Throughput Measures for Delay-constrained Communications in Fading Channels
Baraniuk, Richard G.
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.