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Based on the network flow formulation, the existence of feasible beam-to-beam switching modes for a satellite switched time division multiple access system has been fully and transparently demonstrated, in which simultaneous transmissions are configured in several Carriers in each beam of points. By showing the linear independence of all but one switched switching modes, a new limit of mn + 2 is obtained on the number of switching modes, where m and n are the number of uplink and downlink beams, respectively. The complexity of the time to find the complete sequence of switching modes and to find the initial switching mode are improved to 0 (m / sup 2 / n / sup 2 /) and 0 (min / spl radic / K, (m + N) / Sup 2/3 /) mn), respectively.
More efficient use of satellites in the geostationary orbit can be achieved through the use of antenna beams. The use of point beams is also known as spatial division multiplexing. Further improvements can be made by switching the antenna interconnections in synchronism with the TDMA frame rate, this is known as satellite switched TDMA (SS / TDMA).
Figure 14.27a shows in simplified form the SS / TDMA concept (Scarcella and Abbott, 1983). Three antenna beams are used, each of which serves two earth stations. A satellite switching matrix of 3 is shown. This is the key component that allows the antenna interconnections to be made in a switched way. A switching mode is a connectivity arrangement. With three beams, six modes for complete interconnection would be needed, as shown in Fig. 14.27b, and generally with N beams, N! They are necessary for complete interconnection. Full interconnection means that the signals carried in each beam are transferred to each of the other beams at some point in the switching sequence. This includes the loopback connection, in which the signals are returned along the same beam, allowing the inter-communications between the stations within a beam. Of course, the uplink and downlink microwave frequencies are different.
Figure 14.27: a) satellite switching of three spot beams; (B) connectivity or modes.
Due to beam isolation, a frequency can be used for all uplinks and a different frequency for all downlinks (eg 14 and 12 GHz in the Ku band).