Power grid is a basic energy industry and essential for people's livelihood. Power grid intelligence, known as Smart Gird, is a pillar of China's national energy strategy, and power communication network is at the core of Smart Grid.

5G Brings New Dawn 
In recent years, China has developed rapidly in the power grid domain. Many technologies and businesses such as ultra-high voltage grid, new energy, distributed energy, charging piles, smart sensors and meters have developed vigorously. This also puts higher requirements for power grid communication and control network.
Private power grid communication network built by the power grid operator is the traditional solution, and has the major problems of high network costs and insufficient coverage. For example, the direct access rate of optical fiber at the power distribution network site is less than 20%, and the self-built wireless private networks (such as WLAN, 230 MHz and 1800 MHz wireless private networks) are only deployed in a small number of areas with limited bandwidth and coverage.
The operator’s public network is an important means to carry services of the power grid communication network. In particular, a public wireless access network is widely used to compensate for the insufficient coverage of the power grid network. But the operator's wireless network designed primarily for personal communications, is a closed system, and it does not take into account the service requirements of customers in vertical industries such as the power grid. For example, the traditional public network can hardly meet the vastly different network performance requirements of diverse power grid services or afford flexible solutions to implement end-to-end service partitioning and strict isolation management. How to provide a secure, flexible, customizable, and multi-service solution for public grid network is a difficult problem. 
5G brings a new dawn for the public grid network. It has three major scenarios (eMBB, uRLLC, and mMTC), and provides a network slicing architecture that allows a physical network to be sliced into multiple virtual private networks to serve different customers or services. Thus, it is possible for a public network to serve a large number of public/private customers simultaneously. Strengthening the research on 5G, accelerating the commercial use of 5G and building innovative vertical solutions have become the focus of 5G industry. 5G smart grid has also become a leading industrial application of 5G with its large-scale industry, high technical requirements, and typical services.

ZTE 5G+ Smart Grid Solution
As a pioneer in the 5G industry, ZTE has been making continuous efforts in bringing innovation to 5G products and solutions in recent years. Addressing the problems related to the power grid private network, ZTE has successfully launched its 5G+ smart grid solution based on 5G public network together with operators and power grid partners. Based on the normal 5G soft slice virtual network, ZTE's 5G+ smart grid solution introduces physical resource block (PRB), intelligent scheduling, intelligent adaptive modulation and coding (AMC), key link redundancy and reliability enhancement, local traffic offloading and EdgeQoS functions to ensure enhanced security, low latency and high reliability of the power grid services carried by the public network. At the same time, intelligent scheduling control and traffic offloading are used to maximize the efficiency of the 5G network system. ZTE's smart grid virtual communication network (Fig. 1) carries power services based on the operator's 5G public network, and provides key function settings for power services.

End-to-End Slicing for Power Services of Different Partitions
Network slice is a major architecture innovation of the 5G network. By using the network virtualization technology and service-based architecture (SBA), it can implement end-to-end system orchestration and resource scheduling of the 5G network, and segment a physical network into multiple virtual end-to-end networks. The devices, access, transmission, and core networks in each virtual network are logically independent.
The 5G network slicing allows the smart grid to customize slices for services of different partitions with dedicated sets of parameters. Different slice domains are isolated to achieve the security requirements of a power grid customer, so that one network can carry services of multiple partitions, share the overall resources, and reduce construction costs. 

PRB Hard Slicing for Power Production Services Requiring High Security
In the 5G system, air interface resources are relatively scarce. The conventional 5G public network slices usually use soft slice management to manage and schedule the system resources. 
All slices and services share the whole radio block (RB) resources, and when resource conflicts occur, the RB resources are scheduled according to the 5QI priorities of slices and services.
Soft slicing at the air interface can meet the basic requirements of most conventional power grid information management domain services, but power production and control services need more strict network performance. For example, the power grid real-time monitoring and control services need absolute resource availability and superior priority guarantee to ensure a latency of 10 ms and a reliability of higher than 99.99%. 
How to further modify the 5G resource scheduling mechanism for critical power grid services based on the conventional 5G network slices is a practical requirement. ZTE innovatively proposes the PRB hard slicing solution, which guarantees the reliability of the slicing service by reserving certain PRB resources for a specific slice. PRB resource reservation used for power production services ensures that these services have the highest resource priority and strict isolation. For other non-production services, the common soft slice-based PRB sharing mode can be used so that all network slices can share the resources to maximize system resource utilization.

Intelligent Scheduling Algorithm for Optimal Multi-service QoS
The power grid system is a multi-service system, and each service has different requirements for transmission bandwidth, latency, jitter and reliability. It is necessary to further optimize the system QoS to ensure the network can transport multiple grid services well at the same time.
For this, ZTE has introduced precise network control technologies. Based on the conventional 5QI service scheduling, the network introduces a hierarchical service scheduling mechanism based on service QoS requirements, and uses intelligent AI algorithms to achieve dynamic parameter optimization for different services and wireless environments. For example, for electrical differential protection with extremely high requirements (20 ms latency and 99.999% reliability), it provides a special policy of air interface scheduling on the physical layer and MAC layer. For services with 50 ms latency @100 Mbps in the production area and shared management area, the network E2E latency control and service priority-based scheduling are strengthened. For services purely requiring 99.999% high reliability, it uses duplicated PDCP sessions, lower modulation and coding scheme (MCS) value, and pre-scheduling technologies to strengthen the system concurrent scheduling ability.
Through the above-mentioned dynamic scheduling solution, services with significantly different technical features coexist in the same network or even in the same slice environment, solving the problems of public network in transporting power services.

ZTE NodeEngine Enabling Flexible Deployment of Customized Local Services
To meet the requirements of building some potential independent core network elements and handling some local services for a grid operator, ZTE provides a customized core network system and its innovative NodeEngine solution. By embedding computer and storage resources in gNodeB, the NodeEngine makes gNodeB an edge computer node that facilitates local traffic offloading in power grid network and shortens the service delivery path from 5G public network to the grid private network. At the same time, the NodeEngine provides powerful support for value-added local service processing and developing the grid's self-owned edge cloud services. 

ZTE 5G+ Smart Power Grid Practice
In order to promote the implementation and verification of the 5G+ smart power grid solution, ZTE, China Mobile and China Southern Power Grid jointly built the industry's largest integrated test filed for the 5G smart grid in the Nansha region of Guangzhou. The test network has a scale of more than 100 base stations. All the typical power grid services will be tested and commercially deployed on a large scale.
The test network has already been constructed, and the virtual power grid slices have been successfully deployed on China Mobile’s real commercial 5G public network. The test team has finished the basic 5G+ smart power grid network function and performance test, and is carrying out a large-scale commercial deployment of real power grid services that run concurrently. 44 categories of key power grid services have been successfully deployed, including microsecond-level high-precision timing, millisecond-level differential protection, synchronous phasor measurement unit (PMU), 5G+ power distribution automation, and 5G+ amphibious robot inspection. According to the project plan, tests on all 54 categories of power grid services will be completed in 2021, and a complete 5G smart grid application solution and a clear slice business model will be formed based on the trial, providing a successful reference for the subsequent large-scale commercial application of 5G in the power grid industry.