5G Positioning Reference Signal Configuration for Integrated Terrestrial/Non-Terrestrial Network Scenario

The Fifth Generation (5G) New Radio offers a new Positioning, Navigation, and Timing (PNT) service with larger signal bandwidth and higher frequency carriers than previous generations, delivering more accurate measurements. This allows other vertical industries to benefit from this feature, opening up new possibilities. Furthermore, the 5G network includes Non-Terrestrial Network (NTN) elements such as Unmanned Aerial Vehicle (UAV), High-Altitude Platform Systems (HAPS), and satellites, which are gaining significant attention from the industry to allow for global communication. The future 6G aims to create a single network entity with multiple connectivity layers for all devices in all scenarios. Therefore, when combining both aspects of the 5G networks, the PNT service, and the NTN, there are several benefits such as: an independent and complete communication and navigation system under a single network, higher accuracy on the PNT solution than previous generation, global coverage for join navigation and communication, higher resilience on the positioning estimation, or new services offered. However, this is not free of challenges, as it is expected to achieve an accuracy, at least, similar to Global Navigation Satellite System (GNSS). One of the challenges is the multiplexing of the data and positioning service using a single infrastructure such a satellite. This paper has the purpose of analysing the effect in the accuracy of a delay estimator when a satellite constellation send a Positioning Reference Signal (PRS). Assuming that all satellites share the same frequency carrier and are synchronised between them. This 5G PRS main characteristic is its flexibility in terms of resource usage such as bandwidth, resource element density, symbols periodicity, a muting scheme, etc. This flexibility will be exploited in this paper to get a UE capable to estimate the Downlink Observed Time Difference of Arrival (DL-OTDoA) of the signal. Two challenges are present in this work, both are related to the characteristics of the RF channel between the Next Generation Base Station (gNB) and the User Equipment (UE): the first one is how the UE will cope with the high Doppler shift due to the high speed of the Low Earth Orbit (LEO) gNB increasing the Inter-Carrier Interference (ICI); and the second challenge is the effect of variable delay between OFDM symbols in the same slot and transmitter, increasing the effect of Intersymbol Interference (ISI). The contribution of the authors on this paper is the analysis of different PRS configuration that keeps a low interfere level between the moving gNBs. The result of this research highlight the impact that the length in number of subcarriers and number of OFDM symbol has in the accuracy of the delay estimation. It shows a trade-off in the constellation design, as a higher number of satellites in visibility also increase the ICI and ISI.