µStation: Data Broadcasting using FM Radio on Mobile Devices

Peer-to-peer (P2P) and location-based mobile applications have long been an important focus of ubiquitous computing. The proliferation of such applications requires power-efficient and overhead-free mobile broadcasting technologies.

In this project, we exploit the FM radio that is increasingly available on mobile devices to provide a data broadcasting system for P2P and location-based applications. The mobile FM receiver and transmitter are intended to allow users to listen to the broadcasted programs, and stream music to short-range home and automobile stereos, respectively. However, we go beyond such intended uses of the mobile FM radio and enable data broadcasting applications based on existing hardware.

We provide µStation, a software solution that operates without modification to device hardware, operating system, and the FM radio driver.

Publications

[Ubicomp 2011] "Data Broadcasting using Mobile FM Radio: Design, Realization and Application," Hang Yu, Ahmad Rahmati, Ardalan Amiri Sani, Lin Zhong, Jehan Wickramasuriya, and Venu Vasudevan, in Proc. ACM Int. Conf. Ubiquitous Computing (Ubicomp), September 2011. (PDF)

People

Hang Yu (Lead student)
Ahmad Rahmati
Ardalan Amiri Sani
Lin Zhong
Jehan Wickramasuriya
Venu Vasudevan

Software

Our software development of µStation is based on the Nokia N900 smartphone that adopts Maemo. N900 implements both the FM transmitter and receiver as Video4Linux radio devices and controls them over the hardware bus I²C. Hardware configurations such as switching on and off the FM radio or changing the FM channel can be achieved through the standard Video4Linux APIs.

The audio codec and FM transmitter in N900 do not enable very low-level interfacing, e.g., the user cannot directly send or get a digital audio as a binary stream. Nonetheless, our µStation software indirectly interacts with them using the following methods: for transmission, µStation plays the audio stream as a media which will be automatically captured by the FM transmitter; for reception, µStation records the audio stream from the audio codec with proper sampling frequency, using the PulseAudio utility available in Maemo.

Click here to download the source code of µStation.

How to use

Enable the FM radio on N900. For the FM transmitter, go to setting->connectivity->FM transmitter. Make sure to disconnect the USB cable and earphone while activating the FM transmitter. For the FM receiver, simply start the application ``FM Radio''. The earphone needs to be connected before using this application.
Gain root access through ``apt-get install rootsh'' and ``sudo gainroot'', and install Python and the PulseAudio utility on N900.
Source code for the µStation transmitter, receiver, and a few utilities are located in the tx, rx, and utility folders respectively.
To test the code, execute ``python MicroRS_tx.py'' on the transmitter. Press the ``start'' button on the GUI to broadcast the message; then execute ``parec --rate=44100 --format=ulaw -d "sink.hw0.monitor" | python MicroRS_rx.py'' on the receiver to see the received message.

Demo Application: Sync-Flash

Sync-Flash is a demonstrative application developed using µStation. Sync-Flash is able to coordinate multiple mobile devices to synchronously ``flash'', using their regular LED flash or screen. It can be used in concerts or sports games where the audiences/fans would like to present certain flashing pattern using their smartphones. Another usage of Sync-Flash can be to provide multiple ``slave'' flashes for photography, in order to offer additional light or reduce shadows.

Click here to check out the video demo of Sync-Flash.

Click here to download the source code of Sync-Flash.

How to use:

Prepare at least two N900 phones with root privilege. One of them serves as the ``master'' device, and others as ``slave'' devices.
Place the master and slave devices within the FM radio range of each other (typically <5 meters).
On the master device, run ``SyncFlash_init.py'' in the terminal.
On the slave devices, run ``SyncFlash.py'' in the terminal.
Press the ``Start'' and ``Stop'' button on the master device to enable synchronous flashing patterns on all slave devices.