Radio communication controller for subscriber-requested calling code prefacing
FIELD OF THE INVENTION 
     The invention relates generally to fixed site controllers located within trunked radio communication systems, and particularly to the prefacing of a predetermined calling code in response to a request from one or more roaming subscriber units within such a system. 
     BACKGROUND OF THE INVENTION 
     Trunked radio systems, acting as stand-alone systems or as part of a wide geographic area coverage system, and having telephone interconnect capabilities assigned to specific radios within that radio system, are known. In the stand-alone configuration, subscribers may wish to dial land-line individuals who may be geographically located outside of the calling area, as defined by the calling code, or area code, associated with the Public Switched Telephone Network (PSTN) phone lines at the fixed site upon which the mobile is active. Currently, doing so requires the keyed entry of three or more characters, in addition to the PSTN telephone number of the land-line unit, in order to successfully complete the interconnect call. 
     For wide area systems with a multitude of fixed sites, each fixed site having a set of PSTN phone lines which are associated with a calling code. Some of these codes are common among different sites, while others are unique to that site. Users of subscriber units within the system will be assigned to a specific primary, or home, site and will more than likely be making interconnect calls within that primary site&#39;s area code. This radio user, however, has the ability to roam into another site&#39;s boundaries within the trunked radio system. Once the radio has moved into a new site away from its home site, the user may be required to enter the area code of the radio&#39;s home site if the user wishes to make a telephone interconnect call to a land-line within the area code boundaries of the radio&#39;s home site. This becomes a requirement when the site upon which the radio is active has a different area code than the land-line in its home site. Additionally, a radio user roaming between sites would normally be required to dial the area code of the radio&#39;s home site, if outside the boundaries of that site&#39;s area code. This radio user may roam from these boundaries quite often, but desire to make many calls to individuals located within the area code of the home site. In the case where a subscriber unit is continually roaming along area code boundaries, there may be a requirement to preface the area code of a desired land-line number for every call initiated by that subscriber unit. 
     There are two problems associated with the aforementioned scenario. The first, and perhaps most obvious, is the inconvenience associated with having to dial the area codes necessary for a given land-line interconnect call, in addition to the required seven digit number for that land-line. This condition, is merely a nuisance to the initiating party. The second problem goes beyond that, though. If either the area code is prefaced by the user to the seven digit number when it is not required to do so, or the area code is ignored by the user when its presence is required, the call initiation attempt will fail. This failure results in, at best, a requirement to reinitiate the call. In an emergency situation, of course, the consequences of the aforementioned scenario are more severe. 
     Accordingly, the need exists for a trunked communication system to have the capability of both determining whether or not a calling, or area code is required, and then if there is such a requirement, generating a number by prefacing the appropriate area code to the telephone number keyed by the user of the roaming subscriber unit. 
     SUMMARY OF THE INVENTION 
     The present invention encompasses a radio communication controller coupled to the Public Switched Telephone Network (PSTN) and associated with a PSTN calling code, or area code, capable of accessing a database having an identification code associated with a subscriber unit and another area code, accumulating a PSTN telephone number from the subscriber unit, and receiving a request from the subscriber unit. The controller is further capable of matching the identification of the requesting subscriber unit to a stored identification code and its associated calling code in the database, and comparing this area code with that of the controller site. The controller, as employed by the invention, then decides whether the area code is required for completing the interconnect call. If required, the controller then prefaces the accumulated PSTN telephone number with the area code preselected by the user of that subscriber unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a general diagram depicting the main components of a stand-alone trunked communication system, according to the invention. 
     FIG. 2 is a flow chart showing the relationship of events in one embodiment of the invention. 
     FIG. 3 is table showing some of the contents of a record contained in a database, according to the invention. 
     FIG. 4 is a general diagram depicting the main components of a wide area trunked communication system, according to the invention. 
     FIG. 5 is a flow chart showing the relationship of events in one embodiment of the invention. 
     FIG. 6A and 6B are tables showing some of the contents of two records contained in a database, according to the invention. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     FIG. 1 shows a typical stand-alone trunked dispatch communication system 100. The system consists of a fixed site 102, a dedicated set of public switched telephone network (PSTN) lines 104, a controller 106, at least two repeaters 108 and 109, and one or more subscriber units 110 and 111. Typically one of the repeaters 108 and its associated radio frequencies make up a duplex control channel under which all communication activity is directed. Additional repeaters are utilized for establishing voice channels used to carry out the actual communication data to and from subscriber units within the system. 
     The controller 106 has access to a database having one or more data records which uniquely define the communication capabilities of each subscriber unit on the trunked communication system. FIG. 3 gives a detailed look at a portion of one such data record 300, called a subscriber access code (SAC), which can be partially modified by the subscriber and fully modified by the system administrator at the fixed site. Generally, data records are partitioned into data fields, which fields are accessed via pointers into that record. The field 302 contains a subscriber unit identification code which may be, for example, a sequential integer between one and seven, as shown. The field 304 holds a PSTN calling code, or area code, referred to as a personal area code (PAC), which the user of the associated subscriber unit has preselected. This area code is presumably, but not necessarily, different from the one associated with the PSTN lines at the fixed site. Field 306 holds information which reflects the capability of the associated subscriber unit to make interconnect calls to a land-line telephone system. Without telephone interconnect capability, the storage of a PAC for a given subscriber unit is meaningless, and hence the field 304 is empty, for example as shown with subscriber units `2` and `4`. 
     FIG. 2 shows a flow chart 200 which describes the sequence of events required in the preferred embodiment of the invention. The process 201 begins when a subscriber unit within the coverage area of the stand-alone trunked communication system initiates a request to make an interconnect telephone call. Upon receipt of the request, the controller 106 determines at 203 the identity of the subscriber unit by means of a standardized identification code associated with that subscriber unit. Then, using the aforementioned identification code of the subscriber unit as a pointer into the record 300, the controller 106 reads at 207 the interconnect capability field 306 of that record. At this point, a decision is made at 209 as to whether or not the initiated call request will be granted. This decision depends upon the telephone interconnect capabilities of the subscriber unit initiating the call. If no such capability exists, the routine is exited at 221. If the capability does exist, the controller 106 determines at 211 whether or not the user of the subscriber unit has requested that a PAC be prefaced to the PSTN telephone number that he has keyed from his subscriber unit. If no such request was made, the controller 106 simply issues at 219 the PSTN telephone number exactly as it was keyed by the user of the subscriber unit, and exits the routine at 221. If the subscriber unit has made such a request, the controller 106 reads at 213 the PAC field 304 in the SAC record 300. At this point, the controller compares at 215 the fixed area code (FAC) associated with the PSTN phone lines at the fixed site to the PAC associated with the subscriber unit to check for equality. If the FAC is the same as the PAC, then the controller 106 issues at 219 the PSTN telephone number as keyed by the user of the subscriber unit and then exits the routine at 221. If the PAC and the FAC are not the same, the controller 106 issues at 217 the PAC, issues at 219 the PSTN telephone number as keyed by the subscriber unit, and then exits the routine at 221. Note that, in the preferred embodiment of the invention, the user of the subscriber unit need not know whether or not the area code of the land-line telephone that he wishes to contact is required to successfully complete the interconnect call. 
     FIG. 4 shows a block diagram of a wide area trunked dispatch communication system 400. A controller 401 is connected, for example via wire-line, to a plurality of fixed sites 402, 403, 404 which sites each have a plurality of repeaters 405. Each of the fixed sites 402, 403, 404 is associated with a PSTN area code, which is determined by the geographic location of each site. As in the case of the stand-alone system, the wide area system includes a plurality of subscriber units 406,407, 408 roaming within the coverage boundaries of the system. 
     FIG. 6A shows a portion of an adapted version of a subscriber access code (SAC) record 600. Similar to the SAC record 300 described in FIG. 3, the record 600 contains the information used by the controller 401 for determining the access capabilities of each of the subscriber units 406,407,408 within the wide area system 400. As in the stand-alone system, the record 600 can be modified, at least partially, at either the subscriber end or at the fixed end. Referring to the contents of record 600, the field 601 holds subscriber identification codes for all the subscriber units 406,407,408 which are supported on the system. The field 603, much like the field 306, contains a code which determines the telephone interconnect capability of the associated subscriber unit. The field 605, like the field 304, contains a PSTN calling code selected by each of the subscriber units 406,407,408 and represents the area code of a geographic area that is of interest to that subscriber unit, and similarly called a PAC. The field 607, much like the field 605, contains a home site area code (HAC) which represents the area code of a subscriber unit&#39;s primary fixed site, for example 403, to which the majority of that subscriber unit&#39;s communications are directed. 
     FIG. 6B shows a portion of a data record 602, which represents a fixed site access table (FSAT). Within this record, the field 604 represents identification codes which are associated with each of the fixed sites 402,403,404 within the coverage area of the trunked communication system 400. The field 606 contains information representing the associated fixed PSTN area code (FAC) of the geographic location in which the associated fixed site, for example 403, is located. 
     FIG. 5 shows a flow chart 500 which describes the relationship of events in the preferred embodiment of the invention as employed in a wide area communication system 400. Upon call initiation at 502 in which a subscriber unit, for example 407, initiates a call through a particular fixed site, for example 403, the controller 401 determines at 504 the identification code of the active fixed site through which the call is initiated. Using this identification code as a pointer into the FSAT record 602, the controller 401 then looks up at 506 the associated FAC of that fixed site from the field 606. Next, the controller 401 determines at 508 the identification code of the initiating subscriber unit, then uses this indentification code as a pointer into the SAC record 600, to look up at 510 the interconnect capabilities of that subscriber unit from the field 603. If the subscriber unit is found at 512 to have no such interconnect capability, the routine is exited at 524. If interconnec capability is found at 512 to exist for the subscriber unit, then a decision point is reached at 514. If the call initiator has not requested that a HAC or PAC be prefaced to the keyed PSTN telephone number, the keyed PSTN telephone number is issued at 522 exactly as keyed by the subscriber unit and the routine is exited at 524. If a HAC or PAC has been requested, the controller 401 uses the identification code obtained at the outset of the call to look up at 516 the associated HAC or PAC for that subscriber unit. Then the controller compares at 518 the subscriber units HAC or PAC with the FAC associated with the fixed site to see if they are identical. If they are not the same, the controller 401 issues at 520 the requested HAC or PAC, and then issues at 522 the PSTN telephone number exactly as keyed by the subscriber unit, and exits the routine at 524. If, upon comparison of these two area codes, they are found to be identical, the controller 401 simply issues at 522 the accumulated PSTN telephone number exactly as keyed by the subscriber unit, and exits the routine at 524.