Water-Filling in Multi-Carrier Cooperative Diversity

Regarding any performance criterion, power allocation between source and relay in cooperative diversity is of great importance. On the other hand, in frequency selective channels with a multi-carrier modulation, power allocation among sub-carriers arises. A frequency selective channel could be decomposed into a set of flat fading channels by a multicarrier modulation with cyclic prefix. We have developed power allocation among sub-carriers, as well as, between source and relay to maximize the sum capacity. Two more common schemes: amplify-forward (AF) and decode-forward (DF) have been considered. In DF, because of the independence of power allocation between nodes from total supposed power, water-filling is the optimal solution. In AF it is not the case. However, power assignment procedure could be inspired by the DF counterpart in an iterative fashion.