Re: [STDS-802-11-TGM] CID 6302 "received at the antenna"

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While it might be "cleaner" in some sense to think of measuring field strengths (uV/m) at some point or set of points in close physical proximity to the radiating element (aka the "antenna"), it is totally impractical for a variety of reasons, and it is not useful because of the variability in the RF environment around the radiator. Antennas "couple to" / "are affected by" nearby reflectors/absorbers of RF energy and their "gain patterns" change depending thereon. Put an access point on top of a cable box (like I do in my house), and the gain of the WiFi antenna(s) will be quite different than that realized if the access point is mounted on a drywall ceiling ... AND it doesn't matter.

Furthermore, there is nothing sacred about the transition from electromagnetic fields in a conductor to those in the atmosphere. It's just yet another point where impedance mismatches (and hence RF reflections) can and do occur, and is for all intents and purposes, no different than the "antenna connector. There is nothing "wrong" with considering the antenna (and the cable from the antenna to the input port on a device) as part of the "RF channel" and considering the output of (and input to) that channel to be the "antenna connector". What is important is that the RF reference plane be well-defined (and accessible if you want to measure things!), and that it be the same for rx and tx for channel access calculations ... CCA, etc.

So, while it may be aesthetically pleasing to think about using the "antenna" as the reference point, it's not required from either a theoretical or a practical point of view.

Cheers,

From: ***** IEEE stds-802-11-tgm List ***** [mailto:STDS-802-11-TGM@xxxxxxxx] On Behalf Of Stephens, Adrian P
Sent: Friday, June 19, 2015 11:18 AM
To: STDS-802-11-TGM@xxxxxxxxxxxxxxxxx
Subject: Re: [STDS-802-11-TGM] CID 6302 "received at the antenna"

I’m sorry, but I have to disagree. Although the antenna connector

may be well defined, it is, IMHO wrong.

The antenna gain is part of the “processing” done by the RF chain.

Having a reference point part way up that RF chain seems weird to me.

Best Regards,

Adrian P STEPHENS

Tel: +44 (1793) 404825 (office)
Tel: +1 (971) 330 6025 (mobile) ç please note new number

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From: ***** IEEE stds-802-11-tgm List ***** [mailto:STDS-802-11-TGM@xxxxxxxx] On Behalf Of Richard Roy
Sent: Friday, June 19, 2015 10:58 AM
To: STDS-802-11-TGM@xxxxxxxxxxxxxxxxx
Subject: Re: [STDS-802-11-TGM] CID 6302 "received at the antenna"

--- This message came from the IEEE 802.11 Task Group M Technical Reflector ---

Agreed. The RF reference point (or plane in RF jargon) needs to be accessible so that performance/conformance can be tested. The term "antenna connector" is commonly used to refer to such a reference point/plane. As far as CCA assessment is concerned, the key point is that Tx output power should also be specified and measured at the same RF reference point. What this ensures is a form of "link balance" by ensuring that the "path" losses on rx and tx are the same. Perhaps text to this effect should be added at an "appropriate place".

Cheers,

From: ***** IEEE stds-802-11-tgm List ***** [mailto:STDS-802-11-TGM@xxxxxxxx] On Behalf Of Sigurd Schelstraete
Sent: Friday, June 19, 2015 10:16 AM
To: STDS-802-11-TGM@xxxxxxxxxxxxxxxxx
Subject: Re: [STDS-802-11-TGM] CID 6302 "received at the antenna"

I would assume that “at the antenna connector” is the correct choice. This is the only reference point that is accessible and unambiguous in testing as well.

Regards,

Sigurd

From: ***** IEEE stds-802-11-tgm List ***** [mailto:STDS-802-11-TGM@xxxxxxxx] On Behalf Of Mark Rison
Sent: Friday, June 19, 2015 6:32 AM
To: STDS-802-11-TGM@xxxxxxxxxxxxxxxxx
Subject: Re: [STDS-802-11-TGM] CID 6302 "received at the antenna"

--- This message came from the IEEE 802.11 Task Group M Technical Reflector ---

CCA shall report busy at least

while a high rate PPDU with energy at the antenna above the ED threshold is being received.

or:

CCA shall report busy at least

while a high rate PPDU with energy at the antenna connector above the ED threshold is being received.

So I think we have three options:

1) leave it as is. Assume that "power observed at the antenna" is correct and means effectively "power observed by the antenna and presented to the receiver" (I suppose this is option 1a).

2) change the wording from "...at the antenna..." to either "...at the antenna connector..." or "..at the input port of the receiver...".

3) Account for antenna gain. Something like "power measured at the antenna connector adjusted for antenna gain" . That would take forever to get right and I propose we reject this option straightaway.

I take no particular position on these three, but I note that

"antenna connector" appears 95 times, while "input port" only

appears 11 times and only in the context of testing/test equipment,

so if we go for 2) then I suggest "at the antenna connector".

Mark

Mark RISON, Standards Architect, WLAN English/Esperanto/Français

Samsung Cambridge Solution Centre Tel: +44 1223 434600

Innovation Park, Cambridge CB4 0DS Fax: +44 1223 434601

ROYAUME UNI WWW: http://www.samsung.com/uk

From: gsmith [mailto:gsmith@xxxxxxxxxxxxxxxxxxx]
Sent: 19 June 2015 14:26
To: Mark Rison; STDS-802-11-TGM@xxxxxxxxxxxxxxxxx
Subject: RE: CID 6302 "received at the antenna"

Hi Mark,

In practice a receiver will measure the signal strength, effectively the RSSI measurement. I searched through the text looking for RSSI to see how this is expressed. The only places I found where it states how it is measured is P2291L53, Table 20-1, P2461L47, Table 22-1, P2593L21, Table 23-1. These use the same words "...power observed at the antenna...".

In practice a receiver will measure the RSSI and check the ED limit. I would state that in practice the RSSI is the signal power at the input of the receiver, or, at the base of the antenna, or at the antenna connector to the device or LNA. It is usually tested by applying a signal cabled to the input connector.

So we need to establish what "at the antenna" is specifying or should specify - is it the signal field surrounding the antenna (i.e. a value that does not include the antenna gain) or the signal detected by the antenna and presented to the receiver (i.e. a signal that includes the antenna gain).

If the former, the receiver would need to know the antenna gain in order to establish if the signal strength was exceeding the ED limit. If the latter, the receiver does not need to know the antenna gain and it is a straightforward measurement. In all simulations that I know of, those being carried out in 11ax for example, it is the latter that is used, i.e. the signal strength at the input to the receiver, or at the antenna connector. This is by far the easier to specify otherwise words will be needed to express the idea that the measure RSSI and hence the ED Limit is variable and must be adjusted to take account of antenna gain.

I would say that the term "power observed at the antenna" is definitely biased towards the idea that it would include the antenna gain as how else is it "observed". A higher gain antenna would "observe" a higher signal, is how I would interpret this.

So I think we have three options:

1) leave it as is. Assume that "power observed at the antenna" is correct and means effectively "power observed by the antenna and presented to the receiver" (I suppose this is option 1a).

2) change the wording from "...at the antenna..." to either "...at the antenna connector..." or "..at the input port of the receiver...".

Hence, 1), 1a) or 2).

I think 2) is simpler and is clear.

From: ***** IEEE stds-802-11-tgm List ***** [STDS-802-11-TGM@xxxxxxxx] on behalf of Mark Rison [m.rison@xxxxxxxxxxx]
Sent: Friday, June 19, 2015 4:59 AM
To: STDS-802-11-TGM@xxxxxxxxxxxxxxxxx
Subject: [STDS-802-11-TGM] CID 6302 "received at the antenna"

--- This message came from the IEEE 802.11 Task Group M Technical Reflector ---

The 11mc BRC discussed the resolution to CID 6302 yesterday, and felt

the wider group's input should be sought on the following point.

2227.9 reads (there is similar text at 2281.30):

CCA shall report busy at least

while a high rate PPDU with energy above the ED threshold is being received at the antenna.

The comment was to ask where else a PPDU could be received, and the

change proposed by the commenter was to delete "at the antenna".

However, discussion in the BRC suggested that maybe "at the antenna"

was intended to refer to where the energy thresholding was performed.

There was further discussion of whether this threshold was w.r.t.

the energy at the antenna or rather at the antenna connector (since

in general 802.11 talks of things at the latter).

The question to the group is therefore: was the intent of the above

to say:

CCA shall report busy at least

while a high rate PPDU with energy at the antenna above the ED threshold is being received.

or:

CCA shall report busy at least

while a high rate PPDU with energy at the antenna connector above the ED threshold is being received.

Mark

Mark RISON, Standards Architect, WLAN English/Esperanto/Français

Samsung Cambridge Solution Centre Tel: +44 1223 434600

Innovation Park, Cambridge CB4 0DS Fax: +44 1223 434601

ROYAUME UNI WWW: http://www.samsung.com/uk

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