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In sensor networks, measurements made at the sensor nodes must reach a distinguished node that will process these data and transfer them to a data center. Since the radio consumes a large fraction of the battery energy of a sensor node, the network's medium access control (MAC) protocol, routing protocol, sensor node distribution and antenna design have a decisive influence on battery lifetime. This lifetime determines the cost of network maintenance, and hence whether it is economical to deploy such a network. MAC Protocol: We propose a novel channel access scheme that exploits the application-specific characteristics of sensor networks to meet their power, real-time deadline, fairness, and congestion control requirements. The primary characteristic of the sensor network is that the destination of all the data packets in the network is a central data collector. This central data collector, which is usually denoted as an access point, has unlimited power, whereas sensor nodes have one-battery power for remaining alive for several years. Our protocol PEDAMACS (Power Efficient and Delay Aware Medium Access Protocol for Sensor Networks) uses the access point to directly synchronize and schedule all the nodes in the network by increasing its transmission power [1,2]. After learning the topology information, which includes the neighbor and the next hop to reach the access point, of all the nodes in the network in topology learning and topology collection phases, the access point explicitly schedules the node transmissions and announces this schedule to all the nodes. Assuming that the nodes generate packets periodically at the same rate, we described the goal of the scheduling algorithm to be minimizing the time necessary for all the packets to reach an access point where each node has exactly one packet at the beginning. After proving the NP-completeness of the problem, we developed a polynomial time algorithm that can guarantee an upper bound on the maximum delay experienced by the packets, which is proportional to the number of the nodes in the network. Simulations performed in TOSSIM, which is a simulation environment for TinyOS, show the efficiency of the proposed scheme compared to the conventional random access scheme in terms of power and delay. Routing Protocol: Energy efficiency is essential in the design of sensor networks to provide several years of maintenance-free data gathering platform. A routing protocol is presented to maximize the lifetime of sensor network by balancing the energy consumption in each node given their initial energy [3]. This balance is achieved through the continuous adjustment of the number of packets each node is forwarding. We first formulated this routing problem as a linear programming problem and analyzed the characteristics of the solution for a network where the destination of all packets in the network is a specific data-collecting node. We then approximate this optimization problem with an iterative algorithm based on minimum cost routing where each step can be implemented efficiently in either distributed or centralized manner. Simulations performed in MATLAB show that the lifetime of the network increases by 30-120 days on average with route optimization and that the right choice of cost function in iterative algorithm can make the lifetime of the random networks arbitrarily close to their optimal lifetime. Sensor Node Distribution: Since lifetime is an important metric for sensor nodes that are planned to be deployed once and unattended for long periods of time without maintenance, we perform power analysis of a sensor node by using trace generation feature of HyTech. Furthermore, we simulate a tree sensor network of TinyOS motes by using the programming language SHIFT to determine the lifetime of the network as a function of the distance from the central data collector [4]. Publications: 1) Sinem Coleri, “PEDAMACS: Power Efficient and Delay Aware Medium Access
Protocol for Sensor Networks” Master Thesis, University of California Berkeley, December 2002 supervised by Prof. Pravin Varaiya. 2) Sinem Coleri, Anuj Puri , Pravin Varaiya, “Power Efficient System for Sensor Networks”,
IEEE ISCC, 3) Sinem Coleri and Pravin Varaiya, “Optimization of
Sensor Network Lifetime through Energy Efficient Routing”, in progress. 4) Sinem Coleri, Mustafa
Ergen , Tak-Kuen John Koo, “Lifetime Analysis of a Sensor Network with Hybrid Automata
Modelling”, ACM WSNA
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