I.M.T.R. Al-wazedi and M. Kawai (Japan)
Stop and Pass Circuit (SPC), Multibeam, Multiport coupler, CDMA, Hadamard code, Fast Fourier Transformation (FFT)
A multibeam satellite system must be in a position to interconnect all network earth stations and consequently must provide interconnection of coverage areas. The complexity of the payload is added to that of the multibeam satellite antenna subsystem which is more complex than that of a single beam satellite. For example, the payload for SS-TDMA includes a programmable switch matrix having a number of inputs and outputs equal to the number of beams. Due to its complexity, studies have been done to replace this system with an alternative technique. One study [1] uses Hadamard coded CDMA as a multiple access scheme, and a Multiport coupler onboard. Each earth station chooses the appropriate Hadamard code corresponding to the destination beam. The multiport coupler is a passive device which autonomously controls the routing of the CDMA signals transmitted from the earth stations. However, in this system when a particular earth station wants to communicate with another, using a particular Hadamard code, two earth stations are active at the same time. This is undesirable. For a particular Hadamard code one particular earth station shall receive a signal while the others will not receive any signal at all. Among the four Hadamard codes used in [1], [0000] and [0101] perform very well, while [0011] and [0110] do not. For this reason, in this paper, the system model described in [1] is modified by a replacement of a “stop and pass circuit” for the reliable interconnection among the multibeams.
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