As the volume of wireless communications grows, two challenges are emerging. First, how will we manage all of this traffic? Second, where will we find the engineers who will solve these next-generation problems? Professor Theodore (Ted) S. Rappaport, an experienced researcher in wireless communications and microwave and millimeter-wave applications, wrestles with these issues every day.
Dr. Rappaport is the David Lee/Ernst Weber Professor of Electrical Engineering at the Polytechnic Institute of New York University (NYU-Poly) as well as a professor of computer science at New York University. He also is the founding director of NYU Wireless, the world’s first academic research center to combine engineering, computer science, and medicine.
LF: Tell us something about NYU Wireless and your new assignment there.
TR: NYU Wireless is a new interdisciplinary research center working across electrical engineering, computer science, and medicine. While still in our first year, we have about 100 students and 25 faculty including medical doctors, Wireless engineers, and computer scientists working together on fascinating research problems. This is all part of NYU’s acquisition and integration of Brooklyn Poly’s venerable engineering college (now called NYU-Poly) into the overall NYU campus structure. This is an exciting time to be an engineer at NYU. We have not had engineering since the early ’70s, and now with the acquisition of NYU-Poly for engineering, we are able to produce young engineers with fundamentals across several disciplines at a world-class university.
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LF: What are some of the projects you are working on there?
TR: You can see some of the many projects at nyuWireless.com. We are looking at wireless applications in the operating room, the use of organic sensors for implants and wireless connectivity, the use of RF to provide ultra-precise surgical procedures for cardiologists, new DSP-based compressed sensing algorithms for MRI imaging, and the use of MRI for improved cell-phone emission testing, to name a few. We are also using the New York City campuses to conduct the world’s first channel measurements for futuristic fifth-generation wireless systems that will use the millimeter-wave spectrum, where bandwidth is so much more plentiful than today.
LF: Previously you did some work with millimeter waves at the University of Texas. Are millimeter waves your main focus at NYU? If not, what is?
TR: Our work on millimeter-wave wireless is a research focus, but is only a small part of the breadth of work NYU Wireless is doing. Our industrial affiliate sponsors, which include Samsung, National Instruments, and Interdigital Communications, are pooling resources and gain access to all of our work, including our millimeter-wave research. Intel and Nokia Siemens are also funding the millimeter-wave research segment, as we help drive product concepts, basic knowledge, and new system and circuit designs in this area.
LF: What factors have made millimeter waves more practical today than previously?
TR: Moore’s law has enabled low-cost CMOS circuitry that can work at millimeter-wave bands. The creation of high-gain miniaturized steerable on-chip and on-package antennas also enable millimeter-wave wireless.
LF: Are millimeter waves suitable for the small-cell movement to be rolled out in the coming years?
TR: Absolutely! Our early work in the propagation environments of New York City and Austin, Texas, clearly show that 200-m cell radius is possible for commercially viable systems in the future. We are now looking at MAC (media access controller) and PHY (physical layer) designs that could incorporate spatial processing for future fifth-generation (5G) cellular. The massive amounts of readily available spectrum available at the millimeter-wave bands, combined with highly directional and steerable antenna technology, and repeaters and access points that use the millimeter-wave spectrum simultaneously for backhaul, interconnectivity, and mobile connectivity will bring orders of magnitude more bandwidth to the mobile handset.
LF: What are the potential operating frequencies of such millimeter-wave small cells?
TR: The 28-, 38-, 60-, and 72-GHz bands offer great potential for future 5G cellular systems. At these frequencies, and over distances of a couple of hundred meters, neither rain nor atmospheric absorption pose major problems, and the adaptive antenna technologies will enable flexible, reconfigurable networks for both backhaul and mobiles.
LF: What are some of the key features of millimeter-wave small cells that make them practical?
TR: The ability to implement “cooperative communications,” where lightweight basestation and access points and repeaters/relays are interconnected and able to handle traffic demands, while using spatial processing to find the best radio paths in any environment.
LF: Do you see any practical applications for the spectrum beyond 100 GHz? If so, what?
TR: In 15 to 20 years, I foresee mobile communication systems operating in the 220-GHz band, where 30- to 50-Gbit/s data rates will be possible. That frequency band is well suited for outdoor mobile communications. At 380 GHz, where the attenuation of air is tremendous, and antenna gains so high in an ultra-small form factor, I foresee “whisper radios” that limit coverage to within a meter or so, and these frequencies will bring about fundamental changes in form factors by replacing wiring in everything we use, while transforming how we interact, personally, with electronics.
LF: What have been the greatest challenges in working with millimeter waves?
TR: Finding sufficient RF power is difficult, but will be improved over time. Creating very high-gain multi-element steerable directional antennas for real-world use is tricky, but, again, as experience and markets evolve, this will be perfected. Handling the massive data rates of several gigabits/s at baseband is challenging to do in a lower-power manner, and finding engineers who are well versed in microwave circuit design and broadband wireless will be a challenge for the industry. From the carrier perspective, provisioning backhaul that can handle the massive bandwidths of future 5G systems will be difficult, as it will involve both fiber to the pole as well as distributed wireless “mesh-like” backhaul networks to facilitate cooperation and distribution of the fiber port throughout an urban area (see the figure). Getting into and out of buildings will also be difficult, as our work shows that buildings cause much more attenuation than at today’s cellular frequencies.
The white circle shows the air attenuation for the frequencies where all of wireless has operated in the history of the world, and the green and blue circles represent key future wireless frequencies, with orders of magnitude greater bandwidths, where future wireless networks will operate. (source: T.S. Rappaport, J. Murdock, F. Gutierrez, “ State of the art in 60 GHz Integrated Circuits and Systems for Wireless Communications, Proceedings of the IEEE, August 2011, Vo.99, No 8, pp. 1390-1436)
LF: What are your thoughts on the white space movement as a spectrum solution?
TR: This a wonderful development, as it reflects the evolution of wireless into an era of “cooperation,” where spectrum and user devices are managed much more efficiently than today. Having a database or clearinghouse that can interact with individual users or carriers across specific geographic regions enables better quality and use of spectrum and allows the use of link quality readings to vastly improve the experience of an individual user as well as the overall performance of a group of users. With the advent of smart phones, powerful applications and “behind the scenes” monitoring now can allow a clearinghouse to receive in-the-field readings of spectrum usage and link quality, thereby allowing the carriers or the mobile terminals to make much smarter decisions that will improve mobile wireless coverage as mobiles move about. This is the beginning of a new era in wireless that will become much more important over time.
LF: What do you see as the “next big thing” in wireless?
TR: You have mentioned two of them: millimeter-wave cellular and white spaces. I like to think of white spaces as a sub-part of the new field of “cooperative communications,” where the massive processing capabilities of the phone, new repeaters/relays, and the network are used together to improve coverage and capacity for mobile users. Today, the low microwave bands are where cellular systems are built, and the spectrum there is limited. In the coming years, millimeter-wave is where new cellular systems, with hundreds or thousands times more speed, will operate. At those new bands, the data rates will be so great between the femtocells and access points that the complexity of the large World Wide Web servers of today will be brought out to the edge of the network, in small geographic regions, where advertising, content, and site-specific content will be offered to consumers. Future mobile systems will be multi-banded, and making compact multiband tunable and steerable antennas will be vital to this exciting future of millimeter-wave wireless.
LF: Why do you think more students don’t choose engineering as a major? How can the industry attract more engineering students?
TR: This is a critical question that must be addressed by a private-public solution. Major U.S. companies must actively demonstrate sponsorship and interest in U.S. engineering education by being more visible and financially supportive at the middle/high school level as well as at college campuses across the U.S. Would-be engineers (and their parents) need to see that large U.S. companies care about U.S. students in engineering through the grade school and high school level and need to know there are jobs for them. Imagine the family dinner table in 2002, during the dot-com bubble, when as many as 1 million telecom engineers lost their jobs virtually overnight. That is a real turnoff for pursuing engineering, and the recent recession hasn’t helped.
LF: How can the large companies help?
TR: Large U.S. high-tech firms need to play a leading role in cultivating interest in engineering at every level of a young child’s education. (Some companies like National Instruments do their lion’s share, but much bigger companies are surprisingly absent.) Samsung is an incredibly strong supporter of the Korean education system, and there are other international examples that put America to shame.
LF: Should the government be involved?
TR: We need leadership at the highest levels of the U.S. government to provide engineering initiatives as big as the interstate highway system or the man-to-the-moon program. STEM (science, technology, engineering, and math) initiatives must be a national priority, and industry and university must come together the way it did in the mid 1980s when the National Science Foundation launched the engineering research centers (ERCs), or when Sematech was founded. These were large multidisciplinary research centers aimed at leapfrogging imported technologies, and they galvanized engineering across America while attracting young people to the field. No such initiatives are readily found today for engineering, yet are sorely needed in the U.S. Young people in other countries are bypassing the U.S. when it comes to math, engineering, and science skills, because other national governments are picking winners. U.S. lawmakers must reinvest in STEM education, and U.S. companies must get more involved to help make education and engineering a “winner” in America as the ability for the U.S. to innovate and maintain its relative quality of life is at stake. I remain a professor in hopes of making a small difference in addressing this important issue.
Theodore (Ted) S. Rappaport is the David Lee/Ernst Weber Professor of Electrical Engineering at the Polytechnic Institute of New York University (NYU-Poly); a professor of computer science at New York University’s Courant Institute of Mathematical Sciences; and a professor of radiology at the NYU School of Medicine. He also serves as director of the National Science Foundation (NSF) Industrial/University Collaborative Research Center for Wireless Internet Communications and Advanced Technology (WICAT), a national research center that involves five major universities and is headquartered at NYU-Poly. He is the founding director of NYU Wireless, the world’s first academic research center to combine engineering, computer science, and medicine. Earlier, he founded two of the world’s largest academic wireless research centers: the Wireless Networking and Communications Group (WNCG) at the University of Texas at Austin in 2002 and the Mobile and Portable Radio Research Group (MPRG), now known as Wireless@ Virginia Tech, in 1990. He also founded two companies, both sold to publicly traded firms, that created pioneering products for the wireless industry. He holds BS, MS, and PhD degrees in electrical engineering from Purdue University, and is a Distinguished Engineering Alumnus from his alma mater.