Have you ever found yourself beginning a task by looking up one little thing… realizing much later that one link led to another search and article, which led to another question (and so on)? I think YouTube counts on that to keep you on their site. At this point, I can’t even recall what I was initially researching, but it led me to a good bit of reading on spatial streams, 2×2 vs. 3×3 access points and WiFi in general. I’ll rush through a few links and tidbits while they’re fresh on my mind. Maybe this diversion will be worth someone’s time! 🙂
Vendors have different models of access points for sale. When digging through the tech specs on various models, you might see “2×2”, “3×3” or “spatial streams” mentioned. It’s worth having a general idea about the meaning of these terms, particularly if you’re considering an upgrade to your wireless infrastructure.
Somewhere along the way, you’ll also see an acronym called MIMO. It stands for “Multiple In, Multiple Out.” My understanding is that different AP radios can bounce signals around at different frequencies, allowing you to theoretically take advantage of the multiple, reflected signals and bring those together for a faster connection. This article does a really good job of describing what’s going on.
So, assuming that multiple connections is a good thing and can give me a faster connection, then more must be better (right?). As it turns out, “2×2” and “3×3” are terms to reflect two different ways that MIMO functionality can be implemented. It’s a TxR formula, where the first number is the number of transmitting radio chains and the second number is the number of receiving radio chains. Some good descriptions and drawings can be found here, but you should now understand that a “2×2” access point can provide 2 transmit streams and 2 receiving streams, while a “3×3” provides 3 of each.
That’s good to know, but you will also need to be concerned with the number of “spatial streams” that the solution provides. Honestly, my eyes start to cross at this point, but the traffic going across all of these transmitting and receiving radio antennae has to occur at different frequency spaces in the various wireless spectrums. Most enterprise solutions today will advertise two or three spatial streams, and three is certainly better than two. Be aware that some 3×3 radio solutions may still only provide two spatial streams. In that case, the additional antenna could be used to extend the signal range instead of supplying an additional spatial stream.
Another thing I’ve read lately is 300Mbps and 450Mbps throughput. Each spatial stream, based on wireless standards, is advertised to pass traffic at up to 150Mbps. Two spatial streams naturally leads to a statistic of 300Mbps maximum throughput. Three spatial streams equates to 450Mbps maximum throughput.
What does all of this mean at the client level? There are some really good articles out there that discuss this. This blogger goes through some interesting testing with his iPad on WiFi. Another article here is a good overview of three spatial streams and what it can or cannot mean for you. There are several good points from these articles. All of the talk thus far has been about the access point and the number of concurrent streams that they can support. Many of your clients don’t support multiple streams. In fact, most smartphones and tablets support a single stream. Why? Well, those chipsets for the increased throughput are going to be more powerful and more expensive. As a device maker, I don’t want to be too expensive or have a really short batter life… so most choose to offer lower ‘functionality’ – a single stream – and preserve lower cost and longer battery life.
Several good reads on the client-related testing and limitations can be found here, here and here. There are some additional points to be made about newer devices using a ‘wider’ amount of spectrum in the 5Ghz range that can, in the right configuration, increase throughput.
I suppose the goal here is to educate you to make sure you have some idea about the terms that get thrown around when evaluating wireless solutions. A solution with three spatial streams is indeed better than a solution with two streams… if your goal is to provide connectivity for a larger number of wireless users in a school setting. If, however, the complaint is an individual wireless user that doesn’t think the download speed is what it should be… reference some of the linked material and point out that a best-case scenario might put a single connection in the 35Mbps range, regardless of 2×2, 3×3 or anything of the sort. Here’s one last link on tablets in the WiFi environment. Take care!