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MVP
Posts: 1,110
Registered: ‎10-11-2011

Reduce Cell Size (Rx Sensitivity)

[ Edited ]

I'm looking at implementing the reduce cell size option for a high-density VoWLAN implemenation.  I haven't seen it as a suggestion until the Lync VRD was released, and believe that a benefit can be seen by implementing it.  I've done a lot of research regarding it and have compared it to Cisco's implemenation.  Aruba's implemenation appears to be different in that you reduce the cell sensitivity in dB (floor noise - reduce size size = receive sensitivity) which means it is dynamic, whereas Cisco you set the sensitivity to a static value in dBm (ex: -75dBm).  It seems to me that the receive sensitivity on Aruba APs could change depending on the floor noise, going down/up as floor noise changes, which is a bit concerning.  I've seen APs randomly dip in floor noise as much as 10dB, so it's possible that when those dips occur, the AP may stop hearing clients because the receive sensitivity is much lower than it was before.  Any thoughts on this?

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Aruba Employee
Posts: 10
Registered: ‎08-29-2012

Re: Reduce Cell Size (Rx Sensitivity)

Cell size reduction (CSR) is environment specific. Lync VRD provides some guidelines on CSR, but it is varies deployment to deployment. For example, CSR is tied to client roaming threshold. During the client roam when the signal strength falls below "Noise floor – CSR" value, then AP will stop hearing that client causing loss of packets. So Rx sensitivity needs to be better (by at least 3 - 5dB) than client roaming threshold.

 

Hope this clarifies.

MVP
Posts: 1,110
Registered: ‎10-11-2011

Re: Reduce Cell Size (Rx Sensitivity)

Thanks Ashu.  I did not consider the client roaming threshold.  Are you referring to a configurable threshold (client match knob maybe?) on the controller or the client's roaming algorithm?

 

Assuming the noise floor fluctuates from -95 to -85 (specific to my environment), I can only manage a CSR of 10 otherwise the effective receive sensitivity dips too low.  That's unfortunate because I can't configure the CSR higher in order to get the max benefit as I have to consider worse case scenario (-85).  Can you shed some light as to why this value is specific in dB rather than a static dBm?

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If a reply adequately addresses your issue, please click on the "Accept as Solution" and "Give Kudos" button so this information can benefit other users.
Guru Elite
Posts: 20,761
Registered: ‎03-29-2007

Re: Reduce Cell Size (Rx Sensitivity)

thecompnerd,

 

Quite frankly, Cell Size Reduction is a very advanced topic and is very rarely used.  As you can see, it also requires quite a bit of measurement and study to be used the most effectively.  It is not used often.  I would not use it routinely or without TAC pushing for its use.



Colin Joseph
Aruba Customer Engineering

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