ED threshold for CCA in LTE-Wifi coexistence

[Sab NT]

Hi everyone, 

I want to understand how the CCA is implemented in LAA LTE-Wifi coexistence. As mentioned in the Lbt design document and I checked in the code, LteAccessManager uses a threshold "laaEdThreshold" of value -72 dBm. However, I could not find in the code the comparison with this variable "laaEdThreshold" for CCA implementation.  I could see MaxLossDb takes a noise power of -73 (hardcoded) but not any use of the variable "laaEdThreshold" . Could you please point out how the CCA is taking the "laaEdThreshold" value into account or Is the calculation done in some different way?

I also wanted to check the same CCA threshold in Wifi. I found the attribute "CcaModel1Threshold" in spectrum-wifi-phy.cc whose value is initialized as -62dBm. But Here also, I could not find how the variable "CcaModel1Threshold" is used for CCA implementation. I am probably missing something basic. Could some one please point out how it is done?

Also, one last question on CCA : why are the ED threshold values for Lbt and Wifi chosen different (-72 and -62 dBm respectively)?

Many Thanks in advance.

[Lorenza Giupponi]

Hi,

the ED threshold for LAA is defined in the channel-access-manager.cc. The code you are looking for is in the lbt-access-manager.cc.

Wrt the WiFi ED threshold, Tom will be able to help you better. I would go in the SpectrumWifiPhy and trace from there to search for the code you need.

In WiFi the ED threshold is traditionally set to -62 dBm. In LAA -62 dBm was the initial starting point of the discussion, and after many interactions in 3GPP RAN1 the throushold has been set to -72 dBm to guarantee a higher sensitivity of LAA to WiFi.

Lorenza

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[Tom Henderson]

On 05/03/2016 09:39 AM, Lorenza Giupponi wrote:
> Hi,
> the ED threshold for LAA is defined in the channel-access-manager.cc.
> The code you are looking for is in the lbt-access-manager.cc.
> Wrt the WiFi ED threshold, Tom will be able to help you better. I would
> go in the SpectrumWifiPhy and trace from there to search for the code
> you need.
>
> In WiFi the ED threshold is traditionally set to -62 dBm. In LAA -62 dBm
> was the initial starting point of the discussion, and after many
> interactions in 3GPP RAN1 the throushold has been set to -72 dBm to
> guarantee a higher sensitivity of LAA to WiFi.
> Lorenza
>
>
> 2016-05-03 4:02 GMT+02:00 Sab NT <sab...@gmail.com

> <mailto:sab...@gmail.com>>:

>
> Hi everyone,
>
> I want to understand how the CCA is implemented in LAA LTE-Wifi
> coexistence. As mentioned in the Lbt design document and I checked
> in the code, LteAccessManager uses a threshold "laaEdThreshold" of
> value -72 dBm. However, I could not find in the code the comparison
> with this variable "laaEdThreshold" for CCA implementation. I could
> see MaxLossDb takes a noise power of -73 (hardcoded) but not any use
> of the variable "laaEdThreshold" . Could you please point out how
> the CCA is taking the "laaEdThreshold" value into account or Is the
> calculation done in some different way?
>
> I also wanted to check the same CCA threshold in Wifi. I found the
> attribute "CcaModel1Threshold" in spectrum-wifi-phy.cc whose value
> is initialized as -62dBm. But Here also, I could not find how the
> variable "CcaModel1Threshold" is used for CCA implementation. I am
> probably missing something basic. Could some one please point out
> how it is done?

A little while ago, I wrote up some Wi-Fi documentation on this value;
please have a look at:

https://www.nsnam.org/docs/release/3.25/models/html/wifi-design.html#yanswifiphy-and-wifiphystatehelper

- Tom

[Sab NT]

Hi Lorenza and Tom,

Thank you very much for your reply. Now I went through the Wi-FI document for yansWifiPhy that you shared and understood the CCA process. 

Now I have some basic questions on the role of Wifi modules in the coexistence scenario. The channel manager for laa-wifi-coexistence module is using the wifiPhy from the spectrum-wifi-phy and not using yansWifiPhy class for setting any attribute. But the CCA attributes of the Wifi are defined in YansWifiPhy; So how is the channel manager setting the ED/CCA thresholds for Wifi side? Or the coexistence modules only set the spectrum-channel attributes of the Wifi and let the Wifi use its default values for ED/CCA from yansWifiPhy by its own?

So, if I want to control the Wifi ED/CCA threshold for coexistence from the coexistence channel manager, do I need to create a hook to the yansWifiPhy from the spectrumWifiPhy and then set the values of the threshold? Sorry if my questions are ambiguous and naive but I want to understand how to control Wifi side from the coexistence channel manager.

Many thanks in advance.

[Zoraze Ali]

Hi,

Kindly see in line,

On Thursday, May 5, 2016 at 4:23:36 PM UTC+2, Sab NT wrote:

Hi Lorenza and Tom,

Thank you very much for your reply. Now I went through the Wi-FI document for yansWifiPhy that you shared and understood the CCA process. 

Now I have some basic questions on the role of Wifi modules in the coexistence scenario. The channel manager for laa-wifi-coexistence module is using the wifiPhy from the spectrum-wifi-phy and not using yansWifiPhy class for setting any attribute. But the CCA attributes of the Wifi are defined in YansWifiPhy; So how is the channel manager setting the ED/CCA thresholds for Wifi side? Or the coexistence modules only set the spectrum-channel attributes of the Wifi and let the Wifi use its default values for ED/CCA from yansWifiPhy by its own?

    For LBT or LTE-Duty Cycle functionality, Wifi no longer uses YansWifiPhy, instead it uses SpectrumWifiPhy to allow the reception for LTE signals as an interference. Channel access manager is only responsible for LAA configuration.   

So, if I want to control the Wifi ED/CCA threshold for coexistence from the coexistence channel manager, do I need to create a hook to the yansWifiPhy from the spectrumWifiPhy and then set the values of the threshold? Sorry if my questions are ambiguous and naive but I want to understand how to control Wifi side from the coexistence channel manager.

Many thanks in advance.

 
    You can use SpectrumWifiPhy attributes for Wifi configuration.

 I think it will be helpful for you to read the information at https://www.nsnam.org/wiki/LAA-WiFi-Coexistence. Additionally, you could also generate the documentation at your end by going into the src/laa-wifi-coexistence/doc directory of the repository and typing "make latexpdf"command.

Kind regards,
Zoraze