On Optimization of CSMA/CA based Wireless LANs: Part II - Mitigating Efficiency Loss

Most current deployments of IEEE 802.11 based wireless LANs suffer from various inefficiencies arising from the interactions of MAC and Physical layers. These inefficiencies often limit network users from reaping the full potential of the high physical data rates in these systems. We consider optimizing these systems to mitigate, the following forms of inefficiencies: (i) selfish users exploiting the dependency of DCF channel share achieved on the transmission strategies used, leading to inefficient operating points (Nash Equilibria) (ii) Automatic rate adaptation enabled devices reducing the system throughput even for moderate loads, and, (iii) low data rate users limiting the throughput of high data rate users. In the companion paper, we have proposed adapting CWmin and disabling Exponential Backoff as a simple paradigm of operating CSMA/CA. We show that such a technique is effective in reducing the penalty due to selfish link adaptation and auto rate adaptation. Finally, we propose using multiple channels to improve the throughput of high data rate users. We show that the system throughput can increase super-linearly with the number of channels, with increased benefit when OFDM based IEEE 802.11g high rate users co-exist with low rate IEEE 802.11b users.