The system had to provide sub-metre positioning sufficient to correctly identify probe-vehicles travelling in a high traffic volume motorway network and interchange system. At the same time as position, vehicle velocity had to be given with an accuracy of 0.1 miles/hr or better. Vehicle position and velocity data was passed by cellular communications using SMS and GPRS data structures. The probe cars are run by a highways authority to monitor managed roadway contractor invoices for payment approval. The system had to run continuously without being affected by vehicle use. By example it was a requirement to upload and download data when the vehicle was not in use.
Our CPUpak-4 was modified to include a cellular telecoms card and built-in battery backup to maintain the 24/7 heartbeat services. Using remote cellphones the watch-keepers and maintainers were able to monitor the system through the use of QA messages. Any problem would be reported by SMS or GPRS immediately it occurred with location, vehicle ID and the nature of the fault. For advanced debugging a full fault history could be downloaded to a computer with NAVPak quality control software.
The main navigation was provided by a CPUPak-4 running a real-time O/S. The housing contained a NovAtel OEM4-G2-L band receiver corrected by OmniSTAR L band correction services. The vehicle also used a GPS-600-LB antenna.