An Energy-Efficient Adaptive Modulation Suitable for Wireless Sensor Networks with SER and Throughput Constraints
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Research Article An Energy-Efficient Adaptive Modulation Suitable for Wireless Sensor Networks with SER and Throughput Constraints ´ Carlos Bousono ˜ Calzon, ´ and Ana Garc´ıa Armada J. Joaqu´ın Escudero Garzas, Department of Signal Theory and Communications, University Carlos III of Madrid, Avda de la Universidad 30, 28911 Legan´es, Madrid, Spain Received 16 October 2006; Revised 14 March 2007; Accepted 6 April 2007 Recommended by Mischa Dohler We consider the problem of minimizing transmission energy in wireless sensor networks by taking into account that every sensor may require a different bit rate and reliability according to its particular application. We propose a cross-layer approach to tackle such a minimization in centralized networks for the total transmission energy consumption of the network: in the physical layer, for each sensor the sink estimates the channel gain and adaptively selects a modulation scheme; in the MAC layer, each sensor is correspondingly assigned a number of time slots. The modulation level and the number of allocated time slots for every sensor are constrained to attain their applications bit rates in a global energy-efficient manner. The signal-to-noise ratio gap approximation is used in our exposition in order to jointly handle required bit rates, transmission energies, and symbol error rates. Copyright © 2007 J. Joaqu´ın Escudero Garz´as et al. 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.
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INTRODUCTION
Wireless sensor networks are susceptible to many different applications in diverse fields such as areas of industry and commerce (i.e., environment monitoring and control), home automation and intelligent buildings (i.e., security, lighting, air conditioning), PC peripherals (i.e., mouse, printer), consumer electronics, medicine and personal health care (i.e., monitors, diagnostics, medical body sensors), and surveillance and maintenance among others [1–6]. Furthermore, the availability of commercial products has fostered potential applications; examples are given in [7–11]. Particularly, wireless devices conforming to IEEE 802.15.4 standard and ZigBee specifications seem to be gaining market due to their characteristics of low power, low cost, and low rate. These features make them very well-suited as well for most WSN applications in the so-called personal area networks (PAN). Some relevant parameters are usually considered in the context of PANs such as the type and quality of service, scalability, maintainability, and, specially, lifetime of batteries. Therefore, energy-efficient communication schemes have become a main challenge in the design of these networks. One straight approach towards energy efficiency would be the use of long transmission time intervals, however many applications impose hard delay contraints. This energy-efficiency
delay tradeoff has been recently studied in [12]. An other different appproac
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