Microwave Engineering Europe - January/February 2009 - (Page 25)

WiFi RAN 25 a subscriber makes a call. But with UMA and Wi-Fi, the mobile network can now determine if a subscriber is on the highperformance, low-cost IP network or the traditional cellular network. With this information, it is possible for applications on the handset to behave differently. For example, a streaming video service might upgrade the frame rate and audio quality to take advantage of the bandwidth available on the ﬁxed network. Or an internet radio station might convert to high-deﬁnition streaming when on Wi-Fi. It is also possible for the network to realize the subscriber is in a speciﬁc location, such as his home or ofﬁce. This presents an opportunity to augment traditional mobile services with ‘location awareness.’ For example, a mobile phone could generate an SMS when a person enters or leaves a facility, automatically updating a loved one or a social networking site. Building on these concepts, it is possible for a dual-mode phone to have applications that only run when the device is on a Wi-Fi connection. The phone could automatically synchronize with a media play or upload photos when on the low-cost Wi-Fi network. With Wi-Fi, a UMA-enabled phone quickly becomes part of the connected home. Conclusion Wi-Fi is set to play a critical role for mobile operators in the future. Increasing mobile usage is pushing operators to invest in technologies to ofﬂoad the macro network. The proliferation of Wi-Fi access points in the home and ofﬁce, where subscribers spend most of their time, makes the broadband access network an attractive option for service delivery. Yet Wi-Fi alone isn’t enough. Beyond the protocol optimizations, it’s UMA/ GAN technology that makes Wi-Fi a RAN technology, extending the mobile network over IP. It’s clear that Wi-Fi is poised to become the highest-performance, lowestcost, indoor RAN technology on the market. www.mwee.com/212500578 (Reprinted courtesy of Mobile Handset DesignLine) Researchers claim breakthrough in semiconducting nanotubes A Duke University-led team of chemists has modiﬁed a method for growing long, straight, numerous and well-aligned carbon cylinders only a few atoms thick that paves the way for manufacturing reliable electronic nanocircuits. The team had already described a method last April for growing the crystals, but the modiﬁcation is targeted at making a process speciﬁcally for producing semiconducting versions of the single-walled carbon nanotubes, sometimes called “buckytubes” because their ends, when closed, take the form of soccer ball-shaped carbon-60 molecules known as buckminsterfullerines, or “buckyballs”. The effort is being led by Jie Liu, Duke’s Jerry G. and Patricia Crawford Hubbard Professor of Chemistry. “I think it’s the holy grail for the ﬁeld,” Liu said. “Every piece is now there, including the control of location, orientation and electronic properties all together. We are positioned to make large numbers of electronic devices such as high-current FETs and sensors.” A report on their achievement, co-authored by Liu and a team of collaborators from his Duke laboratory and Peking University in China, has just been published in the research journal Nano Letters. The work was funded by the United States Naval Research Laboratory, the National Science Foundation of China, carbon nanotube manufacturer Unidym Inc., Duke University and the Ministry of Science and Technology of the People’s Republic of China. Liu has ﬁled for a patent on the method. A post doctoral researcher in his laboratory, Lei Ding, was ﬁrst author of the new report as well as the previous study published April 16, 2008, in the Journal of the American Chemical Society (JACS). That earlier JACS report described how the researchers coaxed nanotubes to form in long, parallel paths that will not cross each other to impede potential electronic performance. Their method grows the nanotubes on a template made of a continuous and unbroken kind of single quartz crystal used in electronic applications. Copper is also used as a growth promoter. But that method left one unresolved issue blocking the use of such nanotubes as electronic components. Only some of the resulting nanotubes acted electronically as semiconductors. Others were the electronic equivalent of metals. To work in transistors, the nanotubes must all be semiconducting, Liu said. The researchers now say they have achieved virtually all-semiconductor growth conditions by making one modiﬁcation. In their earlier work they had used the alcohol ethanol in the feeder gas to provide carbon atoms as building blocks for the growing nanotubes. In the new work, they describe how they tried various ratios of two alcohols — ethanol and methanol — combined with two other gases they also used previously — argon and hydrogen. “We found that by using the right combination of the two alcohols with the argon and hydrogen we could grow exclusively semiconducting nanotubes,” Liu said. “It was like operating a tuning knob.” The inert argon gas was used to provide a steady feed of the ethanol and methanol, with hydrogen to keep the copper catalyst from oxidizing. After making the nanotubes by chemical vapor deposition in a small furnace set to a temperature of 900 °C, the researchers assembled some of them into ﬁeld-effect transistors to test their electronic properties. “We have estimated from these measurements that the samples consisted of 95 to 98 percent semiconducting nanotubes,” the researchers reported. The introduction of methanol to complement ethanol is also said to have shrunk the diameters of the resulting nanotubes and improved their atomic alignments with the underlying quartz crystal. The group’s next challenge is to understand at an atomic level how “just so” tuning of growth gas mixtures resulted in the right chirality to produce exclusively semiconducting nanotubes. www.mwee.com/212903476 ● Microwave Engineering Europe ● January/February 2009 www.mwee.com http://www.mwee.com/212500578 http://www.mwee.com/212903476 http://www.mwee.com

Table of Contents Feed for the Digital Edition of Microwave Engineering Europe - January/February 2009

Microwave Engineering Europe - January 2009 News Contents Comment Using KPIs to Ensure Quality in a Converging Network Amplifier Error Vector Magnitude Characterisation Using High-Speed Modular PXI Instruments GPS: Making a Play for Femtocells Accelerating Global WiMAX Adoption: The Move to Picocell and Femtocell Base Stations Addressing PA Efficiency for Multi-Mode Wideband Handset Applications Wi-Fi: Mobile Feature or Fundamental RAN? Products Calendar

Microwave Engineering Europe - January/February 2009

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