Today's IEEE 802.11 Wireless LAN (WLAN) is an excellent solution for the broadband wireless networking. However, it lacks of the capability to support real-time services such as Voice-over-IP (VoIP) properly. In this paper, we present a simple and viable approach to enhance the VoIP performance over the 802.11 WLAN by implementing two queues along with a strict priority queuing on top of the 802.11 Medium Access Control (MAC) controller, e.g., in the device driver of the 802.11 cards. We find via extensive simulations that the proposed scheme is remarkably effective for the VoIP service in the infrastructure-based WLAN in the coexistence with the non-real-time traffic thanks to the flow control mechanism of the TCP protocol, which is typically used for the non-real-time traffic today. Due to its simplicity, the proposed scheme should be readily deployable in the existing WLANs via simple software upgrades for the enhanced VoIP services.
Abstract-Collision awareness has been recognized as a critical component for effective rate adaptation schemes. Recently, several collision-aware rate adaptation schemes have been proposed for IEEE 802.11 Wireless LANs (WLANs), such as CARA (Collision Aware Rate Adaptation) and RRAA (Robust Rate Adaptation Algorithm). These schemes are able to distinguish between channelerror-induced and collision-induced frame losses via adaptive and appropriate usage of RTS/CTS; hence the multiple transmission rates provided by 802.11 physical layers (PHYs) may be fully exploited. In this paper, we propose a unique collision-aware rate adaptation scheme, called PBRA (Probabilistic-Based Rate Adaptation). The key ideas of PBRA include (i) probabilistic-based adaptive usage of RTS/CTS, which is in direct contrast to trialbased RTS Probing in CARA and window-based adaptive usage of RTS/CTS in RRAA; and (ii) threshold-based rate adjustment, which allows a station to make more appropriate rate adjustment decisions, thanks to its accurate estimation of the channel-error-induced frame loss ratio. Simulation results show that PBRA clearly outperforms all other testing schemes (including CARA and RRAA), particularly in random topology networks with fading wireless channels.
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