A Multi-layer UEP Scheme for VOLTE Transmission Using QAM and S-QAM

Voice over Long-Term Evolution (VoLTE) is the basis for evolving mobile voice and communication services for packet switched networks. However, noise and delay interfere with voice transmission over wireless channels, resulting in a poor Quality of Service. This paper proposes four improved transmission systems for VoLTE. The first and second proposed schemes take advantage of the varying importance of the bits produced by an internet Low Bitrate Code codec to provide distinct levels of security for them by placing the significant bits on prioritized Quadrature Amplitude Modulation (QAM) bit positions before transmission. The third and fourth proposals replace the traditional QAM constellation by a Statistical QAM (SQAM) arrangement. The third strategy is derived by placing the critical bits on the SQAM arrangement and the non-critical bits onto the traditional QAM configuration. For the last scheme, all the bits are placed on the SQAM map. A comparative study was also carried out using two frequency transformations: Fast Fourier Transform (FFT) and Discrete Wavelet Transform, namely Biorthogonal Wavelet. The proposed approaches demonstrated better performance as well as improved segmented signal-to-noise ratio by up to 4.86 dB. In contrast to the use of FFT, an increased gain of up to 4 dB is observed with DWT together with 16-QAM at a code rate of 1/3.