CA1219915A - Wide area coverage radio communications system and method - Google Patents
Wide area coverage radio communications system and methodInfo
- Publication number
- CA1219915A CA1219915A CA000468582A CA468582A CA1219915A CA 1219915 A CA1219915 A CA 1219915A CA 000468582 A CA000468582 A CA 000468582A CA 468582 A CA468582 A CA 468582A CA 1219915 A CA1219915 A CA 1219915A
- Authority
- CA
- Canada
- Prior art keywords
- message
- site
- transmission
- sites
- frequencies
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W84/00—Network topologies
- H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
- H04W84/04—Large scale networks; Deep hierarchical networks
- H04W84/08—Trunked mobile radio systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
- H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
- H04B7/2621—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using frequency division multiple access [FDMA]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
- H04W4/06—Selective distribution of broadcast services, e.g. multimedia broadcast multicast service [MBMS]; Services to user groups; One-way selective calling services
- H04W4/10—Push-to-Talk [PTT] or Push-On-Call services
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W76/00—Connection management
- H04W76/40—Connection management for selective distribution or broadcast
- H04W76/45—Connection management for selective distribution or broadcast for Push-to-Talk [PTT] or Push-to-Talk over cellular [PoC] services
Abstract
ABSTRACT A wide area coverage radio communication sys-tem of the type adapted to relay a message sub-stantially simultaneously from a plurality of fixed location sites to a plurality of portable or mobile units includes a plurality of repeaters at each of the sites. Each of the repeaters is ar-ranged to transmit and receive on a respective different frequency duplex pair or channel. Con-trol means at one of the sites senses channel availability at all of the sites and causes one repeater at each of the sites to transmit the mes-sage on its respective different frequency. Access to the system by the portable units is pro-vided on a trunked basis through the control means.
Description
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BACRGRO~7ND OF THE INVENTION
Line of sight radio communication over large or wide geographical coverage areas has posed significant problems in the past. Systems of this type generally must make communication possible between mobile or portable equipment which have low power transmitters and which can move in any direction within the wide coverage area. System configurations which have been used to make such communication possible include systems having a centralized fixed-site receiver and high power transmitter and a plurality of remotely located receivers connected by wireline or microwave back to the central site, systems including mobile re ~eaters which rebroadcast the radio communica- --tions, and systems w~ich simultaneously transmit the radio communication or message from multiple fixed sites on the same fre~uency. Systems of this last type have often been referred to as ~simulcast n systems.
Simu}cast syste~s generally include a plural-ity of radio transmission and reception fixed sites located in spaced apart relation throughout the geographical area to be provided with radio communication coverage~ Ideally, the fixed sites are distributed such that areas not covered by one site will be covered by another site~ As a re-sult, the sites are distributed to create an over-lapping patchwork of individual radio coverage areas which, when taken together, approximates the 30 desired geographic coverage area. The message to -be transmitted from each site is conveyed from one site called the master site to each of the o~her .'
BACRGRO~7ND OF THE INVENTION
Line of sight radio communication over large or wide geographical coverage areas has posed significant problems in the past. Systems of this type generally must make communication possible between mobile or portable equipment which have low power transmitters and which can move in any direction within the wide coverage area. System configurations which have been used to make such communication possible include systems having a centralized fixed-site receiver and high power transmitter and a plurality of remotely located receivers connected by wireline or microwave back to the central site, systems including mobile re ~eaters which rebroadcast the radio communica- --tions, and systems w~ich simultaneously transmit the radio communication or message from multiple fixed sites on the same fre~uency. Systems of this last type have often been referred to as ~simulcast n systems.
Simu}cast syste~s generally include a plural-ity of radio transmission and reception fixed sites located in spaced apart relation throughout the geographical area to be provided with radio communication coverage~ Ideally, the fixed sites are distributed such that areas not covered by one site will be covered by another site~ As a re-sult, the sites are distributed to create an over-lapping patchwork of individual radio coverage areas which, when taken together, approximates the 30 desired geographic coverage area. The message to -be transmitted from each site is conveyed from one site called the master site to each of the o~her .'
-2-sites by microwave or wireline and subse~uently transmitted by all of the sites on the same fre-quency to be received by all of the mobiles and other portables within the wide coverage area.
Unfortunately, some problems are encounterec with such simulcast systems. Because it is virtu-ally impossible to configure the coverage area of each fixed site exactly, overlapping of the in-dividual coverage areas must be allowed to assure complete or total wide area coverage. The cover-age area overlappina of simulcast systems causes problems. Because all of the fixed site trans-mitters transmit on the same frequency, radio Ere-quency carrier beat note interference and demodu lated audio phase ca~cellation can result in the overlapping areas. Correction of these problems is expensive. For example, expensive frequency standards, linear p~.ase microwave multiplex equi~-ment or compensated telephone lines and phase delay equipment are required. The present inven-tion avoids these proble~s by utilizing a differ-ent transmit channel frequency at each of the fixed si~es and a trunXed access system.
Trunked radio systems are well known. In such systems, a fixed n~mber of duplex radio chan-nels is shared amona a large number of potential users. The system through a central controller allocates the radio .hannels to the users depend-ing on their communication need and deallocates the radio channel upon the completion of a user's transmission. Communic~tion between users and t~e central controller occurs on a designated link which can be a separate duplex control channel or some form of subaudible, audible, supra-audio, or subcarrier shared ra~io channel usaye.
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Unfortunately, some problems are encounterec with such simulcast systems. Because it is virtu-ally impossible to configure the coverage area of each fixed site exactly, overlapping of the in-dividual coverage areas must be allowed to assure complete or total wide area coverage. The cover-age area overlappina of simulcast systems causes problems. Because all of the fixed site trans-mitters transmit on the same frequency, radio Ere-quency carrier beat note interference and demodu lated audio phase ca~cellation can result in the overlapping areas. Correction of these problems is expensive. For example, expensive frequency standards, linear p~.ase microwave multiplex equi~-ment or compensated telephone lines and phase delay equipment are required. The present inven-tion avoids these proble~s by utilizing a differ-ent transmit channel frequency at each of the fixed si~es and a trunXed access system.
Trunked radio systems are well known. In such systems, a fixed n~mber of duplex radio chan-nels is shared amona a large number of potential users. The system through a central controller allocates the radio .hannels to the users depend-ing on their communication need and deallocates the radio channel upon the completion of a user's transmission. Communic~tion between users and t~e central controller occurs on a designated link which can be a separate duplex control channel or some form of subaudible, audible, supra-audio, or subcarrier shared ra~io channel usaye.
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-3-It is therefore a general object of the pres-ent invention to provide a new and improved wide coverage area radio communication system.
It is a further object of the present inven-tion to provide such a system having a pluralityof fixed transmission sites and wherein each fixed transmission site is arranged to transmit on a -different respective frequency to avoid beat note -interference and phase cancellation in overlapping :-10 coverage areas. ~
It is a further object of the invention to -provide such a system wherein access of the system is allocated by a trunking system.
It is another object of the present invention to provide a new and improved method of relaying a message substantially simultaneously from a plu-rality of fixed transmitter sites over a wide geo-graphical area.
It is another object of the invention to pro-vide a method of relaying a message by radio com-munication from one ~obile to at least another mobile over a wide geographical coverage area without requiring s~ecial audio conditioning or `
frequency control standards.
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~Z~ 5 SUM~ARY OF ~E INVENTION
The invention proYi~es in a two-way communi-cation system of the type adapted to relay a mes-sage substantially simul aneously from a plurality of fixed location si es, the improvement compris- -in~ radio frequency transmission means at each of the sites arranged for transmitting on a respec-tive differenct freq!1encJ than the transmission frequency of any other o. the sites~ means for selecting among the ?lurzlity of different fre-quencies at said sites to provide corresponding channels at each of said respective sites, and `
control means for selectlng a given channel and causing at least two of the transmission means to transmit the message substantially simultaneously on the respective different frequencies. In ac-cordance with a preferred embodiment of the pres-ent invention, the control means is arranged for causing each of the ,rans.~ission means to transmit the message substantiall~ simultaneously on the respective different trar.s~ission frequencies.
The present invention further provides a two-way communication system for relaying a mes- -sage over a wide area. ~ne system includes a plurality of Eixed transrission means, each fixed transmission means havinc a coverage area and be-ing arranged for trans~itting radio frequency signals on a plurali~y Oc different transmission frequencies, control means for causing each fixed ~
transmission means to trensmit the message on a --respective different tra..s~ission frequency, port-able receiving means locêted within the coverage areas, each portable rec~iving means being ar- -:~Z~L9~5 ranged for receiving on all of the transmission :
frequencies, and each fixed transmission means further including receiver control rneans for caus-ing each portable receiving means within its coverage area to tune to its transmission fre-quency.
The present invention further provides a method of relaying a message substantially simul- .
taneously from a plurality of fixed location sites. The method includes the steps of providing each site with radio frequency transmission means ~
capable of transmitting on a respective different .
plurality of frequencies than the transmission frequencies of any other of the sites, selecting among the plurality of frequencies at the sites to provide corresponding channels at each of the re-spective sites, setting at least two of said transmission means to different respective trans- ..
mission frequencies corresponding to a given one 20 of the channels, and transmitting the message from ~.
the set transmission means.
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~RIEF DESCRIPTION OF THE DRAWINGS .
.'' The features of the present invention which are believed to be novel are set forth with par- ..
ticularity in the appended claims. The invention, together with further objects and advantages ..
thereof, may best be understood by making refer-ence to the following description taken in con-junction with the accompanying drawings, in the several figures of which like reference numerals id~ntify identical elements, and wherein:
Figure 1 is a schematic representation of a .
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wide coverage area communication system embodying the present invention; -Figure 2 is a block diagram of the fixed site identified as site A in Figure 1 and which em ...
bodies the present invention; and Figure 3 is a block diagram illustrating a :
representative one of the other fixed sites of the system of Figure 1 embodying the present inven-tion; and Figure 4 is a flow chart illustrating the operation of the master site controller 60 of Fig~ 2. .
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121~915 D~SCRIPTION OF THE PREFERRED EMBODIMENTS
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Referring now to Figure 1, it illustrates in schematic form a wide coverage area communication system 10 embodying the present invention. The system includes a plurality of fixed transmitting and receiving sites designated as site A, site B, site C, and site D. Each of the sites has a -coverage area indicated by dashed lines with site A having coverage area 12, site B having coverage area 14, site C having coverage area 16, and site D having ~overage area 18. The sites are so lo-cated that radio transmission from and radio re-ception to each of the sites is limited to an es-sentially uniyue geosraphic area. Overlap betweer.
sites may be non-existent or may be total depend-lS inq upon the local terrain or topography of thegeographical area to be covered. For purposes of this embodiment it is assumed that the coverage area of any one site overlaps that of two others so that an entire area of continuous coverage is established.
Each of the fixed sites A, B, C, and D in-cludes radio frequency transmitting and receiving means in the form of transmitter and receiver re-peaters 20, 22, 24, and 26 respectively. Each of the transmitter and receiver repeaters has a fixec antenna 28, 30, 32, and 34. Ea~h of the repeater~
20, 22, 24, and 26 is arranged for transmitting and receiving on a respective different group of frequencies~ with each repeater being assigned a :-predetermined number of duplex channels, for exam-ple five channels, four channels being for system ~-communication, and the fifth channel being used a~ -.
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a control channel. The transmitting and receivi-~ -frequencies of the repeaters are also grouped to-gether so that a transmission frequency of one r~-peater finds three corresponding but different 5 transmission frequencies with the other repeater~. -Each of the sites also includes a microwave transmitter and receiver terminal 36, 38, 40, anc 42. Each of the transmitter and receiver termi-nals 36, 38, 40, and 42 has an associated micro-~0 wave antenna 44, 46, 48, and 50 respectively. T.
microwave transmitter and receivers and the ~icrc- -wave antennas provide a microwave com~unication --link 51 between the various sites. Alternativel~-, a land line could be provided for performing thiC
function.
Each of the sites includes a remote site `
central controller 50, 52, 54, and 56. Each re- -mote site central controller controls the local operation of its respective site and provides for 2~ communication from its site back to a master con-trol siter for example, site A in this embodi-ment. To that end, site A also includes a master site central controller 60. The master site cen-tral controller 60 serves as a control means for ~5 the entire system and supervises and controls the ac~ivities of all sites in the system.
Lastly~ located within the coverage areas of-the sites are mobile units or portables herein after, mobiles, 62, 64, 66, and 68~ Each of the ~
33 mobile units, which may vary in total number, an~ -vary in the number within a individual site co~er- -age area, includes a low power transmitter capabl- -~
of transmitting on any one of the communication channels and any one of the control channels, anc ~2~9~S
9 _ a receiver for receiving on any one of the com-munication or control channels. The mobile units can be related to each other by an automatic grouping of the mobile units into groups of users -who must communicate with each other.
Before the rest of the system is described in ....
greater detail, it may be helpful to follow the progression of a call made on the system 10 of Figure 1. Each mobile unit has a storage device tO which, among other infor~ation, contains its in-dividual identity, a grouping and subgrouping of other units with which the user can selectively communicate, and a listing of control channels -`
which are in use at each site of the system. For a more complete description of such a storage device, reference may be had to U.S. Patent Nos. 4,012,597 or 4,312,070 which are assigned to the assignee of the present invention. The mobile units further inelude equipment which causes its receiver to scan the outbound, or fixed-site transmit frequencies associated with the control channels until a suitably error free data signal is received. The mobile unit stops searching and remains on this control channel outbound frequencv 25 until commanded to tune to another frequency or ~-until the data signal degrades to an unusable level at which time the control channel scan res~mes.
All mobile equipment not engaged in an active call remain tuned to the control channel of the site in the coverage area that it is located in. --~hen a wide area call is selected by a mobile unit and a request for service is initiated by the user -activating the mobile transmitter, the mobile .
9~5 ~ o transmitter transmitts a request to the remote central controller in its coverage area on the in-bound control channel frequency. This request contains the identity of the mobile equipment and group of mobile equipment being called. It also contains the type of service required, for ex-ample, in this instance, a wide area coverage call.
Assuming that mobile unit 66 in coverage ~rea 16 of site C initiates a request for service, the request is received by the fixed site control channel receiver within the transmitter and re-ceiver repeaters 24 and passes to the remote cen-tral controller 56 for interpretation. Since this is a wide area call, the request is relayed by the microwave transmitter and receiver 40 and antenna 48 over the microwave link 51 to the master site transmitter and receiver 36 and then to the master central controller 60 which monitors the activity of all the system channels available for the wide area call. The master site central controller 60 assigns a channel at each site in the system for this wide area call and instructs each of the re-mote central controllers 52, 54, 56, and 58 to transmit a channel assignment instruction address-ed to the mobile units or the group of mobile units requested by the caller. Following the channel assignment instruction, the demodulated audio received from the callin~ mobile unit 66 is relayed by the microwave link from site C to si~e A where the master central controller 60 is locat-ed. The audio is then distributed to the other sites by the microwave link 51 for simultaneous retransmission to the called mobile equipment on a :1219~S
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respective different fre~uency at each of the sites.
The called mobile equipment are tuned to the control channel selected in the scanning mode.
Upon detecting an instruction on the control chan-nel addressed to itself, the called mobile units follow the instruction and tune to the frequency listed in the instruc~ion. On this frequency, the --called mobile equipment user receives the message originated by the calling mobile unit 66.
Upon the completion of the transmission by the calliny mobile unit 66, the master site con-troller 60 is infor~ed of the end of transmission and subsequently instructs the remote central con-trollers 52, 54, 56, and 58 to deallocate the wide area channels. Each remote central controller `
sends an instruction to the mobile equipment in its coverage area monitoring the message channel to retune to its res?ective different control channel. Once the c~annel is cleared in eachsite, the remote central controller of each site notifies the master site central controller 60 by the microwave link 51 that the channel has been cleared. The master site central controller 60 is then free to reassign the channels as desired for another wide area call request.
Referring now to Fig. 2, it illustrates in greater detail the equipment at the master site, site A. The master site includes six repeaters 70, 72, 74, 76, 78, and 80 which comprise the transmitter and receiver repeaters 20 illustrated in Fig. 1. Associat~d with the repeaters is a transmitter combiner 82, such as a Phelps Dodqe TJD 800-5T, and a receiver multicoupler 84, such 11 z~9 as a Phelps Dodqe R~C 800-8N. The transmitter .
combiner is coupled to a transmitting antenna 282 and the receiver multicoupler is coupled to a re- .
ceiving antenna 28b. Four of the repeaters, re-peaters 74, 76, 78, and 80 comprise message chan-nel repeatPrs which are trunked for providing :-voice communication to the mobile units. The re-maining two repeaters, repeaters 70 and 7~ are used for system control of the mobile units. The master site A further includes the remote site central controller 52, such as a T1958 manu-factured by Motorolz, Inc~ which controls the op-eration of the fixed radio equipment such as the repeaters and communicates with the mobile unit logic systems by the ra2io control channel repea'-ers 70 and 72. Repeater 7~ comprises a standby repeater which can be utilized when repeater 70 s not operational, such as, when it is being ser- .
viced. The master site A further includes the master site central controller 60 which is coupl~
to and buffered by a data concentrator 86 which can be, for example, a ~RN 6887A manufactured by Motorola, Inc.... The master site central control- -ler 60 performs higher level system control func-25 tions. Data communication between the master si e .`
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c~ntral controller 60 and the remote fixed sites is provided by data modems 88, 90, and 92 which are connected to three r.ulti?lex channels of a multi-plexer 94. More particularly, data modem 88 is coupled to multiplexer ch2nnel 96, data modem 90 is coupled to multiplexer channel 98, and data modem 92 is coupled to ~.ultiplexer channel 100.
The base band output of multiplexer 94 is fed to the microwave terminal 36 for transmission to th-:~2199~5 other remote fixed sites. A four-way bridge 102 is provided to distribute a common audio signal t~
each remote site through the multiplexer 94 and microwave terminal 36.
Each of the repeaters 70, 72, 74, 76, 78, ar.
80 includes a transmitter which is coupled to th~
transmitter combiner 82, and a receiver which is coupled to the receiver multicoupler 84. As indi-cated, the repeaters are arranged for operating c^.
five different channels. Each channel is indicat-ed with a roman numeral. Hence, the master site '.
transmitting equipment is arranged for transmit-ting on channels AI through AV.
Referring now to Fig. 3, it illustrates the equipment found at one of the remote sites, and more particularly, at remote site B. This is typical of any of the remote sites. -The site B includes six repeaters as does site A, namely, repeaters 110, 112, 114, 116, 11E, and 120. Repeaters 110 and 112 are the control channel repeaters with repeater 112 serving as a standby repeater. In accordance with this pre-ferred embodiment, the bridge 102 allows each mes-sage channel at each site to share a common audio 2S input with one other message channel at each othe-site when a simultaneous transmission of a messac~
by every channel within the common audio groupinc is desired. Consequently, a message channel for group II, group III, group IV, and group V is found at remote site B. Each site has one messac-channel of each group. Control channels are here-in designated as group I but cannot share a co~mc audio input. Each of the repeaters 110, 112, 11', 116, 118, and 120 includes a transmitter section --~
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which is coupled to a transmitter combiner 122, and a receiver section which is coupled to the re- -ceiver multicoupler 124. The transmitter combin~-122 is coupled to a transmitting antenna 30a and receiver multicoupler is coupled to receiving antenna 30b. The receivers of the message repea.-ers 114, lt6, 118, and 120 are also coupled to t~
multiplexer 126 and ~ore specifically to channels 128, 130, 132, and 134 respectively. To provide '0 local control of site B and communication with th?
master site central controller 60, remote site B -includes the remote site central controller 54 which is coupled to a ~ultiplexer channel 136 by 3 -data modem 138. The multiplexer 126 couples the :
remote site central controller and the message re-. . .
peaters to the micro~ave terminal 38. `
Now that the system 10 as illustrated in -Fig. 1 and the portions thereof illustrated in `-Figs. 2 and 3 have been described in general de-tail, a specific call ~rocess will now be descri~-ed. It is assumed that each o~ the mobile units 62, 64, 66 and 68 ha~e locked their receiver and transmitter to the control channel frequency of sites A, B, C, and D respectively. If mobile uni-66 drives out of the coverage area 16 of thetransmitter 24 in site C and into the coverage area of the transmitter 26 within site D, the dat~
transmitted on the control channel of site C will become increasingly deteriorated by noise until .-becomes unusable. hhen a predetermined digitalerror rate is reached, the mobile unit 66 will cause its receiver t~ sequentially tune to the other control channels of the sites in the system. The frequer.cies of the control channels .
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are stored in a storage device in the logic system of the mobile unit 66 equipment. When the re-ceiver within mobile unit 66 receives the control channel signal of site D, the logic system within mobile unit 66 determines that the transmitted data is acceptable error free and causes the re-ceiver within mobile unit 66 to cease scanning and remain on the control channel of site D. Mobile equipment of this type is more specifically des~ribed in the aforementioned U.SO Patent Nos. .,012,597 and 4,312,070.
If the user within mobile unit 62 wishes to-make a wide area call to members of his previously esta~lished group which may, for example, include mobile units 64 and 68, he selects the wide area coverage feature in his mobile equipment and acti-vates his transmitter by pressing a push-to-talk but~on on his transmitter. This causes the trans-mitter within mobile ~mit 62 to transmit a data ~0 word to the remote central controller 52 via the receiving antenna 28b, the receiver multicoupler 84, and the receiver of control channel repeater 70. The remote central controller 52 interprets -the cal} type as a wide area coverage group call and extracts the called group identification from the calling unit identification. The remote cen-tral controller 52 then forwards the request to the master site central controller 60 via the data concentrator 86.
The master site central controller 60 is in-formed of the availability of channels from the remote central controllers 52, 54, 56, and 58 via the microwave link 51, the receiver o~ microwave ~-ter..inal 36, channels 100, 98, and 96 of multi-12~9~S
plexer 94, the data modems 88, 90, and 92, and the .j data concentrator 86. As previously mentioned, .....
the communication channels in accordance with this preferred embodiment, are grouped into five 5 groups. Group I includes all the control channel ..
repeaters and standby equipment of each site.
This group includes repeaters 70 and 72 of site A ....
as illustrated in Figure 2, repeaters 110 and 112 of site B as illustrated in Figure 3, and equiva-lent repeaters for sites C and D. Group II in-cludes one message channel repeater from each site and is represented, for example, by repeater 74 of ..
site A and repeater 114 of site B. Group III in- ....
cludes one message channel repeater from each site .:
including repeaters 76 and 116. Similarly, Group IV includes repeaters 78 and 118, and Group V re-peaters include repeaters 80 and 120. Also as ..
previousl~ mentioned, each repeater operates on a uniquP and discrete frequency duplex pair. .
The master site central controller 60 through an internal comparison alaorithm recognizes that i.
the message channels of Group III, for example, are unutilized and selects this channel group for the message of mobile unit 62 to be simultaneously ..
~5 relayed from the fixed sites A, B, C, and D. The master site central controller 60 then transmits instructions to each remote site central control-ler 52, 54, 56, and 58 to transmit on its respec- -tive control channel to each mobile unit in the called group. The master site central controller 60 sends the instruc~ion to the site A remote cen- ..
tral controller 52 directly from the master site central controller 60 to the data concentrator 86 and to the remote si~e central controller 52. T~.e 3~Z~9~
other sites require the microwave link 51 to re-ceive its instruction. Therefore, the output of the data concentrator 86 for sites B, C, and D
passes through the data modems 88, 90, and 92 for 5 conversion for trans~ission through the multiplex --~
channels 100, 98, and 96 oE multiplexer 94 and transferred to the microwave link 51 through the microwave terminal 36 and its antennas 44. At re-mote site B, illustrated in Figure 3, the base band of the transmitted microwave signal is de-modulated by the microwave terminal 38 and multi-plex channel 136. The demodulated signal is de-multiplexed by multi?lexer 126. The recovered in-formation is passed to data modem 138 for conver-15 sion to a digital fo-mat and presented to the re `
mote site B remote site controller 54~ The remote site controller 54 t-ansmits a data word on the site B control chann~l via repeater 110 and trans-mitter combiner 122 o any and all mobile units with a group identification like the calling mobile unit 62 which happen to be within the coverage area of remote site B. A similar process occurs in sites C and D.
In site 8, the equipment within mobile unit 64 detects and recognizes the group identification of the outbound data word as its own and decodes the remainder of the data word to establish the message channel to w;~ich it should tune its re-ceiver and transmitt~r. As a result, the control means or master site controller 60 has caused the mobile equipment of -.obile unit 64 within site B
to set its receiver and transmitter to the proper :~
frequency for receiv.ng the wide area coverage --transmission. The e~uip~,ent within mobile unit 64 ~Z~99:~5 tunes to the message channel of site B which cor-responds to the Group III message channel for re-ceiving the relayed or retransmitted message of mobile unit 62. A similar sequence of events occurs for mobile unit 68 and all other mobile units within the designated group. For mobile units of dissimilar groups, such as mobile unit 66 within site C coverage area, transmission on the control channels are ignored and the mobile unit_ of dissimilar identification remain tuned to the r respective control channels.
Mobile unit 62, which is the calling mobile unit, is given a message channel assignment of t.e Group III channel at site A by the remote site -15 controller 52 through control channel repeater 7C `
and transmitter combiner 82. The process typical~
ly takes less than one second and occurs in such a manner that the user is unaware of the process.
The user of mobile unit 62, to initiate his call, 20 had pressed and held a push-to-talk button durin -the brief system access time and began his conve -sation on the assigned message channel. His voice -is modulated on the RF carrier of the mobile equipment transmitter of mobile unit 62 and trans-mitted to the site A Group III message channel re-ceiver of repeater 76 via the receiver multi- -coupler 84. The users audio is demodulated in t~.e receiver of repeater 76 and, in response to a co--mand from remote site controller 52, is coupled ~o the four-way bridge 102 where the audio is split three ways. These three outputs are connected to multiplex channels 140 corresponding to channel :
III-B, channel 142 corresponding to channel III _r~
and the channel corresponding to III-D of multi- -12~9~
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plexer 94~ The base band output of multiplexer 94 is modulated on a microwave RF carrier at the -microwave terminal 36 and transmitted by antennas 44 over the microwave link 51 to the remote sites B, C, and D.
At site B, which is representative of the other remote sites, the microwave terminal 38 de-modulates the base band of the microwave signal and couples it to the multiplexer 126 for separa-tion of multiplex channel III-B from the base band. The demodulated audio is coupled to the message channel repeater 116 where, according to an instruction from remote site controller 54, the audio is modulated on an RF carrier for trans-mission to mobile unit 64 and others in the samegrouping within the coverage area of remote site B. ~obile unit 64 and o.hers in the same grouping receive this transmiâsion and demodulate the RF
carrier for the users to hear the message.
When mobile uni, 62 completes his transmis-sion, the push-to-talk switch is released. This causes the equipment within mobile unit 62 to transmit an end-of-transmission signal for the system to deallocate the message channels. Other 25 methods of detecting an end-of-transmission can be -used such as a lack of radio frequency carrier emitted from the mobile equipment, a lack of in- -~
formation modulated on the carrier, or a ti~e-out period expiration. This signal is received on the message channel of Group III by ~essage channel repeater 76 and is couQled to remote site central controller 52. The end-of-transmission signal is detected within the remote site central controller 52 and this detection is transferred to the master 9~s -2a- .
site central controller 60 via the data concen-trator 86. The master site central controller 6C
interprets this detection as the need to deallo-cate all of the Gro~? III message channels. The master site central controller 60 sends a deallo-cation instruction to each remote site central -controller via data concentrator 86. The site A -remote site central controller 52 receives this instruction directly while the site B, C, and D
remote central controllers 54, 56, and 58 receive tAe instruction via the data modems 88, 90, and 92, multiplex channels 100, 98, and ~6 of multi-plexer 94 and microwave terminal 36.
In response to the deallocation instruction, `
the remote site central controller acknowledge the instruction to check for error. If no response from the master site central controller 60 is re-ceived, the remote sit~ central controller 52 cor-poses a data message instructing mobile unit 62 (and other mobile units of the same group within the coverage area of site A) to retune its receiv-er and transmitter to the control channel of site . This data message is sent from the remote sit~
central controller 52 to the Group III message `
channel repeater 76 for modulation at the trans-mitter and transmission to the mobile units via transmitter combiner 82. Upon receiving this dat_ message, mobile unit 62 and others retune to the control channel of site A.
Remote sites B, Cr and D are similar in oper-ation. As a result, the o~eration of site B will be described. The deallocation data message is ---received via microwaJe terminal 38, passed to the multiplexer 126 where channel B is separated fro~
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the base band and passed through the data modem 138 to remote site central controller 54. An acknowledgment is returned to the master site ce,- :-tral controller 60 via the same data channel. I_ :
S no message is returned, remote site central con-troller 54 composes a data message for mobile un-t -64 and other mobiles of the same group which in-structs them to retune their receivers and trans- -mitters to the site B control channel. This datc message is coupled to the Group III message chan-nel repeater 116, modulated on the RF carrier of the transmitter section thereof, and coupled through the transmitter combiner 122 for trans-. .
mission to mobile unit 64 and others. Upon rece~- , 15 tion, mobile unit 64 and return their receivers t~
and transmitters to the control channel of site -.
When remote site central controller 54 com-pletes the process of transmitting the dealloca- f tion data message, it re~orts to the master site central controller 60 via the data modem 138, multiplexer 126, microwave terminal 38, microwav-terminal 36, multiplexer 94, data modem 92, and data concentrator 86 that the Group III message channel in site 8 is clear. With this notifica-tion from site B and the other remote sites C an-D, the master site central controller 60 recog-nizes that the Group III message channels are available for reassignment.
Referring now to Figure 4, it shows a flow diagram illustrating the operation of the master site controller 60 of Figure 2. As will be note-, the master site central controller first deter-mines whether a call request is for wide area se~-vice. If the answer is yes, then the master sit-:lZ~9~1S
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controller recalls tie list of available chan-nels. It then selec~s an unused channel group for assignment. The mas~er site controller then sends channel assignments -o the remote site controllers snd instructs the re~ote site controllers to as-sign the selected ch~nnels to the mobile units.
Thereafter, the master site central controller re-turns.
If the answer t~ the original question was no, the master site controller then causes demodu-lated audio to be di,tributed to all remote site controllers. If the demodulated audio is de- -tected, then the mas-er site controller instructs the remote site cont-ollers to deallocate their channels. The maste- site controller then accepts a channel clear ackn~wledgment from the remote site controllers and channel clear completion from the remote site cont~ollers. The master site con-troller then updates the list of available chan-nels and then determ_nes if all of the availablechannels are cleared. If they are cleared, then the master site cont:oller returns. If they are not cleared, the mas-er site central controller then once again ente s the sequence of instructing the remote site cont:ollers to deallocate their channels.
If the demodula-ed audio distributed to all ;~
of the remote site c~ntrollers is not detected, then the master site central controller determines whether it has recei.ed a channel clear input fro~
the remote site cont-ollers. If the answer is yes, it negates a ch-nnel clear and if the answer is no it returns.
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~23-The present invention therefore provides a new and improved system and method for wide cover-age area radio communication. Becaus~ each of tAe repeaters of the remote fixed sites are arranged for transmitting and receiving on a respective dif erent frequency duplex frequency pair or charnel, the problems encountered in the past with ove-lapping remote site coverage areas are avoid-ed. ~:ore speci~ically, radio frequency carrier ,o ~eat note interference and demodulated audio phase cancellation are avoided. Further, because access of .he system is controlled by a centralized con-trol means in a trunking manner, equal access cf the system to many potential users is provided.
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It is a further object of the present inven-tion to provide such a system having a pluralityof fixed transmission sites and wherein each fixed transmission site is arranged to transmit on a -different respective frequency to avoid beat note -interference and phase cancellation in overlapping :-10 coverage areas. ~
It is a further object of the invention to -provide such a system wherein access of the system is allocated by a trunking system.
It is another object of the present invention to provide a new and improved method of relaying a message substantially simultaneously from a plu-rality of fixed transmitter sites over a wide geo-graphical area.
It is another object of the invention to pro-vide a method of relaying a message by radio com-munication from one ~obile to at least another mobile over a wide geographical coverage area without requiring s~ecial audio conditioning or `
frequency control standards.
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~Z~ 5 SUM~ARY OF ~E INVENTION
The invention proYi~es in a two-way communi-cation system of the type adapted to relay a mes-sage substantially simul aneously from a plurality of fixed location si es, the improvement compris- -in~ radio frequency transmission means at each of the sites arranged for transmitting on a respec-tive differenct freq!1encJ than the transmission frequency of any other o. the sites~ means for selecting among the ?lurzlity of different fre-quencies at said sites to provide corresponding channels at each of said respective sites, and `
control means for selectlng a given channel and causing at least two of the transmission means to transmit the message substantially simultaneously on the respective different frequencies. In ac-cordance with a preferred embodiment of the pres-ent invention, the control means is arranged for causing each of the ,rans.~ission means to transmit the message substantiall~ simultaneously on the respective different trar.s~ission frequencies.
The present invention further provides a two-way communication system for relaying a mes- -sage over a wide area. ~ne system includes a plurality of Eixed transrission means, each fixed transmission means havinc a coverage area and be-ing arranged for trans~itting radio frequency signals on a plurali~y Oc different transmission frequencies, control means for causing each fixed ~
transmission means to trensmit the message on a --respective different tra..s~ission frequency, port-able receiving means locêted within the coverage areas, each portable rec~iving means being ar- -:~Z~L9~5 ranged for receiving on all of the transmission :
frequencies, and each fixed transmission means further including receiver control rneans for caus-ing each portable receiving means within its coverage area to tune to its transmission fre-quency.
The present invention further provides a method of relaying a message substantially simul- .
taneously from a plurality of fixed location sites. The method includes the steps of providing each site with radio frequency transmission means ~
capable of transmitting on a respective different .
plurality of frequencies than the transmission frequencies of any other of the sites, selecting among the plurality of frequencies at the sites to provide corresponding channels at each of the re-spective sites, setting at least two of said transmission means to different respective trans- ..
mission frequencies corresponding to a given one 20 of the channels, and transmitting the message from ~.
the set transmission means.
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~RIEF DESCRIPTION OF THE DRAWINGS .
.'' The features of the present invention which are believed to be novel are set forth with par- ..
ticularity in the appended claims. The invention, together with further objects and advantages ..
thereof, may best be understood by making refer-ence to the following description taken in con-junction with the accompanying drawings, in the several figures of which like reference numerals id~ntify identical elements, and wherein:
Figure 1 is a schematic representation of a .
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wide coverage area communication system embodying the present invention; -Figure 2 is a block diagram of the fixed site identified as site A in Figure 1 and which em ...
bodies the present invention; and Figure 3 is a block diagram illustrating a :
representative one of the other fixed sites of the system of Figure 1 embodying the present inven-tion; and Figure 4 is a flow chart illustrating the operation of the master site controller 60 of Fig~ 2. .
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121~915 D~SCRIPTION OF THE PREFERRED EMBODIMENTS
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Referring now to Figure 1, it illustrates in schematic form a wide coverage area communication system 10 embodying the present invention. The system includes a plurality of fixed transmitting and receiving sites designated as site A, site B, site C, and site D. Each of the sites has a -coverage area indicated by dashed lines with site A having coverage area 12, site B having coverage area 14, site C having coverage area 16, and site D having ~overage area 18. The sites are so lo-cated that radio transmission from and radio re-ception to each of the sites is limited to an es-sentially uniyue geosraphic area. Overlap betweer.
sites may be non-existent or may be total depend-lS inq upon the local terrain or topography of thegeographical area to be covered. For purposes of this embodiment it is assumed that the coverage area of any one site overlaps that of two others so that an entire area of continuous coverage is established.
Each of the fixed sites A, B, C, and D in-cludes radio frequency transmitting and receiving means in the form of transmitter and receiver re-peaters 20, 22, 24, and 26 respectively. Each of the transmitter and receiver repeaters has a fixec antenna 28, 30, 32, and 34. Ea~h of the repeater~
20, 22, 24, and 26 is arranged for transmitting and receiving on a respective different group of frequencies~ with each repeater being assigned a :-predetermined number of duplex channels, for exam-ple five channels, four channels being for system ~-communication, and the fifth channel being used a~ -.
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a control channel. The transmitting and receivi-~ -frequencies of the repeaters are also grouped to-gether so that a transmission frequency of one r~-peater finds three corresponding but different 5 transmission frequencies with the other repeater~. -Each of the sites also includes a microwave transmitter and receiver terminal 36, 38, 40, anc 42. Each of the transmitter and receiver termi-nals 36, 38, 40, and 42 has an associated micro-~0 wave antenna 44, 46, 48, and 50 respectively. T.
microwave transmitter and receivers and the ~icrc- -wave antennas provide a microwave com~unication --link 51 between the various sites. Alternativel~-, a land line could be provided for performing thiC
function.
Each of the sites includes a remote site `
central controller 50, 52, 54, and 56. Each re- -mote site central controller controls the local operation of its respective site and provides for 2~ communication from its site back to a master con-trol siter for example, site A in this embodi-ment. To that end, site A also includes a master site central controller 60. The master site cen-tral controller 60 serves as a control means for ~5 the entire system and supervises and controls the ac~ivities of all sites in the system.
Lastly~ located within the coverage areas of-the sites are mobile units or portables herein after, mobiles, 62, 64, 66, and 68~ Each of the ~
33 mobile units, which may vary in total number, an~ -vary in the number within a individual site co~er- -age area, includes a low power transmitter capabl- -~
of transmitting on any one of the communication channels and any one of the control channels, anc ~2~9~S
9 _ a receiver for receiving on any one of the com-munication or control channels. The mobile units can be related to each other by an automatic grouping of the mobile units into groups of users -who must communicate with each other.
Before the rest of the system is described in ....
greater detail, it may be helpful to follow the progression of a call made on the system 10 of Figure 1. Each mobile unit has a storage device tO which, among other infor~ation, contains its in-dividual identity, a grouping and subgrouping of other units with which the user can selectively communicate, and a listing of control channels -`
which are in use at each site of the system. For a more complete description of such a storage device, reference may be had to U.S. Patent Nos. 4,012,597 or 4,312,070 which are assigned to the assignee of the present invention. The mobile units further inelude equipment which causes its receiver to scan the outbound, or fixed-site transmit frequencies associated with the control channels until a suitably error free data signal is received. The mobile unit stops searching and remains on this control channel outbound frequencv 25 until commanded to tune to another frequency or ~-until the data signal degrades to an unusable level at which time the control channel scan res~mes.
All mobile equipment not engaged in an active call remain tuned to the control channel of the site in the coverage area that it is located in. --~hen a wide area call is selected by a mobile unit and a request for service is initiated by the user -activating the mobile transmitter, the mobile .
9~5 ~ o transmitter transmitts a request to the remote central controller in its coverage area on the in-bound control channel frequency. This request contains the identity of the mobile equipment and group of mobile equipment being called. It also contains the type of service required, for ex-ample, in this instance, a wide area coverage call.
Assuming that mobile unit 66 in coverage ~rea 16 of site C initiates a request for service, the request is received by the fixed site control channel receiver within the transmitter and re-ceiver repeaters 24 and passes to the remote cen-tral controller 56 for interpretation. Since this is a wide area call, the request is relayed by the microwave transmitter and receiver 40 and antenna 48 over the microwave link 51 to the master site transmitter and receiver 36 and then to the master central controller 60 which monitors the activity of all the system channels available for the wide area call. The master site central controller 60 assigns a channel at each site in the system for this wide area call and instructs each of the re-mote central controllers 52, 54, 56, and 58 to transmit a channel assignment instruction address-ed to the mobile units or the group of mobile units requested by the caller. Following the channel assignment instruction, the demodulated audio received from the callin~ mobile unit 66 is relayed by the microwave link from site C to si~e A where the master central controller 60 is locat-ed. The audio is then distributed to the other sites by the microwave link 51 for simultaneous retransmission to the called mobile equipment on a :1219~S
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respective different fre~uency at each of the sites.
The called mobile equipment are tuned to the control channel selected in the scanning mode.
Upon detecting an instruction on the control chan-nel addressed to itself, the called mobile units follow the instruction and tune to the frequency listed in the instruc~ion. On this frequency, the --called mobile equipment user receives the message originated by the calling mobile unit 66.
Upon the completion of the transmission by the calliny mobile unit 66, the master site con-troller 60 is infor~ed of the end of transmission and subsequently instructs the remote central con-trollers 52, 54, 56, and 58 to deallocate the wide area channels. Each remote central controller `
sends an instruction to the mobile equipment in its coverage area monitoring the message channel to retune to its res?ective different control channel. Once the c~annel is cleared in eachsite, the remote central controller of each site notifies the master site central controller 60 by the microwave link 51 that the channel has been cleared. The master site central controller 60 is then free to reassign the channels as desired for another wide area call request.
Referring now to Fig. 2, it illustrates in greater detail the equipment at the master site, site A. The master site includes six repeaters 70, 72, 74, 76, 78, and 80 which comprise the transmitter and receiver repeaters 20 illustrated in Fig. 1. Associat~d with the repeaters is a transmitter combiner 82, such as a Phelps Dodqe TJD 800-5T, and a receiver multicoupler 84, such 11 z~9 as a Phelps Dodqe R~C 800-8N. The transmitter .
combiner is coupled to a transmitting antenna 282 and the receiver multicoupler is coupled to a re- .
ceiving antenna 28b. Four of the repeaters, re-peaters 74, 76, 78, and 80 comprise message chan-nel repeatPrs which are trunked for providing :-voice communication to the mobile units. The re-maining two repeaters, repeaters 70 and 7~ are used for system control of the mobile units. The master site A further includes the remote site central controller 52, such as a T1958 manu-factured by Motorolz, Inc~ which controls the op-eration of the fixed radio equipment such as the repeaters and communicates with the mobile unit logic systems by the ra2io control channel repea'-ers 70 and 72. Repeater 7~ comprises a standby repeater which can be utilized when repeater 70 s not operational, such as, when it is being ser- .
viced. The master site A further includes the master site central controller 60 which is coupl~
to and buffered by a data concentrator 86 which can be, for example, a ~RN 6887A manufactured by Motorola, Inc.... The master site central control- -ler 60 performs higher level system control func-25 tions. Data communication between the master si e .`
.
c~ntral controller 60 and the remote fixed sites is provided by data modems 88, 90, and 92 which are connected to three r.ulti?lex channels of a multi-plexer 94. More particularly, data modem 88 is coupled to multiplexer ch2nnel 96, data modem 90 is coupled to multiplexer channel 98, and data modem 92 is coupled to ~.ultiplexer channel 100.
The base band output of multiplexer 94 is fed to the microwave terminal 36 for transmission to th-:~2199~5 other remote fixed sites. A four-way bridge 102 is provided to distribute a common audio signal t~
each remote site through the multiplexer 94 and microwave terminal 36.
Each of the repeaters 70, 72, 74, 76, 78, ar.
80 includes a transmitter which is coupled to th~
transmitter combiner 82, and a receiver which is coupled to the receiver multicoupler 84. As indi-cated, the repeaters are arranged for operating c^.
five different channels. Each channel is indicat-ed with a roman numeral. Hence, the master site '.
transmitting equipment is arranged for transmit-ting on channels AI through AV.
Referring now to Fig. 3, it illustrates the equipment found at one of the remote sites, and more particularly, at remote site B. This is typical of any of the remote sites. -The site B includes six repeaters as does site A, namely, repeaters 110, 112, 114, 116, 11E, and 120. Repeaters 110 and 112 are the control channel repeaters with repeater 112 serving as a standby repeater. In accordance with this pre-ferred embodiment, the bridge 102 allows each mes-sage channel at each site to share a common audio 2S input with one other message channel at each othe-site when a simultaneous transmission of a messac~
by every channel within the common audio groupinc is desired. Consequently, a message channel for group II, group III, group IV, and group V is found at remote site B. Each site has one messac-channel of each group. Control channels are here-in designated as group I but cannot share a co~mc audio input. Each of the repeaters 110, 112, 11', 116, 118, and 120 includes a transmitter section --~
12~L99~
which is coupled to a transmitter combiner 122, and a receiver section which is coupled to the re- -ceiver multicoupler 124. The transmitter combin~-122 is coupled to a transmitting antenna 30a and receiver multicoupler is coupled to receiving antenna 30b. The receivers of the message repea.-ers 114, lt6, 118, and 120 are also coupled to t~
multiplexer 126 and ~ore specifically to channels 128, 130, 132, and 134 respectively. To provide '0 local control of site B and communication with th?
master site central controller 60, remote site B -includes the remote site central controller 54 which is coupled to a ~ultiplexer channel 136 by 3 -data modem 138. The multiplexer 126 couples the :
remote site central controller and the message re-. . .
peaters to the micro~ave terminal 38. `
Now that the system 10 as illustrated in -Fig. 1 and the portions thereof illustrated in `-Figs. 2 and 3 have been described in general de-tail, a specific call ~rocess will now be descri~-ed. It is assumed that each o~ the mobile units 62, 64, 66 and 68 ha~e locked their receiver and transmitter to the control channel frequency of sites A, B, C, and D respectively. If mobile uni-66 drives out of the coverage area 16 of thetransmitter 24 in site C and into the coverage area of the transmitter 26 within site D, the dat~
transmitted on the control channel of site C will become increasingly deteriorated by noise until .-becomes unusable. hhen a predetermined digitalerror rate is reached, the mobile unit 66 will cause its receiver t~ sequentially tune to the other control channels of the sites in the system. The frequer.cies of the control channels .
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are stored in a storage device in the logic system of the mobile unit 66 equipment. When the re-ceiver within mobile unit 66 receives the control channel signal of site D, the logic system within mobile unit 66 determines that the transmitted data is acceptable error free and causes the re-ceiver within mobile unit 66 to cease scanning and remain on the control channel of site D. Mobile equipment of this type is more specifically des~ribed in the aforementioned U.SO Patent Nos. .,012,597 and 4,312,070.
If the user within mobile unit 62 wishes to-make a wide area call to members of his previously esta~lished group which may, for example, include mobile units 64 and 68, he selects the wide area coverage feature in his mobile equipment and acti-vates his transmitter by pressing a push-to-talk but~on on his transmitter. This causes the trans-mitter within mobile ~mit 62 to transmit a data ~0 word to the remote central controller 52 via the receiving antenna 28b, the receiver multicoupler 84, and the receiver of control channel repeater 70. The remote central controller 52 interprets -the cal} type as a wide area coverage group call and extracts the called group identification from the calling unit identification. The remote cen-tral controller 52 then forwards the request to the master site central controller 60 via the data concentrator 86.
The master site central controller 60 is in-formed of the availability of channels from the remote central controllers 52, 54, 56, and 58 via the microwave link 51, the receiver o~ microwave ~-ter..inal 36, channels 100, 98, and 96 of multi-12~9~S
plexer 94, the data modems 88, 90, and 92, and the .j data concentrator 86. As previously mentioned, .....
the communication channels in accordance with this preferred embodiment, are grouped into five 5 groups. Group I includes all the control channel ..
repeaters and standby equipment of each site.
This group includes repeaters 70 and 72 of site A ....
as illustrated in Figure 2, repeaters 110 and 112 of site B as illustrated in Figure 3, and equiva-lent repeaters for sites C and D. Group II in-cludes one message channel repeater from each site and is represented, for example, by repeater 74 of ..
site A and repeater 114 of site B. Group III in- ....
cludes one message channel repeater from each site .:
including repeaters 76 and 116. Similarly, Group IV includes repeaters 78 and 118, and Group V re-peaters include repeaters 80 and 120. Also as ..
previousl~ mentioned, each repeater operates on a uniquP and discrete frequency duplex pair. .
The master site central controller 60 through an internal comparison alaorithm recognizes that i.
the message channels of Group III, for example, are unutilized and selects this channel group for the message of mobile unit 62 to be simultaneously ..
~5 relayed from the fixed sites A, B, C, and D. The master site central controller 60 then transmits instructions to each remote site central control-ler 52, 54, 56, and 58 to transmit on its respec- -tive control channel to each mobile unit in the called group. The master site central controller 60 sends the instruc~ion to the site A remote cen- ..
tral controller 52 directly from the master site central controller 60 to the data concentrator 86 and to the remote si~e central controller 52. T~.e 3~Z~9~
other sites require the microwave link 51 to re-ceive its instruction. Therefore, the output of the data concentrator 86 for sites B, C, and D
passes through the data modems 88, 90, and 92 for 5 conversion for trans~ission through the multiplex --~
channels 100, 98, and 96 oE multiplexer 94 and transferred to the microwave link 51 through the microwave terminal 36 and its antennas 44. At re-mote site B, illustrated in Figure 3, the base band of the transmitted microwave signal is de-modulated by the microwave terminal 38 and multi-plex channel 136. The demodulated signal is de-multiplexed by multi?lexer 126. The recovered in-formation is passed to data modem 138 for conver-15 sion to a digital fo-mat and presented to the re `
mote site B remote site controller 54~ The remote site controller 54 t-ansmits a data word on the site B control chann~l via repeater 110 and trans-mitter combiner 122 o any and all mobile units with a group identification like the calling mobile unit 62 which happen to be within the coverage area of remote site B. A similar process occurs in sites C and D.
In site 8, the equipment within mobile unit 64 detects and recognizes the group identification of the outbound data word as its own and decodes the remainder of the data word to establish the message channel to w;~ich it should tune its re-ceiver and transmitt~r. As a result, the control means or master site controller 60 has caused the mobile equipment of -.obile unit 64 within site B
to set its receiver and transmitter to the proper :~
frequency for receiv.ng the wide area coverage --transmission. The e~uip~,ent within mobile unit 64 ~Z~99:~5 tunes to the message channel of site B which cor-responds to the Group III message channel for re-ceiving the relayed or retransmitted message of mobile unit 62. A similar sequence of events occurs for mobile unit 68 and all other mobile units within the designated group. For mobile units of dissimilar groups, such as mobile unit 66 within site C coverage area, transmission on the control channels are ignored and the mobile unit_ of dissimilar identification remain tuned to the r respective control channels.
Mobile unit 62, which is the calling mobile unit, is given a message channel assignment of t.e Group III channel at site A by the remote site -15 controller 52 through control channel repeater 7C `
and transmitter combiner 82. The process typical~
ly takes less than one second and occurs in such a manner that the user is unaware of the process.
The user of mobile unit 62, to initiate his call, 20 had pressed and held a push-to-talk button durin -the brief system access time and began his conve -sation on the assigned message channel. His voice -is modulated on the RF carrier of the mobile equipment transmitter of mobile unit 62 and trans-mitted to the site A Group III message channel re-ceiver of repeater 76 via the receiver multi- -coupler 84. The users audio is demodulated in t~.e receiver of repeater 76 and, in response to a co--mand from remote site controller 52, is coupled ~o the four-way bridge 102 where the audio is split three ways. These three outputs are connected to multiplex channels 140 corresponding to channel :
III-B, channel 142 corresponding to channel III _r~
and the channel corresponding to III-D of multi- -12~9~
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plexer 94~ The base band output of multiplexer 94 is modulated on a microwave RF carrier at the -microwave terminal 36 and transmitted by antennas 44 over the microwave link 51 to the remote sites B, C, and D.
At site B, which is representative of the other remote sites, the microwave terminal 38 de-modulates the base band of the microwave signal and couples it to the multiplexer 126 for separa-tion of multiplex channel III-B from the base band. The demodulated audio is coupled to the message channel repeater 116 where, according to an instruction from remote site controller 54, the audio is modulated on an RF carrier for trans-mission to mobile unit 64 and others in the samegrouping within the coverage area of remote site B. ~obile unit 64 and o.hers in the same grouping receive this transmiâsion and demodulate the RF
carrier for the users to hear the message.
When mobile uni, 62 completes his transmis-sion, the push-to-talk switch is released. This causes the equipment within mobile unit 62 to transmit an end-of-transmission signal for the system to deallocate the message channels. Other 25 methods of detecting an end-of-transmission can be -used such as a lack of radio frequency carrier emitted from the mobile equipment, a lack of in- -~
formation modulated on the carrier, or a ti~e-out period expiration. This signal is received on the message channel of Group III by ~essage channel repeater 76 and is couQled to remote site central controller 52. The end-of-transmission signal is detected within the remote site central controller 52 and this detection is transferred to the master 9~s -2a- .
site central controller 60 via the data concen-trator 86. The master site central controller 6C
interprets this detection as the need to deallo-cate all of the Gro~? III message channels. The master site central controller 60 sends a deallo-cation instruction to each remote site central -controller via data concentrator 86. The site A -remote site central controller 52 receives this instruction directly while the site B, C, and D
remote central controllers 54, 56, and 58 receive tAe instruction via the data modems 88, 90, and 92, multiplex channels 100, 98, and ~6 of multi-plexer 94 and microwave terminal 36.
In response to the deallocation instruction, `
the remote site central controller acknowledge the instruction to check for error. If no response from the master site central controller 60 is re-ceived, the remote sit~ central controller 52 cor-poses a data message instructing mobile unit 62 (and other mobile units of the same group within the coverage area of site A) to retune its receiv-er and transmitter to the control channel of site . This data message is sent from the remote sit~
central controller 52 to the Group III message `
channel repeater 76 for modulation at the trans-mitter and transmission to the mobile units via transmitter combiner 82. Upon receiving this dat_ message, mobile unit 62 and others retune to the control channel of site A.
Remote sites B, Cr and D are similar in oper-ation. As a result, the o~eration of site B will be described. The deallocation data message is ---received via microwaJe terminal 38, passed to the multiplexer 126 where channel B is separated fro~
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the base band and passed through the data modem 138 to remote site central controller 54. An acknowledgment is returned to the master site ce,- :-tral controller 60 via the same data channel. I_ :
S no message is returned, remote site central con-troller 54 composes a data message for mobile un-t -64 and other mobiles of the same group which in-structs them to retune their receivers and trans- -mitters to the site B control channel. This datc message is coupled to the Group III message chan-nel repeater 116, modulated on the RF carrier of the transmitter section thereof, and coupled through the transmitter combiner 122 for trans-. .
mission to mobile unit 64 and others. Upon rece~- , 15 tion, mobile unit 64 and return their receivers t~
and transmitters to the control channel of site -.
When remote site central controller 54 com-pletes the process of transmitting the dealloca- f tion data message, it re~orts to the master site central controller 60 via the data modem 138, multiplexer 126, microwave terminal 38, microwav-terminal 36, multiplexer 94, data modem 92, and data concentrator 86 that the Group III message channel in site 8 is clear. With this notifica-tion from site B and the other remote sites C an-D, the master site central controller 60 recog-nizes that the Group III message channels are available for reassignment.
Referring now to Figure 4, it shows a flow diagram illustrating the operation of the master site controller 60 of Figure 2. As will be note-, the master site central controller first deter-mines whether a call request is for wide area se~-vice. If the answer is yes, then the master sit-:lZ~9~1S
--22-- :
controller recalls tie list of available chan-nels. It then selec~s an unused channel group for assignment. The mas~er site controller then sends channel assignments -o the remote site controllers snd instructs the re~ote site controllers to as-sign the selected ch~nnels to the mobile units.
Thereafter, the master site central controller re-turns.
If the answer t~ the original question was no, the master site controller then causes demodu-lated audio to be di,tributed to all remote site controllers. If the demodulated audio is de- -tected, then the mas-er site controller instructs the remote site cont-ollers to deallocate their channels. The maste- site controller then accepts a channel clear ackn~wledgment from the remote site controllers and channel clear completion from the remote site cont~ollers. The master site con-troller then updates the list of available chan-nels and then determ_nes if all of the availablechannels are cleared. If they are cleared, then the master site cont:oller returns. If they are not cleared, the mas-er site central controller then once again ente s the sequence of instructing the remote site cont:ollers to deallocate their channels.
If the demodula-ed audio distributed to all ;~
of the remote site c~ntrollers is not detected, then the master site central controller determines whether it has recei.ed a channel clear input fro~
the remote site cont-ollers. If the answer is yes, it negates a ch-nnel clear and if the answer is no it returns.
....
99~
~23-The present invention therefore provides a new and improved system and method for wide cover-age area radio communication. Becaus~ each of tAe repeaters of the remote fixed sites are arranged for transmitting and receiving on a respective dif erent frequency duplex frequency pair or charnel, the problems encountered in the past with ove-lapping remote site coverage areas are avoid-ed. ~:ore speci~ically, radio frequency carrier ,o ~eat note interference and demodulated audio phase cancellation are avoided. Further, because access of .he system is controlled by a centralized con-trol means in a trunking manner, equal access cf the system to many potential users is provided.
~ .
Claims (26)
1. In a two-way communication system of the type adapted to relay a message substantially simultaneously between a plurality of fixed location sites having corresponding radio coverage areas, the improvement comprising:
radio frequency transmission means at each of said sites arranged for transmitting on a respective different plurality of frequencies than the transmission frequencies of any other of said sites;
means coupled to each said radio frequency transmission means for selecting among the pluralities of different frequencies at said sites to provide corresponding channels at each of said sites whereby said message may be relayed between said sites; and control means for selecting one of said channels and causing at least two of said transmission means to transmit said message substantially simultaneously on respective selected different frequencies.
radio frequency transmission means at each of said sites arranged for transmitting on a respective different plurality of frequencies than the transmission frequencies of any other of said sites;
means coupled to each said radio frequency transmission means for selecting among the pluralities of different frequencies at said sites to provide corresponding channels at each of said sites whereby said message may be relayed between said sites; and control means for selecting one of said channels and causing at least two of said transmission means to transmit said message substantially simultaneously on respective selected different frequencies.
2. A system as defined in claim 1 wherein said control means is arranged for causing each of said transmission means to transmit said message substantially simultaneously on said respective selected different transmission frequencies coupled to said selected channel.
3. A system as defined in claim 1 wherein said control means is located at one of said fixed sites.
4. A system as defined in claim 1 further including at least two remote receiving means for receiving said relayed message, each said remote receiving means being located in the radio coverage area of a corresponding one of said fixed transmission means and wherein said control means includes means for causing each said remote receiving means to tune to the transmission frequency of its corresponding fixed transmission means for receiving said message.
5. A system as defined in claim 1 wherein said pluralities of message transmission frequencies are predeterminedly arranged in groups consisting of one said respective different transmission frequency of each of the fixed transmission means.
6. A system as defined in claim 5 wherein said control means includes means for causing said transmission of said message to one said group of respective different frequencies in response to said one of said groups of frequencies being unoccupied.
7. A system as defined in claim 1 wherein said means for selecting among the pluralities of different frequencies further comprises a microwave communications link.
8. A system as defined in claim 1 further including means for receiving the message at one fixed site and communicating the message via said selected channel to all of said fixed sites.
9. A two-way communication system for relaying a received message over a wide coverage area, said system comprising:
a plurality of fixed sites, each site having a site coverage area comprising part of the wide coverage area each site having a plurality of transmitters tuned to different transmission frequencies, and each site having coupling means to couple each site transmitter to a predetermined group of transmitters, said group having one transmitter situated at each other site and each transmitter within said group tuned to a different transmission frequency;
control means for causing one of said transmitter groups to transmit said received message in response to all transmitters being unused within said group;
at least two remote receiving means located within said wide coverage area, each said remote receiving means being arranged for receiving on all said transmission frequencies; and each said fixed site further including receiver control means for causing each said remote receiving means within its site coverage area to tune to a transmission frequency employed by its corresponding transmitter within said group of message transmitting transmitters.
a plurality of fixed sites, each site having a site coverage area comprising part of the wide coverage area each site having a plurality of transmitters tuned to different transmission frequencies, and each site having coupling means to couple each site transmitter to a predetermined group of transmitters, said group having one transmitter situated at each other site and each transmitter within said group tuned to a different transmission frequency;
control means for causing one of said transmitter groups to transmit said received message in response to all transmitters being unused within said group;
at least two remote receiving means located within said wide coverage area, each said remote receiving means being arranged for receiving on all said transmission frequencies; and each said fixed site further including receiver control means for causing each said remote receiving means within its site coverage area to tune to a transmission frequency employed by its corresponding transmitter within said group of message transmitting transmitters.
10. A system as defined in claim 9 wherein said receiver control means of each said fixed site is responsive to said control means.
11. A system as defined in claim 9 wherein said control means is located at a given one of said fixed site.
12. A system as defined in claim 9 wherein each said transmitter is switchably coupled via a microwave link.
13. A method of relaying a message substantially simultaneously between a plurality of fixed location sites, said method comprising the steps of:
providing each said site with radio frequency trans-mission means capable of transmitting on a respective different plurality of frequencies than the transmission frequencies of any other of said sites;
selecting among the pluralities of frequencies at said sites to provide corresponding channels at each of said respective sites;
selecting one corresponding channel from among said corresponding channels to relay said message between said sites; and causing at least two of said transmission means to transmit said message substantially simultaneously on said selected plurality of frequencies.
providing each said site with radio frequency trans-mission means capable of transmitting on a respective different plurality of frequencies than the transmission frequencies of any other of said sites;
selecting among the pluralities of frequencies at said sites to provide corresponding channels at each of said respective sites;
selecting one corresponding channel from among said corresponding channels to relay said message between said sites; and causing at least two of said transmission means to transmit said message substantially simultaneously on said selected plurality of frequencies.
14. A method as defined in claim 13 including the step of setting a plurality of portable receivers to the transmission frequencies of said transmission means.
15. A method as defined in claim 14 wherein each of said transmission means has a corresponding coverage area, and wherein said method further includes providing a plurality of portable receiving means capable of being tuned to said transmission frequencies; and tuning at least one said portable receiving means to the transmission frequency of the transmission means corresponding to the area of coverage in which each said portable receiving means is located.
16. A method as defined in claim 13 including the further step of distributing said message to be relayed from a given one of said transmission means to all of the other transmission means.
17. A method as defined in claim 13 including the further step of arranging said transmission frequencies of said transmission means in groups so that each trans-mission frequency of one said transmission means corres-ponds to a respective different transmission frequency of each of the other transmission means.
18. A method as defined in claim 17 including the further step of detecting which transmission frequencies are unoccupied, and wherein said message is transmitted in response to all of the frequencies of one of said groups of frequencies being unoccupied.
19. A method as defined in claim 13 including the further step of detecting which of the transmission frequencies is unoccupied, and causing said message to be transmitted when all the transmission means have an unoccupied respective different transmission frequency.
20. A two-way radio communications system for a large geographic area in which a plurality of geographically spaced apart fixed sites having separate radio coverage areas are employed to extend radio coverage over the large geographic area and transmit a message within the large geographic area comprising:
at least two means at each fixed site for trans-mitting radio frequency (RF) signals, each RF signal at a fixed site having a frequency different from any other at the same fixed site;
means for grouping said transmitting means into channels, each channel comprising one said transmitting means from each fixed site and each channel employing dissimilar RF signal frequencies among its group of transmitting means; and means for selecting one of said channels having its group of transmitting means unoccupied, and for routing the message to each fixed site whereby transmission may occur essentially simultaneously from each said transmitting means of said selected channel.
at least two means at each fixed site for trans-mitting radio frequency (RF) signals, each RF signal at a fixed site having a frequency different from any other at the same fixed site;
means for grouping said transmitting means into channels, each channel comprising one said transmitting means from each fixed site and each channel employing dissimilar RF signal frequencies among its group of transmitting means; and means for selecting one of said channels having its group of transmitting means unoccupied, and for routing the message to each fixed site whereby transmission may occur essentially simultaneously from each said transmitting means of said selected channel.
21. A two-way radio system in accordance with claim 20 further comprising means for distribution of the message between fixed sites on said selected channel.
22. A two-way radio system in accordance with claim 21 wherein said means for distributing a channel is a microwave link.
23. A two-way radio system in accordance with claim 20 further comprising a plurality of mobile units to at least one of which the message is directed.
24. A two-way radio system in accordance with claim 23 further comprising means for assigning each mobile unit to which the message is directed to one of said RF signal frequencies corresponding to said selected channel whereby the message may be received.
25. A two-way radio system in accordance with claim 23 wherein the message is generated by a second one of said plurality of mobile units.
26. A two-way radio system in accordance with claim 25 further comprising means located at each fixed site for receiving said mobile unit generated message.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US559,122 | 1983-12-07 | ||
| US06/559,122 US4578815A (en) | 1983-12-07 | 1983-12-07 | Wide area coverage radio communication system and method |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1219915A true CA1219915A (en) | 1987-03-31 |
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ID=24232348
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000468582A Expired CA1219915A (en) | 1983-12-07 | 1984-11-26 | Wide area coverage radio communications system and method |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US4578815A (en) |
| EP (1) | EP0164401A1 (en) |
| CA (1) | CA1219915A (en) |
| IT (1) | IT1219411B (en) |
| WO (1) | WO1985002745A1 (en) |
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| GB1177753A (en) * | 1966-01-18 | 1970-01-14 | Int Standard Electric Corp | Switching System for Telecommunication Circuits |
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| US3749845A (en) * | 1971-08-27 | 1973-07-31 | Bell Telephone Labor Inc | Digital data communication system |
| CH594324A5 (en) * | 1975-08-27 | 1978-01-13 | Autophon Ag | |
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| US4188582A (en) * | 1978-04-10 | 1980-02-12 | Motorola, Inc. | Simulcast transmission system having phase-locked remote transmitters |
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| US4312070A (en) * | 1979-12-07 | 1982-01-19 | Motorola, Inc. | Digital encoder-decoder |
-
1983
- 1983-12-07 US US06/559,122 patent/US4578815A/en not_active Expired - Lifetime
-
1984
- 1984-11-26 CA CA000468582A patent/CA1219915A/en not_active Expired
- 1984-11-29 WO PCT/US1984/001952 patent/WO1985002745A1/en unknown
- 1984-11-29 EP EP85900345A patent/EP0164401A1/en not_active Withdrawn
- 1984-12-06 IT IT49262/84A patent/IT1219411B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| EP0164401A1 (en) | 1985-12-18 |
| IT8449262A0 (en) | 1984-12-06 |
| US4578815A (en) | 1986-03-25 |
| WO1985002745A1 (en) | 1985-06-20 |
| IT1219411B (en) | 1990-05-11 |
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