Challenge to 3G modulation schemes - Brief Article - Product Announcement

Electronics Times, July 24, 2000

Two US-based technology start-ups are set to challenge the status quo in high-speed datacoms.

Formed out of research at Bell Labs, Florian Technologies aims to commercialise a technology that Rajiv Laroia, chief technology officer, claims is much better at handling data than 3G and has a lower processing overhead.

At the same time, EDA company and electromagnetic simulation specialist Ansoft is spinning out a company to exploit a new modulation scheme that can piggyback on other transmission techniques, multiplying the amount of data they can handle.

New Jersey-based Florian has developed a technique that it calls flash- OFDM. Based on the orthogonal frequency domain multiplexing (OFDM) system used in digital terrestrial TV, Florian's `flash' version overlays an approach akin to spread-spectrum to improve the resistance of the signalling technique to interference and fading conditions.

In normal OFDM, data is sent over a set of parallel narrow-band channels. A large number are used to provide high bandwidths for applications such as digital TV.

Flash-OFDM goes one step further by using a hopping code to work out which channel it should use to send each bit of data.

To support high bandwidths, entire data segments are split up and, using different hopping codes arranged to ensure that bits do not clash, then sent in parallel. If the system encounters interference, the system can alter the hopping codes to avoid problem channels.

Laroia says the computational complexity overhead of supporting flash- OFDM was comparatively low. It is relatively simple to implement logic that splits and encodes the data. Most of the work lay in setting up a channel to select the necessary codes.

"It's not as complex as 3G," said Laroia.

Florian has embedded support for acknowledging data packets with comparatively low overheads. Laroia claims that this makes it possible to build a wireless data network with much lower latencies than 3G.

"3G was designed for voice, where you can tolerate errors," he said. "With data transmission, you need a reliable channel and wireless is fundamentally unreliable. So you need a way of checking that data has arrived quickly.

"With existing systems, the overhead of acknowledging data segments is so high that you only do it for every 15 or 20 segments. That means it takes longer to determine whether a segment has been dropped."

Laroia says the flash-OFDM system is able to respond to missing data quickly by checking each data segment and requesting a retransmission immediately, if necessary. Florian's system will handle voice traffic using standard voice-over-IP protocols.

Ansoft's spin-out Altra Broadband is based on electromagnetic simulation work by Dr Lawrence Williams and P Premkumar, who will head up the new company. Altra will develop components and subsystems that exploit a new modulation technology, known as spin-polarised wave division.

Premkumar, who takes on the role of president at Altra, says that its scheme is aimed at communications companies working in wired and wireless techniques.

"Our technology helps them multiply the quantity of data on each channel by exploiting several spin states in each wavelength or frequency," he said.

"During the next five years, the combined effect will lead to an explosion of bandwidth and speed in digital communications networks."

Altra expects its technology to piggyback on existing transmission techniques, such as wavelength-division multiplexing in fibre optics and frequency-division multiplexing in wireless.

By modulating the different spin states of photons, the company reckons it has found a way to multiply the amount of data that can be encoded on each discrete frequency.