  Rate adaptation in 802.11 WLANs has 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 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. Our results provide the means
to design novel rate adaptation schemes that takes energy consumption into
account.
