Abstract:
Communication systems (101, 102) having dedicated communication resources are provided with receivers (111, 116) that monitor the communication resources (104, 108) of other communication systems. Communications between communication units in various systems are interchanged through appropriate interaction of the repeaters and the dedicated receivers so provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation-in-part of prior application Ser. No. 07/358,730, filed May 30, 1989, now U.S. Pat. No. 5,095,529 by Michael David Sasuta and Gary Dean Erickson, the same inventors as in the present application, which prior application is assigned to Motorola, Inc., the same assignee as in the present application, and which prior application is hereby incorporated by reference verbatim, with the same effect as though the prior application were fully and completely set forth herein. 
    
    
     FIELD OF THE INVENTION 
     This application relates to communication systems including, but not limited to, interlinked trunked communication systems. 
     BACKGROUND OF THE INVENTION 
     Trunked communication systems are known in the art. In general such systems include a resource controller, which may be centrally located or distributed, that manages communications between communication units such as, for example, fixed location, mobile, and portable two-way radios, on a plurality of communication resources such as, for example, frequency pairs or time division multiplexing time slots, that are supported by a plurality of corresponding repeaters. 
     A number of such systems are available, including the Smartnet and Privacy Plus systems from Motorola, the Clearchannel LTR system from E.F. Johnson, and the Sixteen Plus and Sweet Sixteen systems from General Electric. 
     In general, such systems tend to operate independent of one another. Therefore, a communication unit located in a first system will generally not be able to communicate with a second communication unit located in a second communication system. 
     Some prior art systems interlink one or more communication systems through use of an appropriate dedicated land line. So configured, communication units in different communication systems may be able to communicate with one another. Such an approach, however, poses several disadvantages, including increased cost and relative inflexibility. 
     A need thus exists for a system and method for economically and flexibly interlinking two or more communication systems. 
     SUMMARY OF THE INVENTION 
     In a communication system comprising a first communication system and a second communication system; 
     the first communication system including at least a first communication unit, a first set of communication resources, and a first resource control means for controlling the first set of communication resources; 
     the second communication system including at least a second communication unit, a second set of communication resources, second resource control means for controlling the second set of communication resources, and second receiver means substantially compatible with the first set of communication resources for receiving communications sourced by the first communication system; 
     the first communication system further including first receiver means substantially compatible with the second set of communication resources for receiving communications sourced by the second communication system; 
     a method for establishing communications between the first communication unit and the second communication unit is disclosed. Briefly, in accordance with the present invention, the method comprises the steps of: 
     (a) receiving, at the first communication system, a request from the first communication unit to communicate with the second communication unit; 
     (b) sourcing, from the first resource control means using the first set of communication resources, a notification for at least the second communication unit of a need to communicate; 
     (c) receiving, at the second receiver means, the notification from the first communication system and providing that notification to the second resource control means; and, 
     (d) sourcing, for the benefit of the second communication unit, at the second resource control means using the second set of communication resources, a notification of the need to communicate. 
     In one embodiment of an intersystem communication system and method, in accordance with the present invention, a receiver may be provided to accommodate each communication resource supported by the other communication system. This embodiment offers a high degree of flexibility in communication resource allocation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 comprises a block diagram depiction of a first embodiment of an intersystem communication system and method, in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a first embodiment of an intersystem communication system and method, in accordance with the present invention, is depicted generally by the numeral 100. The system 100 operates in conjunction with other communication systems. For purposes of this description, only two such communication systems, 101 and 102 will be described. 
     The first communication system 101 includes a resource controller 103 that functions to control allocation of a first set of communication resources. In this embodiment, it will be presumed that the communication resources are supported by a plurality of repeaters 104, and that the communication resources themselves comprise a first set of frequency pairs A-C. In addition, for purposes of this description, it will be presumed that one of the repeaters 104 supports system control information related to resource allocation requests and grants, all as well understood in the art. The resource controller 103 controls the repeaters 104 and interchanges resource allocation request and grant information through the repeaters 104, via an appropriate link 106. 
     The second communication system 102 similarly includes a resource controller 107, repeaters 108 which support communication resources D-F and an appropriate link 109 therebetween. In this embodiment, the communication resources A-C of the first system 101 are different from the communication resources D-F of the second system 102. Therefore, the two systems 101 and 102 are not able to communicate directly with one another through the repeaters provided. 
     The first communication system 101 also includes a plurality of receivers 111 that are capable of compatibly receiving the communication resources D-F of the second communication system 102. Although it would not necessarily be required that a receiver 111 be provided to accommodate each communication resource of the opposite system, in this embodiment such a receiver 111 has been so provided. An appropriate communication link 112 is provided between the receivers 111 and the resource controller 103 to allow operation of the receivers 111 to be controlled, at least in part, by the resource controller 103, and also to allow the resource controller 103 to receive signalling information as received by the receivers 111 and as sourced from the resource controller 107 of the second system 102. In addition, an appropriate link 113 is provided between the receivers 111 and the repeaters 104 of the first system 101. This link 113 is appropriately gated 114 to allow the resource controller 103 to control provision of signals received by the receivers 111 to the repeaters 104. 
     So configured, the resource controller 103 may cause a particular repeater 104 to retransmit a communication, such as a voice message, that has been received by one of the receivers 111. 
     A similar group of receivers 116, links 117 and 118 and gate unit 119 are provided in the second communication system 102 to provide an identical configuration as that described above. 
     Operation of the first embodiment 100 of an intersystem communication system and method, in accordance with the present invention, may now be described. 
     A first communication unit 121 situated within range of the first communication system 101 initiates the process by transmitting a request 122 to communicate with one or more other communication units although this request could be to communicate with a particular identified talk group, for purposes of simplicity, this description will presume that the first communication unit identifies a particular second communication unit 123 as the desired communication target. This talk request is transmitted on the appropriate control resource for the first communication system 101, and is relayed by the appropriate control resource repeater 104 to the resource controller 103 for the first communication system 101. 
     If the resource controller 103 recognizes the communication target as being local as may be determined, for example, by the identification number or &#34;ID&#34; of the communication target, then the resource controller 103 may allocate a communication resource to support the requested communication as is currently done in the prior art. If, however, the resource controller 103 determines that the communication target is not local or, if dealing with a talk group, is not completely local in all instances, then the resource controller may transmit, on the control resource, an outbound signalling word constituting a notification that a communication with the second communication unit is desired. 
     This outbound communication 124 as sourced by the resource controller 103 and as transmitted by the appropriate control resource repeater 104 will be received by whichever of the receivers 116 in the second communication system 102 is monitoring that particular communication resource of the first system 101. That particular receiver 116 will then provide the signalling information via the appropriate link 117 to the resource controller 107 for the second communication system 102. If the second resource controller 107 recognizes the identified communication target as local, the resource controller 107 will assign one of its communication resources to support the communication, and will provide information identifying the allocated resource in an outbound transmission 126 on its control resource. 
     This transmission 126 will be received by the second communication unit 123 and cause the second communication unit 123 to begin monitoring the allocated communication resource of the second communication system. This outbound transmission 126 will also be received by the corresponding receiver 111 of the first communication system 101. This received signalling information will be provided to the resource controller 103 thereof via the appropriate link 112. The resource controller 103 may now determine that the communication target has been located and that a communication resource in the second system 102 has been assigned to support the desired communication, will now assign one of its own communication resources to the first communication unit 121 to support the communication. 
     Thereafter, the first communication unit 121 will transmit its messages for example, voice messages using communication resources of the first communication system 101. The repeater 104 in the first communication system 101 assigned to support this communication will receive these signals from the first communication unit 121 and will repeat them on the allocated communication resource 127. The repeated voice message 127 will be received by the appropriate receiver 116 in the second communication system 102. The resource controller 107 in the second communication system 102 will gate 119 this received voice message to the repeater 108 that has been assigned to support this communication. The assigned repeater 108 will then retransmit the received signal 128 and this retransmission will be received by the second communication unit 123. 
     If the second communication unit 123 were to transmit a response to the first communication unit 121, the same procedure could be implemented in reverse in a transmission trunked mode, or the already allocated resources could be used in a reversed pattern to accommodate a message trunked methodology. 
     While various embodiments of an intersystem communication system and method, in accordance with the present invention, have been described hereinabove, the scope of the invention is defined by the following claims.