Sensor networks can be considered distributed computing platforms with many severe constraints including limited CPU speed, memory size, power, and bandwidth. Individual nodes in sensor networks are typically unreliable and the network topology dynamically changes, possibly frequently. Sensor networks can also be considered a form of ad hoc network. However, here also many constraints in sensor networks are different or more severe. Sensor networks also differ because of their tight interaction with the physical environment via sensors and actuators. Due to all of these differences many solutions developed for general distributed computing platforms and for ad hoc networks cannot be applied to sensor networks. Many new and exciting research challenges exist. This paper discusses the state of the art and presents the key research challenges to be solved, some with initial solutions or approaches.

This paper discusses online power-aware routing in large wireless ad-hoc networks (especially sensor networks) for applications where the message sequence is not known. We seek to optimize the lifetime of the network. We show that online power-aware routing does not have a constant competitive ratio to the off-line optimal algorithm. We develop an approximation algorithm called max-min zPmin that has a good empirical competitive ratio. To ensure scalability, we introduce a second online algorithm for power-aware routing.

We empirically study the effect of mobility and interaction between various input parameters on the performance of protocols designed for wireless ad-hoc networks. An important objective is to study the interaction of the routing and MAC layer protocols under different mobility parameters. We use three basic mobility models: grid mobility model, random waypoint model, and exponential correlated random model. The performance of protocols is measured in terms of various quality of service measures including (i) latency, (ii) number of packets received and (iii) long term fairness. Three different commonly studied routing protocols are used: AODV, DSR and LAR scheme 1. Similarly three well known MAC protocols are used: MACA, 802.11 and CSMA. Our main contribution is simulation based experiments coupled with rigorous statistical analysis to characterize the interaction between the above stated parameters. Such methods allow us to analyze complicated experiments with large input space in a systematic manner. From our results, we conclude the following: No single MAC or routing protocol dominated the other protocols in their class. More interestingly, no MAC/routing protocol combination was better than other combinations over all mobility models and response variables.

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We study the interaction between communication protocols, network topology and packet traffic in wireless static radio networks. A particular interest is to empirically characterize the effect of interaction between the routing layer and the MAC layer on overall system performance. Three well known MAC protocols: 802.11, CSMA, and MACA are considered. Similarly three recently proposed routing protocols: AODV, DSR and LAR scheme 1 are considered. The performance of the protocols is measured with regard to three important parameters: (i) number of packets received (ii) average latency of each packet and (iii) long term fairness.

(MANETs) has received considerable attention, the issue of endto-end latency has been largely ignored. As military MANETs get larger and denser with an increasing number of end-to-end hops, the latency and jitter experienced by packets will be prohibitively high for existing and emerging real-time applications. We present and study a novel mechanism called CAPS (Channel Access over Path Segments) for reducing end-to-end latency. The key idea behind CAPS is to reserve the floor multiple hops (a path segment) at a time. This is accomplished by using multi-hop RTS and CTS frames that acquire the access rights for an entire segment toward the destination, with virtual carrier sense acting on a path basis. Our architecture also includes a cut-through physical layer that pipelines a bit stream through the receive and transmit chains. We present a numerical analysis of the relative performance gain from our ideas, complemented by a simulation-based analysis. Our study shows that, depending upon the parameters used, a 3x to 8x reduction in latency over current systems is possible. I.

This thesis contributes toward the design of a new adaptive quality of service (QOS) paradigm for wireless ad hoc networks. We address some of the key performance problems in the broader realm of wireless ad hoc networks, including mobile ad hoc networks and emerging wireless ad hoc sensor networks. Wireless ad hoc networks represent autonomous distributed systems that are infrastructureless, fully distributed, and multi-hop in nature. Over the last several years, wireless ad hoc networks have attracted considerable research attention in the general networking and performance community. This has been fueled by recent technological advances in the development of multifunctional and low-cost wireless communication devices. Wireless ad hoc networks have diverse applications spanning several domains, including military, commercial, medical, and home networks. The results of all this research activity the wireless ad hoc networks are starting to move from the research domain into the real world and are being gradually integrated into our daily lives. Projections indicate that this will accelerate later in the decade, to the point where some analysts predict that these types of self-organizing

A novel framework is presented for the study of scalability in ad hoc networks. Using this framework, the first asymptotic analysis is provided with respect to network size, mobility, and traffic for each fundamental class of ad hoc routing algorithms. Protocols studied include the following: Plain Flooding (PF), Standard Link State (SLS), Dynamic Source Routing (DSR), Hierarchical Link State (HierLS), Zone Routing Protocol (ZRP), and Hazy Sighted Link State (HSLS). It is shown that PF and ZRP scale better with mobility, SLS and ZRP scale better with respect to traffic, and HSLS scales better with respect to network size. The analysis provides deeper understanding of the limits and trade-offs inherent in mobile ad hoc network routing. Our analysis is complemented with a simulation experiment comparing HSLS and HierLS. An important contribution of this paper is that HSLS is an scalable, easy-to-implement, alternative to hierarchical approaches for large ad hoc networks.