Abstract. While many existing rate adaptation schemes in IEEE 802.11 Wireless LANs result in severe throughput degradation since they do not consider the collision effect when selecting the transmission rate, CARA (Collision-Aware Rate Adaptation) [1] shows improved system performance thanks to its collision-awareness capability. In this paper, we propose two enhancements to the original CARA scheme to further improve the system performance. The first one is called CARA-RI, which extends CARA's collision-awareness capability in making rate increase decisions, while the second one, called CARA-HD, incorporates a hidden station detection mechanism. Simulation results show that the proposed schemes outperform the original CARA significantly under various randomly-generated network topologies.
We develop a new wireless link quality metric, ECOT (Estimated Channel Occupancy Time) that enables a high throughput route setup in wireless mesh networks. The key feature of ECOT is being applicable to diverse mesh network environments where IEEE 802.11 MAC (Medium Access Control) variants are used. We take into account the detailed operational features of various 802.11 MAC protocols, such as 802.11 DCF (Distributed Coordination Function), 802.11e EDCA (Enhanced Distributed Channel Access) with BACK (Block Acknowledgment), and 802.11n A-MPDU (Aggregate MAC Protocol Data Unit), and derive an integrated link metric that enables finding maximum throughput end-to-end routes. Through simulations in randomized topological environments, we evaluate the performance of the proposed link metric and routing strategy to demonstrate that our proposed schemes can achieve up to 354.4% throughput gain over existing ones.
Abstract-This paper analyzes the impact of different MAC (Medium Access Control) and transmission rate adaptation schemes on wireless mesh networks. The considered protocols include three different MAC protocols specified in IEEE 802.11 standards, i.e., 802.11, 802.11e, and 802.11n, and three rate adaptation schemes, i.e., ARF (Automatic Rate Fallback), RBAR (Receiver-Based Auto Rate), and 802.11n rate adaptation. We also study the interactions of these MAC strategies with the state-of-the-art routing metric ETT (Expected Transmission Time). Through comparative simulation evaluations, we investigate the effectiveness of these protocols when they coexist on both single-hop and multi-hop wireless mesh network environments. As these MAC strategies are designed for single-hop WLANs, we observed their limitations on multi-hop wireless mesh networks. We analyze their performances and suggest solutions for improvements. Based on our simulation results, we also argue for the need of a new routing metric that takes advantage of the new emerging MAC features.
Abstract. We present a transmission rate adaptation algorithm called AGILE (ACK-Guided Immediate Link rate Estimation) for IEEE 802.11 networks. The key idea of AGILE is that the transmitter adjusts the transmission rate by means of measuring the SNR (Signal-to-Noise Ratio) during any frame reception including the ACK (Acknowledgment) frame, and estimating the corresponding maximum achievable throughput using a profile, which is materialized by extensive off-line measurement. AGILE is equipped with an advanced RTS (Request-To-Send)/CTS (Clear-To-Send) activation algorithm, eRTS filter that intelligently switches on/off RTS frame transmission to enhance the achievable throughput depending upon the existence of multiple contending (or even hidden) stations. The effectiveness of AGILE is evaluated in our MadWifi-based testbed implementation and we compare its performance with different rate adaptation schemes in various scenarios.
Today, IEEE 802.11 Wireless LAN (WLAN) has emerged as a prevailing technology for the broadband wireless networking. Along with many emerging applications and services over WLANs, the demands for faster and highercapacity WLANs have been growing fast. In this paper, we propose a new medium access control (MAC) scheme for the next-generation high-speed WLANs such as IEEE 802.11n. The proposed MAC, called Multi-user polling Controlled Channel Access (MCCA), is composed of two sub-schemes. The first one is multi-user polling in order to achieve higher network utilization. We also introduce a frame aggregation scheme as the another proposed scheme, which performs aggregations at both MAC and physical (PHY) layers, and can achieve even higher throughput gain as a result. From simulations, we confirm that the proposed MCCA scheme enhances the aggregate throughput of non-qualityof-service (non-QoS) traffic by an order of magnitude from 17.4 Mbps to 129.9 Mbps, while the aggregate throughput and QoS requirements continue to be satisfied.
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