We started by showing that, in the presence of rate diversity, the throughput-based fairness notion implemented by the 802.11's popular MAC protocol and the traditional queuing schemes at the APs leads to a situation in which the aggregate throughput is determined largely by the slowest node.
We next presented a time-based notion of fairness that provides an equal
amount of long-term channel occupancy time to each competing node. This
prevents faster nodes from being dragged down by slower ones. Moreover,
it satisfies what we called the baseline property, i.e., the
achieved throughput of any competing node in a multi-rate WLAN is equal
to what it would achieve in a single-rate WLAN in which all competing
nodes transmit at its data rate. In the presence of rate diversity,
using this definition of fairness can lead to vastly improved aggregate
network throughput, more than 
in some realistic scenarios.
We next described a practical scheme called TBR that works in conjunction with any MAC protocol to provide long-term time-based fairness in AP-based WLANs by appropriately scheduling packet transmissions. We showed that TBR can be implemented in an AP driver in a way that is backwards compatible with existing 802.11 standard. We implemented our scheme in the Linux Hostap driver running on a PC used as the AP, and evaluated it through a series of experiments. In the absence of rate diversity, the performance of our implementation is equivalent to the standard implementation. In the presence of rate diversity, it achieves the predicted gains.
In today's AP-based 802.11b WLANs, rate diversity is already common as our trace analyses show. As newer standards such as 802.11g are deployed, the problem will become worse. For an extended period of time 802.11 WLANs will run in a mixed mode, and if 802.11g clients are slowed down to run at the rate of 802.11b clients, there will be little incentive to upgrade. Already, some vendors, e.g., D-Link and Netgear, are beginning to implement ad hoc proprietary mechanisms to give their 802.11g priority over 802.11b cards in accessing the channels. A more systematic cross-manufacturer solution would be preferable. We believe that switching to time-based fairness is a good option.