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Old 08-30-2009, 06:05 AM
selova selova is offline
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Default 2T2R (2 stream) vs 3T3R (2 stream) vs 3T3R (3 stream)?

Hi, all!

I look at the latest family from Atheros, AR9002AP-4XHG (http://www.atheros.com/pt/AR9002AP-4XHG.htm) and ask: "Step back, to 2T2R, from previous 3T3R family, AR9001AP-3NX2 (http://www.atheros.com/pt/AR9001AP-3NX2.htm) - but why?.."

Moreover, we can read what Atheros wrote about "power of MIMO" (Technical Papers and Resources page http://www.atheros.com/pt/tech_papers.htm):

- Network Processor Strategy for Maximizing 802.11n Wireless LAN Performance (January 2007): 3T3R! (/2 stream)

- Maximizing MIMO Effectiveness by Multiplying WLAN Radios x3 and MIMO Architecture: The Power of 3 (May 2006): 3T3R! (/2 stream)

Also we see, Ralink announced its new RT2883/RT2853 flagship 450 Mbps, 3 stream, 802.11n router chipset with beamforming technology. The RT2883 is an 802.11n 3 transmitter, 3 receiver (3T3R) system on a chip (http://www.smallnetbuilder.com/index...ge=0&Itemid=86 / http://www.ralinktech.com/ralink/Hom...1_07_2009.html).

I don't understand Atheros technical policy:

- 2T2R / 2 stream vs 3T3R / 3 stream (by Ralink)...

- what you think?
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Old 08-30-2009, 03:23 PM
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Three transmitters are required to support three stream (450 Mbps max link rate) draft 11n. No currently shipping products support this, although a few were announced at CES in January.

Any current products with 3T chipsets aren't really using the third transmit channel, or if they are, they are not using it for higher throughput. The third receive channel, however, can provide a benefit for even two stream operation. That's why the most expensive draft 11n routers have three antennas.

So you are seeing manufacturers move to 2T chipsets for cost savings for dual-stream products, since the third transmit channel wasn't providing any benefit.

Atheros will probably reintroduce a 3T3R chipset supporting three stream MIMO when the market needs it. Ralink is just pushing things a bit.
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