This approach is closer to our work, since a cloud-based cooperative MAC protocol is proposed and evaluated. However, there are two key differences with respect to our proposal: (i) RLNC is not considered, and relays transmit the same uncoded packets simultaneously, thus creating virtual multiple-input-multiple-output (MIMO) links; and (ii) the role of the relay cloud is fundamentally different. In particular, each relay in the cloud decides in a distributed way whether to participate in a cooperation phase based on a transmission probability
Energy harvesting or energy scavenging is the process of extracting small amount of energy from ambient environment through various sources of energy. The available energy for harvesting is mainly provided by ambient light (artificial and natural lighting), ambient radio frequency, thermal sources and mechanical sources.
Reduction in size and energetic demands of sensors, and the low power consumption trend in CMOS electronic circuitry opened novel research lines on battery recharge via available power sources. Harvesters can be employed as battery rechargers in various environments, such as industries, houses [1,2], the military (as for unmanned aerial vehicles [3]) and handheld or wearable devices [4�C9]. The possibility to avoid replacing exhausted batteries is highly attractive for wireless networks (Wireless Sensor Networks [10]), in which the maintenance costs due to battery check and replacement are relevant. Another emerging field of application is biomedical systems, where the energy could be harvested from an off-the-shelf piezoelectric unit and used to implement drug delivery systems [11] or tactile sensors [12�C14].
Recent research also includes energy conversion from the occlusal contact during chewing by means of a piezoelectric layer [11,15] and from heart beats [16].We can classify the main energy harvesting technologies by the hierarchy shown in Figure 1. Motion harvester systems can be structured as follows: GSK-3 the harvester collects inputs through its frame, directly connected to the hosting structure and to the transducer; at the end of the system chain, a conditioning circuit manipulates the electrical signals. This paper specifically focuses on piezoelectric motion harvesting techniques.Figure 1.Hierarchy of main energy harvesting technologies.
The possibility and the effectiveness of extracting energy from human activities has been under study for years [17]. As a matter of fact, continuous and uninterrupted power can potentially be available: from typing (~mW), motion of upper limbs (~10 mW), air exhalation while breathing (~100 mW), walking (~W) [18,19] (Figure 2), and in this work we review state of the art of motion based energy harvesting.Figure 2.Estimation of available power that could be harvested during human activities (Adapted from [22]).