Multichannel WLAN chips look toward the sky


Chipsets from startup Engim Inc. that allow one Wi-Fi access point to carry data on multiple channels may end up in networks optimized for high-density environments, including multipurpose wireless infrastructures on airliners.

The Acton, Massachusetts, company is set to introduce on Tuesday its new generation of both silicon and access points for vendors to incorporate into wireless LAN offerings. Engim's EN-3001 Wideband Wireless LAN chipset and access point reference designs for 802.11b and 802.11g are designed to use three channels at once, allowing more clients within a single area to simultaneously use Wi-Fi, according to Scott Lindsay, vice president of marketing at Engim.

Engim is adding to its lineup a thin access point, priced to system makers at about US$100, in which the processing of packets takes place in the chipset rather than on a separate processor. Also new is a feature in Engim's radio chip called "transmit cancellation," which can prevent interference that an access point's transmitting antenna can cause to the same access point's receiving antenna, Lindsay said. The feature subtracts the transmit antenna's interfering signals for the receiving antenna.

At the heart of Engim's approach is multichannel capability. The 802.11b and 802.11g standards use spectrum in the 2.4GHz band that offers at least 11 bands, but generally only three of those can be used because of interference from channel overlap. Each access point typically can only use one of those channels, and simply putting three access points in one location with each on a different channel -- or just building an access point with three chips on different channels -- won't provide good performance because they will interfere with each other, Lindsay said.

That means the zone covered by an access point, typically about 300 feet, can only be served by one channel, leaving two channels unused, said analyst Craig Mathias, founder of Farpoint Group, in Ashland, Massachusetts. That's a waste of spectrum, he said, one that is not a big problem today but is likely to become one in the future, Mathias said.

"Imagine you had a TV set with only one channel. You'd be able to watch whatever they had on that channel at that time," he said. As more clients in a given space start to use Wi-Fi, access points increasingly will have to make use of those other two channels, he said.

Engim built the silicon for three channels into a single chip, with technology that can find the interference on a channel and subtract it out for a clear signal, Lindsay said. A radio for 802.11a, due in two or three months, will allow the use of three 802.11a channels simultaneously.

One of the dense environments that may benefit from Engim's approach is airliner cabins, according to Jim Pristas, founder and chief executive officer of Matrx Aerospace Broadband Technologies LLC, a startup in Arlington Heights, Illinois. Matrx is using Engim's chipset in the demonstration unit of an in-flight wireless infrastructure it is developing, called Galaxy. Matrx plans to work with airlines, aircraft manufacturers and other partners to install the systems, Pristas said. Though he said Matrx, founded in 2001, is backed by a major aerospace company, he would not identify the company.

Galaxy will be able to use multiple wireless bands as well as multiple channels within each band, according to Pristas. The company aims to start out in late 2005 with a version geared primarily to passenger Web access and e-mail over Wi-Fi. Those services are already offered on some airlines, but because Galaxy will be built specifically for airplane cabins, it will offer better performance, in part because of the multichannel capability, Pristas said.

A second version of Galaxy, targeted for 2006, would offer a wider range of services through a system that could include proprietary wireless systems in addition to Wi-Fi, Pristas said. Matrx envisions wireless delivery of multimedia services including video on demand to screens on seat backs, which would eliminate the weight and the maintenance costs of data cables going to every seat. The system might also be used for surveillance cameras, crew communication, handheld point-of-sale devices and other applications. The performance advantages of the purpose-built system could also serve another future application, in-flight wireless phone calls, he said.

In addition to suppressing interference from other Wi-Fi channels, the Engim chipset can take the information it gathers about anything going on in the spectrum band and pass it on to network managers. For example, it can detect interference from other technologies, such as Bluetooth and cordless phones, with location information so network managers can find and turn off or move those sources of interference, Lindsay said.

Prices for the EN-3001 chipset will vary based on volume and the customer's development needs, according to Engim. The chipset, as well as the AP-310 All Services Access Point at about US$120 and the AP-320 Thin All Services Access Point at about $100, are available immediately to system vendors.

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