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Three-stream Wi-Fi hits the mark

In 3-stream vs 2-stream tests, 7 MIMO-based access points deliver impressive performance increases

By Craig Mathias, Network World
March 26, 2012 12:07 AM ET

Network World - The rapid adoption of 802.11n has become a significant milestone in the history of wireless LANs. The MIMO-based technologies used in most 802.11n systems provide enough throughput, reliability, and rate vs. range performance to effectively remove the last major barriers to the broad adoption of WLANs in the enterprise.

But there is a broad range of options specified in 802.11n, and, consequently, many products with highly varying performance are on the market. A given 802.11n product is usually categorized by the number of spatial streams, with nominally 150Mbps of throughput possible per stream, assuming a 40 MHz. channel and a short guard interval.

Today, 600Mbps, via four streams, is the upper bound of the 802.11n standard, with two-stream implementations at nominally 300Mbps the effective norm. But we're starting to see a significant number of three-stream access points promising up to 450Mbps coming into the market.

We'd heard, anecdotally, about a 10% to 15% effective performance increase in three-stream products, which, while not bad, wouldn't set the world on fire. For this test we set out to do a level-playing-field analysis of three-stream products, using three-stream access points from seven different vendors and a two-stream access point as a baseline. Both enterprise-class and consumer/SMB-class products were tested in order to explore a broad range of options.

Is your 802.11n installation already obsolete?

The seven, three-stream access points are: Cisco Linksys E4200, D-Link DIR-665, Belkin N750, Netgear WNDR4500, Meraki MR24, Xirrus XR4830 and Cisco 3600. Our baseline AP was a Netgear WNDR 3800.

Of course, 450Mbps for a three-stream AP represents a maximum over-the-air PHY signaling rate, or, in other words, the speed that the marketing department of any given wireless LAN vendor claims that their product will deliver. Still, one might be led to expect a significant performance increase for three-stream over two-stream implementations, especially using a three-stream client (although a nominal increase with two-stream clients could also be expected) and all other conditions being equal. (See A note on nomenclature.)

There's also an appeal on the economic front: given that prices for three-stream access points are often about the same as those of two-stream products, price/performance should be noticeably improved. And, finally, demand for three-stream products should be significant, given growing requirements for capacity from an onslaught of bandwidth-hungry users wielding a growing arsenal of wireless devices, from handsets and tablets to good old notebooks running ever-more bandwidth-intensive applications. (Watch a slideshow version of this story.)

Results exceeded our expectations

When we average the performance of all access points in this series of tests, we find that the improvement of three-stream over two-stream in the "near case scenario" (when the access point and client are about 4 meters apart in the same room) is an amazing 93.04%.

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