I. Introduction
Wireless devices are normally powered by batteries, which need to be either replaced or recharged periodically. One possible technique to overcome this limitation is to harvest energy from the environment, such as vibration absorption devices, solar energy, wind energy, thermal energy, and other clean energy [1]. In such systems, energy harvesting has become a preferred choice for supporting “green communication.” The system is normally modeled as a sequence of epochs, where for each epoch, an event occurs that may be the transition consequence between transmitting signal packages, with channel fading gain variation or new energy being harvested, or both.