By Shwetha Vittal, Lead Engineer
Long Term Evolution (LTE) is heralded as the next big thing for mobile networks. It brings in promising technologies such as semi-persistent scheduling, transmission time interval (TTI) bundling, and high performance gains on Quality of end user Experience (QoE). In the end, the primary goal of LTE is to deliver ultra-high speed mobile broadband with peak data rates over 100 Mbps. However, in practical applications LTE is facing challenges to provide the same capabilities as a 2G/3G network during the initial stages of trial deployments and operators’ metered investment in broad network build out.
One of the key issues of LTE is the delivery of voice services. Voice remains the “killer application” for operators because it still accounts for a large portion of their revenue. Voice will continue to remain the dominant must-have service in the network for years, and despite the technical challenges of providing service over an all-Internet Protocol (IP) radio access network (RAN), voice is seen as a basic service by the consumer; in short, it is expected. However, voice service continuity is not guaranteed when a Voice over IP (VoIP) subscriber roams between the LTE coverage area and other wireless networks – and it is a significant challenge to deliver voice over LTE networks.
The industry is exploring and evaluating different possibilities to overcome the LTE voice issues. During this evaluation process two options are gaining significant momentum: Circuit Switched Fall Back (CSFB) and LTE VoIP-based Single Radio Voice Call Continuity (SRVCC). The latter is widely supported in the industry and has been recommended by the LTE OneVoice Initiative, which has the support of some of the world’s largest operators and network equipment providers and has been endorsed by the GSM Association (GSMA).
This paper focuses on designing the LTE-IMS (IP Multimedia Subsystem) network framework to support SRVCC with the Circuit Switched network by realizing the 3GPP Standard 23.216 V 8.6. 2009-12: Single Radio Voice Call Continuity (SRVCC) (Release 8). This architecture has great appeal to carriers with a robust IMS Core and both fixed and wireless component assets in order to facilitate a converged VoIP solution.
