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The March 10, 2005 Issue Provided by System Dynamics Inc.
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Wi-Fi's Leap Forward: Adding MIMO To The Mix

Things change fast in the Wi-Fi world. We're now entering the fourth generation of products since we installed the first wireless network in our home five years ago. We started with the original 802.11, switched to 802.11b, and followed by 802.11g. Now we've started seeing precursors to what will become 802.11n.

While standards change fairly slowly--802.11 came out in 1993, 802.11b in 1999, and 802.11g in 2003; 802.11n is not expected to be completed until 2006--technologies change much more quickly. Chip companies no longer wait for published standards to introduce major new non-standard features; they now launch several generations of chips with "enhanced" or "accelerated" or "turbo" modes before standards are formalized to lock in these changes. These chips try to be "back compatible" with current standards to support "mixed networks" but usually work best in networks where all the devices have the same new chips. Sometimes the new chips are based on drafts of new standards, and promise that later software upgrades will make them fully compatible with the evolving standards when they are completed.

We started testing 802.11 devices in our home before the term "Wi-Fi" was invented, and we published the results of our first round of formal in-home testing almost two years ago in "Wireless Is Magic" -- Our Evaluation of 802.11g Wi-Fi (BBHR June 17, 2003). We were somewhat disappointed in those results: marketing claims of "five times faster" turned out to be more like two times when averaged over the nineteen locations we tested. Enthusiastic claims for wireless video networking were not justified by the performance we saw, nor by the inability of the technology to cope with video and data on the same network.

A year ago we published the results of our second round of testing in Wi-Fi Evaluation Round Two (BBHR February 16, 2004). This showed the importance of upgrading firmware and drivers, a positive sign that equipment based on draft standards could indeed be upgraded to obtain improved compatibility and performance in mixed networks. We decided to repeat the full test series to measure the quantitative improvement between the early and mature 802.11g products.


Wi-Fi Round Three Test Results

Belkin Wireless Pre-N Router with MIMO antennas --> Click for larger pictureBy the time we were ready to repeat the full test series, equipment based on early MIMO technology from Airgo Networks had appeared on the market. MIMO will form the technological basis for 802.11n--the next generation of Wi-Fi. While some of these MIMO products are marketed as "Wireless Pre-N", they are really MIMO extensions of 802.11g. We decided to extend the test series to compare the performance of MIMO/11g with "standard" 11g. (See MIMO/802.11n -- An Interview with Airgo (BBHR 2/24/2005) for more about MIMO and 802.11n.)

We tested three access points in round 3 --> Click for larger pictureWe are seeing a remarkable progression of improvements in "Wi-Fi" technology. The mature 11g implementations we've just tested showed considerable improvement over the draft 11g implementations tested in Round One--and some of those were the same devices with updated firmware or drivers. The early MIMO enhancements show the same improvement over standard 11g--a throughput improvement of better than 2X--as the early 11g showed over 11b. Moreover, the newest MIMO devices provide high enough throughput and consistency to support video networking.

Specifically:

  • MIMO/11g showed very impressive improvement in both throughput and range over standard 11g. MIMO/11g throughput averaged 29 Mbps, more than twice the 13 Mbps of mature 802.11g, and more than three times the 9 Mbps from our earlier tests of draft 11g.
  • Combining MIMO/11g with standard 11g gave mixed results. The MIMO/11g notebook adapter showed a 20% improvement over standard 11g most noticeably when distant from the 11g access point. Conversely, the MIMO/11g access point reduced average throughput by about 7% when used with standard 11g notebook adapters.

These tests are covered in detail in the Round Three Wi-Fi Tests pages of our web site.

Many products are now on the market with various forms of "accelerated 11g". We have tested only Belkin products based on the Airgo chipset. We plan to test new products as they become available and update our reports and conclusions.


Wi-Fi at Sanibel

During the time we were running these tests, we took off a few weeks and rented a condo in Sanibel, Florida, our favorite place to get away. We felt the need to stay in touch and were glad the condo complex had a Wi-Fi setup.

From an earlier visit, we knew there was a wireless access point on the roof of the clubhouse in the center of the complex. We had found we could get a reliable connection only if we sat outside on the lanai facing the clubhouse; inside our condo, the signal level was too low for a reliable connection.

Before we left, we had already completed most of our Round Three testing, and had observed range improvements using MIMO adaptors with standard 11g access points. So we brought along some of the wireless equipment we were testing.

Dave using a PC on vacation in Sanibel --> Click for larger pictureOur experience at the condo confirmed our tests at home. As before, we could not get a reliable connection from inside the condo to the clubhouse access point with the 11g and "tri-mode" network adaptor cards. But the MIMO card provided the boost in performance we needed to work inside the condo--just as well as outside.

View of the gulf from our condo --> Click for larger pictureOur Sanibel experience provided another real-world testament to the improvements that have been introduced in this new era of MIMO-enhanced Wi-Fi.

Of course, we found some time to enjoy the beach and the sun, too!


The Outlook for Wireless Video Networking

For the first time in our Wi-Fi testing, we believe wireless video networking is on the horizon. High-quality video has two main requirements: sufficient throughput to carry several channels of standard-definition or high definition video; and a QoS mechanism to give time-sensitive video priority over data when both are used in the same network.

With throughput of 17 Mbps at the worst point in the house, MIMO/11g could carry several channels of standard-definition television or a single channel of high-definition anywhere in a house. Moreover, the Airgo chips support Wi-Fi Multimedia (WMM), which allows video to take priority over data.

This technology can be viewed as a precursor to 802.11n. 11n will certainly include WMM and will almost certainly use MIMO to achieve its stated goal of 100 Mbps throughput. We are now confident that 11n will be able to carry multiple HD channels throughout the home, along with data and voice. Wireless video networking is visible on the horizon.

For further reference:

( www.airgowireless.com ) ( www.belkin.com )