Co-authored by George MacCartney, Jr.
Are you waiting impatiently to get that amazing virtual reality experience in your living room, or chomping at the bit to have high-speed internet at your rural farm, or planning to stream 4K TV on the go? What you probably don’t know is that these exciting new applications begin on sweltering rooftops in New York City and the rural hills of Riner, Virginia, where people like George R. MacCartney, Jr, 2016 Marconi Society Paul Baran Young Scholar, investigate how millimeter-wave (mmWave) frequencies will work in these environments to ensure that 5G wireless delivers on its promise for an enormous increase in bandwidth and data rates.
Let’s start with a bit of history. Just over a year ago, the FCC voted unanimously to make new portions of radio spectrum available for 5G wireless services. This made the US the first country to set aside more than 28 GHz of spectrum for 5G wireless communications and networks and triggered a global race by companies and countries to be “the first” to deliver 5G to their customers. Around the same time, the Marconi Society announced the 2016 Paul Baran Young Scholars, including George R. MacCartney, Jr., a PhD student at NYU specializing in mmWave propagation measurements and models showing that mmWave can work in various environments and scenarios. MacCartney and his groundbreaking work with NYU WIRELESS are helping to bring 5G closer to reality each day.
While media and communications companies tout 5G as a panacea for bandwidth-hungry applications such as streaming, artificial reality (AR) and virtual reality (VR), it can also be the game changer that eliminates the rural broadband gap in the US for 23.4 million Americans who live outside urban areas and who are currently denied the educational and economic opportunities of having readily available broadband.
With such big aspirations riding on a still-developing technology, it’s helpful to understand the current state of 5G and how MacCartney sees the evolution.
What’s the Problem?
The beauty of 5G and mmWave bands is that they offer huge amounts of wireless bandwidth, making them an open playground for applications and business models accessible through a wireless network. This is what makes it a potential delivery mechanism for people who are currently off the grid in both developed and emerging countries, where digging fiber lines and building extensive infrastructure is not an easy or affordable option. The massive bandwidths at mmWave also provide wireless backhaul options from remote stations.
Ultra-high frequencies behave differently than lower microwave frequencies used in our current wireless networks. As frequency increases, wavelength decreases and the resulting signal strength is much weaker in the first meter of propagation compared to traditional cellular bands. This fact has led to the myth that mmWave frequencies are not viable for long-range wireless compared to traditional cellular bands. However, aside from the additional loss in the first meter of propagation, mmWave signals attenuate as a function of distance in a very similar manner to cellular frequencies. Additionally, for transmit and receive antennas that remain the same physical size as frequency is scaled up, the gain of each antenna increases by the square of the increase in frequency such that the path loss in free space in the first meter reduces by the square of the increase in frequency. This means that if you can build highly directional antennas, then mmWave can result in stronger signals than today’s omnidirectional cellular.
Measurements by MacCartney and his colleagues at NYU WIRELESS have helped to dispel the myth and have shown that even with low transmit power (less than one watt) and using high-gain directional antennas, mmWave wireless links can be made at distances as far as 200 meters in non-line-of-sight (NLOS) or obstructed conditions in urban microcell (UMi) environments like Manhattan and Brooklyn, and out to distances of more than 10 km in rural areas. Many in academia and industry believe that the additional loss in the first meter can be easily overcome, even in inclement weather, by using high-gain electrically-steerable phased array antennas – especially since many antenna elements can be packed into a small-form factor when operating at mmWave frequencies. The 200 m range in urban environments is also quite conservative given the lower transmit power and the fact that antenna combining and signal processing techniques will be used in future systems to increase range and link margin.
There are still issues to overcome in terms of blockage at mmWave frequencies, due to pedestrians, cars, and buses, that cause rapid degradation in signal strength . MacCartney has also worked on developing models for characterizing blockage events and will present his recent findings at GLOBECOM 2017. Additionally, MacCartney’s recent work has focused on the use of multiple base stations in an urban small-cell scenario to study how base station diversity can be used to mitigate blockage events and to avoid outages via rapid re-routing, handoff applications, and sectored beam-switching.
Why Do Measurements Matter?
One of MacCartney’s unique contributions to developing 5G is taking real-world measurements with a system called a channel sounder. A lot of researchers don’t take real-world measurements when developing models or systems – they rely on software simulations, which are purely theoretical or calibrated from a few measurements at mmWave or from traditional cellular bands. This is problematic because we do not yet know how mmWave frequencies will interact in dense urban or even rural environments. Simulations are not always realistic, but real-world experiments give insights into the true nature of these frequencies and reveal observations that one might not expect, such as the strong reflective nature of mmWaves off of buildings and their interactions with metallic lamp posts and street signs.
Propagation measurements are difficult and time-consuming but have great merit. “I am passionate about looking at measurements as an asset, rather than as something that is too difficult to do,” says MacCartney. “You don’t understand the channel and the environment until you have measured it yourself.”
First-hand measurements are done mainly in Europe and Asia and much less frequently in the US, mainly because the US funds much less communications research than Europe and Asia do. One of the assets of NYU WIRELESS, however, is the strong support from their 18 Industrial Affiliates and the tireless efforts of professors to generate support from the National Science Foundation (NSF).
Furthermore, taking measurements can be difficult: they are done outside, sometimes in extreme heat or cold. They can take a long time – researchers have to take measurements over many weeks to months and in a plethora of environments and scenarios to collect terabytes of data. Since high-gain narrowbeam antennas are needed for mmWave measurements, many systems implement mechanically steerable horn antennas at the transmitter and receiver, where snapshots of the channel must be taken over a multitude of antenna pointing combinations. This can take considerable time and effort for individual transmitter and receiver combinations. Phased-array technologies are not particularly mature yet at mmWave frequencies for accurate and simple measurements. However, technology and systems are improving, including a promising channel sounder system from AT&T, yet such systems are extremely expensive, difficult to calibrate, and can take years to perfect.
How will 5G Show Up for Users?
Given the media hype around 5G, it is sometimes difficult to remember that we are very early in the technology’s lifecycle. While some carriers claim to be offering the first 5G connections, these are really advancements of the LTE-Advanced (LTE-A) network in the quest to improve capacity and speed. For initial 5G deployments at mmWave, we should expect to first see fixed wireless access as a fiber replacement for ultra-broadband connectivity to the home. For 5G mobile access at mmWave, it is likely that we will first see a rollout of connectivity to tablets or devices larger than a mobile phone, similar to the initial rollout of 4G which included mobile hotspots and dongles.
The Olympics traditionally showcase new mobile and wireless technologies. Anticipate seeing 5G and mmWave on display at the 2018 Winter Olympics in Pyeongchang, South Korea and then even more visibly at the 2020 Summer Olympics in Tokyo. Perhaps mmWave and 5G technologies will be useful for solving connectivity issues like those experienced at a recent Pokemon Go event in Chicago where a densely populated crowd of participants experienced outage and performance issues on most wireless carriers.
Initial applications on the business side will likely increase productivity and make sophisticated services more accessible. Some of the most promising applications include:
- Healthcare using ultra-reliable and high speed 5G networks for telemedicine, supporting breakthroughs such as remote surgery via robotics
- Machine to machine (M2M) communications for manufacturing, an environment where machines need very low latency wireless networks to perform their tasks and cannot tolerate any break in coverage
- High-density environments with extreme traffic that support high-bandwidth applications, such as omni-view, 360 video, and hologram live applications, such as those predicted for Olympic viewers to experience events live while not necessarily physically at the event.
It is likely that initial consumer applications will focus on AR and VR gaming and entertainment experiences.
Just like the Internet, no one knows what the killer applications and business models will be for 5G. In major social impact areas, such as providing broadband coverage for everyone, technology is the easiest thing to solve. Business models and regulation – not technology – will be the gating factors in making broadband truly available for consumers around the world.
“I wanted to work on wireless because it’s still the relatively early days compared to other technological revolutions that have been around for many decades and even centuries, and I believe we are due for an impactful evolution of wireless. Being selected as a Paul Baran Young Scholar has helped me in my work by allowing me to meet and network with other bright and talented Young Scholars and to learn about them, their research, and their passions. It has also given me the opportunity to meet and interact with pioneers and distinguished scholars and engineers in the field of communications, networks, and the Internet,” says MacCartney.
Despite the current vagaries of business models and regulation, we can rest assured that the technology will eventually work based on measurements that are taken by intrepid researchers like MacCartney.