Smart antennas to expand Wi-Fi range

The first generation of Wi-Fi devices for corporate networks has generated a great deal of interest in the untethered workplace, but not as much revenue as many vendors had expected. However, several vendors hope to decrease the number of access points needed to sustain a wireless office by expanding the range of corporate wireless LANs and improving the signal quality using smart antennas.

Most antennas on Wi-Fi switches and routers are "dumb," in that they have no added intelligence beyond their ability to detect electronic signals by locking on to the strongest signal they can find emanating from a client device. A "smart" antenna actively searches an area for Wi-Fi signals, and can blend several weak signals into a strong signal without any prompting from the user.

Smart antennas are not a new technology. Cell phone towers have used this technique for several years in helping to maintain a cell connection while the caller drives down the highway or walks across a city square. But the increasing ability of silicon chips to control the antenna and the cost reductions that come along with chips have primed smart antenna technology for the next generation of Wi-Fi devices.

Smart antennas appeal to universities or owners of large buildings such as airports or convention centers that need to provide Wi-Fi coverage over a large area, but corporations setting up smaller indoor wireless networks probably won't see enough of a performance benefit to justify the acquisition cost, said Chris Kozup, research director with Meta Group Inc. in Stamford, Connecticut.

"Enterprises are looking for tools to make Wi-Fi easier to deploy, easier to manage, and easier to secure," Kozup said "Smart antennas are one of those, but they're not at the forefront of the list in providing that capability."

There is a tendency among enterprise technology buyers to feel overwhelmed when new technologies come out that are more difficult to understand, Kozup said. While an enterprise might have several staff members comfortable with networking technologies, they might not have IT staff comfortable with managing RF (radio frequency) devices, and would find it easier to just buy several cheap access points from an established vendor like Cisco Systems Inc. to guarantee coverage, he said.

The smart antenna vendors present a solid case that the total cost of managing a disparate network of access points might exceed the acquisition cost of more sophisticated technology, "but the best technology doesn't always win," Kozup said.

Vivato Inc. uses the technology in its 802.11b Wi-Fi switches for large indoor or outdoor coverage areas, said Phil Belanger, Vivato vice president of marketing, based in San Francisco. The switches use antennas called planar phased array antennas, which are actually several antenna elements built into a flat-panel device, he said.

The antenna itself does not move, but the antenna elements create a coverage pattern that changes as each packet of information is delivered to the antenna, Belanger said. This allows the switch to send and receive data across 100-degree swath up to 250 or 300 meters depending on line-of-sight restrictions, he said.

The range of WLAN devices built using the 802.11 standards vary from about 15 meters for 802.11a devices to about 30 meters feet for 802.11b or 802.11g devices. These range numbers can vary quite a bit, however, based on the types of building materials used in a home, and the amount of interference from other devices.

Each switch can support about 100 clients, Belanger said. Florida State University in Tallahassee purchased an outdoor switch, which normally costs US$13,000, and installed it in Doak Campbell Stadium to cover the entire stadium, including coach Bobby Bowden's offices underneath the grandstand, he said.

American University in Washington, D.C., recently purchased two outdoor switches from Vivato in order to cover some external spots that couldn't be reached by the university's extensive indoor WLAN setup, said Carl Whitman, executive director of e-operations for the university.

American is trying to get students to move to cell phones and VOIP (voice over Internet Protocol) technology so the university can stop maintaining a traditional phone network, Whitman said. It has wired about 40 buildings on campus for both 802.11b and GSM/GPRS (Global System for Mobile Communications/General Packet Radio Services) networks. The original plan had been to cover outside areas with spillover from the inside networks, but coverage was added for those outside areas to ensure students and faculty could have a seamless connection, he said.

Bandspeed Inc. of Austin, Texas, also sells WLAN access points with smart antenna technology. The company's Gypsy line of switches divides the coverage areas into six unique segments in which up to two radiating elements can be placed, said Blaine Kohl, Bandspeed vice president of marketing.

Because the radiating elements have to focus on only a 60-degree area, the switches can send signals across a long distance, as much as 500 meters, Kohl said. The switch can also host different 802.11 networks, depending on bandwidth needs, she said.

While the antenna is pretty smart, the real intelligence lies in the software Bandspeed has developed to run the switch, Kohl said. Over time, the company wants to move that intelligence into silicon, which would allow it to reduce the cost and complexity of both the antenna and the software, she said.

A semiconductor company in Stamford is working on those chips. Motia is developing a chip that combines signals from different antenna elements and optimizes the signal, said Jack Winters, chief scientist at Motia.

Some access points with multiple antennas merely select the strongest signal to pass onto the user, and drop the signals on the other antennas, Winters said. Motia's chip allows access points to blend different signals together in order to create a signal whose total is greater than the sum of its parts, he said.

Each chip can support an access point with four antennas, Winters said. The technology is designed for indoor corporate environments, and each chip is expected to add about $20 to the cost of an access point when it is released in the first quarter of 2004, said Robert Warner, vice president of sales and marketing for the company.

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