GPS World, March 2011
Road TRANSPORTATION FIGURE 4 SIGNATURE Prototype Onboard Unit OBU approach Using a radio data service RDS broadcast for example ephemeris data and EGNOS corrections could be provided on a continuous basis RDS is an auxiliary signal to the FM radio broadcast system and is used routinely for supplying travel information to in car navigation systems As data is broadcast from known locations and over a de applicable for all users receiving data from a given transmitter A drawback of RDS is that it has a relatively low bandwidth and it takes approximately 35 seconds to broadcast an ephemeris message for a single satellite A further argument against RDS as a long term solution is that analog radio signals are progressively being phased out in favour of digital alternatives With the far greater bandwidth of digital audio bßroadcasting DAB ephemeris data for 12 satellites could be broadcast in less than 1 second We are evaluating alternative message content and trans by providing additional content other than the ephemerides in the assistance message Onboard Unit The SIGNATURE OBU FIGURE 4 is based on a single board computer SBC offering a high degree receivers and positioning algorithms and manipulate differ is a powerful platform for developing and assessing OBU devices and their component parts particularly as it allows lots of useful diagnostic data to be logged The OBU hosts a bespoke receiver which exploits the continuous availability of assistance data available through a high speed data packet access connection and does not attempt to decode navigation data directly from satellite signals This allows its design to focus on rapid signal acquisition with high sensitivity and to achieve a rapid TTFF even in areas where conventional receivers struggle The SIGNATURE prototype has been designed using the well known SAT SURF SAT SURFER platform The receiver developed by the EPFL implements massive parallelization by making use of the fast Fourier www gpsworld com March 2011 GPS World 31
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