ERA: Effective Rate Adaptation for WLANs

Rate adaptation consists of using the optimal rate for a given channel quality: the poorer the channel quality, the lower the rate should be. Multiple rate adaptation schemes were proposed and studied so far. The first generation rate adaptation schemes perform well in collision free environments and manage quite well strict channel degradation. Under a congestion dominated environment, these schemes poorly perform because they do not differentiate losses due to channel degradation from those due to collisions and unnecessarily decrease the rate in response to collisions. A second generation rate adaptation schemes overcome this limitation. However, these most recent schemes usually require RTS/CTS control frames that are not in general used because they constitute an overhead that may heavily lower network performance especially when frame size is small. This work proposes an effective and practical rate adaptation scheme (ERA) that does not require RTS/CTS control frames. ERA judiciously uses fragmentation in compliance with IEEE 802.11 standard to diagnose the cause of frame loss and to promptly recover from frame losses. Through extensive simulations on ns-2, ERA exhibits a significant throughput improvement over other rate adaptation schemes.