GNSS Aircraft Receiver RNAV
There are, broadly speaking, three types of GPSGPS —Global Positioning System (USA) receiver. A sequential receiver looks at the 4 satellites required in for the fix sequence, one after the other. This means is takes longer to process the fix, but is cheap and readily available, and therefore used for car satnavs and phones. A multiplex receiver will have more than one channel, and cycle quickly between (for example) the four satellites in two packs of two. The top end receiver, a multichannel receiver, looks continually at "all in view" - that is, all of the GNSSGNSS —Global Navigation Satellite System satellites that it currently has line of sight with. Although the most expensive, this is used in commercial air transport because of the safety implications, as well as its ability to make use of the RAIMRAIM —Receiver Autonomous Integrity Monitoring and FDEFDE —Fault Detection and Exclusion systems, both of which require looking at more than 4 satellites at once.