Capacity Aspects of Bit Interleaved Coded Modulation

Abstract

Space-time block codes are a recently discovered, attractive modulation scheme for multiple antenna wireless channels. They are capable of providing full diversity over fading channels, at the same time requiring only low computational costs. Over the last few years, several distinct approaches to designing space-time codes have been proposed in the literature, including the layeredarchitecture, trellis codes, turbo codes and the orthogonal designs. Most work on space-time coding has focused on the problem of designing codes to perform well under quasi-static fading conditions. In practice, it is not unusual for a cellular handset to experience conditions which range from fast fading to nearly static within seconds (e.g., a vehicle suddenly braking). It is therefore of interest to design codes that are robust in the sense, that they perform well under a wide variety of channel fading conditions. A robust coding architecture called Bit-Interleaved Space-Time Coded Modulation is proposed for channels with multiple transmit and receive antennas. It is designed to perform well under a wide variety of channel fading conditions and which (when differentially encoded) does not require accurate channel estimates at the receiver. The architecture combines serial concatenation of short, full-diversity space-time block codes (inner code) with bit-interleaved coded modulation.This thesis examines the capacity aspects of this architecture namely, the ergodic capacity, the outage capacity and the ergodic and outage cut-off rates in Rayleigh flat-fading channels. It is shown that, if the inner block codes are chosen properly, not only is the capacity close to the information-theoretic limits, but also a better tradeoff between performance and coding complexity can be obtained.