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FIELD OF THE INVENTION
This invention relates to trunked communication systems, including but not
limited to repeater control in a trunked communication systems. Reference
is made to U.S. patent application No. 07/906,256, titled "Resource
Management by an Intelligent Repeater," filed on Jun. 29, 1992 on behalf
of Mark L. Shaughnessy et al., with the same assignee as the present
invention.
BACKGROUND OF THE INVENTION
Trunked communication systems are known to comprise a plurality of
communication units, a limited number of communication resources that are
transceived via a predetermined number of repeaters, or base stations, and
a communication resource allocator that allocates the limited number of
communication resources among the plurality of communication units. The
communication units may be portable radios and/or mobile radios. The
communication resources may comprise a TDM (time-division multiplexed)
bus, a carrier frequency, a pair of carrier frequencies, or any RF (radio
frequency) transmission means.
Generally, trunked two-way communication systems provide mobile and
portable communication units with wireless services similar to many wired
communication networks. Such examples include full-duplex telephone voice
communication, two-way mobile-to-mobile group dispatch communication, and
two-way mobile-to-dispatcher group dispatch communication. A typical
trunked communication system site, where each different site has a
different physical location, is composed of a member of full-duplex
repeaters, each coupled to a variety of devices to support interconnection
to the public telephone network, mobile-to-mobile calling, and to one or
more dispatcher console positions. These devices typically provide a
centralized control for the repeaters. For example, a single central
controller provides radio channel signalling encode and decode functions,
authorization functions, resource determination functions, and
communication activity logging. A single telephone interconnect switch
typically provides the repeaters with an interface to one or more
telephone lines to support telephone interconnect communication. In
systems employing a single device that is shared among the repeaters, a
failure of the single device may render one or more of the desired
services or functions inoperable, thus impairing communications in the
system. Placing redundant devices within the system is expensive and an
inefficient use of space and resources.
Because breaks in communications must be avoided, a method of providing
centralized control of repeaters without wasteful redundancy is desired.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an intelligent repeater in a trunked
communication system in accordance with the invention.
FIG. 2 is a diagram of an intelligent repeater in a trunked communication
system with public network and private off-site network interfaces in
accordance with the invention.
FIG. 3 is a flowchart showing operation of a trunked communications system
using a single intelligent repeater in accordance with the invention.
FIG. 4 and FIG. 5 depict a flowchart showing operation of a trunked
communications system using multiple intelligent repeaters in accordance
with the invention.
FIG. 6 is a flowchart showing testing of intelligent repeater functions in
accordance with the invention.
FIG. 7 is a flowchart showing distribution of system control functions
amongst a plurality of intelligent repeaters in accordance with the
invention.
DESCRIPTION OF A PREFERRED EMBODIMENT
The following describes a method and apparatus that enables continuous
service in a trunked communication system by eliminating the dependence on
single shared devices for system control. Each of a plurality of
intelligent repeaters is equipped with an arrangement of components that
uniquely distribute these service functions. The functions of radio
channel signaling encode and decode functions, authorization functions,
resource determination functions, and communication activity logging are
distributed among the repeaters such that function placement adaptation
insures continued service operation.
An intelligent repeater 101 and a communication unit 102 interact with
radio frequency (RF) signals 114 and 115, as illustrated in FIG. 1. In the
preferred embodiment, the intelligent repeater includes a transmitter 105,
a receiver 106, a signal processor 104, a central processing unit (CPU)
103, memory 108 for storage of information, and a switch 107. Also
included are interfaces for interfacing control information and processed
signals directly to an external communication network. These interfaces
include, for example, a public interface 117, a private off-site interface
118, and a private on-site interface 119.
RF signals 115 transmitted by the communication unit 102 are received by
the receiver 106 of the intelligent repeater 101 through receive antenna
116. These transmissions may be modulated using a variety of techniques
known in the art, such as, frequency modulation (FM), amplitude modulation
(AM), or a combination of the two. Further, the signals carded by the
modulation may be frequency and/or time division multiplexed. After
reception, the signals are transferred to the signal processor 104, which
may be a digital signal processor or DSP (e.g., a DSP56001 available from
Motorola, Inc.), for further demodulation, decoding, and processing.
Control information is extracted from the signal and transferred to the
CPU 103, which may be a microprocessor (e.g., an MC68302 microprocessor
available from Motorola, Inc.). Other information present in the signal
such as voice, images, and user data are transferred to the switch 107,
which may be a cross-point matrix, time slot interchanger, or
multiple-access packet link for routing. The switch provides a means to
transfer control signals and information signals between the radio
channel, the public network, the private off-site network, and the private
on-site local area network (LAN). The other information may also be
transferred, if necessary, to memory 108, which may be random access
memory (RAM), for temporary storage.
The extracted control information may contain such things as the
communication unit's individual and group identifications (IDs), and type
of service requested. The CPU 103 uses this information in a manner
described in FIG. 3, FIG. 4, and FIG. 5 to allocate resources and
communicate with other system elements in order to appropriately serve the
communication unit 102. The memory 108 is also used by the CPU 103 during
the normal course of its processing to store and retrieve control
information and program steps, as those represented in FIG. 3, FIG. 4,
FIG. 5, FIG. 6, and FIG. 7, system database information, and any dynamic
parameters needed during program execution.
The switch 107, under control of the CPU 103, routes information from the
signal processor 104 to one or more of the interfaces 109, 110, and 111.
The content of the information and the configuration of the external
network(s) determine to which interface(s) the information is routed. The
public interface 109, if needed, is connected to one or more of many
different public networks 117. The public interface 109 may be a standard
telephone subscriber loop line, or it may be a standard data network line,
such as one from an X.25 standard public packet data network. The private
off-site interface 110, if needed, is typically connected to a private
communications network 118 that is used to connect other sites of a
multi-site radio network. The private off-site network 118 may be
constructed of 4-wire analog lines, time division multiplex carriers,
packet data links, and so forth. The private on-site interface 111 is
connected to a LAN 119 that forms a communication link shared by other
intelligent repeaters of the system that are located at the same
communication site, i.e., the same physical space where the intelligent
repeaters are located. The LAN 119 that the private on-site interface 111
is connected to may be a standard LAN, such as a LocalTalk LAN, an
Ethernet LAN, or FDDI (Fiber-Optic Distribution Data Interconnect) LAN.
The switch 107 is also used to route information that flows into the
intelligent repeater 101 from the interfaces 109, 110, and 111, to the
signal processor 104. These signals are then processed by the signal
processor 104 and transferred to the transmitter 105, where they are
transmitted to the communication unit 102 through a transmit antenna 113.
The RF signal 114 that is transmitted to the communication unit 102 may be
modulated using any of the modulation techniques described above.
Some signals to and from the interfaces 109, 110, and 111 may be
transferred directly between the interfaces 109, 110, and 111 and the CPU
103 using a control bus 112, which may be a a multi-drop parallel data
bus, serial data bus, or a time division multiplexed parallel or serial
bus. In the preferred embodiment, each of the interfaces 109, 110, and 111
contains a microprocessor (e.g., an MC68302 microprocessor) that monitors
the signal flow and determines whether the signals should be transferred
to the CPU 103 or to the signal processor 104 via the switch 107.
Intelligent repeaters 201 and 202 and their communication with one or more
communication units 203 is illustrated in FIG. 2. In a trunked radio
system, there may be one or more intelligent repeaters 201 and 202 located
at one or more physical locations or sites. The number of intelligent
repeaters needed per location is based on the required capacity of the sum
of the interfaces provided in terms of radio channel and external network
interfaces. The locations of sites are chosen based on the desired RF
coverage of a particular geographical area.
Communication between intelligent repeaters 201 and 202 is necessary to
enable the repeaters to operate in concert to provide consistent services.
This communication is provided by assigning each component of the call
establishment process to the intelligent repeaters 201 and 202. For
example, a particular intelligent repeater at a site may be dedicated to
transceiving control information to and from the communication unit(s)
203. This particular repeator is considered to provide the "control
channel," a term well known in the art. Other intelligent repeators may be
present at the site to be used for transceiving the typical voice, data,
or image messages to and from the communication units 203. When a
communication unit 203 makes a request for service on the control channel,
that information is passed via the private on-site network 206 to the
other intelligent repeaters 201 and 202 at the site for request
authentication and appropriate resource allocation in accordance with the
methods described below. As a second example, when a communication trait
203 roams from the coverage area of one site into the coverage area of
another, information is passed via the private off-site network 209 using
communication links 207 and 208 such that appropriate resources may be
placed into service at the new site, while the resources that were in
service at the old site are deactivated. As a third example, a
communication unit 203 may request a telephone interconnect call. To
connect this type of service to the communication unit 203, the
intelligent repeater that is transceiving the communication unit's RF
signal 204 is typically connected directly into the public telephone
network 212 via a standard telephone line 211.
A flowchart depicting operation of a trunked communications system using a
single intelligent repeater is shown in FIG. 3. The intelligent repeater
receives a request for service from a communication unit at step 301. The
intelligent repeater decodes the request at step 302 using the signal
processor 104 and CPU 103 to determine what type of service is required by
the communication unit. The request is authorized at step 303 by scanning
a list stored in memory and comparing the ID of the communication unit
sourcing the resource request to the stored list, which is a predetermined
list of authorized IDs and the resources each ID may access, as different
communication units may be authorized to use only certain communication
resources. If the communication trait that sourced the request is not
authorized for the requested communication resource, the request is
rejected at step 305, which entails transmitting a rejection message to
the requesting communication unit, and the processing ends for this call
request.
If at step 304 the communication unit that sourced the request is
authorized to use the requested communication resources, the appropriate
resources needed to service the request are determined at step 306. If at
step 307 the resource required is a public resource, the public interface
is connected to the public resource via the switch 107 at step 308. If at
stop 309 the resource required is a private off-site resource, the private
off-site interface is connected via the switch 107 at step 310. The radio
transceiver, transmitter 105 and receiver 106, in the intelligent
repeater, operably coupled to the signal processor 104, is also connected
via the switch 107 at step 311, and processed signals are transferred
between the communication unit and the requested resources, thus
communications occur.
These connections remain until the completion of the call at step 312, when
the resources are disconnected at step 313 by deactivating the interfaces
and stopping the transfer of processed signals through the switch 107. The
call is logged at step 314 by storing information such as the
communication unit's individual and/or talkgroup IDs, the duration of the
call, and the types of resources used.
A flowchart depicting operation of a trunked communications system using
multiple intelligent repeaters at a trunked communication site is shown in
FIG. 4 and FIG. 5. An intelligent repeater supporting control channel
communications, where resource requests are received from communications
units and resource grants and transmitted in response, receives a resource
request from a communication unit at stop 401. In the preferred
embodiment, the communication unit encodes the information in the resource
request with an error control coding method to provide reliable operation
in the RF environment. The intelligent repeater supporting the control
channel operations decodes 402 the information in the requesting
transmission. The request information contains an ID of the requesting
communication unit and also indicates what type of service is requested.
The present invention enables the distribution of the component tasks of
the call establishment process. Accordingly, the intelligent repeater
supporting the control channel operations decides which of the intelligent
repeaters will authorize access for the communication resource request at
step 403. Each intelligent repeater has a list of which intelligent
repeator is assigned to carry out each component of the call establishment
process so that each stop is directed to the appropriate intelligent
repeator. The appropriate intelligent repeator is either the same
repeater, the local choice, or another intelligent repeator. If the
authorization function is carried out by another of the intelligent
repeaters, then the request information is transmitted via the private
on-site interface over the site LAN to the intelligent repeater that will
carry out the authorization at stop 404. At stop 405, the intelligent
repeator assigned to carry out the authorization compares the identity of
the requesting communication unit against a predetermined list of
authorized communication unit IDs at stop 405, as was previously
described. If at stop 406 the requesting communication unit's ID is not
authorized for access, the request is rejected at step 407, which entails
transmitting a rejection message to the requesting communication unit, and
the processing ends for this call request.
If at step 406 the requesting communication unit is authorized for access,
the intelligent repeater supporting the control channel operations
establishes at step 408 which of the intelligent repeaters will determine
required communication resources to fulfill the communication resource
request. The appropriate intelligent repeater is either the same repeater,
the local choice, or another intelligent repeater. If the resource
determination function is carried out by another of the intelligent
repeaters, then the request information is transmitted via the private
on-site interface over the site LAN to the intelligent repeater that will
carry out the resource determination at step 409. At step 410, the
intelligent repeater assigned to carry out the resource determination
analyzes what resources are required by looking at the type of service
requested and matching it against a predetermined list of resources
required for that service and checking if the resource(s) is available for
that type of call, and the process continues with step 501 of FIG. 5. A
radio channel resource is chosen to serve the requesting communication
unit.
The intelligent repeater providing the radio channel resource may also be
interconnected to the public telephone network and/or to a private network
to establish the desired service. Depending on the availability of the
public interface and private off-site interface locally associated with
the intelligent repeater, the interconnect may be routed through the
private on-site interface to the LAN and to another on-site intelligent
repeater with an available public network or private off-site network
resource. In this way, the distributed resources of the plurality of
intelligent repeaters at the trunked communication site are utilized to
maintain communications at all times.
The intelligent repeater supporting resource allocation decides whether
public and private network resources are to be used, and if so, whether
the resources are local or non-local. At step 501, the public resource
being assigned locally is considered. If at step 501 the public network
interface is not available within the same intelligent repeater, then a
connection is made at step 502 through the on-site LAN to an on-site
intelligent repeater with an available public network resource (interface
109). If at step 501 the local public network interface is available, it
is connected within the same intelligent repeater at step 503.
At step 504, the off-site private resource being assigned locally is
considered. If at step 504 the off-site private network interface to an
off-site private resource is not available within the same intelligent
repeater, then a connection is made through the on-site LAN to an on-site
intelligent repeater with an available off-site private network resource
at step 505. If at step 504 the local off-site private network interface
is available, it is connected within the same intelligent repeater at step
506.
The network interfaces chosen and assigned are connected at step 507 to the
chosen radio resource, such as a frequency-pair channel to complete the
requested call which transfers processed signals. Processed signals may be
voice, data, and image information carried in any one of many formats by
different physical media.
The intelligent repeater tests to see if the call is done at step 508. When
the call is completed, the communication unit transmits a call end signal
that is detectable by the intelligent repeater that provided the
resources. The resources allocated to the call are disconnected by
stopping the transfer of processed signals at step 509. At step 510, a
decision is made where to log the call activity. Logging typically
involves storing key statistics related to the call into the memory of the
intelligent repeater. If the intelligent repeater that is assigned the
logging function is not the intelligent repeater that provided the radio
link, then the call information is passed to that logging intelligent
repeater over the on-site LAN at step 511. The call information is logged
into the memory of the appropriate intelligent repeater at step 512, and
the process ends.
A network of distributed processing elements operates together when each
element has been assigned a particular task related to the overall
objective. In a trunked communication system site comprised of intelligent
repeaters, each intelligent repeater may be capable of performing each
component of the call establishment process, e.g., receiving a resource
request over a radio channel, decoding the request, authorizing access,
determining the required resources, connecting the resources, and logging
the call summary. In the present invention, when a plurality of such
intelligent repeaters comprise a trunked communication system, the
components of the call establishment process may be distributed among the
intelligent repeaters that are capable of each component task. Such an
arrangement is desired to provide non-stop system operation in the event
that one of the intelligent repeaters suffers a partial or complete
failure. It is therefore desirable to determine the capabilities of these
intelligent repeaters by testing the status of their associated major
components. Taking into account the results of such status testing, an
assignment of the call components may be carried out such that the
combination of the intelligent repeaters work efficiently together to
provide the desired communication services.
A flowchart depicting the status testing operation of each intelligent
repeater is shown in FIG. 6. The intelligent repeater powers up at step
601. Alternatively and/or additionally, this procedure could be activated
on a demand basis in response to an status solicitation request from a
device external to the intelligent repeater. The core elements are tested
at step 602. The core elements of an intelligent repeater include the CPU
103, signal processor 104, memory 108, and switch 107. These core elements
are critical to the operation of the intelligent repeater and are tested
and their status summarized together as each must be operational in order
that the intelligent repeater be assigned to any of the call establishment
component tasks. Methods of testing each of these individual core elements
are known in the art. The results of each test are checked to determine if
all core elements passed at step 603. If all of the core elements pass
their test, a status record in the memory is marked as pass at step 604.
If one or more of the core elements fail its test, the status record is
marked as fail at step 605.
At step 606, the status test of the radios (e.g., transmitter 105 and
receiver 106) associated with the intelligent repeater is performed.
Methods to individually test radio devices are known in the art. The
radios or transceivers may operate at any frequency with any type of
modulation and access method as supported by the CPU 103 and signal
processor 104. The results of each test are checked to determine if all
radios passed at step 607. If all of the radios passed, a status record in
the memory is marked as pass at step 608. If one or more of the radios
failed its test, the status record is marked as fail at step 609.
At step 610, a status test of the public network interface associated with
the intelligent repeater is performed. Methods to individually test such
interfaces are known in the art. The interface may be coupled to a public
network by way of any one of many physical line types, e.g., a standard
telephone subscriber loop line or a standard data network line. At step
611, the results of each test are checked to determine if the public
network interface passed. If all of the public network interface tests
pass, a status record in the memory is marked as pass at step 612. If one
or more of the tests fail, the status record is marked as fail at step
613.
At step 614, a status test of the private off-site network interface
associated with the intelligent repeater is performed. Methods to
individually test such interfaces are known in the art. The interface may
be coupled to a private off-site network by way of one of many physical
line types, e.g., 4-wire analog lines, time division multiplex carriers,
or packet data links. At step 615, the results of each test are checked to
determine if the public network interface passed. If all of the private
off-site network interface tests pass, a status record in the memory is
marked as pass at step 616. If one or more of the tests fail, the status
record is marked as fail at step 617.
At step 618, a status test of the private on-site network interface
associated with the intelligent repeater is performed. Methods to
individually test such interfaces are known in the art. The interface may
be coupled to a private on-site network by way of one of many physical
line types, e.g., a standard LAN, such as a LocalTalk LAN, an Ethernet
LAN, or FDDI IAN. The results of each test are checked to determine if the
private on-site network interface passed 619. If all of the private
on-site network interface tests pass, a status record in the memory is
marked as pass at step 620. If one or more of the tests fail, the status
record is marked as fail at step 621.
After completion of testing and temporary storing of the results within the
intelligent repeater performing the tests, the test results, or status
information is transmitted at step 622 to the site resource manager, and
the process continues with step 602 in order to keep the status
information current. The site resource manager is a predetermined
designation maintained by one of the intelligent repeaters at each
communication site.
A flowchart depicting the resource manager operation of an intelligent
repeater is shown in FIG. 7. The resource management function is a process
that runs in a CPU 103 of one of the intelligent repeaters at a trunked
communication system site. At step 701, the resource manager powers up.
The resource manager receives status information reports from each of the
intelligent repeaters at step 702. In the preferred embodiment, the
transmission of status information is carried over the private on-site
LAN.
The resource manager analyzes the status of the first intelligent repeater
at step 703. The status of the core element tests are checked to determine
if all core elements passed at step 704. If there was no pass at step 705,
and the resource manager has not looked at all of the intelligent
repeaters' status reports at step 705, the resource manager checks the
next intelligent repeater in the list at step 706. If all of the
intelligent repeater status records have indicated failure of the core
elements at steps 704 and 705, the site is non-operational and a failure
condition is declared at step 707. Such a situation is highly unlikely and
results in an alarm being triggered to notify the appropriate personnel.
When an intelligent repeater is found, at step 704, to have passed all of
its core element tests, that intelligent repeater is selected at step 708
to perform the authorization of access functions and resource allocation
functions associated with establishing communication services.
The resource manager analyzes the status of the next intelligent repeater
at step 709. The status of the core element tests are checked to determine
if all core elements passed at step 710. If there was no pass at step 710,
and the resource manager has not looked at all of the intelligent
repeaters' status reports at step 711, the resource manager checks the
next intelligent repeater in the list at step 712. When an intelligent
repeater is found, at step 710, to have passed all of its core element
tests, that intelligent repeater is selected at step 713 to perform
logging functions associated with the establishing communication services.
If all of the intelligent repeater status records have indicated failure
of the core elements at steps 710 and 711, the intelligent repeater that
was chosen to carry out authorization and resource allocation is also
selected to carry out the logging function at step 713.
At stop 714, the resource manager informs the intelligent repeators of the
assignment of authorize, allocation, and logging functions to the
particular repeators. Each intelligent repeator is thus able to route call
establishment information to the proper intelligent repeator assigned to
carry out each function of the call process. The resource manager also
informs the resource allocation intelligent repeator of the status
information associated with each of the intelligent repeators at stop 714.
The resource allocator is thus able to allocate communication resources
from the available pool of site resources, such as radio channels, public
network interfaces, or private off-site network interfaces.
New status information is received from each of the intelligent repeators
by the resource manager at stop 715. Critical failure indications are
checked at stop 716. If a critical failure occurs, such as a core element
failure in an intelligent repeator assigned to the authorization,
allocation, or logging functions, the analysis and selection process
repeats from stop 703. If at stop 716 there is no critical failure, the
process continues with stop 714.
When assigning intelligent repeators to the authorize, resource allocation,
and logging functions, the resource manager may assign all functions to
one intelligent repeator, each function to a different repeator, or any
combination in between. Because each repeator is capable of each control
function, the resource manager is able to distribute the needed system
functions throughout the system as needed, thus providing a highly
flexible and reliable communication system. The flowchart of FIG. 7 does
not reflect all of these many possibilities, for the sake of simplicity
and brevity of the drawings. The resource manager may also assign other
control functions not listed here.
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