Robust Receiver Tracking

Description Robust Receiver Design

The TRANSMIT prototype includes a software tool designed to analyse and improve the receiver tracking performance when scintillation is present. The software based tool, whose general scheme is reported in Figure 1, has been implemented to accomplish the following main tasks.

Scintillation monitoring. This is performed by computing the scintillation indices S4 and Phi60 which quantify, respectively, the level of amplitude and phase scintillation.

Robust tracking under scintillation. Three different tracking schemes are available. They are a traditional Phase Locked Loop (PLL) with fixed bandwidth and two types of adaptive KF based PLLs, namely a conventional adaptive KF (AKF) PLL and a Scintillation based Adaptive KF (SAKF) PLL. The latter exploits the knowledge about the scintillation level to tune its covariance matrix. Furthermore different time of integration values can be selected for the different tracking schemes

Interference mitigation. Interference can affect the computation of the scintillation indices and decrease the tracking performance of the receiver. This task aims to remove any RFI present by using either wavelet based or notch filter mitigation techniques.

Figure 1: General overview of the proposed receiver architecture for scintillation mitigation

 

Three different scenarios can be selected based on scintillation levels affecting the signal (low, medium, high) or, alternatively, a scenario where the signal is free of scintillation. Interference scenarios where a continuous wave is present have been proposed based on three different power levels (low, medium, high) with respect to the GNSS signal. Moreover the frequency offset with respect to the IF can be selected out of three values (20 KHz, 500KHz, 1MHz). Once the scenario of interest has been defined, a number of algorithms and parameters characterizing the receiver can be selected. A wavelet or notch filter mitigation technique can be activated to cope with the simulated interference, if it is present. The signal will then be processed by a software based receiver from which the three mentioned tracking architectures, and the related time of integration value, can be chosen. Finally, when the signal and the receiver architecture have been defined, the processor will provide the scintillation indices and some parameters useful to assess and compare the performance of the implemented tracking schemes. Specifically, the following outputs are given:

  • S4 (amplitude scintillation index)
  • Phi60 (phase scintillation parameter)
  • C/N0 (Carrier to Noise Ratio), measures the signal quality and, consequently, reflects the tracking performance
  • Phase Jitter (standard deviation of the phase error), measures the error in the phase estimate
  • PLI (Phase Lock Indicator), indicates the carrier tracking performance. The parameter is ranging between -1 and 1. Parameter values close to 1 indicate good tracking performance.
  • Carrier Doppler, indicates the tracking ability in following the signal dynamics

More details about the processor design can be found in [1] and [2].

References

[1] Susi M., R. Romero, F. Dovis, M. Andreotti and M. Aquino (2014). Design of a Robust Receiver Architecture for Scintillation Monitoring, IEEE PLANS 2014,Monterey, California.

[2] Romero R., M. Susi, M.Vuckocvic, F. Dovis, M. Andreotti and M. Aquino (2014). A GPS and Galileo carrier tracking architecture robust to ionospheric scintillation”, ENC 2014, 14-17 April, Rotterdam, The Netherlands