In 2014, the Ministry of Industry and Information Technology officially issued TD-LTE standard 4G licenses to China Mobile, China Telecom and China Unicom, and China officially entered the 4G era. According to a report from third-party analyst GSMA intelligence, by the end of 2017, there will be more than 500 LTE networks deployed in more than 128 countries worldwide. While providing greater bandwidth and giving people a better mobile Internet experience, 4G will also challenge operators' mobile bearer networks.
With the issuance of domestic 4G licenses, LTE networks have also been rapidly deployed. However, the coverage of the LTE base station is small, and the deployment density is much higher than that of the GSM base station and the 3G base station. The LTE construction will face a large number of new site requirements, and some new sites have a shortage of fiber resources. It is expected that 20% of the new site fiber resources will be missing. Both LTE base station service backhaul and PTN fiber network are under pressure. As an important solution for mobile backhaul, microwave can replace or be used as a supplement to optical fiber to solve the shortage of optical fiber and realize rapid deployment of LTE network. However, the spectrum resources of the traditional microwave frequency band (6 to 42 GHz) are tight, and the channel spacing is small (the current maximum channel spacing in China is 28 MHz), which is difficult to meet the large bandwidth demand of the LTE base station for the bearer network. In this case, the industry has turned its attention to E-Band microwaves that provide ultra-large bandwidth. What is E-Band microwave, and what bandwidth can E-Band microwave transmission provide and which application scenarios?
E-Band band microwave introduction
E-Band RF channel configuration
In 2000, ITU-R and ETSI standards organized the division of high-frequency 71-76 GHz and 81-86 GHz microwaves, which is what we often call E-Band.
Figure 1. E-Band RF definition
At the same time, the industry standard bodies ITU-R, FCC, and CEPT have made relevant recommendations for the E-Band RF channel configuration. The channel division is mainly 250MHz and 1.25GHz. With 250MHz or even larger channel spacing resources, E-BAND microwave single-frequency points can provide more bandwidth. Currently, the industry's largest single-frequency point bandwidth is 2.5Gbps, and even 10G air interface transmission bandwidth can be provided in the future.
Figure 2. E-Band RF channel configuration as defined by ETSI and FCC
E-Band microwave transmission distance
The distance of microwave transmission is affected by free space loss, atmospheric loss and rain attenuation. Next, we will focus on the transmission performance of E-Band microwave:
Free space loss:
The free space path loss from 71 GHz to 76 GHz is about 130 dB, and the free space loss from 81 GHz to 86 GHz is 131 dB. This value is generally higher than the free space loss in the traditional frequency band, which directly causes the transmission distance of the E-Band to be much smaller than other conventional frequency bands.
Atmospheric loss:
In the following atmospheric window diagram, it can be seen that in the range of 71 GHz to 86 GHz, the attenuation of the atmosphere to E-Band is very low, basically less than 0.5 dB/km.
Figure 3. Atmospheric attenuation icon
Rain decay:
For microwaves above 10 GHz, rain attenuation directly limits the distance of microwave transmission. For E-Band microwaves, in very severe cases, such as tropical rain forest rainfall (100 mm / hour), the rain attenuation is around 30 dB / km, but this usually only occurs in a short time, and in the network design, can pass Reserve margins to adapt to weather changes. Some manufacturers also support the adaptive modulation function: that is, the modulation mode can be adjusted to adapt to the weather changes, and the QOS configuration is matched to ensure that high-priority services can communicate normally, thereby improving network reliability.
E-Band is basically unaffected by the clouds. Even a dense fog with a visibility of 50 meters and a density of 0.1g/m3 can only produce 0.4dB/km fading for E-Band, which is basically negligible.
From the actual test situation, the E-BAND microwave can work stably within the transmission distance range of 2 to 3 km.
E-Band microwave application scenario
Compared with the traditional frequency band, the E-Band frequency resource is rich, supporting a larger bandwidth than the traditional frequency band, and the single frequency point bandwidth reaches 2.5 Gbps.
Table 1 Comparison of traditional frequency bands and E-Band
From the above analysis data, E-Band microwave is very suitable for large-bandwidth transmission application scenarios, meeting the bandwidth requirements of LTE for backhaul networks. Combined with the business needs of China Mobile, we can roughly divide into the following four scenarios.
1. The PTN access layer fills the network into a ring:
The ring network can improve the reliability and disaster tolerance of the bearer network. Operators usually have certain requirements for the network ring rate, especially the pursuit of high-quality China Mobile. However, due to various practical difficulties, some sites have missing fiber resources, and a considerable proportion of the access layer still faces looping pressure. The E-Band microwave can be used as a replacement for the optical fiber. The PTN network can be used to form a ring-filled network. The bandwidth of the access ring is 1 Gbps. The PTN network cannot be looped. Ability to improve the reliability of the transmission network.
2. LTE terminal base station access:
In densely populated areas, the bandwidth requirement of a single base station (in S333 configuration mode) is over 900 Mbps. In the short-range scenario of 1~3Km, the E-Band microwave has abundant spectrum resources, which can be used to solve the problem of resource shortage and small transmission bandwidth in the traditional microwave band. As the terminal LTE base station service access, it solves the problem of some new site fiber missing. The problem is to achieve rapid deployment of LTE base stations.
3. Large customer line:
For services such as data service interconnection lines and enterprise link leases with bandwidth requirements above 1 Gbps, some buildings are difficult to deploy due to fiber laying, high cost, and long period of time. E-Band microwaves can be used as IP/MPLS routers or L2 switches. Fiber replacement, solving fiber and deployment difficulties.
4. Integrated service access:
E-Band microwave provides 2.5G large bandwidth, which can easily carry multiple services such as base station/Wi-Fi, large customers, and broadband. In the scenario where the optical fiber is missing and there is a comprehensive service bearer requirement, it can pass the E-BAND microwave. The bandwidth advantage is rapidly deployed to establish a leading brand and attract more high-value customers.
Figure 4. Main four application scenarios of E-Band microwave
E-Band spectrum is currently open in 47 countries around the world. E-Band microwave has been deployed in Europe, the Middle East and other regions. Huawei has successfully commercialized 40 E-band microwaves around the world. However, E-band microwave is still in the experimental stage in China. Recently, China Mobile and Huawei established the nation's first E-Band trial office on Beijing Mobile's existing network. They have completed E-Band physical links, service testing and reliability verification, providing detailed experimental data and technical evaluation for spectrum opening. . At present, the trial office carries the LTE service of the existing network and the PTN hybrid group protection ring network to provide high quality and large bandwidth guarantee.
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