GPS Multipath Estimation and Mitigation Via Polarization Sensing Diversity: Parallel Iterative Cross Cancellation

Chun Yang and Alec Porter

Abstract:	Multipath estimation is affected by both the underlying signal to multipath ratio (SMR) and multipath to noise ratio (MNR). This paper proposes to strengthen the multipath signals for more accurate estimation before their ultimate removal. This is achieved by using a dual circularly polarized antenna. The GPS signal is right hand circularly polarized (RHCP). Upon reflection, it becomes left hand circularly polarized (LHCP) in most cases. Being matched to the RHCP signal, a GPS antenna has an inherent anti-multipath capability. This polarization discrimination, in conjunction with other antenna design features, typically offers a multipath attenuation from 3 ~ 10 dB. This amount of attenuation is not large enough to suppress the multipath signals to a harmless level in the carrier and code phase measurements, but makes the multipath parameter estimation more difficult in the presence of noise. With correlation functions available for both the RHCP and LHCP signals, the paper sets forth a mitigation technique based upon the cancellation of direct and multipath signals on the LHCP and RHCP correlations, respectively, in an iterative manner. The dual polarization architecture allows for parallel iterative cross cancellation (PICC), which is expected to outperform the sequential iterative cancellation (SIC) applied to the RHCP signal alone. Upon convergence, the RHCP signal is multipathfree allowing for accurate estimation of the direct signal timing. The direct signal can be removed from the LHCP signal, leaving clean multipath components for such applications as a multipath meter. Simulation results are presented to show the multipath cancellation performance as compared to the theoretical multipath error envelope and to the thermal noise errors under various SNR conditions for different multipath and polarization parameters. Sensitivity of the approach to the polarization discrimination factor is also evaluated.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	2707 - 2719
Cite this article:	Yang, Chun, Porter, Alec, "GPS Multipath Estimation and Mitigation Via Polarization Sensing Diversity: Parallel Iterative Cross Cancellation," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 2707-2719.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In