VoIP Transmission Cross-Layer Design over Satellite-WiMAX Hybrid Network

This paper presents a study of the cross-layer optimisation of real time traffic transmission over hybrid networks. In particular, we focus on DVB-RCS/S2 satellite and WiMAX. We focus on Voice over IP (VoIP) transmission and we aim at reducing total transmission delay and jitter. We propose an enduser-centric scenario where codec rate adaptation is performed. Two possible cross-layer codec rate adaptations have been analyzed. First, we propose a bank of codec is available at both transmission ends and a codec switch is performed driven by the RTCP (Real Time Control Protocol) reports. In this case a transport-to-application layer cross-layer information flow is required. Second, we propose the use of adaptive wideband codecs (inherently cross-layer across the networks). Realistic modelling is considered for both the terrestrial and satellite (Ka band) channel. We present a preliminary analysis of the two proposed cross-layer mechanisms and we demonstrate that by reducing total transmission delay and jitter through cross-layer design, total capacity increases significantly. Our results thus show the great potentiality of cross-layer design even in a long-delay scenario such as a GEO satellite system.