IoT NTN for Voice Services: Architectures, Protocols, and Challenges

In order to provide voice services with full coverage and high disaster tolerance, satellite communication-based voice solutions utilizing private protocols were proposed, which however cannot be integrated with existing terrestrial voice solutions specified by the 3rd Generation Partnership Project. To overcome this issue, we propose two voice solutions by involving over-thetop (OTT) platform and enhancing Internet protocol multimedia subsystem (IMS), respectively, on the basis of Internet of Things non-terrestrial networks (IoT NTN). The former adopts the advanced hybrid exit linear prediction (AHELP) speech coding and enhanced protocols to adapt to the narrowband and high-latency characteristics of IoT NTN. The latter improves the existing quality of service (QoS) mechanism from the control plane and user plane to achieve an end-to-end QoS guarantee. In addition, a novel Session Initiation Protocol (SIP) signaling adapted to IoT NTN is designed to shorten the calling establishment time, and an NTN voice function is introduced to transform the proposed SIP signaling into typical SIP signaling. A quantitative performance comparison is made between the proposed voice solutions based on OTT and improved IMS through field testing. Finally, some potential trends and challenges for future research are highlighted.