The first GPS III launch has slipped to early 2017. With that I would expect the next three GPS IIF launches to be spread out.
Looking at the details of GPS III there are other possible ways that they could improve GPS.
1/ They will broadcast true L1C that is 3 times stronger than the current L1C/A.
2/ They will have the capability of using PRN numbers from 36 to 63.
3/ They will be considerably lighter, due to various reductions, one being lithium-ion batteries. It will be possible to launch two on one space vehicle.
Considering all three it would be possible using a current launch vehicle to launch one lighter GPS III into a higher geostationary orbit or a geo-synchronized orbit. The higher power signal would be a help at greater distance. Using higher PRNs would keep the 32 satellite galaxy for legacy users. The stronger L1C signal improves ranging accuracy.
Currently our WAAS signals come from payload packages from purpose built for others geostationary satellites. Current geostationary SBAS satellites broadcasting L1 only currently use PRNs above 32 for identification and those receivers with Ashtech Blade technology can put that L1 signal into the mix. Imagine having an L1/L2/L5 signal pretty much exactly SE and SW of your rover position 24/7. Too often I see a string of GPS line up in a SW-NE or NW-ES line overhead with nothing much else to contribute to the geometry.
Other GNSS systems are using geo-synchronized SBAS satellites. Imagine having 5 L1/L2/L5 geo-synchronized satellites in an orbit over the heartland of the USA. That would guarantee a GPS signal to the North 24/7. I imagine that 3 of the imagined satellites in ideal positions with another normal GPS for timing could provide better raw positioning by a factor of 2. I also imagine DOP of 1.5 24/7.
Because of the possibilities it would be standard to need 24 GPS channels per wavelength to keep the constellation in view. Let's see 3*24 = 72. I think I have seen that number a few times.
Paul in PA
Now that is a reason to buy all new GPS in about 2-3 years.
Thanks for the update Paul!