Forum

Hi all,

We are planning to conduct RF site surveys on 10 sites in the UK to  deliver a high density WiFi network (including BYOD and Voice services) supporting about 20-30 users per AP radio.

Since we will provide BYOD services too, we have to consider the capabilities of end user devices. We selected Apple iPhone 5 and checked its specs. iPhone 5 is using a dual band radio with the following TxPower settings:

Band          Tx Power          Antenna Gain          EIRP (dBm)          EIRP mW

2.4 GHz     16dbm               -1.4dbi                    14.6                    about 32mW

UNII1          14dbm               0.14dbi                    14.14                about 25mW

UNII2           13.5dbm            -1.66dbi                    12dbm               16mW

UNII2-e          12dbm               -0.83dbi                   11.2dbm          about 13mW

Our site survey AP supports the following TxPower levels:

2,4 GHz and 5 Ghz

Tx Power level 1: 17dBm

Tx Power level 2: 14dB

Tx Power level 3: 11dBm

Tx Power level 4: 8dBm

Tx Powe level 5: 5dBm

Tx Power level 6: 2dBm

Tx Power level 7: -1dBm

Tx Power levle 8: -4dBm

As far as i can understand, these are not EIRP values but just the Tx power of the AP radio.

The AP is using internal omni antennas, a 2dbi antenna on the 2.4Ghz and 4bi on the 5Ghz bands. So the EIRP values for the 2 bands will be the following:

2.4GHz

L1 --> 19dBm --> 79mW

L2--> 16dBm --> 40mW

L3--> 13dBm --> 20mW

L4--> 10dBm --> 10mW

L5--> 7dBm --> 5mW

L6--> 4dBm --> 2.5mW

L7--> 1dBm--> 1.25mW

L8--> -2dBm --> 0.63mW

5GHz

L1--> 21dBm --> 128mW

L2--> 18dBm --> 64mW

L3--> 15dBm --> 32mW

L4 --> 12dBm--> 16mW

L5--> 9dBm --> 8mW

L6--> 6dBm --> 4mW

L7--> 3dBm --> 2mW

L8--> 0dBm --> 1mW

I have been searching various forums on the Internet and the recommended site survey TxPower for high density or Voice networks is about 12.5 - 25mW. Is this the EIRP or the AP TxPower?

Since the iPhone can transmit up to 32mW on the 2.4GHz and 13mW on the 5GHz band, what is the recommended EIRP on each band to conduct the site survey?
Since the 5GHz signals don't travel as far as the 2.4GHz signals, Is it correct to use the same EIRP values on both bands?

Would you recommend performing the surveys using 5mW EIRP? I know that this will cause a lot of CCI on the 2,4GHz band.

Regards,
Theo

I suggest you first run predictive site surveys, using the actual building floor plans that include the real building materials.  Base it on the highest 5 GHz channel you plan to use.   Then, when you are on-site, you can compare the actual results you get to these designs.  Adapt from there.  You may find that 2.4 GHz behaves differently, so be sure to actually test that too.   

A common belief is that designing for voice will provide the best outcome.   But realize this is based on an acceptable SNR (dB) value, not some magical AP power level.  I’ve heard that 27 dB is a good number to aim for.

From experience, I can tell you that it is very important to have balanced power levels between your clients and AP’s.   That means your AP’s should have the same power levels as the lowest powered client.    It will do no good if the client devices can hear the AP’s, but the AP’s can’t hear the clients.  The reverse condition is also true.

A few sobering thoughts for you to keep in mind:

All manufacturers miss-represent their devices power levels.    Sometimes this is legitimate, and sometimes not.   Output Power could be misstated by 3dB before anyone even accuses them of lying. Realize that measured, meaning the real, power levels are almost always different between different channels, even in the same band.  Likewise, the power levels for different rates within the same channel will usually be different (a legitimate artifact of chipset design). 

For like devices, with the similar output power levels, the biggest factor affecting their range will be their Receive Sensitivity – not their power output !  I have seen this confirmed in literally hundreds of tests.

Antenna specifications can also be misleading.  Often, when single numbers are quoted, the manufacturer is specifying the highest amount of gain from one angle.   Usually the smaller the device, and therefore the smaller the antenna, the more critical this becomes.   It is not uncommon for some antennas to have +1.8 dBi gain in one direction and -0.8 in another.   Always ask for actual antenna test results showing both Horizontal and Vertical measurements.

I have not conducted "dual-band" site surveys myself, so someone else might give you a better recommendation regarding that.

Sorry for my formatting - it didn't import very well, and I couldn't seem to edit it the way I wanted :-(