Contents 1. INTRODUCTION
Minimizing the total energy consumption in both circuits and signal transmission is a critical factor in designing a WSN. For typical WSNs, on the other hand, data rates are usually low. Thus, using complicated signal processing techniques are not desirable. Several energy-efficient approaches have been investigated for different layers of a WSN, including the data-link and the physical layers (see e.g., [1]–[3]). Central to the study of energy-efficient techniques in the physical layer of a WSN is modulation. Although, achieving all requirements (e.g., minimum energy consumption, maximum bandwidth efficiency, low signal processing complexity) is a complex task in a WSN, an energy-efficient modulation scheme should be simple enough to be implemented by state-of-the-art low-power technology. In addition, since sensor nodes frequently switch from sleep mode to active mode, modulation circuits should have fast start-up times. We refer to these schemes as green modulations.
