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Ruckus AP capacity planning/formula

New Contributor III

CLIENTS: Single stream, 802.11ac

Connected to 5Ghz (only) and 20 channel width with theoretical and optimal RF conditions

AP: Single R500

How many concurrent clients can I serve with for example a Netflix 5mbps stream?

What is the formula / model?

Doubling channel width equals raising noise by 3dBm

20 and 40 MHz have the same Tx Power, but 40 is less “concentrated”. That’s also 3dBm

3 dBm + 3 dBm = 6 dBm

6 dBm is according to Free Space Path Loss half the distance

Am I wrong?

Found this as well:

"The 802.11n standard [1] mandates the use of the same maximum transmit power with and without wide channels. In an OFDM system, the transmit energy is uniformly distributed across the subcarriers. Since wide channels use 114 subcarriers and the total transmit power remains the same, the energy per subcarrier is theoretically reduced to 49% of that of 20 MHz bands (approximately halved). Expressed in dB, this translates to about a 3 dB reduction in the energy per sub-carrier."

Sorry but your assumptions are wrong.

Note: dBm is a signature of power i.e. -75dBm and FSPL is loss so 106dB.

Coverage is based on the following basic formulae and this never takes into consideration channel width:

FSPL = 92.4 + 20Log (F) + 20Log (D)


F = Frequency in GHz


D = distance in km

Note: you can calcualte in MHz and miles by altering the constant

RSSI = TX Gain + TX Power - Losses (cabling connectors) - FSPL + RX Gain
TX Gain 4dBi
TX power 16dBm
Path Loss 106dB
RX Gain 1 dBi

4 + 16 - 106 + 1 = -85dBm

As you can see channel size has no impact at all on cell edge.

Did I read the PDF wrong?
"40 compared to 20 is a 3 dB reduction in the energy per sub-carrier"

This is a quote from the CWNP Study Guides:
"An even simpler way to estimate free space path loss (FSPL) is called the 6 dB rule (remember for now that decibels are a measure of gain or loss, and further details of dB are covered extensively in Chapter 3). The 6 dB rule states that doubling the distance will result in a loss of amplitude of 6 dB."

This is also confirmed by WLAN authorities 

@ Samuel - This is first Ive ever heard of fat channel impacting coverage - I'll do some more research on this as it looks to be interesting.