The robustness of transponding commercial satcom to uplink jamming is investigated. It is assumed that the transponder is designed to handle a certain number of simultaneous users using FDMA or TDMA and without considering jamming. The transponder is assumed to have one of the standard nonlinearities. It is shown that multiple access combined with high power amplifier (HPA) backoff provide a form of protection from jamming akin to spread spectrum. The vulnerability to attack on a single user can be overcome by introducing spread spectrum. The jamming level needed to cause all users to have unacceptable error rates must be comparable to the sum of the user powers, and it was found that this level is generally slightly lower than that to cause the transponder to go into saturation. Therefore, transponders were found to have useful inherent robustness. Generic examples are used to illustrate these conclusions.
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