GNSS CODE AND CARRIER TRACKING IN THE PRESENCE OF MULTIPATH

It is well known that multipath represents a major error source in dif ferential GNSS positioning. Errors produced are unique to each antenna position and so are uncorrelated between the reference station and th e mobile receiver. Reduction techniques, such as narrow correlator spa cing(1) and the multipath estimating delay lock loop (MEDLL)(2) have i mproved the situation. However, reflected signals emanating close to t he antenna are not reduced by either technique. Carrier multipath is a particular problem because short delay multipath signals cause maximu m carrier errors. This study describes the analysis that has been carr ied out into code and carrier tracking in the presence of multipath. C ode tracking in this situation produces a non-zero mean error(3) and t he source of this bias has been investigated. Code and carrier multipa th errors of the global orbiting navigation satellite system (GLONASS) have been compared with those of the global positioning system (GPS). The effects of pre-correlation filtering on code and carrier multipat h errors have been determined using data from a measured correlation f unction. The multipath fading bandwidth is also discussed, and fast an d slow fading effects are presented. A comparison has been made of the performance of typical coherent and non-coherent code discriminators in the presence of multipath. The performance of the GPS and GLONASS P code signals have been determined with respect to code and carrier mu ltipath errors. (C) 1997 by John Wiley & Sons, Ltd.