Optimal Bandwidth Assignment on Up- and Downlinks of Satellite with Buffer Capacity

Abstract

This paper considers a satellite communication system with the slotted ALOHA access mode where the satellite is assumed to have on-board regeneration ability and the finite buffer capacity for storing noncollided packets from the uplink. The system is analyzed with the downlink bandwidth restricted to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/L</tex> of the uplink bandwidth, and with the conventional slotted ALOHA system where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L = 1</tex> and the buffer size at the satellite is equal to zero. Maximum throughput and throughput-delay characteristics of this system are analytically obtained. The satellite is given an optimal buffer size to achieve maximum throughput and minimum packet transmission delay. It is shown that the constraints that lead to the downlink bandwidth being lower than the uplink bandwidth do not necessarily result in throughput penalties in a buffered satellite system. Furthermore, when the total bandwidth which can be divided between up- and downlinks is given, if two or three times that of the downlink is assigned to the uplink and if the satellite has buffer storage space only for a few packets, we show that maximum throughput of the system will be improved about 40 percent with little change in delay characteristics in comparison with that of the conventional slotted ALOHA system where the given total bandwidth is equally divided between up- and downlinks.