CA2055459C - Trunking method and apparatus for establishing communication in a two-way mobile radio system - Google Patents
Trunking method and apparatus for establishing communication in a two-way mobile radio systemInfo
- Publication number
- CA2055459C CA2055459C CA002055459A CA2055459A CA2055459C CA 2055459 C CA2055459 C CA 2055459C CA 002055459 A CA002055459 A CA 002055459A CA 2055459 A CA2055459 A CA 2055459A CA 2055459 C CA2055459 C CA 2055459C
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- operable
- subaudible
- method defined
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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
Abstract
An arrangement (10) of a mobile station and a method for establishing communication between at least two of such sta-tions are disclosed. The arrangement includes a transmitter (11), a subaudible tone generator (15), a receiver (12), a subaudible tone decoder (16), and a control circuit (14). When in a receive mode, the arrangement (10) causes the receiver (12) to search a carrier signal and a subaudible-tone signal on the plurality of channels. When these signals are found, the transmitter (11) is en-abled. When in a transmit mode, the arrangement (10) causes the receiver (12) to search for an idle channel. When an idle chan-nel is found, the arrangement causes the transmitter (11) to transmit a carrier signal and a subaudible tone signal, and waits for a reply from the repeater. Upon receiving the reply, the arrangement (10) enables the transmitter (11).
Description
2 0 ~ S 4 ~ 9 PCT/US91/01012 TRUNKING METHOD AND APPA~ATUS FOR ESTABLISHING
COMMUNICATION IN A TWO-WAY MOBILE RADIO SYSTEM
BACKGROUND OF THE INVENTION
The present invention relates to a two-way radio communication system of the type commonly known as "mobile radio". More particularly, the invention relates to a method and apparatus for establishing communication in such a system on a common radio communication "channel" or frequency selected from a plurality of such channels.
As used herein, the term "radio channel" is intended to include a first frequency for transmitting and a second, different frequency for receiving by a plurality of user-operable radio transmitter/receiver stations. Signals transmitted by such user operable stations at the first frequency are received by a nearby radio repeater station and then retransmitted at the second frequency for reception by all the user-operable stations in the vicinity that are tuned to the channel.
As used herein, the term "mobile radio" is intended to describe the type of two-way radio system commonly used to communicate between and among a plurality of mobile or portable transmitter/receiver stations and one or more fixed base transmitter/receiver stations, with the aid of a repeater station. The mobile or portable stations are arranged on mobile vehicles of all types, such as motor r~
WO91/12670 2 0 5 ~ ~ 5 ~ PCT/US91/0101~
vehicles and boats, or hand held. A typical application of such a system is to dispatch and control the operation of taxis, tow vehicles, repair vehicles, delivery vehicles and the like. Normally, fleets of such mobile vehicles are owned and operated by separate business ent1ties, and it is advantageous if all, or a subset of, vehicle operators in a common fleet or business are able to communicate with each other and with a dispatcher at a fixed base station. Such a set of users who can communicate with each other by means of the mobile radio system will be denoted hereinafter as a "group" of users. It is further advantageous if the vehicle operators and fleet dispatcher of one fleet or business (one group of users) are prevented from communicating with, either by transmitting to or receiving from, vehicle operators and dispatchers of other fleets or businesses (other groups of users). Thus, the mobile radio system advantageously operates as a "party line" within each group or subgroup of users, and "private line" as between groups or subgroups of users.
In two-way mobile radio communication systems of this type a plurality of radio channels are allocated for communication between all user-operable radio stations.
Generally there may be, and usually are, many more radio stations than there are available radio channels in a given locality. Consequently, some arrangement is needed for WO91~12670 2 Q S ~ ~ 5 ~ PCT/US91/01012 enabling the communication among a large number of users, in the party line/private line basis described above, on a relatively small number of channels.
The U.S. Patent No. 4,409,687 to Berti et al. describes an arrangement for establishing communication in a mobile radio environment which utilizes a "busy tone" in the middle of the voice band of each ch~nnel. Each user-operable station in the system scans the available channels, in either a '~transmit mode~ or "receive mode", and takes action in dependence upon the presence (or absence) of a busy tone.
Each radio station utilizes a "notch filter" to remove the busy tone from the voice signal before the voice signal is processed. This arrangement is incompatible with other existing equipment in the field since it requires that all radio stations be able transmit, detect and remove a busy tone from the voice band in each channel.
Mobile radio systems, as presently in common use, distinguish between groups of users by so-called "sub-audible group tones"; that is tones in the voice band below 300 ~z. Such tones are ~ariously called "CTCSS" and "DCSS"
tones ~or "continuous tone coded squelch system" and "digital coded squelch system", respectively. In certain mobile radio channels in the United States - that is, in the radio channels allocated in the 4~0 to 470 MHz. range -there are a total of 38 CTCSS tones and 21~ DCSS tones ~05~4~ --closely spaced in the frequency range between 65 and 250 Hz.
The CTCSS tones are simply continuous tones whereas the DCSS
tones repeatedly provide seven bit words that convey the identity of a group. Each mobile radio station includes equipment for detecting the presence of absence of selected CTCSS tones and/or for decoding the transmitted DCSS words.
Although the use of CTCSS and DCSS tones is strictly voluntary on most frequencies, most mobile radios manufactured today are equipped to generate and detect one type of tone or the other, or both.
It is thus common practice to create "private lines"
between groups of users, and "party lines" among groups of users, by selecting a CTCSS or DCSS tone on each separate channel. The CTCSS or DCSS tone need not be the same for each channel provided that the radio stations of all users in a given group have been assigned the same tone for each channel.
Channel selection in mobile radio systems of this type has traditionally been accomplished by manually ad~usting the channel selector or by scanning. Automatic channel selection, for example as described in the aforementioned U.S. Patent No. 4,409,687, has not been thought possible because of the complexity of the system environment that contains mobile radio stations which are not equipped to handle the "busy tone" format.
WO91/12670 2 0 ~ PCT/US91/01012 As used herein, the term "trunking", as used in the mobile radio environment, is intended to describe the automatic selection of an available channel, when in the transmit mode, and the automatic acquisition of a calling channel, when in the receive mode.
SUMMARY OF THE I~V~llON
It is a principal object of the present invention to provide trunking in a mobile radio system, thereby to enable rapid, automatic access to an available communication channel, when in a transmit mode, and rapid, automatic call searching when in a receive mode.
It is another object of the present invention to provide a mobile radio system which ensures privacy in the communication among groups of users.
It is another object of the present invention to provide a mobile radio system which is secure against the reception of transmissions from third parties.
It is another object of the present invention to provide a mobile radio system which permits a two or even three-fold increase in the number of mobile radio stations in a given locality surrounding a repeater station.
It is another object of the present invention to provide a mobile radio system which does not cause interference when a mobile station set up for use within the reception area of , one repeater statlon intrudes into the receptlon area of another repeater, whereln both repeaters operate ln the same general receptlon area and one repeater is not part of the ~ trunk system.
It ls another ob~ect of the present invention to provlde a moblle radio system which is entlrely compatible wlth all existing equlpment on the repeater frequency, whether or not lt ls part of the trunk system.
It ls another ob~ect of the present lnventlon to provlde a moblle radio system whlch ls fully llcensable under the current rules of the Unlted States Federal Communlcatlons Commlsslon ("FCC").
It ls another ob~ect of the present lnventlon to provide a moblle radio system whlch enables each group of users to be subdivlded lnto two or more subgroups 80 as to provlde prlvacy between subgroup~ of users wlthln each user group.
It ls another ob~ect of the present lnventlon to provlde a moblle radlo system whlch enables the user to select between different repeater statlons or groups of repeaters located in dlfferent geographlc areas.
In accordance wlth the present lnvention, there is provlded a two-way moblle radio communlcatlon system comprlslng a plurallty of user-operable statlons and a cooperating repeater station all operatlng on a plurallty of radlo communlcatlon channels of dlfferlng frequency bands wlthout a dedlcated control channel, each user-operable -statlon comprislng, in combination: (a) a radio transmitter;
(b) a radio receiver; (c) user-operable switch means, coupled to said transmltter, for selectively enabling said ~ transmltter to transmlt a carrler slgnal~ (d) carrier operable switch means, coupled to said recelver, for indicating the receipt of a carrier signal when in an activation position; (e) channel selector means, coupled to said transmitter and said receiver, for selectlng the radio channel of operation; (f) means, coupled to said transmitter, for continuously generatlng a selected one of a plurallty of subaudible trunk ldentificatlon signals associated with each given communicatlon channel for transmisslon by said transmltter when operatlng on sald given channel; and (g) means, coupled to sald recelver, for indlcating the presence of sald selected one of a plurality of subaudlble trunk identiflcatlon signals when said receiver is operating on said glven channel 7 the method of automatlcally operatlng the user-operable statlons so as to establlsh communlcatlon between at least two such stations over one of sald plurallty of channels, sald method comprlslng the steps ofs (1) when sald user-operable swltch means ls open and said user-operable statlon ls ln a recelve mode~ (1) lncrementlng sald channel selector means to select a channel7 (11) determlnlng lf sald carrler operable switch means ls in said activation posltlon, thereby indlcating that a carrler slgnal ls present on the selected channelS (ili) if a carrier signal is not present, returning to step (1) (i) 7 .
- a -(lv) if a carrier slgnal i8 present, determinlng if the selected subaudible trunk ldentlfication slgnal ls present on said carrler slgnal; (v) lf the selected subaudlble trunk - identlflcation slgnal is not present on sald carrier slgnal, returnlng to step (1) ~1); and (vl) lf the selected subaudible trunk ldentlficatlon slgnal ls present on sald carrler signal, enabllng sald transmltter for push-to-talk operation; and (2) when sald user-operable swltch means ls closed and sald user-operable station ls ln a transmlt modes (1) if sald carrler operable swltch means ls ln sald activatlon positlon, thereby lndlcating that a carrler slgnal ls present on the selected channel, lncrementlng sald channel selector; (li) lf a carrler slgnal ls not present on the selected channel, transmlttlng a carrler slgnal wlth the æelected subaudlble trunk ldentlflcation slgnal for a prescribed perlod of tlme; (111) determlnlng whether a carrier slgnal wlth the selected subaudible trunk ldentlflcatlon slgnal ls recelved on the selected channel;
(lv) if a carrler slgnal wlth the selected subaudlble trunk identlflcatlon slgnal 18 not received, returnlng to step (2) (l); and (v) lf a carrler slgnal wlth the selected subaudlble trunk ldentlflcatlon slgnal ls recelved returnlng to step (1) (vl) .
In accordance wlth the present inventlon, there is also provlded a two-way moblle radio communicatlon system comprlslng a plurallty of user-operable statlons and at least one cooperatlng repeater statlon all operatlng on a plurallty 205~459 - 7b -of radlo communlcatlon channels of dlfferlng frequency bands wlthout a dedlcated control channel, each user-operable statlon comprising, in combinatlon: (a) a radio transmitter7 - (b) a radio receiver; (c) user-operable switch means, coupled to sald transmitter, for selectively enabling said transmltter to transmit a carrier slgnal~ (d) carrler operable swltch means, coupled to sald recelver, for indicating the receipt of a carrler slgnal when in an actlvation position; (e) channel selector means, coupled to sald transmitter and said recelver, for selecting the radio channel of operation; (f) means, coupled to said transmltter, for contlnuously generatlng a selected one of a plurallty of subaudlble trunk identificatlon slgnals associated with each given communlcatlon channel for transmlssion by said transmitter when operatlng on sald given channel; and (g) means, coupled to sald receiver, for lndicating the presence of said selected one of a plurality of subaudible trunk identification signals when said recelver i5 operating on said given channelS the method of automatically operating the user-operable stations so as to establish communication between groups of such stations over one of said plurality of channels, sald method comprising the steps of:
(1) assigning prescribed ones of said subaudible trunk ldentlficatlon signals to respectlve groups of stations; (2) when said user-operable switch means is open and said user-operable statlon ls ln a recelve mode; (1) incrementlng sald channel selector means to select a channel from among sald - 7c - 2055459 prescrlbed channels; (ii) determinlng lf sald carrler operable switch means is in sald actlvatlon posltlon, thereby lndlcatlng that a carrler signal ls present on the selected - channel; ~111) lf a carrler signal is not present, returning to step (2) (i); (iv) lf a carrler slgnal ls present, determinlng if the selected subaudible trunk identification signal ls present on sald carrler slgnal; ~v) lf the selected subaudible trunk identification signal is not present on said carrier signal, returnlng to step ~2) ~i); and ~vl) lf the selected subaudlble trunk ldentification signal is present on said carrler slgnal, enabling said transmltter for push-to-talk operatlon; and ~3) when sald user-operable swltch means ls closed and said user-operable statlon ls in a transmit mode: ~i) if sald carrier operable switch means ls ln sald activation posltlon, thereby lndlcatlng that a carrier signal ls present on the selected channel, incrementing said channel selected to select a channel from among sald prescrlbed channels; ~11) lf a carrler slgnal ls not present on the selected channel, transmittlng a carrler ~ignal with the selected subaudible trunk identlflcatlon signal for a prescrlbed period of time; ~iil) determinlng whether a carrler slgnal wlth the selected subaudlble trunk ldentlflcatlon slgnal ls received on the selected channel;
~lv) lf a carrier slgnal wlth the selected subaudible trunk identlflcatlon slgnal ls not recelved, returnlng to step ~3) ~l); and ~v) lf a carrler slgnal wlth the selected 72003-g .
- 7d -subaudible trunk ldentlflcation signal is received returning to step (2) (vi).
The above ob~ects, as well as other ob~ects and advantages whlch will become apparent in the discussion that follows, are achieved, in accordance wlth the present inventlon, by provlding a mobile radio system of the type described lmmedlately above in which communication is established between at least two user-operable stations over WO 91/12670 ~ o 5 ~ 3 PCT/US91/010 ~
one of a plurality of channels by operating the user-operable stations in accordance with the following steps:
(1) When in the receive mode (the push-to-talk switch is open):
(i) incrementing the channel selector`to select a channel;
(ii) determining if a carrier signal is present on the selected channel:
(iii) if a carrier signal is not present, returning to step (1) (i);
(iv) if a carrier signal is present, determining if the selected trunk identification signal is present on the carrier signal;
(v) if the selected trunk identification signal is not present, returning to step (l)(i); and (vi) if the selected trunk identification signal is present on the carrier signal, enabling said transmitter for push-to-talk operation.
(2~ When in the transmit mode (the push-to-talk switch is closed):
(i) if a carrier signal is present on the selected channel, incrementing the channel selector;
(ii) if a carrier signal is not present on the selected channel, transmitting a carrier signal with the WO91/12670 2~4~ PCT/US91/01012 selected trunk identification signal for a prescribed period of time;
(iii) determining whether a carrier signal with the selected trunk identification signal is received on the selected channel;
(iv) if a carrier signal with the selected trunk identification signal is not received, returning to step (2)(i); and (v) if a carrier signal with the selected trunk identification signal is received, returning to step (1) (vi), This method of operation is preferably implemented by a programmed microprocessor arranged on a small circuit board.
The microprocessor circuit receives as inputs the carrier operated switch or relay signal and the "mute/unmute" signal from the receiver. The carrier operated relay ("COR") indicates the presence of a carrier signal on the selected channel. The "unmute" signal from the receiver indicates the presence of the selected identification signal (CTCSS or DCSS tone) and unmutes the receiver when such tone is present.
The microprocessor circuit also receives a signal indicating whether the push-to-talk switch is open or closed.
WO91/12670 2 0 5 ~ ~ S ~ PCT/US91/010 ~
The microprocessor circuit produces a pulse signal on an output line to increment the channel selector, as required.
If incrementing by one, one pulse is produced; if incrementing by two or more channels, two or more pulses are produced, as required.
The microprocessor circuit also produces an output signal which enables the push-to-talk operation of the transmitter.
According to a preferred feature of the present invention, the user-operable mobile radio station includes a tone generator connected to the radio loudspeaker for producing one or more audible tones indicative of the station operation. In particular, and in accordance with this feature, a brief beep tone at one audible frequency is produced when the push-to-talk switch is keyed by the operator. A second brief beep tone at a second audible frequency is produced when the COR is activated as a result of keying the push-to-talk switch (i.e., when the repeater station receives the transmitted signal and transmits a carrier in reply). This second beep tone thus indicates to the user that the transmission by the user-operable station has been received by the repeater station and retransmitted for reception by all user-operable mobile radio stations in the area.
According to another feature of the present invention, a mobile radio station user can select a subgroup of users WO91/12670 2~4~9 PCT/US91/01012 .
with whom he or she wishes to communicate. Preferably, the selection can be made by the length of time that the push-to-talk switch is initially keyed when establishing communication. If the push-to-talk switch is keyed momentarily, one subgroup is selected; and when the push-to-talk switch is keyed for a longer period of time, the second subgroup is selected. Preferably, an audible tone, such as a brief single beep, is produced when the push-to-talk switch is keyed for a short period, and a double beep tone or a tone of a different frequency is produced when the push-to-talk switch is keyed for a sufficiently long period to select the second subgroup.
The selection of one subgroup or another can be effected by a number of different methods. In one method, the trunk identification signal (e.g. CTCSS or DCSS tone) for transmission on the carrier signal when in the transmit mode is selected for the particular subgroup desired. According to another method, the available channels are allocated among the different subgroups so that each subgroup can transmit and receive only on certain select channels.
For example, the even channel numbers may be allocated to one subgroup and the odd channel numbers allocated to a second subgroup.
wo gl/12670 2 0 ~ ~ ~>5 ~ PCT/US91/010 ~
The group selection is thus e~fected by~incrementing the channel selector a prescribed number of times to select only those channels for the subgroup desired.
In accordance with the present invention, therefore, the efficiency of mobile two-way radio systems that employ repeaters is improved by selecting one radio channel from a plurality of radio channels by systemmatic examination of each channel to determine the presence of: 1) A user of a desired group on the same system, 2) a user of a non-desired group on the same system, or 3) a user of a group from a foreign system that operates in the same geographic area on the same channel.
The system described in the aforementioned U.S. Patent No. 4,409,687 is designed to operate on channel assignments that are geographically protected non-participating users.
In this known system a busy tone is provided to alert mobile stations to avoid that particular channel not transmitting a busy tone. This arrangement is designed to operate only where each and every mobile in a given system are participants in the system and share circuitry in each mobile that match the arrangement.
The Federal Communications Commission (FCC) issues special "trunking" licenses above 800 MHz. to operators of the type of trunking arrangements disclosed in the U.S.
Patent No. 4,409,687. However, all these prior arrangements WO91/12670 2 ~ ~ 5 4 ~ ~ PCT/US91/01012 .
have exclusive use of each of the channels trunked in a given geographic area. In this fashion, each system can only function in a given geographic area on an exclusive basis. It cannot operate in an environment with other non-participating mobiles, such as exists in the environment below 800 MHz.
The system according to the present invention provides not only a trunking arrangement but also allows other non-trunked users access to each channel and to each repeater in the arrangement.
The present system provides channel monitoring to any type of user, whether part of the system or not.
A user-operable station acquires a channel by an arrangement that analyzes the presence of any user and, if a channel is occupied, continues to ~;ne each subsequent channel from the plurality of channels available in the system. At no point in this system are busy tones used, or is filtering required or used in any equipment.
In the UHF spectrum (450-470 MHz.) for example, channels are licensed by the FCC on a non-exclusive use basis in a given geographic area. The present system is designed to operate in this "co-channel" environment. The system assures that mobile tr~n~ ions only occur on channels that are not currently occupied by either a mobile station that is part of the system, or by a mobile station from a WO91/12670 2 0 S ~ PCT/US91/010 foreign system on the same channel in the same area and, thus, not a part of the system.
The system according to the present invention is therefore designed to operate under current FCC rules and regulations on frequencies below 800 MHz.
The FCC channel assignments below 800 MHz. do not allow for exclusive use of any of the channels needed for trunking. Therefore, prior art systems in the United States cannot operate effectively or legally below 800 MHz. The present system, through careful analysis of each channel, recognizes non-system users and temporarily avoids selection of that channel. This arrangement makes "co-channel"
trunking possible, and meets the legal requirements for channel monitoring applied to frequencies below 800 MHz.
The system according to the present invention also allows a gradual trunking process to take place. A non-trunking repeater can be added to the trunking arrangement and all the,mobile stations previously operating on this repeater can gradually be converted to the trunking arrangement.
This provides much more efficient use of existing channels and reduces the financial hardship for mobile users by allowing a conversion process to the trunking arrangement over a period of time. The system has the ability to allow both trunk and non-trunk users to share repeaters during this period of time.
15 ?~55~
The preferred embodiments of the present invention will now be described with the aid of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram showing a typical repeater station of a mobile radio system of the type to which the present invention relates.
Fig. 2 is a block diagram of a typical mobile radio station having a control circuit in accordance with the present invention.
Fig. 3 is a detailed block diagram of the control circuit shown in Fig. 2.
Fig. 4 comprised of Figs 4A and 4B is a flow chart showing the operation of the control circuit of Fig. 3.
Fig. 5 comprised of 5A and 5B and 5C is a flow chart of operational routines used in the algorithm represented by the flow chart of Fig. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments of the present invention will now be described with reference to Figs. 1 - 5 of the drawings. Identical elements in the various figures are designated with the same reference numerals.
In describing these embodiments it will be assumed that a given locality surrounding a repeater station has been allocated five radio communication channels on a non-exclusive basis (for WO91/12670 2 0 ~ ~ ~ 5 ~ PCT/US91/0101~
example, in the 450 to 470 MHz. range), each channel having a different radio transmitting frequency and radio receiving frequency. As will be understood from the description below, each channel may be shared with other licensed repeaters which are not part of the trunking system.
Fig. l illustrates a five channel mobile radio repeater station having five repeaters Rl through R5, one for each channel, located at a suitable site that provides good radio coverage. Each of the repeaters Rl through R5 includes a transmitter, a receiver, and a so-called "repeater panel"
which will be described below. The repeaters share a transmitting antenna and a receiving antenna through the use of a signal combiner and multicoupler, respectively. For simplex operation in the first repeater Rl, the receiver and receiving antenna would function on a frequency Fl-R, and the transmitter and transmitting antenna would function on a frequency Fl-T which is spaced from the frequency Fl-R by a sufficient amount to provide good frequency separation for the transmitter and receiver. Other frequencies F2-R and F2-T through F5-R and F5-T would be provided for the repeaters R2 through R5. In the same locality, different groups of users may utilize the repeaters with the mobile radio stations (transmitters and receivers) in their respective mobile vehicles for example. Typically, each group has a common basis, such as the vehicles in a given ~ WO91/12670 2 ~ ~ 5 ~ ~ 9 PCT/US91/01012 business. Examples of such businesses are a taxicab company, a towing service and an oil company having a fleet of oil delivery trucks. The number of groups which a repeater can serve depends, among other things, upon the number of vehicles in a group, the amount of time a radio channel is used, and the number of repeater channels available. For example, five repeaters, each operating on separate transmit and receive frequencies, can serve as many as two thousand vehicles. However, the number of vehicles which can be efficiently served may change depending upon the demand for the channels.
The repeater panel of a given repeater station serves five basic functions:
(1) The panel validates the trunk identification signals, such as the CTCSS tones or DCSS tones, received on and demodulated from an incoming carrier to ensure that the received carrier was transmitted by a valid system subscriber;
(2) The panel keys or enables the transmitter whenever the received carrier comes from a valid subscriber;
COMMUNICATION IN A TWO-WAY MOBILE RADIO SYSTEM
BACKGROUND OF THE INVENTION
The present invention relates to a two-way radio communication system of the type commonly known as "mobile radio". More particularly, the invention relates to a method and apparatus for establishing communication in such a system on a common radio communication "channel" or frequency selected from a plurality of such channels.
As used herein, the term "radio channel" is intended to include a first frequency for transmitting and a second, different frequency for receiving by a plurality of user-operable radio transmitter/receiver stations. Signals transmitted by such user operable stations at the first frequency are received by a nearby radio repeater station and then retransmitted at the second frequency for reception by all the user-operable stations in the vicinity that are tuned to the channel.
As used herein, the term "mobile radio" is intended to describe the type of two-way radio system commonly used to communicate between and among a plurality of mobile or portable transmitter/receiver stations and one or more fixed base transmitter/receiver stations, with the aid of a repeater station. The mobile or portable stations are arranged on mobile vehicles of all types, such as motor r~
WO91/12670 2 0 5 ~ ~ 5 ~ PCT/US91/0101~
vehicles and boats, or hand held. A typical application of such a system is to dispatch and control the operation of taxis, tow vehicles, repair vehicles, delivery vehicles and the like. Normally, fleets of such mobile vehicles are owned and operated by separate business ent1ties, and it is advantageous if all, or a subset of, vehicle operators in a common fleet or business are able to communicate with each other and with a dispatcher at a fixed base station. Such a set of users who can communicate with each other by means of the mobile radio system will be denoted hereinafter as a "group" of users. It is further advantageous if the vehicle operators and fleet dispatcher of one fleet or business (one group of users) are prevented from communicating with, either by transmitting to or receiving from, vehicle operators and dispatchers of other fleets or businesses (other groups of users). Thus, the mobile radio system advantageously operates as a "party line" within each group or subgroup of users, and "private line" as between groups or subgroups of users.
In two-way mobile radio communication systems of this type a plurality of radio channels are allocated for communication between all user-operable radio stations.
Generally there may be, and usually are, many more radio stations than there are available radio channels in a given locality. Consequently, some arrangement is needed for WO91~12670 2 Q S ~ ~ 5 ~ PCT/US91/01012 enabling the communication among a large number of users, in the party line/private line basis described above, on a relatively small number of channels.
The U.S. Patent No. 4,409,687 to Berti et al. describes an arrangement for establishing communication in a mobile radio environment which utilizes a "busy tone" in the middle of the voice band of each ch~nnel. Each user-operable station in the system scans the available channels, in either a '~transmit mode~ or "receive mode", and takes action in dependence upon the presence (or absence) of a busy tone.
Each radio station utilizes a "notch filter" to remove the busy tone from the voice signal before the voice signal is processed. This arrangement is incompatible with other existing equipment in the field since it requires that all radio stations be able transmit, detect and remove a busy tone from the voice band in each channel.
Mobile radio systems, as presently in common use, distinguish between groups of users by so-called "sub-audible group tones"; that is tones in the voice band below 300 ~z. Such tones are ~ariously called "CTCSS" and "DCSS"
tones ~or "continuous tone coded squelch system" and "digital coded squelch system", respectively. In certain mobile radio channels in the United States - that is, in the radio channels allocated in the 4~0 to 470 MHz. range -there are a total of 38 CTCSS tones and 21~ DCSS tones ~05~4~ --closely spaced in the frequency range between 65 and 250 Hz.
The CTCSS tones are simply continuous tones whereas the DCSS
tones repeatedly provide seven bit words that convey the identity of a group. Each mobile radio station includes equipment for detecting the presence of absence of selected CTCSS tones and/or for decoding the transmitted DCSS words.
Although the use of CTCSS and DCSS tones is strictly voluntary on most frequencies, most mobile radios manufactured today are equipped to generate and detect one type of tone or the other, or both.
It is thus common practice to create "private lines"
between groups of users, and "party lines" among groups of users, by selecting a CTCSS or DCSS tone on each separate channel. The CTCSS or DCSS tone need not be the same for each channel provided that the radio stations of all users in a given group have been assigned the same tone for each channel.
Channel selection in mobile radio systems of this type has traditionally been accomplished by manually ad~usting the channel selector or by scanning. Automatic channel selection, for example as described in the aforementioned U.S. Patent No. 4,409,687, has not been thought possible because of the complexity of the system environment that contains mobile radio stations which are not equipped to handle the "busy tone" format.
WO91/12670 2 0 ~ PCT/US91/01012 As used herein, the term "trunking", as used in the mobile radio environment, is intended to describe the automatic selection of an available channel, when in the transmit mode, and the automatic acquisition of a calling channel, when in the receive mode.
SUMMARY OF THE I~V~llON
It is a principal object of the present invention to provide trunking in a mobile radio system, thereby to enable rapid, automatic access to an available communication channel, when in a transmit mode, and rapid, automatic call searching when in a receive mode.
It is another object of the present invention to provide a mobile radio system which ensures privacy in the communication among groups of users.
It is another object of the present invention to provide a mobile radio system which is secure against the reception of transmissions from third parties.
It is another object of the present invention to provide a mobile radio system which permits a two or even three-fold increase in the number of mobile radio stations in a given locality surrounding a repeater station.
It is another object of the present invention to provide a mobile radio system which does not cause interference when a mobile station set up for use within the reception area of , one repeater statlon intrudes into the receptlon area of another repeater, whereln both repeaters operate ln the same general receptlon area and one repeater is not part of the ~ trunk system.
It ls another ob~ect of the present invention to provlde a moblle radio system which is entlrely compatible wlth all existing equlpment on the repeater frequency, whether or not lt ls part of the trunk system.
It ls another ob~ect of the present lnventlon to provlde a moblle radio system whlch ls fully llcensable under the current rules of the Unlted States Federal Communlcatlons Commlsslon ("FCC").
It ls another ob~ect of the present lnventlon to provide a moblle radio system whlch enables each group of users to be subdivlded lnto two or more subgroups 80 as to provlde prlvacy between subgroup~ of users wlthln each user group.
It ls another ob~ect of the present lnventlon to provlde a moblle radlo system whlch enables the user to select between different repeater statlons or groups of repeaters located in dlfferent geographlc areas.
In accordance wlth the present lnvention, there is provlded a two-way moblle radio communlcatlon system comprlslng a plurallty of user-operable statlons and a cooperating repeater station all operatlng on a plurallty of radlo communlcatlon channels of dlfferlng frequency bands wlthout a dedlcated control channel, each user-operable -statlon comprislng, in combination: (a) a radio transmitter;
(b) a radio receiver; (c) user-operable switch means, coupled to said transmltter, for selectively enabling said ~ transmltter to transmlt a carrler slgnal~ (d) carrier operable switch means, coupled to said recelver, for indicating the receipt of a carrier signal when in an activation position; (e) channel selector means, coupled to said transmitter and said receiver, for selectlng the radio channel of operation; (f) means, coupled to said transmitter, for continuously generatlng a selected one of a plurallty of subaudible trunk ldentificatlon signals associated with each given communicatlon channel for transmisslon by said transmltter when operatlng on sald given channel; and (g) means, coupled to sald recelver, for indlcating the presence of sald selected one of a plurality of subaudlble trunk identiflcatlon signals when said receiver is operating on said glven channel 7 the method of automatlcally operatlng the user-operable statlons so as to establlsh communlcatlon between at least two such stations over one of sald plurallty of channels, sald method comprlslng the steps ofs (1) when sald user-operable swltch means ls open and said user-operable statlon ls ln a recelve mode~ (1) lncrementlng sald channel selector means to select a channel7 (11) determlnlng lf sald carrler operable switch means ls in said activation posltlon, thereby indlcating that a carrler slgnal ls present on the selected channelS (ili) if a carrier signal is not present, returning to step (1) (i) 7 .
- a -(lv) if a carrier slgnal i8 present, determinlng if the selected subaudible trunk ldentlfication slgnal ls present on said carrler slgnal; (v) lf the selected subaudlble trunk - identlflcation slgnal is not present on sald carrier slgnal, returnlng to step (1) ~1); and (vl) lf the selected subaudible trunk ldentlficatlon slgnal ls present on sald carrler signal, enabllng sald transmltter for push-to-talk operation; and (2) when sald user-operable swltch means ls closed and sald user-operable station ls ln a transmlt modes (1) if sald carrler operable swltch means ls ln sald activatlon positlon, thereby lndlcating that a carrler slgnal ls present on the selected channel, lncrementlng sald channel selector; (li) lf a carrler slgnal ls not present on the selected channel, transmlttlng a carrler slgnal wlth the æelected subaudlble trunk ldentlflcation slgnal for a prescribed perlod of tlme; (111) determlnlng whether a carrier slgnal wlth the selected subaudible trunk ldentlflcatlon slgnal ls recelved on the selected channel;
(lv) if a carrler slgnal wlth the selected subaudlble trunk identlflcatlon slgnal 18 not received, returnlng to step (2) (l); and (v) lf a carrler slgnal wlth the selected subaudlble trunk ldentlflcatlon slgnal ls recelved returnlng to step (1) (vl) .
In accordance wlth the present inventlon, there is also provlded a two-way moblle radio communicatlon system comprlslng a plurallty of user-operable statlons and at least one cooperatlng repeater statlon all operatlng on a plurallty 205~459 - 7b -of radlo communlcatlon channels of dlfferlng frequency bands wlthout a dedlcated control channel, each user-operable statlon comprising, in combinatlon: (a) a radio transmitter7 - (b) a radio receiver; (c) user-operable switch means, coupled to sald transmitter, for selectively enabling said transmltter to transmit a carrier slgnal~ (d) carrler operable swltch means, coupled to sald recelver, for indicating the receipt of a carrler slgnal when in an actlvation position; (e) channel selector means, coupled to sald transmitter and said recelver, for selecting the radio channel of operation; (f) means, coupled to said transmltter, for contlnuously generatlng a selected one of a plurallty of subaudlble trunk identificatlon slgnals associated with each given communlcatlon channel for transmlssion by said transmitter when operatlng on sald given channel; and (g) means, coupled to sald receiver, for lndicating the presence of said selected one of a plurality of subaudible trunk identification signals when said recelver i5 operating on said given channelS the method of automatically operating the user-operable stations so as to establish communication between groups of such stations over one of said plurality of channels, sald method comprising the steps of:
(1) assigning prescribed ones of said subaudible trunk ldentlficatlon signals to respectlve groups of stations; (2) when said user-operable switch means is open and said user-operable statlon ls ln a recelve mode; (1) incrementlng sald channel selector means to select a channel from among sald - 7c - 2055459 prescrlbed channels; (ii) determinlng lf sald carrler operable switch means is in sald actlvatlon posltlon, thereby lndlcatlng that a carrler signal ls present on the selected - channel; ~111) lf a carrler signal is not present, returning to step (2) (i); (iv) lf a carrler slgnal ls present, determinlng if the selected subaudible trunk identification signal ls present on sald carrler slgnal; ~v) lf the selected subaudible trunk identification signal is not present on said carrier signal, returnlng to step ~2) ~i); and ~vl) lf the selected subaudlble trunk ldentification signal is present on said carrler slgnal, enabling said transmltter for push-to-talk operatlon; and ~3) when sald user-operable swltch means ls closed and said user-operable statlon ls in a transmit mode: ~i) if sald carrier operable switch means ls ln sald activation posltlon, thereby lndlcatlng that a carrier signal ls present on the selected channel, incrementing said channel selected to select a channel from among sald prescrlbed channels; ~11) lf a carrler slgnal ls not present on the selected channel, transmittlng a carrler ~ignal with the selected subaudible trunk identlflcatlon signal for a prescrlbed period of time; ~iil) determinlng whether a carrler slgnal wlth the selected subaudlble trunk ldentlflcatlon slgnal ls received on the selected channel;
~lv) lf a carrier slgnal wlth the selected subaudible trunk identlflcatlon slgnal ls not recelved, returnlng to step ~3) ~l); and ~v) lf a carrler slgnal wlth the selected 72003-g .
- 7d -subaudible trunk ldentlflcation signal is received returning to step (2) (vi).
The above ob~ects, as well as other ob~ects and advantages whlch will become apparent in the discussion that follows, are achieved, in accordance wlth the present inventlon, by provlding a mobile radio system of the type described lmmedlately above in which communication is established between at least two user-operable stations over WO 91/12670 ~ o 5 ~ 3 PCT/US91/010 ~
one of a plurality of channels by operating the user-operable stations in accordance with the following steps:
(1) When in the receive mode (the push-to-talk switch is open):
(i) incrementing the channel selector`to select a channel;
(ii) determining if a carrier signal is present on the selected channel:
(iii) if a carrier signal is not present, returning to step (1) (i);
(iv) if a carrier signal is present, determining if the selected trunk identification signal is present on the carrier signal;
(v) if the selected trunk identification signal is not present, returning to step (l)(i); and (vi) if the selected trunk identification signal is present on the carrier signal, enabling said transmitter for push-to-talk operation.
(2~ When in the transmit mode (the push-to-talk switch is closed):
(i) if a carrier signal is present on the selected channel, incrementing the channel selector;
(ii) if a carrier signal is not present on the selected channel, transmitting a carrier signal with the WO91/12670 2~4~ PCT/US91/01012 selected trunk identification signal for a prescribed period of time;
(iii) determining whether a carrier signal with the selected trunk identification signal is received on the selected channel;
(iv) if a carrier signal with the selected trunk identification signal is not received, returning to step (2)(i); and (v) if a carrier signal with the selected trunk identification signal is received, returning to step (1) (vi), This method of operation is preferably implemented by a programmed microprocessor arranged on a small circuit board.
The microprocessor circuit receives as inputs the carrier operated switch or relay signal and the "mute/unmute" signal from the receiver. The carrier operated relay ("COR") indicates the presence of a carrier signal on the selected channel. The "unmute" signal from the receiver indicates the presence of the selected identification signal (CTCSS or DCSS tone) and unmutes the receiver when such tone is present.
The microprocessor circuit also receives a signal indicating whether the push-to-talk switch is open or closed.
WO91/12670 2 0 5 ~ ~ S ~ PCT/US91/010 ~
The microprocessor circuit produces a pulse signal on an output line to increment the channel selector, as required.
If incrementing by one, one pulse is produced; if incrementing by two or more channels, two or more pulses are produced, as required.
The microprocessor circuit also produces an output signal which enables the push-to-talk operation of the transmitter.
According to a preferred feature of the present invention, the user-operable mobile radio station includes a tone generator connected to the radio loudspeaker for producing one or more audible tones indicative of the station operation. In particular, and in accordance with this feature, a brief beep tone at one audible frequency is produced when the push-to-talk switch is keyed by the operator. A second brief beep tone at a second audible frequency is produced when the COR is activated as a result of keying the push-to-talk switch (i.e., when the repeater station receives the transmitted signal and transmits a carrier in reply). This second beep tone thus indicates to the user that the transmission by the user-operable station has been received by the repeater station and retransmitted for reception by all user-operable mobile radio stations in the area.
According to another feature of the present invention, a mobile radio station user can select a subgroup of users WO91/12670 2~4~9 PCT/US91/01012 .
with whom he or she wishes to communicate. Preferably, the selection can be made by the length of time that the push-to-talk switch is initially keyed when establishing communication. If the push-to-talk switch is keyed momentarily, one subgroup is selected; and when the push-to-talk switch is keyed for a longer period of time, the second subgroup is selected. Preferably, an audible tone, such as a brief single beep, is produced when the push-to-talk switch is keyed for a short period, and a double beep tone or a tone of a different frequency is produced when the push-to-talk switch is keyed for a sufficiently long period to select the second subgroup.
The selection of one subgroup or another can be effected by a number of different methods. In one method, the trunk identification signal (e.g. CTCSS or DCSS tone) for transmission on the carrier signal when in the transmit mode is selected for the particular subgroup desired. According to another method, the available channels are allocated among the different subgroups so that each subgroup can transmit and receive only on certain select channels.
For example, the even channel numbers may be allocated to one subgroup and the odd channel numbers allocated to a second subgroup.
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The group selection is thus e~fected by~incrementing the channel selector a prescribed number of times to select only those channels for the subgroup desired.
In accordance with the present invention, therefore, the efficiency of mobile two-way radio systems that employ repeaters is improved by selecting one radio channel from a plurality of radio channels by systemmatic examination of each channel to determine the presence of: 1) A user of a desired group on the same system, 2) a user of a non-desired group on the same system, or 3) a user of a group from a foreign system that operates in the same geographic area on the same channel.
The system described in the aforementioned U.S. Patent No. 4,409,687 is designed to operate on channel assignments that are geographically protected non-participating users.
In this known system a busy tone is provided to alert mobile stations to avoid that particular channel not transmitting a busy tone. This arrangement is designed to operate only where each and every mobile in a given system are participants in the system and share circuitry in each mobile that match the arrangement.
The Federal Communications Commission (FCC) issues special "trunking" licenses above 800 MHz. to operators of the type of trunking arrangements disclosed in the U.S.
Patent No. 4,409,687. However, all these prior arrangements WO91/12670 2 ~ ~ 5 4 ~ ~ PCT/US91/01012 .
have exclusive use of each of the channels trunked in a given geographic area. In this fashion, each system can only function in a given geographic area on an exclusive basis. It cannot operate in an environment with other non-participating mobiles, such as exists in the environment below 800 MHz.
The system according to the present invention provides not only a trunking arrangement but also allows other non-trunked users access to each channel and to each repeater in the arrangement.
The present system provides channel monitoring to any type of user, whether part of the system or not.
A user-operable station acquires a channel by an arrangement that analyzes the presence of any user and, if a channel is occupied, continues to ~;ne each subsequent channel from the plurality of channels available in the system. At no point in this system are busy tones used, or is filtering required or used in any equipment.
In the UHF spectrum (450-470 MHz.) for example, channels are licensed by the FCC on a non-exclusive use basis in a given geographic area. The present system is designed to operate in this "co-channel" environment. The system assures that mobile tr~n~ ions only occur on channels that are not currently occupied by either a mobile station that is part of the system, or by a mobile station from a WO91/12670 2 0 S ~ PCT/US91/010 foreign system on the same channel in the same area and, thus, not a part of the system.
The system according to the present invention is therefore designed to operate under current FCC rules and regulations on frequencies below 800 MHz.
The FCC channel assignments below 800 MHz. do not allow for exclusive use of any of the channels needed for trunking. Therefore, prior art systems in the United States cannot operate effectively or legally below 800 MHz. The present system, through careful analysis of each channel, recognizes non-system users and temporarily avoids selection of that channel. This arrangement makes "co-channel"
trunking possible, and meets the legal requirements for channel monitoring applied to frequencies below 800 MHz.
The system according to the present invention also allows a gradual trunking process to take place. A non-trunking repeater can be added to the trunking arrangement and all the,mobile stations previously operating on this repeater can gradually be converted to the trunking arrangement.
This provides much more efficient use of existing channels and reduces the financial hardship for mobile users by allowing a conversion process to the trunking arrangement over a period of time. The system has the ability to allow both trunk and non-trunk users to share repeaters during this period of time.
15 ?~55~
The preferred embodiments of the present invention will now be described with the aid of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram showing a typical repeater station of a mobile radio system of the type to which the present invention relates.
Fig. 2 is a block diagram of a typical mobile radio station having a control circuit in accordance with the present invention.
Fig. 3 is a detailed block diagram of the control circuit shown in Fig. 2.
Fig. 4 comprised of Figs 4A and 4B is a flow chart showing the operation of the control circuit of Fig. 3.
Fig. 5 comprised of 5A and 5B and 5C is a flow chart of operational routines used in the algorithm represented by the flow chart of Fig. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments of the present invention will now be described with reference to Figs. 1 - 5 of the drawings. Identical elements in the various figures are designated with the same reference numerals.
In describing these embodiments it will be assumed that a given locality surrounding a repeater station has been allocated five radio communication channels on a non-exclusive basis (for WO91/12670 2 0 ~ ~ ~ 5 ~ PCT/US91/0101~
example, in the 450 to 470 MHz. range), each channel having a different radio transmitting frequency and radio receiving frequency. As will be understood from the description below, each channel may be shared with other licensed repeaters which are not part of the trunking system.
Fig. l illustrates a five channel mobile radio repeater station having five repeaters Rl through R5, one for each channel, located at a suitable site that provides good radio coverage. Each of the repeaters Rl through R5 includes a transmitter, a receiver, and a so-called "repeater panel"
which will be described below. The repeaters share a transmitting antenna and a receiving antenna through the use of a signal combiner and multicoupler, respectively. For simplex operation in the first repeater Rl, the receiver and receiving antenna would function on a frequency Fl-R, and the transmitter and transmitting antenna would function on a frequency Fl-T which is spaced from the frequency Fl-R by a sufficient amount to provide good frequency separation for the transmitter and receiver. Other frequencies F2-R and F2-T through F5-R and F5-T would be provided for the repeaters R2 through R5. In the same locality, different groups of users may utilize the repeaters with the mobile radio stations (transmitters and receivers) in their respective mobile vehicles for example. Typically, each group has a common basis, such as the vehicles in a given ~ WO91/12670 2 ~ ~ 5 ~ ~ 9 PCT/US91/01012 business. Examples of such businesses are a taxicab company, a towing service and an oil company having a fleet of oil delivery trucks. The number of groups which a repeater can serve depends, among other things, upon the number of vehicles in a group, the amount of time a radio channel is used, and the number of repeater channels available. For example, five repeaters, each operating on separate transmit and receive frequencies, can serve as many as two thousand vehicles. However, the number of vehicles which can be efficiently served may change depending upon the demand for the channels.
The repeater panel of a given repeater station serves five basic functions:
(1) The panel validates the trunk identification signals, such as the CTCSS tones or DCSS tones, received on and demodulated from an incoming carrier to ensure that the received carrier was transmitted by a valid system subscriber;
(2) The panel keys or enables the transmitter whenever the received carrier comes from a valid subscriber;
(3) The panel strips the trunk identification signals from the received and demodulated carrier and generates new, clean trunk identification signals for transmission by the repeater;
wo gl/12670 2 0 ~ S ~ S ~ PCT/US91/010 ~
wo gl/12670 2 0 ~ S ~ S ~ PCT/US91/010 ~
(4) The panel suppresses noise and adjusts the level of the received audio signal for retransmission by the repeater; and (5) The panel monitors the incoming traffic and maintains a record of the subscriber activity, e.g., for billing purposes.
When the panel keys the transmitter (item (2), above) it causes the transmitter to transmit a carrier for a prescribed period of time after each validated incoming signal has terminated. This transmitter "hang time" - which may be approximately five seconds, for example - allows the system users to maintain control of a channel between individual transmissions from the mobile stations of a group.
The repeater station is normally arranged at an elevated position in the locality and transmits with greater power than the user-operable stations which it serves.
The repeater station, as described above, is well known in the art. A complete station with a repeater panel may be obtained commercially, for example, from ZETRON, Inc., in Belleview, Washington, USA, under the Model No. 38A. No modification of the repeater station is required for the purposes of the present invention.
Given a number of available repeater channels in a particular locality, it is desirable that a group of system WO91/12670 ~ 5 ~4~ 9 PCT/US91/01012 .
users be able to quickly ascertain which channel or frequencies are available, so as to establish communication with the other users in that same group. The present invention provides a system (apparatus and method) for providing and establishing this communication in a relatively simple but reliable fashion.
Fig. 2 illustrates a user-operable station according to a preferred embodiment of the present invention. This station may be a fixed base station, or a mobile station for use on a vehicle or boat, or a hand held unit. For simplicity, this user-operable station will hereinafter be called a "mobile station". The mobile station lO includes a radio transmitter ll capable of operating on any of the frequencies Fl-R through F5-R, and a radio receiver 12 capable of operating on any of the frequencies Fl-T through F5-T. Two frequencies are needed for each channel in order that the mobile stations and the repeater station can function in a simplex or push-to-talk arrangement. Thus, the mobile station lO transmits on a repeater receive frequency (for example Fl-R). A transmission on this frequency Fl-R would be received by the repeater and retransmitted to the other mobile stations in the vicinity on the frequency Fl-T. When transmitting, the other mobile stations would also use the frequency Fl-R. In such an arrangement, a single antenna (not shown) is shared by the W091/12670 ~ 0 5 S ~ ~ 9 PCT/US91/010l~ .
mobile station transmitter 11 and receiver 12, depending upon whether the mobile station is transmitting or receiving.
If full duplex operation were provided, four frequencies would be needed by each repeater for each channel.
It may be assumed that the transmitter 11 and receiver 12 are frequency modulation devices, although they may be amplitude modulation devices. The transmitter 11 includes an oscillator circuit which operates at one of the five frequencies depending upon the signal applied to it by a channel selector 13. The receiver 12 is preferably of the superheterodyne type and includes a local oscillator which also operates at one of the five frequencies depending upon the signal supplied by the channel selector 13. Channel select signals are provided by a control circuit 14 which will be described in detail hereinafter. The channel selector 13 is supplied with these channel select signals and sequentially produces frequency selection signals at its outputs. These selection signals are applied to the transmitter and receiver oscillators to cause the transmitter 11 to be sequentially operable on the radio frequencies Fl-R through F5-R, and the receiver 12 to be sequentially operable on the radio frequencies F1-T through F5-T.
20~S~59 WO91/12~70 PCT/US91/01012 A sub-audible tone generator 15 and a sub-audible tone decoder 16 are provided, respectively, (l) for generating trunk identification signals, such as CTCSS or DCS tones, for transmission by the transmitter ll, and (2) for filtering and decoding such tones received by the receiver 12. These so-called "sub-audible tones" are not truly below the audible range; however, the receiver circuit includes a high-pass filter which allows only that audio signal to pass to the loudspeaker which is above the sub-audible tone range of 50 - 300 Herz.
The mobile station is provided with a microphone, connected to the transmitter ll, and a loudspeaker connected to the receiver 12. In addition, a push-to-talk switch, arranged on the microphone stem or separately situated, is electrically connected to the unit proper.
The mobile station also includes the usual operator controls and indicators (not shown) to enable the operator or user to operate his station and to have indications of the operation of his station. Such controls may include an on-off switch, a manual channel selector and indicator lights which inform the user of the selected channel.
As thus far described, the mobile radio station is well known in the art. Such a mobile station may be obtained commercially, for example, from the Radius Division of :
WO91/12670 2 0 5 5 ~ S 9 PCT/US91/010~
Motorola, Inc. in Schaumburg, Illinois, USA, under the Model Nos. 206 or 214.
In a commercially available mobile radio the push-to-talk (PTT) switch is connected to a push-to-talk (PTT) relay 17 (either mechanical or electronic) which, in turn, keys the transmitter 11. In the preferred embodiment of the present invention, the line connecting the PTT switch to the PTT relay is interrupted and coupled to the control circuit 14 as shown in Fig. 2.
Other inputs and outputs of the control circuit 14 are connected to various available points in the radio in the manner shown in Fig. 2. These inputs and outputs are as follows:
Inputs: (1) the PTT switch; t2) the carrier operated relay (COR) signal indicating that a carrier is present; (3) the "UNMUTE" signal which indicates that a sub-audible tone decode match is present; and (4) the channel signal (1 to 4 lines of various configurations depending on make and model of the radio), which identifies which channel the radio is presently tuned to. This fourth signal is only required when the system is programmed to select among subgroups in the manner described below.
Outputs: (1) transmit key (2) channel step signal (a pulse which causes the radio to step to next channel); (3) auxiliary mute (to quiet the audio while stepping, etc., WO91/12670 ~5~ PCT/US91/01012 .
occurs); and (4) a tone signal (providing a tone or series of tones which inform the user of status, operation and errors).
Fig. 3 is a block diagram of the control circuit 14 itself. The CPU, a Hitachi 6301 microcomputer, has eight digital input lines, each with a protection circuit to prevent overloads. It also has six digital output lines, with open collector outputs, to drive the various functions in the radio. Three inputs share common connector pins with three outputs, only to keep the connector size within reason so as to fit within the smaller radios. One additional output of the CPU is the tone output. It has a tone shaping circuit to assist in generating suitable ~beep" sounds.
The remainder of the circuitry consists of a non-volatile memory (EEPROM), which configures the system, and a few support components such as a voltage regulator and a crystal.
Figs. 4 and 5 illustrate the operation of the software stored and run in the CPU. Within the CPU, there are two "levels" of code. The first of these is called the background level, which has first priority. It operates a timer and counters which provide the necessary circuit timing. The CPU timing is derived from the crystal oscillator. The background level code generally consumes less than 2% of the available CPU time.
WO91/12670 2 0 S 5 4 5 ~ PCr/US91/010 ~
The second level of code, called the foreground level, is what is actually shown in the flowcharts of Figs. 4 and 5.
Beginning the upper left corner of Fig. 4, on the MAIN LOOP
and coming down, the first block of the program is READ
STATUS. At this point the CPU looks at the three digital input lines designated, respectively, CARRIER, UNMUTE and PTT. These three lines give eight possible conditions. Six of these are of concern, the other two being ignored. If one of the six conditions exists, then the program leaves the MAIN LOOP and goes to the selected routine. The receive mode routines are shown in Fig. 4; the transmit mode routines are shown in Fig. 5.
First we will consider the case of the receive or idle mode, (no PTT) in which the mobile station scans the chAn~ls for incoming messages.
Assume that the first channel that the CPU is on does not have a CARRIER and, consequently, does not have an UNMUTE.
It will therefore exit the MAIN LOOP routine at the point marked NO CONDITIONS, going to a routine called RECOOO.
Here the output line or lines called STEP CHANNEL are actuated for a few milliseconds (ms) to increment the channel number; thereafter, the CPU pauses for a prescribed period of time (e.g., 25 ms) to allow the radio to change channels and stabilize. After this delay, the CPU returns to the MAIN LOOP and looks at the status lines again.
2(~55459 Assuming that a carrier is not received on this second channel, the CPU again steps the channel, waits 25 ms, and again looks for a carrier.
The CPU remains in this loop if none of the other stations are transmitting.
If a carrier is found, the CPU exits at the block marked CARRIER ONLY and goes to the routine RECl00. It waits for a sufficient time (e.g., 250 ms) to allow an UNMUTE status to appear; that is, to allow the trunk identification signal (CTCSS or DCSS) to be decoded, if present. If UNMUTE has not appeared by the end of this 250 ms, the CPU returns to REC000 and proceeds as before.
If UNMUTE does appear with CARRIER, the CPU returns to the MAIN LOOP, exits at CARRIER and UNMUTE, and goes to the routine REC300. Here the radio is caused to stay on the selected channel as long as CARRIER and UNMUTE remain active. We would expect to receive a message at this time, as it is another station in the same group that is causing this CARRIER and UNMUTE by transmitting on the channel.
To summarize thus far: The CPU steps through the channels until it finds a CARRIER and, when an UNMUTE also appears, it stops stepping, opens the receiver and listens.
When the CARRIER and/or UNMUTE disappear, the CPU goes back to stepping through the channels.
wo gl/12670 2 ~ 5 ~ 4 5 9 PCT/US91/010 ~
. .
At this time, PTT is made available to allow the user to transmit as desired.
Next we will consider the case of the transmit or channel acquisition mode: CARRIER and UNMUTE are not present and the PTT key is depressed by the user. The object is to have all other stations in the user's group find and lock on to the user's transmitter.
Starting at the MAIN LOOP, the CPU exits at PTT, going to the routine TSX000 (Fig. 5A). The CPU produces a responsive beep tone for 1/4 second, letting the user know that the sequence has started. Next, the transmitter is caused to transmit a carrier for two seconds.
Note that the CPU could not come to this routine from the MAIN LOOP if a CARRIER were already present on the selected channel. Therefore, the station can only transmit on a vacant channel. In addition, and as will be discussed below, the user may choose to transmit on only selected ones of the available channels.
Next the CPU monitors CARRIER and UNMUTE for one second.
If CARRIER and UNMUTE appear, the CPU produces a beep tone and returns to the MAIN LOOP. This beep tone indicates that the repeater has received, and has retransmitted the user's carrier.
If CARRIER and UNMUTE do not appear, the CPU steps the channel and transmits on the next selected channel. It ~ WO91/12670 PCT/US91/01012 keeps trying this procedure on successive selected channels for up to one minute until either a transmission is returned by a repeater or a failure tone is sounded.
If and when CARRIER and UNMUTE appear on a channel, the signal PTT keys the transmitter through the routine TXS300 (FIG. 5B) much as a normal transmitter, except that the station will not go back to the receive mode for a least l second after release.
Next we will consider the case where the transmitter is keyed when a CARRIER, but not an UNMUTE, is present. In this routine TXSlO0 (FIG. 5A) the station is not allowed to transmit, as the channel is occupied. Therefore, the CPU
steps to the next selected channel, waits, and tests for a clear channel again.
In some instances, it may be desirable to limit channel selection to certain clusters of channels, so as to provide two or more subgroups within a group. An example of this situation is where a vehicle with a mobile radio travels between two cities that have different repeater stations tuned to different frequencies. As an example, assume there are a total of six channels, numbered l through 6, with three channels in one city and three in another.
Subgroup I could be allocated channels l, 3 and 5, whereas subgroup II could be allocated channels 2, 4 and 6.
WO91/12670 2 0 5 ~ 4 ~ 9 PCT/US91/010 ~
If, during channel request (PTT without CARRIER), the PTT
is depressed for 1 second, enough for one response beep, subgroup I is selected; if PTT is held longer, two beeps are sounded and subgroup II is selected. Alternatively, a separate subgroup selector switch may be provided on the mobile unit to select between subgroup I and subgroup II.
The EEPROM stores the channels associated within the respective subgroups and otherwise configures the system.
The CPU is thus caused to skip those channels which are not in the subgroup selected.
Another technique for selecting between subgroups is to select among different available trunk identification signals (CTCSS and/or DCSS tones). The EEPROM may be used to store the trunk identification signals for each subgroup, as required.
Fig. 5A illustrates the preferred embodiment of an algorithm for disting~ h;ng between subgroups (indicated as groups 1, 2 and 3) by use of the PTT.
There has thus been shown and described a novel mobile radio communication system which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose ~ WO91/12670 PCT/US91/01012 205~4~9 . 29 the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are intended to be covered by the invention which is limited only by the claims which follow.
When the panel keys the transmitter (item (2), above) it causes the transmitter to transmit a carrier for a prescribed period of time after each validated incoming signal has terminated. This transmitter "hang time" - which may be approximately five seconds, for example - allows the system users to maintain control of a channel between individual transmissions from the mobile stations of a group.
The repeater station is normally arranged at an elevated position in the locality and transmits with greater power than the user-operable stations which it serves.
The repeater station, as described above, is well known in the art. A complete station with a repeater panel may be obtained commercially, for example, from ZETRON, Inc., in Belleview, Washington, USA, under the Model No. 38A. No modification of the repeater station is required for the purposes of the present invention.
Given a number of available repeater channels in a particular locality, it is desirable that a group of system WO91/12670 ~ 5 ~4~ 9 PCT/US91/01012 .
users be able to quickly ascertain which channel or frequencies are available, so as to establish communication with the other users in that same group. The present invention provides a system (apparatus and method) for providing and establishing this communication in a relatively simple but reliable fashion.
Fig. 2 illustrates a user-operable station according to a preferred embodiment of the present invention. This station may be a fixed base station, or a mobile station for use on a vehicle or boat, or a hand held unit. For simplicity, this user-operable station will hereinafter be called a "mobile station". The mobile station lO includes a radio transmitter ll capable of operating on any of the frequencies Fl-R through F5-R, and a radio receiver 12 capable of operating on any of the frequencies Fl-T through F5-T. Two frequencies are needed for each channel in order that the mobile stations and the repeater station can function in a simplex or push-to-talk arrangement. Thus, the mobile station lO transmits on a repeater receive frequency (for example Fl-R). A transmission on this frequency Fl-R would be received by the repeater and retransmitted to the other mobile stations in the vicinity on the frequency Fl-T. When transmitting, the other mobile stations would also use the frequency Fl-R. In such an arrangement, a single antenna (not shown) is shared by the W091/12670 ~ 0 5 S ~ ~ 9 PCT/US91/010l~ .
mobile station transmitter 11 and receiver 12, depending upon whether the mobile station is transmitting or receiving.
If full duplex operation were provided, four frequencies would be needed by each repeater for each channel.
It may be assumed that the transmitter 11 and receiver 12 are frequency modulation devices, although they may be amplitude modulation devices. The transmitter 11 includes an oscillator circuit which operates at one of the five frequencies depending upon the signal applied to it by a channel selector 13. The receiver 12 is preferably of the superheterodyne type and includes a local oscillator which also operates at one of the five frequencies depending upon the signal supplied by the channel selector 13. Channel select signals are provided by a control circuit 14 which will be described in detail hereinafter. The channel selector 13 is supplied with these channel select signals and sequentially produces frequency selection signals at its outputs. These selection signals are applied to the transmitter and receiver oscillators to cause the transmitter 11 to be sequentially operable on the radio frequencies Fl-R through F5-R, and the receiver 12 to be sequentially operable on the radio frequencies F1-T through F5-T.
20~S~59 WO91/12~70 PCT/US91/01012 A sub-audible tone generator 15 and a sub-audible tone decoder 16 are provided, respectively, (l) for generating trunk identification signals, such as CTCSS or DCS tones, for transmission by the transmitter ll, and (2) for filtering and decoding such tones received by the receiver 12. These so-called "sub-audible tones" are not truly below the audible range; however, the receiver circuit includes a high-pass filter which allows only that audio signal to pass to the loudspeaker which is above the sub-audible tone range of 50 - 300 Herz.
The mobile station is provided with a microphone, connected to the transmitter ll, and a loudspeaker connected to the receiver 12. In addition, a push-to-talk switch, arranged on the microphone stem or separately situated, is electrically connected to the unit proper.
The mobile station also includes the usual operator controls and indicators (not shown) to enable the operator or user to operate his station and to have indications of the operation of his station. Such controls may include an on-off switch, a manual channel selector and indicator lights which inform the user of the selected channel.
As thus far described, the mobile radio station is well known in the art. Such a mobile station may be obtained commercially, for example, from the Radius Division of :
WO91/12670 2 0 5 5 ~ S 9 PCT/US91/010~
Motorola, Inc. in Schaumburg, Illinois, USA, under the Model Nos. 206 or 214.
In a commercially available mobile radio the push-to-talk (PTT) switch is connected to a push-to-talk (PTT) relay 17 (either mechanical or electronic) which, in turn, keys the transmitter 11. In the preferred embodiment of the present invention, the line connecting the PTT switch to the PTT relay is interrupted and coupled to the control circuit 14 as shown in Fig. 2.
Other inputs and outputs of the control circuit 14 are connected to various available points in the radio in the manner shown in Fig. 2. These inputs and outputs are as follows:
Inputs: (1) the PTT switch; t2) the carrier operated relay (COR) signal indicating that a carrier is present; (3) the "UNMUTE" signal which indicates that a sub-audible tone decode match is present; and (4) the channel signal (1 to 4 lines of various configurations depending on make and model of the radio), which identifies which channel the radio is presently tuned to. This fourth signal is only required when the system is programmed to select among subgroups in the manner described below.
Outputs: (1) transmit key (2) channel step signal (a pulse which causes the radio to step to next channel); (3) auxiliary mute (to quiet the audio while stepping, etc., WO91/12670 ~5~ PCT/US91/01012 .
occurs); and (4) a tone signal (providing a tone or series of tones which inform the user of status, operation and errors).
Fig. 3 is a block diagram of the control circuit 14 itself. The CPU, a Hitachi 6301 microcomputer, has eight digital input lines, each with a protection circuit to prevent overloads. It also has six digital output lines, with open collector outputs, to drive the various functions in the radio. Three inputs share common connector pins with three outputs, only to keep the connector size within reason so as to fit within the smaller radios. One additional output of the CPU is the tone output. It has a tone shaping circuit to assist in generating suitable ~beep" sounds.
The remainder of the circuitry consists of a non-volatile memory (EEPROM), which configures the system, and a few support components such as a voltage regulator and a crystal.
Figs. 4 and 5 illustrate the operation of the software stored and run in the CPU. Within the CPU, there are two "levels" of code. The first of these is called the background level, which has first priority. It operates a timer and counters which provide the necessary circuit timing. The CPU timing is derived from the crystal oscillator. The background level code generally consumes less than 2% of the available CPU time.
WO91/12670 2 0 S 5 4 5 ~ PCr/US91/010 ~
The second level of code, called the foreground level, is what is actually shown in the flowcharts of Figs. 4 and 5.
Beginning the upper left corner of Fig. 4, on the MAIN LOOP
and coming down, the first block of the program is READ
STATUS. At this point the CPU looks at the three digital input lines designated, respectively, CARRIER, UNMUTE and PTT. These three lines give eight possible conditions. Six of these are of concern, the other two being ignored. If one of the six conditions exists, then the program leaves the MAIN LOOP and goes to the selected routine. The receive mode routines are shown in Fig. 4; the transmit mode routines are shown in Fig. 5.
First we will consider the case of the receive or idle mode, (no PTT) in which the mobile station scans the chAn~ls for incoming messages.
Assume that the first channel that the CPU is on does not have a CARRIER and, consequently, does not have an UNMUTE.
It will therefore exit the MAIN LOOP routine at the point marked NO CONDITIONS, going to a routine called RECOOO.
Here the output line or lines called STEP CHANNEL are actuated for a few milliseconds (ms) to increment the channel number; thereafter, the CPU pauses for a prescribed period of time (e.g., 25 ms) to allow the radio to change channels and stabilize. After this delay, the CPU returns to the MAIN LOOP and looks at the status lines again.
2(~55459 Assuming that a carrier is not received on this second channel, the CPU again steps the channel, waits 25 ms, and again looks for a carrier.
The CPU remains in this loop if none of the other stations are transmitting.
If a carrier is found, the CPU exits at the block marked CARRIER ONLY and goes to the routine RECl00. It waits for a sufficient time (e.g., 250 ms) to allow an UNMUTE status to appear; that is, to allow the trunk identification signal (CTCSS or DCSS) to be decoded, if present. If UNMUTE has not appeared by the end of this 250 ms, the CPU returns to REC000 and proceeds as before.
If UNMUTE does appear with CARRIER, the CPU returns to the MAIN LOOP, exits at CARRIER and UNMUTE, and goes to the routine REC300. Here the radio is caused to stay on the selected channel as long as CARRIER and UNMUTE remain active. We would expect to receive a message at this time, as it is another station in the same group that is causing this CARRIER and UNMUTE by transmitting on the channel.
To summarize thus far: The CPU steps through the channels until it finds a CARRIER and, when an UNMUTE also appears, it stops stepping, opens the receiver and listens.
When the CARRIER and/or UNMUTE disappear, the CPU goes back to stepping through the channels.
wo gl/12670 2 ~ 5 ~ 4 5 9 PCT/US91/010 ~
. .
At this time, PTT is made available to allow the user to transmit as desired.
Next we will consider the case of the transmit or channel acquisition mode: CARRIER and UNMUTE are not present and the PTT key is depressed by the user. The object is to have all other stations in the user's group find and lock on to the user's transmitter.
Starting at the MAIN LOOP, the CPU exits at PTT, going to the routine TSX000 (Fig. 5A). The CPU produces a responsive beep tone for 1/4 second, letting the user know that the sequence has started. Next, the transmitter is caused to transmit a carrier for two seconds.
Note that the CPU could not come to this routine from the MAIN LOOP if a CARRIER were already present on the selected channel. Therefore, the station can only transmit on a vacant channel. In addition, and as will be discussed below, the user may choose to transmit on only selected ones of the available channels.
Next the CPU monitors CARRIER and UNMUTE for one second.
If CARRIER and UNMUTE appear, the CPU produces a beep tone and returns to the MAIN LOOP. This beep tone indicates that the repeater has received, and has retransmitted the user's carrier.
If CARRIER and UNMUTE do not appear, the CPU steps the channel and transmits on the next selected channel. It ~ WO91/12670 PCT/US91/01012 keeps trying this procedure on successive selected channels for up to one minute until either a transmission is returned by a repeater or a failure tone is sounded.
If and when CARRIER and UNMUTE appear on a channel, the signal PTT keys the transmitter through the routine TXS300 (FIG. 5B) much as a normal transmitter, except that the station will not go back to the receive mode for a least l second after release.
Next we will consider the case where the transmitter is keyed when a CARRIER, but not an UNMUTE, is present. In this routine TXSlO0 (FIG. 5A) the station is not allowed to transmit, as the channel is occupied. Therefore, the CPU
steps to the next selected channel, waits, and tests for a clear channel again.
In some instances, it may be desirable to limit channel selection to certain clusters of channels, so as to provide two or more subgroups within a group. An example of this situation is where a vehicle with a mobile radio travels between two cities that have different repeater stations tuned to different frequencies. As an example, assume there are a total of six channels, numbered l through 6, with three channels in one city and three in another.
Subgroup I could be allocated channels l, 3 and 5, whereas subgroup II could be allocated channels 2, 4 and 6.
WO91/12670 2 0 5 ~ 4 ~ 9 PCT/US91/010 ~
If, during channel request (PTT without CARRIER), the PTT
is depressed for 1 second, enough for one response beep, subgroup I is selected; if PTT is held longer, two beeps are sounded and subgroup II is selected. Alternatively, a separate subgroup selector switch may be provided on the mobile unit to select between subgroup I and subgroup II.
The EEPROM stores the channels associated within the respective subgroups and otherwise configures the system.
The CPU is thus caused to skip those channels which are not in the subgroup selected.
Another technique for selecting between subgroups is to select among different available trunk identification signals (CTCSS and/or DCSS tones). The EEPROM may be used to store the trunk identification signals for each subgroup, as required.
Fig. 5A illustrates the preferred embodiment of an algorithm for disting~ h;ng between subgroups (indicated as groups 1, 2 and 3) by use of the PTT.
There has thus been shown and described a novel mobile radio communication system which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose ~ WO91/12670 PCT/US91/01012 205~4~9 . 29 the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are intended to be covered by the invention which is limited only by the claims which follow.
Claims (36)
1. In a two-way mobile radio communication system comprising a plurality of user-operable stations and a cooperating repeater station all operating on a plurality of radio communication channels of differing frequency bands without a dedicated control channel, each user-operable station comprising, in combination:
(a) a radio transmitter;
(b) a radio receiver;
(c) user-operable switch means, coupled to said transmitter, for selectively enabling said transmitter to transmit a carrier signal;
(d) carrier operable switch means, coupled to said receiver, for indicating the receipt of a carrier signal when in an activation position;
(e) channel selector means, coupled to said transmitter and said receiver, for selecting the radio channel of operation;
(f) means, coupled to said transmitter, for continuously generating a selected one of a plurality of subaudible trunk identification signals associated with each given communication channel for transmission by said transmitter when operating on said given channel; and (g) means, coupled to said receiver, for indicating the presence of said selected one of a plurality of subaudible trunk identification signals when said receiver is operating on said given channel;
the method of automatically operating the user operable stations so as to establish communication between at least two such stations over one of said plurality of channels, said method comprising the steps of:
(1) when said user-operable switch means is open and said user-operable station is in a receive modes (i) incrementing said channel selector means to select a channel;
(ii) determining if said carrier operable switch means is in said activation position, thereby indicating that a carrier signal is present on the selected channel;
(iii) if a carrier signal is not present, returning to step (1) (i);
(iv) if a carrier signal is present, determining if the selected subaudible trunk identification signal is present on said carrier signal;
(v) if the selected subaudible trunk identification signal is not present on said carrier signal, returning to step (1) (i); and (vi) if the selected subaudible trunk identification signal is present on said carrier signal, enabling said transmitter for push-to-talk operation; and (2) when said user-operable switch means is closed and said user-operable station is in a transmit mode:
(i) if said carrier operable switch means is in said activation position, thereby indicating that a carrier signal is present on the selected channel, incrementing said channel selector;
(ii) if a carrier signal is not present on the selected channel, transmitting a carrier signal with the selected subaudible trunk identification signal for a prescribed period of time;
(iii) determining whether a carrier signal with the selected subaudible trunk identification signal is received on the selected channel;
(iv) if a carrier signal with the selected subaudible trunk identification signal is not received, returning to step (2) (i); and (v) if a carrier signal with the selected subaudible trunk identification signal is received, returning to step (1) (vi).
(a) a radio transmitter;
(b) a radio receiver;
(c) user-operable switch means, coupled to said transmitter, for selectively enabling said transmitter to transmit a carrier signal;
(d) carrier operable switch means, coupled to said receiver, for indicating the receipt of a carrier signal when in an activation position;
(e) channel selector means, coupled to said transmitter and said receiver, for selecting the radio channel of operation;
(f) means, coupled to said transmitter, for continuously generating a selected one of a plurality of subaudible trunk identification signals associated with each given communication channel for transmission by said transmitter when operating on said given channel; and (g) means, coupled to said receiver, for indicating the presence of said selected one of a plurality of subaudible trunk identification signals when said receiver is operating on said given channel;
the method of automatically operating the user operable stations so as to establish communication between at least two such stations over one of said plurality of channels, said method comprising the steps of:
(1) when said user-operable switch means is open and said user-operable station is in a receive modes (i) incrementing said channel selector means to select a channel;
(ii) determining if said carrier operable switch means is in said activation position, thereby indicating that a carrier signal is present on the selected channel;
(iii) if a carrier signal is not present, returning to step (1) (i);
(iv) if a carrier signal is present, determining if the selected subaudible trunk identification signal is present on said carrier signal;
(v) if the selected subaudible trunk identification signal is not present on said carrier signal, returning to step (1) (i); and (vi) if the selected subaudible trunk identification signal is present on said carrier signal, enabling said transmitter for push-to-talk operation; and (2) when said user-operable switch means is closed and said user-operable station is in a transmit mode:
(i) if said carrier operable switch means is in said activation position, thereby indicating that a carrier signal is present on the selected channel, incrementing said channel selector;
(ii) if a carrier signal is not present on the selected channel, transmitting a carrier signal with the selected subaudible trunk identification signal for a prescribed period of time;
(iii) determining whether a carrier signal with the selected subaudible trunk identification signal is received on the selected channel;
(iv) if a carrier signal with the selected subaudible trunk identification signal is not received, returning to step (2) (i); and (v) if a carrier signal with the selected subaudible trunk identification signal is received, returning to step (1) (vi).
2. The method defined in claim 1, further comprising the step of producing an audible tone when said push-to-talk user-operable switch means is initially closed.
3. The method defined in claim 1, further comprising the step of producing an audible tone when said user-operable switch means is initially closed and said carrier operable switch is thereafter switched to said activation position.
4. The method defined in claim 1, further comprising the step of producing a first audible tone when said user-operable switch means is initially closed and producing a second audible tone when said carrier operable switch is thereafter activated.
5. The method defined in claim 4, wherein said second tone is different from said first tone.
6. The method defined in claim 1, further comprising the step of selecting said trunk identification signal for transmission on said carrier signal when in a transmit mode, thereby to select the group of users which are capable of receiving the transmission.
7. The method defined in claim 6, wherein said trunk identification signal is selected in response to said user-operable switch means.
8. The method defined in claim 7, wherein said user-operable switch means is a push-to-talk switch and wherein said subaudible trunk identification signal is selected in response to the length of time that said push-to-talk switch is initially closed.
9. The method defined in claim 6, further comprising the step of producing an audible tone indicative of the selected user group.
10. The method defined in claim 1, further comprising the step of incrementing the channel selector a prescribed number of times in step 2(i), thereby to select the group of users which are capable of receiving the transmission.
11. The method defined in claim 10, wherein said subaudible trunk identification signal is selected in response to said user-operable switch means.
12. The method defined in claim 11, wherein said user-operable switch means is a push-to-talk switch and wherein said subaudible trunk identification signal is selected in response to the length of time that said push-to-talk switch is initially closed.
13. The method defined in claim 10, further comprising the step of producing an audible tone indicative of the selected user group.
14. The method defined in claim 1, wherein said channel selector is incremented approximately every 25 milliseconds when in the receive mode when a carrier signal is not present on successive channels.
15. The method defined in claim 1, wherein said channel selector is incremented approximately every 250 milliseconds, when in a receive mode, when a carrier signal is present but the selected trunk identification signal is not present on successive channels.
16. In a two-way mobile radio communication system comprising a plurality of user-operable stations and at least one cooperating repeater station all operating on a plurality of radio communication channels of differing frequency bands without a dedicated control channel, each user-operable station comprising, in combination:
(a) a radio transmitter;
(b) a radio receiver (c) user-operable switch means, coupled to said transmitter, for selectively enabling said transmitter to transmit a carrier signal;
(d) carrier operable switch means, coupled to said receiver, for indicating the receipt of a carrier signal when in an activation position;
(e) channel selector means, coupled to said transmitter and said receiver, for selecting the radio channel of operation;
(f) means, coupled to said transmitter, for continuously generating a selected one of a plurality of subaudible trunk identification signals associated with each given communication channel for transmission by said transmitter when operating on said given channel; and (g) means, coupled to said receiver, for indicating the presence of said selected one of a plurality of subaudible trunk identification signals when said receiver is operating on said given channel;
the method of automatically operating the user-operable stations so as to establish communication between groups of such stations over one of said plurality of channels, said method comprising the steps of:
(1) assigning prescribed ones of said subaudible trunk identification signals to respective groups of stations;
(2) when said user-operable switch means is open and said user-operable station is in a receive mode;
(i) incrementing said channel selector means to select a channel from among said prescribed channels;
(ii) determining if said carrier operable switch means is in said activation position, thereby indicating that a carrier signal is present on the selected channel;
(iii) if a carrier signal is not present, returning to step (2) (i);
(iv) if a carrier signal is present, determining if the selected subaudible trunk identification signal is present on said carrier signal;
(v) if the selected subaudible trunk identification signal is not present on said carrier signal, returning to step (2)(i); and (vi) if the selected subaudible trunk identification signal is present on said carrier signal, enabling said transmitter for push-to-talk operation; and (3) when said user-operable switch means is closed and said user-operable station is in a transmit mode:
(i) if said carrier operable switch means is in said activation position, thereby indicating that a carrier signal is present on the selected channel, incrementing said channel selector to select a channel from among said prescribed channels;
(ii) if a carrier signal is not present on the selected channel, transmitting a carrier signal with the selected subaudible trunk identification signal for a prescribed period of time;
(iii) determining whether a carrier signal with the selected subaudible trunk identification signal is received on the selected channel;
(iv) if a carrier signal with the selected subaudible trunk identification signal is not received, returning to step (3) (i); and (v) if a carrier signal with the selected subaudible trunk identification signal is received, returning to step (2)(vi).
(a) a radio transmitter;
(b) a radio receiver (c) user-operable switch means, coupled to said transmitter, for selectively enabling said transmitter to transmit a carrier signal;
(d) carrier operable switch means, coupled to said receiver, for indicating the receipt of a carrier signal when in an activation position;
(e) channel selector means, coupled to said transmitter and said receiver, for selecting the radio channel of operation;
(f) means, coupled to said transmitter, for continuously generating a selected one of a plurality of subaudible trunk identification signals associated with each given communication channel for transmission by said transmitter when operating on said given channel; and (g) means, coupled to said receiver, for indicating the presence of said selected one of a plurality of subaudible trunk identification signals when said receiver is operating on said given channel;
the method of automatically operating the user-operable stations so as to establish communication between groups of such stations over one of said plurality of channels, said method comprising the steps of:
(1) assigning prescribed ones of said subaudible trunk identification signals to respective groups of stations;
(2) when said user-operable switch means is open and said user-operable station is in a receive mode;
(i) incrementing said channel selector means to select a channel from among said prescribed channels;
(ii) determining if said carrier operable switch means is in said activation position, thereby indicating that a carrier signal is present on the selected channel;
(iii) if a carrier signal is not present, returning to step (2) (i);
(iv) if a carrier signal is present, determining if the selected subaudible trunk identification signal is present on said carrier signal;
(v) if the selected subaudible trunk identification signal is not present on said carrier signal, returning to step (2)(i); and (vi) if the selected subaudible trunk identification signal is present on said carrier signal, enabling said transmitter for push-to-talk operation; and (3) when said user-operable switch means is closed and said user-operable station is in a transmit mode:
(i) if said carrier operable switch means is in said activation position, thereby indicating that a carrier signal is present on the selected channel, incrementing said channel selector to select a channel from among said prescribed channels;
(ii) if a carrier signal is not present on the selected channel, transmitting a carrier signal with the selected subaudible trunk identification signal for a prescribed period of time;
(iii) determining whether a carrier signal with the selected subaudible trunk identification signal is received on the selected channel;
(iv) if a carrier signal with the selected subaudible trunk identification signal is not received, returning to step (3) (i); and (v) if a carrier signal with the selected subaudible trunk identification signal is received, returning to step (2)(vi).
17. The method defined in claim 16, further comprising the steps of assigning a first subset of said prescribed channels to a first subgroup and a second subset of said prescribed channels to a second subgroup within said group, and identifying one of said first and second subsets of channels for selection by a user-operable station, whereby each user-operable station within a group is operable on one of a plurality of subgroups.
18. The method defined in claim 17, wherein said user-operable switch means is a push-to-talk switch and wherein said identifying step comprises the step of determining the length of time said push-to-talk switch is closed when said user-operable station is placed in a transmit mode.
19. The method defined in claim 18, further comprising the step of producing at least one tone, in response to the length of time that said push-to-talk switch is closed, indicative of the selected subgroup.
20. The method defined in claim 19, wherein said tone is a signal beep to indicate selection of said first subgroup, and a double beep to indicate selection of said second subgroup.
21. The method defined in claim 16, wherein said user-operable switch means is a push-to-talk switch.
22. The method defined in claim 16, further comprising the step of producing an audible tone when said user-operable switch means is initially closed.
23. The method defined in claim 16, further comprising the step of producing an audible tone when said user-operable switch means is initially closed and said carrier operable switch is thereafter switched to said activation position.
24. The method defined in claim 16, further comprising the step of producing a first audible tone when said user-operable switch means is initially closed and producing a second audible tone when said carrier operable switch is thereafter activated.
25. The method defined in claim 24, wherein said second tone is different from said first tone.
26. The method defined in claim 16, further comprising the step of selecting said subaudible trunk identification signal for transmission on said carrier signal when in a transmit mode, thereby to select the group of users which are capable of receiving the transmission.
27. The method defined in claim 26, wherein said subaudible trunk identification signal is selected in response to said user-operable switch means.
28. The method defined in claim 27, wherein said user-operable switch means is a push-to-talk switch and wherein said subaudible trunk identification signal is selected in response to the length of time that said push-to-talk switch is initially closed.
29. The method defined in claim 26, further comprising the step of producing an audible tone indicative of the selected user group.
30. The method defined in claim 16, further comprising the step of incrementing the channel selector a prescribed number of times in step 2(i), thereby to select the group of users which are capable of receiving the transmission.
31. The method defined in claim 30, wherein said subaudible trunk identification signal is selected in response to said user-operable switch means.
32. The method defined in claim 31, wherein said user-operable switch means is a push-to-talk switch and wherein said subaudible trunk identification signal is selected in response to the length of time that said push-to-talk switch is initially closed.
33. The method defined in claim 30, further comprising the step of producing an audible tone indicative of the selected user group.
34. The method defined in claim 16, wherein said channel selector is incremented approximately every 25 milliseconds when in the receive mode when a carrier signal is not present on successive channels.
35. The method defined in claim 16, wherein said channel selector is incremented approximately every 250 milliseconds, when in a receive mode, when a carrier signal is present but the selected subaudible trunk identification signal is not present on successive channels.
36. The method defined in claim 1, wherein said user-operable switch means is a push-to-talk switch.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US481,974 | 1990-02-16 | ||
| US07/481,974 US5125101A (en) | 1990-02-16 | 1990-02-16 | Trunking method and apparatus for establishing communication in a two-way mobile radio system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2055459C true CA2055459C (en) | 1996-05-07 |
Family
ID=23914140
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002055459A Expired - Fee Related CA2055459C (en) | 1990-02-16 | 1991-02-14 | Trunking method and apparatus for establishing communication in a two-way mobile radio system |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US5125101A (en) |
| EP (1) | EP0515512A4 (en) |
| AU (1) | AU632444B2 (en) |
| CA (1) | CA2055459C (en) |
| WO (1) | WO1991012670A1 (en) |
Families Citing this family (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5247566A (en) * | 1990-03-15 | 1993-09-21 | Aisin Seiki Kabushiki Kaisha | Apparatus for the transmission and reception of data |
| US5396651A (en) * | 1992-04-01 | 1995-03-07 | The Boeing Company | Radio communication system including indication that communication link is established |
| US5649050A (en) * | 1993-03-15 | 1997-07-15 | Digital Voice Systems, Inc. | Apparatus and method for maintaining data rate integrity of a signal despite mismatch of readiness between sequential transmission line components |
| DE4418234C2 (en) * | 1994-05-25 | 1996-07-18 | Innotech Tech Innovationen Gmb | Codable transmitter / receiver unit for data transmission in the event of a contact initiation and method for operating the transmitter / receiver unit |
| FI97503C (en) * | 1995-01-12 | 1996-12-27 | Nokia Telecommunications Oy | Relay tone in a mobile communication network |
| CN1055366C (en) * | 1995-09-28 | 2000-08-09 | 深圳市华为技术有限公司 | Program-controlled exchange based honeycomb concentration system communication method and system |
| DE69818353D1 (en) | 1997-06-16 | 2003-10-30 | Racal Comm Systems Ltd | Radio communication system |
| FR2802380B1 (en) * | 1999-12-13 | 2002-02-15 | Matra Nortel Communications | METHOD FOR CONTROLLING A COMMUNICATION CHANNEL SHARED BY SEVERAL STATIONS, AND TRANSMITTING / RECEIVING STATION FOR IMPLEMENTING THE METHOD |
| US6801524B2 (en) * | 2000-01-31 | 2004-10-05 | Sonim Technologies, Inc. | System for dispatching information packets and method therefor |
| US6950653B2 (en) * | 2002-01-11 | 2005-09-27 | Hubbell Incorporated | Scanning tone remote adapter for land-mobile radio dispatch for use with dispersed dispatch stations |
| US20050222752A1 (en) * | 2004-04-05 | 2005-10-06 | Sokola Raymond L | Method for enabling communications dependent on user location, user-specified location or orientation |
| US7606291B2 (en) * | 2006-07-14 | 2009-10-20 | Motorola, Inc. | Method and system for transmit frequency hopping |
| US7881737B2 (en) | 2006-08-31 | 2011-02-01 | Motorola, Inc. | Method and apparatus for acquiring and establishing a deployable communication system |
| US7612670B2 (en) * | 2006-08-31 | 2009-11-03 | Motorola, Inc. | Method and apparatus for acquiring and establishing a deployable communication system |
| US20080058027A1 (en) * | 2006-08-31 | 2008-03-06 | Motorola, Inc. | Method and apparatus for acquiring and establishing a deployable communication system |
| US20190306639A1 (en) * | 2018-03-27 | 2019-10-03 | Darren La Groe | Apparatus for Controlling the Transmission of Communications Using a Proximity Sensor |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4013958A (en) * | 1975-10-14 | 1977-03-22 | The Magnavox Company | Sampled communication system |
| US4409687A (en) * | 1978-10-30 | 1983-10-11 | General Electric Company | Arrangement and method for establishing radio communication in a system |
| US4360927A (en) * | 1979-03-12 | 1982-11-23 | General Electric Company | Repeater trunking system |
| US4484355A (en) * | 1983-04-11 | 1984-11-20 | Ritron, Inc. | Handheld transceiver with frequency synthesizer and sub-audible tone squelch system |
| US4658435A (en) * | 1984-09-17 | 1987-04-14 | General Electric Company | Radio trunking system with transceivers and repeaters using special channel acquisition protocol |
| US4905302A (en) * | 1987-06-03 | 1990-02-27 | General Electric Company | Trunked radio repeater system |
| US4939746A (en) * | 1987-06-03 | 1990-07-03 | General Electric Company | Trunked radio repeater system |
-
1990
- 1990-02-16 US US07/481,974 patent/US5125101A/en not_active Expired - Fee Related
-
1991
- 1991-02-14 CA CA002055459A patent/CA2055459C/en not_active Expired - Fee Related
- 1991-02-14 EP EP19910904771 patent/EP0515512A4/en not_active Withdrawn
- 1991-02-14 AU AU73316/91A patent/AU632444B2/en not_active Ceased
- 1991-02-14 WO PCT/US1991/001012 patent/WO1991012670A1/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| WO1991012670A1 (en) | 1991-08-22 |
| US5125101A (en) | 1992-06-23 |
| EP0515512A1 (en) | 1992-12-02 |
| AU632444B2 (en) | 1992-12-24 |
| EP0515512A4 (en) | 1993-09-08 |
| AU7331691A (en) | 1991-09-03 |
| US5125101B1 (en) | 1994-01-18 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed | ||
| MKLA | Lapsed |
Effective date: 19990215 |