5G networks need to overcome three major barriers to large-scale commercial use

Although 5G licenses have been issued, the commercial preparations for 5G networks are not yet complete, and there are still a series of challenges to be solved. The author believes that the current commercial use of 5G networks faces three major challenges, namely 5G base station power consumption, 5G indoor coverage, and the reliability of the 5G core network service-oriented architecture.

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Smart operation can reduce the actual operating power consumption of 5G base stations

Base station power consumption is mainly composed of RF power consumption and computing power consumption. Both of these parts of 5G base stations are much higher than 4G base stations, resulting in the overall power consumption of 5G base stations being much higher than that of 4G base stations. In terms of RF power consumption, the Sub 6GHz single-carrier bandwidth defined by 3GPP can reach up to 100MHz. To ensure a certain power spectrum density, the Sub 6GHz 5G base station transmission power is generally 200W, while the LTE FDD base station transmission power is generally 2´20W or 2´40W. Considering that the power amplifier efficiency of the two is comparable, the RF power consumption of 5G base stations is much higher than that of 4G base stations.

In terms of computing power consumption, Massive MIMO is the core technology of 5G. Sub 6GHz mainstream base stations generally use 64 channels, which is much higher than the 2 or 4 channels of LTE FDD base stations. The sharp increase in the number of channels and carrier bandwidth makes the digital signal processing calculation of 5G base stations much higher than that of 4G base stations, resulting in a significant increase in the computing power consumption of 5G base stations. According to China Telecom's actual measurement of the current mainstream equipment in the industry, the full-load power consumption of a 5G single station is about 3.5KW, and the half-load power consumption is about 2.8KW, which are 3.2 times and 3.6 times that of 4G respectively. According to the statistics of the current network, the electricity cost of base stations accounts for about 15~20% of the operating cost of mobile networks. Therefore, the large-scale deployment of 5G base stations will bring severe challenges to the operating cost control of mobile networks.

The original power consumption of base stations is determined by system architecture design and chip integration, while the intelligent operation of mobile networks can reduce the actual operating power consumption of base stations. China Telecom found through actual measurements that the basic power consumption of 5G AAU (i.e., the power consumption of equipment under no-load conditions) reached 650W, accounting for 64% of the full-load power consumption, which shows that there is a large room for energy saving in both product development and network operations. In terms of network operations, China Telecom has proposed a 4G and 5G multi-band integrated energy-saving solution based on AI and application perception.

This solution is based on the premise of ensuring user experience, comprehensively considering the resource usage and energy consumption level of 4G and 5G networks in each frequency band, and reasonably scheduling various applications through AI algorithms to carry them on the appropriate network, reducing the load of high-energy-consuming base stations across the entire network, and then the base station will perform various levels of energy-saving measures such as symbol shutdown, channel shutdown or cell shutdown according to the load situation, so as to effectively reduce the overall energy consumption of the mobile network. The proposal of this solution is based on China Telecom's judgment on the future evolution of the mobile network, that is, 4G and 5G will coexist for a long time, 5G will not replace 4G, and 5G may also be deployed in low frequency bands in the form of base stations with low channel count and low transmission power. Therefore, operators can consider the multi-band integrated networking and energy saving of 4G and 5G in the long run.

The technical basis of this solution is the standard project "Study on Application Awareness Interworking between LTE and NR" led by China Telecom in 3GPP, that is, 4G and 5G interoperability based on application awareness. The 4G and 5G multi-band integrated energy-saving solution based on AI and application awareness can give full play to the respective advantages of 4G and 5G multi-band networks, regulate network load from a higher level, and control the power consumption of base stations across the network at a reasonable level while ensuring user experience, thus realizing the intelligent operation of 4G and 5G integrated networks.

Active + passive solution solves 5G indoor coverage problem

According to the current network test, the outdoor propagation loss of the 3.5GHz band is about 9dB higher than that of the 1.8GHz band, and the building penetration loss is about 5dB higher, so the comprehensive loss of outdoor penetration into the indoor is about 14dB higher. Based on the above data, the outdoor macro base station coverage indoor solution in dense urban areas is calculated (penetration loss 25dB). The planned station spacing of 3.5GHz NR with edge uplink rates that meet the standards of 1Mbit/s, 2Mbit/s, and 10Mbit/s is 1/2 of the planned station spacing of 1.8GHz LTE with the same standard. Although the actual station spacing in dense urban areas is smaller than the planned station spacing of 1.8GHz LTE with the standard of 1Mbit/s, it still does not meet the planned station spacing requirements of 3.5GHz NR (New Radio, i.e. 5G new air interface) with the standard of 1Mbit/s.

At the same time, the co-site test results show that the indoor deep coverage of the 1.8GHz LTE macro station in the direction of its antenna main lobe is better than that of the 3.5GHz NR macro station, while the indoor shallow coverage of the 3.5GHz NR macro station is better than that of the 1.8GHz LTE macro station, and the performance is more even on each floor. In general, NR indoor shallow coverage can be solved by co-deploying 3.5GHz NR macro stations with 1.8GHz LTE macro stations, while NR indoor deep coverage is difficult to solve with 3.5GHz NR macro stations, because the current site spacing does not meet the requirements, and it is extremely difficult to encrypt outdoor sites. In order to solve the NR indoor deep coverage, China Telecom will return its attention to indoor solutions.

Because the existing passive indoor distribution network cannot support the 3.5GHz frequency band, and because the cost-effectiveness of passive indoor distribution in supporting multiple channels is low, 3.5GHz NR indoor coverage is generally solved by building new active indoor distribution. From the perspective of 4G commercial use, the mainstream product in the industry is distributed active indoor distribution, which has high capacity but high cost. The cost is about 1.3 times that of single-stream passive indoor distribution (hotels, etc.), which is not suitable for medium and low traffic scenarios. To this end, China Telecom has proposed a comprehensive 5G indoor coverage solution for medium and low traffic scenarios, which reduces the construction cost of indoor coverage as much as possible while ensuring user experience. The comprehensive 5G indoor coverage solution for medium and low traffic scenarios is a series of solutions, mainly including 5G active + passive solutions and 5G active indoor distribution solutions based on open reference designs.

The 5G active + passive solution is to connect multiple passive antennas to the 5G active indoor RF remote unit, expand the coverage of a single RF remote unit, reduce the density of RF remote units, and thus reduce the overall cost of the indoor system. According to preliminary tests and conservative estimates, in the scenario of hotels, the 5G active + passive solution can save more than 20% of the comprehensive cost compared with the pure active solution.

The 5G active indoor distribution based on open reference design is jointly developed by China Telecom, its friends and partners under the O-RAN framework. At the O-RAN Open Industry Forum at MWC19 Shanghai this year, three domestic operators jointly released a white paper on the open reference design of 5G small base stations, and China Telecom released the industry's first 3.5GHz 5G active indoor distribution RF reference design. The development of the "public version" reference design helps equipment manufacturers converge chip and device selection to form economies of scale and reduce device costs. At the same time, it avoids a large amount of repeated research and development by equipment manufacturers, reduces overall research and development investment, and can also attract more small and medium-sized enterprises to participate in 5G research and development through the decoupling of functional components, thus prospering the 5G ecosystem.

Improving the reliability of 5GC service-oriented architecture by taking steps

Drawing on the technical concepts of cloud computing, virtualization, cloud native and microservices in the Internet industry, 5GC adopts the SBA service-oriented architecture based on NFV. Compared with the EPC using point-to-point closed protocols, its advantages include easy modifiability, scalability, reusability and openness. However, as distributed software, 5GC has the disadvantages of complex architectural reliability design requirements, and the hardware failures, network delays and clock synchronization in the distributed environment are complex and cannot be fully simulated and tested in the laboratory. Although there is no specific live network data to prove it, it can be foreseen that the 5GC system finally delivered to the operator will have more software problems that need to be discovered and repaired after going online, which is very different from the EPC that has undergone strict factory testing and operator networking testing. Therefore, in order to ensure that the availability of 5G services is not lower than or even higher than 4G, operators face great challenges.

To meet the above challenges, operators should have the following DevOps capabilities. First, fault discovery and recovery, which means timely discovery and rapid recovery of faulty nodes to ensure continuous service availability; second, root cause finding and resolution, which means performing root cause analysis in a distributed environment after the event, finding the problem, and developing a solution; and finally, software modification and updating, which means modifying the problematic software and reintegrating, delivering, and deploying it to eliminate the subsequent impact of software problems.

Currently, operators lack experience in the operation and maintenance of service-oriented architectures. Therefore, a "step-by-step" strategy is recommended: in the near term, network construction will be mainly carried out in a vertically isolated manner by supplier, and 5GC maintenance will also be mainly carried out under the guidance of suppliers using special tools; in the medium and long term, in order to improve resource utilization and operation and maintenance efficiency, after accumulating experience, a three-layer decoupled horizontal layered approach will be gradually promoted for network construction, and 5GC maintenance will mainly rely on the operator's own operation system and common tools across suppliers.

China Telecom is currently conducting experiments and verifications in this regard. It has implemented the NFVO function defined by ETSI through the self-developed eMANO system, and has collaborated with VIM and VNFM to achieve the orchestration and automated deployment of 5GC in the test network. In the future, third-party tools will be further introduced to support CI/CD and continuously optimize the software update process. In addition to improving the operation and maintenance tools, more importantly, China Telecom will also learn from the DevOps concept to optimize the operation and maintenance system, cultivate service-oriented architecture software maintenance talents, and build NFV production and maintenance pipelines to meet the various challenges of the 5GC service-oriented architecture.

5G has undertaken the important tasks entrusted by the state, such as strengthening the country's network and upgrading the industry. The early issuance of 5G licenses represents the country's determination to accelerate the pace of 5G commercialization. Although the commercial use of 5G networks still faces three major challenges, through the joint efforts and full cooperation of all parties, I believe that these challenges will eventually be gradually resolved in the commercialization process. At the same time, we must also face up to the price that must be paid to lead the development of a new generation of communication technology. I hope that China Telecom's pioneering work in the 5G field can effectively help achieve the goal of strengthening the country's network and upgrading the industry as soon as possible.