The GPS system was conceived and designed primarily for open-sky operation. In this environment, GPS works extremely well, even in situations with high speed and high dynamic manoeuvres. Today GPS is being used in environments that are extremely challenging, such as built up areas and even indoors. To make things even more difficult, devices used in these environments are often targeted at consumer markets and hence have extremely low cost/price targets.

Optimising device performance in these low power, complex signal environments is a significant challenge. Using a GNSS simulator enables controlled, progressive testing to be undertaken. Spirent’s simulators enable complex environments to be readily created, including effects such as vehicle motion, antenna patterns, multipath and shadowing from buildings. Satellite power levels can be changed by the user or modeled to suit the particular scenario via a number of approaches depending on the situation. Interference, for example as would be seen from terrestrial microwave towers, is also supported by Spirent’s interference simulation system available option on many of our products. In this case, the interference effect is modeled consistent with the movement and orientation of the vehicle.