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Wi-Fi, 'down under' style: university's construction makes a case for a different type of access-point architecture.

Jeff Dowsley knew he did not have the best physical environment for a wireless network, but his customers were virtually demanding wireless access-so he had to find a solution. "We had been exploring putting 802.11a in some of our buildings," says the manager of communications technology, strategy and planning at the University of Ballarat, "but the buildings are steel pin-jointed structures, creating a very poor environment for radio characteristics. We would have needed an awful lot of access points to get the coverage we wanted."

The university's Mount Helen campus is located just outside Ballarat, Victoria, Australia, near Melbourne, and has an enrollment of approximately 5,000 students. Because most of the campus buildings have been constructed with cast concrete floors, hindering the deployment of a cabled network, university officials had been considering deploying a wireless communications network for staff and students for some time.

Rather than fight the construction restrictions to wireless capability, the university decided to try a different approach, using a single access point (AP) enabled with Bandspeed's Gypsy and Listen+Learn architectures. Gypsy is an AP system-on-a-chip with spatial division multiple access (SDMA) architecture.

The Gypsy architecture is different from conventional APs, in that, rather than radiating an RF signal in all directions, as with conventional omnidirectional APs that behave like hubs, APs designed with the Gypsy architecture can dedicate channels of bandwidth in up to six discrete sectors of coverage and up to a 360-degree configuration. Each of these sectors can provide dedicated bandwidth at the maximum signaling rates allowed by the applicable 802.11 standard, and allow the operation of two bands in each sector, in addition to each sector having independent transmit power.

SKEPTICISM MEETS REALITY

After some initial skepticism that the technology could actually do what was claimed in terms of coverage and capacity capabilities, the university agreed to a field trial. Bandspeed donated the AP equipment and the university shouldered the deployment costs.

The university's immediate needs were for wireless coverage in the quadrangle, a central open space where students congregate, and the cafeteria, which faces the quadrangle. After a survey of the campus, the northwest corner of the science building, directly across the quadrangle from the cafeteria, was chosen as the best location for the AP. The AP was mounted on a three-meter pole and installed on the roof, which placed it approximately 20 meters above the ground.

Installation took one day and involved connecting to a standard 240V, 50 Hz, AC power circuit, porting to the Ethernet campus network, and grounding the entire unit to the roof location. On the second day, the AP was secured and configured in four hours. Unlike an omnidirectional AP that transmits equal power in azimuth (360 degrees on an x-y plane), Gypsy-enabled APs use a sectorized design that permits the AP to transmit RF signals directionally, in up to six degrees of freedom, allowing an IT manager to tailor the cell footprint of the desired coverage.

The AP deployed at Ballarat University was configured via simple network management protocol, using the three-channel mode of equal coverage areas, with each sector covering 120 degrees. Other features in the technology, such as spatial diversity, allow the AP to take advantage of multipath, in that the beams are able to bounce off objects more easily instead of being blocked by them. The amount of area where a signal might not otherwise be available is therefore reduced.

Other than some intervening inclement weather, the Ballarat installation went smoothly. The physical installation cost approximately $1,000, which is the equivalent standard price for any roof-mounted outdoor AP in Australia. Since the original site survey recommended using nine conventional APs, the Gypsy-enabled AP offered an installation cost savings of $8,000. A production model of the AP would cost around $3,000, for a total installation cost of about $4,000. The comparable units to be used originally would have cost an estimated $1,500 apicce, resulting in capital equipment expenditure savings of approximately $10,500.

Once the AP was powered up and configured, Bandspeed performed a campuswide site analysis using AirMagnet laptop software to measure received signal strength, and perform data transfer and ping tests. The tests were carried out using a Dell Precision M60 laptop computer with Intel Centrino mobile technology and an iPAC PocketPC with an AirMagnet series card.

COVERAGE EXCEEDS NEEDS

A ping test was conducted to determine whether a wireless station can connect with the AP from a particular location and if the AP responds and transmits information successfully. APs also transmit specific beacons that are used by listening devices to configure connections and determine the signal's strength. Based on the strength of the signal, data rates from different locations around the campus can be determined.

In general, if the signal strength is greater than -86 dBm (decibels), data can be transmitted at 11 Mbps. After finishing the initial measurements, Bandspeed found that Gypsy not only fulfilled the university's original coverage requirements of the quadrangle and cafeteria, but also covered almost the entire campus with an 802.11b signal rate of 11 Mbps.

"We were most impressed because we've been running around campus with laptops to measure the signal strength," says Dowsley. "The property is one-and-a-half kilometers by almost a kilometer, and, in the open areas, we had good signal strength right tip to the property boundaries. We now feel we can service all sorts of outdoor activities, like sports, where in the past we had to run separate cables and links.

"Unfortunately, though the AP gives good coverage into buildings that are facing the AP, on the other side of large buildings it doesn't penetrate that far," he adds. "So we do need smaller APs in areas that are shielded by some buildings.

"This is due not only to the cast concrete and steel pin-joint construction, but also the glass used on a couple of buildings is fairly opaque to the particular radio frequency used in the 802.11 unlicensed spectrum," he says.

Ballarat University has five other remote rural campuses, and Dowsley says they would benefit even mote from a Gypsy-based system because they do not have the construction anomalies present at the Mt. Helen campus. "It's quite feasible," he says, "that a single AP will provide full coverage at one of these campuses, with good results within the buildings, as well."

Right now, only the technical staff uses the wireless LAN (WLAN) at the Mt. Helen campus. The deployment of a virtual private network to provide the needed WLAN security is the next step. University officials want to make sure that anyone who gets onto the wireless network is properly authenticated and authorized before they access various services.

For more information from Bandspeed: www.rsleads.com/408cn-255
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Copyright 2004 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Mobile Computing
Publication:Communications News
Geographic Code:8AUST
Date:Aug 1, 2004
Words:1127
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