U.S. patent number RE32,789 [Application Number 06/548,793] was granted by the patent office on 1988-11-22 for transmission trunk multichannel dispatch system with priority queuing.
This patent grant is currently assigned to Motorola, Inc.. Invention is credited to Charles N. Lynk, Jr., James J. Mikulski.
United States Patent |
RE32,789 |
Lynk, Jr. , et al. |
November 22, 1988 |
Transmission trunk multichannel dispatch system with priority
queuing
Abstract
A communication system of the type wherein a central station
assigns a limited number of information channels to a requesting
one of a plurality of remote stations is disclosed. The requesting
station sends its identification signal along with the request
signal to the central station on a signal channel. The central
station classifies the requesting station in either a priority or a
non-priority queue. The priority queue corresponds to those
stations which are continuing an on-going interchange, whereas the
nonpriority queue contains those stations which wish to initiate an
interchange. Stations are prioritized in the queues on a
first-in/first-out basis. The central station constantly monitors
the information channels and, as channels become available, assigns
the channels first to stations in the priority queue, then to
nonpriority queue stations. A channel becomes "available" when the
central station detects a pause, such as a momentary release of a
push to talk microphone switch, in transmission of that channel. By
this transmission trunking method, the system makes optimum use of
the limited number of available channels. Additional central
station processing provides an acknowledgement signal, which
indicates that the request was received and a channel will be
assigned as soon as one becomes available. Also, the identification
of a requesting station is compared with an associate memory. The
memory provides the identifications of all stations to whom the
requesting station would transmit. Once a channel is available, it
is assigned to the requesting station and to its associated
stations, whereby the associated stations are notified of, and
prepared for, the impending transmission.
Inventors: |
Lynk, Jr.; Charles N. (Bedford,
TX), Mikulski; James J. (Deerfield, IL) |
Assignee: |
Motorola, Inc. (Schaumburg,
IL)
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Family
ID: |
27068941 |
Appl.
No.: |
06/548,793 |
Filed: |
November 4, 1983 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
634962 |
Nov 24, 1975 |
04012597 |
Mar 15, 1977 |
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Current U.S.
Class: |
455/512; 455/514;
455/520 |
Current CPC
Class: |
H04W
84/08 (20130101) |
Current International
Class: |
H04Q
7/28 (20060101); H04Q 007/00 () |
Field of
Search: |
;179/2EB,2E ;370/80,81
;455/53,54,89,95,99,140,151,152,352 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2251168 |
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Oct 1971 |
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DE |
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2442252 |
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Mar 1976 |
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DE |
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2215125 |
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Sep 1971 |
|
SE |
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1010299 |
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Nov 1965 |
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GB |
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1082734 |
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Sep 1967 |
|
GB |
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1387438 |
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Mar 1971 |
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GB |
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1369017 |
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Oct 1974 |
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GB |
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1393614 |
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May 1975 |
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GB |
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1408614 |
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Oct 1975 |
|
GB |
|
Other References
"TASI-Translation (Time Assignment Speech Interpolation)", dated
Dec. 14, 1981--Bill Schaupp. .
Selected Portions of an Article entitled "High Capacity Mobile
Telephone System Technical Report", Dec. 1971, prepared by Bell
Laboratories. (Enclosure consists of cover page and pp. iii [the
Preface], 1-1 through 1-7, 3-31 through 3-37, 3-42 and 3-43, and
A-16.).
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Primary Examiner: Brigance; Gerald L.
Attorney, Agent or Firm: Hamley; James P. Moore; John H.
Claims
We claim:
1. Control apparatus in a communication system having a central
control station for assigning a limited number of information
channels to a plurality of remote stations, each of said remote
stations communicating .[.a message,.]. .Iadd.messages, each
.Iaddend.comprising a plurality of individual transmissions, on its
assigned .[.channel.]. .Iadd.channels.Iaddend., the apparatus
comprising:
each remote station having means to request a channel assignment
from the central station;
means responsive to an assigned channel signal to operate on said
channel;
means generating an end of transmission signal at the conclusion of
each remote station transmission; and
the central station having
means to assign a channel to a requesting remote station; and
means detecting the end of transmission signal from a remote
station and truncating said remote station's channel assignment in
response thereto.
2. The control apparatus of claim 1 wherein the central station
channel assign means further comprises means to predeterminedly
prioritize the remote stations requesting an information channel
and assigning available channels in the priority order.
3. The control apparatus of claim 1 wherein each remote station
further comprises
identification signal means for sending a unique remote station
identification signal to the central station in conjunction with
the channel assignment request.
4. The control apparatus of claim 3 wherein the central station
channel assigning means furthr comprises:
a nonpriority storage register,
a priority storage register;
means for storing said remote station identification signals in
said nonpriority storage register prior to channel assignment and
in said priority storage register subsequent to channel assignment;
and
means assigning available information channels to those remote
stations whose identification signals are in the priority storage
register prior to assigning said channels to remote stations whose
identification signals are in the nonpriority storage register.
5. The control apparatus of claim 4 wherein the central station
assigning means further comprises
means for assigning available information channels to remote
stations whose identification signal is in the priority register on
a first-in/first-out basis.
6. The control apparatus of claim 4, wherein the central station
assigning means further comprises
means for assigning available information channels to remote
stations whose identification signal is in the nonpriority register
on a first-in/first-out basis.
7. The control apparatus of claim 4 wherein the central station
further comprises
means for deleting a station identification signal from said
priority register in response to the absence of a channel request
signal from said requesting station for a predetermined time
interval following said station's prior request.
8. The control apparatus of claim 1 wherein the central station
further comprises
means responsive to a channel request by a remote station for
detecting the absence of an available information channel and
transmitting an inhibit signal to said remote station in response
thereto; and
the .[.more.]. .Iadd.remote .Iaddend.station further comprises
means for detecting said inhibit signal and inhibiting transmission
by said remote station in response thereto.
9. The control apparatus of claim .[.7.]. .Iadd.8 .Iaddend.wherein
the remote station further comprises
an audible alert means for generating a distinct audible signal in
response to said remote station receiving said inhibit signal.
10. The control apparatus of claim 1 wherein the central station
further comprises:
associate means for associating, via a programmed memory, the
requesting station with other particular remote stations to which
said requesting station would transmit; and
means for sending a notification signal to said particular
stations, said notification signal suitable for activating said
particular stations to the channel assigned to said requesting
station.
11. The control apparatus of claim 10 wherein said notification
signal means further comprises
means for sending a transmission inhibit signal suitable for
inhibiting transmissions of said particular stations; and
said remote stations comprise
means for receiving said notification signals and tuning to said
assigned channel and inhibiting transmission in response
thereto.
12. The central station of claim 10 wherein the assigning means
further comprises
.Iadd.a nonpriority queue register;
a priority queue register;
means for storing said remote station identification signals in
said nonpriority queue register prior to channel assignment and in
said priority queue register subsequent to channel assignment;
means assigning available information channels to those remote
stations whose identification signals are in the priority queue
register prior to assigning said channels to remote stations whose
identification signals are in the nonpriority queue register; and
.Iaddend.
means for transferring said associated particular station signals
to the priority queue register,
whereby if one of said particular stations becomes a requesting
station it will be given priority in channel assignment.
13. The central station of claim 12 wherein the assignment means
further comprises
a priority queue deleting means for transferring a station
identification signal out of the priority queue register responsive
to the absence of a channel request from said channel request
station and said particular stations for a predetermined time
interval.
14. In a communication system having a central control station and
a plurality of identifiable remote stations, the central station
routing communications between remote stations over a limited
number of identified information channels, communication between
the remote stations and the central station occurring on a signal
channel, each remote stations adapted for generating an end of
transmission signal at the conclusion of its transmission, the
central station comprising:
means for transmitting to the remote stations;
means for receiving transmissions from remote stations;
channel request responsive means, coupled to the receiver, sensing
for the presence of a signal indicating a remote station request to
transmit a message on an information channel;
station identification, responsive means, coupled to the receiver,
sensing the identification signal of said requesting remote
station;
means for detecting and storing the identification signal of
available information channels;
assigning means, coupled to the transmitter, and responsive to the
request responsive means, for assigning an available channel to the
requesting remote station, the assign means having
a. a nonpriority queue register for storing the identification of
remote stations requesting an information channel,
b. a priority queue register for storing the identification of
remote stations to which channels have been assigned, and
c. priority means for assigning available channels to the stations
in the priority queue register before channels are assigned to
stations in the nonpriority queue register, and
transmission trunking means, coupled to the receiver,
for detecting the end of transmission signal generated by a remote
station on an assigned channel, and, in response thereto,
transferring the identification of said channel to the information
channel storage means such that the channel is available for
assignment to another remote station.
15. The central station of claim 14 further comprising
inhibit means, coupled to the transmitter and to the information
channel storing means for sending a transmit inhibit signal to a
requesting remote station in response to the absence of an
available information channel.
16. The central system of claim 15 wherein the inhibit means
further comprises means for sending a signal suitable for
activating the requesting station to the receive mode on the signal
channel in conjunction with the transmit inhibit signal.
17. The central station of claim 14 further comprising associating
means, coupled to the station identification responsive means,
associating, via a programmed memory, the requesting station
identification signal with particular identification signals of
remote stations to which said requesting station would transmit
when given an information channel.
18. The central station of claim 17 further comprising
notification means, coupled to the transmitter, the associating
means, and the assigning means, for sending an assignment
notification signal to said particular remote stations in response
to the assigning means a chanel to a requesting remote station, the
notification signal suitable for activating said particular remote
stations to said assigned channel.
19. The central station of claim 18 wherein the
notification means further comprises inhibit signal means for
sending a signal suitable for inhibiting transmissions from said
particular remote stations, said inhibit signal sent in conjunction
with said assignment notification signal.
20. The central station of claim 17 wherein
the assigning means further comprises
means for transferring said associated particular stations signals
to the priority queue register,
whereby if one of said particular stations becomes a requesting
station it will be given priority in channel assignment.
21. The central station of claim 20 wherein the assigning means
further comprises
a priority queue deleting means for transferring a station
identification signal out of the priority queue register responsive
to the absence of a channel request from said channel request
station and said particular stations for a predetermined time
interval.
22. The central station of claim 14 wherein the priority and
nonpriority queuing registers are comprised of sequential shift
circuitry such that channel assignments are made on a
first-in/first-out basis to stored station identifications.
23. The central station of claim 14 wherein the assignment means
further comprises
a priority queue deleting means for transferring a station
identification signal out of the priority queue register responsive
to the absence of a channel request from said station for a
predetermined time interval.
24. In a communication system having a central control station and
a plurality of identifiable remote stations, the central station
routing communications between remote stations over a limited
number of identified information channels, communication between
the remote stations and the central station occurring on a signal
channel, each communication including a message by each remote
station, which message comprises a plurality of individual
transmission, each remote station comprising:
controllably tuned transmitter means for transmitting on the signal
channel or on an assigned information channel;
controllably tuned receiver means for receiving transmissions on
the signal channel or on an assigned information channel;
channel requesting means coupled to the transmitter, for generating
and sending a channel request signal, on the signal channel, to the
central station;
identification means, coupled to the transmitter, for generating
and sending a predetermined identification signal in conjunction
with the request signal;
channel assigning means, coupled to the receiver, for receiving a
channel assignment signal from the central station and, in response
thereto, controllably tuning the transmitter and receiver to the
assigned channel; and
end of transmission signalling means for transmitting an end of
transmission signal to th central station at the conclusion of each
of said individual transmissions.
25. The remote station of claim 24 further comprising
inhibit response means coupled to the receiver, for inhibiting said
remote station from transmitting responsive to receiving an inhibit
signal from the central station.
26. The remote station of claim 25 wherein the inhibit means
further comprises
means controllably tuning said remote station receiver to the
signal channel responsive to receiving said inhibit signal.
27. The remote signal of claim 25 further comprising audible alert
means for generating a distinct audible signal in response to the
remote station receiving a inhibit signal.
28. The remote station of claim 24 further comprising
channel notification means, coupled to the receiver, for receiving
a channel notification signal and, in response thereto,
controllably tuning said receiver to the assigned channel and
inhibiting transmission from the remote station transmitter.
29. The remote station of claim 24 wherein the channel requesting
means further comprises means for generating the channel request
signal in response to activation of a push to talk switch activated
microphone.
30. A method .[.of assigning.]. .Iadd.for a central station to
assign .Iaddend.one of a limited .[.number.]. .Iadd.plurality
.Iaddend.of .Iadd.rf .Iaddend.information channels to a requesting
one of a plurality of .Iadd.rf .Iaddend.remote stations for
communication by each of said remote stations of a message on
.[.said.]. assigned .[.channel, said.]. .Iadd.channels, each
.Iaddend.message comprising a plurality of individual
transmissions, the method comprising the steps of:
a. receiving .[.the.]. .Iadd.a .Iaddend.requesting signal;
b. identifying the requesting station;
.Iadd.c. transmitting to the requesting station a signal enabling
the requesting station to operate continuously on an rf channel
identified by the central station until the requesting station
transmits a signal indicative of the end of a complete
transmission; .Iaddend.
.[.c.]. .Iadd.d.Iaddend.. monitoring said requesting station;
and
.[.d.]. .Iadd.e.Iaddend.. truncating the assignation of said
.Iadd.rf .Iaddend.channel to said requesting station .[.at the
conclusion of each of the transmission of.]. .Iadd.in response to
the signal indicative of the end of transmission received from
.Iaddend.said identified requesting station, such that the .Iadd.rf
.Iaddend.channel is available for assignation to a second
requesting station.
31. The method of claim 30 wherein the identifying step further
comprises the steps of:
a. detecting the identify signal from said requesting station;
b. comparing said identity signals in an identity register; and
c. ignoring said requesting station if said identity signal does
not match a corresponding signal in the identity register.
32. The method of claim 30 further comprising the steps of
(a) assigning a priority to said identified requesting station;
and
(b) assigning an available information channel to said station if,
and only if, .[.available.]. channels have .Iadd.already
.Iaddend.been assigned to .Iadd.any .Iaddend.higher priority
stations.
33. The method of claim 32 wherein the priority assigning steps
further comprises the steps of:
a. comparing the identity of said requesting station with the
identities of stations in a priority storage register;
b. transferring said identity signal to a priority queue if said
identity matches a corresponding identity in said priority storage
register; otherwise
c. transferring said identity signal to a nonpriority queue.
34. The method of claim 33 wherein the priority assigning step
further comprises the steps of:
a. assigning said transferred identity signals, in said priority
queue, on a first-in/first-out priority; and
b. assigning said transferred identity signals in said nonpriority
queue on a first-in/first-out priority.
35. The method of claim 34 wherein the channel assigning step
further comprises the steps of:
a. sensing for available channels;
b. assigning said available channels to stations in said priority
queue in the priority order;
c. assigning the remaining available channels to said nonpriority
queue stations in said priority order; and
d. alerting said requesting station if there are no currently
available channels.
36. The method of claim 35 wherein the channel assigning step
further comprises the step of:
transferring the identity of a requesting station to which a
channel has been assigned from the non-priority to the priority
storage.
37. The method of claim 36 wherein the channel assigning steps
further comprise the step of:
deleting from said priority storage the identity signal of said
requesting station responsive to an absence of a channel request
from said station for a predetermined time interval.
38. The method of claim 35 wherein the channel assigning step
further comprises:
a. comparing said identity signal with the identity signals in an
associate station memory; and
b. notifying the particular stations, in said associate station
memory which correspond to said requesting station, to receive on
said assigned channel.
39. The method of claim 38 wherein the channel assigning step
further comprises the step of:
transferring the identity signals of said particular stations to
said priority storage.
40. The method of claim 39 wherein the channel assigning step
further comprises the step of:
deleting from said priority storage the identity signal of said
requesting stations and said particular stations responsive to the
absence of a request signal from said requesting station and said
particular stations for a predetermined time interval. .Iadd.
41. The control apparatus of claim 1 wherein each remote station
includes a microphone activated by a push-to-talk switch, wherein
said means to request a channel assignment further comprises means
for generating the channel request signal in response to activation
of the push-to-talk switch, and wherein said means for generating
an end of transmission signal is responsive to deactivation of the
push-to-talk switch for generating the end of transmission signal.
.Iaddend. .Iadd.
42. The remote station of claim 24 further including a microphone
activated by a push-to-talk switch, wherein said end of
transmission signaling means responds to deactivation of the
push-to-talk switch by transmitting the end of transmission signal,
and wherein said transmitter means is adapted to operate on an
assigned channel continuously until the end of transmission signal
is transmitted. .Iaddend. .Iadd.43. A method as set forth in claim
30 wherein each remote station includes a push-to-talk switch and
wherein the transmission by the requesting station of the signal
indicative of the end of transmission is initiated by deactivating
the push-to-talk switch. .Iaddend. .Iadd.44. A method for a central
station to assign one of a limited plurality of rf information
channels to a requesting one of a plurality of rf remote stations
for communication by said remote stations of messages on assigned
channels, each message comprising a plurality of individual
transmissions, the method comprising, the steps of:
(a) receiving a requesting signal;
(b) identifying the requesting station;
(c) assigning a priority to said identified requesting station;
(d) assigning an information channel to said requesting station in
accordance with the assigned priority;
(e) monitoring said requesting station; and
(f) truncating the assignment of said channel to said requesting
station at the conclusion of each of the transmissions of said
identified requesting station, such that the channel is available
for assignment to a second requesting station. .Iaddend. .Iadd.45.
The method of claim 44 wherein the identifying step further
comprises the steps of:
(a) detecting an identity signal from said requesting station;
(b) comparing the detected identity signal to stored identity
signals; and
(c) ignoring said requesting station if said detected identity
signal does not match a corresponding stored identity signal.
.Iaddend. .Iadd.46. The method of claim 45 wherein the priority
assigning step further comprises the steps of:
(a) comparing the identity of said requesting station with the
identities of stations in a priority storage;
(b) storing an identity signal in a priority queue if said identity
matches a corresponding identity in said priority storage;
otherwise,
(c) transferring said identity signal to a non-priority queue.
.Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates to multichannel communication systems and,
more particularly, to such systems having transmission trunked
channel assignment and requesting station priority queues.
Trunked communication systems are well known in the telephone and
mobile communication art. In such applications, a multiplicity of
subscribers share a limited number of transmission channels. The
channels are assigned to subscribers by a central dispatch station.
Commonly, the central station dedicates a channel to a subscriber
for the duration of an entire interchange message, hence, the name
"message trunking".
The message trunked systems suffer from numerous disadvantages.
First, once a subscriber is assigned a channel he gains full
control over it. Even though numerous others are waiting for
channel assignments, he may conduct a lengthy message with lengthy
pauses. Moreover, at the conclusion of his message he may forget to
return the channel to central station control. A further
disadvantage to such systems is that if a subscriber initiates a
call during a period when all channels are in use, he is not placed
in a priority queue, but rather he must reinitate the call at a
later time. Thus, it is possible that a latecomer could be assigned
a channel before a subscriber who has made a prior request.
OBJECTS OF THE INVENTION
It is an object of the present invention, therefore, to provide an
improved trunking system which assigns a channel to a subscriber
for only so long as his actual transmission.
It is a further object of the invention to provide an improved
trunking system of the above type which gives the user a sense of
system loading.
An additional object of the present invention is to provide an
improved trunking system of the above described type which provides
priority queues for its subscribers.
Basically, according to the invention, control apparatus is
provided for a communication system having a central control
station which assigns a limited number of information channels
among a plurality of remote sections. In the remote station, the
apparatus comprises means for requesting a channel assignment from
the central station, and further means responsive to an assigned
channel signal from the central station whereby the remote station
operates on the assigned channel. In the central station, the
apparatus comprises means which detect the conclusion of a
transmission by a remote station on its assigned channel and
truncates the assignment of the channel to said station in response
to the detected conclusion.
Additional central station apparatus predeterminedly prioritizes
the requesting remote stations and assigns available channels to
the remote stations in the priority order.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a generalized representation of a transmission trunking
system according to the invention;
FIG. 2 illustrates a communication between two remote stations via
the transmission trunking technique;
FIG. 3 is a detailed block diagram of a remote station;
FIG. 4 is a logic flow diagram of the central control station;
FIG. 5 illustrates implementation of the central station in block
diagram form; and
FIGS. 6a, 6b and 7 are logic flow diagrams of the microprocessor
unit utilized in the central station.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
In FIG. 1, a plurality of subscribers 10 are shown, all of which
share a limited number of transmission information channels 12 and
a signal channel 14. The channels 12, 14 are controlled by a
central station 18. In particular, communication is shown between
subscribers A and B, C and D, E and F, and G and H.
System operation is understood with reference to the subscriber A
to subscriber B communication. Assuming subscriber A initiated the
call, his first transmission would be on the signal channel 14 to
the central station 18. Central station 18 decodes the request
message, and determines the identity of the subscriber. Then,
central station 18 determines whether an information channel 12 is
available. If it is, the requesting station A will be assigned a
channel. If not, station A will be placed in a priority queue
whereby as channels become available they are assigned to stations
having the highest priority. If all channels are being used, the
central station will send an acknowledgement signal to station A
indicating that it has received the request signal and that a
channel will be assigned as soon as one becomes available.
Central station 18 is also provided with an associative memory,
whereby the identification of the requesting station, in this
example station A, is associated with the station to which the
requesting station will communicate, e.g. station B. Thus, when an
information channel 12y becomes available, the central station 18
sends an appropriate signal on signal channel 14 to both station A
and station B. The signal to station A indicates that transmission
may proceed, whereas the signal to station B actuates control
circuitry within station B which inhibits transmission and tunes
the station B receiver to channel 12y.
The transmission from station A to station B over information
channel 12y is monitored by central station 18. Once station 18
detects an end of transmission by station A, channel 12y is
automatically made available for assignment to another requesting
station. Thus, when station B responds to station A, it must first
request an information channel on signal channel 14. Since the
transmission from station B to station A is a continuation of a
prior conversation, central station 18 will have assigned a high
priority to station B, such that station B must wait a very short
time, if at all, for channel assignment. As before, once a channel
is assigned, in this case channel 12w, an appropriate message is
sent by central station 18 on signal channel 14 both to station B
and station A whereby B may then proceed with his transmission.
In this manner, central station 18 transmission trunks each
broadcast by a station on an assigned channel whereby the channel
is available for reassignment as soon as the transmission ceases.
Also, stations requesting a channel are assigned priorities. If a
station is initiating a communication, it is assigned a low
priority state, whereas stations which are involved in an ongoing
conversation are assigned a relatively high priority state. Thus,
the central station has full control over the information channels
and is free to assign them in a manner which yields optimum
communication flow.
FIG. 2 illustrates the communication system according to the
invention as used in a mobile radio application. A central or base
station 12 controls communication between a first mobile unit 20
(Mobile I) and a second mobile unit 30 (Mobile II). Each mobile 20,
30 is provided with a transceiver 22, 32 which couples to an
antenna 24, 34, a push to talk switch 26, 36, a status indicator
27, 37 and a control logic 28, 38, respectively.
Assuming that Mobile I desires an information channel for
communication to Mobile II, push to talk switch 26 is depressed
whereby the control logic 28 generates a signal S.sub.1 containing
channel request and, in conjunction therewith, station
identification encoded information. The signal S.sub.1 is
transmitted via transceiver 22 over antenna 24 to central station
12 on the signal channel. The central station 12 includes
processing circuitry which identifies the requesting station, and
assigns a priority in response thereto. Since Mobile I is
initiating communication, it will be assigned a relatively low
priority state.
In response to the request portion of signal S1, central station 12
transmits a response signal S2 on the signal channel to Mobile I.
If all information channels are in use, response signal S2 will
contain acknowledgement encoding, whereby control logic 28 locks
transceiver 22 in the receive mode on the signal channel, and
activates status indicator 27 whereby the operator of Mobile I is
notified that all lines are busy but that he will be assigned a
channel as soon as one becomes available.
For those systems in which a particular requesting station will
always be calling a particular group of mobile stations, as for
example a dispatcher calling his fleet, the central station 12 is
provided with an associate memory. The associate memory is
programmed to recall the identity of stations to whom a requesting
station wishes to communicate. Thus, referring to FIG. 2, once an
information channel becomes available for assignment to Mobile I,
central station 12 sends an appropriate signal S.sub.2 which
enables the control logic 28 to activate transceiver 22 to the
transmit mode on the assigned channel. Also, status indicator 27
indicates to the operator that the system is ready to carry his
message. In addition, the central station sends a signal S.sub.3 to
the Mobile II station. The encoding of signal S.sub.3 enables the
Mobile II control logic 38 to inhibit the transmitter portion of
transceiver 32, and to activate the receiver of transceiver 32 to
the assigned channel. While S.sub.2 and S.sub.3 are shown as
independent signals, it should be clear that they may be encoded
within a single signal.
Thereafter, the operator of Mobile I can send a transmission
S.sub.4 to mobile II over the assigned channel, with the central
station serving as repeater. This transmission is monitored by the
central station 12, and, when the station detects the end of Mobile
I transmission, as, for example, when the operator releases push to
talk switch 26, the central station automatically makes the
assigned channel available for other stations.
Should Mobile II desire to transmit back to Mobile I, it also would
request a channel assignment on the signal channel from central
station 12. Since central station 12 has assigned both Mobile I and
its associated station Mobile II to a priority queue, Mobile II
would ordinarily have a very short wait for channel assignment.
Since each station in the communication system according to the
invention must be assigned an information channel upon every
transmission, the wait for an assignment experienced by the
stations gives them an indication of system loading, and,
hopefully, induces them to restrict the length of their
messages.
FIG. 3 is a detailed block diagram of the Mobile I station of FIG.
2. Identical numbers have been used to indicate the same
components.
Antenna 24 is coupled via antenna switch 54 to either receiver 22R
or transmitter 22T. The discriminator output of receiver 22R is
amplified through audio circuits 50 and applied to a speaker 23.
Also, the discriminator output of receiver 22R is routed through
processing circuitry 40, and applied through parallel line 61a to a
signal register 61. Signal register 61 provides parallel outputs
61b, 61c, and 61d to a synthesizer control and gating block 62, an
identification decode block 63, and a function decode block 64.
Each block, 62, 63, 64 couples to a control logic block 28 via
lines 62a, 63a and 64a, respectively. Parallel lines 62b couple
from the synthesizer control and gating block 62 to a frequency
synthesizer 50. The synthesizer 50 provides a controlled local
oscillator signal to both receiver 22R, and a transmitter 22T.
The logic control 28 provides first and second output lines 28a,
28b to the audio circuits 50. First output line 28a passes control
tones which indicate to the mobile operator that a requested
information channel is either unavailable, or that it is available
and he may proceed in transmission. The second line 28b enables the
audio circuits whereby the receiver 22R output is reproduced
through the speaker 23. A third line 28c from control logic 28
connects through the push to talk switch 26 to circuit ground 27.
The push to talk switch 26 is integral with a microphone 33 which
connects through audio amplifier circuits 52 to the transmitter
22T. The audio circuits 52 are enabled by an output line 28d from
control logic 28. Additionally, control logic 28 provides an output
28e, and parallel outputs 28f, to a signalling word generator 66.
The signalling word generator 66 provides an output control to
transmitter 22T, as does a tone generator and enable block 68 which
is also controlled from a control logic output 28g. Finally,
control logic 28 provides a transmit enable output on line 28h to
transmitter 22T, and a transmit receive control line 28i to the
antenna switch 54.
Mobile operation is understood as follows. When the operator wishes
to initiate a call, he depresses push to talk switch 26 which, via
line 28c, activates the control logic 28. Control logic 28
activates the line 28whereby antenna switch 54 couples antenna 24
to the transmitter 22T. The signalling word generator 66 is enabled
via an activated line 28e and, in response thereto, accepts
commands on parallel lines 28f to generate a request signal and a
unit identification signal which is unique to the Mobile I station.
The signalling word generator adds parity bits and a reference
synchronization signal to the tone code, which is thereafter passed
to the transmitter 22T, now enabled via line 28h. Synthesizer 50 is
in a mode whereby the transmitter 22T is tuned to operate on the
signal channel. Thus, the encoded message is passed through antenna
switch 54 and over antenna 24 on the signal channel to the central
station (not shown). Once the message has been sent, the control
logic 28 deactivates the transmit enable lines, returns the antenna
switch 54 to the receive mode, and activates the receive enable
lines whereby the system awaits a response from the central
station.
In the receive mode, the signal is passed from antenna 24 through
switch 54 to the receiver 22R. The synthesizer 50 normally tunes
receiver 21 to receive signals on the signal channel. The
discriminator output of receiver 21 is low pass filtered via filter
41 and processed through sampler bit detector 42, bit and frame
synchronization circuitry 44, code correction circuitry 43, and
tone detector 45, all of which are well known in the art.
All signals are processed through the signal register 61. Both the
idenfication and function portions of each signal are sent to the
identification decoder 63, and function decode 64, via lines 61c
and 61d, respectively. A comparison is made between the received
identification and the unit's assigned identification, which
identification can consist of individual and group segments. If a
match is found the signal is sent to the control logic 28, where
the function decoding is also received. In response to the address
and function signal, control logic determines whether the
requesting unit is to be activated on the assigned channel. A
signal on line 62a gates the synthesizer control block to decode
the channel assignment portion of the signal and activate and tune
the synthesizer corresponding to this assignment.
Once the control logic 28 receives an information channel
assignment, it determines whether the push to talk switch 26 is
depressed. If the switch 26 is depressed, the logic 28 responds by
assuming that this is the mobile wishing to transmit. Therefore, it
activates transmit enable signals on lines 28d, 28h, and activates
line 28i to operate antenna switch 54 in the transmit mode.
Finally, a talk permit tone is sent via line 28a to the audio
circuits 50, whereby the operator is notified that he may proceed
with transmission.
If, however, when a channel assignment code is received by the
control logic 28 and push to talk switch 26 is not depressed, the
receive audio enable line 28b is activated whereby the system locks
the in the receive mode. If an identification decode signal is
detected through the decoder 63, the control logic activates the
synthesizer 50 to the assigned channel via line 62a, synthesizer
control 62, and parallel lines 62b. Without a proper output from
the identification decoder, the synthesizer 50 maintains the
receiver 22R tuned to the signal channel.
If all information channels are in use, the central station sends a
function decoding signal to the mobile so indicating. The function
decoding signal is processed through the receiver, in processing
circuitry 40, and is detected by the function decoder 64. The
control logic 28 inhibits mobile transmission, and maintains the
system in the receive mode tuned to the signal channel. Also, a
"busy" tone is sent on line 28a to the audio circuits 50. The
characteristic busy tone is reproduced by the speaker, thereby
notifying the operator that a channel is not open for his
transmission.
Once a signal word is receiver which indicates a channel
assignment, the control logic determines whether the push to talk
switch 26 of this mobile had been depressed. If it is, a connect
tone is passed to the tone generator enable block 68 and is
transmitted on the assigned frequency.
At the conclusion of his transmission, the mobile operator releases
push to talk switch 26, which causes the control logic 28 to
activate the tone generator 68 and send a disconnect tone to the
base. Thereafter, control logic 28 returns the system to the
receive mode tuned to the signalling channel.
FIG. 4 is a simplified flow diagram of the signal processing in the
central station. A mobile information channel request message is
received at block 100 and passed to an identification detector 102.
Detector 102 decodes the input signal, and produces at its output
the unique identification signal of the requesting station. A gate
104 compares the identification of the requesting station with
those identifications in identification storage register 106. If an
identification storage signal corresponding to the requesting
station identification signal cannot be found in storage 106, gate
104 causes the central station to ignore the incoming message.
Should the identification storage register 106 contain a signal
corresponding to the identification of the requesting station, this
identification signal is passed to a second gate 108. Gate 108
determines whether the requesting station is located in the
priority storage register 110. If it is, the identification signal
is passed to the priority queue 112; and, if it isn't it is passed
to a non-priority queue 114. Both queues 112 and 114 assign a
priority to incoming identification signals based on a
first-in/first-out basis.
The priority queues 112, 114 feed to a channel assign block 116.
Channel assign block 116 constantly monitors an available channel
storage register 118. As information channels become available for
assignment to requesting stations, the channel assign block 116
sequentially makes assignments to waiting stations in the priority
queue 112. Channel assignments are given to stations in the
nonpriority queue 114 if, and only if, there are no stations
waiting assignment in priority queue 112. If the channel assign
block 116 cannot immediately assign a channel to a requesting
station, a busy signal generator 122 is activated, which in turn
sends a busy signal via a transmitter 124 to the requesting
station.
When a channel is available for assignment to a requesting station,
an appropriate signal is sent via the channel assign block 116
through the transmitter 124 to the station. Also, an associate
memory and inhibit block 128 compares the identification signal of
the requesting station to corresponding signals in the associate
memory. The particular memory signals which correspond to the
channel request station represent stations to whom the requesting
station wishes to transmit once it is assigned a channel. Thus,
associate memory and inhibit block 128 causes transmitter 124 to
broadcast a signal to each of the particular stations which in turn
causes them to tune to the assigned channel, and inhibit any
transmission on their part.
Further, when a channel is assigned to a requesting station, a
third gate 130 enters the requesting station's identification
signal, along with its particular associate stations'
identifications, in priority storage 110. Thus, once a
communication has been initiated, the requesting station and the
particular stations are stored in the priority storage, and applied
to the priority queue 112 when any of these stations subsequently
request a channel. Since the channel assign block 116 gives
priority to priority queue stations, the members of an ongoing
communication are assured of a very short wait for channel
assignment.
Stations are deleted from priority storage 110 via a delete block
136. This block monitors all identified and detected identification
signals of requesting stations. In combination with a clock 134,
the delete block 136 determines the time between channel request of
various stations. If a requesting station and its particular
associated stations, do not request a channel for a given period of
time measured from a prior request, the assumption is made that the
parties have ceased their interchange, and their identification
signals are deleted from the priority storage 110.
The central station has a monitor 140 which constantly monitors the
information channels. A transmission truncate block 142 detects the
conclusion of a transmission by a requesting station on its
assigned channel, and in response thereto truncates the channel
assignment, making the channel available for assignment to other
requesting stations. When used in conjunction with the mobile
station described with respect to FIG. 3, the transmission truncate
block 142 responds to end of message signals which are generated by
the mobile upon release of the push to talk switch, or absence of
carrier. In particular applications, the transmission truncate
block 142 might contain audio detection circuitry which would sense
a sufficiently long pause in a transmission and thereby cause a
truncation of channel assignment.
FIG. 5 is a block diagram representation of the central station,
which is comprised of both signal channel 171 and audio channel 181
processing circuitry. While circuitry for a single audio channel is
shown, it should be understood that duplicate circuitry for each
audio channel is contemplated.
The central station signalling channel transceiver, comprised of a
receiver 200 and a transmitter 300, operates in a full duplex mode
with both receiver and transmitter active at all times.
In the receive mode, signals are passed from antenna 160 through an
antenna coupler 150 to the receiver 200. The discriminator output
of the receiver 200 couples to signal channel receiver processing
circuitry 400. Processing circuitry 400 closely resembles the
mobile processing circuitry 40 discussed with respect to FIG. 3.
The receiver 200 output is low pass filtered by receiver block 401
and passed to a sampler 402. The sampler 402 responds to a bit
synchronization output of clock and synchronization recovery block
402, which also connects to the receiver 200 output, to sample
incoming bits and pass them to a decoder block 409. Indication of a
received frame of bits is sent from the frame synchronization
recovery unit 403 to the decoder 409. If the received work can be
decoded correctly, a clock enable signal from the clock and sync
recovery block 403 activates clock 404. Clock 404, through the
action of gate 405 and counter 406, transfers the decoded data from
the decoder 409 into a serial to parallel conversion register 407.
When the word is transferred completely, an interrupt signal is
generated in the counter 406, which interrupt signal is applied to
a signal input register 408 to which the word transferred. The
counter 406 interrupt signal is also passed to a microprocessor
unit 701. The microprocessor 701 is the control logic for the
central station. It responds to interrupt signals in a
predetermined manner to selectively recall or store information in
one or more of a series of storage registers 702-708 via a data bus
and an address bus.
For example, if an interrupt signal has been generated by a channel
requesting signal the microprocessing unit 701 first reads the
identification of the calling group which is stored in the
signalling input register 408. It then scans through the validation
storage block 707 and determines whether the identified signal is
among the list of addresses of valid users stored in the block. If
the requesting station identification is contained in the address
of validation storage block 707, signal processing continues. If
the requesting station identification is not among the valid
addresses, the microprocessing unit returns to a quiescent state
ready to receive a subsequent interrupt signal.
Upon receipt of a matched validation between validation storage
block 707 and requesting station identification, the microprocessor
701 addresses the information channel storage block 706. A count of
the number of unused information channels is read from block 706 to
the microprocessor 701. If the count is greater than zero, a
channel is assigned. If, however, the count equals zero, no
channels are available, and the call must be queued in one of the
queue storages 702, 703.
The operation of the microprocessing unit 701, especially with
respect to the assigning process, is discussed more fully with
reference to FIG. 6.
Output command signals from the microprocessing unit 701 are
processed through transmitter processing circuitry 700. The
transmitter processing circuitry is comprised of a signal output
register 712 which connects to a parallel-serial block 714. Command
words from the microprocessing unit 701 are passed via a data bus
to the signal output register 712, and thereafter are clocked
through the parallel-serial block 714 to an encoder 717. Additional
address commands are passed via the microprocessing unit 701 by way
of an address bus to a signal address decoder 711 which also
connects to the signal output register 712 and provides an enable
signal therefor. An enable signal for the parallel-serial block 714
is generated by the output register 712 and delayed through a delay
block 713.
The command signal output is bit and frame synchronized by a clock
718 in conjunction with a gate 715 and a counter 716. The clock
receives a start signal from output register 712, and thereafter
increments the synchronization circuitry as well as the encoder
717. The encoder 717 output is passed via the transmitter 300 and
antenna coupler 150 to the antenna 160.
Finally, a real time clock 720 (periodically) produces
microprocessor interrupt signals which initiate priority queue
updates, a process more fully discussed hereinbelow.
The base audio channel processing circuitry is understood as
follows. Attention is first drawn to the receiver portion (blocks
290 and 690). Signal reception is accomplished by means of an
antenna 201 from which the signal passes to the antenna coupling
means 190, and therethrough to the receiver 290. At this point the
signal is demodulated and split into two paths. The voice portion
is sent to the audio processor 591 from which voice can be passed
or blocked. This is explained in detail hereafter.
The second path consists of one of two tones, connect or
disconnect. From the receiver 290 these tones pass through a low
pass filter 691 to a tone detector 692. The tone detector monitors
the channel for the presence of either a connect tone or a
disconnect tone and alerts the MPU 701 in the event of either a
connect tone drop which lasts for a predetermined interval, the
lack of a connect tone for a predetermined interval after the
channel is assigned or the presence of a disconnect tone. The MPU
701 is alerted by the information interrupt line which originates
at the tone detector 692. In the event of an interrupt, the
information interrupt signal also enables an information input
register 693 to accept data from the connect drop and disconnect
lines.
Upon reception of the interrupt, the MPU 701 in the process of
poling all input devices sends out on the address bus the
identification of the information input register 693. An
information address decoder 595 interprets the address and enables
the output gates of the information input register 693. This places
the information input register 693 information on the data bus
which is subsequently accepted by the MPU 701.
Next, consider the transmitter control section (i.e., block 590).
The transmitter is controlled by placing the identification of an
information output register 594 on the address bus. The information
address decoder 595 decodes the identification and enables the
information output registe 594 to accept information from the MPU
701 which is on the data bus. This information provides the connect
or disconnect enable signal to the tone generator 593 and/or the
enable or enable to the audio processor 591.
The connect, disconnect signal determines which tone, if any, is to
be sent by the tone generator 593. The enable signal allows audio
to be passed (or blocked in the event of enable) to a summer 592.
At the summer 592 the signals from the audio processor and tone
generator are combined and passed to the transmitter 390 whereat
the resulting signal is modulated on the RF carrier, amplified and
passed to the antenna 201 through the antenna coupling means
190.
FIGS. 6a, b are flow diagrams of the microprocessor unit 701 shown
in the central station block diagram of FIG. 5.
Microprocessor activity is induced every time it receives an
interrupt signal. The interrupt signals are passed through an OR
gate 800 and applied to a process interrupt block 802. An interrupt
signal will be of one of three types. It may arise through the
signalling channel at block 406, upon receipt of a correctly
decoded signal request message which is discussed with respect to
FIG. 5. A second type of interrupt signal arises through the
presence of a connect or disconnect tone on one of the audio
channels 691.sub.1 to 691.sub.N, described more fully hereinbelow.
The third type of interrupt signal at block 720, is derived from
clock timing of a real time clock. An interrupt signal of this type
results in the timing required of various functions in the
system.
Once the processor interrupt block 802 receives an interrupt
signal, it sequentially polls the status of each channel, including
the signalling channel, in a channel input register 408 and each
information channel, in input register 693, thereby determining
which channel has carried the input message. A gate 410 passes the
interrupt signal to a first signal path if the signal is detected
as originating on the signal channel. This path leads to a block
412 which via register 408, reads the identification of the
requesting station, and feeds this identification to a scan
validation block 404. Validation block 414 compares the
identification signal to the signals stored in a validation storage
block 707 and determines whether the requesting station signal is
among the addresses in the validation storage block. If it is not a
gate 416 returns the system to its quiescent state whereby it is
prepared to receive a subsequent interrupt signal. If, however, the
requesting station is identified as being among those in the
validation storage block 707, the information is passed to a
processing block 418. Block 418 reads the number of available
information channels from an information channel storage register
706. If no channels are available, i.e. if the number of available
information channels is zero, gate 420 activates an acknowledgement
block 422. Acknowledgement block 422 addresses the signalling
channel address decoder, block 711, and the signalling output
register 712. This process enables the signalling channel and
transmits the busy message to the requesting station. Thereafter, a
scan priority storage block 424 scans the priority status storage
block 705 to see if the identification of the requesting channel is
in storage. Each identification within storage block 705 is
sequentially compared with the identification of the requesting
station. A determination is made in each case of match or no match.
If a match is made, indicating priority, a gate 426 passes the
identification to a transfer block 428 which in turn assigns the
identification signal to the lowest priority stage 702 of the
priority queue. In a no match condition, gate 426 routes the
identification signal to a transfer block 430 which in turn passes
it to the lowest priority state 703 of the nonpriority queue.
Having completed priority queue assignment, the system returns to
the quiescent state.
Referring back to gate 420, if the number of information channels
available is greater than zero, gate 420 passes the identification
signal to block 440. At block 440 the address of the requesting
station is written in the priority status storage 705. Block 440
also includes means for determining the last time a channel request
signal was received from a station in the call group. Each time an
address is written into the priority status storage 705 by address
block 440 the time is reset to zero. Block 440 activates block 442
which addresses the information channel status storage 710. At this
point, the available channel which is to be assigned is changed to
the busy state in the information channel status storage 710.
Following block 442, a block 444 sends the identification of the
information channel to be assigned, and the address of the calling
group to the signal address decoder 711 and signal output register
712. An enable block 446 causes a connect tone to be generated
which is sent to register 594 and decoder 595 of the information
channel being assigned. Thus, the entire message of the assigned
channel and connect tone are sent to appropriate calling group
stations. Thereafter the system returns to the quiescent state.
If an interrupt signal originates on one of the information
channels, this is an indication that the transmission on the
channel has ceased. Thereafter, gate 410 activates block 450 which
in turn locates the address of the previously assigned information
channel. A subsequent block 452, via register 594 and decocer 595,
causes a disconnect tone to be generated which notifies all units
to leave the channel and disables audio processor 591 whereby the
previously assigned channel now becomes available for reassignment.
Thus, block 454 which couples to the information channel storage
706 causes the status of the identified channel to change from busy
to available.
Thereafter block 456 reads the number of calls stored in the
priority queue storage 702. If the number of calls in the priority
queue is greater than zero, a gate 458 activates a read address 460
which reads the identification signal of the call group having the
highest priority in the priority queue 702. The identification of
this call group is then passed to the channel assigning sequence,
blocks 440-446 whereby the available channel is assigned to this
group.
If the priority queue is empty, gate 458 activates block 462 which
reads the number of requests in the nonpriority queue 703. If there
are stations awaiting an information channel in the nonpriority
queue, a gate 464 activates block 466 which reads the
identification of the highest priority call in the nonpriority
queue storage 703, routing this identification signal to the
channel assigning sequence block 440-446, as before. If there are
no stations awaiting assignment in the nonpriority queue, the
system returns to it quiescent state.
The third source for an interrupt signal is from a real time clock
720. In this mode, gate 410 passes the interrupt signal down a
third logic path B, which is more fully described with reference to
FIG. 7.
The real time clock 720 generates an interrupt signal every 100
milliseconds. This signal activates a sequencing block 470 which
address the priority status storage 705 and increments each call
group in the storage 705 by one time unit. It should be recalled
that the discussion of block 440 in FIG. 6 indicated that each time
a member of a call group requested a channel, the time increment
corresponding to that group in the priority status storage is
returned to zero. At each clock interrupt interval, the priority
status storage 705 is updated as to the number of time increments
occurring since a member of a call group last requested an
information channel. The total time increment since the last
channel request of each call group is compared with a maximum,
typically one to two seconds, in gate 472.
If the time interval of a group exceeds the allowed maximum gate
472 activates logic block 474 which addresses the priority storage
705 and deletes the instant call group from storage. Thereafter a
gate 476 determines whether each call group in the priority status
storage 705 has been sequenced. If they have, the system is
returned to the quiescent state. However, if there are remaining
elements in storage to be sequenced, gate 476 activates block 478
which feeds back to block 470 thus sequencing to the next storage
call group. Should a particular call group have a time increment
less than the maximum, gate 472 directly activates the sequence
gate 476.
In certain applications it may be desirable to remove call groups
from the priority status once their communication has accumulated a
particular number of transmissions. A logic sequence very similar
to that shown in FIG. 7 could be provided which would count each
transmission of a call group, comparing the total count of each
group with a maximum. If the transmission count of a particular
call group was greater than the maximum, this group would be
removed from priority storage.
In summary, a multichannel dispatch communication system has been
described which assigns a priority queue to requesting stations
awaiting channel assignment, and which provides automatic
transmission trunking whereby maximum utility is gained from the
limited number of available channels.
While a preferred embodiment of the invention has been described in
detail, it should be understood that many modifications and
variations are possible, all of which fall within the true spirit
and scope of the invention.
For example, in high density user areas of plurality of signalling
channels might be required to provide adequate system flow.
In addition, some applications might require more than two priority
queues, a requirement for which the instant system may be easily
adopted.
* * * * *