Wireless Access

Hi gurus,

I am trying to understand the relationship between APs' transmit power and spatial streams. Let's say I have the 303 access point (2x2) which has a 21 dBm aggregate transmit power (18 dBm per chain).

1. If I see in the controller/Instant GUI the AP is transmitting at 12 dBm, for example, does that mean aggregate transmit power (then considering the two SS) or the transmit power per chain (then considering one SS)?
2. For clients which supports only one SS, do I have to ignore the aggregate transmit power then?
3. If according to my maths or predictive site survey tool at one point I should received -70 dBm, does that mean considering the two SS or just one SS?

Many thanks in advance,

Julián

https://community.arubanetworks.com/t5/Wireless-Water-Cooler/Transmit-beam-forming-vs-spatial-multiplexing/td-p/247997

802.11n and 802.11ac use MIMO antenna technologies to transmit and receive multiple data streams via multiple antennas, at the same time. These so-called “spatial streams” provide significantly faster throughput, as compared to legacy SISO technology.

When you purchase an 802.11n or 802.11ac-based device, the number of antennas it can use to transmit and receive are specified, using an “N by M” matrix. 

The Aruba software consistently reports (and expects) RF transmit power as "aggregate or total EIRP", which includes antenna gain, and combines (sums) power from all radio chains.

The 12dBm you see includes all that.

The number of chains used by a client device has no relevance in this, but even a single chain client will benefit from the fact that an AP transmits data from two antennas.

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@onno wrote:

The Aruba software consistently reports (and expects) RF transmit power as "aggregate or total EIRP", which includes antenna gain, and combines (sums) power from all radio chains.

The 12dBm you see includes all that.

The number of chains used by a client device has no relevance in this, but even a single chain client will benefit from the fact that an AP transmits data from two antennas.

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Hi Onno,

Thanks for your interest as always. So now it is clear the Aruba numbers always refers to the aggregate power and consider all the SS.

For the second part, then, if using a 2x2 AP for transmitting, and if you have two identical clients at the same position, but one of them with two antennas and the other with one, will both clients receive the same signal strength?

Regards,

Julián

That depends. If this is a simple switched diversity radio (single receiver chain, multiple antennas), there is no difference, but if the radio has two independent receiver chains, each chain will receive roughly the same amount of RF energy (ignoring the variations resulting from the different antenna locations etc.), and the radio effectively receives a 3dB signal boost.

Hi,

if the radio has two independent receiver chains, each chain will receive roughly the same amount of RF energy (ignoring the variations resulting from the different antenna locations etc.), and the radio effectively receives a 3dB signal boost.

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Many thanks. Then, let's take the case where the clients with two antennas also have two radio chains (which I think is the common case for laptops, for example), will the clients with one antenna receive half of the power (3 dB less) of the clients with two antennas?

Regards,
Julián

Hi,

Any idea?

Regards,

Julián