Christopher Schirmer

Over-the-Air Testing of Cognitive Radio Nodes in a Virtual Electromagnetic Environment

This paper provides an overview of ongoing research in over-the-air (OTA) testing for next-generation communication and data transmission devices with special consideration of cognitive radio (CR). Existing state-of-the-art techniques and their merits and limitations are discussed. We identify the requirements and issues for the OTA test in a virtual electromagnetic environment (OTAinVEE) which needs to address the more complex scenario of future networks, where interference emulation becomes a highly challenging task. A complex interference scenario arises due to the attempt to simultaneously utilize several opportunity dimensions such as frequency, time, direction (space), and polarization, in a dynamic manner in a multiuser scenario. Although MIMO-OTA testing addresses many limitations of single antenna-conducted test systems, more dimensions and parameters to be addressed in the new scenarios imply further increase in cost and complexity. Closed-loop OTA test setups for CR evaluation are discussed along with an overview of other test scenarios.

High time-resolution spectrum occupancy model for testing of cognitive radio devices

The ubiquitous problem of radio spectrum scarcity caused by ever-increasing traffic, e.g. in mobile communications, demands measures. One approach would be secondary use of spectrum by radio devices with cognitive abilities employing dynamic spectrum access. In order to avoid interference with the primary use of the spectrum, such cognitive devices must be thoroughly tested. In this paper, we present a high time-resolution model of spectrum occupancy, stemming from the activity of primary users, for testing purposes. The proposed model is based on a few statistical parameters and includes a novel parameter adaptation procedure that improves the accuracy of current models significantly. The intended use of the model is over-the-air testing of cognitive devices, for instance for prototyping purposes, e.g. evaluation of the achievable performance, or for conformance testing. The model parameters are extracted from measurement data in the GSM 900 downlink band obtained at the Ilmenau University of Technology campus. However, the modeling approach is not restricted to GSM 900 but lends itself to other bands and radio technologies, too.

Setup and verification of a multi-GNSS over-the-air wave field synthesis testbed

In this paper, we describe the principle, hardware/software setup, calibration and verification measurement results of a wave field synthesis (WFS) over-the-air (OTA) testbed for global navigation satellite systems (GNSS). It represents a new approach that, in contrast to conventionally conducted and open-field tests, realistically emulates real world scenarios under controllable and repeatable conditions. This enables the realistic comparison of receivers and algorithms especially for multi/beamforming antenna receivers as well as for receivers with integrated antennas. Having outlined the architecture and hardware setup of the WFS OTA testbed together with the GNSS constellation simulator, we describe the current 2D setup and the upcoming 3D installation. Then we discuss and present results of two different ways of calibration and validation carried out in the 2D setup: firstly, using an electromagnetic field probe, and secondly, using a commercial geodetic GNSS antenna with reference receiver in a 2.5D emulation.

Accuracy of an OTA system emulating a realistic 3D environment for GNSS and multi-satellite receiver testing

In satellite-based systems, such as global navigation satellite systems (GNSS), the use of antenna arrays is becoming increasingly common, as it allows various applications, such as jammer/spoofer suppression or improving the positioning accuracy in multipath-environments. Testing such equipment under realistic and reproducible conditions is often not feasible, for example in the case of a not fully deployed system (e. g., Galileo satellites) or testing of classified transmission technologies (e. g., Galileo public regulated service (PRS) receivers). For tests under reproducible and realistic conditions, we propose 3D wave-field synthesis (WFS) in an over-the-air testbed. This allows a realistic emulation of the radio environment under laboratory conditions. In this paper, a feasibility study for such a testbed is presented. Possible antenna setups for a 3D WFS laboratory environment are proposed. For these setups, the 3D WFS accuracy is investigated for emulating different polarization types and multipath reflections with arbitrary source directions. The results show that with presently available hardware for channel emulation and 3D WFS, a virtual electromagnetic environment can be created for testing receivers with (beamforming) antenna arrays of typical size (120 mm-300mm diameter).