MATLAB: Understanding the “Modeling and Testing an NR RF Receiver with LTE Interference” example

5G5g toolboxinterferencelte

Hello everyone, I have a question about the 5G toolbox example: “Modeling and Testing an RF NR Receiver with LTE Interference”.
The example uses 2140 MHz (Bandwidth = 5 MHz) as the useful carrier frequency (NR) and 2150 MHz (Bandwidth = 3 MHz) as the interfering carrier frequency (LTE). In this case, there is no overlap between the NR and LTE signals.
If I move the interfering carrier too far away (eg, LTE carrier frequency = 2400 MHz) I get similar results when I would expect that moving the interfering carrier spectrally away would not have a significant effect.
Likewise, if I make a practically total overlap of the interfering carrier (for example, LTE carrier frequency = 2141 MHz), I understand that the overlap is total and the useful signal should suffer a high degradation, however I get EVM values very similar ​​to when it was totally remote (EVM about 2% in both cases, a very small difference in the last case).
I always use Interferer Gain = 1 (Waveform NR and LTE with default parameters).
Why this situation maintain similar results regardless of where the interfering carrier is located?
Thanks in advance!

Best Answer

Hi Juan,
Let me start with your first question. If the interfering carrier is moved to 2400MHz, it will still be captured by the Bandpass Filter block and so the interferer will still have an impact in the EVM results (although less impact than the default configuration, as both signals are further apart). If you want to remove the impact of the interferer you can either:
1) Choose an interfering frequency which does not fall within the bandwidth of the Bandpass Filter so that it can be filtered out
2) Change the bandwidth limits of the Bandpass Filter
3) Set the 'Interferer gain' to 0
Regarding your second question, the reason why the EVM is the same in both cases, when the spacing is 10MHz and when the spacing is 1MHz, is that RF Blockset treats each carrier as a separate envelope so, if the carriers are really close to each other (they overlap), then you should probe both carriers at the output and then combine them. However, aggregating both signals at the output means that the thermal noise would be accounted twice, so better to combine them at the input and use a unique carrier/frequency in RF blockset. This way you will get the EVM values you expect.
I hope this helps!
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