hed Fallback Voice over LTE Single Radio Voice Call Continuity 14.6 Summary References 14.1 Introduction LTE radio is designed for the packet connections without any support for circuit switched (CS) connections. Therefore, other voice solutions for voice service are required instead of the traditional CS voice. The voice service is important from the operator revenue point of view even if the share of voice traffic from the data volume point is very low. Every single LTE- capable smartphone needs to have a solution for offering high-quality voice connection. The different voice options including CS fallback and voice over LTE (VoLTE) are presented and the optimization is discussed in this chapter. Section 14.2 illustrates the timing and the main differences of the voice options. Section 14.3 presents CS fallback and Section 14.4 VoLTE solution. The handover from VoLTE to CS voice is called single radio voice call continuity (SRVCC) and is discussed in Section 14.5. The chapter is summarized in Section 14.6. Voice Options for LTE Smartphones The first LTE smartphones used dual radio solution where the terminal included two parallel radios: one for CDMA voice and another for LTE data. It looks like two separate terminals LTE Small Cell Optimization: 3GPP Evolution to Release 13, First Edition. Edited by Harri Holma, Antti Toskala and Jussi Reunanen. © 2016 John Wiley & Sons, Ltd. Published 2016 by John Wiley & Sons, Ltd. LTE Small Cell Optimization Dual radio CDMA + LTE CS fallback VoLTE VoLTE with SRVCC Figure 14.1 Availability of different LTE voice solutions from the network point of view. Such a solution is simple from the network point of view since no network interworking is required. The dual radio has the customer benefit that simultaneous CS voice and LTE data are available. The drawback of the dual radio is the complexity from the device point of view since more radio components are required increasing the cost, size and power consumption. The dual radio approach has been used only by the CDMA operators.