All Things 802.11ac - Question 4: What’s Next with MIMO and Streams?

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802.11ac builds upon the success of MIMO in 802.11n, but in theory (the standard isn’t finished yet, after all...) supports up to 8 streams, which is how we get to the almost 7 Gbps you mentioned in an earlier reply today. Is this really practical, though? And, then, is today’s 1.3 Gbps the likely upper bound, at least for the next few years? And will real-world performance actually scale linearly with the number of streams, or does the signal become so complex that diminishing returns set in?
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Craig Mathias

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Posted 5 years ago

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Matthew Gast

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Speed scales linearly with the number of streams. Hardware complexity does not! It gets a lot harder to build each stream as you go on. The limiting factor on the number of streams is power consumption. MIMO requires a fair bit of signal processing power (mostly for Fourier transforms), and the DSP power goes up significantly each time you add a stream because you need to tease apart all the streams at the receiver.

Our first step is 1.3 Gbps (80 MHz channels with 256-QAM on 3 streams), and that seems like a good place to get a mainstream pause for a while. If the second wave adds another stream and 160 MHz channels, it goes to 3.5 Gbps -- but that depends on getting both 160 MHz available and a reasonable population of 160 MHz clients.
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Craig Mathias

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Excellent point on power. And, given your other notes, does an 8-stream product ever seem likely? And what odds do you give 160-MHz. channels?