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I’ve read articles on Unstrung about WLAN switch boxes (or shared media hubs), and beamsteering antennas. Vivato claims 33 Mbps. over 100x100 meter office area with 802.11b. Aruba claims 2 Gbps. Capacity with 802.11b.
Here’s the thing, 802.11, without counting any interference from overlapped access points, or hidden nodes, or reduced data rate because of blocked signals, will suffer from increasing numbers of collisions-and-retries as the number of users increases. These collisions cost the network real data throughput, and the congested network phenomenon results.
Vivato claims they can support 150 users in a 100x100 meter office space. That’s about 105,000 square feet. This means that each user occupies about 700 square feet of office space. This means 150 devices congesting the wireles LAN. This means that whenever there isn’t sufficient signal strength between a mobile device and the Vivato antenna, the data rates train in steps from 11 Mbps. down towards 1 Mbps.
Any time a mobile device trains down the data rate, it means that packets take longer to transmit on the network. This means there is less network available for other devices. Which in turn means more collisions and more congestion.
Can an 802.11b network deliver more than 2 Mbps. actual data throughput reliably with more than a handful of users? Where does that leave the Vivato system, perhaps 6 Mbps. (upto 3 simultaneous beams claimed), total throughput for 150 users?
Aruba Networks claims 2 Gpbs. capacity using 802.11b. That translates to just over 180 Access Points.
The question is, can you really use the claimed 2 Gbps.? If an Access Point has a coverage radius of 250 feet for 802.11b operation, then 180 AP’s will cover about 35 million square feet. (PI*R*R) * 180.
Since I don’t think that’s what Aruba Networks had in mind, lets try putting the Access Points close together. If you don’t reduce the power, the AP’s will all interfere with each other, let alone all the devices interfering with each other. If you do reduce the power, then the distance that your mobile device can be from the AP and experience the full 11 Mbps. data rate is severly reduced. Even with reduced power, the nearby mobile devices will act as hidden nodes causing interference, while the co-channel interference from the neighboring AP’s will further reduce the actual data throughput of the wireless LAN.
Lets say you use 180 AP’s in the same 100x100 meter space that the Vivato antenna covers. Essentially every AP can hear every other AP. 802.11b has 3 channels. So lets assume that 60 AP’s interfere with each other on each channel. Lets further assume that mobile devices must roam between these AP’s as they move within this office space, causing hidden node problems, and perhaps some unintentional oscillating between AP’s as the mobile devices try to pick the best AP to associate with. Again, how much actual data throughput does the wireless LAN support? Somewhere between 2 – 6 Mbps.?
Maybe it’s a little better than a Vivato antenna, maybe a little worse. Is either one really much better than a dialup modem in the office environment?
Whats really needed is a wireless LAN technology that can scale to real data throughput of 100’s of Mbps., reaching the equivalent of a Gigabit per second wired network, in a 100x100 meter office space.
A technology that is immune to congestion problems, co-channel interference problems, hidden node problems.
A technology that is resistant to temporary moving obstacles, (such as co-workers), between the mobile device and the Access Point.
A technology that can deliver a sustained network efficiency of better than 85% of the actual maximum wireless LAN maximum data rate.
A technology that can deliver better than 45 Mbps. of real data throughput on a 54 Mbps. WLAN network. A technology that is easy to deploy and doesn’t require extensive site surveys to carefully place Access Points, since neither the number of Access Points nor the number of mobile devices has any effect on the performance and throughput of the network.
What do you call such a technology? Where do you find such a technology?
Corporate WaveNet, Inc.’s TRUEratetm at www.corporatewavenet.com.