The UE needs to measure its position and velocity by GNSS in Rel17. There will be frequent broadcasts from the NodeB containing the orbit of the satellite enabling the UE to calculate path loss, timing advance and Doppler. The device will then compensate its uplink signal which means the NodeB will only experience the additional delay compared to terrestrial systems.
The link-budgets and experiments carried out so far show that cellular NTN is feasible with regular handheld devices. One factor to consider is that although the propagation distance is greatly increased, the satellite base-station can utilize directional antennas to achieve large gains.
In 3GPP Rel17 was feature frozen in June 2022 and a completely commercially-deployable Rel17 is targeted for September 2022. Given some development time after this time, NTN services including user equipment will likely become available during 2023.
Yes, several procedures require synchronous connectivity between device and the network core. There is a study item on agenda for R19 on store and forward functionality. This is to mitigate the issue of discontinuous feeder links i.e. ground connectivity for delay tolerant applications.
This depends on the situation. First, there need to be feeder link switch-overs in place to secure connection to ground from any satellite. Secondly the device may have to do cell-reselection if moving into coverage of another cell. If moving out of the tracking area it will have to do tracking area update procedure (TAU). If a connection is established through one satellite this connection can be kept even if the device is moving between tracking areas. It may involve a tracking area update of the device.
Hardware should be re-usable i.e. software-patch-only could be feasible. Some algorithms like uplink transmission segmentation and time-frequency compensation may be too computationally heavy for some chips to do in SW, but will surely be included in HW in the future. The hardware platform must also include GNSS receiver to support compensation algorithms.
In NGSO, Earth fixed cells will require more advanced antennas leading to higher costs. On the other hand it is easier to manage system wise. The industry is divided on which is better and it is difficult to judge at this time which will be least expensive overall. In GEO it is trivial to have earth-fixed cells in a scenario that is very similar to terrestrial cellular with the exception of additional propagation delay and loss.
Depending on the orbit, configuration and antenna system this can be quite different. However 1-2 min of tracking with one CubeSat in LEO at 600km height is possible.
“The first issue with being submerged in water is the additional propagation loss in the water: Water being conductive severely attenuates radio frequencies. So it would be key to stay at a low depth. Better link budget, ie. directional antennas and higher transmission powers, can help overcome this issue to some extend.
The second issue is refraction between the air-water mediums. Refraction happens when a wave travels through a medium of one density into another medium of a different density. This causes the path of the wave to bend and also slows down the speed of the wave which in turn decreases the wavelength, which an underwater receiver must also account for.
In short the underwater scenario is very challenging and it would be advantageous to communicate at the surface.”