Wireless Access

Hi community,

 

I usually use Ekahau site survey for making a predictive site survey and have a general idea of the numbers of APs and their location. For this, I usually use the default Voice + Data requirements, and some of them are:

 

• Signal Strenght = Min. -67 dBm
• Number of APs = Min. 2 at min. -75 dBm
• Channel Overlap = Max. 2 at min. -85 dBm

These three parameters directly impact the number of APs of the design. I have read the "RF and Roaming Optimization for Aruba 802.11ac Networks VRD" which gives some guidelines about the APs transmit power for 2.4 and 5 GHz, and the 6 dB of difference between both bands, which I also use as other input parameters. But I didn't see any document which gives an idea for the "Number of APs" and "Channel Overlap" parameters. The tool has a "Aruba VHD Guideline" template, but many of my designs aren't VHD. I know every design is different and has different requirements, but I would like to know a general idea for these "Number of APs" and "Channel Overlap" numbers for Voice + Date, or if the above numbers are fine according to Aruba guidelines. Anyone with hands-on experience on this? Any answer will be much appreciated.

 

Regards,

Juliáng

Hi guys,

 

Any idea?

 

Regards,

Julián

This is an area of many opinions. So not sure if you will find a definitive answer.

 

Actually, your application and devices should dictate these parameters, not the AP vendor. The minimum signal you mention doesn't look weird to me, I have seen sometimes -65 as well; but that 2 dB shouldn't make a difference between a perfect vs poor functioning environment. On the coverage (2 APs @-75dBm), if you really support roaming you might need to have a somewhat closer look as I have seen environments with thick concrete walls where we had to put APs in hallways (yes... in hallways) to allow the voice handset to be in range of the new candidate AP long enough before it loses connection to the previous AP when the user takes a turn and the concrete moves between user and AP.

 

Also, some voice or special medical/logistics devices might need more than -65dBm as they can be pretty deaf to the signal. The observed signal strength between different types of clients in the same position can be easily 10dB.

 

Haven't tried either if you can achieve 2+ @-75dBm and less than 2 @-85dBm on-channel (CCI); will be challenging on 2.4GHz specifically. Some voice devices only scan specific channels on 5GHz, which brings down the possibilities to achieve low CCI.

 

Again, in general, those numbers don't look bad. I don't think you have a guarantee that the network works properly if you just follow the numbers either. The applications, environment, and devices are as important for a proper design.

Hi Herman,

Very good explanation. You are right and the clients dictate those parameters and not the AP vendor. Although I think they are directly related to the cell overlap, which general guidelines say to have around 15 or 20% of cell overlap. Many thanks.

Regards,
Julián