A transmit-diversity coding framework for cellular systems

Space-time (ST) coding is an efficient technique for combatting short-term fading in telecommunication systems with multiple transmit antennas. This paper presents a multi-dimensional framework for such a system that contrasts two approaches for assigning signal dimensions to antennas. With aggregate transmit antennas (ATA), a dimension is employed by all the antennas while in orthogonal transmit antennas (OTA), each dimension is employed by a single transmit antenna. We provide a diversity order analysis for repetition codes and Tarokh-Seshadri-Calderbank (see IEEE Transactions on Information Theory, vol.44, p.744-64, 1998) codes within our framework over a spatially uncorrelated, block-fading Rayleigh channel. Simulation results for repetition, TSC, and classical convolutional codes using both OTA and ATA transmission are presented. With ATA, classical convolutional codes perform comparably to the known TSC codes, while with OTA diversity gain is easier to obtain than with ATA. All the codes that were considered in this work with OTA show performance gains with respect to ATA.