International Global Navigation Satellite Systems Association
IGNSS Conference 2016
Colombo Theatres, Kensington Campus, UNSW Australia
6 – 8 December 2016
Improving Sensitivity on Kea CubeSat GPS
Receivers
Eamonn P Glennon
The Australian Centre for Space Engineering Research (ACSER)
School of Electrical Engineering and Telecommunications, UNSW, Australia
Phone: +61 2 9385 6702, Email: e.glennon@unsw.edu.au
Andrew G Dempster
The Australian Centre for Space Engineering Research (ACSER)
School of Electrical Engineering and Telecommunications, UNSW, Australia
Phone: +61 2 9385 6890, Email: a.dempster@unsw.edu.au
ABSTRACT
The Namuru and Kea FPGA based GPS receivers have been developed by
UNSW and its partners for over a decade. During this period, the hardware
and firmware have undergone continuous improvement, with the
introduction of L1 carrier phase, inclusion of orbit and high dynamics
modes, and disciplined oscillator and timing outputs being cases in point.
This paper describes the most recent set of upgrades related to improving
receiver sensitivity.
The use of a noise code-phase tap, in addition to the traditional early, prompt
and late code-phase taps, is described here, as are the benefits of such a
design. Different options concerning the use of the noise tap are discussed.
One involves measurement of 1 ms dump statistics and calculation of the
statistics of any pre-detection integration (PDI) with additional non-coherent
(NC) accumulations based on a mathematical model. Others involve direct
measurement of PDI and NC accumulation mean and standard deviations, as
well as direct measurement of PDI and NC distributions. It is explained how
direct measurement of the noise distribution can be performed efficiently,
thereby permitting a threshold to be produced that achieves a given false
alarm rate (FAR).
Also described are the modifications to the tracking loops necessary to
support the requirement for additional sensitivity, while still maintaining
stability. Finally, the need to maintain and achieve bit-synchronisation with
reduced signal levels is also discussed. Matlab simulation results comparing
the various methods are also presented.
KEYWORDS: GPS, receiver, cubesat, detection, threshold, weak-signal,
noise-finger, noise-tap
