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B Multipath Elimination Technology
80 MiLLennium GPSCard SW Version 4.503/4.52 Command Descriptions Manual Rev 2
Figure B-4 Comparison of Multipath Envelopes
SUMMARY
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. SA contributes the most errors
when it is active. Generally speaking, single point positioning systems are not too concerned with multipath
reception unless SA is inactive so that multipath and ionospheric errors are the largest. 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 the GPSAntenna model 600, or good antenna design combined with a
choke ring ground plane are very effective in 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 C/A 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.