Heuristic Algorithms to Adaptive Subcarrier-and-Bit Allocation in Multiclass Multiuser OFDM Systems

Subcarrier-and-bit allocation has been extensively investigated in the literature to improve spectral efficiency of multiuser OFDM systems. However, in previous studies, nearly all the studies are focused on single-class service. In this paper, formulation of adaptive subcarrier-and-bit allocation for multiclass multiuser OFDM system is presented. The objective is to maximize the instantaneous total system revenue with the quality-of-service (QoS) of each class guaranteed. Since complexity to the exact solution is generally high and involves solving of nonlinear objective function and constraints, two suboptimal approaches to this problem are presented. The first approach uses a quadratic approximation to the objective function; while in the second approach, a two-step algorithm is developed to obtain the suboptimal solution. The solution is first relaxed to real numbers with some constraints removed before the integer solutions are obtained. The accuracy and complexity of these two approaches are compared with each other as well as with the optimal solution