MATLAB: Am I unable to recover a 15 MHz signal from a CPRI Tool using lteTestModelTool

bandwidthcprilteLTE Toolboxtestmodel

I'm creating test models (TM) for multiple bandwidths (5, 10, 15, 20 MHz) meant to be transmitted to a CPRI Tool – Sarokal that I'm using. Once the signals are transmitted, I place the CPRI tool in loopback mode to try and recover the signals. When recovering the signals, I seem to run into an issue with the 15 MHz signal. Below are the issues summarized:
1. I get a broad signal 17MHz BW instead of 13.5MHz
2. On loop back, I get file of 230400 lines, while the lteTestModeltool, creates 307200 so I can’t measure EVM, and cant recover the signal.
To recover the signal, I'm following one of your examples – Cell Search, MIB and SIB1 recovery. However, I'm unable to recover the signal and would like to understand if I'm doing anything wrong.

Best Answer

It seems like the problem is that the CPRI tool is expecting a sampling rate of 23.04 Ms/s for the 15 MHz bandwidth signal, but the LTE Toolbox uses 30.72 Ms/s for that bandwidth. In the your code, it seems like you're trying to set the sampling rate of the waveform generated by lteTestModelTool, but this is not possible. What is required is to resample the waveform to match the expected rates. So in "Create_TM_Sarokal.m", the variable 'timeDomainSig' created on line 103 needs to be be resampled to the correct rate in case of the 15 MHz signal using the following line of code:
timeDomainSig = resample(timeDomainSig,3,4);
On the receive side, in the file "load_sarokal_file.m", a call of resample(...,4,3) will need to be added in the appropriate place to convert the 23.04 Ms/s signal captured from the hardware back into a 30.72 Ms/s signal for processing with LTE Toolbox.
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