Signal in space (SIS) analysis of new GNSS satellites

In the last 12 month a number of major milestones were reached by different satellite navigation systems. New satellites of Galileo, GLONASS and COMPASS are in space and can be used for navigation. Especially for the Galileo system has been started an important phase with the launch of the satellites FM-3 and FM-4 in October 2012. Consequently, there are 4 satellites of the Galileo system in orbit and the navigation performance can be tested in real environments on ground for the first time. Although for most of the systems mentioned above the expected signals according to textbooks or ICDs are known, in reality due to imperfections several deviations can be seen. Therefore and, especially, since the complexity of the satellites and also the requirements for a precise and robust navigation are constantly rising, all of the newly available signals of the existing or emerging navigation satellite systems have to be analysed in detail in order to characterize their performance and imperfections as well as to predict possible consequences for user receivers. Since the signals are well below the noise floor, the authors use a specifically developed GNSS monitoring facility in order to characterize the GNSS signals. The core element of this monitoring facility is a 30m high-gain antenna at DLR / Weilheim which raises the GNSS signals well above the noise floor allowing detailed analysis. Doing this analysis differences in the signal quality were found in the different generations of the Chinese navigation satellite system COMPASS, which show influences on the navigation performance. The paper shows an overview of new navigation satellites in orbit. The fully renewed and modernized DLR GNSS monitoring facility is introduced which now allows coherent capturing of two signals at a time. Doing so inter-frequency analysis or axial ratio behaviour of the transmitted satellite signals are possible. For selected satellites a detailed signal analysis is performed revealing important characteristics of these signals. The acquired high gain antenna raw data in combination with a precise calibration are used for a wide range of analyses i.e. signal power, spectra, constellation diagrams to detect anomalies and assess the signal quality. In addition the signal quality not only of selected new satellite will assessed but also the signal quality development over generations will discussed based on an example of the COMPASS/Beidou system with new results of the satellites M4 and M5.