Remember the last time you were on an airplane without WiFi connectivity? Your smartphone all of a sudden seemed a lot less interesting. Most of your applications depend on connectivity, in some cases strong connectivity, in order to download new content such as text, images, sounds, videos, and more. You might play a game or two, but even games that run entirely on your smartphone may require Internet connectivity for downloading ad content, which means paying for that “free” game you downloaded. So you decide to get some work done, until you realize most of your files are stored on the cloud and so you’re stuck with a fancy phone or tablet that can’t do much except play content that you already have on your device. It’s then that you realize how important the network connectivity is to your smart device. The screen, the CPU/GPU, the AI all come together with a strong network connection. Ever try surfing to a modern website with 2G connectivity? Remember those days of 2G phones?

Today our phones and tablets have half a dozen radios, including WiFi/Bluetooth transceivers, GPS receivers, and most importantly 4G LTE transceivers. While WiFi requires an access point, and can be finicky if too many people are logged on (like at an airport – don’t worry 802.11ax aka WiFi 6 will solve this problem), your LTE connection seems to work just about anywhere these days, even while you’re traveling abroad, and these modern 4G radios are just about as fast, or in some cases faster, than your WiFi signal. Isn’t that amazing that a modern basestation can give seamless connectivity to thousands of people with lightning speed and relatively low latency? We all know there’s room for improvement (dropped calls, unresponsive dead zones, etc), but the modern smartphone is a “miracle” only with the network, which is behind the scenes and usually ignored by most people.

We’re living in the 4G era, almost the 4th decade of wireless mobile communication, and we’re about to enter a new era of 5G. These G’s or generations of wireless communication are defined by an international standards organization body (3GPP) to ensure interoperability of equipment and a vision and target for the growth and deployment of wireless networks. Standard bodies such as the IEEE have defined the 802.11 family of radios that we know very well because we buy and install the equipment. On the other hand, the network we use for our phones and tablets is like magic because we simply subscribe with a carrier that maintains and runs the network, and it just works.

Unless you’ve been hiding out in a cave in the mountains without any connectivity, you’ve heard the buzz and hype about 5G. 5G is supposed to solve every problem out there and to make our phones and tablets (and cars and computers, too) even more magical. People talk about 10X or 100X faster connections, more bandwidth and spectral efficiency, millisecond latency, enabling new applications like autonomous driving, AR/VR games, and even control over wireless. What’s real and what’s hype?

What’s truly exciting about 5G is that while it might have a lot of inspiration from science fiction, the technology is actually sound and based on real engineering and science. To understand how this is possible, consider one of the most exciting aspects of 5G, application of the mm-wave spectrum for communication. All of our wireless communication is “sub-6GHz” today, including WiFi and LTE, and even though there’s new spectrum to open up in these lower microwave ranges, there’s an ocean of new spectrum available above 20 GHz, in bands around 24 GHz, 28 GHz, 39 GHz, and 60-90 GHz. Moving to higher frequencies is not a simple matter of opening up new bands, which is in itself very exciting, but it also opens up a new way of communicating using spatial multiplexing. In a nutshell, this means that you can send beams of mm-wave radiation to a handset, rather than spreading the energy out like a ripple in a 3D pond. Think about the fact that most communication is actually point-to-point. A basestation sends you data and it’s intended only for you, so why send the information everywhere else where it just acts like interference? That’s because at lower frequencies it takes a huge dish, or a very large array of transceivers that occupy the size of a wall, to direct information into a beam. As radio transceivers become cheaper and lower power, we will see “massive MIMO” systems deployed in the sub-6 GHz bands, which is very exciting. But in the mm-wave bands we can build massive arrays in a much smaller area using simple phased arrays. At 60 GHz the same array antenna count can be had with one hundredth the area, so think credit card sized versus room sized.

Mm-wave communication can also be used for the backhaul to avoid running fiber to basestations, which help the densification problem. Using mm-wave communication equipment requires more basestations than today’s systems, about a factor of 10 more basestations, but if we do it correctly, we can make these new basestations smaller, less obtrusive, and even solar powered. The key is to make low power circuitry, making it possible to operate from a simple grid connection or even operate in remote locations using solar cells and batteries, to form hierarchical directional mesh networks, obviating the need for fiber. We are definitely not there yet in terms of commercial products, but research results are quickly paving the path.

Incidentally, almost all of the mm-wave technology that we use for communication do double duty as a radar sensor, able to detect the location and speed of other options, which is working behind the scenes in the automatic cruise control systems, and even autonomous driving systems that are deployed today. New generation radar sensors allow higher resolutions and imaging capability (think about airport security scanners) to enable autonomous driving systems to see through smoke and fog and to even detect when an invisible car in the freeway slows down, even before the brake lights ahead of you illuminate.

In our new book Millimeter-Wave Circuits for 5G and Radar, we have invited the top researchers from industry and academia to expound on this exciting new technology from the perspective of circuit designers. The idea for the book originates from our enthusiasm and deep connection with the technology. The coauthors of this book have been intimately connected with the technology behind 5G and radar, many of us going back decades. At UC Berkeley / BWRC we started our 60 GHz CMOS/SiGe mm-wave communication and radar research in 2001 as part of the DARPA TEAM program. Other DARPA “TEAM” members that are part of this book also include IBM T.J. Watson Research Center, which also played a key role in developing SiGe technology for mm-wave, making many important demonstrations of mm-wave circuits and phased arrays. Other coauthors from Intel Corporation, IMEC, IBM, KU Leuven, UC Irvine, Columbia University, Kilby Labs at Texas Instruments, Broadcom, Tokyo Institute of Technology, Oulo University, Ericsson, University of College Dublin, and Samsung represent a broad range of engineering leaders who have all helped pave the way for 5G through the development of research prototype ICs or first generation products.

Future circuit designers will play a pivotal role in taking 5G from a dream to an economically and technologically viable solution. 5G is already hitting the markets, but today’s systems are too bulky, too expensive, and consume too much power. 5G will not be defined by a single moment in history but a technology that will advance and mature for the next decade. The 3GPP standard’s body knows this to be the case and they designed 5G in such a manner to allow a seemingly infinite variety to implement the technology in terms of antenna count, the number of supported MIMO streams, and the number of supported spatial user streams. The cost of flexibility is also complexity, and it’ll take years for engineers to optimize 5G for different deployment scenarios. This book is about the technology that is needed to build such systems, including a fundamental understanding of spatial multiplexing and multi-user MIMO (MU-MIMO) and “massive” MIMO from the system perspective, which drive the specifications on circuit building blocks, to new concepts such as full duplex communication, interference cancellation in transceivers, phased arrays and beam forming for radar and communication. The book covers high bandwidth transceiver design, mm-wave and digitally intensive frequency synthesis, CMOS power amplifier design for 5G, and fundamental technology for 5G such as FinFETs.

Further Reading:

The Berkeley Tale of 5G – Ali M Niknejad