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What will drive 5G to the next level?

Posted: 23 Jul 2015 ?? ?Print Version ?Bookmark and Share

Keywords:5G? millimeter wave? mmW? Wi-Fi?

As carriers and researchers push for 5G cellular during the past year, there has been a significant increase of interest in millimetre waves from 30GHz to 300GHz. According to the head of NYU Wireless, more work in engineering is still needed in spite of the technical progress achieved so far.

NYU Polytechnic's wireless research centre has spent the past several years creating mmW channel models and testing propagation in New York City. Nevertheless, detailed system designs and improved architectures must be developed before mmW products can enter the market in a real way around 2020.

"I think we're beyond the stage where we realise the system is feasible, but we need to characterise it better," said Sundeep Ragan, associate professor of electrical and computer engineering and the acting head of NYU Wireless. "A lot of our partners have systems, but they have much larger budgets. We want to create first prototyping system in a university environment so universities can do more research," he said.

NYU Wireless' prototyping network consists of two National Instruments boxes with FPGAs and base band processing that up-converts a Wi-Fi signal to mmW for transmission, then down converts at the receiver end. Base band processing for high frequencies presents the greatest challenge because existing processors must be fine-tuned for the unique and fickle characteristics of higher frequencies, PhD student Aditya Dhananjay said.

Ragan said his team is primarily concerned with managing power in mmW systems, which could be achieved by making amplifiers more efficient or creating improved power circuitry. Because cellular systems of the future will likely rely on an "always available" network rather than one that is "always on," NYU Wireless is focused on control plane latency and synchronisation functions as a factor in power management. Millimetre waves present additional challenges because communications are "very high power and bursty."

"[Millimetre waves] are challenging because transmissions are very directional and mobiles and base stations have to find each other, so we must quickly refine links," Ragan said, adding that doing local processing could help. "This would still be using multiple antennas but with a fully digital architecture to speed up these transitions."

Future systems with multiple antennas are extremely expensive but likely won't require new silicon for frequencies under 80GHz. (NYU Wireless is primarily studying 28GHz, 38GHz and 73GHz frequencies). High dimensional CMOS antenna arrays have good power consumption and are inexpensive because they are widely used, Ragan noted. Researchers are considering looking at use of indium phosphide for frequencies above 80GHz as that material would be more efficient at higher frequencies.

Meanwhile, Shaloo Rakheja, an NYU associate professor of electrical and computer engineering with a focus on materials science, is modelling new materials for sub-THz and THz communication. 2D materials such as graphene, which are good thermal conductors and tunable, could be good for unidirectional antennas in a large variety of frequencies.

"A lot of new 2D materials have been coming up lately," Rakheja said, citing MoS2 and black phosphorus. "It's really easy to make and compatible with silicon processes, so you don't have to create new fabrication methods."

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