Sidelink-Enabled Cooperative Localization for xG Non-Terrestrial Networks

Location awareness is essential for next-generation (xG) network capabilities, including satellite-terrestrial integration, adaptive beamforming, and vehicle-to-everything (V2X) scenarios. The recent proliferation of low Earth orbit (LEO) satellites offers a high signal-to-noise ratio (SNR) alternative to global navigation satellite systems (GNSSs) for positioning, navigation, and timing (PNT) in mobile ground terminals. However, the timing drift of LEO clocks complicates the localization problem by introducing clock offset variables into the parameter vector used for location inference. Conventional PNT approaches are rigid in their requirements for LEO non-terrestrial network (NTN) size and access to gNodeB (gNB) base stations (BSs). Others relax these constraints and suffer from substantial localization errors and refine the estimate through filtering over time. This paper presents the theoretical foundation for joint cooperative localization and synchronization (JCLS) using time-of-arrival (TOA) measurements from both downlink (DL) and sidelink (SL) signals. System performance simulation results demonstrate meter-level 3-dimensional positioning, highlighting the potential of the proposed approach for robust and efficient localization in challenging electromagnetic environments.