Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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- 1 - 45-MR-224-A
REPEA~ER I'RUNKING SYSTEM
BACKGROVND OF THE INVENTION
This application is a division of Canadian Application
Serial No. 372,379 filed March 5, 1981.
This invention relates generally to radio repeater
systems. More specifica]ly this invention pertains to
systems wherein a plurality of mobile or portable stations
communicate with one another over several communications
channels throuyh repeaters operating on each of such
channels. Even more specifically, this invention is
directed to arrangements for establishing communica-tion
between a first radio station and a second radio station
through a repeater and over a radio channel selected
from a plurality of such channels.
In many localities, a plurality of land mobile radio
frequency channels are allocated for communication
among vehicles. Generally, there may be, and usually
are, many more vehicles having mobile radio stations
than there are available radio channels in a given
locality. Each of these radio channels usually includes
at least two separate and distinct frequencies, one for
transmitting and the other for receiving.
Consequently, some arranyement is needed for enabling
a mobile vehicle user to obtain access to a radio
channel that is not in use and to thereafter establish
communication with another mobile vehicle user over that
radio frequency channel.
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45-MR-22~A
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One such system is disclosed by J.C. Berti et al
in Canadian Patent Application Serial No. 342,007 filed
December 14, 1979 and entitled IMPROVED ARRANGE~ENT
AND METHOD FOR ESTABLISHING RADIO COMMUNICATION IN A
SYSTEM. In the Berti system, each mobile or portable radio
station (including a transmi-tter and receiver) can be
placed in an idle or cell originate mode. When a mobile
station is placed in the call orginate mode, its receiver
scans all of the allocated radio frequency channels in
the system until an unused channel is found. When an
unused channel is found, the station's transmitter and
receiver become operable on that channel. The mobile
station's transmitter sends a busy signal to the repeater
operating on the unused channel. The repeater receives
this busy signal and transmits a busy signal identical to
the busy signal received. When the mobile station that
send the busy signal receives it back from the repeater,
it sends out a group signal identifying a particular
subset of mobile or portable radio stations with which
the user desires to communicate. The group signal is
re-transmitted by the repeater and is recognized by each
radio station within that subset and they are activated
on the channel selected by the busy tone exchange.
In the idle mode~ the receiver of each mobile or
portable station in the system scans all of the allocated
radio frequency channels for its predetermined group
signal. When the receiver detects its predetermined
group tone or tones on a channel, it stops scanning, and
enables the transmitter and receiver on that channel for
communication through the repeater wi-th the station
originating the call. There may be a plurality of such
stations associated with a predetermined group tone or tones.
The Berti system works well under mos-t circumstances.
However, under certain circumstances, a mobile radio
station can erroneously lock onto a channel that is non-
vacant. When a mobile station is placed in the call
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45-MR-224A
originate mode, it scans all of the channels for the
presence of a busy signal. If this scanning takes
place during a fade situation or when for any other
reason the busy signal detector of the call origlnating
station has failed to detect the busy tone, the call
originating station may lock onto a channel that is non-
vacant and it will begin to operate on that channel.
SU~5ARY OF THE INVENTION
Therefore the present invention provides an arrange-
ment for more reliably establishing communication among
mobile radio stations through a repeater. Utilizing the
arrangement according to the present invention, a lock
onto a non-vacant channel is much less likely to occur
than when using previous arrangements.
The arrangement according to the present invention
provides for a positive "handshake" between a mobile
station originating a call and the repeater on a vacant
channel.
In the present arrangement, a mobile station placed
ln the call originate mode searches the available
channels sequentially until an idel one is found on
which no busy marking signal or tone is detected. The
mobile station stops scanning on the vacant unmarked
channel and transmits a busy signal which is normally
used to mark a busy channel. The repeater, upon
detecting the busy signal -transmitted by the mobile
station, transmits an acquisition signal having different
characteristics from the busy signal. This acquisition
signal is transmitted only if the channel is, in fact,
vacant. The call originating mobile station only after
detecting acquisition tone from the repeater will complete
the signalling sequence by transmitting a group signal
identifying the particular mobile stations with which the
user would like to communicate, a sub-group signal, if
subgroups are used and a busy signal. Thus, there is
provided a positive indication by the presence of an
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45-MR-224A
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acquisition signal rather than merely by the lack of
a busy signal to define a vacant channel in the call
originate sequence of signalling.
BRIEF DESCRIPTION OF THE DRAWINGS
_
3 Many of the attendant advantages of the present
invention will be readily apparent as the invention
becomes better understood by reference to the following
detailed description with the appended claims, when
considered in conjunction with the accompanying drawings
wherein:
FIGURE l is a pictorial diagram of a tYpical land
mobile communication system for which the arrangement
of the present invention is intended;
FIGURE 2 is a general block diagram of the repeater
trunking system according to the present invention;
FIGURE 3 shows a block diagram of a repeater station;
FIGURE 4 (FIGURES 4A -through 4D) sets forth a schematic
diagram of that portion of the present invention located
at a mobile station;
FIGURE 5 is a graphical representation of the various
operating modes of the repeater -trunking system according
to the present invention;
FIGURE 6 is a flow chart showing the operation
of the repeater trunking system in the "idle" mode;
FIGURE 7 is a flow chart showing the operation of
the repeater trunking system in the "wait" mode;
FIGURE 8 is a flow chart diagram showing the
operation of the repeater trunking system in the
"ready" mode; and
FIGURE 9 is a diagram illustrating the acquisi-tion
signalling sequence between a mobile station originat-
ing a call and a repeater station.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the figures wherein like reference
numerals designate like or corresponding parts through-
out, and specifically referring to FIGURE 1, there is
shown a pictorial diagram of a typical mobile communica-
tion system for which the present invention is intended.
It is assumed -that a particular georgraphic locality
has been allocated five radio repeater communication
channels (for example in bands around 850 Megahertz),
each such channel having a different -transmitting and
receiving frequencies. For five channels, five repeaters
Rl through R5 are provided and located at an available
site that provides optimum coverage. Each of repeaters
Rl through R5 includes a transmitter, a receiver, a
transmitting antenna, and a receiving antenna.
For simplex operation, in the firs-t repeater, Rl,
the receiver and receiving antenna function on a fre-
quency Fl-R, and the transmitter and transmitting antenna
function on a frequency Fl-T which is removed from fre-
quency Fl-R by a sufficien-t amount to provide good
frequency separation for the transmitter and receiver.
Other frequencies F2-R and F2-T through F5-R and F5-T are
provided for repeaters R2 through R5 respec-tively.
In the same locality, different groups of users
may utilize the repea-ters with -the radio transmitters
and receivers in their mobile vehicles Vl through V5,
for example, Typically, each group has a common basis,
such as -the vehicles in a given business, for example
taxi cabs or 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 repater channels available. For example, five
repeaters (each including a -transmitter and receiver)
operating on a channel different from the o-ther re-
peaters can serve as many as two thousand vehicles.
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However, the number of vehicles which can be efficiently
served may change depending upon the demand for the
channels.
If there are a number of repeater channels available
in a given locality, it is desirable that a group of
vehicles be able to quickly ascertain which channel or
frequencies are available, so as to establish communication
with the other vehicles in that same group. The present
invention provides an arrangemen-t and method for provid-
ing and establishing this communication in a relativelysimple but highly reliable fashion.
FIGURE 2 is a general block diagram of the repeater
trunking system according to the present invention for
use in a mobile station, such as in a vehicle. It is
assumed tha-t the vehicle is one of a group of vehicles
VI through V5, shown in FIGURE 1. The mobile radio
station in the vehicle includes a radio transmitter 11
capable of operating on any of the frequencies Fl-R through
F5-R, and a radio receiver 12 capable of operating on
2a any of the frequencies Fl-T through ~'5-T. Two frequencies
are needed for each channel in order that the mobile
station and the repeater can function in a simplex or
push-to-talk arrangement. Thus, the mobile station
would transmit on a repeater receive frequency (for
example Fl-R~. The signal on frequency Fl-R would be
received by ~he repeater and transmitted to the other
vehicles on fre~uency Fl-T. The other vehicles in the
group would receive the signal on repeater freqeuncy Fl-T.
When transmitting, the other vehicles would transmit on
frequency Fl-R. In such an arrangement, a single
antenna 10 is switched by a relay 19 between the vehicular
or mobile transmitter 11 and receiver 12, depending upon
whether the mobile station is transmitting or receiving.
Full duplex operation could be provided by using
these same two frequencies, but with separate receive and
transmit injection, a duplexer, and separate antennas.
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45-MR-334A
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Or, full duplex operation could be provided by specifiying
four separate and distinct frequencies within each channel
and for the repeater associated with that channel. It
is assumed in this presently preferred, non-limitative,
exemplary embodiment that transmitter 11 and receiver 12
are frequency modulation devices, although they may be
amplitude modulation devices.
Transmitter 11 includes an oscillator circuit
(not shown) which operates at one of five transmit
frequencies depending upon the signal applied to it by
a search generator 13. Receiver 12 is preferàbly of
the superheterodyne type and includes a local oscillator
which also operates at a frequency coresponding to one
of five frequencies depending upon the signal supplied
by the search generator 13. Clock signals are provided
by a clock generator 16. Search generator 13 is supplied
with clock signals which cause it to sequentially produce
frequency scanning signals at each of five outputs 20.
These scanning signals are applied to the transmitter and
receiver oscillators to cause transmitter 11 to be
subsequentially operable on radio frequencies Fl-
~through F5-R, and receiver 12 to be sequentially operable
on the radio frequencies Fl-T through F5-T. Tone encoders,
decoders, and gates 18 are provided for decoding or
filtering tones received by receiver 12 and for encoding
or producing tones to be gated and transmitted by
transmitter 11.
The mobile station includes operator controls and
indicators 14 to enable the user to operate his station
and to have indications of the status of his station.
The user controls permit the operator to place his station
in the call originate mode to establish communication
with another vehicle in the same group, or to place
his station in the idle or scanning mode so that he will
receive communications from other mobile stations in the
same group.
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45-MR-224
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A control circuit 15 supplies clock signals from
clock generator 16 to a sequence generator 17 when the
operator controls place the station in the call originate
mode or to search generator 13 when the operator controls
place the station in the idle mode.
In the call originate mode, control circuit 15 supplies
clock pulses to the sequence generator 17 to cause the
sequence generator to produce signals which provide the
following sequence of functions: first, locating an idle
channel; second, transmitting a busy signal, suitably
an audio tone of a predetermined frequency to the re-
peater -to acquire and enable or activate the repeater
transmitter and receiver on the idle channel; third,
stopping transmission and causing the receiver to listen
for an acquisition signal from the repeater; fourth,
transmitting a group signal, suitably an audio -tone of a
predetermined frequency different from the frequency of
the busy signal to identify other mobile stations wlthin
a predetermined group; fifth, transmitting a subgroup
2Q signal, suitably an audio tone having a frequency
different from both the busy signal and group signal, if
the stations in a given group are further subdivided into
subgroups; sixth, stopping transmitting and causing the
mobile station's receiver to listen and ascertain
whether the repeater is sending out a transmission with
a busy signal on the selected channel; and seventh
repeating the sequence on all available channels if the
repeater transmitter was not enabled or activated in the
second function or if an acquisition signal was not
received. If the repeater transmitter was activated, then
indications are provided to the operator that he has
acquired and activated a repeater, and that his station
and the repea-ter are in a ready mode for operation.
In the idle mode, control circuit 15 supplies
clock pulses to search generator 13 to cause the search
generator to produce signals for changing the frequency
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45-MR-22~A
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of the transmitter and receiver oscillators. This causes
the receiver 12 to sequentially tune to each of the
five frequencies on which repeaters can transmit and,
at the same time, causes transmitter 11 to sequentially
tune to each of the five companion or associated frequencies
on which the repeaters can receive. If the group signal
for that particular mobile station is not detected on a
channel, search generator 13 causes the receiver and
transmitter of that mobile station to tune to the next
channel frequency. This sequence of events continues as
long as receiver 12 is operable, and stops only when it
receivers a busy signal, its predetermined group signal,
and its subgroup signal if utilized. If the group signal
and subgroup signal (if used) are received, control
circuit 15 provides an indication to the user that he is
being called. The user can then pick up his handset or
microphone and communicate with the calling station.
FIGURE 3 is a block diagram of one of the repeaters
shown in FIGURE 1 for use with the trunking system
according to the present invention. In this repeater, an
antenna 30 is connected to a repeater receiver 31 for
receiving a particular frequency, for example F1-R. The
output of repeater receiver 31 is coupled to a busy signa~
notch filter 32 which filters out or rejects the busy
signal, but applies the received audio signals, group
signal, and subgroup signal to a repeater transmitter
33. Repeater transmitter 33 is coupled to an antenna 37
for transmitting on a companion channel frequency Fl-T.
The companion channel frequencies Fl-R, Fl-T are separated
sufficient for proper circuit operation. It is possible
to operate repeater receiver 31 and repeater transmitter
33 on the same antenna, or to operate all of the re-
peaters on the same antenna if proper coupling and
matching networks are used.
The output of repeater receiver 31 is also applied
to a busy signal bandpass filter and detector 34 which
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45 MR-224A
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detects only the busy signal frequency and applies the busy
signal detection signal to a timer 35. Timer 35 produces
an enabling or keying signal at the beginning of and as
lony as a busy signal is detected, and for a selected
period (for example lO seconds) after termination of the
busy signal. This enabling or keying signal turns on or
enables repeater transmitter 33. When the enabling signal
ends, repeater transmitter 33 is turned off automatically
without the need for an idle signal. This feature prevents
repeater transmitter 33 from being erroneously keyed or
enabled in the absence of a busy signal. Timer 35 also
permits a repeater to become available to another sub~
sequent group if transmissions by the acquiring group
do not occur within a predetermined span of time, for
example, every lO seconds. Timer 35 generates a window
for the transmission of an acquisition signal to the call
originating mobile station.
The repeater also includes a busy signal generator
36 and an acquisition signal generator 38, the outputs
f which are coupled to the input of repeater transmitter
33 along with the audio and subgroup signal.
I-t is preferred that the busy signal be regenerated
at the repeater so as to insure that the mobile stations
are kept in operative condition even though there is
momentary absence (for example a few seconds less than
10) of any mobile station transmission. However, the
group and subgroup signals are re-transmitted by repeater
transmitter 33 as detected by repeater receiver 31 from
the mobile transmitter. Each of the individual blocks
Of FIGURE 3 are known in the art, so that a more
detailed description of them is not believed to be
necessary. Each of the repeaters shown in FIGURE 1
is similar to the exemplary repeater shown in FIGURE 3,
but operates at different frequencies.
FIGURES 4~ through 4~ show a detailed circuit
diagram of our mobile station communication es-tablishing
45-MR-224A
arrangement of FIGURE 2. FIGURES 4A through 4D form a
single schematic diagram as shown in FIGURE 5 which is a
composite of FIGURES 4A-4D. For clarity, transmitter 11,
receiver 12, and antenna 10 shown in FIGU~E 2 have been
omitted from FIGURES 4 and 5. In FIGURE 4, search
generator 13; clock generator 16; tone encoders, decoders,
and gates 18; operator controls and indicators 14; and
sequence generator 17 are shown enclosed in respective
dashed line rectangles. The remainder of the circuit
outside these rectangles comprises the control circuit 15.
The circuit shown in FIGURE 4 includes four types of
logic gates, namely an OR gate such as Gl, a NOR gate such
as G2, and AND gate such as G3, and an inverter such as
11. As known in the art, an OR gate produces a logic 1
at its output in response to any of its inputs being at
a logic 1, and produces a logie 0 at its output in re-
sponse to all of its inputs being a logic 0. A NOR gate
produces a logic 0 in response to any of its inputs
being at a logie 1, and produces a logic 1 in response to
all of its inputs being at a logic 0. An AND gate produces
a logic 0 in response to any of its inputs being a-t a
logic 0, and produces a logic 1 in response to all of its
inputs being at a logic 1. An inverter simply produces
the logie inversion of the signal applied to its input.
In this circuit, it is assumed that a logic 1 is a positive
voltage ~V, and that a logic 0 is zero volts or ground.
However, other voltages may be utilized for the logic 1
and logic 0 levels.
The circuit shown in FIGURFS 4 and 5 utilizes a
number of bistable flip-flops, such as the flip-flop
FFl. Flip-flop FFl produces a logic 1 at its Q output
and a logic 0 at its Q output in response to a logic 1
being momentarily applied to its set input S; and
produces a logic 0 at its Q input and a logic 1 at its
Q input in response to a logie 1 being momentarily
applied to its reset input R. The circuit utilizes a
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45-MR-224 A
- 12 -
timer Tl which is normally reset to produce a logic 0 at
is Q output. When timer Tl is set in response to a logic
1 being applied to its set input S, it produces a logic
1 at its Q output for a predetermined time (approximately
.5 seconds in a preferred embodiment). After the predet-
ermined time expiers, the timer Tl resets so -that its
Q output produces a logic O.
Clock generator 16 includes a pulse oscillator that
produces logic 1 pulses of approximately 10 milliseconds
duration approximately every 90 milliseconds.
Sequence generator 17 includes a seven stage shift
register SRl having a clock input C and a reset input R.
When shift register SRl is in an initial or reset
condition, a logic 1 is present in stage 1, and all other
stages are at a logic Q. This logic 1 is sequentially
coupled through the subsequent stages 2 through 7 in
response to clock signals. The stages may include a
number of substages, depending upon the timing function
required for a given stage.
In the preferred embodiment for a five channel
system stage 1 has one substage; stage 2 has one sub-
stage, stage 3 has one substage, stage 4 has six sub-
stages; stage 5 has five substages; stage 6 has two
substages and stage 7 has one substage. This is a
total of 17 substages which, for a clock pulse rate of
90 milliseconds, requires about 1.53 seconds for one
sequence through the shift register SRl. Stage 4 pre-
ferably has a period sufficiently long so that each
receiver in a group has sufficient time to scan all
3n channels for a group signal if it is present. Stage 6
preferably has a time period sufficiently long so that
activation oE the repeater can be determined. These
times will be discussed in more detail subsequently.
When the logic 1 reaches stage 7, it is fed back to the
input for subsequent passage through the stages. In
search generator 13, a five state counter is provided
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45-MR-224A
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for the five to twen-ty channel frequencies. The counter
produces a 5 bi-t BCD code which is decoded -to produce the
required channel frequency.
In tone encoders, decoders, and gates 1~, there is
provided four tone encoder-decoder circuits TC-l...TC-4,
and one decode only TC-5. Each of these circuits includes
a decoder portion having a tone input I coupled to the
audio output of receiver 12. The decoder portion includes
a filter and produces a logic 1 at its Q output in response
to a signal of predetermined frequency. While we have
shown the circuits TC-3, TC-4 with their Q outputs applied
to an OR gate Gll, ~he O outputs could also be switched
for individual selection by another section of a switch
46. Each of the circuits TC-l...TC-4 also includes an
encoder portion which produces a particular signal
frequency depending upon the intended function of the
signal. For the busy signal, a relatively high audio
frequency of 3000 Hertz is preferred, since the higher
frequency passes through filters and operates more quickly.
The group and subgroup signals may be any suitable
frequency, but are preferably in the voice range of audio
frequencies transmitted, namely between about 400 and
30QQ Hertz. Each of the circuits TC-l...TC- 4 ac-ts as an
encoder in response to a logic l applied to a control
input C~ and acts as a decoder in response to a logic
Q applied to its control input.
The outputs o:E the encoder portions of the circuits
TC-l.,.TC-4 are selectively applied through switches S4
through S7 to an amplifier 51. The output of this
amplifier 51 is coupled to transmitter 11 for modula-ting
the transmitted signals in accordance with its output
signal. In tone encoders, decoders, and gates 18, are
provided a tone burst generators 50 which, along with a
ready lamp 41, provide a short audible indication to the
user that he has received a call, or that he has
enabled the repeater to transmit.
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45-MR-224A
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In the circuit, there is utilized a plurality of
switches Sl through S7 indicated by a switch arm
contained in a rectangle. Because the circuit operates
with logic level signals, switches Sl through S7 must be
fast operating, so that we prefer to use a switching
device such as an FET transistor. Each of switches Sl
through S7 responds to a logic signal applied -to a lead
indicated as a dashed line in contact with -the switch
arm. Each switch opens its switch path in response to a
logic 0, and provides a closed path in response to a logic
1.
In the operator controls and indicator 14, we
provide a wait lamp 40 to indicate to a user that his
mobile station is scanning for a vacant channel in call
originate mode; a ready lamp 41 to indicate to an operator
that his control arrangement has enabled the tramsmitter
and receiver for operation; a microphone 42 :Eor trans-
mitting voice signals; a microphone push-to talk button 43
to key or energize the transmitter for transmission; a
loudspeaker 44 fox hearing received audible signals; a
microphone hook switch 45 having an on hook position when
the microphone 42 is placed on the switch 45, and an off
hook position when it is removed from the switch 45;
and finally a subgroup selector switch 46 if subgroup
signals are utilized. We also provide a notch filter Fl
coupled between the receiver audio output and the loud-
speaker switch S2 to remove the busy signal (preferably
3000 Hertz) which would otherwise be heard by a mobile
station user. If desired, microphone 42 and loudspeaker
44 may be replaced by other devices, such as a telephone
handset which can be placed on the hook switch 45.
When a user is in his mobile unit and is expecting
to be called at any time, he places his s-tation in the
idle mode by turning his mobile station on. This provides
power to our arrangement, and the voltage ~V is applied
as a logic 1 through the on hook contact of the switch 45,
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45-MR~224A
- 15 -
capacitor C5 and gate Gl to reset flip-flops FFl, FF3 if
they are not already reset, and through capacitor Cl and
OR gate G16 to reset flip-flop FF2 if it is not already
reset. However, the transmitter is not keyed or radiating,
and the mobile antenna is connected -to the receiver. If
conditions require distinction among mobile stations within
the same group, subgroup signals (one for each desired
subgroup) can be provided. IN FIGURE 4, it is assumed
that there are two subgroups available, and that the
station shown is in subgroup 1. Hence, the switch arm of
subgroup selector switch 46 is shown connected to sub-
group contact 1. This connects tone circuit TC-3 for
subgroup 1 into the circuit, and disconnects tone circuit
TC-4 for subgroup 2 from the circuit. In the idle mode,
the reset flip-flop FFl Q output is at a logic 1 and its
Q output is at a logic 0. Flip-flop FF3 is also reset so
that its Q output is a logic 0. this causes an AND gate
G18 to produce a logic 0 and prevents clock pulses from
being applied to shift register SRl within sequence generator
17.
If no signal is present, a sensor, such as busy tone
decoder TC-l, coupled to gate Gl9 is at a logic 0. This
sensor ma~ detect a carrier signal, or busy signal, or
group signal as desired. We prefer that the sensor
detect the busy frequency. The logic 0 produced by SRl
causes tone circuits TC-2, TC-3, TC-4 to decode. The
output of the OR gate G22 is a logic 0 which causes tone
circuit TC-l to also decode. But if no tones have been
received at this time, the Q outputs of the decoders TC-l,
TC-2, TC-3, TC-4 are at a logic 0. ~lence, the flip-flop
FF4 produces a logic 0. Flip-flop FF2 is also reset so
that its Q output is at a logic 0 and its Q output is
at a logic 1. Under this condition, all inputs to the
NOR gate G2 are at a logic 0 so that gate G2 produces a
logic 1. This logic 1 permits the AND gate G6 to pass
the logic 1 clock pulses as they are produced by generator
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45 MR 224 A
- 16 -
16. These clock pulses are passed by the AND gate G6 to the
clock input C of search generator 13. This causes a sCD
code to be generated at the five outputs of search generator
13. This BCD code, when decoded, contro]s the oscillator
frequency in both the transmit-ter and receiver of the mobile
station so that the transmitter and receiver are tuned to
the frequencies FlR and FlT, F2R and F2T, F3R and F3T,
F4R and F4T and F5R and F5T in sequence.
If a busy signal is present, the busy signal decoder
TC-l produces a logic 1 at its Q output. If a proper group
tone is also detected, the group tone decoder TC-2 produces
a logic 1 at its Q output. This logic 1 is held sufficiently
long by FF4 (time by timer Tl) for detection of the subgroup
1 signal. With receipt o-f the busy signal and group signal,
tone decoder TC-2 produces a logic 1 at its Q output,
causing NOR gate G2 to produce a logic 0. This logic 0 at
gate G2 prevents clock pulses from passing through the AND
gate G6 so that search generator 13 is held in its present
state which activates the receiver oscillator (and also the
transmitter oscillator) associated with the channel frequency
on which the busy and group signals were detected. If the
proper subgroup 1 signal is detected, then the tone decoder
TC~3 produces a logic 1 at its Q ou-tput. This logic 1 is
passed by OR gate Gll. When the decoders TC-l, TC-2, Tc-3
simultaneously produce a logic 1, an AND gate G12 produces
a logic 1 which is passed by an OR gate G13 to set flip-flop
FF2. When flip-flop FF2 becomes set, its Q output supplies
a logic 1 which causes NOR gate G2 to continue producing a
logic 0 that blocks the clock pulses in AND ga-te G6. This
logic 1 from the Q output of the flip-flop FF2 closes
switches S1, S2, and S3. Closed switch Sl connects microphone
42 to the transmitter; closed switch S2 connects -the
loudspeaker 44 through the filter Fl to the receiver
audio output; and closed switch S3 connects the push-to-talk
button 43 to an OR gate G14 for keying the transmitter.
The logic 1 from the Q output of the flip-flop FF2 also turns
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45 MR 224 A
- 17 -
on the ready lamp 41 and energized a tone burst ~enerator 50
(connected to the loudspeaker 44) to indicate to the operator
that he is receiving a call and switches a busy tone
attenuator 101 into the busy tone encode (the busy tone
deviation is reduced in ready mode since voice must be
transmltted with busy -tone) line. The transmitter and
receiver of the mobile unit are tuned to the proper transmit
and receive frequencies for communicating with the repeater
to other mobile units in the group.
The user responds by removing his microphone 42 from the
hook swi-tch 45, or if his microphone 42 is already removed,
the switch 45 supplies a plus voltage or logic l to the off
hook contact. A bush signal from a repeater, as detected by
busy tone decoder TC-l or by the encode control line to busy
tone decoder TC-l keeps a busy tone counter 103 to reset via
a gate G-40 thereby causing a logic "0" at its Q output.
Hence, flip-flop FF2 remains in the set condition. When the
operator wishes to talk, he depresses his microphone push-to-
talk button 43 which provides a logic l through closed
switch S3 to OR gate G14 to key the transmitter and cause it
to radiate and to cause antenna relay 19 (see FIGURE 2) to
switch to the transmitter position. Each time push-to-talk
button 43 is depressed, a logic 1 is applied to OR gate Gl4
to cause a busy signal to be transmitted so as to keep the
repeater timer 35 (see FIG. 3) producing an enabling signal.
Upon release of the push-to-talk button 43, the transmitter
is unkeyed and antenna relay l9 switches to the receive
position so that the operator can hear signals from his
loudspeaker 44.
The user remains on the channel as long as there is
activity. When transmissions cease, the Q output of the
busy tone decoder TC-l becomes a logic 0. This permits
busy tone counter 103 to count a logic l that is passed
by the OR gate Gl6 to reset the flip-flop FF2. This causes
the NOR gate G2 to produce a logic l that permits the gate
G6 to pass clock pulses to the search generator 13. ~lence
45 MR 224 A
- 18 -
that user's receiver returns to the idle mode and scans.
Or when the user is finished communicating, he
places his microphone 42 back on hook switch 45. This
causes a plus voltage or logic 1 to be applied -to -the
on hook contact. This logic 1 is momentarily passed by a
capacitor Cl through OR gate G16 to reset flip-flop FF2.
When flip-flop FF2 is reset, its Q output returns to a
logic 0. The logic 1 from the on hook contact is also
mementarily passed by the capacitor C5 and the OR gate
G3 to reset the flip-flops FFl, FF3 if they are not
already reset. Removal of the busy signal causes flip-flop
FE'2 to produce a logic 0. Hence, NOR gate G2 produces
a logic 1 that permits clock pulses to pass through gate
G6 and cause the search generator 13 to begin searching
once again.
In brief summary, when a mobile station is in the
idle mode/ search generator 13 scans until a signal is
detected. If a busy signal and the proper group and
subgroup signal are received, scanning stops, and an
indication is provided to aler-t the user of a call.
The following description relates -to -the call
originate mode. Once again, it is assumed that the mobile
station is using a group signal and is in subgroup 1,
and that the subgroup 1 signal has been selected by the
subgroup selector switch 46 engaging contact 1 for
connecting the tone circuit TC-3 into the circuit.
Search generator 13 is scanning the channels. The user
may initiate the call originate mode by either momentarily
depressing his push-to-talk button 43 or by removing
his mi,crophone 42 Erom the microphone hook switch 45.
Either action causes a call-originating command signal such
as a positive vol-tage or logic 1 to be momentarily applied
~.~l&~
45-MR-224 A
by capacitors C2 or C3 to an OR gate G17. This logic 1
is applled to the AND gate G3 along with the logic 1 from
the Q output of the reset flip-flop FF2. AND gate G3
produces a logic 1 that sets the flip-flop FFl and places
it in the call originate mode. The ~ output of the flip-
flop FFl switches to a logic 1 which turns on the wait
lamp 40 to indicate to the operator that he must wait
until a channel is established. A Q output of flip-flop
FFl at logic "O" is applied to the reset input R of a
programmable counter 60. Programmable counter 60 allows
sequence generator 17 to run through its entire sequence
for each channel. If proper communication is not establis-
hed after one ~sequence per channel, programmable counter
60 causes its Q output to produce a logic 1 that resets
the flip-flop FFl to the idle mode. The logic 1 from
the Q output of the set flip-flop FFl is also applied
to an A~D gate G4 along with whatever logic is being
produced by the inverter 11. If, at the time the user
switched to the call originate mode, his search generator
13 was on a busy channel, the receiver signal sensor
produced a logic 1 which was inverted to a logic 0 so
that gate G4 produces a logic 0. This permits the search
generator to continue until at idle channel is found
(indicated by lack of a carrier or by the lack of a busy
signal), and the receiver signal sensor produces a logic
0. This logic 0 is inverted to a logic 1 by an inverter
11 so that gate G4 produces a logic 1. This logic 1 sets
flip-flop FF3 and its Q output produces a logic 1 for the
remainder of the call originate sequence. This logic 1
from flip-flop FF3 causes NOR gate G2 to produce a logic
0 so that gate G6 prevents the clock pulses from reaching
search generator 13 for the remainder of the call originate
sequence. The logic 1 from the flip-flop ~F3 is applied
to AND gate G18 to permit the clock pulses from clock
generator 16 to be applied to the clock input of shift
register SRl. Shift register SRl was previously reset so
.
5 ~
45-MR~224-A
- 20 -
that the circulating logic 1 was in stage 1. Logic 1
signals produced by the SR1 stages 2,4 and 5 places tone
circuits TCl, TC2, TC3, or TC4 in the encoding mode.
In the call originate sequence, clock pulses are
passed by the gate G18 to cause the logic 1 to shift from
stage 1 to stage 2 of shift register SRl. This logic 1
is applied by an OR gate G22 to the control input of
switch S4 and also to tone circuit TC-l to switch it to
the encoding mode. Tone circuit TC-l produces a busy
tone of 3Q00 Hertz which is passed by switch S4, amplified
by tone amplifier 51, and applled to the mobile trans-
mitter 11. This logic 1 in stage 2 is also passed by OR
gate G14 to key the mobile transmitter 11 so that the
busy signal is transmitted to the repeater. As mentioned
before, the repeater transmitter 33 of FIGURE 3 is enabled
by receipt of this busy signal, and transmits a new busy
signal on the selected channel to mobile stations. After
the appropriate number of clock pulses, the logic 1 in
stage 2 is then transferred to stage 3 of shift register
SRl. This transfer opens the switch S4 and removes the
busy signal. This activates an acquisition tone decoder
TC-5. If an acquisition tone is not detected, then its
Q output is logic "1". This "1" at G44 resets SRl to
State 1 thru G20 and flip-flop FF-3 through gate G42.
The search generator advances to the next idle channel
and SRl starts over. This continues until an acquisition
signal is found or un-til counter 60 causes the station to
go into idle mode. If an acquisition tone is located,
then shift register SR-l shif-ts to its fourth step. The
transferred logic 1 in stage 4 again passes through the
gate G14 to key mobile transmitter 11. The logic 1 is also
applied to the switch S5 associated with the tone circuit
TC-2. Tone circuit TC-2 is in -the encoding mode. When
the switch S5 is closed, the group signal (for example a
tone of 105Q Hertzl produced by the encoding tone circuit
TC-2 is applied to the tone amplifier 51 and keyed
5~
45-~R-224A
- 21 -
transmitter 11 which transmits this group signal to -the
repeater which retransmits it to the mobile stations.
The logic 1 is held in stage 4 for a sufficient length
of time to permit all of the search generators in the other
mobile stations to pass through all five channels of
their search generator since it is possible -that a search
generator could have just left the acquired channel at
the time communication was being established. Those
stations in the designated group being to respond~
After a suitable number of clock pulses, the logic
1 in the shift register SRl is shifted from state 4 to
stage S. This transfer termina-tes the group signal
provided by the encoder in tone circuit TC-2. The logic
1 in s-tage 5 is passed by gate G14 to key the mobile
-transmitter 11. This logic 1 is also coupled through
subgroup selector switch 46 and its contact to close the
switch S6. (If selector switch 46 had been in position 2
the logic 1 from stage 4 would have been applied to the
switch S7.~ The tone from the subgroup signal circuit
TC-3 (for example a 400 Hertz tone) is passed by the
switch S6 to tone amplifier 51 and applied to transmi-tter
11 which is keyed and transmits the tone to the repeater
which re-transmits it to the other mobile stations.
After a suitable number of clock pulses, the logic
1 is shifted from stage 5 to stage 6 of shift register
SRl. This transfer terminates the subgroup signal provided
by the encoder of tone circuit TC-3. Under this condition,
no logic 1 is applied to the gate G14, so tha-t the mobile
transmitter 11 becomes unkeyed. At this time, both inputs
to the OR gate G22 are at a logic 0, and this logic 0
causes the busy -tone circuit TC-l to switch to -the decode
mode. Since the transmitter is unkeyed, the receiver is
enabled, and is listening on the selected channel. The
repeater should have been enabled and keyed by -this time,
and busy signal should be present on the channel. If
busy tone is present, and received by the call originating
t~43~
45-MR-224A
- 22 -
mobile, the tone causes the decoder of tone circuit TC~l
to produce a logic 1 at its Q output. This logic 1,
along with the logic 1 from s-tage 6 of shift register
SRl, is applied to an AND gate G23 to cause gate G23 to
produce a logic 1. This logic 1 is applied through OR
gate Gl to the reset input R of the flip-flop FFl to reset
that flip-flop, and stop the calling sequence. Resetting
of the flip-flop FFl extinguishes wait lamp 40. This 1ogic
1 from the gate Gl also resets the flip-flop FF3, and its
Q output switches to a logic 0 to prevent any further clock
pulses from passing through AND gate G18. This logic 1
from the gate Gl passes through an OR gate G20 to reset
the shift register SRl. The logic 1 from the gate G23
is also applied through the OR gate G13 to set flip-flop
FF2. When flip-flop FF2 becomes set, its Q output switches
to a logic 1 which turns on the ready lamp 41, closes
switches Sl, S2, S3, and energizes tone burst generator
50 so that the user is alerted that he has obtained a
channel. The closed switches Sl, S2, S3 connect the
speaker 44 to the receiver 12, and connect microphone 42,
and push-to-talk button 43 through the gate G14 to the
transmitter 11. With flip-flop ~F2 held in the set
condition, its Q output of a logic 1 insures that the
gate G2 produces a logic 0 so that clock pulses cannot
be applied to search generator 13, and cause the
established channel to be switched. Each time the operator
depresses his push-to-talk button 43, the logic 1 produced
passes through the OR gate G22 to cause the tone circuit
TC-l to supply busy signal to the mobile transmitter 11.
The attenuator 101 in the busy tone output reduces the busy
tone deviation to allow voice to also modulate the
transmitter.
In the sequence above where a logic 1 was in stage
& of the shift register SRl, if no busy signal had been
detected by the decoder in the tone circuit TC-l, the
flip-flop FFl would have remained set, flip-flop FF2 would
3;~
45-MR-224A
- 23 -
have remained reset, and the flip-flop FF3 would have
remained set. This would permit gate G18 to pass another
clock pulse and cause the logic 1 to be shifted from
stage 6 to stage 7 which rese-ts SRl to state 1.
If a channel is successfully acquired, the opera-tor
can communicate. As mentioned earlier, because of -the
timer 35 provided at the repeater, it is necessary for
a busy tone to be received by the repeater during the
timing interval in order to retain acquisition of the
channel. After the communication between two mobile
stations through a repeater is ended, the control is
restored to the idle by replacing the microphone on the
hook switch 45. This causes a positive voltage or a
logic 1 to be passed by capacitor C5 through the OR gate
Gl to reset flip-flops FFl, FF3 (already reset) and passed
by capacitor Cl through OR gate G16 to reset flip-flop
FF2. Their Q outputs return to a logic 0. The group tone
decoder in circuit TC-2 is producing a logic 0. Hence,
all inputs to the gate G2 are at a logic 0 so that gate
G2 produces a logic 1 to permit clock pulses from the
generator 16 -to be passed by the gate G6 to the search
generator 13. In the event the mobile operator neglects
to hang up the microphone 42 after a communication has
ended and return his radio to the idle mode, a logic "1"
from busy tone circuit TC-l keeps busy tone counter 103
reset~ Once the repeater has timed out, the busy signal
drops off the the channel and a logic "O" appears at the
Q output of TC-l. Busy tone counter 103 counts for
approxiloately one second and provides a logic "1" at its
Q output to reset flip-flop F~'2, returning -the station to
the idle mode.
A logic "1" is fed back from stage 7 of shift
register SRl to gate G20 and to a gate G42 to reset
shift register SRl and flip-flop FF-3. The channel
selection advances for each clock pulse coupled to search
generator 13. Upon receipt of further clock pulses, the
45-MR-224A
- 24 -
sequence described above and staxting at stage 1 ls
repeated. The sequence will continue until the channel
counter reaches 5 (this case~ or if, when the logic 1
reaches stage 6, a busy tone is heard from the repeater,
then flip-flop FF2 becomes set and flip-flop FFl becomes
reset to provide the user an indication that he has
acquired a channel. He should take his microphone 42
off hook before the timer in the repeater times out
(approximately 10 seconds) and rese-ts.
The operation of the repeater trunking system will
be further explained in terms of its various operating
modes.
Referring now to FIGURE 5, there is shown a
pictorial diagram indicating the various modes of
operation of the repeater trunking system according to
the present invention. The "call originate" and "idle"
modes are further broken down into the functional modes
"idle", "wait" and "ready". When power is initially
applied, a mobile station is placed in the idle mode.
In the idle mode, a mobile station scans all channels
for a call identifying a particular group with which it
is associated. All audio circuits are inhibited in this
mode so that the user is undisturbed. If a call is
decoded indicating that a particular mobile station is
within a group being called, that mobile station is placed
in the ready mode.
In the ready mode, the mobile station is locked onto
a channel and ready to communicate. The audio circui-ts are
enabled and the ready lamp 41 is on. Alert beeps (four)
are sounded via speaker 44. If the repeater goes off -the
air or communication is otherwise interrup-ted, the
mobile station will return to the idle mode from the
ready mode (hook switch 45 hung-up at other mobile station).
From the idle mode, if push~to-talk button 43 is
depressed, the mobile station will operate in the wait
mode. Similarly, taking the microphone off of hook switch
45-MR-224A
- 25 -
45 will cause the station to enter the wait mode. In the
wait mode, the station stops on the first idle channel and
attemp-ts to acquire the repeater. The station sends a
busy signal to the repeater and waits to hear an acquisition
signal. During this procedure, wait lamp 40 is on and the
audio circuits are disabled. After all channels have been
tried without acquiring a repeater, a single alert beep
is heard via speaker 44.
If all channels are busy or if the mobile station
has failed to established communication with a repeater,
the station returns to the idle mode. However, if a re-
peater is acquired, as indicated by -the confirming hand
shake of the acquisition signal transmitted by the
repeater and received by the mobile station, the station
proceeds to transmit the desired group signal. Flow
charts indicating the function of the trunking system
according to the present invention with respect to its
various modes are shown in FIGURES 6, 7 and 8.
Referring now to FIGURE 6, there is shown a flow
chart of the operation of the repeater trucking system
according to the present invention operating in the idle
mode. Operating in the idle mode, each of the channels
is scanned so that a mobile station can determine whether
its particular group signal is among any group signals
being transmitted over any of the channels. If the
particular group signal is not detected, this system
determines whether microphone push to talk switch 43 or
the off hook switch 45 has been activated. If either of
these switches has been activated, this system goes into
the wait mode. If neither of these switches has been
activated, then the receiver listens to the next channel
to determined whether the particular group signal is
present.
Once a group signal for that particular mobile
station has been detected, a group latch is set and the
group signal is examined. When the group signal has ended,
53~
45-MR-224A
- 26 -
the receiver looks for a subgroup signal if subgroups
and subgroup signals are being utilized. If the
appropriate subgroup is detected a subgroup latch is
set and the group latch is cleared. The receiver then
listens for a busy signal transmitted by the repeater.
If no busy slgnal is detected the receiver then tunes to
the next channel and again listens for its particular
group signal. However, if a busy signal is detected,
then a call latch is set and the mobile statlon enters
the ready mode to establish communication with the mobile
station calling the group with which it is associated.
Referring now to FIGURE 7, there is shown a flow
chart illustrating the operation of the repeater trunking
system in the wait mode. In the wait mode, wait lamp
40 is lighted. If a busy signal is detected, it is
determined whether or not all channels have been tried,
if not, the next channel in the sequence is listened to.
However, if all channels have been tried a beep alert
sounds through speaker 44 and wait light 40 is extinguished
and the trunking system enters the idle mode. Whenever
a busy signal is not detected, a busy signal is encoded
and an acquisition signal is listened for. If an
acquisition signal is present, then the group signal is
encoded. After the group signal is encoded, the sub-
group signal is encoded. After group and subgroup signals
have been encoded, a busy signal is listened for. If
the busy signal is present, wait lamp 40 is extinguished
the call latch is set and the s-tation enters the ready
mode.
Referring now to FIGURE 8, there is shown a flow
chart illustrating the operation of the repeater trunking
system in the ready mode. Operating in the ready mode,
ready lamp 41 is lit and four alert beeps are sounded
through speaker 44. All audio circuits are turned on.
If the microphone push-to-talk switch 43 is keyed then
53~
45-~R-224
- 27 -
attenuated busy signal is encoded. If the carrier control
timer has timed out then an audio alert is sounded. If
the transmitter is keyed and there are 20 seconds of
audio alter, the transmitter is shut down.
After the audio circuits have been turned on, if
a busy signal is detected, a fade margin counter is
reset and it is again determined whether the microphone
has been keyed. If the microphone has not been keyed
and a busy signal has not been detected, it is determined
whether the fade margin (no busy tone) timer has timed
out. If it has timed out, the call latch is cleared,
ready lamp 41 is extinguished and the station goes into
the idle mode.
Referring now to FIGURE 9, there is pictorially
illustrated the repeater acquisition sequence. This
chart details the hand shake between a mobile station
attempting to access other mobile stations within its
group through a repeater. A mobile station firs-t
searches for a free channel and then transmits a busy
signal. After it has sent the busy signal, the mobile
listens on the channels on which the busy signal is sent
for an acquisition signal. Upon receipt of the acquisition
signal, the hand shake has been effected and the mobile
proceeds to send group, subgroup, and busy signals.
The repeater, when not in use, is listing for a
busy signal. When a busy signal is received from the
mobile, an acquisition signal is sent. Assuming the
acquisition signal is followed by receipt of group,
subgroup and busy signals being sent from the mobile,
the repeater receives all of these signals and in turn
retransmits the group and subgroup signals and re-
generates and transmits a busy signal. This busy signal
serves as notice to all other mobiles not in the particul-
ar group and subgroup defined that the repeater is in
use so that they will not attempt to gain control of the
repeater.
3~J~
~5-MR-224 A
- 28 -
In brief summaryl when a mobile or control station
of the repeater trunking system is in the call originate
mode, the shift register SR2 causes scanning unti1 an
idle channel is found. This causes the shift register
SR1 to go -through its sequence of causing the transmitter
to send a busy signal, listen for an acquisition signal,
and then send a group signal, and subgroup signal to
activate the repeater and appropriate mobile stations.
If the repeater is activated, an indication is provided
to alert the user that he has acquired a channel, and
should transmit within a predetermined time (10 seconds).
If the repeater is not activated, the shift register SRl
goes through its sequence on the next channel, and so on
through each channel until a channel is acquired, or until
all channels have been sequenced. If no channel is
acquired, the user can start the entire sequence over
again and again.
It will thus be seen that there has been provided
a new and improved control circuit and method for
enabling the user of a mobile station to readily and
quickly acquire a single unused radio frequency channel
from a plurality of such channels for transmitting, or
to be called on an available channel. The arrangement
is relatively simple, and does not require extensive or
complex circuits. While there has been shown only
one embodiment of or invention, persons skilled in the
art will appreciate the many modifications tha-t may be
made. For example, -there has been shown a 5 channel
system, but there may be almost any number of
channels and repeaters. ~owever, good trunking practice
limits the channels to abou-t 20. Different logic circuit
arrangement and logic levels may be used, such as a
microprocessor circuit. The various circuits may have
almost any desired timing periods, particularly those
in the shift register SRl and in the timing circuit Tl.
The timers and counters may be in analog or digital form.
~S32~
45-MR-224 A
- 29 -
These are matters of preference and expediency depending
upon the particular communication condltions involved.
If a system is free from radiation interference, the
busy signal may be omit-ted and operation made dependent
upon the proper carrier. Otherwise, it is preferred
that the receiver signal sensor produce a logic 1 in
response to a busy tone, and a logic 0 in response to
the absence of busy signal. While we have shown one
group circuit and two subgroup circuits, one of which
is selectable, additional subgroups may be provided to
provide further selection of the particular mobile units
being called. Or, less subgroup circuits may be provided
so that a more general or less select group of mobiles
may be called. Or, group and subgroup signals may be
transmitted simultaneously rather than sequentially,
or may be frequency stepped functions of one common encoder
and decoder. The arrangement may also be used directly
between mobile stations without the use of the repeater.
Perons skilled in the art will also appreciate that with
a repeater transmitter frequency and a repeater receive-
frequency, only push-to-talk or simplex operation can be
provided. However, additional frequencies or auxiliary
equipment may be provided so that full duplex operation
can be provided. Again, this is a matter of preference
and frequency availability. While it is preferred that
the busy signal and acquisition signal frequencies be
above the audio frequency, for fast operation, the busy
signal and acquisition signal may be almost any desired
frequency or format. Likewise, the group and sub-
group signals may be almost any desired frequency.However, we believe it preferable that the busy signal
and acquisition signal be at a frequency just above the
transmitted audio frequencies, and that the group and
subgroup signals be in the band transmitted voice
frequencies. This present no problem, since the group
and subgroup tones are transmitted only when communication
53;~i
45-MR 224 A
- 30 -
is being established. Therefore, while -the invention
has been described with reference to a particular
preferred embodiment, it is to be understood that
modifications may be made without departing from the
spirit of the invention or from the scope of the claims.
