Note: Descriptions are shown in the official language in which they were submitted.
13~6~
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TRUNKED RADIO REPEATER SYSTEM
This is a division of Canadian Serial Number
616,065 filed May 9, 1991.
This invention is generally directed to the art
of trunked radio repeater systems. It is more
particularly directed to such systems using digital
control signals transmitted over a dedicated control
channel while also using plural working channels which
are assigned temporarily for use by individual radio
units.
The trunking of radio repeaters is well-known.
Early trunking systems used analog control signals
while some more recent systems have utilized digital
control signals. Control signals have been utilized
on a dedicated control channel and/or on different
ones of the working channels for various different
reasons and effects. A non-exhaustive but somewhat
representative sampling of prior art publications and
patents describing typical prior art trunked radio
repeater systems is identified below:
U.S. Patent No. 3,292,178 - Magnuski (1966)
U.S. Patent No. 3,458,664 - Adlhoch et al (1969)
U.S. Patent No. 3,571,519 - Tsimbidis (1971)
U.S. Patent No. 3,696,210 - Peterson et al (1972)
U.S. Patent No. 3,906,166 - Cooper et al (1975)
U.S. Patent No. 3,936,616 - DiGianfilippo (1976)
U.S. Patent No. 3,970,801 - Ross et al (1976)
U.S. Patent No. 4,001,693 - Stackhouse et al (1977)
U.S. Patent No. 4,010,327 - Kobrinetz et al (1977)
U.S. Patent No. 4,012,597 - Lynk, Jr. et al (1977)
U.S. Patent No. 4,022,973 - Stackhouse et al (1977)
1336920
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U.S. Patent No. 4,027,243 - Stackhouse et al (1977)
U.S. Patent No. 4,029,901 - Campbell (1977)
U.S. Patent No. 4,128,740 - Graziano (1978)
U.S. Patent No. 4,131,849 - Freeburg et al (1978)
U.S. Patent No. 4,184,118 - CAnn~lte et al (1980)
U.S. Patent No. 4,231,114 - Dolikian (1980)
U.S. Patent No. 4,309,772 - Kloker et al (1982)
U.S. Patent No. 4,312,070 - Coombes et al (1982)
U.S. Patent No. 4,312,0i4 - Pautler et al (1982)
U.S. Patent No. 4,326,264 - Cohen et al (1982)
U.S. Patent No. 4,339,823 - Predina et al (1982)
U.S. Patent No. 4,347,625 - Williams (1982)
U.S. Patent No. 4,360,927 - Bowen et al (1982)
U.S. Patent No. 4,400,585 - Kamen et al (1982)
U.S. Patent No. 4,409,687 - Berti et al (1983)
U.S. Patent No. 4,430,742 - Milleker et al (1984)
U.S. Patent No. 4,430,755 - Nadir et al (1984)
U.S. Patent No. 4,433,256 - Dolikian (1984)
U.S. Patent No. 4,450,573 - Noble (1984)
U.S. Patent No. 4,485,486 - Webb et al (1984)
U.S. Patent No. 4,578,815 - Persinotti (1985)
Bowen et al is one example of prior art switched
channel repeater systems which avoid using a dedicated
control channel -- in part by providing a handshake
with the repeater site controller on a seized "idle"
working channel before communication with the called
unit(s) is permitted to proceed.
There are many actual and potential applications
for trunked radio repeater systems. However, one of
the more important applications is for public service
1336920
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trunked (PST) systems. For example, one metropolitan
area may advantageously utilize a single system of
trunked radio repeaters to provide efficient radio
communications between individual radio units within
many different agencies. Each agency may, in turn,
achieve efficient communication between individual
units of different fleets or sub-units (e.g., the
police department may have a need to provide efficient
communications between different units of its squad
car force, different portable units assigned to foot
patrolmen, different units of detectives or narcotics
agents and the like). Sometimes it may be important
to communicate simultaneously to predefined groups of
units (e.g., all units, all the squad cars, all of the
foot patrolmen, etc.). At the same time, other
agencies (e.g., the fire department, the
transportation department, the water department, the
emergency/rescue services, etc.) may be in need of
similar communication services. As is well-known to
those familiar with trunking theory, a relatively
small number of radio repeaters can efficiently
service all of these needs within a given geographic
area if they are trunked (i.e., shared on an
"as-needed" basis between all potential units).
This invention also is especially adapted for
special mobile radio (SMR) trunked users. Here, an
entrepreneur may provide a trunked radio repeater
system at one or more sites within a given geographic
area and then sell air time to many different
independent businesses or other entities having the
need to provide efficient radio communication between
13~92~
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individual units of their particular organization. In
many respects, the requirements of an SMR user are
similar to those of a PST user.
In fact, the potential advantages of trunked
radio repeater systems for public services is so well
recognized that an organization known as the
Association of Public-Safety Communications Officers,
Inc. (formerly the Association of Police
Communications Officers) (APCO) has developed a set of
highly desirable features for such a system commonly
known as the "APCO-16 Requirements." A complete
listing and explanation of such requirements may be
found in available publications known to those in the
art.
one of the APCO-16TM requirements is that any
user must have voice channel access within one-half
second after engaging a push-to-talk (PTT) switch.
This same requirement must especially be met in
emergency situations -- and that implies that the
system must be able to actively drop lower priority
users also within a very short time frame. And, of
course, the ability to quickly and efficiently drop
channel assignments as soon as channel usage is
terminated is also important for efficient usage of
the trunked facility even in non-emergency situations.
Prior trunked radio systems have attempted to
more or less "just meet" such APCO-16 requirements of
timeliness. For example, published specifications of
one such prior system indicates an ability to achieve
channel update (in a 19 channel system) within 450
~ 1 3 3 6 9 2RMR 6 2 6A
milliseconds and channel drops within 500 milliseconds.
To achieve this, it utilizes 3,600 bits per second (bps)
digital signalling over a dedicated digital control
channel. Unfortunately, although theoretically the
APC0-16 requirements of timeliness should be met by such
a prior system, in reality, the APCO-16 timeliness
requirements are often not met -- or, are met only at
the expense of suffering with the obviously adverse
effects of somewhat unreliable digital control
signalling (which are, at best, annoying even in
non-emergency situations). Accordingly, there is
considerable room for improvement.
The present invention provides substantial
improvements -- both in timeliness and in reliability
of critical control signalling in a digitally trunked
radio system of this general type. To begin with, a
much higher digital signalling rate (9600 bps) is
utilized. However, rather than using all of the
increased signalling rate to provide a 9600/3600 = 2 . 67
improvement factor in timeliness, a large portion of
the increased signalling rate capacity is utilized to
improve signalling reliability. Accordingly, the
increased timeliness of 19 channel updating capability,
for example, is improved by a factor of approximately
1.58 (e.g., 285 milliseconds versus 450 milliseconds)
while the rest of the increased signalling capacity is
utilized to increase the reliability of control
signalling. At the same time, virtually all of the
increased signalling capacity is utilized to improve
the timeliness of channel drop ability (e.g., 190
milliseconds versus 500 milliseconds).
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As previously demonstrated by Bell System
Technical Journal articles on the AMPS system (e.g.
"Voice and Data Transmission", by Arredondo et al, The
Bell System Technical Journal, Vol. 58, No. 1, January
1979, pp g7 - 122), digital data rates on radio
channels should be either very low (e.g., 200 hertz) or
as high as the channel bandwidth permits. The present
invention utilizes the maximum high speed data rates
(e.g., 9600 bps on the typical 25 KHz bandwidth radio
channel) for critical control channel signalling and
control signalling on the working channels both
immediately before and ; mm^~ iately after the user
communication interval. In addition, sub-audible
low-speed digital data is also utilized on the working
channel during user communications so as to assure
additional signalling reliability -- and to also permit
implementation of additional features.
In the exemplary embodiment, all channels (the
control as well as working channels) are fully duplexed
so that there may be simultaneous in-bound and
out-bound signalling on all channels. In general, this
invention achieves reliable and prompt communication
within a trunked radio repeater system having a digital
control channel and plural working channels, which
working channels are assigned for temporary use by
individual radio units as specified by digital control
signals on the control channel.
Channel assignment is initially requested by a
calling radio unit passing digital request signals to a
control site over the active control channel. In
~ 133692~ ~ 7 - - 45MR-626A
accordance with channel availability, a controller at
the central site assigns a specific then-available
working channel to the requested communication and
passes digital assignment signals out-bound over the
control channel. Both the calling radio unit and the
called unit(s) detect the working channel assignment
and switch their transmitter and receiver operations
over to the proper working channel. Thereafter,
digital hAn~hAke signals are again exchanged between
the control site and at least one of the radio units
(e.g., the calling unit) over the assigned working
channel. In response to a successful handshake on the
assigned working channel, the central site then
transmits digital release signals over the assigned
working channel so as to release the appropriate units
for communication thereover.
As one technique for increasing reliability, the
initial request signals may include three-fold data
redundancy (at least for critical data) while the
channel assignment signals subsequently transmitted
over the control channel may include as much as six
fold redundancy of data (e.g., at least of critical
data such as that representing the called party and the
assigned channel). The handshake signals subsequently
exchanged on the assigned working channel may also
include three-fold data redundancy of at least critical
data. In this manner, some of the increased signalling
capacity made available by the high-speed data rate
(e.g., 9600 bps) is sacrificed in favor of more
reliable channel allocation and communication functions
133~920
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-- while still comfortably exceeding all APCo-16
requirements.
To insure responsiveness to higher priority calls,
sub-audible digital channel assignment update messages
are also transmitted over the assigned working channel.
These are monitored in each unit then residing on the
working channels. Accordingly, if a higher priority
call is directed to some unit already engaged in a
communication, that unit is enabled to promptly switch
operations to a new assigned working channel so as to
immediately receive the higher priority call.
In addition, to accommodate late entry of called
parties to an ongoing communication, digital channel
assignment "late entry" messages continue to be
transmitted on the control channel even after a
successful channel assignment process has been effected
so that late entrants (e.g., those just turning on
their radio, just passing out of a tunnel or from
behind a building or otherwise back into radio
communication after temporary interruption, completion
of a higher or equal priority call, etc.) may
nevertheless be switched onto the proper assigned
working channel as soon as possible. (The late entry
feature, per se, is related to commonly assigned U.S.
Patent No. 4,649,567, issued March 10, 1987 to
Childress.)
To effect prompt and reliable termination of
channel assignments, when the PTT switch of a calling
unit is released, it sends a digital unkeyed message on
1~3~92~
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the assigned working channel and, in response to
reception of this unkeyed message at the control site,
a digital drop signal is transmitted over the assigned
working channel so as to immediately drop all units
therefrom and thus free that working channel for
reassignment. (As will be appreciated, a given radio
unit will automatically revert to monitoring the
control channel upon dropping from an assigned working
channel.)
The system of this invention is sometimes termed a
"digitally" trunked system because trunking control is
effected by digital signals passed over a continuously
dedicated "control" data channel. All units are
programmed so as to automatically revert to the
predetermined primary control channel upon being turned
on or being reset. If the expected control channel
data format is not there discovered, then alternate
possible control channels are successively monitored in
a predetermined sequence until an active control
channel is discovered. In this manner, the usual
control channel apparatus at the central control site
may be temporarily removed from service (e.g., for
maintenance purposes). This same feature also permits
continued trunked system operation in the event that
the regular control channel unexpectedly malfunctions
or is otherwise taken out of service.
The exemplary embodiment of this invention is
designed in such a way that it meets and, in many
areas, surpasses all of the existing APCO-16
requirements. It may also support available voice
1336920
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encryption techniques, mobile digital data terminals
(digital data may be p~Cse~ in lieu of analog voice data
during a trunked radio communication session) and/or
available automatic vehicular location systems.
Preferably, a fault tolerant architecture is used [see
CAn~;An Application Serial No. 566,663 filed May 12, 1988
- Childress et al] so as to maintain trunked system
operation even if the central proc~Ccor happens to fail at
the control site. If digital data is to be communicated
between radio units and/or the central site, then it may be
processed through the system in a manner similar to analog
voice signals. In particular, such digital data
co~ nication will be carried out at a rate accommodated
within the existing audio pass band and will be trunked
just like desired voice communications (i.e., no dedicated
digital data communication ch~n~ are required). To help
increase reliability of digital data communications, data
transmissions (and analog voice transmissions, as well )
may be voted in voting systems employing satellite
receivers connected to the central control site.
In the exemplary embodiment, digital control
signalling messages of the following types are utilized:
Channel TyPe Direction Rate
Control Channel INBOUND 9600 pbs
- Group Call
- Special Call
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45MR-626A
-Status
-Status Request/Page
-Emergency Alert/Group Call
-Individual Call
-Cancel Dynamic Regroup
-Dynamic Regroup - Forced Select
-Dynamic Regroup - Option Deselect
-Dynamic Regroup - Option Select
-Login/Dynamic Regroup Acknowledge
-Logical ID Request
-Programming Request
OUTBOUND 9600 bps
-Channel Assignment
-Channel Update
-Enable/Disable Unit
-Dynamic Regroup
-Preconfiguration
-Alias ID
-Unit Keyed/Unkeyed
-Emergency Channel Assignment
-Cancel Dynamic Regroup
-Dynamic Regroup - Forced Select
-Dynamic Regroup - Optional Select
-Dynamic Regroup - Optional Select
-Assign Group ID an Alias ID
-Assign Logical ID an Alias ID
-Status Acknowledge/Page
-Time Mark
-Emergency Channel Update
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-Site ID
-System Operationa Made
-Site Status
-Logical ID Assignment
-Programming Channel Assignment
Working Channel INBOUND 9600 bps
-Initial Handshake
-Special Call Signalling
-Unit ID-PTT and Reverse PTT
-Miscellaneous
OUTBOUND 01600 bps
-Initial handshake
-Channel Drop
-Status Messages
INBOUND Low Speed
-Confirm Unit PTT
OUTBOUND Low Speed
-Priority Scan
-Falsing Prevention
Some of the general features of the exemplary
embodiment and expected benefits are summarized below:
FEATURE BENEFIT
VERY SHORT AVERAGE Practically instantaneous
CHANNEL ACCESS TIME access doesn't cut off
syllables.
Normal Signal Strength Provides operation which
Areas: 280 Milliseconds is faster than most coded
Weak Signal Areas (12dB squelch systems.
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Sinad: 500 Milliseconds
LATE BNTRY Minimizes missed
Should a mobile turn on conversations, keeps
during the period in which police up to the minute,
its group is involved in a minimizes call backs.
conversation, the mobile
will automatically be
directed to join that
conversation.
AUTOMATIC CHANNEL SWITCHING Frequency coordination of
Mobiles, portables, control the fleets and subfleets
stations, and consoles requires no action on the
automatically switch to the part of any field
appropriate channel. personnel.
HIGH SPEED CALL PROCESSING Dedicated control channel
Processor assigns unit provides more rapid
initiating the call, and all channel assignments on
called units, to an larger systems. System
appropriate working channel. size does not impact upon
Initial channel assignment channel acquisition time.
communication between site Control channel is
controller and radio units available for additional
occurs on the control functions such as status
channel. and unit ID.
CALL RETRY Eliminates the need for
Calling unit will repetitive PTT operations
automatically repeat its by the operator in weak
request up to eight times signal situations.
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if no response is received. Terminating retries also
Retries terminated upon system shortens the signalling
response. time.
UNIT DISABLE In hostage situations,
Trunked units can be these units can be
disabled on an individual assigned to a special
basis. These disabled units group for communication
continue to monitor the with the criminals. Also,
control channel and can be with automatic vehicular
polled to determine their location, these units
status. could be tracked for
apprehension.
SUPPLEMENTARY CONTROL Provides user and system
CHANNEL FUNCTIONALITY operator with system
In addition to providing manager features not
channel assignments, the available on other types
control channel is used for: of systems.
status messages, polling,
system status, logging, late
entry, dynamic regrouping,
system testing and other
system functions.
GROUP PRIVACY Each group has the same
Each group hears only his privacy as having their
own group, unless own channel with the
specifically programmed additional benefits of
otherwise. Dispatcher can being regrouped with
override for individual other complementing
1336920
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units or groups of mobiles functions for emergency
at any time. operations.
CALL ~u~u l~G Maintains orderly entry
When all channels are busy, procedure for busy system.
call requests will be queued Call requests are accepted
until a channel becomes in the order they are
available. Unit requesting received except higher
a channel will be notified priority users go to the
to prevent call backs. head of the line.
Members of groups already in
the queue will not be
reentered in the queue.
DATA COMMUNICATIONS This feature greatly
System has the optional enhances the value of the
capability of using 9600 bps system because it avoids
data on the working the expense of additional
channels. Data RF channels.
communications will take
place on any equipped
working channel and they are
trunked, just as voice
communication.
VOICE ENCRYPTION Voice encryption offers
System has the optional the same encrypted range
capability of using as for clear voice
available 9600 baud voice transmissions. Voice can
encryption. (See, e.g. be passed from each site
commonly assigned US through conventional
13~S920
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Patent No. 4,622,680 voice grade phone lines or
issued November 11, 1986 microwave links. Only minor
to Zinser and r~ n modifications are needed to
Application Serial Nos. the base station interface
494,791, filed November 7, equipment to accommodate
1985 - Szczutkowski et al, such sophisticated voice
498,346, filed December security systems.
20, 1985 - Szczutkowski et Any mobile can be upgraded
al and 494,790, filed to this system.
November 7, 1985 - Any mobile can be upgraded
Szczutkowski et al. 'to this capability by adding
an external module. No
internal changes to the
radio are required.
UNIT IDENTIFICATION Each unit on each
All units are transmission is identified
automatically identified by the same ID regardless of
when they transmit. This the agency, fleet or
is true regardless of subfleet in which he is
whether the transmission currently operating. 4095
takes place on the control is more than twice the
channel or on a working logical number of users in a
channel. The system is fully loaded twenty channel
able to accommodate 4095 system so there is more than
discreet addresses sufficient capacity.
independent of fleet and
subfleet.
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TRAFFIC LOGGING Statistics on system
All system information is usage, such as peak
logged. Each unit trans- loading, individual and
mission causes the units ID, group usage versus time,
agency, fleet, subfleet, as well as many other
channel, time, site and list system parameters, are
of sites involved to be available for tabulation
logged for management and analysis.
reports.
TELEPHONE INTERCONNECT All mobiles and portables
Authorized mobiles have the in the system can be
ability to place and receive interconnected to the
calls and patch them to telephone system. Those
individuals or groups of mobiles not specifically
mobiles which may or may not equipped for this can be
be equipped for telephone patched by their
interconnect. dispatcher to maintain
adequate control of system
loading factors.
GROUP PRIORITY ASSIGNMENT System manager can set
Eight priority levels are individual group
provided in the system. priorities according to
Each group (as well as each the criticality of their
individual) is assigned a service.
priority. The flow of traffic is
more easily maintained by
providing recent users
priority over nonrecent
users of the same priority
level.
133~920
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In the exemplary system, 11 bits are available to
determine the address of a unit within an agency, fleet
or subfleet. Twelve bits are available to determine
the individual identity of a particular unit (i.e., its
"logical ID"). The use of 11 bits for determining
group addresses within an agency, fleet or subfleet
provides great flexibility such that each agency may
have many different fleet and subfleet structures.
Furthermore, unit identification is not limited by a
particular fleet and subfleet structure. The 4,096
unit identification codes can be divided among the
subfleets in a manner that best suits a particular
system.
Some features of this exemplary system which are
believed to be particularly unique and advantageous are
summarized briefly below (order of appearance not
reflecting any order of importance -- nor is this list
to be considered in any way exhaustive or limiting):
a) Widening the Retry Window
If a requested working channel assignment is
not achieved, the request is automatically retried
-- and the time window in which such a retry is
attempted is increased in duration as a function
of the number of prior unsuccessful retries. This
significantly decreases the average channel access
time where noise is the real problem rather than
request collisions -- while still providing a
recovery mechanism for request collision problems
as well.
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b) Better Use of Subaudible Siqnallinq
Rather than using subaudible signalling only
to confirm channel assignments, a simple counter
field is employed to greatly simplify such
validity checking functions and to thus free the
majority of the subaudible signalling capacity for
other uses -- e.g., a priority scan. In the
exemplary embodiment a two bit subaudible "count"
field for a given channel is incremented upon each
new working assignment of that channel. Thus, if
a radio unit observes a change in this field, it
is programmed to immediately drop back to the
control channel.
c) Minimizing PrioritY Communique Fraqmentations
by DYnamically Altering Scan Functions
After initiating a priority call, a radio
temporarily (e.g., for two seconds) disables the
usual multiple group scan on the control channel
-- in favor of looking for the highly probable
returned higher priority call. This reduces the
possibility of getting diverted momentarily into
an ongoing lower priority communique -- and also
perhaps missing a fragment of the next higher
priority communique. A similar temporary (e.g.,
two seconds) scan preference (except for priority
calls) for a just-previously involved call group
also helps prevent fragmentation of non-priority
communiques.
- 20 - 1~ ~ 6 9 24~MR-626A
d) Use of Transmission-Trunked Bit in Channel
Assiqnment
The trunking system has two trunking modes:
a) Transmission Trunked Mode in which the
working channel is de-allocated as soon as
the calling unit unkeys, and
b) Message Trunked Mode in which the working
channel is de-allocated "n" seconds following
a unit's unkeying, unless another unit keys
onto the channel within such "n" seconds.
"n" is called the "hang time".
By dynamically insuring that both called and
calling units "know" that a transmission-trunking
mode is in effect, the calling unit may
immediately revert to the control channel upon PTT
release -- thus immediately freeing the working
channel for drop channel signalling from the
control site. The called units can also be
positively prevented from ever transmitting on the
working channel - thus avoiding multiple keying of
radio units on the working channel.
e) Automatic Addressing of Immediately Returned
Calls
Both the called and calling units/groups are
identified in the initial channel assignment
signalling. The called unit captures the calling
133~32~
- 21 - 45~R-626A
unit ID and is enabled to automatically address a return
call to the just calling radio if the PTT switch is
depressed within a predetermined period (e.g., 5 seconds)
after the just completed communique even if the system is
in the Tr~n~;csion Trunked Mode. Not only does this
simplify the nec~cc~ry call back procedures and minimize
access times, by allowing greater application of the
Transmission Trunked Mode it also increases the probability
of successful message ~h~nges -- especially in poor
signalling areas.
f) 9600 bps Permits "Tnose" Sync~ronization
Use of higher rate 9600 bps signalling permits
simplified bit synchronization to be rapidly achieved by
simple "dotting" seguences (i.e., a string of alternating
ones and zeros 101010...). Thus, there is no need to keep
information transfers precisely synchronized across all
chan~els. This not only reduces hardware requirements
system-wide, it also facilitates a more fault tolerant
architecture at the control site.
g) ImProved Channel DroP Siqnalling
The drop channel signalling is simply an extended
dotting sequence. Therefore, each radio may easily
simultaneouslY look for drop channel signalling and channel
assignment confirmations.
13369~0
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This means that the control site may more
immediately consider a given working channel
available for reassignment -- and, if "loaded
up," immediately interrupt the drop-channel
signalling to issue fresh channel assignment
confirmation signals on the working channel
(which each individual radio will ignore unless
properly addressed to it). As a result, a
"loaded" system (i.e., one where existing channel
requests are already queued) may drop a working
channel within about only 100 msec -- and
immediately reassign it to a queued request.
Radios that happen to enter late into the call
being dropped can detect that fact and properly
drop from the channel because of the ability to
simultaneously look for drop channel signalling
and channel assignment confirmation signalling.
h) Feature Programminq
To avoid cumbersome feature programming (and
reprogramming to add features) by factory or
distribution personnel, novel procedures are
employed which safely permit the end user to
perform all such "programming." All units are
programmed at the factory to perform all available
functions. A function enable bit map and a unique
physical ID are together encrypted at the factory
and provided to the user as "Program Codes." When
the user programs each device, its encrypted
"Program Codes" are input to a Radio Programmer
which, in turn, properly sets the feature enable
133~92~
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bit map in a connected radio unit -- and the
decoded physical ID -- and a "Just Programmed"
bit). The "just programmed" radio device logs
into the central controller with a request for a
logical ID -- based on its apparent physical ID.
If illegal copying of function enabling Program
Codes occurs, then the same logical ID will be
assigned -- and the usefulness of the radio
within the trunked repeater system will be
~;~; ni shed.
i) Double Channel Assiqnment Handshake -- One
Beinq on the Assigned Working Channel
A first 9600 bps channel assignment
signalling exchange occurs on the control
channel. However, a confirmation (i.e., a second
handshake) then occurs on the assigned working
channel. Thus, it is assured that the desired
channel has been successfully assigned and locked
onto before the central controller unmutes the
called units on the assigned channel. The
signalling is such that if the channel conditions
are unsuitable for voice, the handshake will
fail, thus terminating the call automatically.
These as well as other objects and advantages of
this invention will be more completely understood and
appreciated by carefully studying the following
detailed description of the presently preferred
exemplary embodiment taken in conjunction with the
accompanying drawings, of which:
1336~20
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FIGURE 1 is a general explanatory diagram of
trunked radio repeater system in accordance with
this invention;
FIGURE 2 is a simplified block diagram of a
central control site (as well as a satellite
receiver site) in the trunked repeater system of
FIGURE l;
FIGURE 3 is a simplified block diagram of the
general site architecture of the main controller for
the central control site;
FIGURE 4 is a simplified block diagram of the
channel architecture used within each channel of the
central site architecture shown in FIGURE 3;
FIGURE 5 is a simplified general block diagram
of a technical mobile/portable radio unit to be
utilized for communication within the trunked
repeater system of FIGURE l;
FIGURE 6 is a simplified flowchart of typical
call processing sequence in the exemplary embodiment
from the perspective of a calling unit;
FIGURE 7 is a simplified flowchart of a call
processing sequence within a called unit;
FIGURE 8 illustrates the trunked channel
dropping procedure and typical required drop times;
.
1336920
-- 25 -- 45MR--626A
FIGURE 9 generally illustrates call
initiation signalling within the exemplary system
as well as typical timing requirements;
FIGURE 10 is a graphical illustration of the
co~ ol signalling protocol utilized to initiate
and tPrrin~te trunked radio communications on
either an individual or group basis in the
exemplary system; and
Figure 11 is a simplified flowchart of
suitable computer programs which might be utilized
at the site controller, the calling unit and the
called unit so as to achieve the signalling
protocol of FIGURE 10.
An exemplary trunked radio repeater system in
accordance with this invention is generally depicted at
FIGURE 1. As illustrated, individual units of various
groups comml~n;cate with each other (both within and
possibly outside of their own group) via shared radio
repeater channels located at a trunked repeater control
site 100. The dispatch console 102 may be housed directly
at the repeater station site 104 or may be remotely located
via other communication facilities 106 as will be
appreciated by those in the art. There also may be
multiple dispatch consoles 102 (e.g., one for each separate
fleet) and a master or supervisory dispatch console for the
entire system as will also be appreciated by those in the
art.
133692~
- 26 - 45MR-626A
The central site is depicted in somewhat more
detail at FIGURE 2 in conjunction with one or more
satellite receiver sites 100-l. As will be
appreciated, the satellite receiver sites are displaced
spatially from the central site 100 such that radio
reception may temporarily be better at one or the other
of the chosen antenna sites. Thus, received signals
from the satellite sites as well as the central sites
are combined in "voter" circuitry so as to choose the
best available signal for control or communication
processes.
At the central site, a transmitting antenna 200
and receiving antenna 202 (which may sometimes be a
common antenna structure) may be utilized with
conventional signal combining/decombining circuits 204,
206 as will be apparent to those in the art. The
transmitting and receiving RE antenna circuitry 200-206
thus individually services a plurality of duplex RF
channel transmit/receive circuits included in a
plurality of RF repeater "stations" 300, 302, 304, 306,
etc. Typically, there may be 20 such stations. Each
station transmitter and receiver circuitry is typically
controlled by a dedicated control shelf CS (e.g., a
microprocessor-based control circuit) as is also
generally depicted in FIGURE 2. Such control shelf
logic circuits associated with each station are, in
turn, controlled by trunking cards TC (e.g., further
microprocessor-based logic control circuits) 400, 402,
404 and 406. All of the trunking cards 400-406
communicate with one another and/or with a primary site
controller 410 via control data bus 412. The primary
~ 133692~
- 27 - 45MR-626A
site controller (and optional backup controllers if
desired) may be a commercially available general
purpose processor (e.g., a PDP 11/73 processor with
18 MHz-Jll chip set). Although the major
"Intelligence" and control capability for the entire
system resides within controller 410, alternate
backup or "fail soft" control functions may also be
incorporated within the trunking cards 400-406 so as
to provide continued trunked repeater service even in
the event that controller 410 malfunctions or is
otherwise taken out of service. (More detail on such
fail soft features may be found in the aforementioned
Canadian Application Serial No. 566,663.
An optional telephone interconnect 414 may also
be provided to the public switched telephone network.
Typically, a system manager terminal, printer, etc.,
416 is also provided for overall system management
and control (together with one or more dispatcher
consoles 102). A special test and alarming facility
418 may also be provided if desired.
The signal "voter" circuits 502, 504, 506 and 508
are connected so as to receive a plurality of input
digital or analog signals and to selectively output
therefrom the strongest and/or otherwise most reliable
one of the input signals. Thus, received signals from
the central site 100 are input to respective ones of
the channel voter circuits 502-508 while additional
similar input signals are generated from receivers in
~3~6~
- 28 - 45MR-626A
the satellite receiver site 100-1 and also input to the
appropriate respective voter circuits. The results of
the voting process are then passed back to the trunking
card circuits 400-406 where they are further processed
as the valid "received" signals.
A slightly more detailed view of the site
architecture for control data communication is shown in
FIGURE 3. kere, the PDP 11/73 controller 410 is seen to
communicate over a 19.2 Kilobit link 412 with up to 25
trunking control cards TC controlling respective duplex
repeater circuits in those individual channels.
Another high-speed 19.2 Kilobit link 420 is used to
communicate with the hardware that supports the down
link to/from the dispatch console 102. Other data
communication with the central processor 410 is via
9600 baud links as shown in FIGURE 3. The central
processor 410 may include, for example, a 128 Kilobyte
code PROM, 1 Megabyte of RAM and 32 DHV-ll/J compatible
RS-232C ports. It may typically be programmed using
micropower Pascal to provide a multi-tasking,
event-driven operating system to manage all of the
various data communication ports on an acceptable real
time basis.
At each controlled repeater channel, the 19.2
Kilobit data bus 412 (as well as that from an optional
back-up controller if desired) is monitored by an 8031
processor in the TC module. The TC trunking control
module exercises control over the control shelf CS of
its associated repeater with audio, signalling, and
control busses as depicted in FIGURE 4, and may
~ 13~6920
- 29 - 45MR-626A
typically also receive hard-wired inputs providing
clock synchronization and a "fail soft" indication
(e.g., indicating that normal control by the central
controller 410 is not available and that an alternate
distributed control algorithm should then be
implemented within each of the trunking control modules
TC).
The general architecture of a suitable
mobile/portable radio unit for use within the exemplary
system is also microprocessor based as depicted in
FIGURB 5. Here, microprocessor 550 is provided with
suitable memory 552 and input/output circuits 554 so as
to interface with the radio unit display, keypad,
push-to-talk (PTT) switch as well as audio circuits 556
which provide basic analog audio outputs to the speaker
and accept analog audio inputs from the microphone.
Auxiliary control over a modem 558 as a digital
interface (e.g., to voice encryption, vehicle location
or other types of digital communication subsystems) may
also be provided if desired. And, of course, the I/O
circuits 554 also permit suitable programmed control
over RF receiver 560 and transmitter 562 which, via
conventional signal combiners 564 permit two-way fully
duplexed communication over a common antenna 566 as
will be appreciated by those in the art.
A detailed and indepth description of all units
and sub-units of such a sophisticated system would
necessarily be extremely voluminous and complex.
However, since those in this art are already generally
familiar with digitally controlled trunked repeater
1336920
- 30 - 45MR-626A
systems with suitable RF transmitter and receiver
circuits, programmed general purpose computer
controllers, etc., no such exorbitantly detailed
description is believed necessary. Instead, it would
only serve to obscure the subject matter which
constitutes the invention. Accordingly, the remainder
of this description will concentrate on the signalling
protocol utilized to initiate and terminate calls
within the system since this is believed to constitute
a significant improvement (both in reliability and
speed) -- while still facilitating the retention of
many highly desirable system features and meeting or
exceeding all APCO-16 requirements.
Call placement begins by the calling unit
transmitting a special digital channel request signal
on the dedicated control channel to the central site.
In return, the central site transmits, outbound on the
control channel, a special digital channel assignment
signal. The calling unit then responds by switching
immediately to the assigned working channel where the
central site now sends an assignment confirmation
message (also in high-speed digital form). If the
calling unit properly receives the confirming signals
on the working channel, then it responds with an
acknowledgment back to the central site on the working
channel to complete the second handshake (i.e., the
first one was on the control channel and now one has
taken place on the working channel) before the central
site releases the called units to began the requested
communication session on the working channel.
Alternatively, if during this process the calling unit
1336920
- - 31 - 45MR-626A
receives a chAnnel update message on the control channel
addressed to it, then the ch~nn~l request call is
temporarily suspended (unless the channel request under way
is an emergency or higher priority request) and the calling
unit then reverts to the called state so as to receive the
incoming call. If the calling unit receives no response
(or an improperly completed response h~n~ch~ke sequence),
it automatically waits a random period before retrying to
sllccescfully place the call request (up to ma~ of 8
tries).
The called unit initially resides in a standby
configuration where it continually monitors the digital
messages appearing on the ~ L~ol ~h~nnel outbound from the
central site. If it detects a ch~nn~l assignment message
addressed to it as the called party (or perhaps as one
party of a called group), then the called unit immediately
switches its operations onto the assigned working channel.
There, it also detects the confirmation signals outbound on
the working channel from the central site and, if
successfully confirmed, awaits a release or unsquelching
signal on the working channel (e.g., transmitted from the
central site in response to sllcc~ccful completion of a
han~ch~ke with the calling unit on the working channel).
The called unit may also receive a channel update message
indicating that the group is already operating on a working
channel.
The programming for a calling unit is generally
depicted in the simplified flowchart of FIGURE 6.
Here, upon entry into the calling mode, a call request
133692~
- 32 - 45MR-626A
is sent on the control channel CC at step 600. A test
is made at 602 for call queuing. If queued, transfer
is made to wait loop 603 (including a test for a
detected assignment at step 604 followed by a check for
expiration of a 30 second timer at 606 (whereupon
control effectively is passed back to a manual
requirement to restart the calling process via exit
607).
If the call request is not queued, then a test is
made at 608 to see if this particular unit has already
previously been requested as a called party. If so,
then transfer is made at 610 to the called mode of
operation. If not, then a check for a returning
channel assignment is made at 612. If not received at
the expected time, then a random wait is interposed at
614 before a test is made at 616 to see if eight tries
have yet been made to complete this particular call.
If so, then the subroutine is exited at 618. If not,
then the subroutine is re-entered at 600.
If a channel assignment is successfully detected
at either 612 or 604, then the unit operation is
immediately switched to the assigned working channel at
step 620 and a test for the second successful handshake
(confirmed signalling) is made at 622. If
unsuccessfully confirmed on the working channel, then
exit will be made and the call is terminated. However,
if the second handshake (e.g., the handshake on a
working channel) is successfully confirmed and
completed, then the calling unit transmits an elongated
sequence of dotting at 624 (e.g., representing the
133692(3 45MR-626A
successful second handshake) followed by a transmission
of voice at 626 (or data if a digital communication
session has been requested) over the assigned working
channel before exit from the subroutine is taken at 628
(e.g., to a standard monitoring routine which looks for
release of the PTT switch and transmits an unkeyed
signal at 627).
The protocol followed by a called unit is
generally depicted at FIGURE 7 (e.g., representing a
suitable computer program for controlling the unit in
this mode of operation).
Upon entry, the control channel is simply
monitored at 700 for any "good" message (e.g., one
addressed to this particular unit). If such a message
is detected, a check is made at 702 for an "update"
type of message. If the message is of this type, then
a check is made at 704 to see if it is repeated within
about 1.0 seconds. If not, then reentry into the
called mode is made. However, if the update of a
higher priority incoming call is repeated within such
period, then an immediate switch to the there-assigned
working channel is made at 706. If signalling is not
confirmed at 707, then an immediate switch to
unsquelching (716) is made and that channel is
thereafter monitored. If, on the other hand,
signalling confirmation at 707 is achieved, it is an
indication that normal channel assignment is, in
reality, taking place and control is passed to block
714 to look for an unmute message.
~ 1336~2~
_ 34 _ 45MR-626A
If no channel update message is detected at 702,
then the message is checked to see if it was a channel
assignment at 708. If not, then return is made to the
beginning of the subroutine. However, if a proper
channel assignment has been received, then a switch to
the assigned working channel is made at 710 and a check
for proper confirmation signalling on the working
channel is then made at 712. If a proper unmuting
message is thereafter also received on that assigned
working channel at 714, then the called unit
unsquelches at 716. If no unmuting message is received
at 714, then a check for a drop message is made at 718.
If there is no drop message but high-speed signalling
is still present on the working channel (as detected by
720), then a further check is made for the unmute
message at 714. However, if there is no drop message
and the high-speed signalling has ceased at 720, then
the called unit is nevertheless unsquelched at 716.
At the conclusion of a desired audio call, the
calling radio transmitter transmits a special release
PTT signal as depicted graphically in FIGURE 8. After a
suitable transmission and detection delay period, the
assigned working channel responds by transmitting a
drop channel signal on the working channel. As shown
in FIGURE 8, this results in a typical working channel
availability in only 167 milliseconds after the release
PTT signal is initiated.
Typical timing of calling protocol signals is
depicted graphically in FIGURE 9 where it can be seen
that typical calling protocol can be completed and
1336920
-- 35 -- 45MR--626A
communication begun over the desired working channel
within about 290 milliseconds.
Some bit-level maps of some relevant message
formats (and other related signalling formats and
protocol) are graphically illustrated at FIGURE 10.
The control channel transmits an outbound continuous
transmission repeating the format 800 depicted in
FIGURE 10. As will be seen, each 40 bit message is
transmitted three times (including one inverted
transmission where all O's are changed to l's and vice
versa) and there are two such messages transmitted per
recurring message time "slot." As will be appreciated,
the optional dotting prefix (if used) insures continued
bit synchronization by receiving units and the unique
Barker code permits frame synchronization so as to
define bit boundaries between the 40 bit-level messages
which follow. Since the control channel transmits
these message slots continuously, no dotting prefix is
needed and but one transmission of the word framing
Barker code will suffice for each recurrent
transmission cycle. of course, if desired, a
relatively short dotting prefix may be used to even
further insure continued bit synchronization.
Inbound messages on the control channel CC are of
the format 802 shown in FIGURE 10 and may comprise, for
example, group/individual channel assignment requests
transmitted from a calling unit. Here, the dotting
prefix is considerably longer and the word framing
Barker code is repeated three times so as to insure
that the receiving circuits at the central site are
1 3 3 ~
- 36 - 45MR-626A
properly synchronized before the 40 bit messages (again
with three-fold redundancy) are transmitted.
Preferably, suitable transmission timing circuits are
utilized so as to make such incoming control channel
messages synchronously time "slotted" -- meaning that
the messages on the inbound portion of the control
channel occur during the same time slot as outgoing
messages from the central site on the control channel
(as generally indicated by dotted lines in FIGURE 10).
A group call request message format is shown in
expanded scale in FIGURE 10. It includes a two-bit
message type (MT) code (the message-type field may be
extended in a tree-logic fashion to include additional
bits as will be appreciated). This MT-A field thus
distinguishes a group call from an individual call, for
example. A type of communications field comprising
two-bits indicates the type of communication session
being requested. (If desired, a priority field of
one-bit also may be used to indicate if a highest
priority emergency call is being requested.) The called
identification code of 11 bits (representing either a
group or an individual unit) is followed by a 12-bit
field representing the identity of the calling unit
("logical ID"). The 40-bit message concludes with 12
bits of standard BCH code for error detection and
correction purposes as will be appreciated.
The returning channel assignment message actually
comprises a two message pair also having a format as
shown in expanded scale at FIGURE 10. The first two
bits identify the message type (MT) and the next two
133~0
- 37 - 45MR-626A
bits identify the type of communication session which
is to take place. The identity of the calling unit is
next represented by a six-digit field (e.g., with the 6
most significant bits being transmitted in one message
of the two-message pair while the 6 lowest significant
bits are transmitted in the other of such messages).
The next one-bit field identifies whether a group call
or an individual call is involved and the assigned
working channel is identified by the following 5 bits.
The group or individual identity of the called unit(s)
is contained within the next 12 bits followed by 12
bits of BCH errcr detection/correction code.
Once operation reverts to the assigned working
channel, the central site transmits a confirmation
message of format 804 outbound on the working channel.
As will be observed, it is of the same general form as
the continuous transmissions on the control channel CC
except that the message length has been reduced to 32
bits on the working channel. Once again, the message
is sent with three-fold redundancy (one being
inverted). Preferably, the confirmation message is
timed in the working channel so as to be within the
same time slot as messages being transmitted on the
control channel. The format of the 32 bit confirmation
message is also depicted in expanded form at 806 in
FIGURE 10. Here, 4 bits are devoted to the message
type code while 2 additional bits provide a subaudible
frame count useful in framing and otherwise decoding
the lower speed subaudible digital data (which will
subsequently appear on the working channel to be
monitored by units residing thereat). One bit is also
1336920
- 38 - 45MR-626A
devoted to identifying the communication session as one
which is transmission trunked or one which is message
trunked. Another bit of the confirmation message 806
identifies the call as being either of a group or an
individual unit while the identity of the called group
or individual unit is contained within the following 12
bits. The confirmation message 806 concludes with 12
bits of BCH error detection/correction code.
Once the second handshake (i.e., on the working
channel) has been successfully concluded, the calling
unit transmits 384 bits of dotting followed by audio
(in the case of a requested audio communication
session) as is also depicted at FIGURE 10.
The elongated dotted sequence transmitted by the
calling unit on the working channel constitutes an
acknowledgment of the successful handshake sequence
and, in response, the central site transmits an
outbound digital message on the working channel to
positively unmute the called unit(s). The format 808
of such an unmute message is depicted in FIGURE 10.
Once again, the message type code uses the first four
bits while a subaudible frame count constitutes the
next two bits. The next bit denotes trunked status or
non-trunked status (e.g., regular hang-time) while the
next bit is effectively unused (e.g., preset to zero in
all unmute messages) -- but which may be used for other
optional purposes. The identity of the unit(s) to be
unmuted is set forth in the next 12 bits followed by 12
bits of standard BCH error detection/correction code.
1336920
..
- 39 - 45MR-626A
At the conclusion of a communication session on
the working channel, the calling unit again transmits
384 bits of dotting followed by 4 data blocks of 128
bits each. Each such data block includes 16 dotting
bits and a 16 bit Barker code (some of which bits may
be "filler" as will be appreciated) as prefix followed
by 8-bit bytes, each of which is transmitted with
three-fold redundancy (one inverted) -- thus
constituting a 32-bit message characteristic of digital
messages being transmitted on the working channel. The
format of the 32-bit unkey message 810 is also shown in
FIGURE 10. Here, a 4-bit message type code is followed
by 2 unused bits and 2 bits for a block count. The
identity of the calling unit is set forth in the next
12 bits followed by 12 bits of stAn~rd BCH error
detection/correction code.
Finally, in response to receipt of the unkey
message at the central site on the working channel, an
outbound digital message on the working channel of a
super-extended dotting sequence (e.g., 896 to 2816
bits) is transmitted from the central site as depicted
at 812 in FIGURE 10 -- and in response, all units then
on that channel drop from that particular working
channel and revert to the active control channel.
The sequence of programmed events occurring at the
site controller, the calling unit and the called
unit(s) during a typical call origination/termination
sequence is depicted in the parallel flowcharts of
FIGURE 11.
1336920
- 40 - ~ 45MR-626A
Each programmed unit has a quiescent control
channel (CC) monitor routine where, in a quiescent
state, all units and the site controller reside. When
the calling unit enters the calling subroutine from the
CC monitor at 1100, a test is made at 1102 to see if
this calling attempt is a retry. If not, the retry
counter is set to a maximum content of 8 at 1106 and
then decremented by one at 1108 (which step is directly
taken from test 1102 if a retry is in progress). If
the retry counter has been decremented to zero as
tested at 1110, then a failed acquisition audible beep
is generated at 1112 and exit is taken back to the CC
monitor. On the other hand, if the maximum number of
retries have not yet been made, then a channel
assignment request is transmitted on the control
channel and slot synchronization at 1114 (e.g., at time
tl) -
Upon detecting an inbound message, the sitecontroller will receive and store tulle channel
assignment request and assign a free working channel at
step 1200. In the exemplary system, a response to an
inbound request may be supplied within a predetermined
delay. The outbound channel assignment messages (i.e.,
a message pair) are transmitted on the control channel
as soon as possible at step 1204 (time t2). The two
message channel assignment pair is then received and
stored from the control channel in the calling unit at
stem 1118 (the unit will look for the messages up to
the maximum number of slots). If either message of the
two message pair is successfully received, this will
suffice. As previously explained, if a channel update
1336920
- 41 - ~ 45MR-626A
is received in the interim, then an exit may be taken
to a called state (assuming that the call request under
way is not an emergency). If a valid channel
assignment message has not been received as tested at
1120 and the maximum number of slots have been
observed, then a suitable delay is loaded at 1122 an
exit is taken back to the CC monitor (from which a
return entry to the calling subroutine will soon be
taken).
The process of loading in a suitable delay before
retrying may be thought of as a progressive "widening"
of the retry window -- in a consciously controlled
manner. There are three reasons why an inbound data
message from a radio would not get a response: (1) the
inbound message was not successfully detected; (2) the
outbound message was not successfully detected; or (3)
a collision occurred (two or more mobiles sent in a
request on the same inbound control channel slot).
Given that a collision has occurred, unless
mobiles randomly retransmit their requests, collisions
will continue to occur. Consequently, when a radio
fails to receive a response to an inbound message, it
waits a "random" period of time to retransmit its
request. However, if case (l) or (2) has occurred,
there is really no reason to randomize the retry.
Unfortunately, the radio cannot determine the cause of
a failed response.
But, the longer a mobile waits to retransmit, the
longer the average access time becomes in poor
1336920
- 42 - 45MR-626A
signalling areas since that is where the majority of
retries take place. Since often it is noise and not
collisions that cause missed responses, randomizing
retries is often wasteful.
To correct this problem, the present invention
takes some corrective action. First, non-channel-
acquisition messages are caused to have a much slower
retry rate than channel request messages. Access time
for the former is not critical (whereas it is for the
latter). So, if a collision occurs between a radio
sending in a non-channel request message and a radio
sending in a channel request message, the former's
retry rate will be slow enough to guarantee no chance
of a collision with the latter on the next retry.
Second, the random retry rate varies with the
retry number. The retry algorithm (for channel
acquisition messages only) widens the width of the
retry window with each succeeding retry. This
decreases the average access time in the presence of
noise but still provides a recovery mechanism should
the cause for a missed response be a collision.
The preferred embodiment uses the following simple
rule:
1st retry 2 slot random variability
2nd retry 4 slot random variability
succeeding retries 8 slot random variability
1~6920
- 43 - 45MR-626A
It also is possible to vary the retry window
width as a function of the received bit error rate in
order to gain still greater efficiency.
If a valid working channel assignment has been
received as tested at 1120, then the calling unit
switches immediately to the assigned working channel
at 1124 and waits to receive a proper confirmation
message on the working channel at 1126 -- which
confirmation message is being transmitted by the site
controller at step 1206 at time t3. If the
confirmation message is overridden by a drop message
as tested at 1128 or by timeout of a preset timer at
1130, then the calling routine is aborted and return
is taken to the CC monitor. On the other hand, if a
proper confirmation message is received at 1126, then
the calling unit begins to transmit 384 bits of
dotting on the working channel at 1132 followed by
voice transmissions (or other desired communication
session) at 1134.
Back at the site controller, a check is made at
1208 for the acknowledgment dotting of extended
duration on the working channel. If it is not
received, then exit is taken. However, if it is
properly received, then two unit-keyed/unmute messages
are transmitted outbound on the working channel at
step 1210.
While all of the above has been taking place, the
called unit has (if everything is working properly)
received and stored the two-message channel assignment
pair from the control channel at time t2 (at
1336920
- 44 - - 45MR-626A
substantially the same time as the calling unit) as
depicted at 1300. (Once again, seeing either message
of the two message pair is sufficient.) In response,
the called unit is also switched to the assigned
working channel at 1302 and has thereafter monitored
the assigned working channel for the proper
confirmation thereon at step 1304 (and at time t3.)
Only if the proper confirmation message has been
received does the called unit then look for and
receive the unmute message transmitted from the site
controller on the working channel at time t5 and, in
responsé, unmutes the receiver of the called unit on
the working channel at 1306.
During the ensuing communication session on the
assigned working channel between the calling and
called unit(s), the site controller (via the TC's)
continues to send subaudible new channel assignment
(and drop) data to all units on all working channels
at 1212 (thus enabling higher priority calls to be
promptly received and accepted by all units). The
site controller (via the proper TC) also continues to
transmit channel update messages periodically on the
control channel at 1214 (e.g., so as to permit late
entrants to immediately go to the proper working
channel). The site controller informs all TC's of the
channel assignments and drops and, in response, each
TC generates suitable subaudible signalling for its
channel.
In existing systems subaudible signalling
typically is used as a validity check by mobiles. When
1336920
~ 45 ~ 45MR-626A
a mobile is on a working chAnn~l it monitors the
subaudible signalling to make sure it belongs on that
~h~n~el. There are at least two reasons why a radio could
get onto a channel where it does not belong:
1) being correctly within a communique on a
working chAnn~l, it fails to see the channel drop; or
2) monitoring the control channel, it
incorrectly d~co~es a message and goes to an
incorrect channel.
Problem (1) is solved by giving a two bit
subaudible count to all radios on the channel. Every time
a call is placed on a chAn~el, the chAn~l TC increments
its count. Consequently, if a radio sees the count
change, it "knows" it missed a ch~nn~l drop sequence.
As for problem (2), there is a sufficiently high
probability of incorrectly decoding outbound control
messages on existing systems that a quick way to redirect
radios from channels where they do not belong is typically
provided. To do this, subaudible signalling typically is
used exclusively for this purpose. However, with this
invention, advantage is taken of the high information rate
on the control channel, and a mobile is required to see an
update message twice before going to a working channel.
There is a negligible increase in the late entry time, but
the probability of going to an incorrect channel is
~33692Q
- 46 - ~ 45MR-626A
virtually eliminated. As a result, subaudible data
can also be used for another purpose... e.g., a
priority scan.
At the conclusion of the desired communications
session, the unkeying of the PTT switch in the calling
unit is detected at 1136 resulting in the sending of
an unkeyed message on the working channel at 1138
(time t6). If in a transmission-trunked mode, the
calling unit may immediately revert to the control
channel -- thus immediately freeing the working
channel In response, at 1216, the site controller
receives the unkeyed message on the working channel
and, at 1218, sends a super elongated dotting string
(896 to 2816 bits on the working channel at time t7).
The called unit has, of course, also received the
unkeyed message on the working channel at time t6 and,
in response, has already muted the receiver at 1308.
The called unit receives the super-elongated dotting
string outbound from the site controller on the
working channel at time t7 and, in response, reverts
to the control channel at 1310.
A special priority scan sequence is used (in the
preferred embodiment) to minimize communique
fragmentation.
When a radio unit scans for multiple groups and a
call is made to its priority group, the radio
automatically disables the multiple group scan (in
favor of a priority group only scan) for a two second
interval upon returning to the control channel. Since
~ 1336920
- 47 - 45MR-626A
the priority group was just communicating, the
probability is high that another communique will take
place within this interval. If the radio immediately
scanned into another (non-priority) group call (which
by definition is of a lower priority), and another
communique then occurs on the priority group, the
radio would hear a communique fragment from a
non-priority group -- and would have its entry into
the next priority group communique delayed (priority
scan typically may take between 1.0 and 1.5 seconds to
get the radio into the priority group).
Another unique feature used to r;n;~;ze
communique fragmentation is a preference priority the
radio automatically assigns to a just-previously
monitored non-priority group. In essence, if a
non-priority communique is monitored, for two seconds
following the communique the radio will ignore all
other scanned calls (except to the priority group of
course)...similarly to priority group communiques. In
addition, the radio always remembers the last
non-priority group monitored. Upon returning from a
priority group communique, the radio will prefer the
last non-priority group monitored over any other
groups being scanned.
In the example below, a '--' means the group is
involved in a communique channel, and it is assumed
that Group A is the priority group and that its
communiques are separated by less than 2 seconds:
1336920
- 48 - 45MR-626A
Group A ---- ---- -- -----
Group B ------- -----------------
Group C -- ---------------------------
Radio
monitors: BBBAAA AAAA AA AA~ BBBB CCCC
There is a bit (i.e., the message/transmission
trunked bit) in the working channel confirmation
signalling that informs the radios as to whether the
communique is transmission-trunked or message-trunked.
This unique feature offers greater frequency
efficiency.
The calling radio will be on the working channel
and is guaranteed to see the message/transmission
trunked bit. If the bit is set to "Transmission
Mode," the calling mobile known the channel will be
removed as soon as it stops transmitting.
Consequently, when its PTT is released, the calling
radio automatically and immediately goes back to the
control channel. This gains channel usage efficiency
because the working channel TC can begin channel drop
signalling as soon as it detects the calling mobile's
unkey message. That is, one does not have to extend
the signalling to make sure the transmitting mobile
finishes transmitting, gets its receiver on channel
and then has plenty of time to be guaranteed that the
channel drop signalling is detected in the calling
mobile.
Radios that are called also look at this
message/transmission trunked bit, but for an entirely
~ 49 _ 13 3 6 9 2 4sMR-626A
different reason. If the communique is message-trunked,
radios that were called must be able to key on the
assigned working channel in case they must offer a
response before the channel drop. However, if the
communique is transmission-trunked, none of the called
radios should ever transmit on the assigned working
channel. Therefor, if the bit is set to "Transmission"
mode, called radios will not be permitted to key on the
working channel. This is a very useful feature since it
prevents radios from keying on top of each other.
The message/transmission trunked bit thus offers
three system advantages: It makes transmission trunking
more frequency (i.e., channel) efficient by decreasing
the channel drop time (by a factor of three from typical
prior systems), it reduces the dead time between
transmission where users can not key (e.g., on typical
existing systems, if a radio is keyed during the .5
second drop sequence it must wait until the sequence is
complete), and it offers absolute protection from radios
keying on top of each other on a working channel.
To make an Individual Call on the exemplary system,
the calling radio uses a single inbound slot of the
control channel to identify itself and to specify the
radio being called. Both radios are referred, via an
outbound control channel message, to an available
working channel where the confirmation signalling takes
place. The unmute message to the called radio (at the
completion of the high speed confirmation signalling)
_ 50 _ 133 692~5MR-626A
also specifies the ID of the calling radio. The called
radio automatically stores the ID of the calling radio
and, if the PTT switch of the called radio is depressed
within 5 seconds of the last PTT release of the calling
station, will automatically place an individual call
back to the original calling. This capability allows
easy user-convenient transmission trunking, and
therefor better frequency (i.e., channel) efficiency,
during individual calls. It also allows the calling
radio to contact a called radio and converse with no
channel hang time even though the called radio is not
previously programmed to initiate a call to the calling
radio.
The signalling in the exemplary embodiment is
extremely efficient, m;n;m;zing the channel drop time
and therefor increasing system efficiency. It is
unique in that, for example, it is high speed
signalling as opposed to low speed typically used on
all other existing systems. In addition, the
signalling is designed specifically for minimizing
message traffic in a distributed architecture site.
Without such novel channel drop signalling, as the
channel starts dropping, a message would have to be
sent from the working channel TC to the control channel
TC (via the site controller) stopping all updates on
the outbound control channel (i.e., those that are
referring radios to the working channel now being
dropped). Once off the air, the channel TC would have
to send an additional message to the site controller
informing it of such so it can reassign the dropped
1336920
- 51 - 45~-~R-626A
working ch~nnel when appropriate. Besides additional
messages within the central site slowing the channel drop
process, such prior t~hn; ques also incur additional
loading on the site controller. Another aspect of the
problem is that the drop channel signalling that is
transmitted on the working ch~nn~l must be of sufficient
duration to guarantee that timing ambiguities don't permit
a radio to enter late onto the channel once it is
down....or even worse to enter late onto the channel after
the next call has already started to take place on that
channel.
The exemplary embodiment uses unique drop channel
signalling, a unique radio signalling detection algorithm
and timing of when the channel TC sends the drop channel
message to the site controller.
By making the drop channel signalling 9600 bps
dotting, not only can the drop ~h~n~el signalling be
detected and muted in radios prior to the radio operator
hearing the signalling, but the detection algorithm places
a light enough processor loading on the radios that they
can simultaneously look for the dotting and for
confirmation signalling.
The following rules are followed by a working
channel TC as it drops:
1) Transmit 100 msec of dotting.
2) Without interrupting the dotting, send a
channel drop message to the site controller.
3) Transmit an additional 200 msec of
-- 1336920
- 52 - 45MR-626A
dotting...BUT... stop it and start sending a
confirmation message should a channel assignment
message be received from the site controller.
The following rules are followed by the site
controller when it receives a drop channel message
from a given channel TC:
1) Immediately inform the control channel TC so
it can stop transmitting updates to the
working channel TC.
2) Consider the channel immediately available
for reassignment.
The following rules are followed by a radio as
it leaves a working channel:
1) For 1/2 second ignore all channel updates to
the group and channel of the communique
being left.
The following rules are followed by a radio as
it arrives on a working channel:
1) Look for dotting (i.e., of sufficiently long
duration to constitute a drop channel
signal) and confirmation signalling
simultaneously.
2) If drop-channel dotting is seen, leave the
channel.
3) If confirmation is seen then leave the
channel if the ID is not correct,
' 1336921~
- 53 - 45 R-626A
otherwise lock onto the signalling and do
not unmute until told to do so.
4) If confirmation signalling stops, or no
signalling is seen on the channel, look for
subaudible and unmute.
To understand the significance of the net effect
of these procedures, consider two cases: (1) when
the channel is not immediately reassigned and (2)
when it is immediately reassigned.
It is only possible for the radio to enter late
onto the drop channel signalling 100 msec following
the point when the drop channel message was sent to
the site controller. So if the channel is not being
reassigned, a late entering radio will see the
additional dotting being transmitted and will know to
drop off the channel. On the other hand, if the
system is loaded (e.g., call requests are queued in
the site controller) the channel immediately gets
assigned to the first group in the queue. A radio
that attempts to enter late into the call just
dropped will see the confirmation message with the
group of the next call starting to take place and
will know to drop off the channel.
The bottom line is that dropping a channel in a
loaded system requires only 100 msec of signalling and
only one message to the site controller. Radios that
happen to enter late into the call being dropped detect
that fact because of the radios ability to look for the
1336920
- 54 - 45MR-626A
drop channel signalling and the confirmation signalling
simultaneously.
For an increase in the radio price, the PST radio
manufacturer may program additional of these "features"
into radios. The typical prior way to do this is to
burn a unique PROM or an EEPROM at the factory. One
disadvantage of this approach in the expense of
uniquely programming each radio before it leaves the
factory -- and it is inefficient to upgrade a radio
should a customer subsequently desire additional
features.
However, the exemplary embodiment permits one to
eliminate factory programming costs. Since each radio
in programmed in the field (e.g., groups, systems,
etc.) by the customer, features should be programmed
into the radio at that time. The problem is how to
control the programming task sufficiently to make sure
the customer only programs purchased features.
Every shipment of radios that goes to a customer
will have a sheet of paper which lists a set of
Programming Codes and Physical IDs (one pair for each
radio). Each Programming Code is an encryption of a
"feature enable bitmap" and the Physical ID of the
radio.
When a customer programs a radio he/she must do
two things. First, he/she programs the radio. To do
this, he/she selects the Programming Code
representative of the features he/she has purchased for
` 55 133 692 045MR_626A
the radio and enters it in the Radio Programmer.
He/she then programs the radio using the Radio
Programmer while the Programming Code prevents him/her
from programming disabled features. Second, the user
enters the radio onto the system database via the
system manager. The radio's Physical ID must be
specified in order to get the radio into the database.
Anytime the Radio Programmer writes data into a
radio, it sets a "Just Programmed" bit inside the
radio's personality. Whenever a radio is turned on, it
checks that bit. If set, the radio will use its
Physical ID to request a Logical ID from the site
controller before allowing its user to communicate on
the trunked system. The site controller will go to the
system manager data base to determine the Logical ID to
be assigned to the radio. Notice that if a customer
tries using the same Programming ID for programming
different radios he/she will end up with the same
Logical ID in each radio which means unique
identification capability is lost. This is the same
consequence suffered if a customer copied the PROM used
in existing systems.
The result is that one has the same level of
protection, -- while avoiding the need to program
radios in the factory. Adding feature$ to a radio
involves issuing an updated Programming ID, ambiguities
in programming radios are eliminated (e.g., in existing
systems a radio could be programmed to do something it
was not enabled to do...so when a customer programs it
and it doesn't work he/she cannot tell whether the
56 1 33 6924@MR_626A
radio is erroneously programmed or the feature is
disabled), and no special software is written in the
mobiles...just the Radio Programmer. This last benefit
is nice since fixing a software bug relative to feature
enable/disable would involve changing code in just a
few computers rather than for all radios in the field.
Detailed descriptions of the signalling protocols
and formats involved in many different types of call
origination sequences are summarized below:
I. Radio Oriqination, Loqical ID Acquisition Se~uence
A. The CC transmits a continuous stream of
control messages which all inactive mobiles receive.
The messages are sent two messages to a 30-msec frame
in the following frame format:
Dotting = 32 bits
Barker = 16 bits (e.g., ll bits Barker code
plus 5 bits dotting preamble)
Message #1 = 40 bits
Message #1 (inverted) = 40 bits
Message #l = 40 bits
Message #2 = 40 bits
Message #2 (inverted) = 40 bits
Message #2 = 40 bits
B. When mobile power is turned on, it receives a
site ID message from the Control Channel (CC) in the
following format:
1336~20
- 57 - 45MR-626A
MT-A = 2 bits (e.g., 11)
MT-B = 3 bits (e.g., 111)
MT-C = 4 bits (e.g.,lllO)
Delay = 2 bits
Channel = 5 bits
Priority = 3 bits
Homesite = 1 bit
Failsoft = 2 bits
Site ID = 6 bits
BCH code = 12 bits
Delay specifies the maximum number of control
channel slots before a control channel responds to an
inbound transmission. Channel specifies the channel
number for the active control channel. Priority
prohibits mobiles with lower priority from transmitting
on the inbound control channel. Home site bit
specifies whether the site ID is the home (=O) or
adjacent (=l) ID.
C. If desired, and if priority allows, mobile
optionally transmits a login request on the control
channel in synchronism with the received control
channel messages. The frame form is as follows:
Dotting = 152 bits
Barker Code (repeated three times) = 48 bits
(including filler)
Message = 40 bits
Message (inverted) = 40 bits
Message = 40 bits
1336920
- 58 - 45MR-626A
The login message is coded an follows:
MT-A = 2 bits
MT-B = 3 bits
Group ID = 11 bits
Logical ID = 12 bits
BCH Code = 12 bits
If the mobile has no logical ID, it will transmit
the logical ID request message The logical ID request
message is coded as follows:
MT-A = 2 bits
MT-B = 3 bits
MT-C = 3 bits
Physical ID = 20 bits
BCH Code = 12 bits
D. The control channel responds with a logical ID
assignment message.
II. Radio Call Sequence - Radio Origination, Group
Call
A. Control channel transmits a continuous stream
of control messages which all inactive mobiles receive.
The messages are sent two messages to a 30-msec frame
that has the following format:
Dotting = 32 bits
Barker = 16 bits
Message #1 = 40 bits
1336920
- 59 - 45MR-626A
Message #1 (inverted) = 40 bits
Message #1 = 40 bits
Message #2 = 40 bits
Message #2 (inverted) = 40 bits
Message #2 = 40 bits
B. Mobile that wishes to originate a group call
transmits a group channel assignment request on the
control channel in synchronism with the received
control channel messages. The frame format is as
follows:
Dotting = 152 bits
Barker (repeated three times) = 48 bits
Message = 40 bits
Message (inverted) = 40 bits
Message = 40 bits
The group call request message is coded as
follows:
MT-A = 2 bits
Type Communications (e.g., voice, data,
interconnect or voice privacy) = 2 bits
Not used = 1 bit
Group ID = 11 bits
Logical ID = 12 bits
BCH Code = 12 bits
C. The control channel responds with a
channel-assignment two-message pair. Coding is as
follows:
~ 1336~20
- 60 - 45MR-626A
MT-A Code = 2 bits
Type Communications (e.g., voice) = 2 bits
1/2 Logical ID = 6 MSBs or LSBs
Group/Logical = 1 bit
Channel = 5 bits
Group ID = 12 bits
BCH Code = 12 bits
D. All mobiles of the called group switch to
assigned working channel and receive a confirmation
message. Slotted working channel messages are
transmitted using the following frame:
Dotting = 32 bits
Barker = 16 bits
Message = 32 bits
Message (inverted) = 32 bits
Message = 32 bits
The group call confirmation message is coded as
follows:
MT Code = 4 bits
Subaudible count = 2 bits
Message/Transmission Trunking = 1 bit
Group/Logical ID = 1 bit
Group ID = 12 bits
BCH Code = 12 bits
E. Originating mobile receives confirmation
message and transmits 384 bits of dotting, then audio.
~ 1336920
- 61 - 45MR-626A
F. Working channel receives dotting and
transmits two unit-keyed/unmute messages.
MT Code = 4 bits
Subaudible count = 2 bits
Message/Transmission Trunking = 1 bit
Filler = 1 bit
Logical ID = 12 bits
BCH Code = 12 bits
Called mobile receives unmute message and
unmutes audio.
G. Active mobiles on other working channels
receive a subaudible channel assignment message.
H. Control channel transmits channel update
message for late entry mobiles.
I. Transmitting mobile unkeys and sends a
non-slotted unkey message. All non-slotted message
formats are:
Dotting = 384 bits
Data Block #3 = 128 bits
Data Block #2 = 128 bits
Data Block #1 = 128 bits
Data Block #0 = 128 bits
Date Block #3, #2, #1 and #0 are identical --
except for a two block count -- (each block is
repeated four times) and each has the following
format:
o 1336920
- 62 - 45MR-626A
Dotting = 16 bits
Barker Code = 16 bits
Byte 1 = 8 bits
Byte 1 (inverted) = 8 bits
Byte 1 = 8 bits
Byte 2 = 8 bits
Byte 2 (inverted) = 8 bits
.
.
Byte 3 = 8 bits
Byte 4 = 8 bits
Byte 4 (inverted) = 8 bits
Byte 4 = 8 bits
The unkey message is coded an follows:
MT Code = 4 bits
Unused = 2 bits
Block Count = 2 bits
Logical ID = 12 bits
BCH Code = 12 bits
J. Working channel transmits 896 to 2816 bits
of dotting to drop all mobiles from the channel.
III. Radio Call Sequence-Radio Origination, Individual
Call
A. Control transmits a continuous stream of
control messages which all inactive mobiles receive.
1336920
- 63 - 45MR-626A
The messages are sent two messages to a 30-msec. frame
that has the following format:
Dotting = 32 bits
Barker = 16 bits
Message #1 = 40 bits
Message #1 (inverted) = 40 bits
Message #1 = 40 bits
Message #2 = 40 bits
Message #2 (inverted) = 40 bits
Message #2 = 40 bits
B. Mobile that wishes to originate an individual
call transmits an assignment request on the control
channel in synchronism with the received control
channel messages. The frame format is as follows:
Dotting = 152 bits
Barker (repeated three times) = 48 bits
Message = 40 bits
Message (inverted) = 40 bits
Message = 40 bits
The individual call request message is coded as
follows:
MT-A Code = 2 bits
Type Communications (e.g., voice) = 2 bits
Logical ID (called) = 12 bits
Logical ID (caller) = 12 bits
BCH Code = 12 bits
~ 1336920
- 64 - 45MR-626A
C. The control channel responds with a
channel-assignment two-message pair. Coding is as
follows:
MT-A Code = 2 bits
Type Communications (e.g., voice) = 2 bits
1/2 Logical ID = 6 MSBs or 6 LSBs
Group/Logical ID = 1 bit
Channel = 5 bits
Logical ID = 12 bits
BCH Code = 12 bits
D. Both calling (last logical ID) and called
mobile switch to assigned working channel and receive
a confirmation message. Slotted working channel
messages are transmitted using the following frame:
Dotting = 32 bits
Barker = 16 bits
Message = 32 bits
Message (inverted) = 32 bits
Message = 32 bits
The individual call confirmation message is coded
as follows:
MT Code = 4 bits
Subaudible Count = 2 bits
Message/Transmission Trunking = 1 bit
Group/Logical ID = 1 bit
Logical ID = 12 bits
BCH Code = 12 bits
133632~
- 65 -- 45MR-626A
E. Originating mobile receives confirmation
message and transmits 384 bits of dotting, then audio.
E. Working channel receives dotting and
transmits two unit-keyed/unmute messages:
MT Code = 4 bits
Subaudible Count = 2 bits
Message/TrA~:r;~sion Trunking = 1 bit
Unused bit = 1 bit
Logical ID = 12 bits
BCH Code = 12 bits
Called mobile receives unmute message and unmutes
audio.
G. Active mobiles on other working channels do
not receive a subaudible channel assignment message.
H. Control channel transmits channel update
message for late entry mobiles.
I. Transmitting mobile unkeys and sends a
non-slotted unkey message. All non-slotted message
formats are:
Dotting = 384 bits
Data #3 = 128 bits
Data #2 = 128 bits
Data #1 = 128 bits
Data #O = 128 bits
~ 1336920
- 66 - 45MR-626A
Data #3, #2, #1, and #O are identical (repeated
four times) and each has the following format:
Dotting = 16 bits
Barker = 16 bits
Byte 1 = 8 bits
Byte 1 (inverted) = 8 bits
Byte 1 = 8 bits
Byte 2 = 8 bits
Byte 2 (inverted) = 8 bits
Byte 3 = 8 bits
Byte 4 = 8 bits
Byte 4 (inverted) = 8 bits
Byte 4 = 8 bits
The unkey message is coded as follows:
MT Code = 4 bits
Unused = 2 bits
Subcount = 2 bits
Logical ID = 12 bits
BCH Code = 12 bits
IV. Radio Call Se~uence-Radio Origination, EmerqencY
Group Call
-
~ 133~92~
- 67 - 45MR-626A
A. Control channel transmits a continuous stream
of control messages which all inactive mobiles receive.
The messages are sent two messages to a 30-msec. frame
that has the following format:
Dotting = 32 bits
Barker = 11 bits
Message #1 = 40 bits
Message #1 (inverted) = 40 bits
Message #1 = 40 bits
Message #2 = 40 bits
Message #2 (inverted) = 40 bits
Message #2 = 40 bits
B. Mobile that wishes to originate an emergency
group call transmits an assignment re~uest on the
control channel in synchronism with the received control
channel messages. The frame format is as follows:
Dotting = 152 bits
Barker (repeated three times) = 48 bits
Message = 40 bits
Message (inverted) = 40 bits
Message = 40 bits
The emergency group call request message is coded
as follows:
MT-A Code = 2 bits
Type communications = 2 bits
Status/C = 1 bit
~ ~336920
- 68 - 45MR-626A
Group ID = 11 bits
Logical ID = 12 bits
BCH Code = 12 bits
C. The control channel responds with two
channel-assignment messages that are coded as follows:
MT-A Code = 2 bits
Type communications = 2 bits
1/2 Logical ID = 6 MSBs or LSBs
Group/Logical ID = 1 bit
Channel = 5 bits
Group ID = 12 bits
BCH Code = 12 bits
D. All mobiles of the called group switch to
assigned working channel and receive a confirmation
message. Slotted working channel message are
transmitted using the following frame:
Dotting = 32 bits
Barker = 16 bits
Message = 32 bits
Message (inverted) = 32 bits
Message = 32 bits
The emergency group call confirmation message is
coded as follows:
MT Code = 4 bits
Subaudible count = 2 bits
Message/Transmission Trunking = 1 bit
~ 1336920
~`
- 69 - 45MR-626A
Group/Logical ID = 1 bit
Group ID = 12 bits
BCH = 12 bits
E. Originating mobile receives confirmation
message and transmits 384-bits of dotting, then audio.
F. Working channel receives dotting and transmits
two unit-keyed/unmute messages.
MT Code = 4 bits
Subaudible Count = 2 bits
Message/Transmission Trunking = 1 bit
1 bit (unused) = O
Logical ID = 12 bits
BCH Code = 12 bits
Called mobile receives unmute message and unmutes
audio.
G. Active Mobiles on other working channels
receive subaudible channel assignment message.
H. Control channel transmits channel update
message for late entry mobiles.
I. Transmitting mobile unkeys and sends two
non-slotted unkey messages. All non-slotted message
formats are:
Dotting = 384 bits
Data #3 = 128 bits
1336920
- 70 - - 45MR-626A
Data #2 = 128 bits
Data #1 = 128 bits
Data #0 = 128 bits
Data #3, #1, #1 and #0 are identical
(repeated four times) and each has the following
format:
Dotting = 16 bits
Barker = 16 bits
Byte 1 = 8 bits
Byte 1 (inverted) = 8 bits
Byte 1 = 8 bits
Byte 2 = 8 bits
Byte 2(inverted) = 8 bits
Byte 3 = 8 bits
Byte 4 = 8 bits
Byte 4 (inverted) = 8 bits
Byte 4 = 8 bits
The unkey message is coded an follows:
MT = Code = 4 bits
Subaudible Count = 2 bits
Logical ID = 12 bits
BCH Code = 12 bits
V. Radio Call Sequence-Radio Oriqination, Status Call
~ 71 133S9~0 4sMR-626A
A. Control channel transmits a continuous steam
of control messages which all inactive mobiles receive.
The messages are sent two messages to a 30-msec. frame
that has the following format:
Dotting = 32 bits
Barker = 16 bits
Message #1 = 40 bits
Message #1 (inverted) = 40 bits
Message #1 = 40 bits
Message #2 = 40 bits
Message #2 (inverted) = 40 bits
Message #2 = 40 bits
B. Mobile that wishes to originate a status call
transmits a status request on the control channel in
synchronism with the received control channel messages.
The frame format is as follows:
Dotting = 152 bits
Barker (repeated three times) = 48 bits
Message = 40 bits
Message (inverted) = 40 bits
Message = 40 bits
The status request message is coded as
follows:
MT-A Code = 2 bits
MT-B Code = 3 bits
MT-C Code= 3 bits
3 bits (unused) = 000
e 1~3S~
- 72 - 45MR-626A
Auto Response = 1 bit (e.g., yes)
4 bits (unused) = 0000
Logical ID = 12 bits
BCH Code = 12 bits
C. The cantrol channel responds with a status
page message that is coded as follows:
MT-A Code = 2 bits
MT-B Code = 3 bits
MT-C Code = 4 bits
2 bits (unused) = 00
Auto response = 1 bit (e.g., yes)
Status = 4 bits
Logical ID = 12 bits
BCH Code = 12 bits
D. Called mobile transmits a control channel
status message that is coded as follows:
MT-A Code = 2 bits
MT-B Code = 3 bits
MT-C Code = 3 bits
3 bits (unused) = 000
Auto Response = 1 bit (e.g., yes)
Status = 4 bits
Logical ID = 12 bits
BCH Code = 12 bits
E. Control channel responds with a status
acknowledge message that is coded as follows:
_ 73 _ ¦ 3 3692 ~45MR-626A
MT-A Code = 2 bits
MT-B Code = 3 bits
MT-C Code = 4 bits
2 bits (unused) = 00
Auto Response = 1 bit (e.g., yes)
Status = 4 bits
Logical ID = 12 bits
BCH Code = 12 bits
Originating mobile receives status message.
VI. Radio Call Sequence-Radio Origination, Special
Call
A. Control channel transmits a continuous
stream of control messages which all inactive mobiles
receive. The messages are sent two messages to a
30-msec. frame that has the following format:
Dotting = 32 bits
Barker = 16 bits
Message #1 = 40 bits
Message #1 (inverted) = 40 bits
Message #1 = 40 bits
Message #2 = 40 bits
Message #2 (inverted) = 40 bits
Message #2 = 40 bits
B. Mobile that wishes to originate a special
call transmits a special call request on the control
channel in synchronism with the received control
channel messages. The frame format is as follows:
~ 133~9~
- 74 - 45MR-626A
Dotting = 152 bits
Barker (repeated three times) = 48 bits
Message = 40 bits
Message (inverted) = 40 bits
Message = 40 bits
The special call request message is coded as
follows:
MT-A Code = 2 bits
MT-B Code = 3 bits
MT-C Code = 3 bits
2 bits (unused) = 00
Type Communications Code = 2 bits (e.g.,
interconnect)
1 bit (unused) = O
Priority Code = 3 bits
Logical ID = 12 bits
BCH Code = 12 bits
C. The control channel responds with a
channel-assignment two-message pair. Coding is as
follows:
MT-A Code = 2 bits
Type Communication Code = 2 bits
(e. g., intent)
1/2 Logical ID = 6 MSBs or LSBs
Group/Logical = 1 bit
Channel = 5 bits
Logical ID = 12 bits
BCH Code = 12 bits
1336~Q
_ 75 - 45MR-626A
D. Mobile switches to the assigned working
channel and receives a confirmation message. Slotted
working channel messages are transmitted using the
following frame.
Dotting = 32 bits
Barker = 16 bits
Message = 32 bits
Message (inverted) = 32 bits
Message = 32 bits
BCH Code = 12 bits
The special call confirmation message is
coded as follows:
MT Code = 4 bits
Subcount = 2 bits
Hang/time/Trunked = 1 bit
Group/Logical ID = 1 bit
Logical ID = 12 bits
BCH Code = 12 bits
E. Originating mobile receives confirmation
message and transmits a multi-block special call
message. The message frame (shown below) can have
from 1 to 16 blocks.
Dotting = 384 bits
Data #3 Block #1 = 128 bits
Data #2 Block #1 = 128 bits
Data #1 Block #l = 128 bits
Data #O Block #l = 128 bits
1336920
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Data #3 Block #2 = 96 bits
Data #2 Block #2 = 96 bits
.
.
Data #3, #2, #1, #0 are identical in each
block (repeated four times). Coding for Block #1 Data
is:
Dotting = 16 bits
Barker = 16 bits
Byte 1 = 8 bits
Byte 1 (inverted) = 8 bits
Byte 1 = 8 bits
Byte 2 = 8 bits
Byte 2 (inverted) = 8 bits
.
.
.
Byte 3 = 8 bits
Byte 4 = 8 bits
Byte 4 (inverted) = 8 bits
Byte 4 = 8 bits
Data in blocks after block #1 do not have
dotting or Barker code. If telephone interconnect is
required, block #1 data is coded as follows:
Group Count = 4 bits
Individual Count = 4 bits
~ 133692~
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Phone Digit Count = 4 bits
Phone Digit #1 = 4 bits MSD
Phone digit #2 = 4 bits
BCH Code = 12 bits
If no interconnect is required, block #l is
coded as
Group Count = 4 bits
Individual Count = 4 bits
Group/Logical ID = 12 bits
BCH Code = 12 bits
Subsequent blocks are coded with either one
group ID, one logical ID, or five telephone digits as
required to satisfy the block #l counts. The
telephone digits first, then the logical ID's, then
the group ID's. Digit coding is one digit per nibble
(null=1010). ID coding is
8 Bite = 10101010 (8 bits)
Group/Logical ID = 12 bits
BCH Code = 12 bits
F. Working channel transmits a slotted working
channel special call receive bitmap message. Slotted
working channel messages are transmitted using the
following frame:
Dotting = 32 bits
Barker = 16 bits
1336~2~
- 78 - 45MR-626A
Message = 32 bits
Message (inverted) = 32 bits
Message = 32 bits
BCH Code = 12 bits
The special call receive bit map is coded as
follows (use of similar acknowledgment bit maps is the
subject of related commonly assigned Canadian
Application Serial No. 566,662 filed May 12, 1988.
MT Code = 4 bits
Block #1 bit = 1 bit (e.g., OK)
Block #2 bit = 1 bit (e.g., OK)
Block #3 bit = 1 bit (e.g., 0 = repeat)
Block #4 bit = 1 bit
.
.
Block #16 bit = 1
BCH Code = 12 bits
G. Originating mobile receives bitmap message
and transmits a multi-block special call message. The
message frame (shown below) can have from 1 to 16
blocks.
Dotting = 384 bits
Data #3 Block #1 = 128 bits
Data #2 Block #1 = 128 bits
Data #1 Block #1 = 128 bits
~ 79 133 6 92~5MR_626A
Data #O Block #1 = 128 bits
Data #3 Block #2 = 96 bits
Data #2 Block #2 = 96 bits
Data #3, #2, #1, #0 are identical in each
block (repeated four times). Coding for block #1 is
Dotting = 16 bits
Barker = 16 bits
Byte 1 = 8 bits
Byte 1 (inverted) = 8 bits
Byte 1 = 8 bits
Byte 2 = 8 bits
Byte 2 (inverted) = 8 bits
Byte 3 = 8 bits
Byte 4 = 8 bits
Byte 4 = (inverted) = 8 bits
Byte 4 = 8 bits
Data in blocks after block #1 do not have
dotting or Barker code.
Only blocks that have a "0" in their bitmap
bit are transmitted. For example in step E, block #3
in step E would be the first block retransmitted. If
36920
- 80 - 45MR-626A
no bit map is received within 100 msec. after steps E
or G, all blocks are retransmitted.
Steps F and C are repeated until all blocks are
received correctly (BITMAP = l's).
H. Control channel transmits a continuous stream
of control messages which all inactive mobiles
receive. The messages are sent two messages to a
30-msec. frame that has the following format:
Dotting = 32 bits
Barker = 16 bits
Message #1 = 40 bits
Message #1 (inverted) = 40 bits
Message #1 = 40 bits
Message #2 = 40 bits
Message #2 (inverted) = 40 bits
Message #2 = 40 bits
I. The control channel sends from 0 to 16
channel-assignment two-message pairs as required for
the special call. Coding for each message is as
follows:
MT-A Code = 2 bits
Type Communications Code = 2 bits
1/2 Logical ID = 6 MSBs or 6 LSBs
Group/Logical ID = 1 bit
Channel = 5 bits
Logical = 12 bits
BCH Code = 12 bits
` 1336920
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J. All called mobiles go to the assigned working
channel and unmute (same as late entry). From this
point the working channel messages are the same as a
group or individual call.
VII. Radio Call Sequence-Radio Origination,
Dvnamic-Reqroup Call
A. Control channel transmits a continuous stream
of control messages which all inactive mobiles
receive. The messages are sent two messages to a
30-msec. frame that has the following format:
Dotting = 32 bits
Barker = 16 bits
Message #l = 40 bits
Message #l (inverted) = 40 bits
Message #1 = 40 bits
Message #2 = 40 bits
Message #2 (inverted~ = 40 bits
Message #2 = 40 bits
B. Mobile that wishes to originate a
dynamic-regroup call transmits a reguest on the
control channel in synchronism with the received
control channel messages. The frame format is as
follows:
Dotting = 152 bits
Barker = (repeated three times) = 48 bits
Message = 40 bits
Message (inverted) = 40 bits
Message = 40 bits
1336920
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The dynamic-regroup request message is coded
as follows:
MT-A Code = 2 bits
MT-B Code = 3 bits
Group ID = 11 bits
Logical ID - 12 bits
BCH Code = 12 bits
C. The control channel responds with a
dynamic-regroup message that is coded as follows:
MT-A Code = 2 bits
MT-B Code = 3 bits
Group ID = 11 bits
Logical ID = 12 bits
BCH Code = 12 bits
D. Mobile acknowledges the dynamic regroup with a
login message that is coded as follows:
MT-A Code = 2 bits
MT-B Code = 3 bits
Group ID = 11 bits
Logical ID = 12 bits
BCH Code = 12 bits
E. Mobile may request cancellation of the
dynamic-regroup with a message coded as follows:
MT-A Code = 2 bits
MT-B Code = 3 bits
1~369~0
- 83 - 45MR-626A
Group ID = 11 bits
BCH Code = 12 bits
F. Control channel responds with a cancel
dynamic-regroup message that is coded
MT-A Code = 2 bits
MT-B Code = 3 bits
Group ID = 11 bits
Logical ID = 12 bits
BCH Code = 12 bits
G. Mobile acknowledges the dynamic-regroup
cancellation with a login message that is coded
MT-A Code = 2 bits
MT-B Code = 3 bits
Group ID = 11 bits
Logical ID = 12 bits
BCH Code = 12 bits
VIII. Radio Call Sequence-Console Origination,
Group Call
A. Control channel transmits a continuous stream
of control messages which all inactive mobiles
receive. The messages are sent two messages to a
30-msec. frame that has the following format:
Dotting = 32 bits
Barker = 16 bits
Message #1 = 40 bits
1336920
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Message #1 (inverted) = 40 bits
Message #1 = 40 bits
Message #2 = 40 bits
Message #2 (inverted) = 40 bits
Message #2 = 40 bits
B. Console that wishes to originate a group call
transmits a group call message to the downlink. The
group call message is coded as follows:
MID = 1 byte (#0) = 8 bits
# bytes = 1 byte (#1) = 8 bits
Source destination = bytes #2 and #3
= 16 bits
Not Used = 4 bits
MT-A Code = 2 bits
Type communication = 2 bits
Group ID = 12 bits
Logical ID = 12 bits
Parity = 1 byte (#8) = 8 bits
C. The control channel responds with a
channel-assignment two-message pair. Coding is as
follows:
MT-A Code = 2 bits
Type Communications = 2 bits
1/2 Logical ID = 6 MSBs or LSBs
Group/Logical ID = 1 bit
Channel = 5 bits
Group ID = 12 bits
BCH Code = 12 bits
1336920
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D. All mobiles of the called group switch to
assigned working channel and receive a confirmation
message. Slotted working channel messages are
transmitted using the following frame:
Dotting = 32 bits
Barker = 16 bits
Message = 32 bits
Message (inverted) = 32 bits
Message = 32 bits
The group call confirmation message is coded
as follows:
MT Code = 4 bits
Subaudible Count = 2 bits
Hang Time/Trunked = 1 bit
Group/Logical ID = 1 bit
Group ID = 12 bits
BCH Code = 12 bits
E. Originating console receives channel-
assignment from the downlink and switches audio to the
specified channel. Console message is coded as
follows:
MID = 1 Byte (#O) = 8 bits
# Bytes = 1 Byte (#l) = 8 bits
S/D = Bytes #2, #3 = 16 bits
Not Used = 4 bits
MT Code = 2 bits
1336920
- 86 - 45MR-626A
Type communications = 2 bits
Logical ID = 12 bits
Not Used = 2 bits
GR/L ID = 1 bit
Channel = 5 bits
Group ID = 12 bits
Parity = 1 Byte (#9) = 8 bits
F. Working channel transmits two
unit-keyed/unmute messages:
MT Code = 4 bits
Subaudible Count = 2 bits
Hang-time/trunked = 1 bit
1 bit (unused) = O
Logical ID = 12 bits
BCH Code = 12 bits
Called mobiles receive unmute message and
unmute audio.
G. Active mobiles on other working channels
receive a subaudible channel assignment message.
H. Control channel transmits channel update
message for late entry mobiles.
I. Console sends unkey message that is coded as
follows:
MID = 1 Byte (#0) = 8 bits
# Bytes = 1 byte = 8 bits
13369~0
- 87 - 45MR-626A
Source Destination = Bytes #2 & #3 = 16 bits
Not used = 4 bits
MT Code = 4 bits
Not Used = 4 bits
Logical ID = 12 bits
Parity = Byte #7 = 8 bits
J. Working channel transmits 896 to 2816 bits of
dotting to drop all mobiles from the channel.
K. Console receives unkey message:
MID = Byte #0 = 8 bits
# Bytes = Byte #1 = 8 bits
Source Designation = Bytes #2 & #3 = 16 bits
MT-A/B/C = 9 bites
Drop Cr = 1 bit
Not Used = 1 bit
Channel = 5 bits
Logical ID = 12 bits
Parity = Byte #8 = 8 bits
IX. Radio Call Sequence-Console Oriqination,
Individual Call
A. Control channel transmits a continuous stream
of control messages which all inactive mobiles
receive. The messages are sent two messages to a
30-msec. frame that has the following format:
Dotting = 32 bits
Barker = 16 bits
1336920
- 88 - 45MR-626A
Message #1 = 40 bits
Message #1 (inverted) = 40 bits
Message #1 = 40 bits
Message #2 = 40 bits
Message #2 (inverted) = 40 bits
Message #2 = 40 bits
B. Console that wishes to originate an
individual call transmits an individual call message
to the downlink. The individual call message is coded
as follows:
MID = Byte #0 = 8 bits
# Bytes = Byte #1 = 8 bits
Source Destination = Bytes #2 & #3 = 16 bits
Not Used = 4 bits
MT-A Code = 2 bits
Type Communication = 2 bits
Logical ID = 12 bits
Logical ID = 12 bits
Parity = Byte #8 = 8 bits
C. The control channel responds with a
channel-assignment two-message pair. Coding is as
follows:
MT-A Code = 2 bits
Type Communications = 2 bits
1/2 Logical ID = 6 MSBs or LSBs
Group/Logical ID = 1 bit
Channel = 5 bits
Logical ID = 12 bits
1336920
- 89 - 45MR-626A
BCH Code = 12 bits
D. Called mobile switches to assigned working
channel and receives a confirmation message. Slotted
working channel messages are transmitted using the
following frame:
Dotting = 32 bits
Barker = 16 bits
Message = 32 bits
Message inverted = 32 bits
Message = 32 bits
The individual call confirmation message is coded
as follows:
MT Code = 4 bits
Subaudible Count = 2 bits
Hang Time/Trunked = 1 bit
Group/Logical ID = 1 bit
Logical ID = 12 bits
BCH Code = 12 bits
E. Originating console receives
channel-assignment message from the downlink and
switches audio to the specified channel. Console
message is coded as follows:
MID = Byte #O (8 bits)
# Bytes = Byte #1 = 8 bits
Source Destination = Bytes #2, & ~3 = 16 bits
Not Used = 4 bits
1336920
- go - 45MR-626A
MT Code = 2 bits
Type Communication Code = 2 bits
Logical ID = 12 bits
Not used = 2 bits
GR/L ID = 1 bit
Channel = 5 bits
Logical ID = 12 bits
Parity = Byte #9 = 8 bits
E. Working channel transmits two
unit-keyed/unmute messages.
MT Code = 4 bits
Subaudible Count = 2 bits
Hang-Time/Trunked = 1 bit
1 bit (unused) = O
Logical ID = 12 bits
BCH Code = 12 bits
Called mobile receives unmute message and
unmutes audio.
G. Active Mobiles on other working channels do
not receive a subaudible channel assignment message.
H. Control channel transmits channel update
message for late entry mobiles.
I. Console sends unkey message that is coded as
follows:
MID = Byte #0 = 8 bits
1336920
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# Bytes = Byte #1 = 8 bits
Source Destination = Bytes #2 & #3 = 16 bits
Not Used = 4 bits
MT Code = 4 bites
Not Used = 4 bits
Logical ID = 12 bits
Parity = Byte #7 = 8 bits
J. Working channel transits 896 to 2816 bits of
dotting to drop all mobiles from the channel.
K. Console receives unkey message:
MID = Byte #0 = 8 bits
# Bytes = Byte #1 = 8 bits
Source Destination = Bytes #2 and #3 = 16
bits
MT-A/B/C = 9 bites
Drop Ch = 1 bit
Not Used = 1 bit
Channel = 5 bites
Logical ID = 12 bits
Parity = Byte #8 = 8 bits
X. Radio Call Sequence Console Origination, Activate
Patch
A. Control channel transmits a continuous stream
of control messages which all inactive mobiles
receive. The messages are set two messages to a
30-msec. frame that has the following format:
13369~0
- 92 - 45MR-626A
Dotting = 32 bits
Barker = 16 bits
Message #1 = 40 bits
Message #1 (inverted) = 40 bits
Message #1 = 40 bits
Message #2 = 40 bits
Message #2 (inverted) = 40 bits
Message #2 = 40 bits
B. Console that wishes to establish a patch
transmits a patch ID assignment message to the
downlink. The patch ID assignment message is variable
length depending upon the group and individual ID
counts:
MID =29 = Byte #0 = 8 bits
# Bytes = Byte #1 = 8 bits
Source/Destination = Bytes #2, #3 = 16 bits
Not Used = 4 bits
Group Count = 4 bits
Individual Count = 4 bits
Logical ID = 12 bits
Not Used = 12 bits
Logical ID = 12 bits
Not Used = 12 bits
Logical ID = 12 bits
Not Used = 13 bits
Group ID = 11 bits
Not Used = 13 bits
Group ID = 11 bits
Not used = 13 bits
Patch ID = 11 bits
1336920
- 93 - 45MR-626A
Parity = 8 bits
C. Console receives an acknowledgement of the
patch request from the site controller using a special
group ID code (1000 0000 0000):
MID=12 = Byte #0 = 8 bits
# Bytes = Byte #1 = 8 bits
Source/Destination = Bytes #2, #3 = 16 bits
Not Used = 4 bits
MT-A Code = 11 = 2 bits
MT-B Code = 100 = 3 bits
Patch ID = 11 bits
Group ID = 11 bits
Parity = Byte #8 = 8 bits
D. When console wishes to activate the patch it
transmits a patch activate message to the downlink.
MID=27 = Byte #0 = 8 bits
# Bytes = Byte #1 = 05 = 8 bits
Source/Destination = Bytes #2, ~ #3 = 16 bits
Not Used = 4 bits
MT Code = 4 bits (1110)
Not Used = 5 bits
Patch ID = 11 bits
Parity = Byte #7 = 8 bits
E. The control channel responds with alias ID
assignment messages. Group assignment messages are
coded:
1336920
- 94 - 45MR-626A
MT-A Code = 2 bits (11)
MT-B Code = 3 bits (110)
Alias Group ID = 11 bits
Not Used = 1 bit
Group ID = 11 bits
BCH Code = 12 bits
Group alias ID messages are repeated in the
control channel background mode and not acknowledged
by the mobiles.
Individual alias ID assignment messages are
coded as follows:
MT-A Code = 2 bits (11)
MT-B Code = 3 bits (101)
Alias Group ID = 11 bits
Logical ID = 12 bits
BCH Code = 12 bits
F. All mobiles receive assignment messages but
only individual call mobiles acknowledge message.
MT-A Code = 2 bits (11)
MT-B Code = 3 bits (110)
Alias Group ID = 11 bits
Logical ID = 12 bits
BCH Code = 12 bits
G. Console receives patch assignment/activate
messages to confirm patch. One message for each
assignment:
MID=12 = Byte #O = 8 bits
1336920
- 95 - 45MR-626A
# Bytes = Byte #1 = 8 bits
Source/Destination = Bytes #2 & #3 = 16 bits
Not Used = 4 bits
MT-A Code = 2 bits (11)
MT-B Code = 3 bits (100)
Patch ID = 11 bits
Group ID = 12 bits
Parity = Byte #8 = 8 bits
MID=13 = Byte #0 = 8 bits
# Bytes = Byte #1 = 8 bits
Source/Destination = Bytes #2 & #3 = 16 bits
Not Used = 4 bits
MT-A Code = 2 bits (11)
MT-B Code = 3 bits (101)
Patch ID = 11 bits
Logical ID = 12 bits
Parity = Byte #8 = 8 bits
H. Console originates a patch call by
transmitting a group call message using the patch ID:
MID=24 Byte #0 = 8 bits
# Bytes = Byte #1 = 8 bits
Source/Destination = Bytes #2 & #3 = 16 bits
Not Used = 4 bits
MT Code = 2 bits (00)
Type Communication = 2 bits (00)
Patch ID = 12 bits
Logical ID = 12 bits
Parity = Byte #8
1336920
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I. Control channel transmits group call message.
Subsequent steps are same as console originated group
call.
While only one exemplary embodiment of this
invention has been described in detail, those skilled
in the art will recognize that many variations and
modifications may be made in this embodiment while
still retaining many of its novel features and
advantages. Accordingly, all such modifications and
variations are intended to be included within the
scope of the appended claims.
