Adaptive resource allocation in composite fading environments

We obtain optimal resource allocation policies for a single user single-carrier system and a multiple-access multi-carrier-CDMA system when the transmitter adapts to the variations in the short-term mean (slow fade) in a combined slow and fast fading (composite fading) environment. For the single user system, we maximize the average throughput achieved by the user, while in the uplink MC-CDMA system, we maximize the sum of average rates of the users in the system. For each system, we find the optimal resource allocation policies for two scenarios. The first is when is system is designed for voice transmission, where the bit error rate (BER) of each user, averaged over the fast fade, is maintained at a desired value. The second is when the system is designed for data transmission, where the BER of each user is maintained below a desired value for a given percentage of time. We find that, for the single-user system, the solution for both the voice and data transmission cases is waterfilling, and that waterfilling is the asymptotically optimal solution to multi-user problems in both scenarios, i.e is nearly optimal for a large number of users. We also find that, when dealing with a voice system, the solution is independent of the distributions of the slow and fast fades and similar to the solutions obtained for noncomposite fading environments (fast or slow fading).