As indicated in TR 22.891
, the propagation delay is limited by physics, i.e. the speed of light (299 792 458 meters per second) in air and 2/3 of the speed of light in fibre connection. With these limits, 1ms one way transmission latency can be mapped to 300 km air propagation or 200 km for fibre based transmission.
When the distance between 2 sites increases (several thousands of kilometres), the difference in latency between air and optical fibre transmission media may become critical for such applications and hence it is worth considering alternative network options compared to optical fibre based network.
A constellation of Low-Earth orbiting satellites, where each spacecraft is equipped with a gNB and interconnected with other neighbouring spacecraft's via Inter Satellite Links, provides access to UEs. Such a type of constellation system would provide an overlay mesh network for users that have a need for long distance connectivity with improved latency performance or specific end to end security.
The constellation of satellites can be considered as contributing to a single overlay 5G system, or as contributing a many 5G systems as many countries covered by the Constellations for instance.
Global organisations with distributed sites around the world may require long distance connectivity between the sites with critical requirements including low latency, reliability and/or end-to-end security to support critical application domains such as High Frequency Trading (HFT), Banking or Corporate communications.
An organisation is structured on a set of distributed sites throughout the globe that needs to be interconnected. This organisation has strong requirements with respect to security as well as with respect to Quality of Service (QoS), both for bandwidth and latency, since operations are related to these metrics: for mining or oil & gas exploitation, for trading, etc. The case of High Frequency Trading is addressed here.
5.7.2 Pre-conditions Word‑p. 18
The organisation purchases services with a network operator, with a number of UE's:
UE A is located in Paris Stock Exchange. Computers are connected to UE A for HFT.
UE B is located in Tokyo Stock Exchange. UEs including Computers are connected to UE B for HFT.
UE C is located in New York City Stock Exchange. Computers are connected to UE C for HFT.
UEs for other Stock Exchanges London, Chicago, etc. are also connected to the network.
The trading computers need to share information for improving their efficiency. Buy/sell orders need also to be exchanged between trading computers, the optimum route through the overlay mesh network with lowest latency has to be selected to maximise the performance of the organisation.
The operator has access to a number of routes, whether terrestrial or satellite-based, in order to guarantee an end-to-end performance for its customers. Based on the monitoring of the performances (latency influenced by the delay as well as the network load) of the different routes, the satellite network overlay is selected for some UE to UE connectivity case (for instance Paris SE to Tokyo SE, Paris SE to Chicago SE). For other shorter distance cases (Paris SE to London SE), the terrestrial routes may be preferred.
The organisation is offered the highest end-to-end QoS performance for global connectivity, with optimal routes that can be established for each path, including through the satellite overlay.
When considering the delivery of services, with the possibility of global extension of coverage considering some QoS constraints, a satellite global overlay may be considered.
A 5G system with global satellite overlay access shall be able to select the communication link providing the UEs with the suitable quality with respect to latency, jitter and required bit rates.
Two 5G systems with satellite access connected to each other shall be able to select the communication link(s) providing the UEs with the suitable quality with respect to latency, jitter and required bit rates.
A 5G system shall be able to support meshed connectivity between satellites based on 5G RAT.