LO OFFSET present in Indoor OTA transmissions

[Chinenye Tassie]

Hello,

I am using the srslte-otalab profile with the indoor setup and I am noticing the presence of an LO-offset in my spectrograms. In the past, I have corrected this by using uhd commands when transmitting my own signals but I am unsure how to correct this when transmitting srsLTE.

I have attached screenshots of the spectrogram I am getting.

I have my reservation until 6pm EST so I can try any suggestions in real time. Thank you.

[Dustin Maas]

Hi Chinenye,

This profile is using srsLTE v19.12, which does not support passing an LO offset through to UHD. I’m sure the latest release supports this, so one option would be to clone/build the latest release and refer to the documentation about how to pass the lo_freq_offset_hz parameter. Be aware that the configuration files have changed a bit in later releases, so you’ll have to adjust the new default configurations to use the spectrum/bandwidth you have reserved for your experiment if you do this.

Alternatively, if you want to keep using v19.12 and your current configuration files, you could edit the source (e.g. the tune requests starting here: https://github.com/srsran/srsRAN/blob/d045213fb9cbf98c83c06d7c17197a9dcbfddacf/lib/src/phy/rf/rf_uhd_imp.c#L791) to include an LO offset and build a patched version.

We do plan to update this profile to use the 22.04 release in near future.

-Dustin

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[Chinenye Tassie]

Hello,

I was able to install the latest version of srsLTE (now srsRAN) following the steps here: https://docs.srsran.com/en/latest/general/source/1_installation.html

I have specified the lo_freq_offset in the [RF] section of  the enb.conf file. I used this command: device_args = type=x300,clock=external,sampling_rate=11.52e6,lo_freq_offset_hz=11.52e6. One the UE side, I did the same but switched the lo_offset to be -11.52e6.

In the enb.conf, I overrode the dl_earfcn by specifing ul_freq and dl_freq in the [RF] section and for the ue.conf, I specified the aforementioned values in the [rat.eutra] section.

When I run the EPC, ENB and UE commands, it appears that the ENB cannot see the UE. I have attached screenshots of the output in my terminal.

 I would really appreciate any insight into this. Thank you. As a reminder, I am using the srslte-otalab profile with the following nodes: ota-x310-1-comp, ota-x310-2-comp (acting as EPC and eNB), ota-nuc1-b210 (acting as UE)  and ota-nuc2-b210

-Chinenye

[Dustin Maas]

Hi Chinenye,

The error from srsenb is due to the fact that you are trying to use an external clock (clock=external), which we don’t have in the Indoor OTA Lab. Removing that from the device_args should fix the crash. To get rid of the warnings about frame size, just set the MTU for the network interface that is connected to the radio to 9000.

-Dustin

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