Exact and heuristic solutions to adaptive subcarrier-and-bit allocation in multiclass multiuser OFDM systems

Subcarrier-and-bit allocation (SBA) has been extensively investigated in the literature to improve spectral efficiency of multiuser OFDM systems. In this paper, the analysis of adaptive SBA for multiclass multiuser OFDM systems which is generally formulated as a nonlinear integer programming problem is presented, whose solution is highly intricate. Some measures are conducted to ensure convexity and to reduce computational complexity, and the optimal solution to the modified equivalent problem is derived. The instantaneous total system revenue is maximized with the quality-of-service (QoS) in terms of data rate and bit error rate of each class guaranteed. The quadratic fitting scheme is further proposed. to speed up the computation without significant performance penalty. We also discuss how to choose the system parameters appear in the objective function to facilitate the resource allocation.