 include seamless mobility between terrestrial and NTNs as well as dual connectivity (see Section 4.3). In dual connectivity, a UE may be connected simulta- neously with a terrestrial (which can host, e.g. a MgNB) and an NTN (which can host, e.g. a SgNB); this is one possible realization of seamless mobility. 5.3.5 NR Physical Layer Adaptations for NTN The differences in NTN propagation channel characteristics compared with terrestrial systems, which are mentioned above (e.g. long delay, larger cell sizes, fast movements of non-GEO satellites resulting in a high and variable Doppler shift as well as a variable distance between gNB and UE), affect not just the NG-RAN architecture and protocol stack, but also the physical layer. Some of the required PHY enhancements considered in the 3GPP study are described in the present section. For other aspects of the NR physical layer in satellite applications like the cyclic prefix dimensioning and demodulation reference symbols (DMRS) density in time and frequency, no changes are expected in NR (3GPP TR 38.811). Limited impact on the NR PTRS design is expected for scenarios in FR2 (i.e. frequencies between 24.25 and 52.6 GHz), where the maximum received SNR is limited by the phase noise of satellite on-board payloads. 5.3.5.1 Timing and Frequency Acquisition and Tracking A fundamental difference between terrestrial networks and LEO satellite or other non-GEO satellite networks is the relative mobility of the transmission infrastructure (gNB or gNB-DU), causing frequency and timing synchronization and tracking issues in a UE due to high Doppler offsets and drifts (3GPP TR 38.811). In cellular networks, the transmission infrastructure is usually fixed, except when on board a moving platform such as a train. In contrast, the transmission equipment is not static in most cases of NTN: For GEO systems, the transmission equipment is quasi-static with respect to the UE with only a small Doppler shift. For LEO, the satellites move relative to the earth and create higher Doppler shif