L1 Anomaly Analysis based on Measurements with a High Gain Antenna
In early spring this year GPS IIR-20(M) better known as SVN49 was launched which carries a L5 demo payload. This satellite got famous not only by the transmission of the first GPS L5 signals from a Medium Earth Orbit (MEO) in space shortly after its launch but rather by the detection of an anomaly on the L1 and L2 legacy navigation signal. This anomaly is caused by a L1/L2 signal reflection on the L5 payload via the auxiliary antenna port where the L5 payload is connected. Consequently the satellite transmitted not only the nominal L1, L2 and L5 signals but also an inherent multipath signal on L1 and L2 which has shown to be elevation dependent.
The paper gives a brief overview of the SVN49 and its transmitted signals. In the following the paper presents the L1 and L2 anomaly in detail and shows the effect on a GNSS receiver. Then a method is introduced for determining the multi-path error on L1 signal from calibrated measurement data taken with the high gain antenna. In a simulation a multi-path delay, attenuation and phase shift is added to a reference signal of SNV49 to create a distorted constellation diagram that matches the real SVN49 IQ constellation which was recorded using the high gain antenna. So it is possible to assess delay, power and phase of the multi-path…
…Evidently, the best way of coping with the SVN49 induced signal errors consists in the use of specialized tracking techniques that are insensitive to multipath in the specific domain of range delays. Once the cause of the SVN49 signal anomaly had been traced back to a reflection in the transmission chain an immediate effort has been made by Javad GNSS to adapt their advanced multipath mitigation techniques for the Triumph receivers to the specific case of this satellite…
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