Chengdu Telecom: Establishing a Good Reputation for 5G Coverage Through Precise Planning and Macro/Micro Coordination

After multiple phases of construction, the 5G network of Chengdu Telecom has achieved continuous outdoor coverage in urban areas and counties. In order to improve the depth of the coverage, increase 5G network availability and offer a smooth 5G user experience, Chengdu Telecom and ZTE set up an integrated project team to explore the construction of a 5G network with a strong reputation by focusing on key scenarios.

The project team took eight scenarios for a trial, including universities, high-density residential areas, high-traffic business areas, high-speed rails, subways, large stadiums, traffic hubs, and hospitals (Fig. 1). Considering the characteristics of different scenarios and macro sites, as well as the advantages of micro sites, the project team implemented innovative solutions such as precise planning & construction, macro-micro site coordination, and vertical networking and achieved a steady increase of the coverage, capacity, and offloading ratio of the 5G network. 

The integrated project team of Chengdu Telecom and ZTE put forward a five-step precise planning approach, i.e. requirement analysis, network evaluation, site survey, solution customization, and solution implementation.

—Requirement analysis: Analyze the network construction objectives, networking strategies, deployment scenarios, and site resources.

—Network evaluation: The 4G/5G multi-dimensional data is used to analyze the network structure, coverage and capacity. The network value is evaluated based on the number of MR reports, number of terminal access times, traffic data, offloading ratio and scope of VIP areas.

—Site survey: Site survey is carried out in accordance with service requirements, product features, network structure, and feasibility.

—Solution customization: In the scenario-based design phase, precise simulation, AI-based capacity prediction, and customized antenna pattern planning are required.

—Solution implementation: In the final closed-loop verification phase, the accuracy of the solution is enhanced through continuous iteration of measured data and correction of key planning parameters.

Based on the "five-step precise planning" approach, eight solutions have been developed in accordance with characteristics of each specific scenario.

Universities: Macro/Micro Coordinated Networking

As a high-traffic scenario, universities are of great significance for operators to develop users and build brand. To simultaneously enhance the network coverage and capacity for spots such as dormitory buildings and canteens, the project team conducted high-precision three-dimensional simulation in combination with correction by actual tests to accurately predict planning indicators, calibrate macro & micro coverage capabilities and form guidelines.  

In the A university project, the coverage rate in simulation is 99.23%, highly consistent with the rate of 99.48% in actual test after site deployment. In addition, the project team collected historical data for machine learning analysis of user perception in the existing network, and completed AI-based capacity prediction and capacity planning to improve user perception. For the communication guarantee during the fall opening in 2021, macro/micro sites were deployed at scale, and the drive test showed that the coverage rate was increased by 1.8%, the traffic by 133.09%, and the 5G traffic ratio by 8.5%.

Residential Areas: Horizontally-Installed Micro Sites and Spotlight Antennas for Macro Sites  

Complaints about weak 5G coverage, ratio of MRs with weak coverage and backflow traffic are the most prominent problems in residential areas. To solve the difficulty of deploying macro sites in residential areas, the team innovatively deployed micro sites and medium- and high-frequency macro sites to cover high-rise buildings.

The iMacro is installed horizontally to cover one side of building B. It can cover 30-40 floors vertically and 35-40 meters horizontally. The RRU works with large-angle spotlight antennas to cover high-rise residential building C. The 2.1 GHz band is used to cover one side of the building and the corridor to provide basic coverage whereas 3.5 GHz one side of the building to enhance capacity of high-value buildings if needed.

Commercial Buildings: 1+X SSB Solution for Macro Sites

There are a large number of commercial buildings with complex architecture in Chengdu. In the case of limited indoor investment, the 1+X synchronization signal and PBCH block (SSB) solution for macro sites can be used to rapidly enhance the in-building coverage. For the coverage of a 85.8-meter-tall, 22-story commercial building D, SSB 1+3 pattern is adopted. In the indoor corridor test, the coverage field strength is increased by 7.33 dB. In the indoor fixed-point test, the coverage field strength is increased by 6-8 dB, downlink traffic by 54%, and 5G traffic ratio by 6%. 

By December 2021, in areas where the 5G network is constructed by ZTE, SSB 1+X solution had been applied to 50% outdoor cells, and the number of 5G subscribers in the whole network had been increased by 9.46%, the traffic by 9.98%, and the distribution ratio by 1.66% with the SSB 1+X function enabled.

High-Speed Railways and Subways: Shared Network with 4G-5G Coordination

The train body signal penetration loss in high-speed railway scenarios is high. During the network planning for high-speed railways, the optimal distance from the rail to a site (normally 150-200 m) should be considered. Frequent handovers can be avoided by combining cells. Passenger-dedicated railway E connects the Southern Sichuan cities, and 2.1 GHz 20 MHz NR + 20 MHz LTE solution is used to quickly achieve 4G/5G dual-layer network coverage at low cost. A total of 81 2.1 GHz NR sites with an average inter-site distance of 732 meters are planned based on standards of an uplink edge rate of 2 Mbps, a downlink edge rate of 50 Mbps and a -110 dBm field strength.

Subway scenarios, including station halls, platforms, office/equipment areas, and tunnels, are characterized by a complicated environment, high construction costs, intensive passenger flows, and heavy traffic requirements. The existing DAS and POI solutions cannot support the construction of the 3.5 GHz network. The network planning should not only meet the 5G offloading requirements, but also release the suppressed 4G traffic, so as to improve the spectrum efficiency. Therefore, it is urgent to build a network co-constructed and shared by China Telecom and China Unicom. In this case, the carrier sharing solution of 1.8 GHz 40 MHz LTE + 2.1 GHz 40 MHz NR is adopted, saving the space in the BBU equipment room, as well as increasing the 4G resource utilization rate and traffic. With the deployment of 2.1 GHz 40 MHz NR, evolution to 5G NR is thus achieved and user perception improved, setting a leading 5G brand image for both the subway company and operator.

Traffic Hubs and Large Stadiums: QCells with External Antennas

Open space scenarios like the waiting hall of traffic hub and the grandstand at a stadium demand extremely high capacity. The interference can be reduced and the capacity be increased by deploying QCells connected with external directional antennas. In the case of the waiting hall of the Chengdu high-speed railway station F, the CL dual-mode equipment is replaced by the 4G/5G dual-mode QCell equipment, achieving both 5G network deployment and 4G network capacity expansion. The walk test shows that the average field strength reaches -81.33 dBm and the average downlink rate of 650.46 Mbps. For the large 18,000-seater capacity stadium G, the solution of QCells with beamforming antennas is adopted for the grandstand to precisely control the inter-cell interference. In this case, the average field strength reaches -76.8 dBm, and the average downlink rate of 625 Mbps.

Smart Healthcare: Intelligent 5G Indoor Distribution Solution

To cover hospitals with 5G, teaching buildings, outpatient buildings, and inpatient buildings are the focus. These scenarios feature heavy traffic all the year round, a wide variety of services, and great difficulty in access and later maintenance. Especially, the impatient buildings have a complicated environment and diversified new service applications, such as immersive visiting system, intelligent robot inspection and long-distance expert consultation. It is necessary to consider the dual-mode 4G/5G network for better coverage and capacity performance.

The 4G/5G dual-mode QCell equipment is used to replace dual-mode CL equipment to ensure that the 4G network quality remains unaffected. The 5G network is mainly dedicated to smart medical services. One pRRU covers three wards on one side, and the number of cells can be flexibly planned according to the user distribution and service characteristics. The average 5G field strength and average downlink rate of the impatient building are -71.63 dBm and 890.7 Mbps respectively. With the help of 5G network, Chengdu Hospital G takes the lead in implementing smart healthcare.

By December 2021, the 5G traffic offload ratio of the areas where the 5G network is constructed by ZTE had increased to 30.55%.

In the future, both parties will continue to strengthen cooperation in communication guarantee for the university games, 5G coverage portrait of buildings, refarming 2.1 GHz for 5G, prediction and improvement of 5G traffic offload ratio, so as to improve the networking performance and user experience for key scenarios.