[srsran-users] Injecting custom waveform at specific PRB and Subframes

[Stephan Ollivier Korsgaard Larsen]

Hello,

TL:DR;
I am working on something where I want to inject a custom made waveform
for some specific amount of time at specific PRB intervals for some
specific sub frames.

Unfortunately I am having a hard time reverse engineering where this
information about the timing and where the injection should happen -
hoping some of you might be able to help.

Long story:
Having the srsRAN EPC and eNB running on one PC (with an USRP B210) and
the UE on another PC (also with an USRP B210) I have a NB-IoT network
running where I can ping over - so far so good.

I've also successfully modified the "lib/examples/usrp_txrx.c" to tx
some custom wavefrom by generating some complex samples to the cf_t
tx_buffer.

Moving on to modifying the srsenb source, I've gotten as far as looking
at the sf_worker.cc and think the sf_worker::work_imp() might be the
right place to inject my waveform - but when trying to overwrite the
tx_buffer through its set_combine() function I get a segfault.
Also it is not clear to me how the worker functions and the schedulers
are structered and passes data to eachother, which I guess is necessary
for me to be able to either extrapolate the timing of the PRBs I want
or if it is possible to get this data from one of the workers.

Any help or pointers in some directions would be of help as my C++
skills are somewhat limited :)

Best regards,
Stephan