Abstract: A satellite communication system (SCS)(100) and method (300) are provided that provide a geographically co-located user assignment system. For unit-to-unit communication, each group of subscriber units is instructed to operate in a half-duplex unit to unit mode. The geographically co-located user assignment system comprises an assignment unit (201), a storage unit (203), and an instruction unit (205) such that a first subscriber unit (204) initiates unit to unit communication with at least a second subscriber unit (206, . . . ) in the first subscriber unit's user group utilizing a multiple access channel assigned to that group by transmitting on an assigned satellite downlink frequency of the multiple-access channel on a push-to-talk basis.

Abstract: A key management system for encryption keys removes the effect of secure communications loss during a rekey period in a secure communications system. Use of key indexes to partition encryption keys into usable subgroups such that during a rekey period, continuous secure communications are maintained throughout the entire secure communications system.

Abstract: In a secure trunking communication system, limited secure service is provided during periods of limited service or failsoft operations using the following method. When the limited service or failsoft condition is detected, a limited secure service message or a failsoft service message, respectively, is transmitted to those system components utilizing encryption keys, including console interface units (CIU) (106-107) and communication units (111-113). Upon reception of the limited secure service message, the communication units load at least one limited service key. Simultaneously, the console interface units also load the at least one limited service key. Upon reception of the failsoft service message, the console interface units load at least one failsoft key. Simultaneously, the communication units also load the at least one failsoft key. The communication units and the CIUs use the limited service keys or the failsoft keys until normal operation is restored.

Abstract: The present invention includes a low-earth satellite-based paging broadcast system (100) and method (200, 300) that maximizes spectral efficiency and minimizes power expenditure for the broadcast of paging messages by broadcasting the messages to terminator- or originator-selectable portions of the total system coverage area. The terminator selects a long-term preferred geographic area (LTPGA), and optionally, a short-term preferred geographic area (STPGA). The originator provides the terminator ID, the message, and optionally provides a customized preferred geographic area (CPGA). Terminators and originators can easily modify the selectable geographic areas (SGA(s)): LTPGA(s), STPGA(s), and CPGA(s). The gateway converts the SGA(s) to addressable coverage areas (ACA(s)), and transmits a signal including the paging information, and ACA(s) to at least a first communication satellite (COM SAT).

Abstract: A trunked communication system having a control resource that encrypts system control messages. In one embodiment, the encryption includes controlling a bit interleaving process (208, 311) as a function of an encryption key (203, 321). In another embodiment, the encryption process includes reordering (202, 302) the information bits that constitute the message itself. If both encryption processes are used, the controlling encryption key can either be the same for both processes, or different.