4,870,408
`[11] Patent Number:
`[19]
`UllltEd States Patent
`
`Zdunek et a1.
`[45] Date of Patent:
`Sep, 26, 1989
`
`[75]
`
`[54] METHOD FOR DYNANLICALLY
`ALLOCATING DATA CHANNELS ON A
`UNKE
`MIMUN'I
`STEM
`TR
`D co
`CATIDN SY
`Inventors: Kenneth J. Zdunek, Schauniburg;
`Garry C, Hess, Hanover Park;
`fichnrd A" Go
`' Dundee, all of
`['13] Assignee: Motorola, 1118., Schanmburg, 111.
`[21] Appl. No: 44,525
`[22] Filed:
`Apr. 30, 1987
`[51]
`Int. c1.4
`HIM-B 7/14; H04Q 11/00
`[52]
`11.8. C]. ............................ 340/825.030; 370/911;
`455/34
`340/325030, 825.01;
`[58] Field of Search
`370/95, 1‘1; 455/17, 33, 34, 54, 56, 62
`Ref
`n
`Cited
`ere cos
`U.S. PATENT DOCUMENTS
`
`56]
`
`[
`
`4,012,591 3/ 19‘1”?
`4.191500 4/1930
`4,352,133 9/1932
`4,551,352 11/1985
`4,553,262 11/ 1935
`4,55 6,972 12/1985
`4,513,206 2/19 36
`4,574,163
`3/1936
`
`455/53
`
`Lynk, Jr. et a1.
`Klein 0’: al.
`.....
`Davis et a].
`.....
`Gravel et a1.
`COB ...'..............
`Chan et al.
`......
`Grauel et a].
`
`Zato
`
`..
`
`455/33
`3/1936 Persinotti
`4,573,815
`310/1101
`6/1986 Wombat-g et al.
`4,593,389
`
`379/243
`9/1936 Franklin et a].
`.....
`4,609,778
`370/11
`11/1931
`Irvin
`4,679,137
`
`4,698,805 10/1937 Sasuta eta]. .......... 455/17
`
`........................ 370/124
`4,707,332 11/1937 Glenn et a1.
`Primary Examiner—Donald J. Yuslto
`Assistant Examiner—Edwin C. Holloway, III
`Attorney, Agent, or Firm—Wayne J. Egan; Thomas G.
`”my
`ABSTRACT
`[57]
`Disclosed is a method to dynamically allocate a number
`of data channels on a “linked radio system (100} The
`data activity is monitored during a predetermined time
`interval. If activity is above a predetermined maximum.
`an additional channel may be reserved for data use.
`Conversely, if data traffic is low. a data channel may be
`reallocated for voice message use. Moreover, should
`the amount of data traffic among the available data
`channels be unbalanced, the present method contem-
`plates reassigning subscriber units (114 or 116) to the
`available data channels to balance the data traffic load,
`thereby providing superior access time and system per-
`formance.
`
`14 Claims, 6 Drawing Sheets
`
`
`
` (00m CHANNEL)
`
`VOICE ONLY
`
`SUBSCRIBER
`
`
`
`
`
`
`
`- CONTROLLER
`
`NETWORK
`
`
`
`Page 1 0f 12
`
`PETITIONER'S EXHIBIT 1008
`
`EXHIBIT
`
`EX. 1008
`
`EX. 1008
`
`Page 1 of 12
`
`PETITIONER'S EXHIBIT 1008
`
`

`

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`Page 2 of 12
`
`PETITIONER'S EXHIBIT 1008
`
`Page 2 of 12
`
`PETITIONER'S EXHIBIT 1008
`
`
`

`

`US. Patent
`
`Sep. 26, 1989
`
`Sheet 2 of 5
`
`4,870,408
`
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`Page 3 of 12
`
`PETITIONER'S EXHIBIT 1008
`
`Page 3 of 12
`
`PETITIONER'S EXHIBIT 1008
`
`
`
`
`
`
`

`

`US. Patent
`
`Sep. 26, 1939
`
`Sheet 3 of 5
`
`4,870,408
`
`FIXED—END
`
`4-0
`
`402
`
`INITIALIZE
`
`RES Er/START TIMER
`
`MEASURE VOICE/DATA
`ACTIVITY
`
`'
`
`O
`
`FIG.4
`
`YES
`
`403
`
`YES
`
` CURRENT
`CHANNEL-1
`
`< ’3’.le
`
`
` CURRENT
`
`NO
`CHANNELS-+1
`
` > "4"“ DATA
`
`CHANNEL
`AcnvITY
`UNEIALéfiNCED
`
`N0
`
`YES
`
`ADD ONE DATA
`CHANNEL
`
`;
`
`NO
`
`418’
`
`a
`
`LOAD LEVELING
`
`Page 4 of 12
`
`PETITIONER'S EXHIBIT 1008
`
`Page 4 of 12
`
`PETITIONER'S EXHIBIT 1008
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`

`

`US. Patent
`
`Sep. 26, 1989
`
`Sheet 4 of 5
`
`4,870,408
`
`LOAD LEVELING
`
`TRANSMIT. REVERT
`TO MASTER 05W
`
`500 FIG. 5A
`
`
`
`
`
` 502
`
`
`
`i
`TRANSMIT SEED
`OFFSET T0 SUBSCRIBER .
`
`504-
`
`TRANSMIT NUMBER OF
`DATA CHANNELS AND
`IDENTITY INFORMATION
`
`
`SYSTEM MESSAGE
`
`FIG.5B TRANSMIT, REVERT
`
`
`
`
`
`
`
`
`
`T0 MASTER OSW
`
`TRAN SM IT
`SYSTEM MESSAGE
`
`TRANSMIT NUMBER OF
`DATA CHANNELS AND
`IDENTITY INFORMATION _
`
`50 6
`
`508
`
`Page 5 0f 12
`
`PETITIONER'S EXHIBIT 1008
`
`Page 5 of 12
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`PETITIONER'S EXHIBIT 1008
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`

`

`US. Patent
`
`Sep. 26, 1989
`
`Sheet 5 of 5
`
`4,870,408
`
`SUBSCRIBER
`
`INITIALIZE
`
`
`
`
`RECEIVE DATA CHANNEL
`ALLOCATION INFORMATION
`
`600
`
` 602
`
`
`604
`
`1710.6
`
`RANDOMLY SELECT A
`DATA CHANNEL
`
`-.
`
`608
`
`G
`
`OPERATE 0N ASSIGNED
`DATA CHANNEL
`
`
`510
` REVE RT
`TO MASTER
`CHAN NEL
`
`
`N0
`
`YES
`
`512
`
`GO TO MASTER DATA
`CHANNEL AND RECEIVE
`ALLOCATED INFORMATION
`
`B
`
`616
`
`_ B
`
`614-
`
`YES
`
`618
`
`NO
`
`NO
`
`YES
`
`620
`
`RAMDOMLY RE—SELECT
`A DATA CHANNEL
`
`Page 6 0f 12
`
`PETITIONER'S EXHIBIT 1008
`
`Page 6 of 12
`
`PETITIONER'S EXHIBIT 1008
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`

`

`1
`
`4,870,408
`
`METHOD FOR DYNAMICALLY ALLOCATING
`DATA CHANNELS ON A TRUNKED
`COMMUNICATION SYSTEM
`
`TECHNICAL FIELD
`
`This invention relates generally to trunked communi-
`cations systems and more particularly to trunked com-
`munication systems that transceive both voice and data.
`BACKGROUND ART
`
`In a basic RF trucked system there exists a high de-
`gree of flexibility to partition voice conversations be
`tween different groups so that no one group of users is
`specifically aware when another group of users makes
`use of the system. Typically, these groups are subdi-
`vided into subgroups so that calls may be made upon
`either a group, subgroup or individual basis depending
`upon the type of communication desired by an initiating
`subscriber.
`To establish a voice communication between a group
`of units operating on a trunked system, a subscriber unit
`transmits a data packet called an “inbound signalling
`word" (ISW) on a control channel that is maintained for
`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 chan-
`nel a data pocket called an “outbound signalling word”
`(05W) to all subscriber units, which continuously mon-
`itor the control channel when not participating in a
`voice conversation. The OSW is a channel grant which
`contains the talk-group code of the requesting unit, and
`the voice channel number assigned for the conversa-
`tion. The OSW causes the requesting unit to move to
`the voice channel and cammence transmitting, while
`simultaneously causing all other subscriber units in the
`same talk-group to move to the voice channel as listen-
`ing units. In this way a group call is set up. If, however,
`all voice channels are in use when a subscriber unit
`transmits an ISW, the central controller typically sends
`the requesting subscriber a “busy 08W".
`In 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 tnmked
`data 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 subscriber to transmit an [SW and
`receive a channel grant 05W from the central, and the
`time it takes to set-up and clear-down the call on the
`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 obtain a channel (approximately 0.5
`seconds). Thus, assigning a data channel pursuant to the
`same procedure as assigning a voice channel would be
`wasteful of spectrum and consume precious system time
`that could be better used to transmit data messages.
`Other trucked 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 basic principles of trunked
`communication systems, which strive to allocate chan—
`nel resources across a plurality of users as required.
`Therefore, the practice of having dedicated data chan-
`
`it)
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`SS
`
`65
`
`2
`nels, permanently removed from the channel allocation
`“poo ” 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 the data traffic load
`across the available data channels. Such systems typi-
`cally permanently assign a subscriber unit to a data
`channel thereby building in future problems as the num-
`ber of data subscribers increases on a particular channel.
`Accordingly. there exists a need for a trunked com-
`munication system that can accommodate both voice
`and data signals, and that operates in true truuked man-
`ner to efficiently utilize spectral resources.
`SUMMARY OF THE INVENTION
`
`Accordingly, it is an object of the present invention
`to provide an improved trunlted communication sys-
`tem.
`
`It is another object of the present invention to pro-
`Vide a procedure to dynamically allocate data channels
`011 a trunked radio system.
`It is a further object of the present invention to redis~
`tribute or balance the data traffic load on the particular
`number of data channels currently available.
`It is another object of the present invention to pro-
`vide a rapid and convenient method to broadcast system
`wide data messages to all data subscribers
`Accordingly, these and other objects are achieved by
`the present invention’s dynamic allocation of data chan-
`nels in a trunked radio system.
`Briefly, according to the invention, a method is dis-
`c10sed to dynamically allocate a number of data chan-
`nels on a trunked radio system. The data activity is
`monitored during a predetermined time interval. If ac-
`tivity is above apredetennined maximum, an additional
`channel is reserved for data use. Conversely, if data
`traffic is low, a data channel is reallocated for voice
`message use. Moreover, should the amount of data traf-
`fic between the available data channels be unbalanced.
`the present
`invention contemplates reassigning sub-
`scriber Imits to the available data channels to balance
`the data traffic load, thereby providing superior access
`time and system performance.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The features of the present inventiou which are be-
`lieved to be novel are set forth with particularlity in the
`appended claims. The invention, together with further
`objects and advantages thereof, may be understood by
`reference to the following description, taken in con-
`junction with the accompanying drawings. and the
`several figures of which like referenCEd numerals iden-
`tify like elements, and in which:
`FIG. I is a block diagram of a trunked radio system
`that may employ the present invention;
`FIG. 2 is an illustration of the preferred signalling
`format for a master data channel;
`FIG. 3 is an illustration of the preferred signalling
`format for other data channels;
`FIG. 4 is a flow diagram illustrating the steps exe-
`cuted by the fixed-end equipment of FIG. 1 in accor-
`dance with the present invention;
`FIG. 50 is a flow diagram illustrating the steps exe-
`cuted by the fixed-end equipment of FIG. 1 to perform
`the load leveling of subscriber units to available data
`channels in accordance with the present invention;
`
`Page 7 of 12
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`

`. 4,870,408
`
`3
`FIG. 5b, is a flow diagram of the steps executed by
`the fixed-end equipment of FIG. 1 to transmit a system
`message to the subscriber units in accordance with the
`present invention; and
`FIGS. 6:: and 6b are flow diagrams illustrating the
`steps executed by the 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 a trunked
`voice/data communication system (100) that may em-
`ploy the present invention. The centralized or fixedvend
`equipment comprises a central controller 102, which is
`responsible for allocating the channel resources (repre-
`sented here by repeaters lO4n-104N) amongst the many
`subscriber units. Of the available communication chan—
`nels, one (repeater 104a) is selected to be a voice control
`channel, which communicates with any trucked sub-
`scriber capable of transmitting voice traffic.
`Preferably, each of the repeaters lotto—N 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 inter-
`faces 122 are reSponsible for encoding outbound data,
`decoding and error correcting inbound data, repeater
`control, and providing an interface between the re-
`peater and the network controller 103. Alternately, a
`predetermined subset of the total number of repeaters
`may be equipped for data or used as a control channel.
`Typically, the particular repeater selected to be the
`control channel (1040) is periodically changed as a con-
`trol measure.
`The data network comprises at least one host com-
`puter 106, which is coupled (i.e., wireline) to a network
`controller 108. The network controller 108 is responsi-
`ble for data traffic routing and 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 103 and
`the central controller 102 are co-located, the intercou—
`plings (124—128) may be direct. However, should re-
`mote locations be desired, suoh communications may be
`maintained through the use of data modems as is known
`in the art. Optionally, or additionally, the trunked voi-
`ce/data communication system 190 may employ one or
`more radio frequency (RF) coupled host computer's
`118. The RF host 118 communicates as a trunked con-
`trol 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 communi-
`cate directly (i.e., via both the inbound and outbound
`frequencies of a data equipped repeater) with the RF
`host, whereas the wirelint: host 106 transceives all infor-
`mation via the inbound or outbound frequencies of a
`data equipped repeater. Accordingly, the data network
`of the present invention may employ several computers
`in either a centralized or distributed processing arrange-
`ment.
`
`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 communication system. Typical examples of
`such parameters include the maximum number of as
`signable 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 real-
`
`4
`located to voice traffic. Thus, at any particular time, the
`trunked communication system of the present invention
`need not have any channels allocated for data traffic.
`Conversely,
`if voice traffic is low, or if data traffic
`enjoys a priority status or is particularly heavy, one or
`more channels may be allocated for data communica-
`non.
`
`ll]
`
`15
`
`20
`
`25
`
`30
`
`35
`
`do
`
`45
`
`55
`
`60
`
`65
`
`According to the present invention, a predetermined
`channel ordinarily comprises the first channel
`to be
`allocated for data. Preferably, this first assigned data
`channel (hereinafter “the master data channel”) has the
`same frequency as any single frequency data-only sub-
`scribers (116) to provide maximum compatibility with
`existing data equipment. Altemately, a random channel
`may be the first assigned data channel; however, the
`data-only subscribers must scan the available channels
`to find it. Thus, the present invention prefers to first
`assign a selected channel, and, thereafter, assign any
`other data equipped (122) channel as an additional data
`channel.
`The present invention allocates data channels for 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 parameters. By reserving a channel for data
`use over a time period, data channel requests are mini-
`mized and spectral efficiency is maximized since a data
`subsoriber need not request a data channel for each
`separate data transmission.
`As a general principle, the goal of any trucked com-
`munication system is to effectively allocate the limited
`channel resources amongst a plurality of subscriber
`units. 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 800m, manufactured by Motorola,
`Inc., 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. In this way, the trunked
`system of the present invention accommodates existing
`equipment, while providing enhanced communication
`capabilities. SubScriber units are typically comprised of
`either mobile. portable or control stations. Typically,
`mobile units are understood to be transceivers designed
`to operate in a vehicle. A portable unit is typically un-
`derstood to be a transceiving or receive-only device
`designed primarily to be carried on or about the person.
`Control stations are usually permanent or semi-perma-
`nent installations in buildings or other such fixed loca-
`tions. These are collectively referred to herein as sub-
`scriber units, which communicate with one another
`through the fixed-end equipment.
`As previously mentioned, the first data channel allo-
`cated is defined as the master data channel, the identity
`of which is periodically transmitted to all subscribers
`over the control channel. Additionally, or optionally,
`the identities of all other allocated data channels are
`periodically transmitted over both the voice control
`channel and the master data channel.
`Those skilled in the art will appreciate that some
`criteria is required to decide how to distribute data users
`when multiple data channels are present. According to
`
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`PETITIONER'S EXHIBIT 1008
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`

`5
`the present invention, the data subseribers (114 and 116)
`each determine their own assigned data channel by
`randomly selecting one of the available data channels.
`It should also be understood that other bases are
`
`available and the particular basis used in any particular
`implementation is not critical to the practice of the
`present invention. Random number (selection) genera-
`tors are well known in the art, and the particular algo—
`rithm used is not critical to the practice or understand-
`ing of the present inventive method. Of course, the
`particular data channel assignment will depend upon
`the actual number of data channels currently available.
`For example, a particular subscriber unit may select
`data channel one if the current number of data channels
`is two. If the number of channels is three, channel two
`may be selected, and so on. Of course, if there is only
`one data channel available, all data subscribers will use
`that channel. In this way, data subscribers may select a
`data channel and up-load or down-load information to
`or from the host computer 106 (or 118). As used herein,
`"up-load" means the transference of data or executable
`code from a subscriber unit to a host computer. The
`term “down-load" means the transference of data or
`executable code from a host computer to a subscriber
`unit.
`‘
`
`When a particular number of data channels is as-
`signed,
`the central 102 monitors the voice activity,
`while the network controller 103 monitors the activity
`on the data channels. This activity monitoring is prefer-
`ably performed for a predetermined period of time. For
`example, the monitoring activity may be done by the
`hour {or half hour) so that during peak loading times the
`trunked system (100) can quickly adapt to reallocate the
`channel resources. If the network controller determines
`that the data activity on the assigned data channels has
`exceeded a predetermined supervisor selected thresh-
`old, the network controller 108 requests the central to
`allocate another channel for data traffic. Conversely, if
`the central determines that voice activity has exceeded
`a predetermined threshold, the central 102 requests the
`network controller to relinquish a data channel. In this
`way. the trucked system 100 adapts to reallocate the
`channel resources.
`According to the present invention, reallocation be-
`gins by transmitting a “revert to master” command over
`all currently assigned data channels. When the sub«
`scriber units receive this command, they all revert to
`the master data channel to listen for new data channel
`assignments. The allocated data channels may be incre-
`mented or decremented by a predetermined number
`(one of the preferred embodiments) and the new alloca-
`tion or number of data channels may be broadcast along
`with the identity of each data channel. The subscriber
`units receiving this information determine the number
`of available data channels and randomly select an as-
`signment. In this way, the number of data channels can
`be conveniently incremented or decremented depend-
`ing upon data traffic.
`the
`In addition to overall data traffic monitoring,
`network controller 100 may determine that the data
`traffic load on a particular data channel is excessive.
`Accordingly.
`the present
`invention contemplates a
`method to balance the data traffic over the available
`data channels. Load leveling may be accomplished by
`simply transmitting a “revert to master” command over
`all currently assigned data channels. When the sub-
`scriber units receive this command, they all revert to
`the master data channel to listen for new data channel
`
`10
`
`IS
`
`20
`
`25
`
`30
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4, 870,408
`
`6
`assignments. For load leveling, the actual number of
`allocated data channels may not have changed. The
`data subscribers are merely forced to randomly re-select
`a data channel assignment. However, it is possible that
`the data subscribers may not be able to effectively re-
`distribute the data traffic using this simple approach.
`Accordingly, the present invention contemplates trans-
`mitting an offset “seed” to some or all the subscribers
`for the random selection algorithm. In this way, there is
`a statistical probability that the load will be spread over
`the available data channels as opposed to being con-
`geared onto a particular data channel. The data trellic
`may then be monitored over the next operating period.
`and if the load is still unbalanced a different offset seed
`may be transmitted to again redistribute the data load.
`Those skilled in the art will appreciate that it is often
`desirable to communicate with all subscriber units at
`one time in response to either an emergency, or to dis-
`tribute a message of general concern. For example, a
`message announcing some emergency condition, or that
`the host computer 106 (or 118) will be down for repair
`are examples of messages that would be convenient to
`transmit to all subscribers at one time. Accordingly, the
`present invention achieves this Operation by transmit-
`ting the revert to master command over all allocated
`data channels. All subscribers respond to this command
`by listening to the master data channel. Just prior to
`retransmitting the current number of data channels and
`their identities (which may be unchanged), a system
`broadcast message is transmitted so that all subseribers
`may receive the message prior to receiving the data
`channel information. In this way rapid system wide data
`communication is provided by the present inventive
`method After receiving the system message, the data
`subscribers may retum to their assigned data channels.
`Referring now to FIG. 2, an illustration of the pre-
`ferred signalling format for the master data channel is
`shown. The signalling format 290 begins with a pream-
`ble portion 202, which may include synchronization or
`framing information for the data subscriber units. Fol-
`lowing the preamble 202 is an optional block 204
`wherein either a system message or an offset seed may
`be transmitted to effectuate either the system message
`operation or the load leveling procedure previously
`mentioned. Of course, during normal operations format
`block 204 would not be used and the preamble 202
`would directly precede black 206.
`Basically, block 206 transmits the total number of
`currently available data channels (be it 1, 2, 5, etc.) in
`any suitable form. Following block 206 are a plurality
`of blocks (203:: through 208a) which transmit the iden-
`tity of the data charmels. In the preferred embodiment,
`the transmitted identity of the data channels is the actual
`frequency of the channels. Alternately, the channels
`could be assigned a designated number and the selected
`ones available for data use transmitted. For example, if
`a particular system has five channels. it may be conve-
`nient to label them 1—5. Then, assuming the subscribers
`knew the frequencies, the numbers “4" and “5" may be
`transmitted to indicate that channels four and five are
`the data channels. The preferred method, however, is to
`transmit the actual frequencies. since this allows for
`simple expansion of the system, and limits the amount of
`information required to reside in the subscriber units.
`Therefore, if there is one data channel (i.e., the master
`data channel),
`that frequency will be transmitted in
`block 208a. If there are five data channels currently
`available (the master data channel plus four other data
`
`Page 9 of 12
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`PETITIONER'S EXHIBIT 1008
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`Page 9 of 12
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`PETITIONER'S EXHIBIT 1008
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`

`

`4, 870,408
`
`7
`.
`channels), those frequencies may be transmitted (for
`example in blocks 208a through 2082), and so on.
`After the transmission of the identity of the last avail-
`able data channel, the master data channel may be used
`by the subscriber units as a data channel as is illustrated
`by block 210.
`To effectuate a recovery process, in case any particu-
`lar subscriber unit should temporarily lose its data chan-
`nel assignment, the central 102 and the network control-
`ler 108 may periodically transmit the signalling format
`200 over the voice control channel and the master data
`channel, respectively. If through some error the data
`channel assignment is lost, the present invention pro-
`vides that all data mode subscriber units automatically
`revert to the master data channel. In this way, a sub-
`scriber unit may receive the periodic transmissions of
`the channel assignments from the master data channel
`and return to the proper data channel assignment. In the
`event a subscriber unit loses the identity of the master
`data channel, the present invention further provides
`that the subscriber units revert to the voice control
`chanml to receive the data channel allocation informa-
`non.
`
`Referring now to_ FIG. 3, the preferred format for
`other (i.e., not the master) data channels is shown. Basi-
`cally, the format of a data channel 300 begins with a
`preamble 302, which may include synchronization and
`framing information. The preamble 302 precedes a plu-
`raiity of variable length data messages 304—308.
`As previously mentioned, the request for assignment
`of a data channel is prohibitively long compared to the
`typical data message transmission time. Therefore, the
`present invention contemplates a subscriber unit going
`to its assigned data channel and transmitting the data
`information without re—requesting the channel. Operat-
`ing in this manner conserves spectrum and speeds trans-
`mission by eliminating the requirement to request a data
`channel. Of course, there exists the possibility that there
`will be data collisions on the data channels? However,
`data collision avoidance mechanisms and methods are
`widely known in the art and any suitable data collision
`avoidance and recovery method will be suitable for use
`in the present invention.
`As illustrated in FIG. 3, the lengths of data messages
`1, 2 and 3 (304, 306 and 308), are all of a variable dura-
`tion depending upon the amount of information to be
`transmitted. Thus, once a subscriber unit gains access to
`a data channel, the subscriber may transmit data for as
`long as required to complete a data message. Of course,
`a second subscriber unit attempting to transmit data
`may be required to wait until the first subscriber has
`completed transmitting. Thus, a data channel may be in
`constant or near constant use. During periods of high
`data channel use, the preamble portion 302 need not be
`transmitted since the subscribers may still be synchro-
`nized to the incoming data. However, if the data chan-
`nel use is low. the network controller 108 or a data
`subscriber may transmit the preamble portion 302 prior
`to transmitting.
`Referring now to FIG. 4, there is shown a flow dia-
`gram illustrating the steps executed by the fixed—end
`equipment
`to implement the present
`invention. The
`routine begins with initializing step 400, wherein the
`central controller 102 and the network controller 108
`may set aside memory space or perform other such
`functions as any particular system may require. The
`routine next proceeds to step 402, which starts the per-
`iod timer over which the central controller 102 moni-
`
`8
`tors the voice activity and the network controller moni-
`tors the data activity. In step 404, these measurements
`are taken such as by calculating the air-time billing
`information or other such suitable means. Following
`step 404, decision 406 determines whether or not the
`timer has elapsed. If the timer has not elapsed, a loop is
`formed with step 40% until decision 406 determines that
`the timer has expired.
`Decision 408 determines whether the voice activity is
`high when compared to a selected threshold that may
`be specified by the system supervisor. If the determina-
`tion of decision 408 is that the voice activity is high,
`decision 410 determines whether the current number of
`data channels minus a predetermined offset (one in the
`preferred embodiment) would be less than the minimum
`number (if any) of data channels specified by the system
`supervisor. If so, decisioa 410 returns control to refer-
`ence letter A, which resets the timer and the routine
`begins again. If, however, decision 410 determines that
`removing a channel would not be below the minimum
`allowed data channels, or there is no minimum, the
`routine proceeds to step 412, which de-allocates a chan-
`nel from data traffic and returns it to voice traffic. The
`routine then proceeds to reference letter A of FIG. 4.
`If the determination of decision 408 is that the voice
`activity is not high, the routine proceeds to decision
`414, which determines whether the data activity is high
`compared to a predetermined threshold selected by the
`system supervisor. If the determination of decision 414
`is that the data activity is high, the routine proceeds to
`decision 416, which determines whether the current
`number of channels plus one (in the preferred embodi-
`ment) is greater than the maximum number (if any)
`specified by the system supervisor. If the determination
`of decision 416 is that the additional channel would
`exceed the maximum, the routine returns control to
`reference letter A. If, however, decision 416 determines
`that the addition of a data channel will not exceed the
`maximum, the routine proceeds to step 418, which allo-
`cates an additional channel from voice traffic to data
`traffic. The routine then returns control to reference
`letter A of FIG. 4.
`Additionally, the fixed-end equipment may take traf-
`fic priorities into account before the allocation step 418
`and the de-allocation step 412. If, for example, a particu-
`lar system favored voice traffic, an additional data chan-
`nel may not be allocated if voice trafiic were above a
`predetermined minimum. Alternately, for a system hav-
`ing a data traffic preference, :1. data channel may not be
`reallocated for voice traffic if data traffic was above a
`predetermined threshold.
`In the absence of either a
`voice traffic or data traffic preference, the absolute
`allocation and de-allocation procedure of FIG. 4 is
`preferred.
`Referring still to FIG. 4-, ifthe determination of414 is
`that the data activity as a whole is not high, the routine
`proeeeds to decision 420 to determine whether the data
`traffic across all available data channels is balanced or
`unbalanced. If the determination of decision 420 is that
`the traffic is essentially balanced, the routine returns
`control to reference letter A, which resets the timer of
`step 402. If, however, decision 420 determines that the
`data traffic is imbalanced the routine proceeds to the
`load leveling routine of FIG. 50.
`Referring