VoLTE SRVCC optimization as interim solution for LTE networks with coverage discontinuity

This paper is focused on the mobile networks with deployment of LTE offering Voice over LTE (VoLTE) services and existing WCDMA layer - in which voice call continuity is ensured through the Single Radio Voice Call Continuity (SRVCC) feature. SRVCC feature enables handover of voice call in LTE to WCDMA layer when users enter poor LTE coverage area. In this paper, it is envisaged that quality of call measured through Mean Opinion Score (MOS) is always better in LTE compared with WCDMA layer. Due to better call quality, maximizing the voice call duration in LTE layer is recommended through SRVCC serving cell threshold optimization. In order to properly set the optimal SRVCC threshold setting, radio condition at which uplink block error rate (UL BLER) increasing higher than 10% and the acknowledgement rate (ACK Rate) degrading below 90% is evaluated. The Transmission Time Interval (TTI) bundling feature improving the uplink VoLTE coverage is also taken into consideration. This paper proposes serving cell SRVCC threshold RSRP = -108dBm for networks without TTI bundling and RSRP = -117dBm for networks with TTI bundling deployment.