SCA Core Framework and AM, FM and P25 Waveforms running on an Android Smartphone
This article is based on excerpts of a White Paper from the Advanced Radio Systems group at the Communications Research Centre Canada.
The Communications Research Centre Canada (CRC) Software Communications Architecture (SCA) Core Framework, SCARI-GT, enabled Android™ smart phones to host JTRS SCA public safety waveforms: AM, FM, and APCO-P25.
Given their ability to host a wide variety of applications, commercial smart phones are surging in popularity and reaching new markets like public safety and military. Smart phones have essentially become computers with transmit and receive capabilities.
With this achievement, CRC demonstrated that the high performance general purpose processors now equipping these mobile platforms can be used to execute complex signal processing functions required for a wider set of communications protocols.
This accomplishment was the first step in turning smart phones into “smart radios”, as they can be reconfigured on the spot to adapt to the current tactical needs. Using the same commercial device, first responders and military personnel could switch from commercial networks to their own private networks, while continuing to have access to the plethora of other Android applications.
The demonstration worked as follows. To transmit from the smart phone to the commercial handset, the voice input was obtained via the phone microphone. An SCA Audio Device read the voice samples from the phone sound card device driver and fed the SCA waveform application. The waveform application performed the required signal processing (vocoder, modulator, squelch tone injector, etc.) and used an SCA RF Device to tune and transmit at a specific frequency. The SCA RF Device did not run on the smart phone. The demonstration works using any of the following: SDR4000 from Spectrum Signal Processing, a USRP1 or a USRP E100 both from Ettus Research LLC.
When the SDR4000 was used, the SCA RF Device actually was hosted on the PowerPC located on the SDR4000 blade itself. Using the USRP1, the SCA RF Device was hosted on a laptop connected to the USRP1. Using the USRP E100, the SCA RF Device was hosted on the ARM Cortex A8 located on the GumSTIX Overo inside the USRP E100 enclosure.
The SCA waveform applications communicated with the SCA RF Device via CORBA which provided location transparency. The smart phones were running ORBexpress™ for Android (C++ and Java) from OIS. The SCA waveform application was unaware of the actual physical location of the SCA RF Device which was being hosted by a remote processor. This made it very easy to run this demonstration using different hardware, which is exactly what the SCA specification was designed to allow.
Once the waveform reached the SCA RF Device, a signal was transmitted over the air to commercial-off-the-shelf public safety handheld devices. The waveform running on the smart phone used a virtual push-to-talk button to allow the user to toggle between transmission and reception modes.
The transmission from a commercial-off-the-shelf public safety handheld device to the smart phone used the reverse path. In this situation, the SCA RF Device fed the application with samples of the signal received over the air. The waveform applications performed the entire signal processing (demodulator, squelch detection, filtering, etc.) on the smart phone platform. And the resulting voice signal was sent from the waveform application to an SCA Audio Device which used the smart phone speakers to play the samples.