Method for placing a communication group call in a multiple site trunked system

In a multi-site trunked communication system, a method for allowing a communication unit to place a unit directed group call consists of identifying, by the unit initiating the communication, a target unit and transmitting identification information of the target unit and a group call request to a communication resource allocator. Upon receipt of the identification information and the group call request, the communication resource allocator processes the request and when a resource is available in the site that the target unit is located in, allocates the resource such that the target unit and any other units of the communication group in the site can participate in the group call.

FIELD OF THE INVENTION 
This invention relates generally to communication systems and, more 
particularly, to placing a group call in a multiple site trunked 
communication system. 
BACKGROUND OF THE INVENTION 
Wide area trunking communication systems are known to comprise a plurality 
of communication units, a plurality of sites, a limited number of 
communication resources, and a communication resource allocator. 
Typically, the plurality of communication units are arranged into 
communication groups. A wide area trunking communication system allows a 
communication unit to communicate with its communication group from any 
site in the system. 
A difficulty arises in a wide area trunked communication system, when a 
member of the communication group is in a site that does not have an 
available resource. In such situations, one prior art solution was to wait 
until all sites, currently supporting some portion of the group 
population, had an available resource and then place the call. This 
allowed the group call to be fully processed, however, there was the 
potential of extended wait time while awaiting communication resource 
availability at all the sites for the call. Another approach was to allow 
the requesting communication unit to override the busy condition such that 
the resource allocator need only address resource availability at some 
pre-determined, select set of sites, instead of all the sites currently 
supporting some portion of the group population. This has the potential to 
reduce wait times over that experienced by awaiting resource availability 
at all the populated sites for this group. See Felderman U.S. Pat. No. 
5,101,502 for a further discussion of busy override in a wide area trunked 
communication system which is incorporated herein. 
In many communications, the requesting communication unit does not need to 
talk to the whole group, rather only a portion of it. Thus, the methods 
for communicating with a communication group described above waste 
communication resources and delay access time for small audience calls. 
Therefore, a need exists for a method that allows a group call to be 
directed to only a portion of the communication group.

DESCRIPTION OF A PREFERRED EMBODIMENT 
In general, this invention provides a method for placing a group call that 
allows the unit initiating the group call to select a target unit, such 
that the group call may be processed when a communication resource is 
available in the site containing the target unit. The unit initiating the 
group call selects a target unit by transmitting the ID of the target unit 
in the request for group call service. Upon receipt, the communication 
resource allocator allocates a resource, when available, for the 
communication in the site that the target unit is located, and may 
optionally allocate resources in other sites where units of the same 
communication group are located if a resource is available in those sites. 
This unit directed method of placing a group call eliminates the need to 
wait for an available resource in each site containing a communication 
unit member, therefore, reducing delays and wasted resources. 
The invention can be more fully described with reference to FIG. 1, FIG. 2, 
and FIG. 3. FIG. 1 illustrates a communication system comprising a 
communication resource allocator 100, a plurality of communication sites 
(only four shown) 101, 102, 103, 104, a limited number of communication 
resources 105, 106, 107, 108, at each communication site and communication 
network links 109, 110, 111, 112. The communication resources are 
comprised of control channel resources for communication service request 
and grants, and traffic channel resources for voice communication. The 
plurality of communication units 113-124 are distributed among the 
communication sites as shown, but are free to roam from site to site, and 
are capable of utilizing resources at each site for communication 
services. The communication units 113-124 depicted in FIG. 1 are members 
of one of three communication groups, Group A, Group B, or Group C. (FIG. 
1 shows only 3 groups for convenience of illustration, however, in 
practice, any number of groups may be serviced.) Communication Group A is 
comprised of communication units 113, 114, 115, 116, and 117; 
communication Group B is comprised of units 118, 119, and 120; and 
communication Group C is comprised of communication units 121, 122, 123, 
and 124. 
FIG. 2 illustrates a logical flow diagram that the communication resource 
allocator and communication units may utilize to implement the present 
invention. Note that the communication resource allocator and/or the 
communication units may require additional memory and processing devices 
to store and execute the present invention. At step 200, a requesting 
communication unit of a particular communication group makes a 
communication group call request to the communication resource allocator. 
This group call request includes identification information of the 
particular communication group and may include identification information 
of at least one target communication unit of the particular communication 
group. The communication resource allocator determines if the received 
group call request indicates a desired target unit for the requested 
communication group service 201. If a target unit is identified, the 
communication resource allocator determines which communication site(s) of 
the communication system need to be involved in the requested group call 
204. 
Subsequently, the communication resource allocator determines if 
communication resources are available at the determined communication 
sites 205. When communication resources are available, the communication 
resource allocator allocates these communication resources to the group 
call and allows the communication to take place 208. All members of the 
communication group located in the targeted communication site and the 
site that the initiating communication unit is located in will be involved 
in the communication group call. 
Optionally, once communication resource availability has been attained at 
the target communication sites, the call may be processed to include all 
other communication sites which have both an available resource and a 
member of the communication group population 207. This would increase the 
number of units in the group call to include all communication group 
members at the initiating group call site, the targeted group call site, 
and communication group members at additional sites that have a 
communication resource available. 
If resources are not available at the target site(s) 205, the communication 
resource allocator will repeatedly check for an available resource until 
either a resource becomes available or the initiating unit terminates the 
group call request 206. 
For clarity, an example of the above follows. Referring again to FIG. 1, 
communication unit 113 of Site 1 101 requests a group call for group A, 
indicating unit 117 as the target unit for the group call. Currently 
communication unit 117 resides at Site 4 104 of the communication system 
100. The communication resource allocator 100 determines that the 
communication sites currently populated by members of the communication 
group A include sites 1 (101), 3 (103), and 4 (104). However since the 
call request indicates a desired target unit for the group call, only the 
initiating site and the target unit site need be involved in the group 
call. The communication resource allocator then assigns communication 
resources (105) at Site 1, and communication resources (108) at Site 4 to 
this group call. The group A communication now may commence and will 
include the communication units 113 and 114 at Site 1 (101) and 
communication unit 117, at site 4 (104). Note that communication units 115 
and 116 at site 3 (103) are not involved in the requested group call, nor 
is communication site 2 (102), which does not have an active portion of 
the communication group A population. 
Optionally, assume that a portion of the communication group A populated a 
non-target site, in this example site 3 (103), that has a communication 
resource available at the time the group A group call is processed. 
Communication site 3 (103) will be included in the group call, by 
allocating a resource, such that communication units 115 and 116 are able 
to participate in the group A group call communication. 
In a general group call request, if a target unit identity has not been 
supplied at the time of the group call service request, the communication 
resource allocator cannot direct the call to a particular communication 
site, but can still compose a semi-private group call for the duration of 
this particular group call activity. Referring again to FIG. 2, if a 
target unit is not identified, the communication resource allocator will 
record the identity of the initiating communication unit as a transmitting 
communication unit affiliated with this particular communication group for 
future reference 202. The communication resource allocator references a 
current list of all recently transmitting communication units for this 
particular communication group 203. The communication sites containing the 
recently transmitting communication units compose the necessary set of 
sites to be involved in the group call. By default, if this is the first 
transmission for this group, include all communication sites containing 
communication group units in the group call and begin to construct a new 
recent transmitting unit list for this particular communication group. The 
communication resource allocator will determine when communication 
resources are available at the indicated communication sites, and when all 
sites have available resources, the communication resource allocator will 
process the group call request. 
The list of recently transmitting communication units associated with a 
particular communication group is only retained for a predetermined period 
of time. The entries in the list will be retained as long as new group 
call activity for this particular communication group continues. Once call 
activity lapses for a predetermined period of time, typically tens of 
seconds or less, the entries in the list are deleted. The next group call 
request for this communication group, which does not indicate a unique 
target unit, will, by default, include all communication sites containing 
communication group units in the group call and begin to construct a new 
recent transmitting unit list for this particular communication group. 
FIG. 3 illustrates a logic diagram that allows the communication system to 
support multiple communications within the same communication group. At 
step 300, the communication resource allocator receives a second group 
call request from a second requesting unit and determines that at least 
one second target unit is identified 302. The target communication sites 
necessary to complete this second group call are determined by the 
communication resource allocator 303. The communication resource allocator 
then determines if any of the indicated second target sites are presently 
involved in a previous group call involving the group associated with this 
second group call request 304. If a second target site is involved in a 
previous group call for the group associated with this second group call 
request, the second group call request can not be processed at this time 
305. If there is no conflicting group activity, the resource allocator 
will process the second group call in the same manner the first group call 
was processed (see FIG. 2 steps 205, 207, and 208). 
Assume the above communication group A group call example is active, with 
the exception that the optional portion involving additional sites has not 
been enabled. The group call includes the initiating unit 113 and unit 114 
at site 1 (101) and target unit 117 at site 4 (104). Note that 
communication units 115 and 116 at site 3 (103) are not involved in the 
group call. Now assume that while the first group A group call is active, 
unit 115 at site 3 requests a second group A group call indicating unit 
116 as the intended target unit (second target unit identity). Since both 
initiating unit 115 and the target unit 116 are resident at site 3 (103), 
which is not involved in the first group A group call, the second group A 
group call will be processed, while the first group call is active, if 
resources are available at site 3 103. 
The present invention provides a method for placing a communication unit 
directed group call in a manner that reduces system access time. This is 
achieved by excluding some communication group members from the group call 
while guaranteeing the inclusion of certain other communication units 
(i.e. targeted units). This invention also allows a portion of the 
communication group to place a group call involving a limited number of 
communication units, while another group call is taking place in different 
sites.