Wireless Data In the Great Outdoors

Bridges are more than just long-range wireless access points; they are the core of a wireless ISP's (WISP) infrastructure. Most bridges do not use 802.11 protocols, which are designed for short ranges.

"Many people just attach a large high-gain directional antenna to an AP [and call it a bridge. But there are several things wrong with that approach," according to John Richey, senior technologist for wireless equipment-maker Agere Systems. "First, 802.11 uses the CMSA/CA protocol. In simple P2P bridging, this is not a problem. But in P2MP over long distances, an AP [access point often cannot detect that another AP is transmitting packets in time to avoid collisions."

Then there's the "hidden node" problem, Richey says. "When outdoor nodes cannot 'hear' each other due to [physical or RF interference, they cannot hold their packets until the channel is clear," he explains.

Packet collisions result, and throughput drops by up to 80 percent due to retransmissions. Agere and many other vendors overcome those problems by using a polling protocol, which is part of the TurboCell family of wireless protocols licensed from Karlnet. TurboCell also provides bandwidth management, firewalls, SNMP management and other features useful to wireless ISPs.

Wireless bridging "is still an emerging market, [though we're seeing 20 to 30 percent annual growth," says Eric Lee, president of Solectek, a wireless bridge products manufacturer that offers the SkyWay, MP and AirLan families of wireless bridges and routers. Much of that new business, he adds, is P2MP networks connecting branch offices to central databases.

Solectek's SkyWay series of wireless bridges and routers can span distances of up to 30 miles, according to the company. SkyWay modules are available for P2P and P2MP applications. The MP bridge/router products feature IP/IPX routing, and nine antennas are available to suit specific applications and environments. Solectek's AirLan series is a complete plug-and-play P2P bridge kit with selectable ranges of two and five miles.

Agere released a similar product, the Point-to-Point Radio Backbone Kit. The kits all reflect a trend toward prepackaging of wireless components matched for in-demand applications, making a VAR's design and installation tasks easier,and keeping them within the law. "802.11 radios cannot broadcast more than four watts in one direction, per FCC regulations," Richey notes. Matching the wrong antenna to a bridge can put a system over that limit.

Wireless ISP Gear

The simplest example of a wireless bridge in use features a bridge at the customer's premises and another at the WISP's Internet point-of-presence (POP). To extend coverage areas, remote base stations can be erected on towers or rooftop poles and their traffic backhauled to the POP via wired or wireless links. To increase the bandwidth available within a covered area, more base stations can be added to a tower on different radio channels. Such deployments enable a WISP to serve more customers within an area or deliver higher bandwidth to each customer.

It really is simple,as long as there is a clear line-of-sight (LOS) between the base stations and customer-premises equipment (CPE). Omar Nuseibeh, founder and owner of Midwest Data, which sells Solectek wireless solutions, says his biggest challenge is finding appropriate locations for base-station towers in the hilly terrain of southern Indiana.

WISPs using first-generation equipment find they can typically achieve clear LOS to only 30 to 40 percent of potential subscribers in high-rise urban areas. This low penetration rate prompted major carriers such as Sprint and AT&T to suspend their WISP rollouts until vendors developed non-LOS (NLOS) solutions.

But the industry first had to define NLOS, a task completed after IEEE standard 802.16a was approved in July 2001. The standard establishes six channel models,from LOS to completely NLOS,for fixed-wireless systems operating in license-exempt frequencies from 2 GHz to 11 GHz. The channel models provide a benchmark for determining how effectively a product can penetrate foliage and walls, circumvent hills, resist radio interference, etc.

Iospan Wireless helped draft and

then champion the 802.16a standard, so it's no surprise it has the first product that satisfies all six channel models. Iospan's AirBurst technology is based on multiple input/multiple output orthogonal frequency division multiplexing (OFDM). Variants of OFDM are used in fixed-

wireless systems that are made by Cisco, Wi-Lan and others to achieve "near-LOS" performance.

"Our system contains multiple antennas separated slightly in space," says Bob Powell, Iospan's marketing director. "There are two antennas at the head-end, and three in each CPE unit, giving us a total of six different channels."

A data stream is split and transmitted via all six channels simultaneously, then reassembled at the receiving end. The spatially separated channels even out fluctuations in signal strength, providing greater penetration, resistance to interference and significantly lower power requirements. In a recent field trial, a San Francisco apartment, 4 miles from its WISP base station, was equipped with AirBurst CPE. Download rates averaged 7 Mbps, according to Iospan's Powell, with peak performance of 13.6 Mbps. Upload rates averaged 5 Mbps to 6 Mbps, "something vendors and service providers had never seen in NLOS before," he says.

Another firm taking a software approach to NLOS is EtherLinx Communications. Software engineers Layne Holt and John Furrier developed Smart Spectrum software to replace the firmware of inexpensive 802.11 dual-radio cards. "Decoupling firmware from hardware is key for ISPs," Furrier says. "The cost of radios will keep coming down as they become basically a box for [software intelligence. This gives ISPs more margin between deployment costs and service charges."

In EtherLinx's system, one radio handles long-range data relays, while the other supplies standard 802.11 connectivity to wired or wireless local devices. Each CPE device acts as a repeater, relaying data to other nodes. This "mesh architecture" extends the range of the network and overcomes any hidden node obstacles.

Roughly 20 vendors offer mesh architecture products, including Nokia's RoofTop Wireless Routing, FHP Wireless' RoutePoint, MeshNetworks' MeshLAN and Radiant Networks' MeshWorks.

Hotspot-In-A-Box Vendors

Hotspots provide public Internet access to mobile devices equipped with 802.11 radio cards. More than 1,200 airports, hotels, convention centers, cafes and other public venues currently offer hotspot services, and analysts predict up to 10,000 hotspots may be in operation by 2005.

While a hotspot can be created from off-the-shelf components, integrated "in-a-box" systems are now appearing to make a VAR's job easier and more profitable.

"Hotels, especially, are begging us to send them VARs [to install hotspots," says Tim Barrett, vice president of Airpath Wireless, which builds and interconnects hotspots. "Their first efforts to offer Internet service failed because they tried to become ISPs. They bought lots of equipment, kept closed networks and charged too much. Now they're learning. They don't want anything to do with the technology end."

Airpath's ARC 100C system supports up to 100 simultaneous users. It includes routing, firewall, Radius AAA, embedded roaming and traffic-management functions. Airpath's billing software enables creation and management of user accounts and service prices, and connects hotspots to Airpath's roaming network. Airpath handles end-user billing and credit-card processing, taking a portion of the fees set by each hotspot operator. The ARC100C can be purchased for $1,295 or leased.

Competitor Boingo Wireless offers a hotspot-in-a-box system, priced at $895, which can be combined with the Colubris CN3000 or Agere's Smart Access Point. Unlike Airpath, Boingo sets end-user prices: $24.95 per month buys up to 10 days of connectivity; unlimited usage is $74.95 per month; and a single day costs $7.95. Boingo pays hotspot operators $20 per new subscriber plus $1 per connection/day.

"We often partner with managed network providers," says Christian Gunning, director of product development for Boingo. "They install network infrastructure and billing systems for hotels, and sell Boingo hotspots as a revenue-generating add-on that attracts occupants. Our partners earn installation revenue and commissions on Boingo fees generated by their hotspot installations."

David Hakala (davidhakala1@attbi .com) is a freelancer based in Denver, Colo.