Browsing by Author "Saha, Amit"
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Item A MAC protocol for Multi Frequency Physical Layer(2003-01-23) Kumar, Rajnish; PalChaudhuri, Santashil; Saha, AmitExisting MAC protocols for wireless LAN systems assume that a particular node can operate on only one frequency and that most/all of the nodes operate on the same frequency. We propose a MAC protocol for use in an ad hoc network of mobile nodes using a wireless LAN system that defines multiple independent frequency channels. Each node can switch quickly from one channel to another but can operate on one channel at a time. We simulate the proposed protocol by modifying the wireless extension. Our simulations show that the proposed protocol, though simple, is capable of much better performance in the presence of multiple independent channels than IEEE 802.11which assumes a single frequency channel for all nodes. As expected, the proposed protocol works as well as IEEE 802.11 in the presence of a single channel.Item Probabilistic Clock Synchronization Service in Sensor Networks(2003-04-16) Johnson, David B.; PalChaudhuri, Santashil; Saha, AmitRecent advances in technology have made low cost, low power wireless sensors a reality. Clock synchronization is an important service in any distributed system, including sensor network systems. Applications of clock synchronization in sensor networks include data integration in sensors, sensor reading fusion, TDMA medium access scheduling, and power mode energy saving. However, for a number of reasons, standard clock synchronization protocols are unsuitable for direct application in sensor networks. In this paper, we describe a probabilistic service for clock synchronization that is based on the Reference Broadcast Synchronization protocol. In particular, we use the higher precision of receiver-to-receiver synchronization, as described in Reference Broadcast Synchronization protocol. We extend this deterministic protocol to provide a probabilistic bound on the accuracy of the clock synchronization service, allowing for a tradeoff between accuracy and resource requirement. We derive expressions to convert service specifications (maximum clock synchronization error and confidence probability) to actual protocol parameters(minimum number of messages and synchronization overhead). We also extend this protocol for maintaining clock synchronization in a multi hop network.Item Routing Improvements using Directional Antennas in Mobile Ad hoc Networks(2003-07-03) Johnson, David B.; Saha, AmitIn this paper, we present the design and evaluation of two techniques for routing improvement using directional antennas in mobile ad-hoc networks. First, we use directional antennas to bridge network partitions by adaptively transmitting selected packets over a longer distance, using the capabilities of the directional antenna, yet still transmitting most packets shorter distance in order to reduce power consumption and interference. Through simulations, we demonstrate the effectiveness of our design by modifying the Dynamic Source Routing (DSR) protocol, an on-demand ad hoc network routing protocol. Our simulations show that the modified protocol is able to effectively bridge network partitions, and that the protocol is otherwise equivalent to the original protocol when no partitions are present. Second, we propose a method to use directional antennas to repair routes in use when an intermediate node moves out of wireless transmission range along the route. By using the capability of a directional antenna to selectively transmit packets over a longer distance, we bridge the break in the route caused by the intermediate node's movement, thus reducing packet delivery latency and avoiding dropped packets and additional routing overhead. We present the results of simulations giving a preliminary performance evaluation of this technique demonstrating its effectiveness.Item Self-Organizing Hierarchical Routing for Scalable Ad Hoc Networking(2005-02-08) Druschel, Peter; Du, Shu; Johnson, David B.; Khan, Muhammed; PalChaudhuri, Santashil; Post, Ansley; Riedi, Rudolf H.; Saha, AmitAs wireless devices become more pervasive, mobile ad hoc networks are becoming increasingly important, motivating the development of highly scalable ad hoc networking techniques. In this paper, we present the design and evaluation of a novel protocol for scalable routing in ad hoc networks, as part of the Safari project. Safari leverages and integrates research in both ad hoc networking and peer-to-peer networking. We develop a probabilistic, elf-organizing network hierarchy formation protocol that recursively forms the nodes of the ad hoc network into an adaptive, proximity-based hierarchy of cells. We develop a hybrid routing protocol that uses this hierarchy, with reactive and proactive routing, to scale to large number of nodes. The mapping of unique node identifiers to hierarchical addresses is done using a distributed hash table that leverages the hierarchical network structure. We evaluate this design through analysis and simulations, under increasing network size, increasing fraction of mobile nodes, and increasing offered traffic load. Our analysis is well matched by our simulations, and our results demonstrate the protocol's scalability.