Abstract: A narrow band RF carrier acquisition method suitable for Demand Assigned Multiple Access (DAMA) networks having multiple narrow band carriers operating with channel frequency spacing that may be less than the frequency uncertainty on the link. The present invention uses a variable database of active narrow band carrier frequency assignments for the ground stations in the system, which, together with a knowledge of the approximate magnitude of the frequency errors, can be exploited to allow a receiving ground station to optimize the process of narrow band carrier frequency acquisition. The optimization employs alternative procedures depending upon different acquisition circumstances, thereby allowing the receiving ground station to utilize the optimal acquisition method under any given set of circumstances, where the circumstances are individual and changing for each ground station in the system but are known and communicated from a system database.

Abstract: A pilot signal for implementing automatic frequency control in a satellite communications system is continuously transmitted by a designated ground station. Its frequency lies in the middle of the communications band so that it will undergo the same frequency shifts or distortions as the overall communications signal. A second ground station monitors the presence of the pilot signal, and if it is lost for a predetermined time, this second station then transmits the pilot signal to ensure the continuation of the AFC function throughout the system. If the pilot signal is lost at the second station, however, an uncertainty might exist as to whether the failure is in the designated ground station or the second ground station. To resolve this uncertainty a secondary pilot signal, having a frequency different from but in the same band as the primary pilot signal, is transmitted by a third ground station.