In the US, the FCC has specifically allocated 3.5ghz for open use[0]; paying for a license just gives you priority access to the spectrum. Use of the band requires checking in with a server to lease spectrum at a granularity of about 4 minutes. This is akin to if your Wi-Fi router could ask the FCC to give it a channel known to not have any users within a certain radius of itself.

[0] https://en.wikipedia.org/wiki/Citizens_Broadband_Radio_Servi...

If I want to deploy a custom 5G base station on this band 38, what hardware do I need? Are there free software solutions?

It's Band 48 and there are 321 FCC approved devices as of today

> Convenience of CBRS (Citizens Broadband Radio Service) in the US with no need to acquire spectrum licenses.

From: https://d1.awsstatic.com/reInvent/re21-pdp-tier1/private-5g/...

With 5G, many countries have reserved space and/or licensing mechanisms to get spectrum access for small local deployments.

Which other countries have such free spectrum ?

There is a ton of bandwidth up in the millimeter wave area if line of sight is not too obstructed. One whole GHz is nothing while with legacy WiFi it could be almost half the actual carrier frequency.

it's probably CBRS based system. there are a SAS (spectrum access system) administrators that in charge of managing spectrum so different users won't sit on same frequency. kinda like this https://www.comsearch.com/wp-content/uploads/2020/02/cbrs-sa...