By Jiang Kun
VoLTE can fully leverage the superior spectrum utilization of LTE to provide a superior voice experience. In fact, it's universally acknowledged as the ultimate voice solution for the LTE era. Compelled by fierce competition, HKT decided to act on VoLTE while most carriers were still talking.
A new era with VoLTE
Hong Kong is home to seven million people and even more smart devices, with a user penetration rate exceeding 220%. Average data consumption is a whopping 716MB per month. With five mobile operators and ten LTE networks in play, mobile competition is fierce. To stand out, carriers must ensure a superior user experience through the most comprehensive and highest-quality LTE service available.
In May 2014, HKT kicked off a new era of voice communication in Hong Kong with Voice over LTE (VoLTE), and became the first operator in the world to support enhanced single-radio voice-call continuity (eSRVCC), thus creating a complete ecosystem from network device to terminal to chip.
With VoLTE, HKT user experience is noticeably superior, a clear competitive advantage. A marketing campaign was also launched, centered on the theme "Not even a second more." HKT highlighted the advantages of VoLTE on its website, specifically its rapid and crystal clear connection. They also offered free switching between voice and video, and provided a detailed mobile phone upgrade guide.
To help subscribers switch to VoLTE seamlessly, HKT offered its "Ultimate Mobility 4G" bundle, which integrates voice and SMS service. The bundle provides unlimited voice and SMS service at a fixed price and does not charge additional fees for VoLTE. With the same price yet better services, HKT has encouraged many subscribers to migrate to VoLTE. Since May 15 of this year, there has been an average of 1000+ upgrades per day.
Despite the quickly increasing traffic, the VoLTE network has performed exceptionally. With a call connection rate of 99.3%, it's more reliable than the typical circuit-switched (CS) network.
Overall VoLTE deployment in 12 months
To assure that it was first-to-market with VoLTE, HKT turned to Huawei. It took a mere 12 months of joint effort for HKT to complete its overall VoLTE deployment, which was announced on November 11, 2013. Over the next six months, HKT finished interoperability testing of its network with devices, including a VoLTE/eSRVCC-enabled smartphone. Many E2E deployment challenges were met during this year-long process, but with considerable expertise in user database integration and minimization of legacy network impact, HKT and Huawei were able to resolve every issue.
Minimizing legacy operation
To achieve quick VoLTE deployment, impacts upon the current CS network had to be minimized. HKT adopted a single-radio voice-call continuity (SRVCC) interworking function (IWF) proxy solution, which allows SRVCC function deployment on one or more MSCs that act as SRVCC-IWF proxies, avoiding the need for large-scale MSC upgrade or transformation of the current CS network, which would be laborious, costly, time-consuming, and potentially disruptive. With SRVCC-IWF proxy, HKT was able to concentrate its resources and energy solely on the construction process for VoLTE.
Integration of user data
To help 2G/3G users migrate smoothly to LTE without changing their SIM or phone number, and to simplify the provisioning and management of user data, telcos must integrate the home location register (HLR) and system architecture evolution-home subscriber server (SAE-HSS) with the IMS-HSS. HKT planned to complete its user database integration in three steps. During LTE deployment, it completed the HLR/SAE-HSS integration. During VoLTE deployment, HLR/IMS-HSS service data was synchronized automatically to ensure the consistency of LTE and 2G/3G services. During the last stage, HKT finished integrating the three front-ends (FEs) – the HLR, SAE-HSS, and IMS-HSS, with all public data stored and shared, and a single profile for each user.
Seamless service experience
All-LTE coverage cannot be achieved overnight. To ensure continuity for voice and other services during switching between 2G/3G and 4G, eSRVCC was leveraged.
Seamless voice through eSRVCC
HKT uses 1800MHz for LTE coverage and 2600MHz for capacity. In Hong Kong's central business district, the high concentration of skyscrapers means that 3G networks still have advantages over LTE. To guarantee a seamless user experience, Huawei's eSRVCC technology was leveraged to ensure seamless switching between 3G and LTE. In fact, HKT's eSRVCC test results now show an E2E call latency of less than 230ms, which users can hardly perceive.
Complete inheritance of traditional services
HKT's CS network currently serves over 1.6 million subscribers. Local users subscribe to many mobile VAS's such as ring-back tone (RBT) or voice mail, so HKT must ensure that the user experience of these services is not degraded after LTE migration. Detailed network planning and design were carried out before VoLTE deployment, with 20 service priorities, 300 service announcement scenarios, and 1,000 billing policies analyzed. After this comprehensive and systematic process, HKT elected to migrate 29 traditional services, including 12 supplementary services and 17 exclusive Hong Kong VAS's. These measures enabled users enjoy their familiar services with a high-level experience.
Forging a better future
HKT regards its recent VoLTE deployment as merely the first step in a continuing journey. In the future, its VoLTE network will interconnect with local and global telcos, and enable roaming services of global telcos. HKT also plans to migrate one of its rich communication suite (RCS) services from its private platform to the IMS, and carry out RCS standardization.
HKT intends to monetize its IMS. Through communication as a service (CaaS) and web real-time communication (WebRTC), HKT can open its communications capabilities to third-party applications and devices. By leveraging the innovation of these third parties, HKT can better meet the growing demands for mobile VAS's in Hong Kong.