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Since low-orbit satellites operate at low altitudes, they have the advantage of low communication latency compared to other satellites due to the short round-trip time of radio waves.

 

By linking low-orbit satellite communication and private 5G, it is expected that it will be possible to eliminate the shadow areas of terrestrial network communication such as remote areas and mountains, and to replace the ground network in the event that communication is impossible due to the destruction of the terrestrial network infrastructure due to war or natural disasters.

We examined the service scenarios that can link low-orbit satellite communication and private 5G, and examined the possibilities of providing services at the current level of technology implementation. 

 

1. Private 5G data network connection using low-orbit satellite communication

 

 

2. Control communication connection of Private 5G using low-orbit satellite communication

 

 

 

1. Private 5G data network connection using low-orbit satellite communication

When the N6 (Data Network) section of the private 5G network is linked using satellite link backhaul 

 

The test was conducted using HFR's my5G and my5GBox systems and SpaceX's Starlink to simulate a scenario in which private 5G was installed in areas with shadow terrestrial network communications, such as remote and mountainous areas where terrestrial network infrastructure is difficult to install, and connected to the data network using low-orbit satellite communication. 

 

The private 5G system was installed at the HFR office building located in Seongnam, South Korea, and the data network of the private 5G system was linked to the Internet using Starlink. The communication performance between a user's device (Samsung Galaxy S22) located in Korea and a server located in Japan was measured using Speedtest.

Throughputs of 271 Mbps and 33 Mbps were measured for downlink and uplink, respectively, and RTT was measured at 70 ms. RTT showed a very large variation between the presence and absence of downlink or uplink traffic. 

 

Table 1. Data Communication Performance of my5GBox Using Starlink (Speedtest)

 

Using satellite terminals, test servers, and private 5G networks, tests were conducted on servers located in Japan and South Korea.

 

1.1 Performance test results for satellite segments

In order to check the performance of the satellite section itself, the throughput of the section between the satellite terminal and the speedtest server connected to the satellite G/W was measured. The download speed was 293 Mbps, the upload speed was 36.5 Mbps, and the RTT (Round Trip Time) was measured at 49.3 msec.

1.2 Performance test results for satellite backhaul of private 5G networks
 

In order to link the N6 interface of the private 5G network to the Internet network, the performance test was conducted on the case of connecting to the test server through satellite terminal and satellite G/W.

 

The test results, including private 5G networks, showed a download speed of 271 Mbps and an upload speed of 33 Mbps, similar to the test results of the satellite segment itself. As a result of the latency measurement, the RTT (Round Trip Time) was measured at 70msec with the addition of the latency of the private 5 networks.

In the case of satellite backhaul of the N6 interface of the private 5G network, the same test was conducted when the test server was located in Korea. Including the satellite leg and the internet network, we measured an RTT of 106.3 msec.

 

Table 2. Data Communication Performance of my5GBox Using Starlink (Rakuten Server, NIA Server)

 

2. Control communication connection of Private 5G using low-orbit satellite communication
When the N1/N2 (Control Plane) section of the private 5G network is backhaul through a satellite link. 

 

When the N1/N2 (Control Plane) section of the private 5G network is backhaul through a satellite link.

It is possible to consider the case of a shared service of the 5G Core control unit, in which a radio access network (RAN) and a user plane function (UPF) are built within the target area of private 5G service, and the CP (Control Plane) of the 5G Core is provided as a data center or cloud service of the 5G operator.

In the case of the 5G Core control unit sharing type through satellite linkage, the N1/N2/N4 interface section of the private 5G network is connected through the satellite section. 

 

Figure 5 RAN and UPF of Private 5G Network are built on-premise, and the control unit is interlocked through Starlink 

 

2.1 Using IPSec VPN Tunneling
In a private 5G network, data is transmitted using SCTP (Stream Control transmission Protocol) to the N2 interface, which is the AMF section between CU/DU and Core.

 

It has been confirmed that SCTP messages on the N2 interface are not being transmitted normally over the satellite link (Starlink) (it is believed that the message is blocked by Starlink).

 

The test environment was configured so that control messages from the N2 interface could be sent and received normally using an IPsec VPN tunnel between CU/DU and AMF of Core.

2.2 Interval RTT Measurement
RTT measurements were performed for each section of the test environment configuration. The RTT measurement for each section was 14.2 ms for the 5G network (RAN-UPF-DN) section of Section A, 49.7 ms for the satellite section of Section B, and 36.3 ms for the Internet network between Korea and Japan.

2.3 5G Initial Call Connection
In the case of using a satellite link for transmitting control messages, measurements were made for the initial 5G call connection time for performance comparison. The initial call connection time was measured from the time CU/DU sent the Registration Request message to the receipt of the PDU session establishment acceptance message.

 

In order to send and receive messages between CU/DU and AMF of Core, a total of 5 times of transmission and reception are required for latency. As a result of the measurements, it was found that it took 0.62 seconds more when the satellite link section was included.

 

In the test environment, it can be confirmed that the delay in the satellite link section is not a factor of serious transmission delay in the configuration of the entire private 5G network, and it has been confirmed that the service can be provided without any problems through the network configuration using the satellite link even in the core control plane shared model. 

 

Table 3. Remote CPF Call Access Time for my5GBox Using Starlink

 

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