Method for automatically revising a wireless communication unit scan list

A method for automatically revising (405) a scan list (201-203) in a wireless communication unit (103-106) employs the provision of a scan list that includes talk group identifiers (202) and reception-priority levels (203) associated the talk groups (202). A wireless message (114) that includes a first talk group identifier (116) and a corresponding reception-priority level (117) instructs the receiving communication untis to revise their scan lists to include the first talk group identifier (116) and the corresponding reception-priority level (117).

TECHNICAL FIELD OF THE INVENTION 
The present invention relates generally to wireless communication systems 
and in particular, to a method for revising the scan list within wireless 
communication units. 
BACKGROUND OF THE INVENTION 
Wireless communication systems are known to include a plurality of 
communication units, a limited number of wireless communication resources, 
and a communication resource controller. A typical communication unit, 
which may be a mobile radio, portable radio, or radio/telephone, offers 
its user a variety of features, such as group calls (i.e., one-to-many 
communications), telephone interconnect calls (i.e., one-to-one 
communications), and data communications. To access one of these services, 
the user must request access to one of the limited number of wireless 
communication resources and specify the type of service requested. This 
request is sent from the communication unit to the communication resource 
controller via a control channel, wherein the control channel is one of 
the communication resources that has been selected to function as the 
control channel. Upon receiving the request, the communication resource 
controller determines whether the requesting communication unit is 
authorized to access the requested service and, if so, whether a 
communication resource is available for allocation. When both conditions 
are met, the communication resource controller allocates a communication 
resource to the requesting communication unit, thereby facilitating access 
to the requested service. 
Dispatch communication systems typically employ digital addressing to 
enable the predetermined partitioning of the communication units into talk 
groups. Generally, talk groups allow for organization of the communication 
units into groupings of similar function or geographic affiliation. A talk 
group call initiated by a requesting member of a talk group results in a 
one-to-many wireless communication, such that other members of the same 
talk group will receive the same message simultaneously. Multiple talk 
group selections are programmed into the communication units to allow the 
user to select and operate on more than one talk group, however, a typical 
communication unit supports operation within only a single talk group at 
any given time. This point is clarified with the following discussion of a 
communication system feature commonly referred to as "talk group scan." 
Talk group scan is employed by a communication unit to display to the user 
scrollable list that includes secondary talk groups contained within the 
communication unit--i.e., identities of those talk groups with which the 
communication unit can presently communicate. Typically, the communication 
units are associated with a primary/home talk group that reflects its 
functional or geographic affiliation. The primary/home talk group may be 
the communication path used to dispatch new assignments to the user, while 
monitoring secondary scan talk groups may be carried out to merely provide 
the communication unit user with background information. Today, such 
information includes an occasional request for assistance from other talk 
groups across functional or geographic boundaries. 
The operation of talk group scan may be best explained by way of example. 
Suppose talk groups A, B, and C are in the communication unit's scan list 
(i.e., the communication unit monitors talk group traffic on any of the 
talk groups A, B or C, one at a time). When talk group A becomes active, 
the communication unit monitors talk group A. During that time, if talk 
group B becomes active, the communication unit will only monitor the talk 
group B traffic once the traffic ends on talk group A. This type of 
operation is also known as non-priority talk group scan. 
Non-priority talk group scan fails to direct a scanning communication unit 
back to a primary/home talk group in the event that the home talk group 
becomes active while the unit is monitoring other system traffic. 
Accordingly, this prior art technique results in certain missed 
communications. U.S. Pat. No. 4,716,407 issued to Borras et. al., 
describes a wireless communication system that overcomes this problem by 
providing so-called priority-monitor operation. Borras teaches 
transmission of a sub-audible word on the current voice channel, thereby 
causing the communication unit to revert to the control channel to receive 
a priority call assignment. To employ this technique, the communication 
unit must store a table in its memory listing each talk group to be 
scanned and their respective receive-priority, as known in the art. Of 
course, this table of scannable talk groups is predetermined, and is 
therefor limited in terms of flexibility. 
Wireless communication systems used in public safety applications are 
relied upon to provide important communications in various emergency 
situations such as civil violence, police procedures, and rescue 
operations. Often, emergency situations require assistance from additional 
users outside a particular talk group, including units that make up the 
public safety operation of another area. To carry out this assistance 
re-assignment, the users from the various other talk groups must 
communicate on a single common talk group where the current emergency 
exists. Since many of these emergency events involve life or death 
situations, it is desired to accomplish this re-assignment automatically 
and without error. Further, efficiency of dispatch, i.e., the best 
candidates for reassignment are immediately re-assigned to the talk group 
in need, would be highly desirable. 
The aforementioned priority monitor scheme does not provide an adequate 
solution, as it allows for collecting only those units having a common 
priority talk group in their pre-programmed lists. In other words, the 
communication units must know, prior to the emergency, which talk group 
they might receive having priority. 
Today, dispatchers, or other communication system authority figures, are 
relied on to first detect an event requiring assistance and then to 
broadcast a verbal or textual message to all talk groups requesting 
assistance for the effected talk group. This does not address the 
aforementioned requirements, as it relies on a human to detect the event, 
select one or more appropriate talk groups to assist in the emergency and 
broadcast a message to the selected talk group(s). Further, this solution 
fails when the communication units in the selected talk group are not 
pre-programmed with the identities of all target talk groups that might 
require assistance. 
Another solution, described in U.S. Pat. No. 5,014,345, issued to Comroe 
et. al., provides for a re-programming station to send commands to a 
communication unit for re-programming the communication unit with a 
selected talk group. While this provides for the addition of a previously 
unknown talk group code to a communication unit by way of a wireless 
command, it does not teach an automatic method of detecting a triggering 
event and choosing talk groups for assistance. Thus, this solution is also 
inadequate, as the detection and talk group selection mechanisms are prone 
to human error. 
In yet another prior art system, U.S. Pat. No. 5,146,538, issued to Sobti 
et. al., discloses a method for a wireless communication unit user to 
select a target communication unit using the spoken word. Speech 
recognition is used to select a target user and its communication system 
identity within the initiating communication unit. For example, the 
initiator simply says "call Jim" and the initiating communication unit 
detects "Jim" by comparing the real time speech with pre-stored speech 
samples. The word "Jim" is then cross-referenced with a communication 
system identity used in normal signaling to establish a unit-to-unit 
communication. 
While the communication system described in U.S. Pat. No. 5,146,538, 
teaches a convenient method for detecting a particular predetermined 
target user of a future communication, it does not teach a method to 
automatically detect an emergency situation. Further, it does not teach a 
method of automatically selecting a set of assisting talk groups based on 
a combination of the identity of the talk group needing assistance and the 
nature of the emergency. Lastly, it does not teach a method of 
automatically updating the talk group scan receive priority and talk group 
entries in a set of one or more assisting talk groups. 
Accordingly, a need exists for a method of automatically providing a common 
communication talk group for assisting users outside of a particular home 
talk group. Since many emergency events involve life or death situations, 
it is desired to accomplish this re-assignment automatically without error 
and efficiently such that the best candidates for reassignment are indeed 
re-assigned to the particular talk group that has the emergency or 
situation requiring assistance.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Generally, the present invention provides a method for automatically 
revising the scan list in a wireless communication unit in response to the 
detection of a predetermined event, or trigger component. This is 
accomplished by receiving, at a base site, a wireless message from a 
source communication unit that includes a predetermined trigger component 
and an identification of a first talk group to which the source 
communication unit belongs. Next, the base site analyzes the wireless 
message to identify the predetermined trigger component. Once this 
happens, the base site transmits to a plurality of communication units, a 
wireless command message that includes a second talk group identifier and 
an instruction to cause recipient communication units to add the second 
talk group identifier to their scan lists. The recipient communication 
units then automatically revise their scan lists to include the second 
talk group identifier and the corresponding reception-priority level. From 
that point forward, the recipient communication units will be capable of 
scanning subsequent transmissions from the first talk group. 
With such a method, automatic revision of a communication unit scan list is 
carried out to provide assistance capability for communication units 
outside of a first talk group. That is, communication units of the first 
talk group and those outside the first talk group can communicate on a 
common talk group. 
The present invention can be more fully described with reference to FIGS. 
1-5. FIG. 1 illustrates a communication environment 100 that includes 
communication units 103-104 that constitute a north communication talk 
group 101 and communication units 105-106 that constitute a south 
communication talk group 102. The communication system further includes 
base stations 107-109, a communication controller 110, a trigger detection 
system 111, including a digital signal processor (DSP) 112, and a memory 
113. 
The communication units 103-106 transceive information with the base 
stations 107-109 over a wireless communication path that may comprise a 
time division multiple access (TDMA) scheme, a frequency division multiple 
access (FDMA) scheme, or a code division multiple access (CDMA) scheme. Of 
course, all of these communication schemes are known in the art, so no 
further discussion of the type of wireless link will be provided. The 
communication units, which can be MIRS.TM. portable radios manufactured by 
Motorola, Inc., provide voice and/or data messages 118 in the form of 
compressed digital audio and compressed data transfers, respectively. A 
typical transmission 118 contains a talk group identifier 119 and a 
message 120. The base stations 107-109, which may comprise MIRS.TM. base 
station radios manufactured by Motorola, Inc., transceive RF carriers that 
are allocated among the communication units 103-106 by the communication 
controller 110. The base site transmissions 114 comprise several fields, 
including an opcode 115, a talk group ID 116, and a receive, or reception, 
priority level 117. Use of these fields is described later. 
The communication controller 110, which can be a MIRS.TM. dispatch 
application controller (DAP) manufactured by Motorola, Inc., provides the 
allocation control of a plurality of wireless communication resources 
107-109 in response to requests from the communication units 103-106. The 
communication controller 110 is also operably coupled to the DSP 112 
within the trigger detection system 111 to receive trigger detection 
indications from the DSP 112. The DSP 112, which can be a 560001 
manufactured by Motorola, Inc., is operably coupled to the base stations 
107-109, to provide a comparison of the received contents of communication 
unit messages 120 to that of predetermined triggers stored in the memory 
113 to produce a trigger indication when a match is made. The memory 113, 
may be a random access memory (RAM), read only memory (ROM), magnetic 
storage media, optical storage media, or any other storage type capable of 
storing a set of predetermined triggers. The predetermined triggers may 
comprise speech fragments such as single words, phrases, sentences, or 
even paragraphs. The predetermined triggers may also comprise varying 
lengths of data strings of text or images. 
As earlier stated, the present invention provides a method for 
automatically revising the scan list in a wireless communication unit in 
response to the detection of a predetermined trigger component. This is 
best described by example with reference to FIG. 1. Assume that the north 
communication unit talk group 101 is active and communication unit 103 is 
transmitting a transmission 118 to a base station 108. The wireless 
transmission 118 includes a predetermined trigger component, such as a 
speech component like "officer down", within a message 120 and an 
identification of a first talk group 119 (north talk group) to which the 
source communication unit 103 belongs. Next, the DSP 12 analyzes the 
message 120 to identify the predetermined trigger component by comparing 
the message components to the predetermined stored triggers in the trigger 
detection system 111 memory 113. If this comparison produces a match, then 
the DSP 112 signals the communication controller 110 with an indication of 
which trigger was detected and for which source talk group. Next, the 
communication controller 110 instructs the base stations 107-109 to 
transmit to the plurality of communication units 103-106, a wireless 
message 114 that includes a second talk group identifier 116,a receive 
priority level 117, and an instruction opcode 115 to cause recipient 
communication units 103-106 to add the second talk group identifier 116 to 
their scan lists. In this example, the second talk group identifier 
identifies the north talk group. 
Recipient communication units 103-106 automatically revise their scan lists 
to include the second talk group identifier 116 and the corresponding 
reception-priority level 117. The scan lists will be discussed in more 
detail later with reference to FIG. 2. From that point forward, the 
recipient communication units 103-106 are capable of scanning subsequent 
transmissions from the first talk group. In this example, the south 
communication units 105-106 are now able to automatically monitor any 
subsequent transmissions from the north talk group, so that they can 
communicate directly with--and thereby provide support for any required 
assistance to--users of the north communication units. 
The revision of the communication unit scan lists can be described by way 
of illustrating a set of revision commands and the scan list before and 
after the commands. FIG. 2 illustrates a set of temporal communication 
unit scan lists 201-203 (in ascending order, related to time advancing), 
and a set of base site transmissions 204-205 corresponding to the temporal 
scan list changes 202 and 203, respectively. As shown, the scan lists 
201-203 comprise talk group fields 202, 208, 214, and receive priority 
fields 203, 209, 215, respectively. For each scan list 201-203 there is a 
corresponding entry number one 204, 210, 216, and a corresponding entry 
number two 205, 211, 217, and a corresponding entry number three 206, 212, 
218, and a corresponding entry number four 207, 213, 219. Those skilled in 
the art will recognize that the number of scan list entries is a design 
choice to strike a balance between the users' maximum scan list member 
requirement, and the processing and memory capabilities of the 
communication unit. 
The talk group entry field 202 contains the talk groups that the 
communication unit monitors, while the receive priority field determines 
the sequential order in which the talk groups are monitored. For example, 
scan list 201 contains an entry 204 for the north talk group to be scanned 
at a receive-priority level 5, while entry 205 shows the east talk group 
to be scanned at a receive-priority level 3. (It should be noted that a 
lower receive-priority number generally relates to more important 
priority--i.e., to be scanned before talk groups having higher 
receive-priorities.) The receive-priority level is typically within the 
range of 1-5, or more. In this example, the communication unit monitors 
the north talk group, but only if the east talk group is not active. When 
the east talk group becomes active, the unit leaves the north talk group 
to monitor transmissions involving the east talk group. A more detailed 
description of such receive-priority operations may be found in Borras, 
U.S. Pat. No. 4,716,407, incorporated herein by reference. 
In a preferred embodiment, the contents of the communication unit scan 
lists are dynamically revised in response to commands transmitted from the 
base site. The base site transmissions 204-205 include opcode fields 220, 
226, talk group fields 221, 227, and receive priority fields 222, 228, 
which together constitute base site commands. The command set of the 
opcode field includes add and delete. The add command results in adding a 
new entry, or replacing an existing entry with the same talk group 
identifier, while the delete command results in deleting an existing 
entry. 
Using FIG. 2, a temporal example of the scan list revisions made in 
response to the base site commands is hereafter described. An 
initial--i.e., before revision--scan list 201 contains two talk group 
entries, one for each of the north and east talk groups. Next, based on 
the detection of a trigger component in a message from a communication 
unit within the south talk group, the communication controller determines 
that the scan lists in the communication units of at least one other talk 
group should be revised to include the south talk group. To carry this 
out, a command message 204 is formatted and transmitted from the base site 
to the communication units. The opcode field 220 contains an add command, 
the talk group field 221 is set to the south talk group, and the priority 
field 222 is set to a receive-priority level of two, as shown. Upon 
receiving this command message 204, the communication unit checks to see 
if the south talk group is already in the scan list 201. If so, then it 
simply updates the priority level associated therewith, using the priority 
level found in the priority field 222. In this example, the south talk 
group was not in the initial scan list 201, so the communication unit 
checks to see if there is room left in the scan list to add a new entry. 
Entries 206 and 207 are both empty in the initial scan list 201, so the 
communication unit adds the south talk group and its associated 
receive-priority level (see entry 212 in the first modified scan list 
202). 
Next, assume for the continuing example that the base site detects a 
trigger component in a message from a communication unit in the east talk 
group, such as a speech component "scene secure." In response, the 
communication controller determines that the scan lists in the 
communication units of at least one other talk group should be revised to 
exclude the east talk group, since it is no longer necessary for others 
outside of the east talk group to monitor those communications. To carry 
this out, a command message 205 is formatted and transmitted from the base 
site to the communication units. The opcode field 226 contains a delete 
command, the talk group field 227 is set to the east talk group, and the 
priority field 228 is set to a receive-priority level of three, as shown. 
Upon receiving this command message 205, the communication unit checks to 
see whether the east talk group is already in the scan list 202. If not, 
then a fault is flagged resulting, for example, in a message being sent to 
the system manager. In this example, because the east talk group is found 
(note entry 211 of scan list 202), the communication unit deletes entry 
211, thereby resulting in a null entry 217 in the final scan list 203. 
FIG. 3 shows a table 300 used within the communication controller 110 
(shown in FIG. 1) to illustrate one embodiment of the present invention. 
As shown, the table 300 contains a source talk group field 301, a trigger 
type field 302, a trigger content field 303, a target talk group field 
304, an opcode field 305, a talk group field 306, and a receive priority 
field 307. Each field contains elements, which together constitute table 
entries 308-312. The table 300 is predetermined and entered by a system 
manager responsible for maintenance of the communication controller. Using 
FIGS. 1 and 3, the following example describes how the table elements are 
used from each entry as the communication controller 110 processes the 
communication traffic within the communication environment 100. Assume 
that communication unit 105 transmits a message to members within its 
south talk group 102, through base station 109. The communication 
controller 110 searches for the identifier for the south talk group within 
the source talk group field 301 in table 300. If it is not found, no 
special action is taken. However if the appropriate identifier is found, 
as shown in entry 308, then the communication controller 110 issues an 
instruction to the trigger detection system 111. This instruction directs 
the trigger detection system 111 to analyze the messages from the south 
talk group, looking for the trigger content listed in the trigger content 
field 303 when the incoming messages are of the type shown in the trigger 
type field 302. 
The instruction from the communication controller 110 also includes channel 
information, which is routed to the trigger detection system 111 so it can 
monitor the correct base station 109 for communications from the source 
communication unit 105. Based on entry 308, the communication controller 
110 instructs the trigger detection system 111 to search for the two word 
speech component "officer down", when the message type is speech, for the 
duration of the message. If this trigger component is not found, then no 
special action is taken. However, when the "officer down" speech trigger 
is found within the message 120 from communication unit 105, then the 
communication controller 110 formats a wireless message 114 for 
transmission, by the base stations 107-109, to the talk group indicated in 
the target talk group field 304. In this example, the north talk group 101 
receives a message instructing them to "ADD SOUTH TALK GROUP WITH PRIORITY 
2", as set forth in fields 305-307 of entry 308 shown in table 300. 
After receipt of the message 114, the north communication units 101 
automatically monitor (e.g., via priority scan) transmissions from the 
south communication units 102 at a receive-priority level of two. It is 
important to note that the talk group field 116 in the scan list revision 
command 114 is determined from table 300 in the talk group field 306, not 
from the source talk group. This allows a talk group to be added to a scan 
list where the added talk group need not be the same as the talk group 
from which the trigger event was detected. Another trigger component might 
include a user location, such that when a member of one talk group roams 
into the location area of another talk group, the latter talk group 
members monitor communications from the roaming members talk group. As an 
example, entry 310 illustrates a trigger that may be detected when a 
member of the north talk group sources a call that includes location data 
indicating that it has roamed into the south location, thereby triggering 
a scan list revision command instructing south talk group members to 
monitor communications on the north talk group. The foregoing examples 
illustrate a flexible and automatic scan list revision technique that uses 
a wide array of triggering events and response combinations. 
FIG. 4 illustrates a logic diagram depicting operation of the communication 
units 103-106, in accordance with the present invention. After the 
communication unit receives (401) a wireless message from the base site, 
the message type is checked (402) to determine whether or not the message 
is a scan list update revision command. If not, no special action is taken 
and the communication unit continues to receive messages. If the message 
is a scan list update, the talk group field is read to determine (403) the 
talk group identifier. The talk group identifier is the talk group 
identification of a talk group to be added or deleted from the 
communication unit's scan list. The priority field in the message is then 
read to determine (404) the receive-priority level. The receive-priority 
level is used subsequently in the communication unit's scan process to 
prioritize the order of preference that the communication unit will 
monitor transmissions. The communication unit's scan list is then revised 
(405) by inspecting the opcode from the scan list revision command, as 
next described. 
When the opcode indicates (406) an add command, a decision is reached to 
determine (407) whether there is room in the scan list for a new entry. In 
addition, if the talk group indicated in the scan list update command is 
already an entry in the communication unit's scan list, then that entry 
can be overwritten with the receive-priority level from the scan list 
update command. If there is room for a talk group not already contained in 
the scan list, then the new scan list entry is made by adding (408) the 
appropriate element. This comprises inserting the received talk group 
identifier into the talk group field of the scan list and the received 
reception-priority level into the receive-priority level field of the scan 
list. If the talk group in the scan list update was not already in the 
communication unit's scan list and no empty scan list entries are found, 
then a fault is flagged (409). This flag may be a bit set in the 
communication unit memory that might be subsequently transmitted, or it 
may also be an error message directed to a visual display device in the 
communication unit, so its user is aware of the event. In the latter case, 
the user might manually replace an existing scan list entry with the talk 
group sourcing the trigger event that started the scan list revision 
process. 
When it is determined (406) that the command is not an add command, the 
opcode is compared (410) with the delete command. If the opcode is not a 
delete command, the command might be another type reserved for other uses 
beyond the scope of the present invention, in which case they are 
processed (413). If a delete command is received, the scan list is 
searched to determine (411) whether the received talk group element is in 
the list. If not, the message is assumed to contain other information 
necessary for further processing (413) according to a method outside the 
scope of the present invention. If the talk group identifier is found in 
the scan list, the entry is deleted (412) from the scan list. Deletion is 
accomplished by erasing the talk group and receive-priority elements in 
the scan list entry. Automatic deletion may be initiated by the 
communication controller in response, for example, to a trigger component 
indicating that there is no longer a situation active that requires 
assistance across talk group boundaries. Thus, the talk group originally 
requiring assistance might issue an "all clear" message of the data or 
speech type. Automatically deleting a scan list element when it isn't 
required improves the communication system's effectiveness, as the limited 
scan list entries are made available for those talk groups requiring 
assistance. Upon deletion of the appropriate element, or upon completion 
of the processing of another command, the communication unit continues to 
monitor the control channel, until the next wireless message is received 
(401). 
FIG. 5 illustrates a logic diagram depicting operation of the base site, in 
accordance with the present invention. Upon receipt (501) of a wireless 
message (i.e., message 118 shown in FIG. 1) from a communication unit, the 
communication controller identifies (502) which talk group the sourcing 
communication unit belongs to (i.e., from talk group field 119 shown in 
FIG. 1). The communication controller then determines (503) whether or not 
the identified talk group is represented in its source talk group field 
(i.e., field 301 in FIG. 3). If not, no special action is taken until the 
next wireless message is received (501). However, if the talk group is 
found in the talk group list, then the communication controller instructs 
the trigger detection system 111 to analyze (504) the message for the 
trigger component associated with the talk group entry. As earlier noted, 
the communication controller includes channel information in the same 
instruction, so the trigger detection system 111 can monitor the correct 
base station 107-109 for communication from the source communication unit. 
If the trigger component is not found (505), then a check for the end of 
the message is made (506). A message end identifier is well known in the 
art to include an end of transmission (EOT) signal. If the message is not 
over, the base site continues to analyze (504) the message, searching for 
the trigger component during the message. 
When the message is over, the next wireless message is received (501) and 
processed as discussed above. When the trigger component is found within 
the message 120 from the source communication unit, the communication 
controller determines (507) the target talk group, scan list revision 
opcode, talk group identifier, and receive-priority level (i.e., based on 
the entry in table 300 for the sourcing talk group). The communication 
controller then formats a wireless message 114 for transmission, by the 
base stations 107-109, to the talk group indicated in the target talk 
group field 304 of the entry of table 300. The wireless message 114 
contains the scan list revision opcode, talk group identifier, and 
receive-priority. Upon receipt of the wireless message 114, the target 
communication units automatically scan transmissions from the sourcing 
talk group using the receive-priority level associated therewith. After 
the message is transmitted (508), the base site continues to receive (501) 
wireless messages and processing them as discussed above. 
In the foregoing manner, the present invention provides a method for 
automatically revising the scan list in a wireless communication unit in 
response to the detection of a predetermined trigger component. Thus, 
recipient communication units are made capable of scanning subsequent 
transmissions from a talk group requiring assistance during an emergency. 
Likewise, the present invention contemplates the deletion of certain talk 
groups from the scan list, thereby enabling the communication units to 
return to normal, efficient scanning operations. Further, such a method is 
not constrained by the shortcomings of prior art schemes that rely on 
human intervention for directing talk groups to monitor communications 
from another talk group requiring assistance.