System aspects of the 3GPP evolution towards enhanced voice services

The Enhanced Voice Services (EVS) codec was standardized by 3GPP in 2014. This codec offers significant gains in voice quality, efficiency, channel error robustness over any other existing speech codec and far better music quality. Operators run voice services on a large installed base of 3GPP Circuit-Switched (CS) 2G (GERAN) or 3G (UTRAN) radio networks. These networks offer mobile voice service either as HD voice using the AMR-WB codec, or as traditional narrowband (NB) voice service, based on the AMR codec. Voice over LTE (VoLTE) is currently being deployed throughout the world with HD Voice. The EVS codec will be first introduced as a straightforward VoLTE upgrade. It is also expected that EVS will be deployed over 3G CS networks. This paper describes system aspects relating to EVS codec introduction in VoLTE and CS networks as well as interworking and mobility with legacy systems and services.