hello
im really intrested in making a gsm bts with osmo bts and i read the articles about calypso based gsm bts but calypso chipsets are obsolete and hard to find, also i know that its feasible with usrp, bladerf and sdr boards. but these are really expensive boards for my budget, so i found that cheap Texas instruments ics cc11xx can operate as rf transciver in 960mhz. so is it practically possible that i for example use cc1125 as rf transciver to launch osmobts gsm?
Hmm, it certainly would be out of spec as you need a higher symbol rate than the datasheet claims it can support.
Then there also is the issue of the sync sequence being in the middle of the burst, so those chips probably wouldn’t be able to sync themselves to it… so you would need to have some sort of capturing raw samples and then trying to do it in software.
thank you for replying. what about something like cc1350 with upto 2.4 ghz maximum frequency, for first step i dont what it to be a real bts that multiple devices can register on it with routing and other stuff, i just want a single phone be able to register on it and i forward voip calls over gsm call and texts over sms. i know openbts can do something like this with limesdr but it has over 250$ price tag and my students cant afford it. but if i manage to make something cheap, affordable and easily available i may make them intersted in this stuff
I am not an expert in those chips, but I would be very surprised if they would be anywhere near the requirements you’d need for a GSM base station, which is (among other things) 270kSymbols/s GMSK modulation (not exactly MSK or FSK), full-duplex operation, and continuous operation. All those low cost wireless ICs that you’re mentioning are meant for short burst, half-duplex communication.
If it was so easy to use a random low-cost radio IC to implement GSM, people would have done it.
You’d either have to use a RF transceiver IC specifically designed for GSM. Those are really all EOL these days (and were meant for the MS side, not the BTS side, so you have to pray you can tune them to the other band and use two of them, like in the CalypsoBTS hack). Or you go for a general-purpsoe SDR approrach. And general-purpose SDRs with full-duplex and sample timestamping are sadly rather expensive. They’re of course overkill as they’re targeted at wideband communications. For GSM all you need is 270kHz narrow-band. But that’s very exotic. All more modern communications systems either user even narrower bandwidth, or much wider bandwidth.
ok, thanks for clarification and guidance, i searched for gsm ics with no luck as you mentioned they all are obsolete now but for wcdma there are some ics that arent obsolete yet. specifically i found ADI max2550 wcdma femtocell ic. this ic isnt obsolete yet and has a very good price tag, under 10$.
https://octopart.com/en/max2550etn%2Bt-analog+devices-124213711
i also found its refernce designs here:
do you think that its possible to make some sort of voip to wcdma (3g) bridge with this?
it might be possible, if you have the equivalent of multiple person-years of developer capacity. The data sheet looks relatively complete (at first glance). But I’m sure you noticed that you need to interface the ADC/DAC with high-speed differential drivers, and the DAC are 1bit, and hence require you to do the sigma-delta in the digital baseband side. So that means you’d have to implement all of that in a FPGA. Plus get the analog RF side (trace impedance, stray capacitance, etc.) sorted out. Plus develop a PHY layer, or port something like OpenBTS-UMTS. And all of that to replicate the partial functionality you can get off-the-shelf from a UMTS femtocell from ebay (assuming you can “root” the femtocell as has been done by various people on various models even a decade ago)?
