in many time slots when no useful information is being transmitted. In this Letter, we introduce two new complex orthogonal STBCs for eight transmit antennas having less unused time slots. In the first of these new codes, one of the variables is repeated twice and in the second code, one variable is repeated four times per every transmit antenna. These properties can be further exploited to increase the code rate over 1=2 using more sophisticated modulation schemes, where the higher number of information bits is associated with those signals that appear in more than one time slot per each antenna.