Radio channel allocation based on location of mobile users

3-2sal4 - 202~3~3 RADIO CHANNEL ALLOQTION BASED ON LOCATION OF MOBILE USERS FIELD OF THE INVENTION The present invention pertains ln general to broadcast two-way radio communlcations and in particular to mobile communications in a system havlng multlple repeater statlons.

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202~3~ :BACXG}~UND OF TE~E INVENTION Mobile radio communicatlon between lndlvldual vehicles, as well as base stations, has a limited range for dlrect communication.

To extend the range of communication, transmltting and receiving statlons, repeaters, are provlded whlch have antennas mounted on towers, tall buildings, mountains, etc., so that each covers an extended geographic area.

By properly spacing the towers, communication can be maintalned between vehicles and base stations over a very large area.

To even further extend the range of operation, the stations can be interconnected with wired or wireless networks In typical operation wlth repeater stations, a mobile radio in a vehicle transmits a request to a partlcular station for access to any one of a plurality of communlcation channels available at that station.

If the one requested station hears the request from the mobile radio, and a channel is avallable, that one station allocates a channel whlch ls then used by the mobile radlo for two-way communicatlon.

However, to insure contlnulty of communlcatlon over a large geographlc area, the zones of the transmit/recelve statlons must overlap to some extent.

Further, variations in propagation conditions can change the distances at which a mobile radlo can communlcate with a station.

Thus, lt frequently occurs that a request for a channel from a mobile radlo is not servlced by the requested statlon.

When thls occurs, the moblle radio sequences to a second statlon and addresses lts servlce ` request to that statlon, even though the second station may be further away.

If the second addressed station receives the request and allocates a channel, that station must also use a narrow-band communication channel back to the original station and further request . . .

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, 2~2~3~3 a communication channel for use at that statlon.

In the lnstances where the mobile radio requlres communlcatlon only wlth other moblle radios ln the zone of the first statlon, there is an unneeded allocatlon of the channel at the second station together wlth an unneeded allocatlon of an inter-statlon narrow band communlcatlon llnk.

Thus, there ls a waste of channel capaclty and an lnter-zone llnk when communicatlon ls only requlred wlthln one zone.

The radlo frequency spectrum avallable for two-way communlcatlon ls very llmlted, and ls therefore very valuable.

Thus, any excess allocation of channels or llnks ln the lnterconnectlon network is a substantial economlc loss.

In vlew of thls problem, there exlsts a need for a method and apparatus for llmltlng the allocatlon of communlcation channels in a two-way radlo system to the absolute mlnlmum number of channels and llnks requlred for the deslred communlcatlon.

~ : ' ~;UMMARY OF THE INVENTION In accordance with one aspect of the invention there is provided a method for allocating a communication channel in a broadcast communication system having a plurality of geographic zones, each zone having a corresponding transmit/receive station, the system having a control system for directing communication through broadcast communication channels with mobile radios, the method comprising the steps of: determining a geographic location for a one of said mobile radios by apparatus located with said one mobile radio, said one mobile radio being a member of a user group restricted to a one of said zones, transmitting said determined geographic location by said one mobile radio to any of said stations for transfer to said control system, said control system having a geographical reference defining each of said zones, transmitting a request for a communication channel from said one mobile radio to a selected one of said transmit/receive stations, said one transmit/receive station not being the station corresponding to the zone in which said one mobile radio is restricted, said control system comparing said received geographic location to said geographic reference to determine if the requesting mobile radio is located in said restricted zone, and if said requesting mobile radio is located in said restricted zone, allocating to said one mobile radio a communication channel of the transmit/receive station corresponding to said restricted zone.

A selected embodiment of the present invention is a method for allocating a communication channel or block of communication channels in a broadcast radio communication system which operates over a plurality of geographic zones.

Each zone has a corresponding transmit/receive station for providing communication through communication channels with ~obile radios.

In a first step, apparatus ' ' , located with the mobile radio determines the geographic location for the mobile radio.

The geographic location is transmitted by the mobile radio to a control unit or multiple control units for the communication system.

The mobile radio also transmits a request for allocation of a communication channel.

The control system determines the one of the zones in which the mobile radio is located based upon the geographic location transmitted by the mobile radio.

The control system then allocates to the mobile radio a communication channel of the transmit/receive station corresponding to the determined zone in which the mobile radio is located.

A further embodiment of the present invention is a mobile radio system which includes an automatic locator apparatus together with a geographic reference defining nonoverlapping geographic zones for each of the stations within a broadcast system. A control, preferably a computer connected to the mobile radio, reads the automatic vehicle locator to determine the location of the mobile radio when a transmission is to be initiated.

The location of the mobile radio is compared to the geographic reference to determine the operation zone in which the radio is located. A table is maintained for channels to be used by the mobile radio in the various zones.

The mobile radio is then tuned to the selected : ~ :

~02~3~3 , s c:hannel whlch corresponds to the zone in which it ls located.

In a stlll further aspect of the present invention, a control unit for the broadcast system receives repeated updates of the location for moblle radios wlthin the system.

The geographic reference is malntained to deflne the operatlon zones for each of the stations within the system.

When the mobile radio transitlons from a first of the zones to a second of the zones, the control unlt for the system hands-off the moblle radlo from the prevlous zone to a station in the new zone.

Thls is preferably done when there ls a break in communication by the moblle radlo to prevent an interference at the time of hand-off.

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' 202~3~3 ~RIEF DESCRIP~ION OF THE DRAWINGS For a more complete understandlng of the present inventlon and the advantages thereof, reference ls now made to the following descriptlon taken in con~unction with the accompanying drawings in which:

FIGURE 1 is a schematic lllustratlon of a broadcast two-way communicatlon system having three overlapping geographic zones, each zone havlng a transmlt~recelve repeater statlon and a correspondlng control computer system, FIGURE 2 is a block diagram for a moblle radio system for use ln accordance with the present invention, FIGVRES 3a and 3b are flow diagrams lllustrating the operation of the control computer systems shown ln FIGURE 1, FIGURE 4 ls a table lllustratlng a flxed allocatlon of channels for multlple geographlc zones, FIGURE 5 is an illustration of a three zone broadcast communication system having a single control computer system, FIGURE 6 ls a flow dlagram lllustratlng the operation of the computer system, shown ln FIGURE 5, for performlng the function of tracking moblle radlos and handing-off a mobile radio from one zone to the next.

2024~3 DETAILED DESCRIPTION A broadcast two-way radio communicatlon system 20 is lllustrated in FIGURE 1.

The system 20 ln~ludes three transmit/recelve stations 22, 24 and 26 whlch functlon as repeaters.

Each statlon lncludes a tower havln~ an antenna operatlng in con~unctlon wlth radlo transmlttlng and recelving equipment.

Each statlon may have one or more channels for communlcatlon.

For the example of system 20, each station has four channels whlch are deslgnated hereln as A, B, C and D.

Statlon 22 provldes communlcatlons over a geographlc area whlch ls designated as zone 28.

Likewlse, statlon 24 has a zone 30 and station 26 has a zone 32. AS shown, the zones do not necessarlly have lS clrcular shapes due to varlatlons ln terraln, propagatlon condltions and antenna conflgurations.

To lnsure contlnulty over the entire area, the zones must be made large enough to overlap.

Zones 28 and 30 overlap ln a reglon 34. zones 30 and 32 overlap ln a reglon 36.

Zones 32 and 28 overlap in a reglon 38.

All of the zones 28, 30 and 32 overlap ln a reglon 40.

To enhance the communlcatlon through the system 20, there are provlded lnter-zone trunks for lnterconnecting the stations. A trunk 46 connects stations 22 and 24, a trunk 48 connects stations 24 and 26 and a trunk 50 connects stations 26 and 22.

The trunXs may be, for example, microwave or telephone links.

The trunks typlcally have multlple narrow-band channels for volce and data communicatlon.

Each of the statlons 22, 24 and 26 has a respectlve assoclated control computer system 52, 54 and 56.

The broadcast communlcatlon system 20 ls typlcally operated by a communlcatlon suppller who provldes services to multiple users.

Such users can be, for 202~3~3 example, taxi companles, delivery services or bus systems. A user group typlcally leases one or more channels ln the system 20.

The moblle radlos and repeater statlons can communlcate uslng voice, data or both.

The users utlllze the channels for communlcatlon wlth vehicles, such as 62, 64 and 66 as shown in FIGURE 1.

Each of these vehicles has a correspondlng mobile radio 62A, 64A, and 66A.

A user group ls typlcally dlrected ln lts operatlon from a central base statlon 68, which has lts own communlcation antenna 70.

A user group may have vehlcles whlch operate throughout all of the zones or may be llmited to a particular zone, which is typically less expensive than having access to all zones.

In conventional operation of the user group, one channel ls used for both transmittlng and receiving.

When a transmlssion is made from a moblle radio or from the base station, that transmission is received by all of the other radios.

Thus, only one party can speak at one time.

However, all parti~s monltor the designated channel and can hear a common transmisslon or make a common transmisslon.

The trunks 46, 48 and 50 are utllized to extend the communication range for the vehicles ln the system 20.

Should a transmlssion be made from the base statlon antenna 70, it would likely be heard only withln a portion of the zone 32.

However, lf the slgnal from antenna 70 ls retransmitted by statlon 26, the coverage can be extended to the entlre zone 32.

If lt is desired to cover the entlre region o~ the system 20, the volce or data signal transmltted by the antenna 70 ls provlded through the trunks 48 and 50 to the statlons 24 and 22 for transmlssion from these statlons.

In such a : ~ ;

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- 20~3~3 configuratlon, the entirety of zones 28, 30 and 32 are included wlthin the communicatlon range of the base statlon 68. A moblle radlo can likewlse operate through the repeater statlons.

The control computer systems 52, 54 and 56 serve to allocate the available communlcation channels A, B, C and D at each of the statlons 22, 24 and 26.

Each of the radlos 62A, 64A, 66A and the base statlon 68 can be tuned to transmlt and recelve on any one of these channels.

The system 20 includes a home channel whlch serves as a data communlcation link for establlshlng two-way communlcatlon as requlred.

When the transmitter of a moblle radlo or base statlon ls actlvated, keyed, it sends a request to a selected statlon on the home channel, or a deslgnated free channel, for allocatlon of a communlcation channel.

The transmission also includes an ldentlflcatlon ~ID) for the requestlng radlo.

In routlne operatlon, thls request ls recelved at the selected statlon where the local control computer system selects a free channel and allocates thls channel for use by the requestlng moblle radlo.

If an allocated channel ls not utilized for a predetermined length of tlme, the control computer system, for that statlon, deslgnates that channel as 2s belng free, that ls, avallable for use upon request.

When a channel has been allocated to a partlcular user, based upon an ID whlch is transmltted along with the channel request, a transmission ls made from the statlon, such as 26, to all members of that user group identlfying the allocated communlcatlon channel.

Each of these mobile radlos, and any base statlon, then tunes to receive the transmissions on that channel, and to make any transmlsslons on that channel to other partles ln the course of the communicatlon exchange.

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2~2~353 If the requestlng moblle radlo ls a member of the user group whlch has access to all of the zones, and other members of thls user group could be located anywhere ln these zones, then the control computer system at the recelvlng statlon must make a request to each of the other statlons for an avallable channel for communicatlon to moblle radios whlch may be in these other zones.

A radlo, such as 62A, for use ln the present invention, is illustrated in FIGURE 2.

Thls radlo lncludes an antenna 80, a radio transmitter~receiver 82 together wlth a microphone ~4 and a speaker 86.

The antenna 80, transmitter/receiver 82, microphone 84 and speaker 86 are connected together and operate in a conventlonal manner.

The mobile radio 62A further lncludes an automatic vehlcle locator (AVL) 88 which functlons to determine the geographic locatlon of the moblle radlo 62A.

The locator 88 may use any one of several technologles.

The preferred embodlment ls based on the well known LORAN system.

Thls ls a system that determlnes locatlon based upon radlo transmlsslons from LORAN transmlttlng sltes.

In recent years, the electronic equlpment requlred for a LORAN receiver have become relatlvely inexpenslve, while stlll providlng good location accuracy.

An alternative to the LORAN system is GPS, a posltion determining technology based on satelllte transmlsslon.

Thls system, whlle providlng extremely high accuracy, is relatlvely expenslve. A further technology for an automatlc vehlcle locator ls that of dead reckonlng.

This can be based elther upon gyroscopes or a comblnation of compass dlrectlon in con~unctlon wlth odometer measurement.

~0-2~4~3 The actual locatlon data produced by the locator 88 can be a measurement of latitude and longltude, a reference to a predetermlned locatlon or an ldentlflcation for a cell wlthin an arbltrary geosraphlc grld.

Referring to FIGURE 2, the actual locatlon of the moblle radlo 62A ls produced as a number which is transferred to the radlo transmltter/recelver 82.

It ls further provlded to a computer 90 whlch ls ltself connected to the radlo transmltter/recelver 82.

Also provlded in con~unction wlth the computer 90 ls a clock 92 and a memory 94.

The computer 90, clock 92 and memory 94 are optlonal for the mobile radlo 62A in accordance wlth various embodiments of the present lnventlon.

For the embodlments descrlbed ln reference to the baslc system shown ln FIGURES 1 and S, these optional elements are not requlred.

In the system 20, each of the moblle radios, such as 62A, perlodlcally reads the location generated by the automatlc vehlcle locator 88 and transmlts this geographlc locatlon, together with an ID for the mobile radio.

This transmisslon ls recelved by one of the statlons 22, 24 and 26.

The locatlon and ID of the radlo can also be transmltted each tlme that the microphone 84 is keyed for starting a communication, or can be transmltted periodlcally, even durlng transmlssion, by use of a sub-audible tone se~ or low speed data.

As descrlbed above, when an operator keys the microphone 84, a request may be generated, if a channel ls not already allocated, by the radlo 62A for allocatlon of a channel for communication.

Each of the moblle radios, such as 62A, can be automatically tuned to operate on any one of a plurallty of communication channels. A commercial radio whlch operates in thls 2~2~3 manner ls a model SMS 815T manufactured by Unlden Amerlcan Corporatlon.

The broadcast equlpment for system 20, as described above, can be a model MRS 804T made by Uniden Amerlca Corporation.

For each of stations 22, 24 and 26 there is defined an operation zone, which does not necessarily correspond to the communication zones 28, 30 and 32.

The operation zones for each of the statlons 22, 24, and 26 do not overlap any other operation zone.

These zones are geographically dlstlnct.

As an example, the operatlng zone for statlon 26 may be the entlrety of zone 32.

For the statlon 22, the operatlng zone may be the actual zone 28 excluding reglons 36, 38 and 40.

The station 24 would then have an operating zone whlch consists of the zone 32 less reglon 36, 40 and 46.

Thus, there is no overlap in this speclflcatlon for the operation zones of the stations 22, 24 and 26.

For the present example, there is assumed to be one user group whlch has mobile radios 62A, 64A and 66A in vehlcles 62, 64 and 66.

The operation of the user group ls directed from base statlon 68 whlch operates through antenna 70.

For thls example, the radlo locatlon and ID are transmitted each time that the mlcrophone is keyed and are perlodlcally transmltted.

The computer systems, such as 52, 54 and 56, either ~olntly or as a single system, carry out the operatlons descrlbed ln FIGURES 3a and 3b.

The operatlon of the system ls descrlbed ln reference to an overall computer system for convenlence.

The computer system beglns lts functlonal operatlon at an operation block 100 for receivlng moblle radio locatlon reports, together wlth an identiflcation for the moblle radio and stores this ln a location flle, together with the tlme of recelpt, for each moblle radlo.

202~36~ 13 When a moblle, or base station radlo, requlres a channel for communicatlons, a channel request ls made by that radlo to a selected station.

Thls example wlll describe a request by a mobile radio.

The request includes the identity of the mobile radio, its current locatlon and the ldentity of the selected station.

This ls carrled out ln operatlon block 102.

After recelpt of a channel request, the computer system must determine lf this partlcular moblle radlo ls a member of a zone-restrlcted user ~roup.

This ls done in a questlon block 104.

As noted above, certaln moblle radlo users can be llmlted to a partlcular zone lf thelr buslness and operatlons do not extend beyond thls zone.

In such clrcumstances, thls ls generally a less 1~ expensive~ service.

If the response to question block 104 ls yes, that is, the requestlng mobile radlo ls a member of a zonerestrlcted user group, the computer system then transfers to a question block 106 to determine lf the requestlng moblle radlo is located within its restricted zone.

If it ls not operating within its restrlcted zone, the ~equest ls lgnored and control is returned to the operatlon block 100.

If the mobile radio ls operatlng within lts restrlcted zone, as indlcated by lts locatlon report, the computer system transfers to a question block 108.

Wlthin thls question block, the computer system determines if the statlon whlch received the channel request corresponds to the zone in which the mobile radlo is located, and ls authorlzed to operate.

If no response ls recelved, the moblle radio selects a next station and makes a channel request.

If the zones of the zone-restrlcted moblle radio and the selected station colnclde, there is a yes response to questlon block 108.

The computer system .

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20243~3 14 then determlnes ln a question block 110 if any channels are available at the selected station.

If channels are available at the selected station, control is transferred to an operatlon block 112 ln whlch the computer system selects a free channel for allocatlon at the selected station.

Next, ln an operatlon block 114, the computer system commands the selected statlon to allocate the selected free channel for use by the user group of the requestlng moblle radlo.

Next, ln an operatlon block 116, the station transmlts the channel allocatlon to all of the members of the requestlng mobile radlo user group.

These radlos then tune thelr transmitters and recelves to appropriate allocated channel and communlcation then commences.

Upon completlon o~ the transmission of the channel allocatlon, control is returned to the operatlon block 100.

Referrlng back to questlon block 108, if the moblle radlo zone and the selected statlon zone do not colnclde, the computer system transfers to a questlon block 120 to determlne if a channel læ avallable in the zone of the user group.

If a requesting, zonerestrlcted, moblle radio has made a request to a statlon outside of its zone, that station should attempt to have communicatlons set up wlthin the proper zone for the reguestlng moblle radlo.

The fallure of the requestlng mobile radio to make lmmediate contact wlth lts primary statlon may have been due only to a transitory propagatlon conditlon.

In most lnstances, the most favorable communlcation condltions can be establlshed between a mobile radlo ln the statlon coverlng the zone ln whlch the mobile radlo ls located.

If a channel ls avallable ln the zone of the user group, the yes exlt is taken from the questlon block 120 and control is 202~3~3 transferred to an operatlon block 122 where a free channel is selected for a}location to thls user group.

Next, in an operation block 124, the computer system causes the statlon to allocate the partlcular selected channel.

In operation block 125, the statlon transmlts the allocated channel to all the members of the requestlng moblle radlo user group.

Upon completlon of thls transmlsslon, control is returned to the operatlon block 100.

io Further referrlng to questlon block 110, lf no channels are available at the selected statlon, the computer system takes steps to attempt to set up communlcatlons for the requestlng moblle radlo.

As shown ln FIGURE 1, there can be substantlal overlap between the coverage areas of the varlous statlons. A geographlc flle is malntained to deflne the overlap zones in which lt ls llkely that a statlon for one zone can extend its operations into a portion of another zone.

This extenslon of area is termed an overlap zone and a statlon which can perform this function ls termed, for thls purpose, an overlap station.

In an operatlon block 126, the computer system checks the locatlon flle, prevlously establlshed, to determine if any members of the user group are located ln an overlap zone from an ad~acent station.

If so, the statlon which has the overlap capability is identified.

In a question block 126, the computer system determlnes if any such overlap zones and statlons exlst.

If no such zones exlst, there ls then no possibllity of establishing communlcation wlth the requesting moblle radlo and control ls returned to operation block 100.

When this occurs, the moblle radlo pauses for a short tlme and then makes another channel request.

202~3~3 16 If there ls a posltlve response to the question block 127, a free channel ls selected at the overlap statlon.

Thls is carried out ln an operation block 128.

Next, ln an operatlon block 130, the overlap statlon allocates the selected channel for use by the user group of the requestlng mobile radio.

Finally, the overlap statlon ls commanded to transmlt the channel allocation to all members of the requestlng moblle radlo user group.

Thls ls done ln an operation block 132.

After operatlon block 132, lt ls hlghly desirable, as soon as possible, to transfer communlcatlon back to the station that dlrectly supports the zone ln whlch the mobile radio and its user group are located.

When an overlap station is used in the manner described above, the control system transfers to a questlon block lgO which perlodically makes a request to determlne lf a channel ls available in the zone of the user group.

If such a channel ls avallable, control is transferred to the sequence of operatlon blocks 122, 124 and 125 to allocate the avallable channel.

If a channel ls not avallable, control ls transferred to a questlon block 142 to determlne lf the communlcatlons between the members of the user group have termlnated. A communlcatlon event is terminated when there has been a predetermined time wlthout any communication by the members of the user group.

When thls time out perlod has elapsed, control ls returned to the operation block 100.

If the tlme out period has not elapsed, the no exit is taken from question block 142 and control ls returned to the question block 140 to again determine if there may be a channel available at the zone assoclated with the user group.

Further refPrring to FIGURE 3a and the questlon block 104, if lt ls determlned that the requesting . . ~ ~ , .

202~35~ mobile radio ls not a member of a zone-restrlcted user yroup, the no exit ls taken to an operatlon block lS0.

A non-restrlcted moblle radlo ls a member of a user ~roup in which the moblle radlo can be located ln any of the zones wlthln the system 20.

However, lf the act~ve members of a partlcular user group are located only wlthln certaln zones withln the entlre system, then only those zones should be allocated for use by the user group.

The allocatlon of addl~lonal zones ls a waste of spectrum capacity.

Further, the members of the user group have no need to utllize the channels wlthln these unoccupled zones.

However, as further descrlbed below, lt ls necessary to track the actual locatlons of the users and if they should enter a new zone, not prevlously allocated, then the station ln the new zone should allocate a channel for use by the members of thls group.

Llkewlse, lf all members of the user group leave a zone, then the channel allocated for thls group can be cancelled and made avallable to other users.

However, lt may be preferable ln certaln sltuatlons to allocate channels ln all of the available zones for a partlcular user group.

Thls may be due to a particular user group always being active ln the zones or a system ln which there are only a llmited number of zones.

After the functlons ln operatlon block 150 have been carried out by the computer system for the communlcatlon system 20, operatlon ls transferred to a question block 152 to determlne lf there ls a free channel avallable ln each of the determlned zones.

If not, control ls transferred to an operation block 154 to check the location flle and determlne lf any members of the user ~roup are ln an overlap zone from an ad~acent statlon whlch could service those users through the . , 2~2~3~3 .

18 overlap zones.

If so, these overlap statlons are :Ldentified.

Subsequent to operation block 154 or lf a positive xesponse ls made to questlon block 152, control ls transferred to an operatlon block 156.

Within thls operation block, the computer system selects a free channel at each of the available statlons and at any requlred overlap statlons to account ~or as many users as possible.

Next, ln an operatlon block 158, each of the stations allocates the corresponding free channel for use by the members of the user group for the requestlng moblle radlo.

Flnally, ln operation block 160, each statlon transmits lts correspondlng channel allocation to all members of the requestlng moblle radlo user group.

Communlcations then begln for the members of this user group.

Control ls then returned to the operatlon block 10~.

Further referrlng to FIGURES 3a and 3b, a negatlve response to question block 120 lndicates that there ls no channel available ln the zone of the user group.

At this point, a zone-restrlcted mobile radlo has made a channel request to a statlon outside of lts zone.

The computer system then enters a questlon block 170 to determlne if a channel ls avallable at the selected statlon which received the request from the moblle radlo.

If so, control ls transferred to an operatlon block 172 wherein a free channel ls selected for - allocation at the selected station.

Next, in an operation block 174, the selected channel ls allocated by the selected station for use by the user group.

In an operatlon block 176, the selected station transmlts the channel allocation to all members of the requestlng moblle radlo user group.

However, ln this sltuatlon, communications are belng carrled out wlth the members of ` ~ ':

2~2~3 19 t;he mobile radio user group by a statlon whlch is not physically located closest to the members of the user group.

Therefore, the system attempts to transfer c:ommunication back to the station whlch covers the zone ln whlch the members of the user group are located.

This ls done through the sequence of operatlons carrled out ln blocks 140 and 142, descrlbed above.

Referrlng further to questlon block 170, if a channel ls not avallable at the selected station, control ls transferred to an operatlon block 180.

At this polnt the system determlnes by referrlng to the locatlon file lf any members of the requestlng user group are ln an overlap zone from an ad~acent station and an ldentlty ls made for the overlap station.

Next, control ls transferred to a questlon block 182 to determine lf there are any overlap zones.

If no overlap zones are avallable, control ls returned to the operatlon block 100 and the moblle radlo request for a channel ls unsuccessful.

It must try at a later tlme to obt~in a channel allocatlon.

If, however, overlap zones are avallable, an operatlon block 184 ls entered to select a free channel for allocatlon at the overlap station.

Next, the selected channel ls allocated at the overlap statlon and made avallable for communlcatlon purposes ln an operatlon block 186.

Flnally, the overlap statlon transmits the channel allocatlon to all members of the requesting moblle radlo user group.

Thls ls done ln an operatlon block 198.

However, since communlcatlons are not belng carried out wlth the primary statlon which covers th~ zone ln whlch the users ara located, control ls transferred to the blocks 140 and 142 in an attempt to transfer communicatlon back to the home statlon for the user group when a channel becomes available.

-`` 202~3~3 A further embodlment of the present lnvention utillzes the full system for the mobile radio 62A shown in FIGURE 2 together wlth a channel allocation table illustrated in FIGURE 4.

This embodlment does not S require the operations descrlbed ln FIGURES 3a and 3b for the control computer systems, such as 52, 54 and 56.

In thls embodiment, the table shown ln FIGURE 4 ls malntained ln the memory 94 of radio 62A.

Each mobile radlo has a predetermined channel of operation for each zone in which it may operate.

Whenever the radio 62A ls keyed through microphone 84, the computer 90 is activated to read the automatlc vehlcle locator 8~ output and compare lt to a geographic reference stored in memory 94.

The memory 94 lncludes a geographlc deflnltion for each of the operatlon zones ln the system 20.

These are defined, nonoverlapping zones in a broadcast system, such as shown ln FIGURE 1.

The computer determines, by use of the zone geographlc lnformatlon, the operatlon zone ln which the moblle radlo 62A ls located.

The table shown in FIGURE 4 ls then referenced to determine the communlcation channel for use by the moblle radlo 62A.

For the presently descrlbed embodiment, the mobile radlo 62A operates on channel A when in zone 1, channel B when ln zone 2 and channel C when ln zone 3.

The channel allocations must be conslstent for all the members of a particular user group.

This embodiment requlres no calculatlons or allocatlons of channels by the control computers or statlons.

The statlons, for thls embodiment, operate 3a purely as transponders for extendlng the range of the mobile radlos.

A still further embodlment of the present inventlon ls described ln reference to FIGURES 2, 3a, 3b and 5. A broadcast communicatlon system 200 has stations 202, 204 . .

., : , . :

2~3~ and 206.

The stations have respective zones 208, 210, and 212. zones 208 and 210 overlap ln a reglon 214, zones 210 and 212 overlap in a region 216 and zones 212 and 208 overlap ln region 218.

All of the zones 208, 210 and 212 overlap in a region 220.

The statlons 202 and 204 are connected together by a trunk 230, statlons 204 and 206 are connected by a trunk 232 and the statlons 202 and 206 are interconnected by a trunk 234.

As noted ln reference to FIGURE 1, these trunks can be, for example, telephone or mlcrowave llnks.

The system 200 further lncludes a control computer system 224 whlch ls connected through a bl-dlrectlonal llne 226 to statlon 204.

The computer 224 controls each of the statlons 202, 204 and 206.

Control ls exerclsed at the statlons 202 and 206 by commands sent vla the trunks 230 and 232.

For the system 200 there ls shown a user group whlch lncludes a base statlon 236 connected through a line 238 to statlon 206.

The user group further lncludes vehlcles 240, 242 and 244.

These vehicles lnclude respectlve radlos 240A, 242A and 244A.

The baslc dlfferences between the systems 20 and 200 is that the system 200 has a centrallzed control computer system 224 for directing the channel allocation and operatlon of the system 200, rather than the lnterconnected control computer systems 52, 54 and 56 shown in FIGURE 1.

The functlons performed by the system 200 are the same as descrlbed in FIGURES 3a and 3b for system 20.

The system 200 utilizes a radlo such as the radio 62A shown ln FIGURE 2, but lt does not necessarlly require the lnclusion of the computer 90, clock 92 and memory 94;

-` 2~2~3~ 22 A further functlon of the computer 224 ln system 200 ls descrlbed in reference to the flow dlagram shown ln FIGURE 6.

As the moblle radlos move through the geographlc area of the system 200, they can leave the range of one transmlttlng/receivlng statlon and must therefore be transferred to a channel provided by another one of the statlons.

In conventlonal systems, such as cellular telephone systems, thls hand-off ls carrled out when the amplltude of the signal received I0 from the moblle radlo drops to a certaln threshold~ However, the hand-off ln accordance wlth the present lnventlon ls carrled out ln an entlrely dlfferent manner.

It ls totally lndependent of the amplltude of the radlo slgnal from the mobile radlo.

Instead, the computer 224 tracks the actual locatlon of each moblle radio and when a mobile radlo crosses an operatlon zone boundary, a hand-off ls made between the stations for the prevlous zone and the new zone.

In a s~lll further aspect of the present lnvention, the computer system 224 walts for a transmlsslon break to make the transitlon.

As a result, the hand-off can be made virtually undetectable to the users.

Referrlng now to FIGURE 6, there is shown the tracklng operation by the computer 224.

Following the start, the computer 224 enters an operatlon block 280 whereln it receives a perlodlcally transmltted moblle radlo ID and locatlon.

Next, the computer enters operatlon block 281 wherein the moblle radlo locatlon, ID and tlme of locatlon are stored ln a table.

This corresponds to block 100 shown in FIGURES 3a and 3b.

Followlng block 281, the computer 224 enters a question block 282 for determining if the recelved moblle radlo is in a communlcatlon mode, that ls, lts user group ls actlve. rf not, the NO exlt ls taken and :

2~2~3`~3 23 control is returned to operation block 280.

If the moblle radio is ln a communication mode, the YES exlt is taken to a question block 284.

Within the question block 284, the computer 24 s determines if the mobile radlo has changed operatlon zones slnce the last location report.

Thls ls done by reference to the geographlc zone table malntalned for each station operating zone.

If the moblle radlo has not changed operatlon zones slnce the last locatlon report, the N0 exlt ls taken and control ls returned to the operatlon block 280.

If, however, the moblle radlo has changed operation zones slnce the last locatlon report, the YES ls taken to an operatlon block 286.

If the moblle radlo has changed operatlon zones since the last location report, the YES exit is taken to a question block 286.

In block 286, the computer 224 determines if there is already an allocated channel in the new zone for the user group of the monitored mobile radio.

If not, control is transferred to an operational block 288 for selecting a free channel for allocation-in the new station zone.

Following block 288, the computer 224 enters operation block 290 to allocate the selected channel ln the new station zone.

This ls carried out by sending appropriate commands to the new station.

Following operational block 290, control is transferred to an operation block 292.

If there previously was an allocated channel for the user group in the new zone, control ls transferred through the YES exlt of block 286 to the lnput of ~0 operation block 292.

Wlthln the operatlonal block 292, the computer 224 monitors communlcations from the active moblle radlo to detect a break in the communication stream.

Typically this is done by monltorlng the amplitude of .. . . . . . .

. ~ .

2~2~3~ 24 communlcations on an allocated channel.

When the amplltude drops below a predetermined threshold for a short time, this ls deemed to be a break ln communlcatlon.

After such a break ls detected, operation ls transferred lnto an operatlon block 294.

Immedlately following detection of the break, the computer 224 transmlts a channel allocatlon command ln block 294 for the new zone.

The moblle radlo ls then tuned to the new channel.

Thus, as shown ln reference to the operatlon descrlbed ln FIGURE 6, moblle radlos are handed off from one station to the next as a functlon of the locatlon of the moblle radlo wlthln predetermlned operation zones assoclated wlth each of the transmlttlng/recelvlng statlons.

There ls a hand-off made even though the quallty of communlcatlon wlth a particular statlon ls more than adequate.

However, by doing the hand-off on an arbltrarlly defined geographlc basls, there is a tendency to have a more unlform distrlbutlon of vehlcles ln the zones and the operation of the system 200 ls made less dependent upon local propagation features and terraln.

Further, the quality of the communicatlon ls not permltted to degrade to a marglnal level before the hand-off ls made, as ls often the case ln conventlonal systems.

In summary, the present lnventlon ls the method and apparatus for allocating radio communication channels in a multl-station system based upon the geographic location of a mobile radio withln predetermlned operating zones assoclated with each statlon.

Such allocatlon optlmizes the use of llmited communication spectrum.