On the impact of selfish behaviors in wireless packet scheduling

In many practical scenarios, wireless devices are autonomous and thus, may exhibit non-cooperative behaviors due to self-interests. For instance, a wireless user may report bogus channel information to gain resource allocation advantages. Such non-cooperative behaviors are practicable as the device's software could be modified by the user. In this paper, we first analyze the impact of these rationally selfish behaviors on the performance of packet scheduling algorithms in time-slotted wireless networks. Using a mixed strategy game theoretic model, we show that the traditional Maximum Rate packet scheduling algorithm can lead non-cooperative users to undesirable Nash equilibriums, in which the wireless channels are used inefficiently. By using repeated game to enforce cooperation, we further propose a novel game theoretic approach that can lead to an efficient equilibrium. ©2008 IEEE.published_or_final_versio

Near-Optimal Deviation-Proof Medium Access Control Designs in Wireless Networks

Distributed medium access control (MAC) protocols are essential for the proliferation of low cost, decentralized wireless local area networks (WLANs). Most MAC protocols are designed with the presumption that nodes comply with prescribed rules. However, selfish nodes have natural motives to manipulate protocols in order to improve their own performance. This often degrades the performance of other nodes as well as that of the overall system. In this work, we propose a class of protocols that limit the performance gain which nodes can obtain through selfish manipulation while incurring only a small efficiency loss. The proposed protocols are based on the idea of a review strategy, with which nodes collect signals about the actions of other nodes over a period of time, use a statistical test to infer whether or not other nodes are following the prescribed protocol, and trigger a punishment if a departure from the protocol is perceived. We consider the cases of private and public signals and provide analytical and numerical results to demonstrate the properties of the proposed protocols.Comment: 14 double-column pages, submitted to ACM/IEEE Trans Networkin

Concevoir une stratégie de défense face aux comportements égoïstes de noeuds utilisant le protocole MAC IEEE 802.11

La coopération de l’ensemble des noeuds d’un réseau ad-hoc permet de garantir le fonctionnement optimal de celui-ci. Un noeud peut toutefois avoir un comportement égoïste au niveau de la sous-couche MAC du protocole IEEE 802.11 qui gère le contrôle de l’accès au médium. Ce comportement égoïste peut se traduire par une diminution de la taille de la fenêtre de contention afin d’augmenter la priorité d’émission. La conséquence d’un tel comportement pour un noeud est une amélioration de sa capacité d’émission, de son débit, entrainant une dégradation de la bande passante de l’ensemble du réseau. Dans cette étude nous concevons une stratégie de défense basée sur la stratégie Tit-for-Tat (TFT), développée en théorie des jeux pour faire face à ces comportements égoïstes. Nous démontrerons pourquoi et comment une telle stratégie vise à obtenir l’équité dans le partage de la bande passante. Nous introduirons des variantes de TFT comme un Tit-for-Tat généreux (GTFT), où l’introduction d’un facteur de générosité va permettre de s’adapter aux contraintes du médium. Enfin nous discuterons du choix et de l’influence des paramètres d’une telle stratégie sur le comportement d’un noeud et du réseau

The 802.11 MAC protocol leads to inefficient equilibria

Abstract — Wireless local area networks (WLANs) based on the family of 802.11 technologies are becoming ubiquitous. These technologies support multiple data transmission rates. Transmitting at a lower data rate (by using a more resilient modulation scheme) increases the frame transmission time but reduces the bit error rate. In non-cooperative environments such as public hot-spots or WLANs operated by different enterprises that are physically close to each other, individual nodes attempt to maximize their achieved throughput by adjusting the data rate or frame size used, irrespective of the impact of this on overall system performance. In this paper, we show both analytically using a game theoretic model and through simulation that the existing 802.11 distributed MAC protocol, DCF (for Distributed Coordination Function), as well as its enhanced version, which is being standardized at part of 802.11e, can lead non-cooperative nodes to undesirable Nash equilibriums, in which the wireless channel is inefficiently used. We show that by establishing independence between the allocation of the shared channel resource and the transmission strategies used by individual nodes, an ideal MAC protocol can lead rational nodes to arrive at equilibriums in which all competing nodes achieve higher throughputs than with DCF. I

Quality of service differentiation for multimedia delivery in wireless LANs

Delivering multimedia content to heterogeneous devices over a variable networking environment while maintaining high quality levels involves many technical challenges. The research reported in this thesis presents a solution for Quality of Service (QoS)-based service differentiation when delivering multimedia content over the wireless LANs. This thesis has three major contributions outlined below: 1. A Model-based Bandwidth Estimation algorithm (MBE), which estimates the available bandwidth based on novel TCP and UDP throughput models over IEEE 802.11 WLANs. MBE has been modelled, implemented, and tested through simulations and real life testing. In comparison with other bandwidth estimation techniques, MBE shows better performance in terms of error rate, overhead, and loss. 2. An intelligent Prioritized Adaptive Scheme (iPAS), which provides QoS service differentiation for multimedia delivery in wireless networks. iPAS assigns dynamic priorities to various streams and determines their bandwidth share by employing a probabilistic approach-which makes use of stereotypes. The total bandwidth to be allocated is estimated using MBE. The priority level of individual stream is variable and dependent on stream-related characteristics and delivery QoS parameters. iPAS can be deployed seamlessly over the original IEEE 802.11 protocols and can be included in the IEEE 802.21 framework in order to optimize the control signal communication. iPAS has been modelled, implemented, and evaluated via simulations. The results demonstrate that iPAS achieves better performance than the equal channel access mechanism over IEEE 802.11 DCF and a service differentiation scheme on top of IEEE 802.11e EDCA, in terms of fairness, throughput, delay, loss, and estimated PSNR. Additionally, both objective and subjective video quality assessment have been performed using a prototype system. 3. A QoS-based Downlink/Uplink Fairness Scheme, which uses the stereotypes-based structure to balance the QoS parameters (i.e. throughput, delay, and loss) between downlink and uplink VoIP traffic. The proposed scheme has been modelled and tested through simulations. The results show that, in comparison with other downlink/uplink fairness-oriented solutions, the proposed scheme performs better in terms of VoIP capacity and fairness level between downlink and uplink traffic

Improving aggregate user utilities and providing fairness in multi-rate wireless LANs

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 159-166).A distributed medium access control (MAC) protocol is responsible for allocating the shared spectrum efficiently and fairly among competing devices using a wireless local area network. Unfortunately, existing MAC protocols, including 802.11's DCF, achieve neither efficiency nor fairness under many realistic conditions. In this dissertation, we show that both bit and frame-based fairness,the most widely used notions, lead to drastically reduced aggregate throughput and increased average delay in typical environments, in which competing nodes transmit at different data transmission rates. We demonstrate the advantages of time-based fairness, in which each competing node receives an equal share of the wireless channel occupancy time. Through analysis, experiments on a Linux test bed, and simulation, we demonstrate that time-based fairness can lead to significant improvements in aggregate throughput and average delay. Through a game theoretic analysis and simulation, we also show that existing MAC protocols encourage non-cooperative nodes to employ globally inefficient transmission strategies that lead to low aggregate throughput. We show that providing long-term time share guarantees among competing nodes leads rational nodes to employ efficient transmission strategies at equilibriums.(cont.) We describe two novel solutions, TES (Time-fair Efficient and Scalable MAC protocol) and TBR (Time-based Regulator) that provide time-based fairness and long-term time share guarantees among competing nodes. TBR is a backward-compatible centralized solution that runs at the AP,works in conjunction with DCF, and requires no modifications to clients nor to DCF. TBR is appropriate for existing access point based networks, but not effective when nearby non-cooperative nodes fall under different administrative domains. Our evaluation of TBR on an 802.1lb/Linux test bed shows that TBR can improve aggregate TCP throughput by as much as 105% in rate diverse environments. TES is a non-backward compatible distributed contention-based MAC protocol that is effective in any environment, including non-cooperative environments. Furthermore, the aggregate throughputs sustained with increased loads. Through extensive simulation experiments, we demonstrate that TES is significantly more efficient(as much as 140% improvement in aggregate TCP throughput) and fairer than existing MAC protocols including DCF.by Godfrey Tan.Ph.D