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5G NTN

In 3GPP release 17, the so-called non-terrestrial networks were introduced. NTN is a generic term that encompasses satellites (GEO, LEO) as well as high-altitude vehicles.

Frequencies

The two initial frequency band groups specified by 5G NTN are called FR1 and FR2.

5G NTN FR1

There are two specified 5G NR bands in NTN FR1: n255 (L-Band) and n256 (S-Band).

Band Common name Uplink Downlink Duplex spacing
n255 L-Band 1626.5-1660.5 1525-1559 -101.5
n256 S-Band 1980-2010 2170-2200 190

Deployed networks

Skylo / Bullitt

One of the first commercial NTN deployments appears to be Bullitt Sattelite who is using network provided by Skylo .
It is using rented transponder capacity on existing Echostar 21 (S-Band, Europe) and Inmarsat (L-Band) GEO sattelites. Given that those (Like Echostar XXI) are in orbit for many years, they presumably are just traditional "bent pipe" satellites.

Echostar also appears to be in the process of setting up a separate 28-LEO-sattelite constellation just for NTN, where the actual gNB (or at least part of it) is in the sattelite itself. That's not deployed as of now (2023).

Peek at the network in July 2023

tnt had a quick look at the network in July 2023.

Receiver setup:

The setup was not ideal since the antenna was not the most appropriate (linear polarization while the sat should be LHCP) and the view is also partially obstructed. A good setup should be able to provide higher signal strength.

Here's what the spectrum in the upper part of `n256` looks like :

fosphor screenshot of received Echostar 21 s-band spectrum

There seems to be 4 carriers that look like 4G/LTE NBIoT.

RF Recordings :

Using SRS 4G suite (more specifically cell_search_nbiot and npdsch_ue examples), it was possible to sync and decode some information from the strongest signal.

cell_search_nbiot find a cell :

NSSS with peak=2.118723, cell-id: 11, partial SFN: 0
[INFO]: CELL SEARCH: Found peak PSR=9.212, Cell_id: 11
Found CELL ID 11.

And then we can decode it with `npdsch_ue` which will also save the MIB/SIB into a pcap : Show

The resulting PCAP and associated decode are attached:

In the decoding, you can see for instance that the PLMN is 901/98 which is indeed assigned to Skylo Technologies.

Files (3)
screenshot_spectrum_echostar21_20230712.png View screenshot_spectrum_echostar21_20230712.png 2.68 MB fosphor screenshot of received Echostar 21 s-band spectrum tnt, 07/13/2023 06:57 AM
npdsch.pcap npdsch.pcap 289 Bytes NPDSCH recorded by npdsch_ue tnt, 07/13/2023 07:16 AM
npdsch_decode.txt npdsch_decode.txt 15.5 KB NPDSCH recorded by npdsch_ue - Decoded by wireshark tnt, 07/13/2023 07:16 AM

Updated by tnt 8 months ago · 2 revisions

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