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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.