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Build 5G networks using open-source software, general-purpose hardware (2021)

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Re: Build 5G networks using open-source software, general-purpose hardware (2021)

#21

Post by tonyarkles »

anfractuosity wrote: post #16

Has anyone ever seen a software defined radio based phone/client out of interest? Also I've not properly read the paper yet but it mentions a VCTCXO (Voltage Controlled Temperature Compensated Crystal Oscillator), used with some of the SDRs. A while ago I bought a rubidium clock, which I thought may have been decommissioned from a cell tower. I'm curious how important the clock used is, for a cellular system?

I too have some kind of GPS-disciplined high accuracy clock (I don’t recall the exact tech but I think rubidium sounds right). From what I recall, precision timing is quite critical on the infrastructure side of things so that the user device can sync to it and accurately transmit and receive in the correct TDD windows.

One of the niftiest things was using the 10MHz reference clock as the clock source for my SDR, and tuning the receiver to the centre carrier of a nearby cell tower. I got a ~0.25Hz beat frequency out of it, which means this cheap eBay clock is accurate to about 1/3.2e9 Hz (cell tower was around 800MHz). Neat!

Re: Build 5G networks using open-source software, general-purpose hardware (2021)

#22

Post by teeray »

7to2 wrote: post #14
ackbar03 wrote: post #12

Earlier quoted context omitted.

What are the rules for broadcasting though? I thought you get hit with a fine without a lisence if you transmit any sort of radio-frequency

Doesn't 5G share some of the frequencies used by normal wifi? IIRC devices implementing one standard even cooperate with devices implementing the other to coordinate frequency use.

There is CBRS, which some phones are equipped to use. However, I believe it’s used only in conjunction with licensed bands rather than independently. It’s more of a capacity thing rather than a way to have a carrier using unlicensed spectrum (carriers are quite happy with the license barrier to entry).

Re: Build 5G networks using open-source software, general-purpose hardware (2021)

#23

Post by anfractuosity »

detaro wrote: post #20
anfractuosity wrote: post #16

Has anyone ever seen a software defined radio based phone/client out of interest? Also I've not properly read the paper yet but it mentions a VCTCXO (Voltage Controlled Temperature Compensated Crystal Oscillator), used with some of the SDRs. A while ago I bought a rubidium clock, which I thought may have been decommissioned from a cell tower. I'm curious how important the clock used is, for a cellular system?

> I'm curious how important the clock used is, for a cellular system Very, that's why they bother with things like rubidium holdover clocks. A lot of things depend on precise synchronization, both locally and between multiple towers.

Thanks, that makes sense, curious how they seem to get away with a VCTCXO in this case (or at least I couldn't seem to find mention of rubidium clocks in addition).

Re: Build 5G networks using open-source software, general-purpose hardware (2021)

#25

Post by zxexz »

steeve wrote: post #9

Shout out to Fabrice Bellard's Amarisoft, which deploys software defined 5G stations. [1] https://www.amarisoft.com/ [2] https://bellard.org/lte/

Fabricd Bellard is a rare person who seems to do and understand everything. I often just grab a cup of coffee and read through the code for random projects[0] of his.

[0] https://bellard.org/

Re: Build 5G networks using open-source software, general-purpose hardware (2021)

#26

Post by pgorczak »

anfractuosity wrote: post #16

Has anyone ever seen a software defined radio based phone/client out of interest? Also I've not properly read the paper yet but it mentions a VCTCXO (Voltage Controlled Temperature Compensated Crystal Oscillator), used with some of the SDRs. A while ago I bought a rubidium clock, which I thought may have been decommissioned from a cell tower. I'm curious how important the clock used is, for a cellular system?

Yes, for example there is srsue in https://github.com/srsran/srsRAN_4G (the predecessor of the stack used in TFA)

Re: Build 5G networks using open-source software, general-purpose hardware (2021)

#27

Post by detaro »

anfractuosity wrote: post #23
detaro wrote: post #20

Earlier quoted context omitted.

> I'm curious how important the clock used is, for a cellular system Very, that's why they bother with things like rubidium holdover clocks. A lot of things depend on precise synchronization, both locally and between multiple towers.

Thanks, that makes sense, curious how they seem to get away with a VCTCXO in this case (or at least I couldn't seem to find mention of rubidium clocks in addition).

Different qualities: Quartz crystals are better than Rb when looking at short periods. Long-term stability is normally provided by GPS. Rubidium beats crystals when it comes to stability over hours - it is added as a fallback for when GPS fails. If you don't have a requirement that your system can work lets say 24 or 48 hours without GPS sync, you can skip the Rb.

Re: Build 5G networks using open-source software, general-purpose hardware (2021)

#28

Post by fuzzyset »

seszett wrote: post #3

Is there anything one can actually do with a home-sized 5G network? As an individual, without being an actual telecom operator and all that.

I used to attend O-RAN meetings for a major telecom, and this was always the major hurdle I envisioned for the adoption of these things. On the technical side, it's a fun problem and interesting work, but O-RAN and open source cellular lacks the organic growth other open source projects can enjoy. A comparison point was always the networking space. Open source routers/switches broke into the Juniper/Cisco market, but it doesn't work as well in cellular. Small businesses can buy 1 or 2 open source switches and in aggregate that can start to change the market. No small business is going to own their own spectrum and deploy an open source cell network. And moving to shared spectrum eliminates most of the advantages over WiFi.

Re: Build 5G networks using open-source software, general-purpose hardware (2021)

#29

Post by moffkalast »

muyuu wrote: post #17
7to2 wrote: post #14

Earlier quoted context omitted.

Doesn't 5G share some of the frequencies used by normal wifi? IIRC devices implementing one standard even cooperate with devices implementing the other to coordinate frequency use.

short answer is no, but the frequencies aren't far off wifi operates at 2.4Ghz most typically and also at 5Ghz (shorter range but faster) 5G will be ranges of frequencies, depending on jurisdictions, but typically between these two frequencies which are the sweet spot for domestic usage in the US, 5G carries AFAIK have ranges between 2.5Ghz and just under 4Ghz in the UK we have EE, O2 and Three operating ranges aroun…

It always amazes me how pulsing some electricity into a wire at a specific frequency can get you arrested lmao. I really don't understand why there's any legislation at all covering anything above 1GHz where there's enough bandwidth for literally everyone to do whatever they damn well want and not enough range to do any damage at all.

Re: Build 5G networks using open-source software, general-purpose hardware (2021)

#30

Post by sybercecurity »

teleforce wrote: post #8

Systems Approach has a new book on Private 5G [1], with a hands-on implementation example in the Appendix [2]: [1] Private 5G: A Systems Approach: https://5g.systemsapproach.org/ [2] Hands-On Experience Appendix: https://5g.systemsapproach.org/software/overview.html

There is also a substack: https://systemsapproach.substack.com/

This weeks post covers the same thing as this post - how easy/difficult is it to actually set up a private 5G network compared to a similar WiFi deployment.

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