HEED

  ecent advances in electrical engineering and computer science, esp ecially in micro- electro-mechanical systems (MEMS), very-large-scale integration (VLSI) and op erating system theory, have made wireless sensor network (WSN) technologies an imp ortant and promising research area. As the circuitry b ecame smaller and cheap er, the idea of co op eratively sensing physical or environmental conditions, such as magnetic eld intensity, temp erature, light intensity, sound, vibration, pressure, motion or p ollutants with the help of a network of sensor no des has b ecome feasible.