Design of a medium access protocol and scheduling algorithm for multimedia traffic over a DVB-RCS satellite link using a cross-layer approach.
Satellite networks provide an alternative to terrestrial networks where cost and lack of infrastructure are driving parameters. For a satellite network to be cost effective one needs to be able to increase the efficiency of the network: this is accomplished by focusing on the parameters that affect the performance of the system and improving on them where possible. The factors affecting the network performance include the capacity, the propagation delay, the protocol used, and the channel error rate, among others. There are various ways to implement a satellite network depending on the satellite orbit, the architecture used, the access technique used, the radio interfaces used, etc. This thesis work describes the chosen satellite standard, Digital Video Broadcasting – Return Channel via Satellite (DVB-RCS) and the associated Medium Access Control (MAC) protocols. Two protocols were designed and investigated under ideal channel conditions, these being the Combined Free/Demand Assigned Multiple Access with Piggy Backing – Packet Dropping (CF/DAMA-PB-PD) protocol; and the Combined Free/Demand Assigned Multiple Access with Piggy Backing – Prioritised Earliest Deadline First (CF/DAMA-PB-PEDF) protocol, both derived from the Combined Free/Demand Assigned Multiple Access with Piggy Backing (CF/DAMA-PB) protocol. The multimedia traffic models for voice, video and web classes are described, validated through simulations and presented; these provide the heterogeneous vi traffic required for evaluating the performance of the satellite system implemented and the designed protocols. Under the multimedia traffic, CF/DAMA-PB-PD was shown to excel in average packet delay reduction while reducing the overall system throughput. The CF/DAMA-PB-PEDF does not contribute to an improvement over the CF/DAMA-PB-PD protocol. The effects of a non-ideal channel on the CF/DAMA-PB-PD protocol was investigated and presented along with the design of three MAC protocols that take the channel characteristics into account to improve on the system performance. The cross-layer interactions, more specifically the interaction between the physical and data–link layers, were used, investigated and presented. The channel state information in terms of signal-to-noise ratio (SNR) was used to improve the system performance. The five protocols evaluated under non-ideal channel conditions were the CF/DAMA-PB, CF/DAMA-PB-PD, CF/DAMA-PB-BSNRF, CF/DAMA-PB-DD and the CF/DAMA-PB-BSNRF+DD. The best overall performance, both in average packet delay while maintaining good QoS levels and throughput was shown to be that of the CF/DAMA-PB-DD protocol.