The TIDGET - A Low Cost GPS Sensor for Tracking Applications

In thii paper a low cost GPS sensor is described which has been specifically designed for use in a GPS tracking system. A variety of applications exist for GPS where the navigation data is not required onboard the host vehide, but only at a remote tracking site. These include tracking weather sensors (radiosondes). drifting buoys carrying oceanographic sensors, sonobuoys, wildlife tracking, and personnel and emergency location devices. In all these applications, cost is the driving factor. Also common to these applications is the lack of a requirement to provide a navigation solution at the source. The only requirement is for sufficient data to be relayed back to the tracking center for the location of the sensor to be determined. Previously, GPS tracking systems employed either low cost GPS receivers as sensors or GPS translators. With a translator, no processing is performed in the sensor. Instead, the GPS signals are simply retransmitted at a different frequency to a processing system where the location of the translator is computed. The problem with this approach is that the translated GPS signal requires a 2 MHz data bandwidth, which results in a very expensive communication link. The cost of the communication link generally results in the translator being more expensive than a full GPS receiver. A GPS receiver based tracking system operates by processing the GPS signals to provide either a position and velocity solution or just raw satellite measurements. This data is relayed back to a central facility where the location of the receiver is displayed. This requires only a low bandwidth data link, but increases the cost of the equipment through the addition of custom digital signal processing (DSP) chips and a microprocessor to process the GPS signals. The TIDGET’” sensor developed by NAVSYS provides a solution that combines the best features of a GPS translator and a GPS receiver. The TlDGET does not indude either a DSP chip or a processor yet can operate with a lower bandwidth data link than a translator through the use of a patented data compression technique. This unique approach has allowed the development of a GPS sensor that can be manufactured for less than $190 in quantity.