Adaptively Steered Antenna Array and Receiver Testing with Multi-RF Output GNSS Simulator NavX®-NCS Professional

Thorsten Lück and Günter Heinrichs, Achim Hornbostel

Abstract:	The modernization of existing and creation of new global and regional navigation satellite systems as well as the modern threats to navigation receivers like intentional and unintentional interference rises the need for realistic testing of GNSS receivers not only under normal conditions but also under severe environments with low received power levels, shadowing and/ or massive multi path as well as under interference conditions. The innovative and advanced design of the NavXR-NCS Professional GNSS Simulator gives users significant advantages in terms of flexibility and upgrade potential, allowing to simulate the RF signals received by one or more GNSS antennas as realistic as possible by maintaining full reproducibility and configurability of the simulated environment. The objective of this paper is to show specific capabilities and strengths of IFEN’s premium-grade GNSS simulator. For this purpose different tests were conducted with the GALANT receiver of DLR IKN. GALANT utilizes an array antenna with four radiator elements and applies adaptive array processing after correlation of the signals of each of the four antenna channels. Because the array processing is applied after correlation, the directions of arrival of the GNSS satellite can be estimated and individual antenna beams can be adaptively steered to the satellites in view by adaptive digital beam forming. Additionally, strong interference signals are suppressed by generation of nulls during the beam forming process. By comparison of the estimated satellite directions with the known satellite positions from the decoded almanac the attitude of the array itself can be determined. In order to achieve a high accuracy in the direction of arrival estimations and the attitude determination a continuous calibration of the differential carrier phases between the four receiver hardware channels is performed by utilization of a special PRN code. For real antenna measurements the calibration PRN code is generated internally within the receiver, mixed up to RF and fed into a calibration port of the array antenna, from where it is distributed to the four antenna channels. However, in the hardware simulations no antenna is used and the simulator signals are directly fed into the receiver RF frontend [2, 1]. As these techniques exploits the different carrier phases of the observed GNSS RF signal in each antenna element, the correct simulation and generation of the differential carrier phase for all antenna elements is crucial. With the NavXR-NCS, the carrier phases for all antennas can be simulated and generated with an absolute accuracy of better than one half of a degree (approximately 0.3 mm with respect to the L1 carrier). To support DLR’s calibration technique, the NavXR-NCS can be programmed to simulate a zero-range/zero-doppler calibration signal using a configurable pseudo-random code (PRN). With this, the receiver’s internal calibration routine achieved an accuracy of about 1°. Exploiting the capabilities of the NavXR-NCS, it is also possible to simulate a phase coherent, modulated or un-modulated interference signal for all antenna elements. This allows to demonstrate the awesome interference mitigation capability of the GALANT adaptive antenna array. The present paper starts with an overview of the NavXR-NCS Professional GNSS Simulator that gives the user the potential to simulate a total of 108 channels. Any GNSS constellation and frequency may be freely assigned to any channel and re-assigned, as required, in subsequent test scenarios. The assortment of channels is totally under the control of the user and allows the same hardware to simulate a wide range of signals. The user has the option to use the same hardware to simulate different signals, in different test scenarios, and simulate up to nine different signals simultaneously. Furthermore, it keeps significant upgrade potential, giving the NavXR-NCS Professional GNSS Simulator outstanding versatility. The NavXR-NCS Professional GNSS Simulator may be fitted with up to 4 independent RF outputs. That could be used to simulate multiple vehicles (for example, for real time kinematic (RTK) or formation flying scenarios), or multiple antennas on the same vehicle (for example, for attitude determination scenarios), or for separate elements of a Controlled Reception Pattern Antenna (CRPA). In addition to the independent RF outputs the Simulator is fitted with a combined RF output for standard single output testing. The complete GNSS constellation simulator fits in a 2 high-units / 19 inch housing plus the control computer, which could be either a powerful notebook or a one height-unit / 19 inch computer. The paper discusses the GALANT adaptively steered antenna array and receiver and demonstrates the test scenarios generated with the GNSS simulator. Exemplary results of different static and dynamic test scenarios will be presented, demonstrating the attitude determination capabilities as well as the interference detection and mitigation capabilities.
Published in:	Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014) September 8 - 12, 2014 Tampa Convention Center Tampa, Florida
Pages:	363 - 371
Cite this article:	Lück, Thorsten, Heinrichs, Günter, Hornbostel, Achim, "Adaptively Steered Antenna Array and Receiver Testing with Multi-RF Output GNSS Simulator NavX®-NCS Professional," Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014), Tampa, Florida, September 2014, pp. 363-371.
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