How Many Wi-Fi APs Does it Take to Light a Lightbulb?

The global move toward wireless access point (AP) densification has alluded toward the possibility of harvesting the unused ambient RF energy, especially in the 2.4-GHz unlicensed band, in order to power useful electronic devices, which collectively make up the so-called low energy Internet of Things (LE-IoT). Despite the huge market demand for free ambient energy and the research community's efforts in prototyping efficient rectifiers, there is, however, little knowledge about the available power densities in dense indoor and outdoor AP deployments. Obtaining this information is, therefore, vital for engineering the power requirements of LE-IoT devices and managing expectations for their subsequent commercialization. In this paper, we present power density measurements in a controlled indoor ultra-dense deployment corresponding to approximately one AP per square meter. We detail our methodology and hardware and offer a variety of ambient RF measurement results suggesting that Wi-Fi AP densification cannot solely power personal devices such as wearables, but at best can trickle charge them in the hopes of extending battery life, the main hurdle being the small form factor of such mobile devices. In contrast, our measurements suggest that household devices, such as smoke detectors, can be powered by ambient RF harvesting. To this end, AP densification aids in increasing the total available power density, but also in distributing a smooth blanket of available RF energy thus minimizing harvesting-holes.