Impact of Omitting Intermodulation Products on Ranging Performance in Satellite Navigation

Abstract

Current global navigation satellite systems (GNSS) form and transmit navigation signals utilizing intermodulation (IM) products in their multiplexing schemes to enable the operation of the satellite’s high power amplifier (HPA) with a constant envelope input. Feeding a constant envelope signal into an HPA allows for an efficient operation close to its saturation point minimizing the output power backoff (OBO) while additionally minimizing phase distortions. However, IM products applied in the context of satellite navigation can be regarded as a waste of scarce satellite power. IM products are transmitted within the composite navigation signal, but neither provide ranging possibilities nor convey navigation data while restricting the available transmit power of signal components usable for navigation. Increasing the transmit power of usable signal components would be desirable as better ranging performance is achieved. Omitting IM products to a certain extent might be one way to enable GNSS satellites to form usable signal components with increased power but might lead to increased OBO losses and distortions arising at the HPA. Hence, we investigate in this paper the trade-off between increased usable signal power and amplifier efficiency when varying the portion of IM products in existing composite satellite navigation signals. We evaluate the performance by optimizing achievable receiver efficiency and then time of arrival (TOA) estimation error standard deviation. The results suggest that the scalable Interplex methodology is in most cases able to increase the ranging performance of each signal component.