Re: [STDS-802-11-TGM] "space-time stream" (11md CID 76)

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“space-time stream: A stream of modulation symbols created by applying a combination of spatial and

temporal processing to a spatial stream of modulation symbols.”

Without defining a “spatial stream” and “modulation symbol”, none of this makes much sense it seems to me. And defining “spatial stream” is going to be a challenge because it’s an oxymoron of sorts. Streams are temporal things; space is “stationary”. Secondly, defining “modulation symbol” is going to also be a challenge because symbols are objects that arise as a consequence of modulation of an RF carrier. How does one “spatially and temporally process a spatial stream” to create anything meaningful?

In short, the above text is confusing at best, and not really meaningful.

My two cents …

From: ***** 802.11 REVm - Revision Maintainance List ***** [mailto:STDS-802-11-TGM@xxxxxxxx] On Behalf Of Mark Rison
Sent: Friday, December 8, 2017 9:25 AM
To: STDS-802-11-TGM@xxxxxxxxxxxxxxxxx
Subject: [STDS-802-11-TGM] "space-time stream" (11md CID 76)

We had a discussion a couple of teleconfs ago on the definition of

a space-time stream, since the spec currently only defines

space-time streams (plural):

space-time streams: Streams of modulation symbols created by applying a combination of spatial and

temporal processing to one or more spatial streams of modulation symbols.

The question was whether it was:

space-time stream: A stream of modulation symbols created by applying a combination of spatial and

temporal processing to one or more spatial streams of modulation symbols.

or whether it was necessarily:

space-time stream: A stream of modulation symbols created by applying a combination of spatial and

temporal processing to a spatial stream of modulation symbols.

I have consulted PHY colleagues here, and the conclusion was that

Spatial streams and Space-time Streams are the same except when an STBC encoder is applied (the STBC encoder expands both space and time)

When STBC is applied a single spatial stream is mapped to two space-time streams.

and that for example for HT the possible mappings are:

For 1SS -> 2 STS via 2x2 STBC coding

For 2SS -> 3 STS via 2x2 STBC for 1^st SS and 1:1 mapping for 2^nd SS

For 2SS -> 4 STS via 2x2 STBC for 1^st SS and 2^nd SS

For 3SS -> 4 STS via 2x2 STBC for 1^st SS and 1:1 mappings for 2^nd and 3^rd SS

Therefore I think the following definition is correct:

space-time stream: A stream of modulation symbols created by applying a combination of spatial and

temporal processing to a spatial stream of modulation symbols.

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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