Browsing by Author "Yu, Wei"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Rate Efficient Wireless Image Transmission using MIMO-OFDM(2003) Yu, Wei; Safar, Zoltan; Liu, K.J. Ray; Liu, K.J. Ray; ISRIn this paper, we propose a rate efficient JPEG 2000 image transmission system over hybrid wireless networks using MIMO-OFDM. The objective is to minimize the expected end-to-end distortion given the rate constraint, which is achieved by jointly adjusting source coding schemes and channel coding rates. In this system, MIMO-OFDM is used to increase the channel capacity and mitigate the inter-symbol interference, variable rate space frequency codes and Reed Solomon codes are adopted to combat the channel errors, and error resilient source coding schemes are applied to restrict the error propagation. In case network congestion may happen, packet erasure codes are used to alleviate the packet dropping. The advantages of the proposed system lie in three aspects: adaptivity, optimality, and low complexity. Based on the characteristics of the image content, the estimated channel conditions, and the distortion constraint, the proposed low-complexity joint source channel coding and rate control algorithm adjusts the coding and transmission strategies adaptively, which can approximate the optimal solution with a tight bound.Item SECURING WIRELESS AD HOC NETWORKS UNDER NOISE AND IMPERFECT MONITORING(2006-07-05) Yu, Wei; Liu, K.J. Ray; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)While wireless communication has dramatically changed the way people work and interact, the wireless era continues to be plagued by insufficient security. Without necessary countermeasures, even a few attackers can break down the whole network. On the other hand, attacker detection can be extremely challenging in realistic scenarios because misbehavior may also be caused by various other factors, such as noise and uncertainty, and perfect monitoring is either impossible to achieve or too expensive to afford. In this dissertation we have investigated how to secure wireless ad hoc networks against insider attacks in noisy and hostile environments, based only on local and imperfect monitoring. In traditional ad hoc network applications, nodes usually belong to the same authority and pursue some common goals. The inherent cooperative nature of such networks makes them extremely vulnerable to insider attacks. For example, by dropping other nodes' packets and/or injecting an overwhelming amount of traffic, insider attackers can easily break down the whole network. In this dissertation we have first studied how to secure such ad hoc networks against insider attacks under noise and imperfect monitoring. Besides devising a set of efficient monitoring and attacker detection mechanisms to defend against routing disruption and injecting traffic attacks, we have also formally analyzed the dynamic interactions between good nodes and attackers under a game theoretic framework, where both the optimal defending strategies and the maximum damage that can be caused by insider attackers have been derived. In many civilian applications, nodes in ad hoc networks tend to act selfishly. Stimulating selfish nodes to act cooperatively poses one key research challenge, especially in realistic contexts. In this dissertation we have also investigated how to design attack-resistant cooperation mechanisms for such networks. We have first designed an attack-resistant cooperation stimulation strategy for mobile ad hoc networks, then formally analyzed the issue of secure cooperation in ad hoc networks under a game theoretic framework. Finally, we have derived a set of reputation-based attack-resistant and cheat-proof cooperation strategies for such ad hoc networks that can work well in noisy and hostile environments under imperfect monitoring.