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HIGH PRECISION KINEMATIC POSITIONING USING
SINGLE DUAL-FREQUENCY GPS RECEIVER
Y. Gao and A. Wojciechowski
Department of Geomatics Engineering
The University of Calgary
Calgary, Alberta, Canada T2N 1N4
gao(@geomatics.ucalgary.ca
KEY WORDS: GPS, Precise Point Positioning, Precise Orbit and Clock Products, Direct Geo-referencing
ABSTRACT:
Currently, high precision kinematic GPS positioning with centimetre level accuracy can only be carried out using differential GPS
(DGPS) positioning techniques which require the deployment of base receiver stations. The requirement to deploy base receiver
stations, however, spatially limits the operating range of the rover receiver to about 20 km from the base stations. As a result, it not
only increases the operational costs of equipment and human resources but also significantly increases the logistical complexity for
many applications such as land geodetic surveying and airborne geo-referencing and mapping. With the increased availability of
precise GPS satellite orbit and clock data in real-time from the International GPS Service (IGS) and many other organizations, high
precision kinematic positioning at centimetre to decimetre level is now possible using a single GPS receiver. Presented in this paper
are the methods and algorithms that have been developed at the University of Calgary for high precision kinematic positioning using
a single dual-frequency GPS receiver. Different from the conventional DGPS approach, the new system does not need a base station
since the position determination is based on the processing of un-differenced GPS code and carrier phase observations. This
eliminates the range limitation related to the conventional methods, resulting in instant advantages in field operations. A software
system developed at the University of Calgary will also be described along with numerical results to demonstrate the obtainable
positioning accuracy and its potential for various applications.
1. INTRODUCTION
Current carrier phase positioning with centimetre level
accuracy requires the combination of observations from a
minimum of two GPS receivers. At least one of these serves as
the base station with known coordinates, and the others serve as
rover stations whose position coordinates are to be determined
relative to the base station(s). Drawbacks of this approach
include the practical constraints imposed by the requirement
that simultaneous observations need to be made at the rover and
base stations, and that the rover station should be in the vicinity
of the base station(s), typically within 20 kilometres. These
constraints increase the operational cost and logistical
complexity in the field. Airborne mapping is a typical example
where direct geo-referencing using GPS currently requires the
deployment of a number of base stations on the ground if the
surveying and mapping is to be conducted over large areas. For
remote and rough terrain regions, the difficulty level would be
further increased. Direct geo-referencing using GPS without the
need to establish ground base stations would be advantageous
in such applications because it can reduce both equipment and
labor costs and simplify the field operations.
This paper describes a positioning method using un-differenced
code and carrier phase observations from a single dual-
frequency receiver, aided by precise orbit and clock data. Since
this positioning approach has no requirement for the
deployment of base station(s), it is a global positioning
approach capable of providing greater solution consistency with
increased operational flexibility. A software package developed
at the University of Calgary that achieves centimetre to
decimetre level accuracy with a single GPS receiver will also
be described.
845
The remainder of the paper is organized into four sections. The
concepts of kinematic positioning using a single dual-frequency
GPS receiver are first described in Section 2. Software
developed at the University of Calgary specifically for un-
differenced carrier phase processing is described in Section 3.
Results obtained from the software are presented in Section 4,
using various external solutions for reference. Concluding
remarks are provided in Section 5.
2. CONCEPTS OF PRECISE POINT POSITIONING
Conventional Standard Point Positioning (SPP) is based on un-
differenced GPS data processing and is subject to the influence
of all error sources. Major error sources include those
introduced by broadcast orbits and clocks, as well as
atmospheric effects. Since SPP is only able to provide position
solutions with an accuracy level of several metres, it is not
suitable for applications that require higher positioning
accuracy such as geo-referencing in airborne mapping.
With the advent of precise orbit and clock products with
centimetre level accuracy, the two errors associated with the
broadcast orbits and clocks can be significantly reduced. Once
these errors are removed from the observations, higher
positioning accuracy can be expected even when a single GPS
receiver is used, provided that new data processing algorithms
are developed. To date, there are many organizations, including
the International GPS service (IGS), Natural Resources Canada
(NRCan) and Jet Propulsion Laboratory (JPL), which offer
precise data in post-mission and real-time modes.
The method that derives high precision positioning solutions by
processing un-differenced carrier phase observations from a
