Optimal relayed power allocation in interference-free non-regenerative cooperative systems

Consider a fixed wireless TDMA system with non-regenerative relaying capabilities. Since TDMA users are active only during their allocated time slot, we can utilize all the idled users as relays provided that they transmit on different frequency bands. For this TDMA-type cooperative system we show that maximizing mutual information for each user under total power constraint is a strictly quasi-concave maximization problem whose global optimal solution can be found efficiently. In fact, we provide a simple analytic formula for the optimum power allocation strategy, which is reminiscent of the water-filling principle. We also illustrate how the fixed TDMA setup can be extended in order to allow for user mobility.