A Software Defined Radio Experimental Platform for GPS/GNSS Signal Reception Analysis

Abstract

GPS is becoming a crucial element in daily life and in global information infrastructure. GPS nowadays is becoming more reliable thanks to the technology of A-GPS and D-GPS which uses the Internet and cellular network to enhance the accuracy. However, there is still plenty of room for improvement in the GPS operations. A versatile experimental platform that allows researchers to directly receive raw data from satellites is critical to advance further research.

We use a software defined radio (USRP) platform with open source GNSS software to perform the related experiments. We choose the USRP N200 as the software defined radio (SDR) for our work, because of its very good signal processing performance at an affordable price. Unlike mobile phones, or even most GPS chip evaluation kits. The GPS data received from USRP can be utilized to compute pseudo ranges based different satellites. And the pseudo range can be valuable when analyzing the accuracy of computing the locations. With the open source software, the users can easily access and customize their own software development to target the specific application.

We built a portable experimental environment based the USRP to carry out field tests at various locations. Two additional limitations of GPS chip evaluation kits are their low quality clocks, and very limited computing resources for more sophisticated experiments.

This thesis will talk about this portable software platform and the project which was conducted on it to explore and investigate some crucial problems existing in today’s GNSS technology, for example, multipath problem and hybrid GNSS system problem.

By investigating into these problems using SDR GNSS receiver, the benefits of adopting this software oriented approach will be talked about and how this approach in the future can save valuable research and experiment time will also be demonstrated.