  Rate adaptation and transmission power control in 802.11 WLANs have received
a lot of attention from the research community, with most of the proposals
aiming at maximising throughput based on network conditions. Considering energy
consumption, an implicit assumption is that optimality in throughput implies
optimality in energy efficiency, but this assumption has been recently put into
question. In this paper, we address via analysis, simulation and
experimentation the relation between throughput performance and energy
efficiency in multi-rate 802.11 scenarios. We demonstrate the trade-off between
these performance figures, confirming that they may not be simultaneously
optimised, and analyse their sensitivity towards the energy consumption
parameters of the device. We analyse this trade-off in existing rate adaptation
with transmission power control algorithms, and discuss how to design novel
schemes taking energy consumption into account.
