WO1991005429A1

WO1991005429A1 - Trunking network with automatic roaming without centralized control

Info

Publication number: WO1991005429A1
Application number: PCT/US1990/004783
Authority: WO
Inventors: Sewim F. Ablay; Michael D. Sasuta; Richard H. Coe
Original assignee: Motorola, Inc.
Priority date: 1989-09-29
Filing date: 1990-08-24
Publication date: 1991-04-18
Also published as: AU6277790A; CN1050964A

Abstract

A network (100) of trunked communication systems (A, B and C) supports communication with communication unit (112) roaming about the geographic area covered by said network by having control computers (106) associated with the individual trunking systems communicate directly with each other, transferring information about the roaming communication unit between themselves. The identification and privileges of the roaming communication unit (112) are passed about the network (100) by the computers (106) giving the roaming communication unit the ability to exchange data across the network directly, or, through telephone interconnects in the various trunking systems, to communicate via a voice message through the public switch telephone network (108A, 108B, 108C).

Description

TRUNKING NETWORK WITH AUTOMATIC ROAMING WT_raOUT CENTRALIZED CONTROL

BACKGROUND OF THE INVENTION

This invention relates generally to trunked communications systems. In particular this invention relates to trunked communication systems (including cellular telephone systems and dispatch systems) that enable communication units to roam from one trunking system to another and is directed to a trunked communication network that support nationwide roaming. Trunked communications systems are well known. In U.S. patent number 4,833,701, issued to Comroe et al., a trunked communication system with nationwide roaming capability is described but which requires a central hub computer communicating with each trunking system in the network to permit a communication unit away from its base system to communicate through new, foreign trunked communication systems. (A communication unit normally has one base trunked system. A foreign trunked communication system, as the term is used herein, shall be considered to be a ti uiMng system other than its base system.)

As described in Comroe, a trunked communication system typically consists of a resource controller that allocates a limited number of communications resources (such as frequency pairs or TDM time slots) among a plurality of communication units. A communication unit may be considered a mobile unit (typically installed in a vehicle), a portable unit, (typically carried on or about the person), or a control station, which is a trunked communication unit designed to be permanently or semi-permanently installed in a building or other fixed location. Each communication unit in a trunked communication system has an identification code which, together with other information, is transmitted to the resource controller on a control resource to the resource controller when the communication unit desires access to a communications resource. Upon recognition of the identification code of the requesting unit on the control resource and the controllers granting of a communications resource, the resource controller directs other communication units associated with the requesting communication unit to monitor and communicate via a particular communications resource and permit the requesting communication unit and the receiving communication unit to communicate on that available resource. (Communication unit associated with the requesting unit would typically be other subscribers functionally related to the requesting unit, such as other police vehicles, other delivery vehicles etc.) In a network of trunked communication systems, as described in the Comroe patent, a communication unit roaming from one trunked communication system to another must be able to find the control resource of the system, register with or identify itself to the resource controller of the new trunked communication system, and thereafter have the resource controller grant communication privileges to the visiting communication unit to permit the communication unit to communicate through the new trunking system. In Comroe, the new trunking system verifies the validity of the visiting communication unit through a hub computer which interfaces to control computers of all the trunking systems making up the network of trunking systems before granting communication privileges to the roaming communication unit.

A problem with the trunked communication system as described by Comroe is that the hub computer is the only data link between the computers of several trunking systems. The hub computer must continually communicate with the local computers of the associated trunking systems to update its data base to keep track of the location of roaming subscribers.

In a nationwide network of trunking systems, the host or hub computer of Comroe can become a bottleneck through which all of the data traffic for this nationwide trunking communication system must flow. In the event of a loss of the hub computer the network of trunked communication systems would be completely disabled, network of trunked communication system that avoids the data bottleneck of a single central hub computer and reduces the susceptibility of a complete system failure brought about by the failure of the hub would be an improvement over the prior art.

SUMMARY OF THE INVENTION

There is disclosed herein a network of trunked communication systems communicating with each other through networked control computers. In the preferred embodiment, each of several control computers is associated with a trunking system. In addition to other trunking system supervisory functions, the control computer for a trunking system tracks subscribers within its trunking system as well as foreign or visiting subscribers that are based in other trunking systems.

A visiting communication unit in a geographic coverage area of a foreign trunking system desiring communication through the foreign system first finds the control resource (the control channel in some systems) for the foreign trunking system and confirms that the new resource controller supports roaming subscribers. (Trunking systems that support roaming could broadcast either a unique outbound signalling word, an identifier signal, an identifiable bit pattern in existing OSWs, or other signal from which a roaming communication unit could ascertain whether or not the new trunking system supports roaming.)

When a roaming communication unit finds a controller that supports roaming, the communication unit can thereafter attempt to log-on or register with the local computer of the new trunking system. The roaming communication unit would typically send a request for service to the local controller of the new trunking system. In the preferred embodiment, the requesting communication unit will identify itself and its base system to the new controller when the communication unit requests service from the new controller. The controller of the new trunking system sends the identity of the communication unit, the request for service, along with other identification data of the roamer, to the controller of the base trunking system via a data network linking all the control computers of the network of trunking systems. Upon receipt of the data from the controller of the new system, the controller of the base trunking system attempts to identify the roaming communication unit, its base system privileges and confirm its validity (to guard against unauthorized users). Upon verification of the identity of the roamer by the home system controller, the home system controller can download to the controller of the new system, the privileges granted to the roamer in the roamer's base system to the new controller. The controller for the new system may thereafter grant identical privileges to the roamer or greater or lesser privileges at the discretion of the operator of the remote system. (For example, the roaming communication unit may have telephone interconnect privileges in its base system while the new system might not have telephone interconnect capability. In such a case, granting telephone interconnect in the new system would be impossible.)

Once the roaming communication unit is registered in the new trunking system, data or other information (including possibly voice information) from the base trunking system can be communicated to the communication unit via the data network linking all the computers of the trunking systems together. The controller for the roaming subscriber's base system will know where the roamer is located in the network and will know where to send user information, a message, or data destined for the communication unit. An example of data exchange would be a text data message from the roaming subscriber's dispatcher (located within the base system) to the roaming communication unit in the new system. Similarly, the new communication unit in the foreign system can send data back to the controller for subsequent delivery elsewhere, perhaps to its dispatcher. Voice communication with the communication unit may be permitted if the new system supports an interface to the local public switched telephone network. Direct contact with parties may occur via public switched telephone network (PSTN). If the data network linking the computers together had sufficient capacity (bandwidth, for example) voice communication between a roaming communication unit and its base system could occur over the data network. Alternate voice paths would include a microwave link between the foreign system and the base system for example.

In some instances, a trunked communication system may not be coupled to a network of trunked communication systems. In these cases, communication privileges could still be granted to a roaming communication unit in an isolated foreign trunked communication system if the roaming communication unit has the capability of requesting the local controller for communication privileges. Instead of having a data transfer occur between local computers on the network, a similar data transfer occurs between the roaming communication unit and the local controller. After the controller receives the request from the communication unit, the controller grants privileges commensurate with set of privileges allowed roaming communication units.

BRIEF DESCRIPTION QF THE DRAWINGS

Figure 1 is a block diagram of the networked trunked communication system supporting automatic roaming without a central controller.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 1 shows three trunked communication systems (A, B, and C) arranged to form a network of such systems that permit a communication unit (112) to roam from one system to another without losing communication capability. Each trunking system (A, B, and C) making up the network includes a central controller (102A-C), a local computer (106A-C), repeaters (104A-C), and public switched telephone network interface units (108A-C). The controllers (102A-C) operate under the control of local computers (106A-C) and allocate operating resources of the repeaters (104A-C) within the trunking systems (A, B, and C). The local computers (106A-C) in each of the three trunking systems perform several administrative functions including allocating and assigning ID codes to subscribers in the coverage area of the trunking systems (A, B and C), decoding ID codes sent in from communication unit, and reprogramming roaming communication unit (112) so that the roaming units may operate within the particular system controlled by the local computer (106). The local computers (106A-C) are also directly coupled to each other, forming a network of such computers, through data networks (10, 12, and 14) which are described below in greater detail.

In the embodiment shown in figure 1, the local computers (106A-C) are coupled to the PSTN through local PSTN interfaces (108A-C) so that subscribers (112) in communication with any of the central computers (102) could make telephone interconnected calls through the repeaters (104A-C) the local computers (106A-C), and through the local PSTN interface (108A-C) (Assuming of course that telephone interconnect privileges are granted to the communication unit; the technical description of the telephone interconnect feature is well know in trunked communications systems and will not be described further.)

If both the base system (A, for example) and the foreign system (B, for example) support telephone interconnection to trunked subscribers (112), the network of trunked communication systems (100) could support call forwarding. A communication unit with telephone interconnect privileges in system A may be reached anywhere in the network (100) via telephone when a party wishing to contact the communication unit (112) dials the telephone number for the communication unit when the communication unit is present in system A. If the communication unit (112) is out of the geographic coverage area of its base system (A), telephone interconnect is ordinarily not possible. If the foreign system (B) supports telephone interconnect, the foreign system can assign telephone interconnect privileges to the communication unit (112) while it resides in the foreign system (system B) and can forward to the local computer of the base system (system A), the new phone number of the PSTN interface in system B. The local computer for system A can thereafter forward incoming calls to the communication unit (112) to the new systems PSTN interface, perhaps dialing the new number of the new PSTN interface for the caller such that the call forwarding is transparent to the caller. The principal feature of this invention, however, is improved communications between the different trunking systems by networked local computers; from this improvement flow other improvements.

In figure 1, the network of trunking systems supporting automatic roaming (100) is improved by directly coupling the local computers (106) of one trunking system (A, for example) to the local computers (106B-C) of other trunking systems (B and C). In the network (100) shown in figure 1, each local computer (106) is coupled to every other local computer comprising the network (100), improving data handling between computers and increasing the networks reliability.

In the preferred embodiment, the local computers (106A-C) are coupled together via commercial data services that provide the physical links between the computers as well as define the protocol used by the computers. (Private, hard-wired connections between the computers may be preferred in some circumstances.) The local computer of system A (106A) is typically coupled to the local computer of system B or C by leased data lines (10 and 14). These data lines could include packet switch data networks (PSDN). As shown in figure 1, the local computer for system C communicates with the local computers for systems A and B by similar data networks (10 and 12) as does the local computer of system B communicate with the local computer of system A and C over data networks 14 and 12. The physical networks coupling these computers together could be any combination of appropriate networks including a microwave based data link, a satellite based data link, leased telephone lines; or network of leased data lines. The physical links between local computers (106A-C) could also be arranged in other orientations. (Instead of the nearly parallel connection of local computers as depicted in figure 1, the links between several local computers could also be an electrical in-series connection. One local computer might receive data from another, decode the data and send it on to the next local computer in a linear string of local computers. Such an arrangement might suffer the same drawbacks as Comroe, however, with one computer at or near the center of the network handling virtually all the roaming-related data.) The data transfer on the physical links could be by way of any appropriate protocol. For example, an X.25 : rotocol, well known in the art, could be used on the networks. Each local computer (106) in the network of trunking system

(100) includes its own separate copy of important data in local data bases (107A-C). As described in Comroe, each local computer (106A-C) will typically assign a roaming ID to a communication unit (112) that is visiting its system that is based in another system. This information would typically be retained locally in the local data base (107). In the preferred embodiment herein, the local computers can assign unique identification codes (ID's) to the roaming subscribers when they are granted privileges and can de- assign ID's when the subscribers leave or are inactive. The status of these ID's would ordinarily be kept in the local data bases (107A- C). These ID's could also be used to identify the privileges granted the roamer.

As a communication unit (112) leaves a new trunking system within which it is visiting, or roams from system to system, a local computer will typically include means for periodically polling the status of visiting subscribers to establish whether or not these subscribers are considered to be active within the trunking system.

In the preferred embodiment, the local computers are programmed to periodically contact visiting subscribers based upon the contents of a table of assigned roaming ID's and look for a response from the visiting subscribers by the data resource broadcast from the local computer. If no response is detected by the central computer from the visiting communication unit after some predetermined time limit and number of re-tries, the local computer might consider the visiting communication unit to have either left the trunking system or be out of service in which case, the local computer may mark the visiting communication unit as vacant, return the ID code of the visiting communication unit to a table of available ID codes, and mark the visiting communication unit as no longer resident within its trunking system coverage area. In the event the roaming communication unit is temporarily out of service, the local computer might employ multiple time-outs, the expiration of which might be required before marking the roamer as absent.

As described above, each roaming communication unit includes the capability of scanning for control resources (control channels in some systems) and identifies the control resources from local computers that support roaming trunking communication protocol. On leaving the coverage area of one trunking system (as detected by increased data errors on the control resource for example), roaming subscribers would typically scan a set of radio frequencies designated as control resource frequencies for trunking communications systems. When scanning possibly several hundred different frequencies corresponding to several hundred different control resources, the communication unit might have to employ different algorithms to identify an optimum control resource to lock onto. (The communication unit of course would have to have radio transmission and reception capabilities compatible with the various trunking systems comprising the network (100).)

Having found a control resource, the communication unit must detect whether or not the local computer supports roaming communications by decoding data on the control resource. Upon the detection and identification of a control resource from a local computer that supports roaming, the communication unit radio (112) must logon and identify itself to the local computer (106B) of the roaming trunking system (B). The radio might send its group number, if any, and ID number, if any. (As well as any password used by the network (100)) to the local computer of the foreign trunking system (B) and request from the trunking system local computer (106B) a roaming ID which the radio and the trunking local computer would thereafter use to identify this communication unit. Upon receipt of the data from the communication unit (112) (a part of which identifies the base system of the roamer to the new local computer), the local computer of the new system (106B) can thereafter proceed to contact the local computer (106A) for the roaming subscriber's base system (A) via an appropriate data path (through 14 directly or possibly through 12 then 14 as described above). The base computer can use the data sent from the foreign local computer to identify the roamer based upon data in its own data base (107A) and down-load to the foreign local computer the operating privileges granted to the roamer in its base system. In the system of figure 1, communication of the communication unit (112) in a foreign trunking system (i.e., the trunking system) is primarily intended to be a data communication. A dispatch terminal (113) within the base trunking system (A) desiring to communicate with the communication unit (112) in a foreign trunking system may pass a data message, either a packet type message or free-format text, to the communication unit (112) via the data networks between the local computers (10, 12, 14).

In the embodiment shown, the dispatch terminal (113) is coupled to the local computer (106A) through a data link (114) similar to the other data links (10,12, 14). Since the communication unit (112) is out of communications range of the local computer of its base station, direct voice communication between the communication unit (112) and the dispatcher at the dispatch terminal (113) would therefore be impossible via the base trunking network. Alternatively, voice communication between the dispatcher (113) in the base trunking system (A) could take place via the existing telephone communication network. (Alternate embodiments would include voice communication over the data networks (10, 12, and 14) if these networks have either the capability of passing analog voice information or the capacity to pass digitized voice.) A dispatcher (113) desiring to communicate over a voice resource with a communication unit could place or receive a call to the communication unit using an interface to the Public Switch Telephone Network existing in the foreign trunking system (System B as shown in figure 1). The communication unit could either place or receive telephone calls through the foreign trunking system (System B) and its interface to the Public Switch Telephone Network system (108B) thereby permitting voice communications with the dispatcher in the base trunking system (System A).

An alternate embodiment of the invention would include isolated trunked communication systems (i.e. systems not coupled to a network of local control computers but having at least one local control computer), granting communication privileges to a roaming communication unit (112). The roaming communication unit (112) that finds a control resource for an isolated system that supports roaming communication units could grant communication privileges after the unit (112) requests the local computer of the isolated system to grant it communication privileges commensurate with privileges allowed the unit in its base system. (Alternatively, the local computer of the isolated system to grant privileges to the roaming communication unit greater than the privileges granted to the unit by its base system.) The controller for the isolated system would inform the communication unit of all its necessary parameters with the exception of possibly one parameter, the units' serial number. If the roaming communication unit could not successfully perform this initialization on the system, or if the unit received a reject of its attempted logon, the communication unit would begin looking for the control resource of another system upon which to attempt initialization.

A trunked system supporting roaming but not coupled to a network can be seen in figure 1 by presuming that the data networks linking the computers (10, 12 and 14) do not exist, are disabled, or, do not carry data between local computers. In this type of system, the roaming unit would have to upload the operating privileges to the local computer which would grant communication privileges to the unit (112) based upon the data sent to the local computer from the communication unit.

What is claimed is:

Claims

1. A network of trunked communication systems constructed and arranged to support a communication unit roaming from one trunked communication system to another retaining substantial communications capability comprising:

a plurality of trunked communication systems;

a plurality of control computers, at least one control computer being associated with each trunking system of said plurality of trunked communication systems, a control computer associated with a trunked system communicating with a communication unit within its associated trunked system and being coupled to other control computers associated with other trunked communication systems forming a distributed network of computers;

a plurality of communication units identifiable throughout said network as based with at least one trunked communication system in said network by a communication unit identifier, at least some of which have:

means for communicating with said plurality of control computers and requesting communication privileges from a control computer associated with a trunked system.

2. The network of claim 1 where said plurality of subscriber units include means for determining that communication with a control computer associated with a trunked communication network is not possible and thereafter scanning communications resources to communicate with other control computers.

3. The network of claim 1 including means for interfacing a communication unit in its base trunking system in said network to the public switched telephone network.

4. The network of claim 1 including means for interfacing a communication unit in a foreign trunking system in said network to the public switched telephone network.

5. The network of claim 1 where said plurality of communication units include identification means for uniquely identifying themselves, base trunked communication systems and its trunked radio privileges to said control computers.

6. The network of claim 1 where said plurality of communication units include identification means for identifying trunked radio privileges to said control computers.

7. The network of claim 1 where said means for communicating with said plurality of control computers includes radio means for monitoring control channels associated with trunked radio communication systems comprising said network and decoding control data on said control channels.

8. The network of claim 5 where said means for determining that communication with a control computer associated with a trunked communication network is not possible includes a means for measuring errors on said control channels.

9. The network of claim 1 where said plurality of control computers communicate directly with other control computers via a data network.

10. The network of claim 9 where said data network is a packet switched data network.

11. The network of claim 1 where said plurality of trunked communication systems each include a plurality of trunked repeaters.

12. A radio for use in a network of trunked communication systems, said network constructed εmd arranged to support radios roaming from one trunked communication system to another retaining substantial commυni cations capability, each trunked communication system of said network having an associated control computer and broadcasting control data on a control resource, said radio comprising:

means for detecting a control resource from a resource controller of a trunked communications system of said network; means for identifying said resource controller as supporting roaming trunked radios from data broadcast from said resource controller station; means for requesting communications privileges from said resource controller; means for identifying said radio to said control computer; and means for accepting a temporary identifier from said control computer.

13. In a network of trunked communication systems constructed and arranged to support a communication unit belonging to a plurality of units roaming from one trunked communication system to another while retaining communications capability, each roaming communication unit having a base system and each trunked communication system of said network having a control computer, said computer of each trunked communication system being coupled to computers of other trunked communication systems of said network, each computer having a data base of information of privileges granted to a roaming communication unit, said plurality of roaming units having varied communications privileges in various trunked communications systems, a method of establishing communications privileges for a communication unit in a foreign trunking system: comprised of:

scanning control channels of said trunked communication systems;

identifying a foreign trunked communication system that supports roaming communication unit;

requesting communication privileges from said foreign system and identifying the requesting radio to said foreign system;

verifying communication privileges granted to said communication unit in its base system;

downloading data from its base system computer to the foreign system computer describing said radio's communication privileges in said base system.

14. The method of claim 13 including the step of granting data transfer privileges between said base system and said foreign system.

15. In a network of trunked communication systems constructed to support a communication unit roaming from one trunked communication system to another, each trunked communication system in said network having a control resource on which control data for said system is exchanged with communication unit, and having a control computer transmitting and receiving data on said control resource, said communication unit having a designated base trunked system and roaming from said base system to foreign systems, a method of allowing a communication unit in a foreign system, communications in said foreign trunking system comprising:

linking control computers associated with trunking systems of said network as a distributed computer network;

receiving requests for service from communication unit visiting a foreign trunked communication system on a corresponding control resource;

processing said request for service by said network of control computers to identify the validity of the communication unit and communication privileges for the communication unit;

granting communication privileges to a valid roaming communication unit within said foreign trunking system while said roaming communication unit is within said foreign trunking system;

revoking said communications privileges from said roaming communication unit after said communication unit leaves said foreign trunking system.

16. A trunked communication systems constructed and arranged to support a communication unit roaming from one trunked communication system to another retaining substantial communications capability comprising:

a trunked communication system;

a control computer associated with said trunked communication system;

a communication unit identifiable to said control computer as based with at least one trunked communication system in said network by data within said communication unit, said communication unit having:

means for communicating with said control computer and requesting communication privileges from said control computer associated with a trunking system.

17. The trunked communication system of claim 16 where said subscriber unit include means for determining that communication with a control computer associated with a trunked communication network is not possible and thereafter scanning communications resources to communicate with other control computers.

18. The trunked communication system of claim 17 including means for interfacing a communication unit in a foreign trunking system to the public switched telephone network.

19. The network of claim 17 where said communication unit includes identification means for uniquely identifying itself, base trunked communication systems and its trunked radio privileges to said control computers.