Abstract
If a Kalman Filter (KF) is applied to Global Positioning System (GPS) baseband signal preprocessing, the estimates of signal phase and frequency can have low variance, even in highly dynamic situations. This paper presents a novel preprocessing scheme based on a dual-filter structure. Compared with the traditional model utilizing a single KF, this structure avoids carrier tracking being subjected to code tracking errors. Meanwhile, as the loop filters are completely removed, state feedback values are adopted to generate local carrier and code. Although local carrier frequency has a wide fluctuation, the accuracy of Doppler shift estimation is improved. In the ultra-tight GPS/Inertial Navigation System (INS) integration, the carrier frequency derived from the external navigation information is not viewed as the local carrier frequency directly. That facilitates retaining the design principle of state feedback. However, under harsh conditions, the GPS outputs may still bear large errors which can destroy the estimation of INS errors. Thus, an innovative integrated navigation filter is constructed by modeling the non-negligible errors in the estimated Doppler shifts, to ensure INS is properly calibrated. Finally, field test and semi-physical simulation based on telemetered missile trajectory validate the effectiveness of methods proposed in this paper.
Highlights
The navigation errors of Global Positioning System (GPS) are not divergent with time, but a receiver usually performs less well in highly dynamic situations because there are external signals to be dealt with
In the static field test, the integration of GPS and Inertial Navigation System (INS) is not involved, and only GPS is utilized to compare the performance of the baseband signal preprocessing models based on signal-filter and dual-filter structures
This paper proposes a baseband signal preprocessing model, which has two pre-filters and uses state feedback values to control the generation of local carrier and code
Summary
The navigation errors of GPS are not divergent with time, but a receiver usually performs less well in highly dynamic situations because there are external signals to be dealt with. The baseband signal preprocessing is generally completed by a single pre-filter [11] Both carrier tracking errors and code tracking errors are included in the state vector, namely, these two kinds of tracking errors are tightly coupled through the state and observation equations. The rest of this paper is organized as follows: first, a baseband signal preprocessing model is designed based on a dual-filter structure, while the state feedback control values of carrier and code loops are derived in detail. This paper sets Xk “ ∆θk f k fk as the state vector of pre-filter 1, where k is theepoch, epoch, ∆θcarr is the carrier phase error (unit: rad), fkcarr is the input carrier frequency, and fkcarr is k carr thek changing rate ofphase the input carrierrad), frequency.
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