A new, robust, high data rate digital FM subcarrier system for mobile ITS applications

Intelligent transportation systems (ITS)-formerly called IVHS-are essentially mobile information utilities, designed to deliver information about the status of the surface transportation system to users in mobile vehicles, pedestrians, and people in offices and homes. Except for the last class of users, mobile communications by radio is the only viable means for delivering this information. By far the largest volume of data that needs to be transferred from the infrastructure to mobile users concerns the state of congestion on highways. Since this can be done in a one-way broadcast mode, significant savings in communications cost and radio-frequency (RF) spectrum acquisition time can be achieved if an existing, widely available medium is used. For ITS purposes analog subcarriers have neither the capacity nor the robustness in a mobile environment to perform traffic data distribution. What is needed is a true digital subcarrier system that has enough capacity to reliably distribute traffic data with low latency in a mobile environment. This paper describes the design, development and testing of a new high-speed digital subcarrier system (HSDSS) called the Subcarrier Traffic Information Channel (STIC). STIC provides a digital data capability that performs extremely well in a multipath fading environment and yields a user data rate of about 8 kilobits per second (kb/s). Another important feature of the system is that it provides all of this capability from a single FM station; a critical factor for U.S. ITS deployment.