Nikkei Electronics Asia -- February 2007
Tech Feature
6Gbps Achieved over Wireless Point-to-Point Connection

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Jan 26, 2007 16:24 Nikkei Electronics Asia
As demand for ever-faster untethered communication grows, Australia's CSIRO Information & Communications Technology (ICT) Center's Wireless Technologies Laboratory has been working on developing what is claimed to be the world's fastest all-electronic wireless link. For this, CSIRO - the Commonwealth Scientific & Industrial Research Organization - is utilizing the millimeter-wave spectrum above 55GHz, which makes data speeds of 10Gbps or more possible.

Radio spectrum is a finite natural resource under increasing demand. CSIRO is using the emerging millimeter-wave spectrum, above 55GHz, because it has not yet become congested in most countries, and it creates the opportunity for a 100x improvement in data rates compared with microwave systems such as wireless LANs (see Fig).

The CSIRO ICT Center recently demonstrated that it has attained a speed of over 6Gbps over a point-to-point wireless connection - with what is claimed to be the highest efficiency (2.4bps/Hz) ever achieved for such a system.

According to Dr Jay Guo, director of the Wireless Technologies Lab, multi-gigabit links operate at speeds that leave current wireless networks far behind. "For example the entire works of Shakespeare can be transmitted over our 6-Gbit link in under seven thousandths of a second, or a full DVD movie in just over 6 seconds."

A test bed has been installed at CSIRO to help with propagation modelling above 55GHz. The test bed is 250m long, 10m above the ground and 95m above sea level. It includes a commercial 60GHz link and the CSIRO-developed 83.5GHz Gbit link. Propagation data (at 60GHz and 83.5GHz) is continuously recorded. The CSIRO team has transmitted 16 simultaneous streams of DVD quality video over its 250-meter link with no loss of quality or delays, utilizing just one quarter of the capacity of the link.

"This breakthrough is just a first stage towards direct connections of up to 12Gbps," said Guo. Gbit wireless networks can be used to complement high-speed fiber connections, in infrastructure for mobile services, and for ad-hoc communications services. "The system is suitable for situations where a high-speed link is needed but it is too expensive or logistically difficult to lay fiber, such as in congested urban environments, and across valleys and rivers."

Increased Viability
Multi-gigabit data-rate millimeter-wave networks are becoming viable due to the spectrum allocation and cost reduction in semiconductor devices. The 60GHz band has been allocated in many countries as free spectrum. Owing to the higher propagation loss by oxygen absorption, 60GHz systems are more suited for indoor and short-range (<20m) applications.

The recently allocated 71-76GHz and 81-86GHz bands provide opportunity for links with longer range and higher data rates, ideally suited for fiber replacement and backhaul of mobile communications networks. Current commercial products deliver data rates up to 1.25Gbps, and new products up to 10Gbps have been promised for the future.

Researchers at the ICT Center have developed an all-electronic 6Gbps millimeter-wave point-to-point link in the 85GHz band using 8 PSK (phase shift keying) modulation and achieving 2.4bps/Hz spectral efficiency - said to be the highest spectral efficiency to date for a millimeter-wave system. The system can be easily upgraded to achieve 12Gbps, or more if the full 5GHz bandwidth of allocated commercial bands, 71-76GHz or 81-86GHz, is used.

The core technologies in the CSIRO multi-gigabit system include innovative architecture, millimeter-microwave integrated circuits (MMIC) for radio transceivers, novel modulation schemes and digital signal processing algorithms.

The biggest challenges facing development of future Gbit wireless networks are: finding ways of reducing the cost and size of the integrated radio modules; and increasing the speed of digital signal processing while reducing the size of the digital modules. And to tackle these challenges, CSIRO has brought together researchers from a diverse range of backgrounds - in millimeter-wave techniques, antennas, digital signal processing.

by Neil Munro