Return-path: Received: from mout.gmx.net ([212.227.15.18]:49661 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756330Ab3EBUcc (ORCPT ); Thu, 2 May 2013 16:32:32 -0400 Received: from mailout-de.gmx.net ([10.1.76.16]) by mrigmx.server.lan (mrigmx001) with ESMTP (Nemesis) id 0MGlNX-1UlWhz1ucb-00DYXs for ; Thu, 02 May 2013 22:32:30 +0200 Message-ID: <5182CD59.8060509@rempel-privat.de> (sfid-20130502_223240_175767_182A00FE) Date: Thu, 02 May 2013 22:32:25 +0200 From: Oleksij Rempel MIME-Version: 1.0 To: Felix Fietkau CC: Adrian Chadd , ath9k-devel@lists.ath9k.org, linux-wireless@vger.kernel.org Subject: Re: [ath9k-devel] [PATCH 1/2] ath9k_htc: add STBC TX support References: <1367482308-9882-1-git-send-email-linux@rempel-privat.de> <1367482308-9882-2-git-send-email-linux@rempel-privat.de> <5182A341.8050704@rempel-privat.de> <5182A9DC.6030203@openwrt.org> In-Reply-To: <5182A9DC.6030203@openwrt.org> Content-Type: text/plain; charset=UTF-8; format=flowed Sender: linux-wireless-owner@vger.kernel.org List-ID: Hi Felix, thank you for your explanation and being pation with me. I learn it by my self and keywords you gave help me to find needed information. So, i continue to digg in to google books and wikis now. I see now, that my initial assumption that STBC some thing like "frequency diversity" is wrong. Well, it say by itself Space and Time, no freq :) Am 02.05.2013 20:01, schrieb Felix Fietkau: > On 2013-05-02 7:32 PM, Oleksij Rempel wrote: >> Am 02.05.2013 18:55, schrieb Adrian Chadd: >>> On 2 May 2013 01:11, Oleksij Rempel wrote: >>> >>>> +#define WLAN_RC_TX_STBC_FLAG 0x20 /* TX STBC */ >>>> +#define WLAN_RC_RX_STBC_FLAG 0xC0 /* RX STBC ,2 bits */ >>> >>> I thought we covered this; why are you marking two bits here? >> >> becouse firmware checks for two bits (and then use it as bool ;)), so i >> pass what firmware can handle. >> >>> Atheros 11n hardware only supports 1-stream STBC RX. >> >> Did you got my email with lots of assumptions and questions? >> What do you mean by 1-stream STBC RX? After i did some home work on STBC >> i see that it encoded from at least two spatial streams. >> Is >> 1-stream STBC RX = 2 spatial streams with mirrored data? >> and >> 2-stream STBC RX = 4 spatial streams with mirrored data? >> >> or >> >> 1-stream STBC RX = compatibility mode for one stream hardware(so only of >> two streams received)? > When you're talking about 'streams', please specify where you're talking > about Spatial Streams (Nss, defined by the MCS), or Space-Time Streams > (Nsts). STBC is useful whenever the number of possible Space-Time > streams exceeds the number of Spatial streams, i.e. if the number of tx > chains is bigger than the number of spatial streams. > There's an asymmetry between Rx and Tx here. If a receiver has 1 chain > and the transmitter has 2 chains, tx can use 2 Space-Time streams to > encode 1 Spatial stream to improve the reliability of the signal. > The HT STBC capability field indicates the maximum number of Spatial > Streams, not Space-Time streams. Atheros hardware only supports STBC > with Nss = 1, so announcing 2-stream STBC is definitely wrong. Ok, i finally found it on ieee 802.11 specification. For STBC: Nsts=2 - Nss=1 Nsts=3 - Nss=2 Nsts=4 - Nss=2 Nsts=4 - Nss=3 >> That would make sense for 1x1:1 hardware, but if you say all atheros N >> hardware support only 1-stream STBC RX, will mean that STBC is useless >> on this hardware. > Only STBC With Nss=1, Nsts=2 is supported, but this does not make it > useless at all. It helps, even if the receiver only has one antenna. Found it too.. :) Thx! -- Regards, Oleksij