A Downlink Rate Adaptation Scheme in IEEE 802.11 WLANs using Overhearing

IEEE 802.11 Wireless LANs support multiple data transmission rates at physical (PHY) layer. Various rate adaptation schemes that select optimal transmission rate according to the receivers' channel condition have been proposed. Among these protocols, Automatic Rate Fallback (ARF) is the one that is widely implemented in commercial devices due to its simplicity. However, it is well-known that the performance of ARF deteriorates when the wireless channel condition is unstable or many frame collisions occur. On the other hand, RBAR (Receiver Based Auto-Rate) that achieves the good performance is rarely used because it introduces extra control overhead. In this paper, we propose a novel rate adaptation scheme that performs well without control overhead. The key idea of our proposed scheme is that if a station successfully overhears a downlink transmission whose data rate is higher than its current rate, then it requests the AP to increase the data rate to overheard frame's transmission rate. We compare our scheme with previous rate adaptation schemes in terms of throughput performance via the simulation study. The performance results indicate that our scheme achieves better performance than RBAR.