F I G U R E 1 I M A G E B Y M I K E D A R C Y O F A M N ; F I G U R E 2 I M A G E B Y E U A N M I L L A R O F E N S E M B L E

support renewable energy sources, OC also features two internal solar charge controllers for external sealed lead acid and internal lithium ion batteries. The internal lithium-ion battery, with a built-in UPS system, works as a backup to allow the system to fail gracefully when the local grid fails. This suite of power cleaning and support systems allows OpenCellular systems to coexist in the chaotic reality of rural power.

For network, OpenCellular includes a built-in out-of-band satellite backhaul. This is not designed to be used for daily communications (as the cost could be prohibitive) but instead to reduce the cost of debugging a failed network. Operators will not need to send an engineer out to the system (see Figures 1 and 2) if the backhaul has failed and instead can use the satellite link to gather critical data about the issues with the system, such as the status of individual hardware components or stability of power or backhaul subsystems. This collected information can also be relayed to the local maintainer (potentially by the access point itself) who can then assist in maintenance (for example, cleaning the solar panels) even when the main power and backhaul is down.

The highly variable power and network situation in rural areas invites another design imperative: OC optimizes for low cost over reliability. In rural areas, the vast majority of downtime will be due to failures in the related infrastructure, including power and network. Increasing the reliability of the OC system itself will only marginally increase the overall uptime of the network. Instead, it is better to be cheap and easy to replace or repair.

Recent estimates have GSM cellular coverage at 80% of the world. 11 These networks have stopped expanding as operators instead invest in higher-revenue urban 3G or LTE installations. Ironically, while ubiquitous connectivity may be a myth, the ubiquity of the cellular phone itself is not. In our travels, we have yet to come to a location where these devices were not already woven into the fabric of the community. For example, when we first set up our network in Papua, Indonesia, the network recorded over 3,000 unique mobile phones despite being a four-hour drive from the closest cellular network. 9 It may seem counterintuitive for there to be cellular phones where there is no network, but the devices are more than just phones. They are also rugged rural entertainment consoles, with built-in battery power, speakers, and headphone jacks. Where there is no cell network there is often no radio and instead, people bring their entertainment with them. All the while, many members of the rural community regularly travel to dense urban areas where there is coverage and use their phones there.

This situation—a large installed
base of mobile phones in areas without
any cellular access—provides an op-
portunity for novel connectivity solu-
tions. OC is designed to meet the cur-
rent capabilities and needs of users in
these communities. The first revision,
OC-SDR (OpenCellular Software De-
fined Radio), is a GSM cellular base sta-
tion with support for basic GPRS/Edge
data connectivity. The second revision,
OC-LTE is an LTE-based extension of
the platform. These two access points
allow locals to get on the network using
their existing phones. Then the opera-
tor can determine various services the
community would like (for example,
using IVR for low-literate populations)
and eventually upgrade to broadband
as economics and availability of other
associated infrastructure (such as pow-
er for smartphones) matures.

Power and Backhaul

To keep costs low, one must leverage what infrastructure is available in the remote communities. Surana et al. 9 found that grid power was unreliable in rural India, producing both brownouts and voltage spikes capable of destroying equipment. They also learned that the lack of general Internet access was a huge issue in diagnosing failures. OpenCellular mitigates these problems by building backhaul and power solutions into the system. The platform includes power cleaning, variable input voltages, and support for Power-over-Ethernet (PoE). The system also supports PoE’s power sourcing equipment (PSE) standard, allowing the OpenCellular access point to “daisy-chain” power to phone chargers or even another OC instance. To better

While ubiquitous
connectivity may be
a myth, the ubiquity
of the cellular phone
itself is not.

Figure 1. An OpenCellular operator working in remote location. Figure 2. OC operator in community location.