On May 15, 2014, Huawei and HKT released the commercial VoLTE network in Hong Kong. This was the world's first VoLTE network complying with 3GPP Release10 and supporting enhanced Single Radio Voice Call Continuity (eSRVCC). Because of its extremely smooth handovers, users cannot perceive a voice call handover from an LTE network to a 2G or 3G network. For this project, Huawei integrated and maintained service provisioning and charging interfaces and retained all traditional services on the live network, fully demonstrating the fast integration and deployment capabilities of VoLTE. 

VoLTE fully leverages spectrum resources and provides excellent and diversified voice services. Therefore, it has been recognized as an industry-leading voice solution in the LTE era. To compete in the Hong Kong mobile market and acquire more customers, HKT took the initiative to deploy the VoLTE network while most of other carriers waited to act. 

A New Era of Voice Services

Although Hong Kong has a population of only 7 million, the penetration rate of smart terminals is high and the competition in the mobile market is incredibly fierce. Five mobile carriers have deployed 10 LTE networks with a user penetration rate exceeding 220%. The average monthly traffic of a single user is 716 MB. To get ahead in the saturated mobile market, users must be provided with comprehensive and high-quality LTE services.

In May, 2014, HKT ushered in a new era of voice services and became the first carrier providing VoLTE services in Hong Kong. HKT service centers offered the Samsung Note3 supporting VoLTE. Existing Samsung Note3 users could enjoy a new voice experience by simply upgrading software for free. In addition, HKT was the world's first carrier that provided VoLTE services supporting eSRVCC. This marked the formation of a complete industry chain from network devices to terminals and microchips. 

HKT used VoLTE to provide a noticeable difference in experience and initiated a series of effective "VoLTE Myth" themed marketing campaigns. On its official website, HKT not only introduced new VoLTE services highlighting high-speed voice connection, clear video calls, and instant handover between voice and video, but also provided detailed upgrade guides for mobile phones. To ensure a smooth evolution to 4G, HKT continued to use the "Ultimate Mobility" package plan, which included voice and SMS charges, this stably maintained revenue, and provided unlimited voice and SMS traffic for users. Superior services at the same price will motivate users to migrate towards VoLTE. 

Since its launch on May 15, 2014, more than 1000 subscribers daily have become VoLTE users. While the number of VoLTE users was growing rapidly, stable VoLTE operation allowed the call completion rate to reach an average of 99.3%, indicating that VoLTE performance was much better than that of traditional CS networks. 

Requirement Surveys and Network Deployment Completed Within 12 Months

HKT and Huawei launched the VoLTE project and became the first to commercially deploy VoLTE networks. They spent only 12 months completing the VoLTE deployment on the entire network and announced that VoLTE network was capable of providing services on November 11, 2013. In the six months that followed, HKT performed interworking tests for terminals in early stages and implemented commercial uses of the first VoLTE/eSRVCC terminals in the industry, which were released on May 15, 2014. Even without previous experience, HKT completed end-to-end VoLTE deployment, and spent 12 months completing requirement surveys, network design, and network deployment. Reducing VoLTE impact on the live network and converging user databases certainly proved to be a worthwhile experience. 

Reducing VoLTE Impact on the Live Network

Minimizing VoLTE impact on existing CS networks was a key factor in quickly deploying VoLTE. HKT used the SRVCC-IWF Proxy solution and deployed the SRVCC-IWF Proxy on one or several MSC, avoiding a large-scale MSC upgrade on the entire network in its early stages. Reconstructing existing CS networks was previously difficult, time-consuming, and costly, and could interrupt ongoing services. This solution addressed these problems and implemented VoLTE deployment. 

Converging User Databases

To ensure that 2G or 3G subscribers did not need to change cards or cell phone numbers, and keep service subscription data consistent, carriers were required to converge the original Home Location Register (HLR), System Architecture Evolution-Home Subscriber Server (SAE-HSS), and newly added IMS-HSS. In addition, the delivery and management of user data should be simplified. Based on service development, HKT planned to implement user database convergence in three steps. In the preliminary stages of LTE deployment, HLR and SAE-HSS data were converged. During VoLTE deployment, the shared supplementary service data of HLR and IMS-HSS were automatically synchronized to meet the requirements for service consistency. Finally, the HLR, SAE-HSS, and IMS-HSS databases were converged through further optimization. User databases were converged by having the public database use shared storage, in which only a profile of each user was saved.

Providing Seamless Service Experience

LTE coverage cannot be achieved overnight. Providing continuous voice services in LTE coverage holes and inheriting traditional services through smooth migration were essential to VoLTE development. HKT implemented seamless transition from 4G to 3G voice services and inherited all traditional services using eSRVCC. 

eSRVCC Implementing Seamless Voice Call Handover

HKT used LTE 1800 MHz as a coverage layer and used LTE 2600 MHz as a capacity layer. Although HKT had laid a solid foundation for LTE network coverage, 3G networks had advantages over LTE in bustling business centers and densely-populated buildings in Hong Kong. HKT used the Huawei eSRVCC to ensure voice call continuity evolving from an LTE network to a 3G network and to provide excellent user experience. According to test results of the eSRVCC on the live network, average end-to-end call interruption delay during a handover was less than or equal to 230 ms and users were not able to distinguish handovers. 

Inheriting All Traditional Services

HKT provides diversified CS services for 1.6 million subscribers. Special mobile value-added services, such as ringback tones and voice mails have long been used by certain user groups. HKT must ensure that after the migration from 2G or 3G to 4G, usage habits and experience of traditional services remained unchanged. Based on an in-depth analysis of priorities of 20 types of services, voice scenarios of 300 types of services, and 1000 types of charging policies, HKT conducted detailed network planning and design for VoLTE deployment. After completing tests and verification, HKT inherited 29 traditional services, including 12 common supplementary services and 17 special value-added services, ensuring the continuity of traditional services and inheritance of usage habits. 

Building A Better Future

HKT has maintained that VoLTE network deployment is only the first step. Interworking with VoLTE networks of other Hong Kong and international carriers, as well as roaming are the next step. HKT has planned to transfer RCS services "KingKing" based on proprietary platforms onto standard IMS platforms, and implement standardization and reconstruction of RCS. In the long run, HKT will explore IMS monetization using new technologies such as Communication as a Service (CaaS) and web real-time communication (WebRTC) to open network communication capabilities to third-party applications and devices. Mobile value-added services are optimized by third-party developers to meet the growing requirements of the Hong Kong mobile market.