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Mark Borgerson

In article ,
says...
Mark Borgerson wrote in
.net:

"For civilian L1-band applications, the GPS system is actually a simple
spread-spectrum communication system.4 Figure 2 shows the signal
generation block for civilian applications. First, the 50-b/s navigation
message is repeated 20 times to produce a 1000-b/s bit stream, then the
repeated signal is spread by a unique Coarse/Acquisition (C/A) code with
a length of 1023 chips (the rate at which the pseudorandom noise code is
applied). The result is a baseband signal of 1.023 Mchips/s. As a result
of this spread-spectrum approach, the total processing gain (G) of the
GPS system can resolve a signal well below the thermal noise level."

-159dbm....wow. Too bad the spread spectrum on the damned CDMA/GSM
cellular systems don't work that well. -105dbm and my cellphone goes dead.

I think that the GPS has an advantage in that it only needs a few
hundred bits per second throughput. At that bandwidth there is a lot
more redundancy for the signal processing. A cell phone with 200
Hz bandwidth would result in less than optimal audio clarity! ;-)

(Remember that GPS works by measuring time (or phase) differences on
multiple signals. The actual digital bits are used to update ephemeris
information and transmit the time signals. Not quite audio bandwidth
there.)

Mark Borgerson