CARA: Collision-aware rate adaptation for IEEE 802.11 WLANs

Today's IEEE 802.11 WLANs (Wireless LANs) provide multiple transmission rates so that different rates can be exploited in an adaptive manner depending on the underlying channel condition in order to maximize the system performance. Many rate adaptation schemes have been proposed so far while most (if not all) of the commercial devices implement a simple open-loop rate adaptation scheme (i.e., without feedback from the receiver), called ARF (Automatic Rate Fallback) due to its simplicity. A key problem with such open-loop rate adaptation schemes is that they do not consider the collision effect, and hence, malfunction severely when many transmission failures are due to collisions. In this paper, we propose a novel rate-adaptation scheme, called CARA (Collision-Aware Rate Adaptation). The key idea of CARA is that the transmitter station combines adaptively the Request-to-Send/Clear-to-Send (RTS/CTS) exchange with the Clear Channel Assessment (CCA) functionality to differentiate frame collisions from frame transmission failures caused by channel errors. Therefore, compared with other open-loop rate-adaptation schemes, CARA is more likely to make the correct rate adaptation decisions. Through extensive simulation runs, we evaluate our proposed scheme to show that our scheme yields significantly higher throughput performance than the existing schemes.