Utility maximization for OFDMA systems over discrete sets

The main task in OFDM downlink scheduling design is to maximize some kind of utility considering user specific as well as system induced constraints. A typical example is the weighted sum rate maximization under a sum power constraint and possibly additional rate requirements. A major challenge is to incorporate the fact that in real systems the number of modulation depths and coding schemes is limited due to technical conditions. Thus, the scheduling problem results in a discrete optimization problem with non-differentiable non-convex objective. In this paper a new approach is presented that can deal with this kind of constraints in a general way. By transforming the discrete problem in a suitable weight matching problem an efficient algorithm which is easy to implement is devised. The performance of this algorithm is evaluated by simulations with parameters obtained from the recently proposed OFDM-HSDPA concept [1].