Cross-layer Loss Differentiation Algorithm to Improve TCP Performances in WLANs

International audienceLoss Differentiation Algorithms (LDA) are currently used to determine the cause of packet losses with an aim of improving TCP performance over wireless networks. In this work, we propose a cross-layer solution based on two LDA in order to classify the loss origin on an 802.11 link and then to react consequently. The first LDA scheme, acting at the MAC layer, allows differentiating losses due to signal failure caused by displacement or by noise from other loss types. Moreover, in case of signal failure, it adapts the behavior of the MAC layer to avoid a costly end-to-end TCP resolution. The objective of the second LDA scheme, which acts at the TCP layer, is to distinguish a loss due to interferences from those due to congestions and to adapt consequently the TCP behavior. The efficiency of each LDA scheme and of the whole cross-layer solution are then demonstrated through simulations

Cross-layer design and optimization of medium access control protocols for wlans

This thesis provides a contribution to the field of Medium Access Control (MAC) layer protocol design for wireless networks by proposing and evaluating mechanisms that enhance different aspects of the network performance. These enhancements are achieved through the exchange of information between different layers of the traditional protocol stack, a concept known as Cross-Layer (CL) design. The main thesis contributions are divided into two parts. The first part of the thesis introduces a novel MAC layer protocol named Distributed Queuing Collision Avoidance (DQCA). DQCA behaves as a reservation scheme that ensures collision-free data transmissions at the majority of the time and switches automatically to an Aloha-like random access mechanism when the traffic load is low. DQCA can be enriched by more advanced scheduling algorithms based on a CL dialogue between the MAC and other protocol layers, to provide higher throughput and Quality of Service (QoS) guarantees. The second part of the thesis explores a different challenge in MAC layer design, related to the ability of multiple antenna systems to offer point-to-multipoint communications. Some modifications to the recently approved IEEE 802.11n standard are proposed in order to handle simultaneous multiuser downlink transmissions. A number of multiuser MAC schemes that handle channel access and scheduling issues and provide mechanisms for feedback acquisition have been presented and evaluated. The obtained performance enhancements have been demonstrated with the help of both theoretical analysis and simulation obtained results

Unleashing Exposed Terminals in Enterprise WLANs: A Rate Adaptation Approach

The increasing availability of inexpensive off-the-shelf 802.11 hardware has made it possible to deploy access points (APs) densely to ensure the coverage of complex enterprise environments such as business and college campuses. However, dense AP deployment often leads to increased level of wireless contention, resulting in low system throughput. A promising approach to address this issue is to enable the transmission concurrency of exposed terminals in which two senders lie in the range of one another but do not interfere each other\u27s receiver. However, existing solutions ignore the rate diversity of 802.11 and hence cannot fully exploit concurrent transmission opportunities in a WLAN. In this paper, we present TRACK - Transmission Rate Adaptation for Colliding linKs, a novel protocol for harnessing exposed terminals with a rate adaptation approach in enterprise WLANs. Using measurement-based channel models, TRACK can optimize the bit rates of concurrent links to improve system throughput while maintaining link fairness. Our extensive experiments on a testbed of 17 nodes show that TRACK improves system throughput by up to 67% and 35% over 802.11 CSMA and conventional approaches of harnessing exposed terminals

Improving the Performance of Wireless LANs

This book quantifies the key factors of WLAN performance and describes methods for improvement. It provides theoretical background and empirical results for the optimum planning and deployment of indoor WLAN systems, explaining the fundamentals while supplying guidelines for design, modeling, and performance evaluation. It discusses environmental effects on WLAN systems, protocol redesign for routing and MAC, and traffic distribution; examines emerging and future network technologies; and includes radio propagation and site measurements, simulations for various network design scenarios, numerous illustrations, practical examples, and learning aids