Multi-carrier vector phase locked loop for ionospheric scintillation mitigation

Patrick Henkel, Kaspar Giger, Christoph Günther

Research output: Contribution to conferencePaperpeer-review

Abstract

A new multi-carrier phase locked loop is proposed to improve carrier tracking during severe ionospheric scintillations and other frequency selective distortions. The kernel is a multi-carrier weighted least square phase estimator that predicts carrier phase information on all frequencies. The weighting coefficients represent the variances of the phase measurements and are derived from carrier wavelength, scintillation affected carrier to noise ratio, loop bandwidth, predetection integration time and phase scintillation variance. Amplitude scintillation results in a Nakagami-m distribution of the carrier to noise ratio with deep fades of more than 20dB. The proposed multi-carrier phase estimator uses time-differenced ionosphere-free phase measurements to eliminate ambiguities and both receiver and satellite biases. Initial simulation results indicate robust carrier tracking even if both E5a and E5b signals suffer from severe amplitude scintillation of -20 dB and a standard deviation of 20 degrees for the scintillated phase. The ionospheric drift is estimated in advance by a new geometry-free, ionosphere-preserving linear combination. The time-difference of such a combination includes only the ionospheric drift and the combined phase noise. Note that ranges, clock errors and troposphere are removed by the geometry-free condition. These geometry-free, ionosphere-preserving linear combinations can be computed from two or more frequencies and benefit from a low noise level: The time-differenced L1-E5a combination amplifies the elementary phase noise only by a factor 2.5. If three or more frequencies are available, the additional degrees of freedom are used to minimize the impact of ionospheric scintillation on the ionospheric drift estimation. Scintillation patches often cover only a small part of the sky and do not affect more than two satellites simultaneously. Therefore, the multi-carrier PLL is extended to a multi-carrier Vector-PLL that commonly tracks the phase measurements of all satellites. The tracking is performed in position domain and includes the change in position, the drift of the user clock and the temporal gradient of the troposphere zenith delay. The phase estimates of the multi-carrier phase estimator are ionosphere-free. Consequently, the loop filter is also ionosphere-free with a reduced noise level at its output. This is an advantage over a traditional PLL that also includes the filtered ionosphere.

Original languageEnglish
StatePublished - 20 Mar 2008
EventEuropean Navigation Conference, ENC-GNSS 2008 - Toulouse, France
Duration: 23 Apr 200825 Apr 2008

Conference

ConferenceEuropean Navigation Conference, ENC-GNSS 2008
Country/TerritoryFrance
CityToulouse
Period23/04/0825/04/08

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