question about configuration of wifi antenna gain in ns3-lbt

[John Young]

In scenarioHelper, I see the following code.

ConfigureWifiAp

// XXX until LTE eNB rxGain is implemented, compensate by increasing TxGain

  // at AP and decreasing RxGain the same amount at UE, in Wi-Fi

  spectrumPhy.Set ("TxGain", DoubleValue (phyParams.m_bsTxGain + phyParams.m_bsRxGain));

  spectrumPhy.Set ("RxGain", DoubleValue (phyParams.m_bsRxGain));

ConfigureWifiSta

// XXX until LTE eNB rxGain is implemented, compensate by increasing TxGain

  // at AP and decreasing RxGain the same amount at UE, in Wi-Fi

  spectrumPhy.Set ("TxGain", DoubleValue (phyParams.m_ueTxGain));

  spectrumPhy.Set ("RxGain", DoubleValue (phyParams.m_ueRxGain - phyParams.m_bsRxGain));

Could anyone tell why it does so?

Why is there a decrease in sta RxGain with an increase in ap's TxGain ?

[Tom Henderson]

It is explained in the comment.

The TR36.889 scenario states that AP/eNB gain should be 5dBi and UE/STA
should be 0 dBi. However, there was no way to configure 5 dBi receive
gain on the LTE eNB, with the current API. To compensate for this, we
adjusted the AP gain upwards so that for a given power, the gain on the
AP to eNB path was 10 dB, but all at the AP. This, however, caused the
gain on the path from AP to STA to be 5 dB too high, so it was corrected
on the Rx gain of the STA. This type of configuration is not ideal but
accomplished the goal of getting the gains aligned on the main
communications paths of interest (eNB->AP, eNB->STA, AP->eNB and
AP->STA), but not for AP->UE; however, AP->UE is not as of much interest
to this scenario.

- Tom

[John Young]

Thanks a lot. But I wonder why enb rxGain is not configured. I see the DlSpectrumPhy and UlSpectrumPhy are configured with the same antenna model, and when multi-model-spectrum-channel notifies the UlSpectrumPhy, the rxGain is correctly subtracted from the pathLoss. So I am not clear what you mean by "there is no way to configure 5dBi receive gain on enB"?

在 2016年11月22日星期二 UTC+8上午12:58:09，Tom Henderson写道：

[John Young]

And with such a configuration, would the enb -sta path be given a non-existent 5 dB attenuation?

在 2016年11月22日星期二 UTC+8上午12:58:09，Tom Henderson写道：

On 11/21/2016 12:49 AM, John Young wrote:

[Tom Henderson]

I haven't been able to answer your question easily; maybe tomorrow.
This is a detail that I wasn't fully tracking at the time, and it was
about 18 months ago when this was done. There was some problem at the
time in trying to assign 5 dBi rx gain to the eNB. It may have been
fixed since then and we need to update that part of the code to which
you refer. There is a difference between how antenna gain is handled in
the Wifi SpectrumPhy (within the phy object) and in LTE (where it is
part of the antenna model in the channel object), and maybe that is
where the problem was. I will check and report back.

- Tom

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[John Young]

Ok, thanks.

在 2016年11月22日星期二 UTC+8下午2:01:06，Tom Henderson写道：

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