Note: Descriptions are shown in the official language in which they were submitted.
lZ9~ 3
-- 2 --
Technical Field
This invention relate~ generally to trunk~d
communications ystems and ~ore particularly to trunked
communication system~ that transceive ~otll volce an~ ~ta.
Back~round Art
In a basic RF trunked system there exists a high
degree of flexibility to partition voice conversations
between different groups so that no one group of users is
epecifically aware when another group of ugers makes use
of the system. Typically, these groups are subdivide~
into subgroups 80 that callq may be made upon eit~er a
group, subgroup or individual basis depending upon the
ty~e of communication desired by an initiating ~ubscriber.
To establish a voice communication between a
group of unit~ operating on a trunked ~stem, a ~ubscriber
unit transmits a data packet called an "inbound signalling
word" (ISW) on a control ahannel that ig maintainecl ~or
such purposes. The ISW contains at least the requesting
unit's unique ID code, which may contain or be used to
~ obtain the requesting subscriber's current talk-group.
The request is forwarded to a central controller, which
decodes the request, and transmits on the control channel
a data packet called an "outbound æignalling word" (OSW)
to all subæcriber units, which continuously monitor the
control channel when not par~icipating in a voice
conversation The OSW is a channel grant which contains
the talk-group code of the reque6ting unit, and the voice
channel number asæiqned for the conversation. The OSW
causes the requesting unit to move t~ the voice channel
and commence transmitting, while simultaneously causing
all other subscriber units in the game talk-yroup to move
to the voice channel as listening units. In this way a
yroup call is set-up. If, however, all voice channels are
in use when a subscriber unit transm;ts an ISW, the
central controller typically sends the requesting
~ 6ubæcriber a"Busy OSW".
`.~
.~
. ..
~2~ 3
-- 3 --
lIn addition to voice messages, it is desirable to
send data information across a trunked radio channel. In
some data systems, a subscriber unit obtains a trunked
da~a communication channel via the same procedure used to
obtain a voice channel. However, this practice is
inefficient and spectrally wasteful, due to the time it
takes for a requesting subscri~er to transmit an ISW and
rece~e ~ chan~e~ ~r~n~ OS~ fro~ the central and the time
it takes to set up and elean-down calls on a voice
channel. At contemporary data transmission rates, it is
anticipated that an entire typical data message would take
substantially less time to transmit than the time required
to set up a channel (approximately .5 seconds). Thus,
assigning a data channel pursuant to the same procedure as
assigning a voice channel would be wasteful of spectrum
and consume pr~cious ~y~tem time that could be better used
to transmit data messages.
Other trunked communication systems desirous to
accommodate data traffic have permanently dedicated one or
more channels to handling data traffic. While this avoids
the access time problem noted above, this technique is
contrary to the ~2Si¢ principles of trunked communication
systems, which strive to allocate channel resources across
a plurality of users as re~uired. Therefore, the practice
2~ of having dedicated data channels, permanently removed
from the channel allocation "pool" of frequencies, is
wasteful of spectral resources and leads to inefficient
system operation. Moreover, the dedicated data channel
systems lack the capacity to dynamically redistribute or
allocate ~he data ~raffic load across the available data
channels. Such systems typically permanently assign a
subscriber unit to a data channel thereby building in
future problems as the number of data subscribers
increases on a particular channel.
~X~7~3
Accordingly, there exists a need for a trunked
communication system that can accommodate both voice and
data signals, and that operates in true trunked manner to
efficiently utilize spectral resources.
Summary of the Invention
Accordingly, it is an object of the present
invention to provide an improved trunked communication
system.
It is a further object of the present invention
to proviae a trunked communication system capable of
accommodating both voice and data traf~ic.
It is a further object of the present invention
to accommodate data traffic without permanently removing
one or more channels from the trunked channel resources.
It i8 yet another object of the present invention
to provide a voice/data ~ubscriber unit capable of
operating in the trunked communication system of the
present inventionO
It is yet a further object of the present
invention to provide a voiceldata subscriber unit capable
of operating in a plurality of data modes.
It i~ yet another object of the present invention
to provide a trunked voice/data communication system which
accommodates prior voice only and data-only subscribers.
It is yet a further object of the present
invention to provide a voice/data trunked communication
system which permits prior data-only subscribers to
communicate notwithstanding the absence of an assigned
data channel.
It is y~t a further object of the present
inventio~ to pr~Yide a trunked communication system that
minimizes spectrally wasteful access time while providing
trunked data communication.
Briefly, according to the invention, a trunked
voice/data communication system is provided wherein a
31 ;~9~ 73
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plurality of trunked voice reyeaters are adapted to
accommodate both voice and data traffic. Data channels
are ~hereafter assigned for a dynamically varying period
of time depending upon, for instance, traffic load or time
of day. Once the sys~em establishes a data channel, any
sub¢criber data unit may transmit witho~t re-requesting a
data channel. In this way, the protracted re~uest-grant
delay times are avoided. After the time interval, or if
higher priority voice traffic exists, the data channel may
be reallocated to voice traffic. Thereafter, another data
channel reguest can result in a similar data channel grant
for another time interval on another, or the same, channel.
Brief Description of the Drawings
The eatures of the present invention which are
believed to be novel are set forth with particularity in
the appended claims. The invention, together with further
objects and advantages thereof, may be understood by
reference to the following description, taken in
conjunction with the accompanying drawings, and the
several figures in which like reference numerals identify
like elements, and in which:
Fig. 1 is a block diagram of the trunked
communication ~ystem of the present invention;
Figs. 2a throuyh 2c are flow diagrams
illustrating the steps executed by the fixed-end equipment
of Fig. l;
Figs. 3a through 3f are flow diagrams
illustrating the steps executed by the voice/data
subscribers of Fig. l;
Fig 4 is a state diagram illustrating the
operation of the voice/data subscribers of Fig. 1.
Detailed Description of the Preferred Embodiment
Referring now to the drawings, and in particular
to Fig. 1, there is shown a block diagram of the trunked
voice/data com~unication system (100) of the present
~.Z~7~3
invention. The centralized or fixed-end equipment
compri~es a central controller 102, which is responsible
for allocating the channel resources ~repreRented here by
repeaters 104a-104N) among the many subscriber units.
Of the available communication channels, one (repeater
104a) is selected to be a voice control channel, which
will communicate with any trunked subscriber capable of
transmitting voice traffic. ~ypically, the particular
repeater selected to be ~he control channel (104a) is
periodically changed as a control measure.
Preferably, each o~ the repeaters 104a-~ are
capable of operating as a voice channel, control channel,
or data channel. To accommodate data traffic, such
repeaters are equipped with a data interface 122. The
data interfaces 122 are responsible or encoding outbound
data, decoding and error correcting inbound data, repeater
¦ control, and providing an interface between the repeater
and the network controller 108. Alternately, a
predetermined subset o~ the total number of repeaters may
be equipped ~or data or use a~ a control channel.
The data network comprise6 at least one host
aomputer 106, which is coupled (i.e., wireline host) to a
network controller 108. The network controller 108 is
responQible for data traffic routing ~nd communicating
with the central controller 102 to request the allocation
of a data channel. Those skilled in the art will
appreciate that if the host computer 106, the network
controller 108 and the central controller 102 are
co-located, the intercouplings (124-128) may be direct.
However, ahould remote locations be desired, such
communications ~ay be maintained throuyh the use of data
~odems as i~ known in the art. Optionally, or
additionally, the trunked voice/data communication system
100 may employ one or more radio frequency (RF) coupled
35 host computers 118. The RF host 118 communicates as a
~1.29~7~73
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trunked control station via any suitable data transceiver
120. The primary difference between the wireline host 106
and the RF host 118 is that the data subscribers
communicate directly (i.e., via both the inbound and
outbound frequencies of a data equipped repeater) with the
RF host, whereas the wireline host 106 transceives all
information via the inbound or outbound frequency of a
data equippea r~peater. Accordingly, the data network of
the present invention may employ several computers in
either a centralized or distributed processing arrangement.
Generally, the fixed-end equipment also includeS
a system manager console 110 that enables the supervisor
of a communication service provider to set a number of
operational parameters that control the operation of the
trunked communic~tion system. Typical examples of such
paramet.ers include the maximum number of assignable data
channels (if any), whether voice or data will be the
priority traffic, and various threshold values that
. control when data channels may be added or reallocated to
voice traffic. Thus, at any particular time, the trunked
communication system of the present invention need not
have any ch3nnels allocated for data traffic. Conversely,
if ~oice traffic is low, or if data traffic enjoys a
priority status or is particularly heavy, one or more
channels may be allocated for data communication.
According to the present invention, a
predetermined channel ordinarily comprises the first
channel to be allocated for data. Preferably, this first
assigned data channel ~h~re~a~ter "the master data
channel"~ has the sa~e ~requency as any single frequency
data-o~ly subscribers (116) to provide maximum
compatibility with existing data equipment. Alternately,
a random channel may be the f irst assiyned data channel;
however, the multi-channel data-only subscribers may have
to scan the available channels to find it. Thus, the
1~967~3
- 8 -
present invention prefers to first assign a selected
channel, and, thereafter, assign any other data equipped
(122) channel as an additional data channelO
The present invention allocates data channels for
S a time interval determined by either the system manager or
a default parameter. The length of the allocation period
may vary with the time of day, system loading or other
such para~eter~. ~y reserving a channel for data use over
a time period~ data channel requests are minimized and
spectral efficiency is maximized since a data subscriber
need not request a data channel for each separate data
transmission.
As a general principle, the goal of any trunked
communication system is to effectively allocate the
limited channel resources amongst a plurality of
subscriber unit~. The present invention contemplates
three classes of subscriber units: voice-only subscribers
112, voice/data subscribers 114, and data-only subscribers
116. The voice-only subscribers 112 are contemplated to
be any existing trunked subscriber unit having a
Compatible signalling protocol to allow interaction with
the system (100). The data-only subscribers (116) are
contemplated to be any multiple or single channel data
transceivers such as the KDT 800 , manufactured by
Motorola, Inc~ t or functional equivalent. Of course,
receive-only data devices, such as any of the Motorola
family of display pagers, may also operate to receive
paging data over an assigned data channel.
Additionally, the present system contemplates a
voiceldata subscriber 114 capable of operating within the
trunked system 100. In this way, the trunked system of
the present invention accommodates existing equipment,
while providing enhanced communication capabilities.
Subscriber units are typically comprised of Pither mobile,
portable or control stations. Typically, mo~ile units are
~2~6773
g
understood to be transceivers designed to operate in a
vehicle A portable unit is typically understood to be a
transceiviny or receive-only device designed primarily to
be carried on or about the person. Control stations are
usually permanent or semi-permanent installations in
buildings or other such fixed locations. ~hese are
collectively referred to herein as subscriber units, which
com~unicate with one another through the fixed-end
equipment.
The steps executed by the fixecl-end equipment are
illustrated in Figs. 2a through 2c. Referring now to Fig.
2a, in step 200, the central 102 receives a data channel
request either from the network controller 108 or from a
voice/data subscriber 114. The voice/data subscriber 114
may communicate such a data channel request via the
contro~ channel 104a when the sub~criber has data to
transmit. The network controller 108 may communicate a
similar request over the connection 126 to the central
controller in several circumstances to be hereinafter
described.
For a single channel data-only subscriber 116 to
request a channel, a request may be made over the master
data channel to the network controller since the data-only
subscribers cannot transceive on the voice control
channel. According to the present invention, the
_ data-only subscribers ~ay communicate with the network
controller irrespective of the fact that no data channels
are currently assigned. The reason for this is that a
de-keyed repeater continues to operate as a receive-only
device. In this way, the network controller 108 can
"hear" a data channel request from a data-only ~ubscriber
116 and repeat it to the central controller 102. If a
data channel is available, the central controller will
format and return a data channel grant both over the
control channel 104a (to the voicetdata subscribers 114)
and to the network controller 108 via the connection 126.
,
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~29167~3
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Accordingly, decision 202 tests to determine
whether a data channel has been granted by the central.
If not, the routine proceeds to step 204, where the
networX controller (or data subscriber) waits a
predetermined time interval before returning to reference
letter A of Fig. 2a to again request a clata channel. If
the central 102 grants a data channel, the routine
proceeds to step 206, where the central transmits the data
channel assignment over the control channel 104a and to
the network controller 108. Thereafter, data-only
subs~ribers 116 and voice/data subscribers 114 operating
in the data mode may communicate over any of the assigned
data channels.
Data operation may continue without further data
channel requests for the allocated time period, which may
be determined by the system manager 110. When the
allocation time period has expired, or higher priority
voicé traffic exists, the central controller 102 transmits
an instruction to the network controller 108 to relinquish
the da~a channel. Thus, decision 208 tests to see whether
the central has so instructed. If so, the routine
proceeds to reference letter B of Fig. 2b where the
channel is relinquished. If not, the routine proceeds to
decision 210, which tests to see whether an additional
data ~annel is needed.
If the data channel traffic on any existing data
channel exceeds a predetermined threshold, the network
controller 108 may requested an additional data channel
from the central controller 102. To do this, the network
con~roller proceeds to referen~e letter A of Fig. 2a to
transmit another data ~h~n~el req~st to the centra~. If
another data channel is available for data traffic, the
central may assign an additional data channel.
Of course, when another data channel is assigned,
the data traffic load, per channel, is uneven.
~2~67'73~
Accordingly, the present invention contemplates levelling
the data load among the available data channels to
maximize data communication. Two preferred methods for
load are described in two co-pending applications filed
on an even date herewith. The first is by Garry Hess
(attorney docket number CM-00243H), and the second is by
Ken Zdunek (attorney docket number CM-00262H), and both
are entitled "Method for Dynamically Allocating Data
Channels On a Trunked Communication System", with each
being assigned to the same assignee as th~ present
invention. The first reference corresponds to United
States Patent 4,831,373 (Hess), issued on May 16, 1989
and the second reference corresponds to United States
Patent 4,870,408 (Zdunek et al), issued
September 26, 1989.
Referring again to Fig. 2a, if decision 210
determines that another data channel is not needed, the
routine proceeds to reference letter D of Fig. 2a, which
~orms the fixed-end operational loop comprising decisions
208 and 210. the fixed-end remains on this loop until
either a data channel is requested to be relinquished or
another data channel is requested.
Referring now to Fig. 2b, the steps executed to
relin~uish a data channel are shown. Assuming that the
central controller 102 has requested the network
controller 108 to give up a data channel, the network
controller transmits a "return to control channel"
command 212 over the data channel to be relinquished.
All data compatible subscribers receiviny this command
return to the control channel 104a. Of course, single
channel data-only subscribers continue to monitor their
particular single frequency. In step 214, the network
controller 108 releases the data channel to the central
controller. In step 216, the central 102 may now assign
~;296773
- lla -
this channel for a voice call. After this, decision 218
determines whether there are remaining data channels. If
the network controller 108 has released only one of
several data channels, the routine proceeds to reference
letter D of
....
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- 12 -
Fig. 2a to continue data operation. However, if the sole
data channel was relinquished, the routine proceeds to
reference letter C of Fig. 2c.
Referring now to Fig. 2c, the network controller
108, after relinquishing the sole data channel, starts a
request timer in step 220. Decision 222 determines
whether this timer has expired. If so, the routine
returns to reference letter A of Fig. 2a to request a data
channel. If the timer has not expired, the network
10 controller 108 determines whether the host computer 106
has any data for trans~ission. If the determination of
decision 224 is that the host has data to transmit, the
routine proceeds to reference letter A of Fig. 2a to
request a data channel. Otherwise, the ne~work controller
determines in deaision 226 whether a data message has been
received fro~ a data-only sub3criber or an RF host
co~puter. If the determination of deci~ion 226 i5 that
such a data ~essage was received, the networX controller
108 "knows" that the channel which carried the data is
idle and that a data-only subscriber wishes to
communicate. Accordingly, the routine returns to
reference letter A of Fig. Zat where the network
controller re~uest~ a data channel to allow it to
communicate with the data-only subscriber. However, if
the network controller 108 has received no such data
message, the routine continues by returning to reference
letter C of Fig. 2c, which forms a waiting loop until
either the request timer expires or some data activity
occuxs .
The .s~eps executed by the data/voice subscriber
114 are shown in Figs. 3a through 3f. Referring now to
Fig. 3a, in step 300 of Fig. 3a, the subscriber unit
powers up. During power up, the subscriber unit may
execute any self-check routines and initialize operational
flags and variables. During this ti~e, the subscriber
: '~
~ ~9~73
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unit determines in decision 302 whether to operate
primarily in the voice mode. If so, deci~ion 302
transfers control to reference letter E of Fig. 3b for
voice mode operation. If not, decision 304 tests whether
the subscriber operates primarily in the data mode. If
decision 304 determines that the subscriber normally
operates in the data mode, the routine proceeds to
reference letter F of Fig. 3d for data mode operation.
Alternately, the subscriber unit may use its last
mode of operation. Thus, if the last communication was a
voice call, the ~ubscriber unit would operate in the voice
mode. Conversely, if the last communication was a data
transmission, the subscriber would operate in the data
mode. Decision 306 determines if the last mode
operational option is selected. ~f not, the routine
proceeds to step 30~, which signals that a unit ault has
occurred or ~allure to determine one of the only three
available modes o~ operation. However, i the
determination of decision 306 is that the last mode was
selected, decision 310 determines whether the last
activity was a voice call. If so, the routine proceeds to
reference letter E of Fig. 3b for voice mode operation.
If the determination of decision 310 was that a aata
transmission was last made, the routine proceeds to
reference letter F of Fig. 3d, for data mode operation.
Referring now to Fig. 3b, the steps executed by a
voice/data ~ubscriber 114 in the voice mode are shown. In
step 312, the subscriber unit monitors the control
channel. According t~ the present invention, the voice
mode subscriber unit must at all ti~es be either
monitoring the control channel, or participating in a
voice call on one of the available voice channels.
Accordingly, the voice mode subscriber continuously
monitors the control channel until a command is received
or the operator transmits. According, decision 314
,. ... ::
~ 2~
- 14 -
determines whether the subscriber operator has pressed the
push-to-talk (PTTj switch. If so, tep 316 translaits a
voice call request over the control channel to the central
controller 102. Following this, the subscriber returns to
reference letter E of Fig. 3b to monitor the control
channel. If the PTT switch was not newly depressed, the
routine proceeds to decision 31~ to determine whether a
channel assignment has been received over the control
channel.
If the determination of decision 318 is that a
channel assig~ent has been received, ~he routine proceeds
to step 320, where the subscriber goes to the assigned
voice channel to participate in the call. After the
completion of the call, the routine returns to reference
letter E of Fig. 3b to again moni~or the control channel.
If the subscriber operator has entered data for
transmission, decision 322 changes the gubscriber's
operating mode to the data mode and the routine proceeds
to reference letter F of Fig. 3d. Decision 324 determines
whether the voice mode subscriber has received a command
over the control channel to go to the data mode to receive
a message from the host computer 106. Preferably, the
central 1~2 ~e~ps track of the subscribers operating in
the voice mode. Th~ ne~work controller 108 thereby avoids
wasted trans~issi~l ~ime by not transmitting a data
message to ~ subscriber known not to be monitoring one of
the assigned data channels. Thus, the network controller
can request the central to command a voice mode subscriber
to an assigned data channel to receive a data message.
Upon receiving such a command, decision 324 routes the
program to rsference letter G of Fig. 3d to participate in
the data transmission.
While operating in th~ ~oice mode, any subscriber
unit monitoring the control channel may receive any data
channel allocation information transmitted from the
,'''~. '
.~
~2~773
- 15 -
central 102 over the control channel. Accordingly,
decision 326 tests to determine if such data channel
allocation information has been received. If so, the
routine proceeds to step 328, where the information is
stored for later use. If not, decision 326 routes the
program to reference letter E of Fig. 3b where the
subscriber continues to operate in the loop of Fig. 3b.
Referring now to Fig. 3d, the steps executed by
the voice/data subscriber 114 while in the data mode are
shown. According to the present invention, a voice/data
sub~cri~er may operate in the data mode in any one of
three ways: ~he data monitor mode, the voice monitor
mode, and the last channel mode. In the data monitor
mode, the subscriber unit monitors one of the assigned
data channels unti} commanded to return to the control
channel or the ~oice mode. In the voice monitor data
mode, a subscriber unit may operate in the data mode,
while monitoring the control channel, thereby enabling
rapid participation in any voice messages. In the voice
monitor data mode, a subscriber unit may operate in the
data mode, while monitoring the control channel, thereby
enabling rapid participat~on in any voice messages. In
the voice monitor mode, a subscriber may momentarily go to
the data channel to transceive data and thereafter
immediate~ return to the control channel upon completion
of the trans~ission or reception. Alternately, as the
name implies, the last channel mode comprises the
subscriber monitoring either the data channel or the
control channel depending upon the last communication
type.
Accordingly, decision 330 determines whether the
subscriber should monitor the data channel. An
affirmative decision results for a data monitor mode
subscriber, or a last mode subscriber that had previously
transmitted or received on the data channel. In all other
~2~67'73
- 16 -
cases, the determination of decision 330 causes the
subscriber to monitor the control channel, step 332 of
Fig. 3c. T~is is also designated as reference letter L in
Fig~ 3c. Refer~ing no~ to once monitoring, the c~ntrol
channel, the subscriber continuously attempts to decode
commands and channel assignments. Accordingl~, decision
334 determines whether a voice mode command has been
received. A voice mode co~mand causes t~e subscriber ~o
revert to the voice mode as illustrated in Fig. 3b.
Failing this, decision 336 determines whether a data
channel assignment has been received from the central
controller 102.
As previou~ly mentioned, the central 102 keeps
track o~ the subscribers operating in the voice mode. The
network controller 108 avoid~ wasted transmission time by
not transmitting a data message to a gubgcriber known not
to be monitoring one of the assigned data channels. Thus,
the network controller re~uests the central to command a
voice mode su~scriber to an assigned data channel to
receivP a data message. Accordingly, if decision 336
determines that a data channel command has been received,
control reverts to reference letter F of Fig. 3d wherein
the subscriber moves to monitor the data channel. If not
assigned to a data channel, the routine proceeds to
decision 338, which determines whether new data channel
allocation information has been received. If so, the
information is convenie~tly ~ored in step 340 and the
routine return~ t~ the refet-~nce letter H to again monitor
; the cont~ol channel.
Decision 342 determines whether the operator has
activated the pu h-to-talk switch to initiate a voice
conversation. If the determination of decision 342 is
that the push-to-talk switch has been depressed, the
routine proceeds to reference letter E of Fig. 3b, thereby
switching to the voice mode of operation to participate in
~2~7~3
- 17 -
a voice call. A high degree of flexibility is afforded in
the present invention by allowing the subscriber unit to
operate in the data mode, while monitoring the control
channel. Thus, in decision 344 the sub~criber determines
whether a voice channel grant has been received on the
control channel. If so, subscriber unit operates (step
346~ to process the call and then returns to the data mode
of operat~on t~ monitor the control channel (reference
letter H of Fig. 3c.)
If no voice ~rant has been received, decision 348
determines whether the subscriber has data to tra~smit.
If so, the routine proceeds to reference letter F of
Fig. 3d, where the subscriber goes to the data channel to
await data transmission. If a subscriber has no data to
tra~smit, the routine reverts to reerence letter H of
Fig. 3c to continually monitor the control channel, while
checking for commands and assignments in the subscriber
unit`s operational loop.
Referring now to Fig. 3d, assuming an affirmative
determination from decision 330, the subscriber unit
monitors an assigned data channel (step 3501. Step 352
starts an inactivity timer, which causes the subscriber to
revert to the control channel if there has been no data
activity ~y any subscriber for the predetermined timer
interval~ ~ccordingly, decision 354 determines whether
there is any current activity on the data channel. If so,
the routine proceeds to reference letter I of Fig. 3e,
where the subscriber unit operates to receive the data and
process it. If there is no activity, the routine proceeds
to decision 356, w~ich determines if the subscriber has
any data to transmit to the host compu~er 106 (or 118)~
If so, the routine pr~ceeds to reference letter J of
Fig. 3f for the subscriber data mode transmission
routine. If the subscriber has no data to transmit,
decision 358 determines whether the subscriber's operator
~',
~l29~
18 ~
has activated the PT~ switch. If so, the routine proceeds
to reference letter E, thereby changing to the voice
mode. If the PTT was not activated, dec;sion 359
determines whe~her the timer has expired. If the
determination of decision 359 is that the timer has not
expired, the routine proceeds to reference letter K of
Fig. 3d, to form a loop checking for data channel
activity. If, however, there has been no data activity
for the period of the timer, decision 359 routes control
to reference letter H of Fig. 3c, where the subscriber
unit begins to monitor the control channel (step 332),
while remaining in the data mode.
Referring now to Fig. 3e, the data mode receive
sequence is illustrated. In step 360, the data is
lS extracted from the data channel and received by the
subscriber unit. Decision 362 determines whether the
received data has an ID portion corresponding to the
subscriber's ID. If not, either the data has been
received in error or the data was not addressed to this
subscriber unit. Accordingly, step 364 resets the
activity timer and control is returned to reference letter
K of Flg 3d to again monitor activity on the data channel.
; If the determination of decision 362 is that the
ID is valid, the subscriber unit processes the information
to receive the data and/or commands from the host computer
106. Decision 366 determines whether a voice mode`command
has been received. If ~o, the routine proceeds to
reference letter E of Fig. 3b, where the subscriber unit
switche~ to operate in the voice mode. If the
determinatio~ G ~ ion 366 is that a voice mode command
was not received, dec-ision 368 determines whether a
"go-to-control-channel" command was received. If so,
subscriber unit remains in the data mode, but adapts to
monitor the control channel. Accordingly, program control
~; 35 is routed to reference letter H of Fig. 3c.
:
.
12967~3
-- 19 --
If the received data did not contain a voice mode
or go-to-control-channel command, the routine proceeds to
decision 370, which determines if the subscriber operator
has pressed the push-to-talk switch to initiate a voice
call. If the subscriber has initiated a voice call, the
routine proceeds to step 371, which stores any received
data for later processing, and returns control to
reference ~e~ter E of Fig. 3~ to process the voice call.
If the operator has not initiated a voice call,
step 372 processes the received data in accordance with
any instructions previously received or contained in the
received data. Step 374 resets the data activity timer
since data activity was recently received.
Decision 376 determines whether the subscriber
unit operates in the voice monitor modet If 80, the
routine proceeds to reerence letter H o~ E'ig 3c to
monitor the control channel. However, i~ the subscriber
is a data monitor subscriber or a last mode subscriber,
decision 376 returns control to reference letter F of
Fig. 3d, and the data channel is monitored ~step 350).
Referring now to Fig. 3f, the data transmit
~equence of the data mode is illustrated. In step 378,
the subscriber unit transmits the data onto the data
channel u~ing any suitable form of data modulation.
Decision 380 determines whether the subscriber's
transmission has collided with the transmission of another
subscriber. Such collision detection schemes are well
known in the art and the selection of any particular one
scheme i8 not essential to the understanding of the
invention. Assuming the determination of decision 380 was
that a collision had ~ccurred~ the ~outine proceeds to
step 382, which ~JaitS an arbitrary interval before
returning control to reference letter J of Fig. 3f to
retransmit the data. If, however, no collision was
detected, the routine proceeds to step 384, which resets
.
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the activity timer since the subscriber has ju~t
transmitted on the data channel. In step 386, the
subscriber determines whether it operates in the voice
monitor mode or whether it should continue to monitor the
data channel (i.e., either last used mode or the data
monitor mode). If the determination of decision 386 is
that the sub~crîber should monitor the control channel,
the routi~e proceeds to reference letter H of Fig. 3c.
Otherwise, the routine proceeds to reference letter F of
Fig. 3d to monitor the data channel.
Refe}ring now to Fig. 4, a state diagram 400
illustrating the operation of the subscriber unit i5
shown. According to the present invention, the subscriber
unit must always be on either the control channel, an
L5 assigned voice channel or an assigned data channel.
In ~tate 402, the subscriber is operating in the
voice mode on the control channel. The subscriber unit
may participate in the voice call in ~tate 404 by
receiving a channel grant, and returns to the control
channel state 402 b~ receiving a disconnect or timing out
; at the end of the call. Additionally, the subscriber may
receive priority messages while participating in a voice
call Accordingly, if the subscriber receives a priority
data mode command, the subscriber may abandon the voice
call and enter state 406.
In state 406, the subscriber operates in the data
mode, while monitoring the control channel. The
subscriber may enter and leave this state via command of
the host computer vi~ the network controller and central
controll~r~ The commands can eithe~ return the subscriber
to th~ voice ~d~ in state 402 or remain in the data mode
~` monitoring the data channel in state 408. In either of
the data mode states ~406 or 408), a push-to-talk command
returns the subscriber to state 402. Additionally,
receiving a channel grant rapidly moves the subscriber
~LX96~773
- 21 -
from state 406 directly to state 404 to participate in a
voice call. Thus, the voice/data subscriber may move
from one sta~e to another state alony any of the defined
paths of the state di~gram 400.
While a particular embodiment has been described
and shown, it will be understood that the present
invention is not limited thereto since many modifications
can be made. It is therefore contemplated to cover by the
present application any and all such modifications that
fall within the true spirit and scope of the basic
underlying principles disclosed and claimad herein.
`
