An experiment in reducing cellular base station power draw with virtual coverage

Lack of access to cellular service often goes hand-in-hand with lack of access to power. For example, the GSM Association estimates that 95% of people living without cellular access in East Africa also lack access to grid power. This situation forces cellular network operators to build out power infrastructure along with their network infrastructure, dramatically increasing costs. While numerous equipment providers offer "low-power" GSM Base Stations (BTS) for use with renewable energy sources, these have a power floor of roughly 70W, which still necessitates a large upfront expenditure. The naïve solution to this problem is duty-cycling---simply turning off the equipment for portions of the day, usually at night. This commonly-adopted approach prevents important use cases such as all-hours emergency calling. Recently, we proposed a technique called virtual coverage to provide on-demand cellular coverage by introducing a "sleep" mode for cellular equipment. The solution turns off the BTS during low-utilization periods, but allows users to power the system back on using specialized autonomous radios if they need to communicate. Incoming communications also wake the BTS, facilitating two-way correspondence. While a potential solution, no real-world deployments have yet validated virtual coverage. The core goal of this work is do just that; we utilize virtual coverage to provide both low power consumption and on-demand access in a real cellular network during a six-month deployment in rural Papua, Indonesia. We demonstrate that the system was used and understood by customers, with more than half of subscribers using the system during "night" (i.e., on-battery) hours, making 730 outbound and receiving 755 inbound communications. Our scheme also allowed the BTS to be in low-power mode for 87% of night hours, reducing night power draw by 56.6%. We believe these results demonstrate that virtual coverage is a viable solution for reducing power draw in rural cellular networks.