In a dense deployment of DAPs, transmit power control can mitigate the effects of interference between DAPs on the same channel [20], and increase spatial reuse. Since we do not wish to modify clients, we must do do power control at DAPs alone. However, such unilateral power level can cause the clients and APs to operate at different transmit power levels. Prior work [20] has shown that asymmetric transmit power levels can increase the number of hidden terminals in a WLAN coverage area.
We have implemented and tested several adaptive power management schemes in our testbed. We do not present detailed results due to lack of space. Briefly, our results confirm the observations in [20]. Based on these results, as well as those reported in prior work, we conclude that unilateral power control at DAPs is undesirable, and the best policy is to simply use the maximum power level. A secondary benefit of this scheme is that it provides better coverage in the intended coverage area.
Two other parameters that can also affect the overall WLAN capacity are the Clear Channel Assessment (CCA) threshold used by each DAP [19], and the autorate algorithm implemented on each DAP. The wireless cards we used in our testbed do not allow us to change the CCA threshold. Auto-rating algorithms have been studied extensively by prior research. DenseAP nodes use the autorate algorithm described in [25].
NSDI-2008
