Strongly robust adaptive signaling for time-varying channels

In this paper, the development of robust adaptive signaling schemes is considered for communication systems that have outdated estimates of a fading channel available at the transmitter. After briefly reviewing pertinent design criteria for both systems employing adaptive trellis coded modulation and systems employing adaptive uncoded quadrature amplitude modulation (QAM), results are presented for these systems when only a single outdated fading estimate is available. The desire to extend the observed bandwidth efficiency gains to systems operating over channels that exhibit higher rates of variation motivates the non-trivial consideration of robust adaptive signaling schemes for systems that employ multiple outdated fading estimates. Under each of two adaptive signaling schemes, results are presented for a system that employs adaptive uncoded QAM and multiple outdated fading estimates; the latter of the two schemes explicitly guarantees the desired strong robustness criterion and demonstrates for a simple uncertainty class the ability to extend bandwidth efficiency increases to systems operating over channels that have higher rates of variation.