Millimeter wave is the technology closest to our lives
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The millimeter wave band ranges from 30 to 300 GHz, between the ultra-high frequency band and the far infrared band, and the lower part of the far infrared band is the terahertz band. The wavelength of radio waves in this band ranges from 10 mm to 1 mm; this band is called millimeter wave mmWave. The International Telecommunication Union (ITU) named this band of radio frequencies "extra high frequency" (EHF).
Millimeter waves have several uses, including communications, short-range radar, sensors, and airport security scanners. Different parts of the millimeter wave band are used for various applications:
The ITU has allocated non-exclusive passive frequencies from 57-59.3 GHz for atmospheric monitoring in meteorological and climate sensing applications, for which purposes oxygen in the Earth's atmosphere is important due to its absorption and emission properties.
Wireless Personal Area Networks (WPANs) operating in the 57-66 GHz range.
IEEE 802.16 Wireless Metropolitan Area Network (WMAN), also known as WiMAX, operates in the 10-66 GHz frequency band.
60 GHz: IEEE 802.11ad Multi-Gigabit Wireless System (MGWS).
24 to 39 GHz frequency band: 5G cellular telecommunications technology.
Millimeter-wave radars are used in short-range fire-control radars on tanks and aircraft and in automatic guns on naval ships to shoot down incoming missiles.
Traffic police use the Ka-band (33.4- 360 GHz) for speed radar guns.
Clothing and other organic materials are transparent to certain frequencies of millimeter waves. One recent application is scanners that can detect weapons and other dangerous items hidden in clothing, such as in airport security.
Millimeter wave attenuation has both negative and positive effects
Millimeter waves propagate only via line-of-sight paths. The ionosphere does not reflect them, nor do they propagate along the Earth like lower frequency radio waves. At typical power densities, they are blocked by building walls and suffer significant attenuation when passing through foliage. Absorption by atmospheric gases is a significant factor across the entire band and increases with frequency. However, it is greatest at a few specific absorption lines, primarily oxygen at 60 GHz and water vapor at 24 GHz and 184 GHz. At the "atmospheric window" frequencies between these absorption peaks, millimeter waves have less atmospheric attenuation and a greater range, so many applications can be used. However, millimeter waves are still subject to line-of-sight propagation and other limitations.
The so-called "atmospheric window" here refers to the 35GHz, 45GHz, 94GHz, 140GHz, and 220GHz frequency bands. Near these special frequency bands, millimeter wave propagation is less attenuated. Generally speaking, the "atmospheric window" frequency band is more suitable for point-to-point communication and has been adopted by low-altitude air-to-ground missiles and ground-based radars. The attenuation near the 60GHz, 120GHz, and 180GHz frequency bands has a maximum value, about as high as 15dB/km or more, which is called the "attenuation peak". Usually these "attenuation peak" frequency bands are preferred by multi-channel diversity covert networks and systems to meet the requirements of network security coefficients.
Atmospheric attenuation (dB/km) as a function of frequency in the millimeter wave band. Absorption peaks at specific frequencies are a problem due to the influence of atmospheric constituents such as water vapor and oxygen. The vertical scale shows an exponential change.
In addition, millimeter waves are severely attenuated during rainfall. The size of raindrops is similar to the wavelength of millimeters, so precipitation causes additional attenuation due to scattering (rainfall attenuation) and absorption. Compared with microwaves, millimeter wave signals are much more attenuated under harsh climatic conditions, especially during rainfall, which seriously affects the propagation effect. After research, it is concluded that the attenuation of millimeter wave signals during rainfall is closely related to the instantaneous intensity of rainfall, the distance and the shape of raindrops. Further verification shows that: Generally speaking, the greater the instantaneous intensity of rainfall, the farther the distance and the larger the raindrops, the more severe the attenuation caused. Therefore, the most effective way to deal with rainfall attenuation is to leave enough level attenuation margin when designing millimeter wave communication systems or communication lines.
High free space loss and atmospheric absorption greatly limit its effective propagation. This has a positive effect on the development of high-density communication networks (5G and WPAN) because it improves spectrum utilization by reusing frequencies in a relatively small geographical area.
The high bandwidth and short transmission distance of mmWave also make it very useful in applications such as short-range wireless transmission of ultra-high-definition video and communication of small, low-power IoT devices. Due to its limited propagation distance and high data rate, mmWave can play a role in communication between autonomous vehicles.
mmWave sensors can make the driving experience safer and simpler by analyzing and reacting to the surrounding environment
mmWaves and 5G
Given mmWave’s ability to provide low-latency, high-bandwidth communications over short distances, the ITU has defined three main use cases for 5G, namely the well-known enhanced mobile broadband (eMBB), massive machine-type communications (mMTC) for the Internet of Things, and ultra-reliable and low-latency communications (URLLC).
Millimeter wave technology provides ultra-wide bandwidth and high-speed capabilities to support eMBB transmission.
The 5G framework structure shows good results in terms of URLLC latency requirements by utilizing different transmission time intervals (TTIs) for URLLC and eMBB to meet the expected spectral efficiency (SE). For example, URLLC traffic can be scheduled on a smaller TTI duration to achieve low latency targets, and eMBB traffic can be scheduled on a longer TTI duration to maintain its extreme SE requirements.
URLLC-centric applications require end-to-end data delivery with the reliability, security, and minimal latency supported by mmWave technology. The ITU has set specific Quality of Service (QoS) requirements for URLLC, such as 1 millisecond air interface latency and 99.999% system reliability. For selected applications, the URLLC QoS requirements are as follows:
Although this FAQ focuses on mmWave, 5G consists of two separate frequency bands; FR1 and FR2. The frequency range of the FR1 band is 450MHz-6GHz, also known as the sub 6GHz band; the frequency range of the FR2 band is 24.25GHz-52.6GHz, commonly referred to as millimeter wave (mmWave)
Therefore, 5G in FR1 frequencies can use the same RF architecture currently used in LTE phones, Bluetooth, and similar devices. The FR1 portion of 5G will be able to use similar RF modulation/demodulation structures and similar analog front ends. They won't be exactly the same because 5G will have more bandwidth than LTE. But the increased bandwidth can be accommodated by similar technologies.
The importance of millimeter wave to the development of 5G cannot be overstated. In the field of 5G networks, the mobile industry can use millimeter wave radio spectrum to provide the required bandwidth for 5G networks to meet the needs of high-speed mobile networks. According to the GSMA report, driven by the innovative services brought by 5G millimeter wave, China will account for 53% of the US$212 billion economic growth in the Asia-Pacific region by 2034.
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