Abstract
Methods for providing good spectral efficiency, without
disadvantaging the delivered quality of service (QoS), in
time-varying fading channels are presented. The key idea is to
allocate system resources according to the encountered channel.
Two approaches are examined: variable-size burst construction, and
adaptive modulation. The first approach adapts the burst size
according to the channel rate of change. In doing so, the
available training symbols are efficiently utilized. The second
adaptation approach tracks the operating channel quality, so that
the most efficient modulation mode can be invoked while
guaranteeing a target QoS. It is shown that these two methods can
be effectively combined in a common framework for improving system
efficiency, while guaranteeing good QoS. The proposed framework is
especially applicable to multistate channels, in which at least
one state can be considered sufficiently slowly varying. For such
environments, the obtained simulation results demonstrate improved
system performance and spectral efficiency.