We note that the general idea of temporal sharing in the context of multi-rate WLANs has been mentioned before by Sadeghi et al. [23]. They have proposed an opportunistic rate adaptation scheme (called OAR) that achieves significant throughput gain over previously proposed rate adaptation schemes [11,16]. The key idea behind OAR is to allow nodes that have high-quality channel condition to transmit more than one packet at a time taking advantage of time-correlated channel conditions. OAR simply allows a node that can transmit at 11 Mbps 5 times more opportunities than the node transmitting at 2 Mbps. OAR justifies this by saying that nodes are achieving similar time-shares as when they both are transmitting at 2 Mbps. OAR is a DCF-based protocol mainly intended for ad hoc networks and requires modifications to DCF. Unlike AP-based networks, ad hoc networks, in which nodes communicate with each other without using access points, are more suitable when communications among wireless nodes are dominant or no wired infrastructure exists. In contrast, AP-based networks are designed for communications among wireless nodes and other nodes that can be reached via a wired infrastructure to which APs are connected.
Unlike the previous work, we investigate and explain the differing impacts of the fairness notions on the network performance and our work focuses on providing fair time shares among competing client nodes in AP-based 802.11 networks in which the queuing scheme at the AP significantly impacts the channel capacity allocation.
Recently, Heusse et al. have shown through simulations and experiments that performance degradation occurs when two nodes are sending at different data rates [10]. Through analysis, authors show that the node sending at a lower data rate will achieve the same throughput as other nodes sending at higher data rate. The authors do not suggest any mechanism to mitigate this effects.
Efforts have been made in developing distributed fair scheduling algorithms that are suitable for the shared wireless medium. [20,22,27]. Like the schemes proposed in wired networks [8,9,24], these wireless scheduling algorithms [20,22,27] do not take into account the impact of transmission rate diversity and do not take into account the channel resource for both downlink and uplink traffic as most schemes [22,27] were targeted for ad hoc wireless networks.