Space–Time Codes for Wireless Communications

Abstract

Space‐Time Coding is a new coding/signal processing framework for wireless communications systems with multiple transmit/receive antennas. This new framework offers the best tradeoff between spectral efficiency and power consumption by optimum combination of modulation, coding, and diversity gains over flat‐fading channels. Space‐time trellis codes offer the maximum possible diversity and coding gains without any sacrifice in transmission bandwidth. Their decoding requires a vector Viterbi algorithm. Alamouti‐type Space‐time block codes offer maximum diversity gain, much lower decoding complexity, and full rate transmission but sacrifice coding gain. The first part of this article reviews the fundamentals of space‐time coding for frequency‐flat fading channels. For frequency‐selective fading channels, we describe, in the second part of the article, several competitive joint equalization and decoding schemes for space‐time codes that further exploit the temporal diversity of the channel. Channel estimation issues are also discussed. Exploiting the rich structure of space‐time codes is critical in simplifying the channel estimation, equalization, and decoding schemes.