Software-Based GPS Receiver a Research and Simulation Tool for Global Navigation Satellite System
ABSTRACT
Global Navigation Satellite Systems (GNSS) have been used for the past 20-30 years
successfully both in civil and military community. Transit, GPS and GLONASS are examples of
GNSS. GPS has already proved it’s availability and reliability for many applications. In near
future, new GNSS called Galileo, will be launched by Europe. However, the receivers for all
these systems are built using application specific integrated circuits (ASICs), which we often
call hardware GPS receiver. A user has the least level of flexibility in setting or implementing
the parameters in this type of receiver. Especially, the level of flexibility is limited for the
researchers and developers to implement their own algorithms. Software-based GPS Receiver
(SGR) helps us processing the GPS signal at the lowest level of GPS raw signal data from the
antenna. A SGR consists of a front-end device that converts the radio frequency signal from the
antenna to an intermediate frequency in digital format. The signal thus converted is processed by
high level programming language to compute position and velocity. In SGR, it is possible to do
acquisition and tracking using different parameters and threshold values, which give a user total
flexibility of operation. This helps in processing weak signal, multipath mitigation and simulate
“what-if” scenarios. In this paper, we will discuss about software-based GPS receiver and show
how it can be used for research and simulation in the field of Global Navigation Satellite System.
1 INTRODUCTION
Global Navigation Satellite System has become a necessity tool for navigation and positioning
in both civilian and military field and applications. Global Positioning System (GPS) is a
satellite-based navigation system. It is based on the computation of range from the receiver to
multiple satellites by multiplying the time delay that a GPS signal needs to travel from the
satellites to the receiver by velocity of light. GPS has already been used widely both in civilian
and military community for positioning, navigation, timing and other position related
applications. The system has already proved it’s reliability, availability and good accuracy for
many applications. Due to this nature, in future, other countries like Europe are going to launch
new satellite-based navigation system called Galileo. There is also a proposal to launch Quasi
Zenith Satellite System for navigation in Japan.
It is necessary to simulate and analyze new signal structures for the development of new
satellite-based navigation systems. In the research community, many researchers come out with
new ideas and algorithms for better accuracy of GPS by mitigating or minimizing various types
of errors and effects like multipath. However, it is quite difficult to implement the user
developed algorithms in the current hardware-based GPS receivers. The hardware-based GPS
receivers contain ASICs that provide the least user flexibility. Thus, it is necessary to have
Software-based GPS receivers, at least in the research community for easy and quick
implementation, simulation and analysis of algorithms, parameters and threshold values. Since,
the CPU processing power is increasing with reduced cost, it is now possible to build real-time
software-based GPS receivers at least for static or low dynamic environments. As predicted by
Moor’s Law, the CPU power is increasing and we hope that this trend will continue in future as
well and hence, it will be possible to develop real-time all environment software-based GPS
receivers. In this paper, we briefly introduce the architecture of a SGR, signal processing
technique and give some examples of simulation using SGR.
