MULTIPLE ACCESS STUDIES OF MULTIBEAM COMMUNICATION SATELLITES.

摘要

The next generations of communications satellites are expected to employ satellite switched multiple spot beams to increase the system capacity. In this thesis, we study the use of such systems in a packet-switched environment with a large number of small "bursty" users. A system is considered which achieves frequency reuse by using N(,z) non-overlapping spot beams with N(,t) frequency translating transponders, where N(,t) (LESSTHEQ) N(,z). Promising system architectures are studied and six multiple access protocols are proposed to provide for the efficient use of the satellite channel; i.e., to reduce average packet delays while maintaining high throughput.; Three of the protocols are based on a fixed switching sequence; the first uses a fixed station access technique, the second uses demand assigned station access and the third has a random station access. In the next protocol, station access slots and switch settings are both assigned on demand, on a packet-by-packet basis. We show that the problem of optimal switching of spot beams is equivalent to the problem of maximum matchings in bipartite graphs, a fairly complex combinatorial problem when many spot beams are involved. In view of this, some efficient sub-optimal algorithms are proposed for setting the switch assignments on demand. The last two protocols assume buffering on-board the satellite, and the satellite operating as a store-and-forward node.; Delay vs. throughput curves are obtained for the six protocols by analysis and simulation, for various combinations of system parameters and traffic characteristics. Performance is compared and evaluated taking into consideration the complexity of implementation.