How do you mitigate GPS multipath errors in aviation receivers?

Multipath occurs when GPS signals reach the receiver via reflected paths in addition to direct path, causing ranging errors. Mitigation techniques: Antenna design - choke ring antennas attenuate low-elevation signals, pinwheel/helical antennas have controlled gain patterns; Receiver processing - narrow correlator spacing (reduces multipath error envelope), double-delta correlators, multipath estimating delay lock loops (MEDLL), and vision correlator techniques; Signal processing - carrier smoothing of code (dual-frequency benefits), multi-frequency combinations (L1/L5), and RAIM monitoring for gross errors; Site selection - antenna placement to minimize reflections (ground plane, avoid structures). For precision approach, GBAS ground stations characterize local multipath. Future multi-constellation, multi-frequency receivers have inherent multipath resistance through signal combination.