Optimal Throughput and Energy Efficiency for Wireless Sensor Networks: Multiple Access and Multipacket Reception
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Optimal Throughput and Energy Efficiency for Wireless Sensor Networks: Multiple Access and Multipacket Reception Wenjun Li Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695-7914, USA Email: [email protected]
Huaiyu Dai Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695-7914, USA Email: huaiyu [email protected] Received 9 December 2004; Revised 1 April 2005 We investigate two important aspects in sensor network design—the throughput and the energy efficiency. We consider the uplink reachback problem where the receiver is equipped with multiple antennas and linear multiuser detectors. We first assume Rayleigh flat-fading, and analyze two MAC schemes: round-robin and slotted-ALOHA. We optimize the average number of transmissions per slot and the transmission power for two purposes: maximizing the throughput, or minimizing the effective energy (defined as the average energy consumption per successfully received packet) subject to a throughput constraint. For each MAC scheme with a given linear detector, we derive the maximum asymptotic throughput as the signal-to-noise ratio goes to infinity. It is shown that the minimum effective energy grows rapidly as the throughput constraint approaches the maximum asymptotic throughput. By comparing the optimal performance of different MAC schemes equipped with different detectors, we draw important tradeoffs involved in the sensor network design. Finally, we show that multiuser scheduling greatly enhances system performance in a shadow fading environment. Keywords and phrases: throughput, energy efficiency, multiuser diversity, scheduling, slotted-ALOHA, linear multiuser detector.
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INTRODUCTION
Wireless sensor networks have become one of the burgeoning research fields in recent years, as they are envisioned to have wide applications in military, environmental, and many other fields [1]. Since sensors typically operate on batteries, replenishment of which is often difficult, a lot of work has been done to minimize the energy expenditure and prolong the sensor lifetime through energy efficient designs across layers [2, 3, 4, 5, 6]. Meanwhile, the sensor network should be able to maintain a certain throughput (which is equivalent to a certain delay constraint), in order to fulfill the QoS requirement of the end user, and to ensure the stability of the network. Typically, the throughput and the energy efficiency are inconsistent, and there exists a tradeoff between the two measures. The objective of this work is to explore the maximum achievable throughput under certain network This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
configurations and receiver structures, as well as optimal network designs that achieve the desired throughput with minimal energy consumption. We consider the reachback problem where all sensor nodes in the sensor fi
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