Introduction to 80GHz E-Band Microwave Applications

On December 4, the Ministry of Industry and Information Technology officially issued TD-LTE 4G licenses to China Mobile, China Telecom, and China Unicom, marking China's official entry into the 4G era. According to a report by the third-party analysis firm GSMA Intelligence, by the end of 2017, over 128 countries worldwide will have deployed approximately 500 LTE networks. While 4G provides greater bandwidth and a better mobile internet experience, it also poses challenges to operators' mobile backhaul networks.

With the issuance of domestic 4G licenses, LTE networks will be deployed rapidly. However, LTE base stations have smaller coverage areas and require much higher deployment density than GSM and 3G base stations. LTE construction will face a large number of new site requirements, and some new sites lack fiber resources. It is estimated that about 20% of new sites in China will have insufficient fiber resources, putting pressure on LTE base station service backhaul and PTN fiber network ring formation. Microwave, as an important mobile backhaul solution, can replace or supplement fiber to solve the fiber shortage problem and enable rapid LTE network deployment. However, spectrum resources in traditional microwave bands (6–42GHz) are strained, and channel spacing is narrow (the current maximum channel spacing in China is 28MHz), making it difficult to meet the large bandwidth requirements of LTE base stations on the backhaul network. In this context, the industry has turned its attention to E-Band microwave, which can provide ultra-large bandwidth. What is E-Band microwave, how much bandwidth can E-Band microwave transmission provide, and what application scenarios is it suitable for?

Introduction to E-Band Microwave

E-Band RF channel configuration

In 2000, ITU-R and ETSI standard organizations defined the allocation of high-frequency bands 71–76GHz and 81–86GHz for microwave, which later became commonly known as E-Band.

Figure 1. E-Band RF definition

Meanwhile, industry standards bodies ITU-R, FCC, and CEPT have made relevant recommendations for E-Band RF channel configurations, with channelization primarily based on 250MHz and 1.25GHz. It is precisely because of the 250MHz or even larger channel spacing resources that E-Band microwave can provide greater bandwidth at a single frequency point. Currently, the industry's maximum single frequency point bandwidth reaches 2.5Gbps, and in the future it can even provide 10G over-the-air transmission bandwidth.

Figure 2. E-Band RF channel configurations defined by ETSI and FCC

E-Band Microwave Transmission Distance

Microwave transmission distance is simultaneously affected by free-space loss, atmospheric loss, and rain attenuation. Next, we will focus on analyzing the transmission performance of E-Band microwave:

Free-space loss:

The free-space path loss at 71GHz–76GHz is approximately 130dB, and at 81GHz–86GHz it is 131dB. This value is generally higher than the free-space loss in traditional bands, which directly results in E-Band transmission distances being much shorter than those of other traditional bands.

Atmospheric loss:

In the atmospheric window diagram below, it can be seen that within the 71GHz–86GHz range, atmospheric attenuation on E-Band is very low, essentially less than 0.5dB/km.

Figure 3. Atmospheric attenuation diagram

For microwaves above 10GHz, rain attenuation directly limits transmission distance. For E-Band microwave, under very severe conditions such as tropical rainforest rainfall (100 mm/hour), rain attenuation is around 30dB/km, but this generally only occurs over short periods. During network design, margin can be reserved to accommodate weather variations. Some manufacturers also support adaptive modulation: by lowering the modulation mode to adapt to weather changes, combined with QoS configuration, high-priority services can maintain normal communication, thereby improving network reliability.

E-Band is essentially unaffected by clouds and fog. Even dense fog with visibility of 50 meters and a density of 0.1g/cubic meter only causes attenuation of 0.4dB/km on E-Band, which is essentially negligible.

Based on actual test results, E-Band microwave can operate stably within a transmission distance range of 2–3km.

E-Band Microwave Application Scenarios

Compared with traditional bands, E-Band has abundant frequency resources and supports larger bandwidth than traditional bands, with single frequency point bandwidth reaching 2.5Gbps.

Table 1. Comparison between traditional bands and E-Band

Based on the analysis data above, E-Band microwave is highly suitable for large-bandwidth transmission application scenarios, meeting LTE backhaul network bandwidth requirements. Combined with China Mobile's business needs, we can broadly categorize the following four scenarios.

1. PTN access layer network completion and ring formation:

Ring networks improve the reliability and disaster recovery capability of the backhaul network. Operators typically have certain requirements for network ring formation rates, especially China Mobile, which pursues high quality. However, due to various practical difficulties, some sites lack fiber resources, and a considerable proportion of access layer networks still face ring formation pressure. E-Band microwave can serve as a fiber replacement, working with existing PTN equipment for ring formation and network completion (currently access ring bandwidth is 1Gbps), solving the problem of PTN networks being unable to form rings due to fiber shortages, providing ring network protection capability for PTN networks, and enhancing transmission network reliability.

2. LTE edge base station access:

In densely populated urban areas, a single base station (in S333 configuration mode) has a bandwidth demand of over 900Mbps. In short-distance scenarios of 1–3Km, E-Band microwave has abundant spectrum resources and can be used to solve the problems of strained traditional microwave band resources and limited transmission bandwidth, serving as service access for edge LTE base stations, addressing fiber shortages at some new sites, and enabling rapid LTE base station deployment.

3. High-value customer dedicated lines:

For services requiring bandwidth above 1Gbps, such as data service interconnection dedicated lines and enterprise link leasing, some buildings cannot be deployed due to difficulties in fiber installation, high costs, and long lead times. E-Band microwave can serve as a fiber replacement between IP/MPLS routers or L2 switches, solving fiber and deployment difficulties.

4. Integrated service access:

E-Band microwave provides 2.5G large bandwidth and can easily carry multiple services simultaneously, including base stations/Wi-Fi, high-value customers, and broadband. In scenarios where fiber is lacking and integrated service carriage is required, the large bandwidth advantage of E-Band microwave enables rapid deployment, thereby establishing a leading brand and attracting more high-value customers.

Figure 4. Four main application scenarios of E-Band microwave

E-Band spectrum has currently been opened in 47 countries worldwide. E-Band microwave has begun large-scale deployment in regions such as Europe and the Middle East, and Huawei has 40 successful commercial E-Band microwave deployments globally. However, E-Band microwave is still in the experimental stage in China. Recently, China Mobile and Huawei established the first E-Band trial site in China on the Beijing Mobile live network, completing E-Band physical link, service testing, and reliability verification, providing detailed experimental data and technical evaluation for spectrum opening. Currently, this trial site carries live LTE services and forms a hybrid protection ring network with PTN, providing high-quality, large-bandwidth assurance.

Source: C114 China Communication Network