WAAS is the"Wide Area Augmentation System" developed by Stanford under contract to the FAA. The intent is to improve the accuracy of GPS so that it can possibly be used in the approach phase for commercial aircraft. This has been under development for almost 10 years.

New INMARSAT satellites (geosynchronous) are used to transmit differential GPS correction data to remove some of the common mode range error noise. There are a geographically dispersed array of GPS reference stations that produce a set of range error contours for each GPS satellite that are then relayed through the INMARSAT links to your receiver where you calculate the corrections that are appropriate for your approximate current location.

Since the correction data is transmittesd in "L-band" as are the GPS signals the receiver is little more complicated and the performance greatly improved, however, this is much less important now that S/A (Selective Availability) has been turned off.

An OEM unit should be a little more rugged and therefore better suited for an automotive application where it can be mounted in the location that best suits the reception of the signals. Controlling it completely (power on/off etc.) from the serial port will also lead to a more finished solution.

Lynn