t than for GEO systems. For HAPS, the transmission equipment is moving around or across a theoretical central point but creates a small Doppler shift. In order to synchronize to the 5G network, the UE has to detect the Primary Synchroniza- tion Signal (PSS) and the Secondary Synchronization Signal (SSS). Those synchronization signals allow time and frequency correction, as well as Cell ID detection. The requirement for a UE in a cellular network is to get a one-time detection probability at an SNR of the FDD downlink baseband signal of -6.4 dB with less than 1% false alarm rate (3GPP TS 38.101-4), 5 NG-RAN Evolution with robustness against initial frequency offset up to 5 ppm (3GPP TR 38.802). It is assumed here that these requirements apply to an NTN UE as well (in practice, it may be possible to relax these requirements to some extent). The Doppler shift depends on the relative satellite or HAPS velocity with respect to the UE, and on the frequency band. In terms of Doppler shift, the worst-case example that was considered in 3GPP TR 38.811 is a non-geostationary satellite at an altitude of 600 km with a satellite speed of 7.5 km/s. The resulting Doppler shift in the downlink signal yields up to +48 kHz at 2 GHz (equal to 24 ppm) and +480 kHz at 20 GHz center frequency. These Doppler offsets exceed the maximum initial frequency offset of 5 ppm for the synchroniza- tion requirement. To meet the 5G requirement of 5 ppm, the satellite altitude needs to be at least 13 000 km. As a solution, satellites can pre-compensate the Doppler offset for each of its spot beams, for example, for the beam center. The remaining Doppler offset within a beam footprint/satellite cell is significantly less than without pre-compensation. The movement of non-GEO satellites result in a drift of the Doppler offset of up to 544 Hz/s at 2 GHz and 44kHz/s at 20 GHz according to 3GPP TR 38.811. However, the remaining Doppler variation after pre-compensation for the individual satellite spot beams can be tracked by a UE in a way similar to te