Fixing" wireless

Enter NLOS. A number of technologists and investors believe that this relative newcomer can overcome the problems faced by existing line-of-sight wireless services. Briefly, the challenge they have to meet is to establish communication links with signal-to-noise ratios high enough to support broadband communications with easily installed, preferably indoor, antennas.

That goal may be achieved in several ways. Local-area networks, like those based on the popular IEEE 802.11b standard, do it by limiting the distance between transmitter and receiver. Cellphones operate over longer distances, but offer no broadband connectivity. LOS systems rely on a high-power transmitter at the base station, an unimpeded line of sight between transmitter and customer, and a highly directional outdoor antenna at the customer premises, all of which add up to a technology too expensive for the residential market.

NLOS attacks the problem with smart antennas, advanced modulation techniques, and, in some cases, a mesh architecture in which nodesthe individual routers on the customer's premisesare connected by multiple links [see figure, What a Mesh!].

What a Mesh!: Mesh networks solve the problem of connecting widely separated wireless routers that can't see each other by using many intermediate points, each of which can be seen by its neighbors. Shown here are four "AirHoods" each of which is served by a base station, called an "AirHead," that connects it to an aggregation point and thence to the Internet.

The mesh architecture helps keep signal strength up by replacing single, long radio links with multiple short ones.

Dave Beyer of Nokia's Wireless Routing Group smiles from behind an array of decorated wireless routers, which when mounted on subscribers' buildings will configure themselves into a mesh network.

Whereas LOS base stations use omnidirectional or sectorized antennas that spew energy over large areas, non-mesh NLOS systems (those built around a central tower) fit their towers with small antenna arrays that direct the energy where it is needed. The advanced modulation techniques like orthogonal frequency-division multiplexing (OFDM) use the available radio spectrum with great efficiency, maximizing the number of bits per second they transmit per hertz of spectrum bandwidth. OFDM does that by sending data over multiple carriers within a frequency band.

Players in the NLOS field include equipment manufacturers like Nokia Corp. (Espoo, Finland) and Navini Networks Inc. (Richardson, Texas); companies like Iospan Wireless Inc. (San Jose, Calif.), which provide transmitter and receiver designs and chips; and Internet service providers (ISPs) like Vista Broadband Networks Inc. (Petaluma, Calif.) and T-Speed (Dallas), which sell wireless access service to customers.