Mobile telecommunications carriers around the world have proclaimed 5G cellular wireless networks as the next major step in communications technology. They will do what cellular network generations before them could not, operating at frequencies and data rates never possible. They will serve billions of users worldwide (if not just in China) and provide the bandwidth required for a future filled with Internet of Things (IoT) devices for smart homes, smart factories, and smart cities, as well as the near-zero-latency signals for autonomous vehicles on smart highways.
The future of 5G certainly looks bright but what about the present? The hyperbole about 5G New Radio (NR) networks and technology is enormous, but how close is it to becoming reality?
The primary need for 5G is additional wireless capacity: it will provide service for more cell phones and other wireless devices. The global demand for wireless devices and services continuous to grow, eclipsing the capacities of the first four cellular generations. 5G will add capacity along with enhanced performance in support of emerging applications powered by IoT devices. Its extended frequencies, bandwidths, and associated technologies are not meant to replace earlier cellular wireless network generations, such as 3G and 4G Long Term Evolution (LTE), but to work alongside them.
FR1 and FR2
While a great deal of the novelty associated with 5G networks is their reach into millimeter-wave (mmWave) frequencies, much of their operation will be performed within a frequency range that has come to be known as “FR1” for signals below 6 GHz, compared to higher-frequency signals (above 6 GHz) within a range known as “FR2.” More specifically, 5G networks are being designed for multilayer spectrum coverage, occupying licensed and unlicensed frequencies in three bands: low-band signals below 1 GHz, mid-band signals from 1 to 6 GHz, and high-band signals above 6 GHz at centimeter-wave (cmWave) and millimeter-wave (mmWave) frequencies.
Spectrum sharing will allow current wireless applications to coexist with low- and mid-band 5G network signals. As an example, China is experimenting with sharing frequency bands below 1 GHz (470 to 806 MHz) between existing broadcast television systems and emerging 5G multimedia mobile communications applications. Depending on 4G/5G network configurations, some shared spectrum may even involve uplinked versions of sub-1-GHz signals within crowded spectrum to take advantage of available wireless connections at higher frequencies, such as from 3.3 to 3.8 GHz in Europe.
Frequency spectrum around the world is being allocated and, in some cases, auctioned for use by 5G carriers. The costs of licensing frequencies and bandwidth can vary widely by region, from the FCC’s high-cost auctioning of frequencies according to its 5G Facilitate America’s Superiority in 5G Technology (5G FAST) plan, to China’s allocation of frequency bandwidth to its four government-owned 5G carriers.
Spectrum auctions by the FCC in the U.S. include FR1 bands of 3.100 to 3.550 GHz and 3.7 to 4.2 GHz, and FR2 bands of 27.50 to 28.35 GHz and 37 to 40 GHz. In contrast, in China, FR1 bands of 3.3 to 3.6 GHz, 4.4 to 4.5 GHz, and 4.80 to 4.99 GHz, and FR2 frequencies of 24.25 to 27.50 GHz and 37.00 to 43.50 GHz are being deployed. And in Japan, 5G will operate within FR1 bands of 3.6 to 4.2 GHz and 4.4 to 4.9 GHz, and FR2 frequencies of 27.50 to 28.28 GHz.
Proper Infrastructure
Standards for 5G performance and protocols—established by organizations such as the IEEE and Third Generation Partnership Project (3GPP) and its TS 38.104 V15 specifications for 5G base stations—are essential for creating wireless networks and UE devices that will be compatible within a given operating region. In some locations, such as downtown Beijing, China, 5G network infrastructure has been deployed to investigate the limits of higher-frequency 5G signals compared to earlier-generation cellular wireless networks (Fig. 1).
Many carriers have been aggressive in their claims of providing 5G network coverage, offering computerized coverage maps that indicate availability by frequency. The use cases for 5G coverage include enhanced mobile broadband (eMBB) applications like smartphones, massive machine-type communications (mMTC) such as in automated factories, and ultra-reliable low-latency communications (URLLC) such as in robotic surgery and vehicle-to-vehicle (V2V) communications for autonomous vehicles.
Infrastructure for 5G networks is being built “on top of” earlier cellular wireless generations, with 5G base stations being added whenever possible to 3G and 4G installations as non-standalone (NSA) 5G base stations. For voice and noncritical data applications, such installations can provide service by means of 3G or 4G networks, reserving 5G at its highest frequencies for low-latency, high-speed-data applications.
Transfer of data at high rates requires large amounts of contiguous bandwidth, which can be found with the lack of applications at 24 GHz and above. However, the higher path losses of those higher-frequency signals mean that they will not be as freely available in wireless networks without additional hardware and software assistance compared to lower-frequency signals.
To fill holes in the signal coverage between NSA base stations using mmWave signals, smaller 5G standalone (SA) base stations will be constructed. These will have much closer spacing between them because of the high path losses for cmWave and mmWave signals.
Both SA and NSA base stations will be important parts of 5G wireless networks. However, the two types of sites will have different functionality and capabilities requiring, for example, different test strategies to characterize 4G LTE equipment in NSA base stations compared to the higher-frequency transceivers in 5G NSA base stations. Due to the challenge of achieving coverage with mmWave signals, 5G networks will employ higher-frequency signals (and their support of high data rates) where they do the most good, such as in office buildings and heavily populated areas.
Investing in 5G
With its higher frequencies and technologies to support their use, investment in 5G wireless networks is not trivial—it’s required the rapid growth of wireless users through 3G and 4G LTE networks. The adoption rate of 5G UE devices and services throughout the world is expected to quickly eclipse the rates at which customers took to 3G/4G devices and services.
South Korea, the first country to commercialize 5G wireless networks and UE devices, already has over 2.5 million 5G mobile broadband users. The South Korean government is very involved in the commercialization, subsidizing the sales of UE devices and cutting taxes on network infrastructure construction for service providers. That government feels 5G will have many vertical business branches that will boost its economy, such as autonomous driving in smart cities and digital wireless healthcare, and the technology is well worth its involvement and investment.
Throughout the U.S., for example, 5G service providers such as AT&T, Sprint Nextel, T-Mobile, and Verizon have made major investments in their wireless networks, adding frequencies, capacity, and performance. AT&T, for example, quotes an investment of $145 billion in its wireless network over the past five years, while T-Mobile has invested over $30 billion in 5G network infrastructure that involves 25,000 new cell sites and towers. For all carriers and networks, performance will improve over time with the addition of bandwidth at higher frequencies. Some offer “offshoots” of full-featured 5G technology based on network availability, such as Verizon’s broadband internet Home 5G Service.
At present, 5G coverage in the U.S. is limited to select major cities and to performance levels that only begin to scratch the surface of 5G’s ultimate performance capabilities. As coverage extends to more rural areas, networks will evolve with functionality and services provided as needed. The networks support 5G smartphones from several major manufacturers, such as the Galaxy S10 5G phone from Samsung (Fig. 2). Within a 5G network, it’s capable of the fast upload/download data rates promised by 5G technology. Outside 5G coverage, it operates according to a network’s capabilities, serving largely as a fully functional 4G LTE smartphone.
Customers for 5G smartphones are getting an idea of the much higher costs of those devices compared to 4G phones—and this is with limited service. Service providers worldwide are in the process of constructing their 5G networks, currently offering very limited coverage mostly at lower frequencies and with some experimental or “pilot” cells operating at mmWave frequencies.
Very little is known about signal frequencies at 24 GHz and higher in actual use and these test cases provide the means to discover the effects of real-world operating environments, such as rainfall attenuation, on mmWave signals. Signals at mmWave frequencies used in 5G systems for high-data-rate transmission and reception suffer much higher path loss than lower-frequency signals with longer wavelengths. They can be attenuated by a building, foliage, or even a user’s hand placed too close to the antenna array within a 5G smartphone.
Many service providers are learning a great deal from their users of these early 5G network sites, reporting positive results from the use of multiple-input, multiple-output (MIMO) antennas and active antenna systems (AAS) on extending coverage with mmWave signals. Antennas in 4 × 4 MIMO configurations have been successfully applied in 4G LTE networks. Much larger antenna arrays are typically being used in 5G networks. These are often 8 × 8, 64-element active antenna arrays capable of controlling the phase and amplitude of each element to form a beam of directed energy between a base station and a user at mmWave frequencies.
Most 5G carriers expect about a five-year buildup period for their networks with major investments in hardware, since the cost of RF/microwave components tends to increase with increasing frequency. Leading device manufacturers such as Intel, Qualcomm, and Texas Instruments are working to reduce the costs of RF/microwave components such as radio transceivers at higher mmWave frequencies. They’re accomplishing this through the dense integration of components within ICs and multilayer circuit modules that can serve both 5G UE devices and base stations. In general, 5G UE devices and base stations will be highly integrated, which is notable at higher frequencies where array antennas are tightly integrated with radio electronics, making it difficult to characterize 5G radio circuits using traditional test methods.
Testing the Future
In 5G SA base stations, the multiple-band radio equipment will operate on its own, while in NSA base stations, it will share real estate with earlier-generation wireless base stations. The radio portion of a 5G base station will be a separate unit than the controller electronics, a remote radio head (RRH), with the two units interconnected by optical cables. Due to the propagation characteristics of mmWave signals (poor penetration of solid objects such as building walls), RRHs will be mounted where needed for maximum coverage, such as on building rooftops and within buildings (Fig. 3). However, such locations may make access with test equipment difficult.
Due to the many hundreds and thousands of base stations and microcells that will be needed and constructed during the next five years, different measurement approaches will be required to characterize and maintain the performance of 5G RRHs. This includes over-the-air (OTA) testing for locations where it’s impractical to make a physical (coaxial cable) connection between the RRH and a signal analyzer (Fig. 4).
OTA testing performs measurements of a UE device or base station at some distance from the antennas in the device under test (DUT) using a calibrated measurement antenna connected to the signal analyzer. In the case of a smaller DUT such as a smartphone, OTA measurements are performed within a shielded room or enclosure. Once installed, 5G base stations can also be checked for performance levels and coverage within an area using OTA measurements.
Clearly, 5G wireless network coverage is in its infancy in many locations. Some locations, such as China, Japan, and South Korea, are further along in constructing the 5G network infrastructure needed to meet the bold claims of 5G service providers. However, the investments and the commitments to building 5G wireless networks are strong.
It’s clear that the next five years will be active times for suppliers of UE device chipsets, for infrastructure radio equipment suppliers in both FR1 and FR2 frequency ranges, for suppliers of test hardware and software in support of OTA measurements, and even for suppliers of the potentially millions of kilometers of fiber-optic cables needed in the integration of 5G base-station subsystems. It’s important to remember that 5G networks will be multilayered systems operating in basically three different frequency bands and wireless functionality and performance will grow as 5G infrastructure builds up.
Many functions remain well-served by 4G LTE systems. As 5G networks expand, they will add to the possibilities of 5G technology especially in vertical markets, such as autonomous vehicles, wireless and IoT-enabled robotic factories and warehouses, and wireless healthcare and remote medical care.