Signal distortions at GNSS payload level

With the development of Galileo and modernized GPS and the increase in performance of the associated signals (ALTBOC, MBOC, BOCcos...), various contributors, often neglected, may become essential factors in the payload design to better characterize the navigation signals and to asses their best achievable performance. In navigation systems these contributors could be: - the phase noise introduced by the satellite and receiver clocks oscillators, - the signal distortions due to payload amplifier, The aim of this paper is to analyze and optimize, thanks to simulations, the phase noise and the signal distortions introduced by the payload amplification unit. These distortions will be compared to the distortions due to the clock unit phase noise and their impact at different stages of the payload will be evaluated for a signal similar to the signals used in navigation systems. The first part of this paper will present the payload model chosen for the simulations and particularly the amplification unit. The clock phase noise model and the amplifier characterization will also be exposed. Then, the simulated navigation signal will be defined. Afterwards using Matlab simulations, the influence, on the receiver performance, of clock phase noise and amplifier non-linearities will be studied. Moreover, the influence of the filters position and bandwidth in the payload and the influence of the value of the amplifier input back-off (IBO) will be examined. To conclude, the suitable operating point of the payload amplifier and the best payload configuration will be determined.