Here is somethings to add to the FAQ.
Q: How to determent if WAAS is working and active while gpsd is running? If WAAS is not working, how to make it work?
I own a BU-353 S4 by Globalsat which has WAAS, but I do not see how to check that it is working.
Also, I saw where someone used 4 units to impove the data from GPSes some years ago, and I thought it can be done by simple software and 4 units.
Q: How to have 4 GPS units working at the same time on one computer?
I plan on buying 4 units and have them separated by a small distance (less than the 1.5 m length of usb connector) and a USB hub to combine the data to bring to a computer. I think this paper (I have not see it but the abstract is on the same line of thought) might help http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6166295 The problem that I see is the software related to each gps talking with the combining software.
John W. Nicholson