Wireless technology in the form of cell phones and their supporting networks has been a part of personal communications for almost five decades, now reaching its fifth generation (5G). From humble analog first-generation systems, cellular networks have become increasingly complex, with great expectations for 5G wireless networks to connect billions of people and things at speeds never possible with wireless networks.
The new 5G networks aren’t being introduced to replace 4G LTE wireless networks, but rather to work with them, adding capacity and functionality to reduce dropped calls and speed data download rates. However, with so many wirelessly interconnected people and things, will 5G networks be able to handle the data generated?
Fourth-generation (4G) wireless cellular communications systems were designed and installed to provide new levels of wireless performance. The systems were designed for peak data rates to 1 Gb/s for fixed links, although rates are more typically 100 Mb/s for mobile users. The “Long Term Evolution” (LTE) of 4G refers to improvements to the initial network infrastructure. Further refinements, such as faster data rates, have been made in the “advanced” version of 4G LTE (4G LTE-A).
In contrast to 4G LTE, 5G network developers are targeting peak data rates about 10X those of 4G LTE, or 20 Gb/s. Greater wireless network capacity is needed for increasing numbers of wireless cellular users, both people and things. More things than people will require wireless connectivity, such as Internet of Things (IoT) sensors throughout “smart” buildings and “smart” cities, let alone connected cars on smart highways. Increased capacity for 5G networks compared to earlier generations calls for more frequency spectrum and more efficient use of available frequency spectrum, by the application of innovative technologies.
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Making 5G Work
Frequency spectrum is limited and that’s what’s needed for 5G to manage large amounts of data. The success of 5G depends on enough bandwidth at different frequencies to support billions of users and things on the wireless network. That bandwidth will come from unlicensed and licensed frequency bands, below 1 GHz (600 MHz), from 1 to 6 GHz, and above 6 GHz, notably at millimeter-wave (mmWave) frequencies from 24 through 60 GHz for high-speed, fixed wireless access in network hotspots.
The buildout of 5G wireless networks involves intelligent use of available frequency spectrum. Since many lower-frequency bands are already occupied by Wi-Fi, Bluetooth, and other wireless devices, spectrum is limited. Thus, 5G service providers must try to assemble required bandwidth by purchasing or leasing frequency spectrum allocated by such organizations as the International Telecommunication Union (ITU) in Europe and the Federal Communications Commission (FCC) in the United States.
For example, the FCC has promoted the development of 5G networks with numerous spectrum auctions at higher-frequency bands, including the 24- and 28-GHz bands. The FCC is also encouraging 5G development at what are called “mid-band frequencies, from 2.5 through 4.2 GHz, “low-band” frequencies within 600-, 800-, and 900-MHz bands, and within unlicensed frequency bands from below 6 GHz to above 95 GHz. The FCC has shown its strong interest in 5G by unveiling its “5G FAST Plan,” which is a comprehensive strategy to facilitate America’s superiority in 5G technology (FAST). The plan has three key components: pushing more spectrum into the marketplace, updating infrastructure policy, and modernizing outdated regulations.
Radio-frequency signals propagate differently depending on frequency. Consequently, 5G system designers and service providers must try to make the best use of those differences for the network services and functions of 5G.
Signals at higher frequencies have shorter wavelengths than signals at lower frequencies—higher-frequency signals lose power over distance faster than lower-frequency signals. This makes lower-frequency signals better suited for transmissions over longer distances, providing better cellular radio coverage at lower frequencies. Higher-frequency signals, such as mmWave signals, suffer more attenuation from foliage, rainfall, and building materials than lower-frequency signals, leading to poor reception at long distances and inside buildings.
Earlier generations of cellular communications systems have achieved satisfactory coverage at lower frequencies with widely spaced cell sites. With its mix of frequencies, including mmWave signals for short-range, high-data-rate transmissions, 5G will require many smaller cell sites to achieve wide coverage, especially in densely populated areas such as cities with many subscribers.
For 5G service providers, the amount of bandwidth within each frequency band is a determining factor for how a frequency band is applied, since higher data rates require wider bandwidths. At lower-frequency bands, 5G competes with many other wireless technologies for available bandwidth. But at 24 GHz and above, bandwidth is readily available in support of high data rates, although for shorter-range transmissions.
A challenge remains in delivering coverage at mmWave frequencies efficiently and cost-effectively. The mmWave frequency bands that have been reserved for 5G use in the United States include 24, 28, 37, 39, 47, and 60 GHz, with some additional frequency bands in other countries. Such high radio frequencies have never been used in commercial communications systems, and they represent one of the key differences when comparing 5G to earlier generations of wireless cellular communications systems.
By using these higher frequency bands, 5G wireless networks are expected to reach new levels of performance compared to previous-generation wireless systems. If 4G LTE data rates typically hit a maximum rate of 1 Gb/s, 5G data rates are aiming at 10 Gb/s and expected to easily exceed 2 Gb/s for wireless interconnections with low latency (about 1 ms latency for 5G compared to about 40 ms for 4G LTE). The low latency may be more important for the “things” than the people. Low latency enables such functions as remote control of industrial robots and intelligent monitoring and control of autonomous vehicles by means of wireless access to in-vehicle sensors. High-data-rate, low-latency connections are important requirements for smart highways and intelligent traffic systems relying on 5G for wireless connectivity in real time.
The use of mmWave frequencies in 5G systems and their large available bandwidths enable high data rates and transfer of large amounts of data, like that generated by smart buildings and smart highways with their connected vehicles. Whether driven or autonomous, the vehicle-to-anything (V2X) communications among vehicles and the traffic-management system will rely on wireless interconnections on 5G with millisecond latency and gigabit-per-second data rates to keep traffic flowing without accidents.
Novel 5G Technologies
The coordination of multiple frequency bands by 5G networks is one of the novelties of this latest generation of wireless technology. 5G will have many more, much smaller, lower-power cell sites than earlier wireless networks, often mounted on utility poles (Fig. 1) and spaced much closer together than the cell sites of 4G LTE and earlier cellular generations.
1. 5G wireless networks will rely on small, closely spaced cell sites for extended coverage at higher frequencies. (Courtesy of syracuse.com)
Since many of those smaller cells may use frequencies as high as 60 GHz, antennas in 5G small cells will be smaller than in the base stations of 4G LTE or earlier cellular communications generations. A typical 4G LTE cell site uses a dozen antennas, eight to transmit and four to receive. Sites are often miles apart, providing coverage over large areas.
A much smaller 5G cell site might have 100 or more antennas for different frequencies, with smaller antennas for mmWave frequencies. Those arrays of mmWave antennas provide extended coverage using active beamforming techniques and massive multiple-input, multiple-output (MIMO) technology to efficiently orchestrate the transmit and receive functions of so many different antennas and arrays of antenna elements. 5G cell sites are closely spaced for optimum coverage, typically about 1000 ft. apart.
In connection with the large antenna arrays, full-duplex technology in 5G networks allows for simultaneous transmission and reception of signals to increase network capacity. The transceiver in a cellular handset and the transmitters and receivers or transceivers in cell sites typically transmit and receive on the same frequency at different times (time division duplex, TDD). Or they transmit and receive at the same time but on different frequencies (frequency division duplex, FDD). Full-duplex capability enables transmit and receive on the same frequency at the same time for greater network capacity and efficiency.
Major telecommunications service providers, such as AT&T, Sprint, T-Mobile, and Verizon, are specifying the components needed for 5G wireless networks. They range from mmWave amplifiers and antennas to waveguide terminations on the analog side through high-speed analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) on the digital side. Smaller cell sites require smaller components, especially when using MIMO antenna technology, driving component suppliers to miniaturize and integrate components where practical.
An example of that integration is in active antenna systems (AAS), which integrate radio transceivers with passive antenna arrays to create compact subsystems that achieve high capacity and wide wireless coverage from a small-volume cell site enclosure. The integration reduces the use of coaxial-cable interconnections between antenna elements and active components, cutting the insertion losses associated with those cables.
The increased integration still requires reliable, high-speed interconnections within the AAS. That can be achieved with advanced connectors such as ERFV coaxial connectors from TE Connectivity, which have been developed with 5G small cells in mind (Fig. 2). They work over the lower-frequency portions of 5G, from dc to 10 GHz, and feature a one-piece compressive design that aids in assembling multiboard PCB assemblies with different board heights. The low-cost connectors have better than 20-dB return loss and more than 60-dB isolation to 6 GHz.
2. Component innovations such as this compressive connector for multiple-PCB assemblies will enable the multi-frequency coverage of 5G’s smaller cell sites. (Courtesy of Mouser Electronics)
Effective use of mmWave frequencies, even in tightly controlled parts of a 5G network such as for short-range line-of-sight data links in densely occupied areas, requires the right components in those small cells. Due to the high signal losses that have traditionally plagued signals at mmWave frequencies, they will be limited in range and coverage within a 5G network. Therefore, only people and things within the range of those small cells will benefit from the wide bandwidths and high data rates.
However, as field trials by some of the major service providers are showing, mmWave signals are capable of better-than-expected penetration of building materials and other obstacles. And, with proper combinations of analog and digital components in those small cells, 5G networks may be able to support the future data needs of billions of people and IoT devices.