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GPS (GNSS) System Evaluation

Introduction

GPS (Global Positioning System) is often mistakenly used as the generic term for satellite-based position determination. Other systems such as Galileo, Beidou, GLONASS or NavStar also fall into the same category and are used by navigation systems to determine the position of the antenna on the earth. The correct generic term would be GNSS – Global Navigation Satellite System.

Allsystems need well working antennas. These can be tested in different measurement scenarios. On the one hand, the 3D directional diagram provides an overview of illumination and shadowing of the antennas.

On the other hand, live tests in various scenarios allow the antennas to be examined with real satellite signals. Both static long-term measurements, i.e. the antenna is stationary for several hours under “clear sky”. The data are recorded and evaluated afterwards. Here one can draw parallels to the 3D directional diagram. Short static measurements are also possible, where the received signal is attenuated more and more until the signal-to-noise ratio drops. A kind of system reserve can be determined and the data can be used to compare it with the manufacturer’s specifications.

Of course, dynamic tests, i.e. driving tests, are also possible. Here there are various possibilities to test the system. If, for example, the question is to compare different antenna positions or antennas, we at ATC can measure up to four antennas simultaneously per trip. This ensures that all environmental parameters (satellite constellation, weather, etc.) are identical for each antenna. To investigate versatile and challenging scenarios, we have established various test tracks for our customers. Among others, they include bridge underpasses and various urban and rural scenarios. In addition, we can take your individual needs into account to realistically design the desired application area of your GNSS application.

Figure 1: Tunnel with 5 m height and with 22m typical length corresponding to a highway width without opening between driving directions.

We can record typical GNSS data using four identical receivers to evaluate the most important parameters for signal strength and accuracy such as C/N0 (Carrier to Noise Ratio), DOP (Dilution of Precision) etc.. The simultaneous tracking with 4 receivers allows us to directly compare the statistical means or to determine the tolerance. These values represent a real added value in every development phase of your product, because you can identify and compare problems or advantages of single antenna configurations at an early stage.


In summary, GNSS antennas are an indispensable part of today’s and tomorrow’s world and analysing their behaviour in the real world is an important step in analysing and optimizing performance to ensure reliable reception of position data even under adverse environmental conditions.

Figure 2: Examples for statistical evaluation of recorded measurement data.