GORA: Goodput Optimal Rate Adaptation for 802.11 using Medium Status Estimation

Rate Adaptation for 802.11 has been deeply investigated in the past, but the problem of achieving optimal Rate Adaptation with respect not only to channel-related errors but also to contention-related issues (i.e., collisions and variations in medium access times) is still unsolved. In this paper we address this issue by proposing 1) a practical definition of the Medium Status in a multi-user 802.11 scenario in terms of channel errors, MAC collisions and packet service times, and a method for its estimation based on measurements; 2) an analytical model of the goodput performance as a function of the Medium Status; 3) a rate adaptation algorithm, called Goodput Optimal Rate Adaptation (GORA), which is based on this model. Unlike other Rate Adaptation schemes proposed in literature, which require either modifications to the IEEE 802.11 standard or cooperation among nodes, GORA is totally stand-alone and standard compliant. In fact, the Medium Status Estimation used by GORA is obtained by using standard MAC counters that are commonly collected by commercial MAC drivers, and no explicit interactions with the other devices in the network is required. Therefore, GORA offers the advantage of being readily deployable on real devices. The performance of GORA is evaluated through NS2 simulations which reveal that, as expected, GORA outperforms other well-known Rate Adaptation algorithms in several scenarios and can be used as a new reference benchmark.