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Multipath Elimination Technology

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 MiLLennium GPSCard Software Version 4.50 Command Descriptions Manual Rev 1

Any localized propagation delays or multipath signal reception cause biases to the GPS ranging measurements that
cannot be differenced by traditional 

DGPS

 single or double differencing techniques.  Generally speaking, single

point positioning systems are not too concerned with multipath reception, as the system errors are quite large to
begin with.  However, multipath is recognized as the greatest source of errors encountered by a system operating
in differential mode.  It has been discussed that careful site selection and good antenna design combined with a
choke ring ground plane are fairly effective means of reducing multipath reception.

Internal receiver solutions for multipath elimination are achieved through various types of correlation techniques,
where the "standard correlator" is the reference by which all other techniques can be compared.

The Narrow Correlator tracking technology has a two fold advantage over standard correlators: improved ranging
measurements due to a sharper, less noisy correlation peak, and reduced susceptibility to multipath due to rejection
of 

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 code delays of greater than 1.0 chip.  When used with a choke ring ground plane, the Narrow Correlator

tracking technology provides substantial performance gains over standard correlator receivers operating in
differential mode.