SPECTRAL EFFICIENCY BOUNDS FOR ADAPTIVE CODED MODULATION WITH OUTAGE PROBABILITY CONSTRAINTS AND IMPERFECT CHANNEL PREDICTION

Adaptive coding and modulation (ACM) is a technique designed to combat the temporal variations of (slow) multipath fading channels. The main objective of an ACM scheme is to improve the spectral efficiency (SE) while accommodating a predefined bit error rate. The av rage spectral efficiencyof an ACM scheme can be measured against the channel capacity for idealized conditions such as perfect knowledge of future states of the communication channel, the ability to instantly change channel code when the channel quality changes, and use of infinitely many channel codes of arbitrary length. Clearly, these conditions do not hold for a practical system. In this paper we shall present upper bounds on the SE of an ACM scheme that take into account imperfect knowledge of the channel state information, and a limited number of codecs. These bounds are also found for a given constant of the outage probability.