Automated Test-bench Infrastructure for GNSS Receivers – Case Study of the TUTGNSS Receiver

S. Thombre, J. Raasakka, T. Paakki, F. Della Rosa, M. Valkama, J. Nurmi

Abstract:	The prototype Global Navigation Satellite System receiver (TUTGNSS) developed at the Department of Electronics and Communications Engineering (ECE) of Tampere University of Technology (TUT) is now in the performance testing phase. TUTGNSS is a GPS/Galileo L1/E1 + L5/E5a dual-frequency dual-constellation receiver jointly developed by TUT and its international partners under 2 European Union Framework Programme (EU-FP) research grants. Testing of GNSS receivers requires active participation of humans to initiate, control, record results of, and terminate the test cases. These operations are extremely inefficient in terms of person-hours and lead to measurement inaccuracies and inconsistencies, which renders the test results unreliable, especially in time-critical and power-critical tests such as sensitivity and time to first fix (TTFF). Furthermore, accessing the internal signals of the receiver at different stages of processing is necessary to pinpoint the exact location of anomalies. Using traditional black-box techniques, it is only possible to test the final outputs of the receiver. This paper describes the automated test-bench developed at TUT for analyzing the overall performance of multi-frequency multi-constellation GNSS receivers. The proposed test-bench includes a data capture tool (dCAP) to extract internal process information, and the overall controlling software, called automated performance evaluation tool (AutoPET), that is able to communicate between all modules for hands-free, one-button-click testing of GNSS receivers. The first section of the paper is dedicated to a background literature review of state-of-art in similar tools. It is observed that, currently there are very few solutions available in the commercial or academic domain which can perform end-to-end fully automated, yet customizable testing of GNSS receivers [1], [2]. A commercial testing tool [3] was recently unveiled, which claims to perform similar automated testing of GNSS receivers. However, it is not fully customizable by the end-user, and it has the limitation that it can be used only with its parent company’s own proprietary signal simulators. The proposed dCAP is a hybrid (software controlled hardware) entity that extracts the user-defined internal process data from the different modules (acquisition, tracking, bit decoding, etc.) of the GNSS receiver under test (RUT) and stores it in a computer via a 100 Mbps Ethernet link. This data can then be post-processed to investigate for any anomalies in the intermediate stages of the RUT. The dCAP is controlled by the AutoPET, and it is possible to specify within its configuration file the various internal parameters that need to be extracted from every stage of the RUT. The dCAP is designed to be flexible enough to allow additional parameters to be defined without affecting the original coding structure. The AutoPET is implemented completely in software and communicates with the RUT via RS-232 and NMEA protocol and with a commercial GNSS signal simulator via an RS-232 link. It holds the GNSS test-cases with user-defined iterations and other system settings. The experimental version of AutoPET has already been used for making test runs on the TUTGNSS receiver with positive results. It is now possible to initiate the overall testing of the receiver with a single button-click and the results are stored in the computer without any human intervention. Test scenarios currently included in the ‘library’ of the tool are: time-to-first-fix (TTFF), position accuracy, acquisition sensitivity, tracking sensitivity, C/No estimation accuracy, and reacquisition time. A user-friendly Graphical User Interface (GUI) ensures that the AutoPET and dCAP can be replicated for any future GNSS receiver with minimal effort, and it can be operated by persons without deep knowledge of the receiver technology itself. Another innovative aspect of the AutoPET is that it uses considerable multi-threading to perform the receiver testing. Multiple threads are necessary to keep track of the receiver operations and simulator feeds simultaneously, so that an appropriate interrupt can be generated when the receiver has performed the desired operation. The next section of the paper is dedicated to describing in detail the GPS L1 performance tests subjected upon the TUTGNSS receiver using the two proposed automation tools. It also describes the results of the tests while comparing them with the desired specifications. Comparisons show that, the TUTGNSS receiver conforms to the desired specifications quite well, and in case of discrepancy, for example the tracking sensitivity, suggestions are provided on how improvements can be made. For simplicity, only results from the GPS L1 single frequency tests are included in this paper. The techniques and tools described can easily be replicated for more complex combinations of frequencies and constellations by making simple configuration modifications. The next section of the paper is dedicated to describing how this can be implemented. In conclusion, added to the benefits of automation in terms of improved accuracy and personnel efficiency, the proposed automated testing tool is a cost-effective solution to anyone working on GNSS receiver technology. This test-tool is portable (software platform-independent), easy to install and execute on any computer with the basic scientific software. From an academic point of view, the dCAP is useful for teaching the spectral characteristics of GNSS signals at every stage from deep inside the receiver to researchers or university students in laboratory exercises. In one instance, the experimental-dCAP was used to extract detailed baseband tracking information that helped to locate signal anomalies caused by electro-magnetic interference/modulation with the 50Hz power supply line. Such anomalies would have been impossible to detect with traditional black-box testing practices. In other words, the proposed research has a practical as well as academic appeal. References: [1] S. Thombre, E. S. Lohan, J. Raquet, H. Hurskainen, J. Nurmi, Software-based GNSS Signal Simulators: Past, Present and Possible Future, Proceedings of the European Navigation Conference (ENC GNSS 2010), October 2010 in Braunschweig, Germany. [2] P. Boulton, R. Borsato, B. Butler, K. Judge, GPS Interference Testing: Lab, Live, and LightSquared, InsideGNSS, July/August 2011. Available at: http://www.insidegnss.com/node/2674 [3] Spirent Communications UK, TestDrive GNSS: Simplify testing, reduce cost, increase efficiency of GNSS test, Product Datasheet, March 2012. Available at: http://www.spirent.com/~/media/Datasheets/Positioning/TestDrive%20GNSS.pdf
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	1919 - 1930
Cite this article:	Thombre, S., Raasakka, J., Paakki, T., Della Rosa, F., Valkama, M., Nurmi, J., "Automated Test-bench Infrastructure for GNSS Receivers – Case Study of the TUTGNSS Receiver," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 1919-1930.
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