Advice on getting started with LTE


#1

After reading a lot i’m looking into running a LTE network in the 13CM ham band.
This band allows some spacing for Digital communication (Which should include LTE)

For example there are these chunks in the 13cm bandplan 
2355.000	2365.000	Digital Communication (10Mhz/2*5Mhz)
2392.800	2400.000	Digital Communication (5Mhz)

According to the LTE frequency bands this overlaps nicely with Band 40
Band	Duplex  F(MHz)	Common name	Uplink/Downlink(MHz)	Duplex	Channel bandwidths(MHz)
40	TDD	2300	S-Band		2300 – 2400		N/A	5, 10, 15, 20

This should provide the possibilty to run a 5 or 10 Mhz channel in TDD mode at the respective frequency.
Both are in the range of the LimeSDR-Mini

Now i could use some advice on soft- and hardware, because documentation is either overwelming or incomplete.

As for now i found 3 capable opensource projects:
	1	OpenAirInterface AOI
	2	OpenLTE
	3	srsLTE
Which on would be most suitable for TDD in this application?
What are the hardware requirements at these Rates? (ie can they run on a SBC/RPi)
Any examples or other projects?

Last the uSim, to test this with an off the shelf UE(mobile phone) one would need a programmable Sim Card and programmer.

As for now i found 2:
	1	Sysmocom sysmoUSIM-SJS1 (10 pack only)
	2	Open cells SIM card (also has programmer)
Will Both work in this use-case?
Are there other sources or forum members offering them?

Any additions, comments hint and tips are welcome.


#2

I’ve heard it said that OpenAirInterface are not actively supporting LimeSDR hardware, which is a shame if true and while we’d love to be able to provide support on all the FOSS stacks out there, it just isn’t practical. Though may be worth a shot and could be there is just some minor “bit rot”.

Have anecdotally heard of people having more success with srsLTE.

Others, e.g. @cswiger, may be better positioned to comment.


#3

Likely, as OAI is rapidly moving into the 5g world. Sticking with specific versions of LimeSuite and OAI seems to work better than continuously patching the latest and greatest to try to keep up.

Like the idea of operating in the ham band - one speaker stated that the 900MHz European band is in the US ISM/ham band, and to be perfectly legal would need to be unencrypted and have a 10 minute cw id :slight_smile: I have the LimeSDR operating on 925.2 nearly permanently now.

Have not had a lot of luck with LTE - takes a lot of dedication and have moved on to other projects.


#4

Thanks gents,

Didn’t notice that OAI didn’t actively supports LimeSDR :frowning:
OAI also seem to be much more complex compared with srsLTE

Albeit that srsLTE seems not to support TDD as far as i could find browsing the code, only FDD
Probably if u where in the US you could realize it FDD in the 900Mhz band already. :slight_smile:

Still not sure how to approach this in FDD,. Will have to investigate that some more. Before a transatlantic LTE call could be made on HAM bands

Also orders some sims and a programmer at open-cells , have to wait for them to see if they work.

Feel free to add to this.


#5

So it’s not LTE, but the gr-gsm developers have had GSM running in 2.4GHz band, using this as an SDR PHY with OsmocomBB, then a modified Osmocom-based BTS/network stack.

Stream tags support is currently being added to the gr-limesdr blocks, which should mean that we can also try this out before too long. I must admit that I quite like the idea of running GSM in ISM and amateur bands. If you’re interested in voice and SMS it makes far more sense than LTE anyway, as you occupy much less bandwidth, less power is used and the range will be a lot better.


#6

Actually i did some puzzling before all this. and had a look at the bands for GSM, UMTS, LTE and even 5G

To make it more accessible to get started, being able to use a normal phone would be wishfull. It’s one thing to put a carrier somewhere, but pretty useless if users can’t connect. So running GSM in 2.4 outside the defined band/frequency’s would force us to use a special pc/sdr based UE

Unfortunately i could find no shared US space that overlaps with the Dutch bandplan were both could use the same frequency for 3G Gsm. Like @andrewback suggests

Guess for the US @cswiger ment the 33 cm band 902-928 MHz. which is used over here. (and if i’m correct you can’t fit the 45MHZ UL/DL spacing)
All tough there is also the same space in the US 13 cm band as over here. At least as far as i could figure out.

This lead me to LTE and that band 40 TDD. Otherwise i would indeed take the easy gsm route and also benefit from it’s smaller channels/spectrum and probably better range.
Also TDD doesn’t use 2 frequency’s in the spectrum

One more note, one would need either dual antennas
Or, if one wants to use a PA
for FFD a duplexer
for TDD a TRX switch (and a some modifications to switch it over GPIO’s


#7

Indeed, e.g. gr-gsm PHY + OsmocomBB mobile, then similarly with an SDR-based network.

Agree that being able to use actual handsets would be preferable.


#8

Just received the sim card but had no time to test them.
Unfortunately i also got confirmed srsLTE only supports FDD at this moment.

There might also be possibility to use band 30 WDS
The downlink would be between 2350- 2360 10Mhz BW
Only the uplink would be outside the ham band 2305- 2315
alltough this would be transmitted by the handset, not on the lime