VoLTE coverage improvement by HARQ and RLC segmentation when TTI bundling is ON

The 3GPP Long-Term-Evolution system applies pure packet-switch architecture. Meanwhile, the LTE radio access has a short Transmission Time Interval (TTI) of 1ms in order to reduce end-to-end delays. Such burst transmission cause major difficulty in voice transmission over LTE (VoLTE), especially for uplink transmission at the cell edge. TTI bundling has been proposed to enhance the coverage of VoLTE. In this paper we investigate the effect of conventional coverage enhancement technologies of HARQ and RLC segmentation on VoLTE when TTI bundling is applied. We consider the uplink transmission and the coverage capability is defined as the required signal power to successfully decode the voice packets. We build a simulation platform according to the 3GPP specifications. Conclusion and suggestion then are proposed to optimize a practical network.