Millimeter wave (mmWave) is becoming a buzzword in the 5G era. A few years ago, millimeter wave was only a niche technology in the laboratory stage. Today, millimeter wave has become a popular technology that global operators are researching and piloting.
According to the 3GPP agreement, 5G networks mainly use two frequencies: FR1 frequency band and FR2 frequency band. The frequency range of the FR1 frequency band is 450MHz~6GHz, also known as the Sub-6GHz frequency band; the frequency range of the FR2 frequency band is 24.25GHz~52.6GHz, usually called millimeter waves. If the low frequency band is the basic coverage network of 5G, millimeter wave is an important hot spot blind technology for 5G. Millimeter wave and Sub-6GHz technology will complement each other to unleash the full potential of 5G.
The transmission rate of 5G should be more than ten times faster than that of 4G, that is, the transmission rate of 5G can achieve 1Gb/s. There are basically two methods for wireless transmission to increase the transmission rate. One is to increase the spectrum utilization, and the other is to increase the spectrum bandwidth.
Compared with improving the spectrum utilization, the method of increasing the spectrum bandwidth is simpler and more direct. The commonly used frequency bands below 5GHz are already very crowded. In order to find new spectrum resources, the method that major manufacturers think of is to use millimeter wave technology.
Definition of millimeter wave
Microwave bands include: decimeter waves, centimeter waves, millimeter waves and submillimeter waves.
Among them, millimeter wave (millimeter wave) usually refers to electromagnetic waves with a frequency band of 30 to 300 GHz and a corresponding wavelength of 1 to 10 mm. Its operating frequency is between microwave and far-infrared waves, so it has the characteristics of both spectrums. The theory and technology of millimeter wave are the extension of microwave to high frequency and the development of light wave to low frequency.
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Millimeter wave has many advantages
Compared with frequency bands below 6GHz, millimeter wave has the advantages of rich spectrum and low time delay.
Zhang Li said:
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First, the millimeter wave spectrum resources are abundant, the carrier bandwidth can reach 400MHz/800MHz, and the wireless transmission rate can reach more than 10Gbit/s.
Second, the millimeter wave has a narrow beam, good directivity, and high spatial resolution.
Third, the millimeter-wave wavelength is short, the antenna size is small, and the miniaturization and lightweight of large-scale arrays are easier to achieve.
Fourth, the millimeter wave sub-carrier spacing is large, and the single slot period (120kHz) is 1/4 of the low-frequency Sub-6G (30kHz), and the air interface delay is reduced, which can meet the needs of the industry.
Fifth, the millimeter wave indoor and outdoor isolation is good, which is more conducive to eliminating indoor and outdoor interference when using different frame structures indoor and outdoor.
The biggest feature of millimeter wave is large bandwidth.
In Zhang Li's view:
Compared with frequency bands below 6GHz, millimeter wave can provide a higher user experience rate, which can meet the business needs of large-capacity concurrent public network and industry users, and further enhance the 5G network capabilities.
Considering the large loss of millimeter wave frequency band, poor penetration and diffraction ability, easy to be affected by the external environment, and limited coverage distance, it is suitable for areas with rich reflection paths and less open space. It is generally used for the supplement of the capacity layer and hot spot coverage. And fixed wireless access.
"But we still need to see that the millimeter wave frequency band has large propagation loss and weak coverage, so continuous coverage is difficult and application scenarios are limited." Zhang Li emphasized that this will cause millimeter wave network construction to have higher technical requirements for base station products , In the absence of scale, the cost of equipment and overall network construction is high.
Overall, both the millimeter wave networking solutions of operators and the cost control of equipment manufacturers will face greater challenges.
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Global 5G millimeter wave research is in full swing
Because millimeter waves have technical advantages such as large bandwidth and low latency, telecom operators currently have a clearer positioning of millimeter waves, that is, they are used in public network service hotspots and high-value industrial networks that require high traffic and low latency.
In Zhang Li's view, since the United States did not have a frequency spectrum plan below 6GHz in the early stage of 5G, it first developed FWA (fixed access) services based on millimeter waves, and then provided eMBB services, but the deployment scale was limited and coverage continuity needed to be optimized. Commercial applications are being planned in Japan, South Korea, Europe and other regions.
Countries are guided by application requirements, show regional characteristics, and have various deployment strategies. The country is also actively carrying out millimeter wave spectrum planning and technical research work to prepare for subsequent network construction.
Zhang Li said that the WRC-19 conference allocated the 17.25GHz frequency band for IMT. China covers the 26GHz frequency band and the 40GHz frequency band, a total of 9.75GHz bandwidth frequency. The current domestic research focus is on 26GHz (24.75GHz～27.5GHz).
Zhang Li said:
At present, 3GPP has completed the formulation of the two versions of Rel-15 and Rel-16, and is working on the standardization of Rel-17.
Among them, Rel-15's millimeter wave system has completed the definition of basic functions, including multi-beam-based synchronization and access mechanisms, quasi co-location mapping relationship of antenna ports, layer 1 RSRP measurement and reporting, beam failure recovery, etc. and millimeter wave Technology related to beam management and transmission.
In Rel-16, the system configuration of millimeter wave has been optimized to reduce delay and overhead. In Rel-17, research work is being carried out for mobility, more scenarios and higher frequency bands. The specific commercial time and commercial version are related to the frequency allocation strategy and time of each country, and need to refer to the policies and regulations of each region.
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It will take time for the millimeter wave to mature
Zhang Li believes that millimeter wave needs to be gradually optimized in terms of technical solutions, electrical performance indicators, product maturity, and cost. In terms of chips, the mass production capacity of domestic 5G millimeter-wave chips needs to be verified. Currently, they are mainly developed in universities and research institutes, and it is urgent to promote the maturity of the domestic industrial chain.
In terms of base station equipment, millimeter wave application technology and maturity are not high, and the cost of equipment is currently high, which is not conducive to market promotion. Further research on cost reduction solutions is needed; in terms of terminal equipment, the types and numbers of terminals that support millimeter waves still need to be abundant; In terms of test schemes, millimeter-wave base station test technology is quite different from the frequency band below 6GHz, and some performance, index and reliability test schemes need to be further improved.
China Mobile actively promotes the maturity of millimeter wave technology, and cooperates with the Ministry of Industry and Information Technology to carry out a series of end-to-end tests of outdoor stations + commercial terminals (smartphones and CPE). The tests cover direct radiation coverage, penetration, and rate delay. index.
In addition, China Mobile has conducted in-depth research on millimeter-wave outdoor propagation models and beamforming schemes in conjunction with pilots and tests, compared and analyzed various base station hardware architectures, and investigated the capabilities of domestic and foreign chip and equipment industries, and made sufficient efforts for subsequent network construction. Technology accumulation.
Edit | Chen Jinglan
Proofreading | Zhong Miaoli
Audit | Huang Xiaoming
Source | Communication World Network
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