GPS is incapable of getting even close to the resolution required from radar altimeter, and altitude ranging in GPS was always worse than its circular error pro

GPS is incapable of getting even close to the resolution required from radar altimeter, and altitude ranging in GPS was always worse than its circular error probable in 2d - and the best accepted dynamic, unaided GPS deviation is big enough to show the same result between correct landing, missed landing, and a fiery crash. The problem is that radar altimeter is very precise device that for best precision needs to use all of its 200MHz bandwidth on transmit. And there are no methods to recognize that as part of the return in its own 200MHz band (or in the guard band) a random CDMA-encoded signal radiated outside of allocated spectrum (happens) reflected of random crap around the airport and gets interpreted as valid data. This is an analog system where the analog characteristics are core to how it works, so the methods that allow tight channel spacing in communications tech do not work for radar altimeters