Wireless Access

Hi experts,

 

I have heard and read many times (and I also agree) that the AP's transmit power shouldn't be so high, since clients such as tablets and phones have little transmit power (according to some Cisco paper around 10 dBm). So the APs transmit power should be equal or less of the least powerful client for a proper design.

In today's Ekahau webinar, they browsed the web http://clients.mikealbano.com/ where you can find the maximum transmit power of many vendor devices. Take two examples: if you filter for Samsung they are around 18 dBm, if you filter for iPhone they are around 21 dBm.

Taking this into account, it makes sense on one hand to configure the APs to transmit at around 20 dBm. But on the other hand it sounds too much transmit power according to me.

APs' high transmit power has many disadvantages (high CCI, sticky clients, bad roaming and so on). One disadvantage is to have the client not beeing able to reach the AP and it has been discussed many times, but it was by thinking that phones and tablets can transmit at 15 dBm at most, but it seems it is not according to the previous web and others.

So, only taking into account this last disadvantage about the balance of APs and clients transmit power, does it make sense to design the WLAN by having the APs transmitting at around 20 dBm?

 

Regards,

Julián

According to the website the last phone to transmit at 21 or above was the iphone5s.  All the others seem to be between 18 and 19.

 

The short answer is "it depends".  There are other factors like AP density and obstacles between clients and access points that could affect your transmit power.  Matching the access point transmit power to the client transmit power is a starting point, and not a destination.

Remember as well that the max tx power listed on Mike's site is specifically the max power that the device states in the association request, not the actual power measured. I don't believe this number includes antenna gain (or loss), nor does it measure/reflect the device's actual operating behavior, so actual power output could be different.

Hi Colin and Charlie,

 

Then about the client transmit power what is an average value to take for laptops, phones and tablets? For example:

 

Laptops: 30 dBm

Phones: 10 dBm

Tablets: 15 dBm

 

I don't know if those are correct, I mean an average just to take into account. Because in the previous web and the others the values for phones are around 19 dBm, but you say those are not actual powers. What values can I take as an average? Or what values you take into account? Or is there any source to get this information?

 

Regards,

Julián

You should tune your network to your least capable mobile device, in general. Handhelds are more important for mobility than laptops that don't move as often. This advice is merely a starting point, because there are many factors that would affect transmit power like AP density and if you have walls. A properly done site survey would give you alot of information, but a site survey buy itself would not give you all the information you need.

In a voice network, you would need to make your voice clients roam really well, so you would focus on those devices. In a data network, you would have less need for roaming. There are many variables and the advice I gave is only a starting point....

Hi Colin,

 

I really agree with you. My last question is more about what are the values I can take as an average for phones/tablets/laptops transmit power? Or what are the values you normally take into account?

 

Regards,

Julián

I don't take any values in to account, really.  I make my maximum transmit power 18 and if clients don't roam properly I keep lowering it.