1. Finally, the subsystem includes the Motorola GPS receiver and integrated serial communication package. This unit was chosen for two reasons: First, it was readily available, inexpensive, and matched the existing serial communication protocol. Secondly, the unit is capable of receiving DGPS corrections generated by a second receiver. The use of differential GPS allows a reduction in positional error on the order of 50-60%, resulting in a nominal radial positional error of less than 2 meters. While DGPS corrections are currently available over marine-band broadcast, it is impractical to install a secondary receiver on the UAV for this purpose alone. Instead, a second GPS receiver is integrated with the base station, and after fixing its location by averaging over a period of many hours, the base station can compute real-time DGPS corrections which are then broadcast to the UAV over the 900MHz telemetry link. This system allows for a high degree of positional accuracy without the associated bulk and cost of a marine-band DGPS receiver.
2. One of the key advantages offered by the use of Windows XP Embedded is that it can utilize any driver written for the full Windows XP. As a result we have been able to integrate our devices incredibly fast, and with the support of the device manufacturer. With six serial devices, we were able to leverage the power of Dot Net by simply dropping in the Sax.Net communications module and using regular expression matching to parse out the info from the varied data streams. Data Processing