Enhancing and improving voice transmission quality over LTE network : challenges and solutions.

Summary LTE (Long Term Evolution) was developed and standardized by the 3GPP (3rd Generation Partnership Project). It is a packet switched network. This means that Voice over LTE (VoLTE) is a VoIP service with guaranteed quality of service requirements instead of transmitting in a circuit-switched network such as existing systems (2G/3G). VoLTE is deployed in a fully IP network combined with IMS (IP Multimedia Subsystem). Because of this, the deployment of VoLTE is quite complex and how to ensure the quality of voice transmission over LTE networks is a very big challenge. Thus, several different solutions are needed to enhance and improve the voice transmission quality over LTE networks. In this thesis, we present solutions to improve the voice transmission quality over LTE networks for both narrowband and broadband audio services. For this, we will need different complete factors in solutions. One of them is QoE (Quality of Experience) which is a new trend. And in order to determine the user perception for the real-time service such as VoLTE, we use the extended E-model and WB (wideband) E-model for narrowband and wideband audio services respectively. The solutions proposed here focus on key elements in LTE networks, such as string coding, MAC (Medium Access Control) scheduling systems and monitor voice quality described as follows. First, improved algorithms to enhance the LTE chain codec (encoder and decoder) have been proposed. To enhance the LTE chain coder, a joint adaptation algorithm has been deployed. The goal of this algorithm is to minimize the redundancy generated by chain coding with a slight reduction in the user's perception. Then, in order to improve the LTE chain decoder, an improved Log-MAP algorithm was presented. This algorithm aims to achieve BER (Bit Error Rate) performance that is closest to Log-MAP with reduced computational complexity compared to the state of the art. Secondly, the enhanced user perception and VoIP priority mode scheduling QoS chain and systems have been proposed. These planners are deployed for both wideband and narrowband audio users. Numerical results show that they outperform several featured schedulers such as FLS, M-LWDF and EXP/PF in terms of delay, packet loss rate, cell rate, index and fairness and spectral efficiency in almost all cases. Finally, to ensure voice quality transmission over the LTE network, prediction of user satisfaction is essential. For this reason, we present two non-intrusive models for measuring voice quality on LTE networks. These models are used for both narrowband and broadband audio users. The proposed models do not refer to the original signal. Therefore, they are very suitable for predicting the voice call quality on LTE networks.