Performance Evaluation of Hybrid SAMA VSAT with FMCSA and Reservations
Date: September 24 - September 27, 2012
In this paper, we describe our work on developing and evaluating detailed OPNET simulation models of an enhanced Very Small Aperture Terminal (VSAT) satellite Internet gateway and an enhanced satellite hub based on Cerona SkySPAN technology with capacity and latency optimizations in a hybrid random access and reservation based return channel so as to allow significantly higher number of users and a better user experience. The Cerona SkySPAN technology uses Digital Video Broadcast via Satellite 2nd standard (DVB-S2) in the forward channel and Spread Aloha Multiple Access (SAMA) protocol in the return channel. We augment the SAMA return channel protocol with a hybrid random access and reservation based Dynamic Channel Allocation (DCA) scheme. The overall goal of the DCA algorithm is to make the system behave like a random access system at low loads for small messages so as to provide low message delay and to behave like a MF-TDMA reservation based system at high loads as well as for real time traffic so as to provide high maximum throughput and a better user experience. The random access protocol used at low loads is SAMA enhanced with Fast Multi-channel Slotted Aloha (FMCSA) protocol. FMCSA combines Multi-Channel Slotted Aloha (MCSA) with packet level forward error correction for new messages and scheduled retransmissions for partially received messages. This protocol increases the maximum possible throughput of SAMA and reduces the delay of multi-slot short messages while providing more robust delay performance with respect to load fluctuations, thus resulting in a much better user experience at low loads. The system transitions into a reservation based system at higher loads and for real time traffic so to support higher maximum throughput and achieve good QoS for real time traffic. The satellite return channel is divided into multi-frequency periodic frames. Each frame has mini-slots used for sending reservation requests in contention mode and larger data-slots used for sending data in either contention mode (FMCSA) or reservation mode (where the HUB allocates data-slots based on requests). We show via OPNET simulations that the enhanced SAMA VSAT with the hybrid DCA algorithm improves the throughput, latency and robustness of the SkySPAN SAMA system. We also compare, via OPNET simulations, the enhanced system with a DVB-RCS system to show the improvements in user experience both in terms of delay and throughput.