Understanding the Limitations of Transmit Power Control for Indoor WLANs

摘要

A wide range of transmit power control (TPC) algorithms have been proposed in recent literature to reduce interference and increase capacity in 802.11 wireless networks. However, few of them have made it to practice. In many cases this gap is attributed to lack of suitable hardware support in wireless cards to implement these algorithms. In particular, many research efforts have indicated that wireless card vendors need to support power control mechanisms in a fine-grained manner - both in the number of possible power levels and the time granularity at which the controls can be applied. In this paper we claim that even if fine-grained power control mechanisms were to be made available by wireless card vendors, algorithms would not be able to properly leverage such degrees of control in typical indoor environments. We prove this claim through rigorous empirical analysis and then build a tunable empirical model (Model-TPC) that can determine the granularity of power control that is actually useful. To illustrate the importance of our solution, we conclude by demonstrating the impact of choice of power control granularity on Internet applications where wireless clients interact with servers on the Internet. We observe that the number of feasible power was found to be between 2-4 for most indoor environments. We believe that the results from this study can serve as the right set of assumptions to build practically realizable TPC algorithms in the future.