9/23/2016
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`Flash-OFDM ‘hops’ wireless data communications into the main stream
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`News | August 10, 2000
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`FFlash-OFDM ‘hops' wireless data communications into
`the main stream
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`Flarion capitalizes on the benefits of OFDM to develop a mobile broadband
`network architecture that enables wireless Internet
`By Laurie Ann Toupin
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`High speed. High capacity. Interactive. Affordable. Scaleable.
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`Such are the claims made by a new company, Flarion Technologies Inc., about their wireless data
`communication technology, flash-OFDM (Orthogonal Frequency Division Multiplexing), which
`forms the heart of the company's RadioRouter Networks.
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`Lucent Technologies launched Flarion (Bedminster, NJ) in February 2000 in order to
`commercialize flash-OFDM, an air interface technology and a network architecture developed at Bell
`Labs by Rajiv Laroia, the founder and CTO of Flarion.
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`"Ours is a new application of an existing technology," says Ray Dolan, president and CEO of Flarion.
`OFDM, a 20-year-old robust signal-processing scheme, is becoming increasing popular in the
`wireless world because of its ability to handle impairments such as noise, fading and multi-path
`interference. OFDM divides the available bandwidth into a number of discrete tones (frequencies)
`and users signal on different tones. For example, the Flarion system is designed for 5 MHz channels.
`Four hundred discrete tones are assigned to each channel, each at a slightly different frequency.
`OFDM makes the tones orthogonal to each other.
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`Using this signal-processing scheme as their base, Laroia and associates turned OFDM into a spread
`spectrum system by adding, "flash." "Flash refers to fast hopping between tones (frequencies)," says
`Laroia. In a cellular multiple-access environment, users are assigned a certain number of tones. "In
`flash-OFDM, we ‘hop' these users tones to randomize interference," says Laroia. "For example, say
`that a given user in a given time slot uses a certain tone. He will use a completely different tone in
`the next time slot. It is a pseudo random selection of tones from an available set."
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`There are inherent advantages to a spread spectrum technology in cellular environments, says
`Laroia. A spread spectrum system shares the available spectrum with all other cells and uses coding
`to deal with interference from other cells. For example, transmission by users in neighboring cells
`becomes interference in your cell. With flash-OFDM this interference between adjacent cells is
`averaged and its effect minimized. "This is important," Laroia says, "since spectrum is a precious
`resource."
`In addition, spread spectrum provides the benefit of frequency diversity. Cellular channels have a
`tendency to fade out. Typically, the entire available spectrum does not fade but, for example, 2
`megahertz of a 5-megahertz band may fade. Flash-OFDM quickly jumps the signal among the
`various tones within the 5 Mhz band. This converts the signal into a fast-moving, psuedo-random
`spread spectrum signal where only part of the signal fades but not all. With the part that gets
`through, users can still communicate.
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`Scalability
`Today, erecting a cellular phone tower in a town or on a piece of property in the middle of no where
`can be quite controversial. And as wireless technology becomes ubiquitous, more towers will be
`essential. "You can't put a 50 meter tower every ½ mile. Nobody would allow this and it would not
`be economical to do so," says Laroia. Flarion developed the RadioRouter network so that each
`basestation can be deployed in form of a short monopole or attached to the side of buildings or other
`already existing structures (See Diagram). "This is ideal for dense network deployments with high
`data capacity," says Laroia. "Operators only need to install and activate a RadioRouter within their
`existing network, without the need for frequency or timing synchronization between the
`basestations, as required by other technologies."
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`Flarion's equivalent to a cellular basestation is the RadioRouter, which combines some of the IP networking capabilities of
`regular routers with Flarion's flash-OFDM airlink. RadioRouter Networks can be deployed using RadioRouters with low
`power, omni-directional antennas in dense clusters (high area bandwidth) and/or as more widely-spaced RadioRouter
`towers with directional antennas and sectorized cells (wide area coverage).
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`Synchronization is not necessary, continues Laroia, because
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`Flarion technology uses OFDM as the air-interface and the enhancements made to it allow
`basestations to be independent of each other. "It is also one of the enabling factors that allows us to
`shift most of the networking intelligence from within the network (in traditional wireless systems)
`into the terminal of flash-OFDM based RadioRouter networks.
`Appropriate for wireless data
`Flarion's enhancements to the flash-OFDM network go beyond independent basestation operation.
`"We started with a clean slate and asked ourselves what was the best way to carry real-time,
`interactive data," says Laroia. This approach is important as data and voice communication
`requirements are not the same, he continues. Voice is a more of a continuous low bandwidth
`application (8 – 10 kBps) that tolerates occasional errors. Data on the other hand is oftentimes
`"bursty," but does not tolerate any errors, making retransmission over the airlink to correct errors a
`must for any efficient wireless data system.
`Not only was the focus on data important says Laroia, but economics were also at the heart of the
`design. "The popularity of transmitting data is intimately tied to its cost," he says. If people worry
`about how much a transmission costs whenever they turn their device on, they will never use it."
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`Flarion's RadioRouter network system reflects this mentality. Third generation design is supposed
`to maximize bits per hertz per second per basestation. "Our philosophy is to maximize bits per
`second per hertz per dollar spent on infrastructure," says Laroia. "We wanted to minimize the cost of
`the infrastructure to the service providers to enable them to reduce the cost to the end user and
`enable broadband wireless data market to take off."
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`The Flarion technology supports high data rates at low latencies (minimized packet and delay
`losses) over a distributed all-IP wireless network. Flarion's Dolan foresees end-users with an always-
`on wireless IP connection that will allow real-time interactive and multimedia applications in a
`mobile environment.
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`Flash-OFDM looks for a niche
`Presently, Flarion is in the throws of showing their technology to industry analysts. Ira Brodsky,
`president of Datacomm Research Company, says, "I don't know enough about them. Qualcomm
`[however] showed that a small company with a radically different solution can win. But it takes
`years of effort. Flarion must show that their technology offers significant competitive advantages.
`They must win over operators and manufacturers one by one. If they are going to succeed, they must
`either build bridges to their technology from CDMA or play in a different (and therefore smaller)
`space."
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`Flash-OFDM is not directly compatible with either CDMA or GSM/TDMA from the technical
`perspective, says Lars Johnsson, Director of Business Development for Flarion. "But for the wireless
`network operator who has investments in CDMA/TDMA and is operating voice networks, our flash-
`OFDM would allow him to enter the wireless data market with a very effective data network for
`mobile broadband."
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`Flash-OFDM ‘hops’ wireless data communications into the main stream
`This is like the airline industry, Johnsson continues. Initially people and cargo were transported on
`the same planes until air-cargo traffic exploded and required a dedicated system of cargo planes and
`routes that have different needs than people-planes. This analogy reflects the intersection of the
`wireless industry as it tries to address the emerging data market.
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`"As much as the industry seems to coalesce around two technology standards for third generation
`networks," says Dolan, "the industry is still looking for the ultimate solution with respect to high
`speed data." Technical trials during the fourth quarter of 2000 should help network operators
`determine if flash-OFDM could be that solution. Dolan expects Flarion's products to be on the
`market during the course of 2001.
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