That's where 802.11a comes in. Although first approved in 1999, 802.11a has been slow to take off, not only because engineering 11a chipsets is challenging but also because the success of 802.11b has made that system a de facto standard. The landscape changed in 2001, however, when Atheros Communications began volume shipment of its 802.11a chipset. Until then, a war of white papers raged, with some touting 11a as the solution to emerging WLAN performance and capacity problems and others speculating that 11a products would have range limitations of 30 feet. Thus, when we took a look at the first 802.11a offerings, we didn't have high expectations. When the dust settled, we discovered some truth on both sides of the battle line. The best 802.11b products did have significantly greater range than 11a offerings, particularly in walled-office environments. Still, 11a range was better than expected, well in excess of 100 feet in many cases, and 11a was fast.
When we set out, we recognized that the market is still developing. Atheros is still the only vendor shipping 11a chipsets, though we expect to see credible competition emerging in coming months from Cisco Systems, Intel, Intersil and others. Interoperability will become a nonissue in the near term. We also recognized that many of the first 802.11a products making their way onto the market were not targeted at the enterprise. Nonetheless, we thought it was worthwhile to examine what was available, so we invited D-Link Systems, Intel Corp., Intermec Technologies Corp., Linksys, NetGear, Proxim Corp., SMC Networks and Sony to submit their access points for testing. All but D-Link and Sony accepted; neither provided a reason for declining, but since both target the consumer space, we don't consider it a big loss. We conducted all testing at and around our Syracuse University Real-World Labs®.
802.11a: The Details
The secret behind 802.11a is its OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme, which offers significant performance benefits compared with more traditional spread-spectrum systems. Both 11a and 11b share a common MAC (Media Access Control) interface, but they share nothing in common at the physical layer except that they both employ radio frequency technology. While 11b systems max out at 11 Mbps (around 5.5 to 6 Mbps effective throughput with overhead), 11a systems offer a data rate of 54 Mbps and a maximum throughput of around 24 Mbps. Most of the products we tested also include proprietary turbo modes that use channel aggregation to boost performance to 72 or even 108 Mbps, but that's clearly a nonstandard offering.