True 5G requires millimeter wave band support and SA operation.
5G's ultra-high-speed characteristics depend on utilizing millimeter wave bands.
Beamforming reduces interference with surrounding users and transmits data.


5G is a wireless communication standard that will be developed and used for more than 10 years, like LTE.

5G has three advantages. First, it is ultra-fast. 5G NR is 20 times faster than 4G LTE. Its maximum transmission speed is 20 Gbps, with a typical speed of 10 Gbps. Second, it is ultra-low latency. 5G transmission latency (1 ms) is 10 times shorter than LTE (10 ms). Finally, it is hyper-connectivity. 5G can support up to 1 million devices per ^square kilometer, ten times more than LTE's 100,000 devices.

However, for 5G to realize the above advantages, several issues must be resolved.

5G operates in two modes: standalone (SA), which operates solely as 5G, and non-standalone (NSA), which operates alongside LTE. There are also two frequency bands: sub-6Ghz and millimeter wave (mmWave). Currently commercialized 5G is 5G NSA, which uses sub-6Ghz bands. Therefore, to achieve true 5G, it must be able to operate in SA mode while also utilizing mmWave bands.

In particular, the ultra-high-speed characteristics of 5G can only be achieved through the use of millimeter wave bands. Millimeter wave bands have short wavelengths, allowing for smaller and lighter antennas and devices, and their broad bandwidth allows for the transmission of large amounts of data. However, the diffraction ability to avoid obstacles is low, so it must be supplemented with technologies such as beamforming.

To fully realize the potential of 5G and address its shortcomings, major countries are accelerating the establishment of millimeter wave band infrastructure and securing related technologies.

AT&T in the US aims to build a nationwide 5G network based on sub-6 GHz and millimeter wave bands by the first half of 2020, and China Mobile announced that it will launch 5G millimeter wave band services in 2022. In Korea, the 3.5 GHz band and the 28 GHz millimeter wave band were each allocated to the three mobile carriers through a 5G spectrum auction in June 2018.

Although sub-6 GHz bands are still insufficient, major countries' 5G plans include the construction of millimeter wave infrastructure. Therefore, securing relevant technological capabilities is expected to significantly impact corporate competitiveness in the future.

We asked Jongpil Han, a FAE at Analog Devices (ADI), why the commercialization of the 5G millimeter wave band is being delayed, and what capabilities are required to develop related products when the millimeter wave band is fully commercialized.


Q. Why is commercialization of 5G millimeter wave bands delayed?
A. This is because the high propagation loss and environmental vulnerability to blocking associated with the use of high-frequency bands make millimeter-wave operation unsuitable for mobile cell coverage, making it difficult to achieve. To address these limitations in 5G NR, research is being conducted on related antennas, RF components, power supplies, and beamforming technologies.


Q. What is the potential of the 5G millimeter wave band?
A. The advancement of millimeter wave technology is about creating 5G NR networks that meet the expectations of industry and consumers. Its high-frequency band and ability to utilize wide-band spectrum resources enable 5G networks that can support data-intensive devices such as connected and autonomous vehicles, AR and VR, connected medical devices, smart cities for security and environmental monitoring, and IoT sensors.


Millimeter-wave wireless communication technology utilizes ultra-high frequencies between 30 and 300 GHz, with bandwidths exceeding 1 GHz. This allows for the control of millimeter waves, which offer abundant bandwidth, and short wavelengths in the millimeter (mm) range, enabling the real-time transmission of large amounts of data, increasing transmission capacity.


Q. Beamforming technology is a key technology for complementing 5G. Could you explain beamforming?
A. Beamforming is a technology that enables stronger, faster, and more stable wireless communication by transmitting wireless signals in the direction of the beamformer (router) toward the beamformer (client). In other words, it is a traffic forwarding technique that identifies an efficient data transmission path for a specific user, which can reduce interference with surrounding users.

There are several ways to implement beamforming in 5G networks, depending on the circumstances and technology. Structurally, there are analog beamforming, digital beamforming, and hybrid beamforming, which combines the two.


Q. What are the differences between downlink beamforming and uplink beamforming, and what are the challenges?
A. Downlink beamforming utilizes constructive interference between RF signals transmitted from antenna elements. By appropriately adjusting the phase of the antenna element input signal for each beamformed layer, constructive interference can be used to transmit the signal in the desired direction. This phase adjustment can be performed by the radio unit (RU) via a series of phase shifters (Analog BF) or through precoding at the baseband (Digital BF).

Beamforming in the uplink, for example, involves adapting the uplink Rx directional patterning, generating peak gain toward the user equipment from the base station, rather than toward the user equipment that transmits the beam toward the uplink. This includes creating beam directions and nulls toward the user equipment that are not needed, similar to interference rejection combining (IRC).


Q. What technology is needed to avoid interference between beamforming devices?
A. In space-division multiple access systems, inter-beam interference (IBI) occurs between adjacent beams formed by BSs in the same cell and BSs in adjacent cells. The beam formed toward user equipment in each cell can cause significant interference to user equipment in adjacent cells, especially user equipment at cell boundaries.

To overcome this, various precoding techniques have been used to reduce multi-user channel interference in existing low-frequency systems, but millimeter-wave systems that use a large number of antennas require training and feedback overhead, making it difficult to obtain full channel information at the base station. Therefore, low-complexity precoding techniques are needed to overcome this.


Q. To communicate in the millimeter wave band, data must be converted to millimeter waves. What components are used for this and what are the requirements for these components?
A. The fundamental specifications required for components supporting 5G are wideband, low loss, low power, and high linearity. While there are some differences depending on the architecture employed, the transmission side requires a Gsps DAC capable of converting digital signals to wideband RF signals, a wideband up-converter, power amplifiers, switches, and filters.

On the receiving side, interference signal removal is required, a down converter with FEM and image signal removal in mind that allows low-noise signal amplification, and a local signal with low phase noise characteristics common to Gsps ADCs with high dynamic range are required.