ABSTRACT
CONTENTS 13.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356 13.2 Review of Energy Saving Schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357
13.2.1 Hardware Power Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357 13.2.1.1 Dynamic Voltage Scaling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357 13.2.1.2 Power Source Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
13.2.2 Energy-Efficient Wireless Communications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359 13.2.2.1 Contention-Based MAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359 13.2.2.2 TDMA-Based MAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360
13.2.3 Energy-Efficient Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360 13.2.3.1 Adaptive Sensing Duty Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360 13.2.3.2 Coordinated/Collaborative Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . 361
13.3 Alternate Sensing Schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364 13.4 Performance Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367 13.5 Networkwide Coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
13.5.1 Theoretical Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369 13.5.2 Simulation Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
13.6 Open Problems and Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372 13.7 Conclusions and Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374
In a wireless sensor network (WSN), energy efficiency is one of the primary concerns because the sensor nodes typically rely on batteries to operate. A sensor node is usually composed of two parts: the sensormodule for takingmeasurements and the radiomodule for wireless communications. Although many energy saving schemes have been proposed for the wireless communications module, very few have addressed the issue of energy savings of the sensing module. Recent measurement results show that the sensor nodes spend a lot of energy when taking many measurements, and the energy expenditure of sensing is comparable to that of data communications. As a result, it is necessary to study energy saving schemes for sensing.
