Drivers’ Warning Application Through Image Notifications on the FM Radio Broadcasting Infrastructure

In this paper a new application for transmitting image notifications on the FM radio broadcasting infrastructure, dedicated to warn drivers about significant road events and to increase the traffic safety is presented. The paper analyzes different technical solutions suitable for transmitting and receiving real-time image notifications in different scenarios by using the software-defined radio concept. In the first scenario, the image notifications are QPSK modulated and transmitted with 8 kb/s bit-rate by using a mono FM radio channel. In order to increase the speed of data transmission, the second scenario uses the FM subcarrier channels dedicated for broadcasting alternate services. In this case, a stereo FM radio channel is used to transmit data with 40 kb/s, 60 kb/s and 80 kb/s bit-rates, by using QPSK, 8-PSK and 16-PSK modulations, respectively. A new software solution to perform the real-time carrier synchronization for 8-PSK/16-PSK modulation based on a decision-directed PLL and non-linear decision block is also presented. The functionality of the proposed application was demonstrated by simulations for both transmission scenarios. Moreover, the first scenario was tested experimentally by using a professional FM transmitter and a simple RTL-SDR dongle as receiver. The customized baseband modulating signal including audio, data (image notification) and RDS signals was generated by using a device built by the authors. The receiver provides the digital signal through a USB interface to a software program, running on a processing unit, for demodulation. An experimental method for plotting the bit error rate vs.
$E_{b}/N_{0}$
ratio, based on signal-to-noise ratio measured with a software spectrum analyzer is also proposed. This method allows the characterization of the data transmissions performed by using an experimental setup and give hints about the QPSK signal power level compared to the other ones (audio and RDS signals).