Аннотация
With its several inherent advantages, an ultra-tightly coupled GPS/INS/PL
system will have a dramatic increase in both commercial and defence
applications. Integrating the correlator measurements, I (in-phase)
and Q (quadrature), with position, velocity and attitude from INS
in a Kalman filter characterises this type of system. The Doppler
feedback derived from the corrected INS is then fed back to the carrier-tracking
loop to remove the dynamics from the GPS/PL ranging signal, thereby
reducing the carrier tracking bandwidth. This reduction in bandwidth
is the principal reason behind its popularity. Some of the applications
where this system can be used are: dynamic scenarios, weak signal
conditions, interference & jamming environments, etc. Although the
code loops are not directly aided by the INSderived Doppler in an
ultra-tightly coupled system, accurate knowledge of Doppler information
from INS results in better code thresholds. This improvement in threshold
further increases the accuracy of raw measurements and also the jamming
immunity. Normally the code loop bandwidth is about 1 to 3 Hz in
an unaided case, but in this type of integrated system the bandwidth
is typically less than 1 Hz as the code dynamics are mitigated as
well. In this paper, the mathematical analysis pertaining to code
dynamics is presented. An E-L/E+L discriminator is utilised as a
software-based receiver is used for the experiments. Various trajectories
with different dynamics are generated and the code-tracking loops
are tested, and the results show substantial improvement in the code
thresholds.
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