Reliable communication over slow-fading channels under delay constraints

The throughput potential of multiple-input multiple-output (MIMO) channels in fading environments encourages researchers to create new space-time coding architectures without undue complexity. At the same time, the digital wireless communications demand requires careful investigation of fading phenomena under a variety of strongly related practical constraints. In this work we develop a new approach to low-complexity communications over slow flat-fading MIMO channels. Presently the available range of information-theoretic tools cannot fully accommodate the increasingly complicated fading channel models. We define a new fading channel performance measure which allows for the realistic information-theoretic treatment of practical communication systems that are subject to strict delay constraints.; The system we analyze is based on the Bell Labs layered space-time (BLAST) architecture when implemented with so-called horizontal coding (H-BLAST). Its general idea is to partition the data transmitted through the MIMO channel into several single-input single-output (SISO) channels which are called layers. Our proposed scheme differs from H-BLAST on two accounts. First, receiver complexity is reduced by having a fixed order for decoding the layers; second, the transmission rates and powers for the layers are allowed to differ between layers. Within this framework, the layer rates and powers are optimally designed to maximize the outage capacity, resulting in a Rate/Power-Tailored BLAST (RPT-BLAST). Comparing the analytically derived outage capacity of RPT-BLAST to the Monte-Carlo determined outage capacity of H-BLAST, it is found that their performances are similar; depending upon the scenario, either RPT-BLAST or H-BLAST may have a slightly larger outage capacity.; The existing approach to analyzing fading channels is based on the concept of outage capacity, determined by the probability that the channel cannot support a given rate, and it assumes that the codewords are infinitely long. An example of a slowly varying environment is the indoor wireless local area network. The concept of outage comes into play when the fading in such a system is approximated as quasistatic. On the other hand, a broad range of wireless communication systems are delay constrained, which signifies their sensitivity to the amount of time allotted for data transmission. (Abstract shortened by UMI.)...