Throughput performance of adaptive modulation in cellular systems

Adaptive modulation techniques have the potential to substantially increase the spectrum efficiency and to provide different levels of service to users, both of which are considered important for third generation cellular systems. In this work, we propose a general framework to quantify the potential gains of such techniques. We characterize the optimum throughput of the system with adaptive modulation and power control, and then propose an iterative algorithm that converges to this optimum. Numerical analysis shows that (i) adaptive modulation even without power control has significant throughput advantage over SIR-balancing power control; and (ii) the proposed iterative algorithm converges to the optimal in very few steps. The first observation is especially important from an implementation point of view. Adjusting the modulation level without changing the transmission power does not involve the repeated measurements and feedback, which significantly simplifies the implementation. This work provides valuable insight into the performance of adaptive modulation in multi-user environments.