Minimum Rates Scheduling for Ofdm Broadcast Channels

In this paper, we solve the weighted sum rate problem for an orthogonal frequency division multiplexing (OFDM) broadcast channel (BC) under a sum power constraint, if minimum rates have to be guaranteed in each fading state and perfect channel state information (CSI) is assumed at the base station and the mobiles. The problem is subdivided into two problems. First, we tackle the problem of feasibility, which occurs since the system is power limited and not all required rates might be supportable. Subsequently, the optimal resource allocation in case of feasibility is derived. Moreover, the optimal decoding order, which is not determined by the problem formulation itself, is obtained as the ordering of the Lagrangian factors of the main problem. Finally, we show that the problem is closely related to the weighted rate sum maximization and sum power minimization and all three can be interpreted in a unifying framework embedded in a higher dimensionality