Handheld Satellite Phone

I developed the MMI application layer for a handheld satellite communications device, built under iDEX Challenge 19, part of India's Innovations for Defence Excellence programme.

Reaching the hardware#

The application implements native SPI, UART, GPIO and I2C interfaces through the Android NDK. On a stock Android device none of those are reachable. The peripherals a satcom handset depends on sit well below anything a userspace application is permitted to touch, and no permission exists to request them.

The platform itself had to change. I modified AOSP to provision the application as a privileged system app on a Telit smart module, which gave it direct peripheral access and allowed its background services to run persistently rather than at the mercy of the ordinary process lifecycle.

This generalises. On embedded Android, asking whether an application is allowed to do something is usually the wrong question. The useful question is what the platform must grant, and whether you control the platform well enough to grant it.

Capabilities#

The handset supports satcom voice calling and messaging, offline maps, conversation threads and full-duplex live streaming. A network monitoring service sits underneath all of it, managing failover to a Wi-Fi-linked external high-gain antenna.

That failover service attracts no attention when it works, which is the point. Link quality on a handheld satcom device is not stable, and the handset has to absorb that instead of passing it to the operator.