Wireless Access

Hi,

How do we interpret the Tx power per chain versus the aggregate Tx power?

Below is the excerpt from 315 datasheet:

• Maximum (conducted) transmit power (limited by local regulatory requirements):

- 2.4 GHz band: +18 dBm per chain , +21dBm aggregate (2x2)

- 5 GHz band: +18 dBm per chain , +24dBm aggregate (4x4)

http://www.arubanetworks.com/assets/ds/DS_AP310Series.pdf

Hi Adnan,

Did you solve this? I have the same doubt.

Regards,

Julián

Per-chain conducted power is what comes out of each of the radio chains, at the connectors on the radio boards.

For aggregate EIRP you should sum power from all chains (which adds 3dB for a 2x2 radio, 4.8dB fr a 3x3 radio, or 6dB for a 4x4 radio), and add antenna gain.

Aggregate conducted only sums the power from all chains (no antenna gain).

(Post 1)For aggregate EIRP you should sum power from all chains (which adds 3dB for a 2x2 radio, 4.8dB fr a 3x3 radio, or 6dB for a 4x4 radio), and add antenna gain.

(Post 2)Aggregate conducted only sums the power from all chains (no antenna gain).

Thanks Onno.

Is your post 2 an small rectification over your post 1?

So are these values stated below are fixed?

3 dB for 2*2 radio

4.8 dB for 3*3 radio and

6 dB for 4*4 radio

Not a rectification but a clarification. Aggregate conducted power and aggregate EIRP power have an offset equal to the antenna gain.

Yes, those values are fixed. Multiplaction by 2 equals +3dB.

Thanks Onno.

Was going through an another informative link of you:http://community.arubanetworks.com/t5/Wireless-Access/transmit-power-in-IAP92/td-p/28160

Excerpt:

The max transmit power for MIMO APs is typically the "aggregate" power, meaning the total power from all radio chains combined.

Is the max transmit power for the MIMO APs is influenced by the regulatory domain's max allowed tx power. Suppose the regulatory domain max tx power is at 20 dBm, and their are 3*3 MIMO APs in the network, then can we avail an max tx power of 20dB+ 4.8 dB = 24.8 dB on the regulatory domain which restricts the APs to max tx power of 20 dB? Please let me know if I am missing something.

What we list in our datasheets is the max capability of the hardware, ignoring regulatory restrictions (there should be a note for that caveat).

Regulatory rules will mean that we may need to enforce additional restrictions, which will vary by country. For example, most countries simply will limit the total amount of power (expressed in an aggregate EIRP level) that can be transmitted in a given band. There may be other regulatory limits (band-edge or out-of-band emissions for example) that force us to further limit the power.

This is all taken into account by our software.

So in your example, if the regulatory limit is 20dBm, you would typically have to subtract both antenna gain and MIMO gain to find the max setting for the per-chain conducted power limit. Which in this case will be far less than what the hardware is capable of.

Excerpt:

So in your example, if the regulatory limit is 20dBm, you would typically have to subtract both antenna gain and MIMO gain to find the max setting for the per-chain conducted power limit. Which in this case will be far less than what the hardware is capable of.

Thanks Oharms,

So if I need to substract even the MIMO gain to match the regulatory domain limit then wont I end up having the transmission power even lesser than what is allowed in a particular regulatory domain if the clients don't match the MIMO capabilities of the Access Point?

Eg: If the AP is 4*4 MIMO and the clients in network are just 1*1 & 2*2 capable.

20 dBm - (External Antenna Gain) - 6dB(aggregate EIRP from all chains) for 4*4 MIMO AP

The client capabilities are irrelevant when calculating the max transmit power setting for the AP.

Consolidating for ease of reference:

Per-chain conducted power: Power that comes out of each of the radio chains, at the connectors on the radio boards.
Aggregate conducted/Max conducted power: Sum of power from all chains(which adds 3dB for a 2x2 radio, 4.8dB fr a 3x3 radio, or 6dB for a 4x4 radio) + no antenna gain
Aggregate EIRP Power/Max EIRP Power: Sum of power from all chains(which adds 3dB for a 2x2 radio, 4.8dB fr a 3x3 radio, or 6dB for a 4x4 radio) + antenna gain