Trunked radio repeater system

A digitally trunked radio repeater system provides substantial improvements in timeliness of channel acquisition and channel drop, and in reliability of critical control signalling. The system uses a much higher digital signalling rate than is typically found in prior art systems, and uses a control channel to convey digital channel request and assignment messages between the central site and mobile transceivers. The mobile radio transceivers transmit channel requests on the control channel (if no response is received, the mobile retries during a retry time window which increases in duration in dependence on the number of retries). The mobile transceiver switches to a working channel in response to an assignment message received on the control channel. Subaudible digital signals transmitted on the control channel and on active working channels allow late entry, shifting to higher priority calls, and other advanced functions. Message and transmission trunking capabilities are both present so as to maximize working channel usage without compromising channel access for high priority communications. During transmission trunking, called and calling transceivers return to the control channel after each transmission (and called transceivers may be inhibited from transmitting) but grant higher priority to calls from the other transceivers being communicated with to ensure continuity over an entire conversation. Additional functions and fault tolerant features further increase the versatility and reliability of the system.

BACKGROUND AND SUMMARY OF THE INVENTION 
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 diferent 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. Pat. No. 3,292,178--Magnuski (1966) 
U.S. Pat. No. 3,458,664--Adlhoch et al (1969) 
U.S. Pat. No. 3,571,519--Tsimbidis (1971) 
U.S. Pat. No. 3,696,210--Peterson et al (1972) 
U.S. Pat. No. 3,906,166--Cooper et al (1975) 
U.S. Pat. No. 3,936,616--DiGianfilippo (1976) 
U.S. Pat. No. 3,970,801--Ross et al (1976) 
U.S. Pat. No. 4,001,693--Stackhouse etal (1977) 
U.S. Pat. No. 4,010,327--Kobrientz et al (1977) 
U.S. Pat. No. 4,012,597--Lynk, Jr. et al (1977) 
U.S. Pat. No. 4,022,973--Stackhouse etal (1977) 
U.S. Pat. No. 4,027,243--Stackhouse etal (1977) 
U.S. Pat. No. 4,029,901--Campbell (1977) 
U.S. Pat. No. 4,128,740--Graziano (1978) 
U.S. Pat. No. 4,131,849--Freeburg et al (1978) 
U.S. Pat. No. 4,184,118--Cannalte et al (1980) 
U.S. Pat. No. 4,231,114--Dolikian (1980) 
U.S. Pat. No. 4,309,772--Kloker et al (1982) 
U.S. Pat. No. 4,312,070--Coombes et al (1982) 
U.S. Pat. No. 4,312,074--Pautler et al (1982) 
U.S. Pat. No. 4,326,264--Cohen et al (1982) 
U.S. Pat. No. 4,339,823--Predina et al (1982) 
U.S. Pat. No. 4,347,625--Williams (1982) 
U.S. Pat. No. 4,360,927--Bowen et al (1982) 
U.S. Pat. No. 4,400,585--Kamen et al (1982) 
U.S. Pat. No. 4,409,687--Berti et al (1983) 
U.S. Pat. No. 4,430,742--Milleker et al (1984) 
U.S. Pat. No. 4,430,755--Nadir et al (1984) 
U.S. Pat. No. 4,433,256--Dolikian (1984) 
U.S. Pat. No. 4,450,573--Noble (1984) 
U.S. Pat. No. 4,485,486--Webb et al (1984) 
U.S. Pat. No. 4,578,815--Persionotti (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 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 of 
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 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-16 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 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 APCO-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). 
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 97-122), 
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 
immediately 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 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 
handshake 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--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 entrats (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 copending 
commonly assigned application Ser. No. 725,682, now U.S. Pat. No,. 
4,649,567, filed 22 Apr. 1985.) 
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 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 encryption techniques, 
mobile digital data terminals (digital data may be passed 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 related copending commonly assigned 
application Ser. No. 057,046, filed concurrently herewith] so as to 
maintain trunked system operation even if the central processor 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 communication 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 
channels 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 
INBOUND 9600 pbs 
Channel 
Group Call 
Special Call 
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 
Site ID 
System Operationa Made 
Site Status 
Logical ID Assignment 
Programming Channel Assignment 
Working 
INBOUND 9600 bps 
Channel 
Initial Handshake 
Special Call Signalling 
Unit ID-PTT and Reverse PTT 
Miscellaneous 
OUTBOUND 9600 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 instan- 
CHANNEL ACCESS TIME taneous access 
doesn't cut off syl- 
lables 
Normal Signal Strength Provides operation 
Areas: 280 Milliseconds 
which is faster than 
Weak Signal Areas (12dB 
most coded squelch 
systems. 
Sinad: 500 Milliseconds 
LATE ENTRY Minimizes missed 
Should a mobile turn on 
conversations, keeps 
during the period in which 
police up to the 
its group is involved in 
minute, minimizes 
a conversation, the mobile 
call backs. 
will automatically be 
directed to join that 
conversation. 
AUTOMATIC CHANNEL SWITCHING 
Frequency coordi- 
Mobiles, portables, control 
nation of the fleets 
stations, and consoles and subfleets 
automatically switch to 
requires no action 
the appropriate channel. 
on the part of any 
field personnel. 
HIGH SPEED CALL PROCESSING 
Dedicated control 
Processor assigns unit channel provides 
initiating the call, and 
more rapid channel 
all called units, to an 
assignments on larger systems. 
appropriate working channel. 
System size does not 
Initial channel assignment 
impact upon channel 
communication between site 
acquisition time. 
controller and radio units 
Control channel is 
available for 
occurs on the control additional functions 
channel. such as status and 
unit ID. 
CALL RETRY Eliminates the need 
Calling unit will for repetitive PTT 
automatically repeat its 
operations by the 
request up to eight times 
operator in weak 
signal situations. 
if no response is received. 
Terminating retries 
Retries terminated upon 
also shortens the 
system response. signalling time. 
UNIT DISABLE In hostage situa- 
Trunked units can be tions, these units can 
disabled on an individual 
be assigned to a 
basis. These disabled units 
special group for 
continue to monitor the 
communication with 
the criminals. 
control channel and can be 
Also, with automa- 
polled to determine their 
tic vehicular loca- 
status. tion, these units 
could be tracked for 
apprehension. 
SUPPLEMENTARY CONTROL Provides user and 
CHANNEL FUNTIONALITY system operator 
with system 
In addition to providing 
manager features 
channel assignments, the 
not available on 
control channel is used 
other types of 
for: status messages, systems. 
polling, system status, 
logging, late entry, 
dynamic regrouping, 
system testing and other 
system functions. 
GROUP PRIVACY Each group has the 
Each group hears only his 
same privacy as 
own group, unless having their own 
channel with the 
specifically programmed 
additional benefits 
otherwise. Dispatcher of being regrouped 
can override for individual 
with other comple- 
menting functions 
units or groups of mobiles 
for emergency oper- 
at any time. ations. 
CALL QUEUING Maintains orderly 
When all channels are entry procedure for 
busy, call requests will 
busy system. Call 
be queued until a channel 
requests are accep- 
ted in the order 
becomes available. Unit 
they are received 
requesting a channel will 
except higher prior- 
ity users go to the 
be notified to prevent head of the line. 
call backs. 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 
capability of using 9600 
of the system be- 
cause it avoids the 
bps data on the working 
expense of addi- 
channels. Data tional RF channels. 
communications will take 
place on any equipped 
working channel and they 
are trunked, just as 
voice communication. 
VOICE ENCRYPTION Voice encryption 
System has the optional 
offers the same 
encrypted range as 
capability of using for clear voice 
available 9600 baud voice 
transmissions. Voice 
encryption. (See, e.g. can be passed from 
commonly assigned US each site through 
U.S. Pat. No. conventional voice 
4,622,680 
grade phone lines 
and application Serial or microwave lines 
Nos. 661,597 filed 17 Only minor modi- 
fications are needed 
October 1984, 661,733 to the base station 
filed 17 October 1984 
and 661,740 filed 17 
October 1984.) 
interface equipment 
to accommodate 
such sophisticated 
voice security 
systems. Any mobile 
can be upgraded 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 automatically 
transmission is 
identified when they identified by the 
transmit. This is true same ID regardless 
regardless of whether the 
of the agency, fleet 
transmission takes place 
or subfleet in which 
on the control channel he is currently 
or on a working channel. 
operating. 4095 is 
more than twice 
The system is able to the logical number 
accommodate 4095 discreet 
of users in a fully 
addresses independent of 
loaded twenty 
fleet and subfleet. channel system so 
there is more than 
sufficient capacity. 
TRAFFIC LOGGING Statistics on system 
All system information is 
usage, such as peak 
logged. Each unit trans- 
loading, individual 
mission causes the units 
and group usage 
versus time as well 
ID, agency, fleet, sub- 
as many other 
fleet, channel, time, site 
system parameters, 
and list of sites involved 
are available for 
to be logged for manage- 
tabulation 
analysis. 
ment reports. 
TELEPHONE INTERCONNECT All mobiles and 
portables in the 
Authorized mobiles have 
system can be inter- 
the ability to place and 
connected to the 
receive calls and patch 
telephone system. 
them to individuals or Those mobiles not 
specifically equip- 
groups of mobiles which 
ped for this can be 
may or may not be equipped 
patched by their dis- 
for telephone interconnect. 
patcher to maintain 
adequate control of 
system loading 
factors. 
GROUP PRIORITY ASSIGNMENT 
System manager can 
Eight priority levels are 
set individual group 
provided in the system. 
priorities according 
Each group (as well as to the criticality of 
each individual) is their service. 
assigned a priority. The flow of traffic 
is more easily main- 
tained by providing 
recent users priority 
over nonrecent 
users of the same 
priority level. 
______________________________________ 
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. 
(b) Better Use of Subaudible Signalling 
Rather than using subaudible signalling only to confirm channel 
assignements, 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 Fragmentations 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. 
(d) Use of Transmission-Trunked Bit in Channel Assignment 
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 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 Transmission Trunked Mode. Not only does this simplify the 
necessary call back procedures and minimize access times, by allowing 
greater application of the Transmission Trunked Mode it also increases the 
probability of successful message exchanges--especially in poor signalling 
areas. 
(f) 9600 bps Permits "Loose" Synchronization 
Use of higher rate 9600 bps signalling permits simplified bit 
synchronization to be rapidly achieved by simple "dotting" sequences 
(i.e., a string of alternating ones and zeros 101010 . . . ). Thus, there 
is no need to keep information transfers precisely synchronized across all 
channels. This not only reduces hardware requirements system-wide, it also 
facilitates a more fault tolerant architecture at the control site. 
(g) Improved Channel Drop Signalling 
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. 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 Programming 
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 use 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 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 diminished. 
(i) Double Channel Assignment Handshake--One Being 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.

DETAILED DESCRIPTION OF PRESENTLY EXEMPLARY EMBODIMENTS 
An exemplary trunked radio repeater system in accordance with this 
invention is generally depicted at FIG. 1. As illustrated, individual 
units of various groups communicate 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. 
The central site is depicted in somewhat more detail at FIG. 2 in 
conjunction with one or more satellite receiver sites 100-1. 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 RF 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 FIG. 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 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-J11 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 commonly assigned 
concurrently filed application Ser. No. 057,046 entitled "Fail Soft 
Architecture For Public Trunking System".) 
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 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 FIG. 3. Here, 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 FIG. 3. The central processor 410 
may include,for example, a 128 Kilobyte code PROM, 1 Megabyte of RAM and 
32 DHV-11/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 FIG. 4, and may typically 
also receive hard-wired 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 
FIG. 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. Auxilliary 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 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 
inititate 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 begin the requested communication session on 
the working channel. Alternatively, if during this process the calling 
unit receives a channel update message on the control channel addressed to 
it, then the channel 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 handshake sequence), it automatically waits a random 
period before retrying to successfully place the call request (up to a 
maximum of 8 tries). 
The called unit initially resides in a standby configuration where it 
continually monitors the digital messages appearing on the control channel 
outbound from the central site. If it detects a channel 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 successful 
completion of a handshake 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 FIG. 6. Here, upon entry into the calling mode, a call 
request 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 atep 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 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 FIG. 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. 
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 FIG. 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 FIG. 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 FIG. 
9 where it can be seen that typical calling protocol can be completed and 
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 FIG. 10. 
The control channel transmits an outbound continuous transmission 
repeating the format 800 depicted in FIG. 10. As will be seen, each 40 bit 
message is transmitted three times (including one inverted transmission 
where all 0's are changed to 1'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 
FIG. 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 
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 FIG. 10). 
A group call request message format is shown in expanded scale in FIG. 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 FIG. 10. The first 
two bits identify the message type (MT) and the next two 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 error 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 FIG. 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 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 FIG. 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 FIG. 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. 
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 FIG. 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 standard 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 FIG. 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 
FIG. 11. 
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 t.sub.1). 
Upon detecting an inbound message, the site controller will receive and 
store the 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 t.sub.2). The two message channel 
assignment pair is then received and stored from the control channel in 
the calling unit at step 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 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 (1) 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 across 
time becomes in poor 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 
______________________________________ 
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 t.sub.3. 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 t.sub.2 (at 
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 t.sub.3. 
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 t.sub.5 and, in response, 
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 a mobile is on a working channel it monitors the 
subaudible signalling to make sure it belongs on that channel. There are 
at least two reasons why a radio could be onto a channel where it does not 
belong: 
(1) being correctly within a communique on a working channel, it fails to 
see the channel drop; or 
(2) monitoring the control channel, it incorrectly decodes 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 channel, the channel TC 
increments its count. Consequently, if a radio sees the count change, it 
"knows" it missed a channel 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 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 
t.sub.6). 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 
t.sub.7). The called unit has, of course, also received the unkeyed 
message on the working channel at time t.sub.6 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 t.sub.7 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 had 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 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 minimize 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: 
______________________________________ 
Group A 
Group B 
Group C 
Radio BBBAAA AAAA AA AAAAA BBBB CCCC 
monitors: 
______________________________________ 
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 knows 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 being 
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 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 
0.5 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) 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, 
minimizng 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 working channel when appropriate. Besides 
additional messages within the central site slowing the channel drop 
process, such prior techniques 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 channel 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 channel 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 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, 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 
later 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 radio's ability to look for the 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 is 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 is 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 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 features 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 
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 cell origination sequences are summarized below: 
I. RADIO ORIGINATION, LOGICAL ID ACQUISITION SEQUENCE 
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., 11 bits Barker code plus 5 bits (dotting preamble) 
Message #1=40 bits 
Message #1 (inverted)=4 bits 
Message #1=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: 
MT-A=2 bits (e.g., 11) 
MT-B=3 bits (e.g., 111) 
MT-C=4 bits (e.g., 1110) 
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 (=0) or adjacent (=1) 
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 
The login message is coded as 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 
Message #1 (inverted)=40 bits 
Message #=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: 
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. 
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 
Data Block #3, #2, #1 and #0 are identical--except for a two bit block 
count--(each block is repeated four times) and each has the following 
format: 
______________________________________ 
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 as follows: 
MT Code = 4 bits 
Unused = 2 bits 
Block Count = 2 bits 
Logical ID = 12 bits 
BCH Code = 12 bits 
______________________________________ 
The unkey message is coded as 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. 
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 
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 
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 
Unused bit=1 bit 
Logical ID=12 bits 
BCH Code=12 bits 
Called mobile receives unmute messages 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-slotting unkey message. All 
non-slotted message formats are: 
Dotting=384 bits 
Data #3=128 bits 
Date #2=128 bits 
Data #1=128 bits 
Data #0=128 bits 
Data #3, #2, #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 as follows: 
MT Code=4 bits 
Unused=2 bits 
Subcount=2 bits 
Logical ID=12 bits 
BCH Code=12 bits 
IV. RADIO CALL SEQUENCE-RADIO ORIGINATION, EMERGENCY 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=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 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 emergency group call request message is coded as follows: 
MT-A Code=2 bits 
Type communications=2 bits 
Status/C=1 bit 
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 messages 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 
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)=0 
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 
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 as follows: 
MT=Code=4 bits 
Subaudible Count=2 bits 
Logical ID=12 bits 
BCH Code=12 bits 
V. RADIO CALL SEQUENCE-RADIO ORIGINATION, STATUS CALL 
A. Control channel transmits a continuous steam of control messages which 
all inactive mobiles recieve. 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 
Auto Response=1 bit (e.g., yes) 
4 bits (unused)=0000 
Logical ID=12 bits 
BCH=12 bits 
C. The control 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=12 bits 
E. Control channel responds with a status acknowledge 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 
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 wit 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 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)=0 
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., intcnt) 
1/2 Logical ID=6 MSBs or LSBs 
Group/Logical=1 bit 
Channel=5 bits 
Logical ID=12 bits 
BCH Code=12 bits 
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 trasmits 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 
Data #0 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 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 
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 #1 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 #1 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 
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 
copending application No. 056,923 filed June 3, 1987): 
______________________________________ 
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. T1 -Dotting = 384 bits - Data #3 Block #1 = 128 bits - Data #2 
Block #1 = 128 bits - Data #1 Block #1 = 128 bits - Data #0 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 F, block #3 in step E would be the first block 
retransmitted. If no bit map is received within 100 msec. after steps E or 
G, all blocks are retransmitted. 
Steps F and G are repeated until all blocks are received correctly 
(BITMAP=1'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 
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, DYNAMIC-REGROUP 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 dynamic-regroup call transmits a 
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 dynamic-regroup request message is coded as follows: 
MT-A Code=2 bits 
MT-B Code=3 bits 
Group ID=11 bits 
Logical ID-2 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 
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='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 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 
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 (#0)=8 bits 
# Bytes=1 Byte (#1)=8 bits 
S/D=Bytes #2, #3=16 bits 
Not Used=4 bits 
MT Code=2 bits 
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)=0 
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 
Source Destination=Bytes #2 and #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 and #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 ORIGINATION, 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 
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 and #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 
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 #0 (8 bits) 
# Bytes=Byte #1=8 bits 
Source Destination=Bytes #2, and #3=16 bits 
Not Used=4 bits 
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 
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)=0 
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 
# Bytes=Byte #1=8 bits 
Source Destination=Bytes #2 and #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 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 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: 
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 1902, #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 
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, and #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: 
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 #0=8 bits 
# Bytes=Byte #1=8 bits 
Source/Destination=Bytes #2 and #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 and #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 and #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 
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.