Very Small Aperture Terminal Networks Research Articles

Ku‐Band satellite data networks using very small aperture terminals—part I: Multi‐access protocols

AbstractThis two‐part paper presents a comprehensive overview on the technology of very small aperture terminal (VSAT)‐based satellite data networks, which have received increasing attention in recent years because of a combination of technical and economic factors. Ku‐band networks with customer‐premise earth‐stations can overcome the inherent local access bottleneck in wide‐area terrestrial data networks by suitably exploiting the unique multi‐access and broadcast features of satellite communication. In this part of the paper, the issue of multiple access, which is an important critical path technology in the ongoing evolution of VSAT data networks, is considered in detail. Satellite multi‐access protocols are classified in terms of channel synchronization (slotted and unslotted) and the qualitative nature of message access (fixed assigned, contention and reservation). In addition to well known techniques such as ALOHA, slotted ALOHA, tree CRA, packet CDMA and demand assigned (DAMA) TDMA, a number of new approaches to efficient unslotted access, including selective reject (SREJ) ALOHA, time‐of‐arrival CRA and locally synchronous reservation, are discussed. The general review is followed by a detailed performance comparison of a number of candidate first‐generation VSAT protocols, namely ALOHA, slotted ALOHA, SREJ‐ALOHA, DAMA with TDMA reservation access and DAMA with slotted ALOHA reservation access. The performance evaluation, based on detailed simulations with VSAT equipment and transaction traffic parameters, is summarized by curves of average delay and throughput vs. number of VSATs per channel for each of the protocols considered. Higher‐order differences in delay performance are illustrated with appropriate delay distribution results and the sensitivity of performance with respect to key equipment and traffic parameters is investigated. For the transaction traffic model under consideration, the results suggest the use of SREJ‐ALOHA among contention techniques or DAMA with slotted ALOHA reservation among controlled access alternatives. The trade‐off between contention and reservation access is shown to be more complex, depending on the combination of average delay, peak delay, transmission cost and equipment complexity suited to the particular application.In Part IITo published in the next issue of this paper on Ku‐band VSAT networks, the issue of overall system design is considered.