Improved Measurement System for the Evaluation of GNSS Receivers for Timing Applications

Cyber-Physical Systems (CPS) are distributed systems, which intensively interact with their environment, which they are seamlessly embedded into. Some CPS solutions must operate in real-time, as the embedding application is safety-critical, such as industrial control systems in Industry 4.0 applications or vehicular networks (e.g., Automotive/TSN Ethernet). The centerpiece of real-time operation is time synchronization, i.e., the nodes of the system must establish a common knowledge of time by exchanging messages over the standard communication channel. For this purpose, the IEEE 1588 protocol and its derivatives were developed. However, devices supporting IEEE 1588 are expensive for educational purposes and use closed software, making modifications for research impossible. Therefore, our larger goal is to create a low-cost IEEE 1588 master clock on an Open Hardware, Open Software basis to facilitate education and research. For this, one of the first steps is the selection of a GNSS (Global Navigation Satellite System, e.g. GPS) receiver. However, this is not a straightforward task; the different receivers need to be carefully evaluated by collecting and analyzing empirical data. So, we created a measurement system to compare, analyze, and evaluate different GNSS receivers. In this paper, we introduce the measurement system improved with time measuring capabilities and describe its theory of operation. Then we present the results and conclusions of an 11-day comparison measurement between a u-blox NEO-M8T timing receiver and a low-cost Quectel L86 general-purpose receiver with timing functions (our initial choices for implementation).