Impacts of Evolving Wireless Communications
Theodore S. Rappaport
Polytechnic Institute of NYU
ABSTRACT
This paper reviews the key technological drivers for the future of wireless communications and what wireless will bring to cities of the future. Trends and challenges in licensed, unlicensed, and public safety technologies are discussed, as are applications and explorations at a new research center at NYU-Poly called NYU WIRELESS.
INTRODUCTION
Wireless communication services may be viewed in three ways. First is cellular, which uses licensed spectrum bands for which companies pay billions of dollars. Cellular spectrum is owned and controlled by federal governments and tightly regulated to ensure a lack of interference from unauthorized users; cellular carriers invest billions of dollars in infrastructure to make the service work in “protected” bands while collecting revenues from a large subscriber base. Second, there is the unlicensed spectrum, which is used for Wi-Fi and Bluetooth and provides short-range free access (e.g., in public places such as hotels and Starbucks). Third is public safety and government wireless communications, a big part of the telecommunication services used by cities for government activities and public safety (e.g., mass transit, fire departments, police). Although these public service organizations must use public safety radio frequencies, this kind of spectrum is in short supply and
often does not receive the benefit of the technology upgrades that occur in the cellular and Wi-Fi world (where markets are much bigger and prices much lower due to market scale).
CELLULAR SYSTEMS
There is a global push to rapidly deploy fourth-generation (4G) cellular systems, including long-term evolution (LTE) technology, which has been in development for about ten years. This technology exploits advances in wireless communications and provides a completely new over-the-air interface for new cellular infrastructure equipment (e.g., base stations and access points) as well as for Internet-ready phones that can handle the massive data transmission rates now available through the fixed telecommunication infrastructure.
The first 4G LTE products came out in the United States in 2010, and to bring these new capabilities to customers cellphone carriers like AT&T and Verizon are spending billions of dollars modernizing the cabinets, antennas, and equipment at hundreds of thousands of base stations around the country, while they simultaneously introduce to customers new 4G LTE smartphones made by numerous vendors.
LTE supports data rates of several tens of megabits per second (Mbps) to cellphone subscribers, and this will scale to over 100 Mbps with LTE Release 12. Older models of cellphones, such as the iPhone 3 and phones that are not “smart,” default to pre-LTE technologies, clogging up the cellular network and hampering the speed of 4G, which is built for data efficiency and not the old voice-centric networking.
The analog world is transitioning to the packet data world of the Internet, so carriers are trying to bring older phones off the network and replace them with newer packet-ready 4G phones that support more data-centric applications. Such advances are happening around the world, and the United States and Japan are leading Europe by a few years.
While 4G LTE cellular technologies promise unprecedented cell phone data rates, the expected data demands for consumers are increasing at a much greater rate than the development cycle of technological standards. As discussed further in this article, there is an enormous opportunity for the wireless industry to leapfrog existing capacity limitations by using much greater radio spectrum allocations than have previously been available. Global cellular systems of today operate in the 1 to 2 Gigahertz (GHz) bands (shown on the far left side of Figure 1 by the white bubble in the lower left)
FIGURE 1 Radio Spectrum and Oxygen Attenuation (Above Free-Space Propagation Path Loss) for 1 km Coverage Distance (Reprinted from Rappaport et al. 2013)
and the industry has, until recently, incorrectly believed that higher frequencies would not be viable for mobile communications because of both rain attenuation and atmospheric absorption. However, recent research has shown that there are great opportunities at microwave and millimeter wave frequencies, in the spectrum bands from 3 to 300 GHz, that will expand—by orders of magnitude—the amount of radio spectrum available for wireless communications services, thus expanding the data rates available to users. Figure 1 shows that the millimeter wave spectrum is viable for both outdoor mobile radio (where attenuation due to atmosphere is only about 1 decibel (dB) per km, as shown by the two bubbles at 80–100 and 200–220 GHz), and very short distance local area or personal area networks (with attenuation over 20 dB per km, as shown in the four bubbles along the top of the figure).
UNLICENSED (WI-FI) SPECTRUM
Some very exciting things are happening in Wi-Fi. A relatively recent technology standard for wireless local area network (WLAN), called IEEE
802.11n, allows manufacturers to build multiple-input multiple-output (MIMO) antenna systems (Rappaport et al. 2011; Khan and Pi 2011). The IEEE 802.11n standard is raising the data rates of Wi-Fi connections from 54 Mbps to 500 Mbps. To put this data rate in perspective, a super high resolution movie (say from Netflix) takes about ten gigabytes of data to download (although it could be as small as a few hundred megabytes of data on a smaller, low-resolution screen). Downloading a movie can take several tens or even hundreds of minutes on a very slow Internet connection, or a minute or so on a faster connection, but with Wi-Fi for data rates of 500 Mbps, movies and other huge data files can be downloaded in seconds.
Today there are even more breakthrough technologies that combine MIMO and much higher frequency bands. Technology standards known as IEEE 802.11ac and IEEE 802.11ad, and new industrial consortia and standards called Wi-Gig and wireless HD, are bringing data rates to many gigabits per second (Gbps). These technologies have been developed to operate at an order of magnitude higher frequencies than today’s cellular and Wi-Fi networks–about ten times higher than today’s 2.4 and 5.2 GHz Wi-Fi networks.
The new spectrum where Wi-Fi is taking hold is at 60 GHz, where radio wavelengths are about the size of a human fingernail and antennas can be tiny, allowing the use of phased arrays and very directional, steerable antennas. Consider the fact that global cellular and Wi-Fi systems now operate at frequency bands of about 1 to 5 GHz, around the frequency range of a microwave oven. Wi-Gig and wireless high definition (HD) operate at a carrier frequency about ten times higher, with a 60 GHz carrier frequency, the millimeter wave frequency band. The commensurate bandwidth that can be carried over a “narrowband” signal increases by a factor of ten as well, meaning that amazing amounts of raw data can be carried by wireless devices as the carrier frequency is increased. Figure 2 illustrates the vast amount of spectrum that carriers and manufacturers are beginning to consider for both unlicensed Wi-Fi and cellular (Khan and Pi 2011; Rappaport 2012). A UC Berkeley spinoff company, SiBeam, helped pioneer 60 GHz broadband wireless devices and was sold in 2011 to Silicon Image, a publicly traded company that makes chips, including wireless HD.
The first applications of this 60 GHz multi-Gbps data connectivity are for gamers, so that they can have mobility with their keyboard in the living room connected to the monitor, and for in-home entertainment buffs who wish to mount flat screen displays without visible connections from the set-top box to the display screen.
FIGURE 2 Wireless carriers are beginning to realize that semiconductor capabilities can unleash amazing new capabilities at frequencies much higher than current cellular or Wi-Fi bands. Reprinted with permission from Khan and Pi (2011).
Wireless HD is already replacing HDMI cables, and there are other applications, but soon it is going to be available for all Wi-Fi, so everyone will be able to have data rates as great as the fastest wired connection today, deployed wirelessly at very low cost. That is the reality of where wireless is going, in the home and in institutions, government, and industry.
PUBLIC SAFETY RADIO FREQUENCIES
The FCC and the federal government have agreed for the first time to allow a radio spectrum band to be used for all public safety services, enabling first responders to communicate without interference from others in emergency situations.
But there is a huge business problem. No one is sure how the infrastructure is going to be financed and who will pay for the “rebanding” needed to move incumbents off the spectrum. Are states, cities, taxpayers, or the federal government going to pay for the new gear needed to bring together all the systems of various public safety offices? There is debate both in Congress and at the state level, and it will probably take a couple of years to figure out how or whether this type of “unified” public safety network is viable.
For now, the spectrum is allocated and the plan is that fire, police, and other first responders will use a variant of the 4G cellular standard and move some or all of their radio equipment and operations to a new standard with the new public safety spectrum. This is a problem for cities like New York, where some first responders, such as the fire department, know that for many in-building emergency applications, analog FM radio works best—the older
FM technology ensures radio coverage through the large granite walls of skyscrapers.
First responders must have radio service that is very reliable, so there is some concern in cities about a federal mandate for shared spectrum while forcing new digital technology. Any modernization of communication technology for public safety must work flawlessly. Lives are at risk and uninterrupted communication must be guaranteed. This is just a simple, single example of some of the problems for public safety that are on the horizon.
NYU WIRELESS AND FURTHER APPLICATIONS
NYU-Poly has played a role in creating the knowledge and human capital needed to engineer the exciting future of wireless, and continues to play a role in this future. At NYU WIRELESS amazing things are being explored, including applications of wireless to medicine and computing. In summer 2012, students made measurements of radio propagation of future millimeter wave cellular coverage throughout Manhattan and Brooklyn for the first time. In 2011 we conducted similar measurements in Austin, Texas (Rappaport et al. 2011).
The idea is to use the higher millimeter wave frequencies for cellular networks. It should be noted that very few in the industry have been thinking about this. Cellular systems of the future will become truly ultrawideband as the millimeter wave spectrum is considered for future wireless access. The myth in the industry is that if you go up higher in frequency, radio signals will not bounce off building walls or you will not be able to make electrically steerable antennas that can exploit the propagation characteristics at low enough cost. But at NYU WIRELESS we have shown through our measured propagation data that cellular can function effectively at these higher millimeter wave frequencies (close to the spectrum bands used by WiGig and wireless HD). This means that as the technology and engineering expertise becomes mature in the Wi-Fi unlicensed world, it is going to gravitate toward creating new technologies for the cellular world, and in five to ten years cell phones will have a multi-Gbps data rate.
New York subways do not have wireless infrastructure, so it is not possible to place or receive a call in the subway. But with propagation modeling and relatively simple software, we are now able to predict where radio coverage will be and where to put a priority for the location of a base station, and any relay, to provide the coverage needed in urban environments.
There is a peace dividend from the big data movement, the semiconductor movement, the geographic information systems (GIS) movement, and it is coming to the wireless community. With it, wireless will enable us to deploy computing and communication networks much more reliably and much more power efficiently than today.
Finally, on the topic of interoperability, especially for public safety users and future Wi-Fi and cellular users, there is an exciting field called cognitive radio, which calls for smart signal processing and being able to make radios work adaptively. Future phones and other devices will be complex and must “think” for themselves. Clearinghouse databases will allow the radio spectrum to be monitored and reported to and between different smartphones and wireless carriers, allowing dynamic spectrum access (e.g., open spectrum usage). Smartphones will actually be able to break up and handle information with the priority needed and will be much better able to handle multiple users. The cost benefit of wireless devices and the improved ability to understand and predict their coverage and their performance, together with new antenna technologies, will result in much better wireless networks when combined with the semiconductor improvements that are coming from the chip industry.
These advances will enable much higher frequencies with the much greater commensurate bandwidths and lower power points. There will be unprecedented abilities for wireless to replace things such as, for example, a laptop hard drive with a wireless radio frequency identification (RFID) card; at any computer the card could make a wireless connection at a multi-Gbps data rate. The RFID card would actually be the personal hard drive and could be carried in a wallet or pocket, thereby reducing the weight of the laptop.
CLOSING REMARKS
This is the future that wireless will bring. Wireless not only will be useful for saving cost, weight, and power while enabling flexibility in all we do, it also will empower completely new sensing and monitoring capabilities. There are so many applications, the future of wireless in cities is quite remarkable. And the “laboratory” of New York City is a rich and wonderful location to experiment and test the capabilities and possibilities of this exciting future. New York City is where cellular telephony was first tested and launched, with the first base station on the Empire State building, and now there is a chance to bring wireless to its renaissance, with the fifth generation of cellular, also in New York.
REFERENCES
Khan F, Pi J. 2011. Millimeter-wave mobile broadband: Unleashing 3-300 GHz spectrum. IEEE Wireless Communications and Networking Conference (WCNC), Quintana-Roo, Mexico.
Rappaport TS. 2012. Wireless communications in the massively broadband® era. Microwave Journal, Op-ed piece. Available online at www.microwavejournal.com/articles/18753-wireless-communications-in-the-massively-broadband-era. Also see www.nyuwireless.com. [“Massively broadband” is a registered trademark of Prof. T.S. Rappaport.]
Rappaport TS, Murdock JN, Gutierrez F. 2011. State of the art in 60-GHz integrated circuits and systems for wireless communications. Proceedings of the IEEE 99(8):1390–1436.
Rappaport TS, Sun S, Mayzus R, Zhao H, Azar Y, Wang K, Wong GN, Schulz JK, Samimi M, Gutierrez F. 2013. Millimeter wave mobile communications for 5G cellular: It will work! IEEE ACCESS 1:335–349.
