Throughput Measures for Delay-constrained Communications in Fading Channels
Baraniuk, Richard G.
throughput; fading channels; block fading; outage; capacity
Fading channels, often seen in wireless systems, provide an unfavorable environment for reliable communications. Current methods for evaluating the performance of fading channels include ergodic capacity and <i>epsilon</i>-capacity. Ergodic capacity quantifies the ultimate reliable communication limit of the fading channel. It is only achievable with infinite coding delay, making it impossible to achieve in practice. <i>epsilon</i>-capacity, achievable with finite coding delay, does not provide a measure of error-free communications performance. Since practical communication systems are delay-constrained, it is possible to retransmit codewords when errors occur. We provide a new analysis framework that accounts for codeword retransmission in the analysis of fading channels. We introduce new measures, maximum zero-outage throughput and maximum <i>epsilon</i>-throughput, that predict the performance of practical systems and show that ergodic capacity and <i>epsilon</i>-capacity are special cases of our definitions. We also provide a measure that characterizes the performance of a system with more complex receiver design, using "incremental diversity" to improve throughput.