This paper investigates the interference challenges of Non-Terrestrial Networks (NTN) enabling Positioning, Navigation and Timing (PNT) services. Current mobile communication standards already provide native positioning methods for terrestrial networks (TN), especially by implementing the positioning reference signal (PRS) in the downlink transmissions. This capability has been demonstrated to achieve sub-meter level positioning, even with flying base stations in dedicated networks. Upcoming releases of the Third Generation Partnership Project (3GPP) standardization are expected to expand even more the positioning capabilities by integrating them over NTN deployments. Combining navigation and communication signals enables the concept of multi-layer PNT systems in a cost-effective manner. In a multi-layer PNT system, the transmitted PRS from different platforms, such as satellites, High Altitude Platforms Stations (HAPS) and drones, experience distinct time delays and Doppler shifts received at the user equipment (UE). In contrast to TN with ground-fixed base stations, the high time-delay variation and Doppler shifts of low Earth orbit (LEO) NTN constellations cause interference among the PRS transmissions. This inter-satellite interference certainly needs further investigation. Guidelines and a novel metric are proposed to illustrate the impact of PRS interference transmitted from a LEO constellation, in order to design NTN-based PRS transmissions together with communication signals in an optimized approach for PNT purposes. By approximating the PRS interference as additive white Gaussian noise (AWGN), a general guideline can be stated: the higher the bandwidth, the lower the degradation of the ranging accuracy due to interference. This paper shows the achievable ranging accuracy for an example LEO constellation considering relevant inter-satellite interference scenarios for NTN PNT systems.      «

This paper investigates the interference challenges of Non-Terrestrial Networks (NTN) enabling Positioning, Navigation and Timing (PNT) services. Current mobile communication standards already provide native positioning methods for terrestrial networks (TN), especially by implementing the positioning reference signal (PRS) in the downlink transmissions. This capability has been demonstrated to achieve sub-meter level positioning, even with flying base stations in dedicated networks. Upcoming rel...     »