LIMESDR on SRSLTE : unable to find network on LTE device

#1

hi guys,

I was following a post (https://cyberloginit.com/2018/05/03/build-a-lte-network-with-srslte-and-program-your-own-usim-card.html) on setting up an LTE network with the lime sdr over srsLTE interface.

Strangely, when i run my epc and enb, its all good, even a spectrum analyser can pick up the signal of the base station. But when i try to search for the LTE network on my phone, i get nothing. the network doesnt show up. I’ve tried changing the earfcn frequency to other values but nothing still.

i even tried putting the programmed sim card in the phone and searching, still nothing.

what am i missing?? if you have an idea, please help out.

#2

There was a good talk about a month ago at the 2019 CCCamp on the limitations of general purpose SDR. And it focused on “Why an SDR board like a USRP or LimeSDR is not a cellular base station” https://media.ccc.de/v/Camp2019-10248-the_limits_of_general_purpose_sdr_devices (and the exact same same video is also at https://www.youtube.com/watch?v=JgRCvzTuGkE ). Which may contain the answer to your question.

The on-board clock for both the limeSDR-USB and LimeSDR-Mini are given as +/- 1 ppm initial, +/- 4 ppm stable. So my guess with almost zero knowledge about LTE would be that you probably need a more accurate external reference clock, something along the lines of : http://www.leobodnar.com/shop/index.php?main_page=index&cPath=107

And if you configure your external reference clock to be 30.72 MHz for the LimeSDR-USB, that would probably require the least effort.
ref: https://wiki.myriadrf.org/LimeSDR-USB_hardware_description#Clock_distribution

Or configure your external reference clock to be 40MHz for the LimeSDR-Mini (but you also need to make a hardware change to a mini to enable the external reference clock and (permanently) disable the on-board VCTCXO).
ref: https://wiki.myriadrf.org/LimeSDR-Mini_v1.2_hardware_description#Clock_Distribution the actual position of the resistor to move is detailed a bit clearer here Enabling External Clock on LimeSDR mini 1.2?

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