Browsing by Author "Dhar, Aditya"
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Item A dynamic distributed transmission power control MAC protocol for mobile ad hoc networks(2003) Dhar, Aditya; Johnson, David B.Ad hoc networking involves multihop, peer-to-peer communication between a group of wireless mobile nodes in a network with a dynamically changing topology. Achieving energy-efficient communication in such a network is more challenging than in cellular net works due to the absence of a centralized access point that can administer power control. For example, the commonly used MAC protocol for ad hoc networks, the IEEE 802.11 MAC protocol, uses a fixed power for all packet transmissions, for reasons of simplicity and to maintain the correct operation of its collision avoidance mechanism. In this thesis, I propose a distributed power-control based MAC protocol for ad hoc networks that uses variable transmission power for the control (RTS, CTS) packets and the minimum required transmission power for the DATA and ACK packets. The proposed solution, called PACA (Power-controlled Access with Collision Avoidance), improves both energy consumption and throughput, by reducing the energy used for most packet transmissions and by allowing simultaneous transmissions by different nodes, depending on the location of the respective receivers. PACA also improves the fairness among contending flows, in terms of the channel access time-share. I perform an extensive set of ns -2 simulations to study the impact of factors such as offered load, topology, number of flows, and node mobility on the performance of the proposed protocol and compare it to the IEEE 802.11 MAC protocol. The performance improvements are more pronounced in clustered networks with localized source-destination pairs because they utilize the available spectral reuse more efficiently.Item Multilevel coding of broadcast video over wirless channels(2002-05-20) Cakareski, Zeljko; Ahmed, Nasir; Dhar, Aditya; Aazhang, Behnaam; Center for Multimedia Communications (http://cmc.rice.edu/)This paper addresses the problem of broadcasting video over wireless channels. In such a scenario, different end users perceive the video signal through channels with different quality. We propose a source-channel coding system, that partitions the video data in such a way that maintains a baseline quality of service even for the user with the worst channel. The system consists of a layered source representation that is robust to error propagation effects, combined with a multilevel channel coding scheme that provides an unequal error protection to the different layers of the encoded video. Experimental results show that our system is robust and guarantees a baseline quality of service to all users over a wide range of channel conditions.