Consulting with Cisco, Georgia Tech decided to try some newer access points, with external antenna mounts, and selected one of Cisco's certified partners, Tessco's Ventev Wireless Infrastructure division, to supply the directional antennas. The TerraWave products also are compatible with access points from Aruba, Juniper, Meru, Motorola and others.
Patch antennas focus the radio beam within a specific area. (A couple of vendors, Ruckus Wireless and Xirrus, have developed their own built-in "smart" antennas that adjust and focus Wi-Fi signals on clients.) Depending on the beamwidth, the effect can be that of a floodlight or a spotlight, says Jeff Lime, Ventev's vice president. Ventev's newest TerraWave High-Density products focus the radio beam within narrower ranges than some competing products, and offer higher gain (in effect putting more oomph into the signal to drive it further), he says.
One model, with a maximum power of 20 watts, can have beam widths of 18 or 28 inches vertically, and 24 or 40 inches horizontally, with a gain of 10 or 11 dBi, depending on the frequency range. The second model, with a 50-watt maximum power output, has a beamwidth in both dimension of 35 degrees, at a still higher gain of 14 dBi to drive the spotlighted signal further, in really big areas like a stadium.
At Georgia Tech, each antenna focused the Wi-Fi signal from a specific overhead access point to cover a section of seats below it. Fewer users associate with each access point. The result is a kind of virtuous circle. "It gives more capacity per user, so more bandwidth, so a better user experience," says Lime.
The antennas come with a quartet of 36-inch cables to connect to the access points. The idea is to give IT groups maximum flexibility. But the cables initially were awkward for the IT team installing the antennas. Lawrence says they experimented with different ways of neatly and quickly wrapping up the excess cable to keep it out of the way between the access point proper and the antenna panel [see photo, below]. They also had to modify mounting clips to get them to hold in the metal grid that forms the dropped ceiling in some of the rooms. "Little things like that can cause you some unexpected issues," Lawrence says.
The IT staff worked with Cisco engineers to reset a dedicated controller to handle the new "high density group" of access points; and the controller automatically handled configuration tasks like setting access point power levels and selecting channels.
Another issue is that when the patch antennas were ceiling mounted in second- or third-story rooms, their downward-shooting signal cone reached into the radio space of access points in the floor below. Lawrence says they tweaked the position of the antennas in some cases to send the spotlight signal beaming at an angle. "I look at each room and ask how am I going to deploy these antennas to minimize signal bleed-through into other areas," he says. "Adding a high-gain antenna can have unintended consequences outside the space it's intended for."
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