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Analysis: Fixed Wireless: Page 2 of 11

Neither Snow, Nor Wind ... Well, Maybe Wind

Last time we evaluated fixed wireless systems, in summer 2005, we set up an outdoor test bed at our University of Florida Real-World Labs®--just in time for Hurricane Dennis (see "Bridging the No Cable Divide"). After scrambling to haul the gear off roofs to avoid the tropical-storm-force winds predicted by the National Weather Service, we made an appointment to have our collective head examined.

This time out, in the depths of winter, we decided to connect fixed wireless products from Alvarion, Motorola and Proxim Wireless in our Syracuse University Real-World Labs® using a combination of variable and fixed attenuators to simulate distance; see our testing scenario, on page 60, for more details. Yes, removing obstructions, including trees and precipitation, means we couldn't see how the great outdoors influenced performance. On the flip side, eliminating extraneous environmental factors simplified troubleshooting--when we had problems with a radio, the vendor couldn't blame Mother Nature.

We were impressed by what we saw. Actual throughput generally equaled 70 percent to 80 percent of the products' advertised data rate; this compares favorably to 802.11's throughput, which is only 40 percent to 50 percent of the advertised data rate, mostly due to overhead in the protocol. Performance ran the gamut, from 23.5 Mbps (Proxim Tsunami MP.11) on the low end to 277.5 Mbps (Motorola PTP 600) on the high end, not surprising considering each caters to a different market segment.

Latency was variable, from 0.6 milliseconds to 14 milliseconds. We were pleasantly surprised at the sub-millisecond latency times offered by the higher-end Tsumani.GX 90, Tsunami.GX 200 and Motorola PTP 600 systems, which use more complex modulation schemes and radios with higher receive sensitivity to achieve better performance. Because the products support 802.1Q VLAN trunking, enterprises could use them to extend a LAN to another building to tie a branch office to a main office or to assign a remote location to its own subnet.