Editor's note: For the full version of this article, see: "Testing Draft IEEE 802.11n systems - Part 1: Not all "n" is created equal"

Wireless LAN systems based on draft-compliant IEEE 802.11n chipsets from four vendors are significantly outperforming 802.11g-based systems—although with notable variations between products.

Since the Wi-Fi Alliance began certifying draft 802.11n products on June 25, the number of certified devices has been growing steadily and is now over 50. The Wi-Fi Alliance expects these products to interoperate and to deliver approximately twice the range and five times the throughput of legacy 802.11a/b/g networks.

The 802.11n draft is more than just a new physical layer for 802.11. In many ways it is a whole new standard, with performance enhancements on the MAC and PHY layers. The greatest boost in throughput is achieved through spatial multiplexing and doubling of the channel width. Spatial multiplexing is a technique of sending multiple streams of data in the same channel simultaneously. Transporting two spatial streams has the potential of doubling the throughput. Operating in double-width 40 MHz channels can also double the throughput. Additional throughput improvements can be achieved by means of more efficient OFDM and lower overhead at the MAC layer.

To evaluate the accuracy of the claims made on behalf of 802.11n and to provide a baseline comparison between a few of the early "n-compliant" systems, octoScope conducted rigorous testing.

The main objectives of the test were as follows: Measure and compare the throughput of the AP/client pairs in the home and office environments. Measure and compare video prioritization performance of the AP/routers. Measure throughput performance of the Gigabit Ethernet AP/routers between the WAN and the LAN ports. Analyze the competitive performance of the products from different vendors. Analyze differences in performance among the 2-2, 2-3 and 3-3 MIMO configurations.

The testing, sponsored by D-Link, Atheros and Ubicom, focused on verifying the throughput versus range performance of draft 802.11n equipment. Because 802.11n is expected to support high-definition video distribution to multiple TV sets in the home, specific measurements were conducted to see whether the equipment under test prioritizes a video stream over background data traffic when network load exceeds capacity. The measurements were performed in office and home environments on equipment from Netgear, D-Link, Belkin and Linksys incorporating chipsets from Atheros, Broadcom and Marvell.

All of the draft 802.11n products exhibited impressive throughput and range performance. At close range, the measured throughput was nearly 140 Mbits/s. The Atheros-based devices exhibited the longest range and provided throughput above 30 Mbits/s even with 180 feet of operating range and through seven walls. This level of throughput is more than adequate for an HDTV video stream and represents a true breakthrough in the new generation MIMO WLAN technology.