United States Patent [19J
`Ayerst et al.
`
`I 1111111111111111 11111 lllll 111111111111111 1111111111 lllll 111111111111111111
`US005521926A
`[11] Patent Number:
`[45J Date of Patent:
`
`5,521,926
`May 28, 1996
`
`[54] METHOD AND APPARATUS FOR
`IMPROVED MESSAGE RECEPTION AT A
`FIXED SYSTEM RECEIVER
`
`[75]
`
`Inventors: Douglas I. Ayerst, Delray Beach; Brian
`J. Budnik, Schaumburg, both of Ill.;
`Malik J. Khan, Lake Worth, Fla.
`
`[73] Assignee: Motorola, Inc., Schaumburg, Ill.
`
`[21] Appl. No.: 283,369
`
`[22] Filed:
`
`Aug. 1, 1994
`
`.•••.••••••••••••.••••.....••...••.••••••.•.••••.•.•••.• H04J 3/06
`Int. Cl.6
`[51]
`[52] U.S. Cl. ..................... 370/953; 370/100.1; 455/51.1;
`375/356
`[58] Field of Search .................................. 370/95.1, 95.2,
`370/95.3, 94.1, 110.1, 94.2, 85.2, 85.7,
`85.8, 85.1, 100.1; 455/33.1, 34.1, 34.2,
`54.1, 54.2, 51.1; 340/825.07, 825.08; 375/356
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,377,192 12/1994 Goodings et al ...................... 370/95.3
`
`Primary Examiner-Benedict V. Safourek
`Assistant Examiner-Ajit Patel
`Attorney, Agent, or Firm-James A. Lamb
`
`[57]
`
`ABSTRACT
`
`A fixed system receiver (107), which includes a forward
`receiver (305), a reverse receiver (310), and a response timer
`(215), is for use in a radio communication system (100)
`having a forward radio channel and a reverse radio channel.
`A command is transmitted in a forward channel radio signal
`to a selective call transceiver. The forward receiver (305) is
`for receiving, demodulating, and decoding the command.
`The reverse receiver (310) is for receiving and demodulating
`the reverse channel radio signal. The response timer (215),
`which is coupled to the forward receiver (305) and the
`reverse receiver (310), is for determining a response period
`beginning substantially at a scheduled response time
`included in the command and having a duration which is
`substantially a designated length of the data unit included in
`the command, and for generating a control signal which
`enables the reverse receiver (310) during the response
`period.
`
`4,918,437
`
`4/1990 Jasinski et al ..................... 370/825.94
`
`21 Claims, 9 Drawing Sheets
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`ANTENNA
`
`RESPONSE
`TIMER
`
`ROUTING CONTROLLER
`
`225
`
`TELEPHONE
`INTERFACE
`
`215
`
`L
`
`220
`
`Apple Exhibit 1007
`Apple Inc. v. Rembrandt Wireless
`IPR2020-00033
`Page 00001
`
`

`

`U.S. Patent
`
`May 28, 1996
`
`Sheet 1 of 9
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`5,521,926
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`U.S. Patent
`U.S. Patent
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`May 28, 1996
`May28, 1996
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`Sheet 2 of 9
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`5,521,926
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`IPR2020-00033 Page 00003
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`

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`U.S. Patent
`
`May 28, 1996
`
`Sheet 3 of 9
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`5,521,926
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`IPR2020-00033 Page 00007
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`

`

`U.S. Patent
`
`May 28, 1996
`
`Sheet 7 of 9
`
`5,521,926
`
`(71Q
`
`-
`
`SYNCHRONIZE TO FORWARD
`CHANNEL FRAME SYNCHRONIZATION
`PATTERN
`
`---------------
`
`r
`
`(720
`
`RECEIVE BLOCK INFROMATION
`WORD OF FORWARD CHANNEL
`TRANSMISSION
`
`---------------
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`l r
`
`(730
`
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`WORD TO FIND FORWARD/REVERSE
`AND SCHEDULED/UNSCHEDULED
`BOUNDARY
`
`, ,
`--------------
`
`DECODE ADDRESSES TO IDENTIFY
`SELECTIVE CALL TRANSCEIVER AND
`ASSOCIATED SCHEDULED
`RESPONSE TIMES AND DESIGNATED
`DATA UNIT LENGTHS
`
`(740
`
`, ,
`-------------------
`
`SET RESPONSE TIMER TO ENABLE
`REVERSE CHANNEL RECEIVER DURING
`RESPONSE PERIODS
`
`(750
`
`FIG. 7
`
`IPR2020-00033 Page 00008
`
`

`

`U.S. Patent
`
`May 28, 1996
`
`Sheet 8 of 9
`
`5,521,926
`
`810
`
`820
`
`830
`
`ESTABLISH REVERSE
`CHANNEL START TIME
`
`CONTROL SIGNAL ENABLES
`REVERSE CHANNEL RECEIVER
`DURING SCHEDULED RESPONSE
`PERIOD
`
`DECODE DATA UNITS RECEIVED
`IN THE REVERSE CHANNEL RADIO
`SIGNAL AT SCHEDULED RESPONSE
`IMES DURING THE RESPONSE PERIOD
`
`850
`
`DISCARD THE
`RECEIVED
`DATA UNIT
`
`860
`
`ROUTE THE RECEIVED DATA
`UNIT TO A SYSTEM CONTROLLER
`
`FIG. 8
`
`IPR2020-00033 Page 00009
`
`

`

`U.S. Patent
`
`May 28, 1996
`
`Sheet 9 of 9
`
`5,521,926
`
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`IPR2020-00033 Page 00010
`
`

`

`5,521,926
`
`1
`METHOD AND APPARATUS FOR
`IMPROVED MESSAGE RECEPTION AT A
`FIXED SYSTEM RECEIVER
`
`FIELD OF THE INVENTION
`
`This invention relates in general to a selective call radio
`communication system providing a received message
`response and in particular to a message response in a
`selective call radio communication system having fixed
`system receivers and scheduled response messages.
`
`BACKGROUND OF THE INVENTION
`
`5
`
`IO
`
`2
`system, the fixed receiver may need a predetermination of
`when the radio frequency is being used for the reverse
`channel, to avoid misinterpreting information that is actually
`forward channel information as reverse channel information.
`The message and response information communicated
`within systems such as given in the examples described
`above may be transmitted in packets of one or more prede(cid:173)
`termined fixed lengths. A first packet of a group of packets,
`or a single packet, transmitted by a selective call transceiver
`typically includes a packet synchronization portion at the
`start of the packet, which provides bit synchronization and
`identifies the beginning of a second portion of the packet
`consisting of data words. Packets in a group of packets,
`which are not the first packet of the group, may derive their
`15 bit and word synchronization from the first packet in the
`group and therefore not include a synchronization portion.
`Using the predetermined modulation and reverse channel
`timing information, a fixed receiver can recover most of
`such packets transmitted in the reverse channel by the
`20 selective call transceivers, when the packets are received
`within radio signals having a signal strength above a mini(cid:173)
`mum threshold. However, there are circumstances which
`may prevent the fixed receivers from recovering some of
`these radio packets. These circumstances arise when the
`fixed receiver's synchronization pattern detector is falsed by
`noise, resulting in a false detection of a synchronization
`pattern, further resulting in a false indication of the begin(cid:173)
`ning of the word portion of a packet. When this happens, the
`fixed receiver can miss the decoding of the synchronization
`30 pattern and code words for a transmitted packet because the
`fixed receiver is incorrectly processing data symbols from
`the transmitted packet which are out of word synchroniza(cid:173)
`tion sequence, due to the false detection of a synchronization
`pattern prior to the actual start of the transmitted packet. As
`35 a result of such false synchronization detections, packets and
`groups of packets are not decoded that otherwise could be,
`and the message throughput and message sensitivity perfor(cid:173)
`mance characteristics are therefore not as good as they
`otherwise could be.
`Thus, what is needed is a method to improve the message
`sensitivity and message throughput performance character(cid:173)
`istics in digital radio communication systems having a
`forward and reverse channel and using forward channel
`scheduling for messages and responses transmitted in the
`reverse channel by one or more selective call transceivers
`
`25
`
`In a selective call radio communication system having a
`forward channel for transmitting digital messages to selec(cid:173)
`tive call transceivers from a system controller and receiving
`digital messages and responses at the system controller from
`the selective call transceivers in one or more reverse chan(cid:173)
`nels, a known means of organizing the responses in the
`reverse channels is to schedule the responses, using infor(cid:173)
`mation transmitted in the forward channel to the selective
`call transceivers to perform the scheduling. This is a general
`approach used in a variety of radio systems.
`A first example of such a system is a single frequency half
`duplex system having one or more transmitters for trans(cid:173)
`mitting the digital messages at a radio carrier frequency
`from the system controller and one or more fixed receivers
`for receiving the messages and responses from the selective
`call transceivers on the same radio carrier frequency. The
`transmissions from the system controller are typically sus(cid:173)
`pended to allow responses from the selective call transceiv(cid:173)
`ers. The responses may be transmitted from the selective call
`transceivers using a random or semi-random method, or they
`may be organized by information transmitted from the
`system controller. The organized method works particularly
`well in a system having a large percentage of acknowledg(cid:173)
`ments or other demand type of responses. The demand type
`of responses can be scheduled during the transmission from
`the system controller which generates
`the demand 40
`responses. The selective call transceivers can include in
`random responses information indicating to the system
`controller that additional messages are being held within the
`selective call transceivers, awaiting scheduled transmission
`to the system controller. With this information, the system 45
`controller can schedule the held messages for transmission
`on the reverse channel.
`A second example of a system using scheduled responses
`in a reverse channel is a duplex system having one or more
`transmitters for transmitting the digital messages at a radio 50
`carrier frequency from the system controller and one or
`more fixed receivers for receiving the messages and
`responses at a second radio carrier frequency from the
`selective call transceivers. In this system, the transmissions
`from the system controller do not need to be stopped to 55
`allow responses from the selective call transceivers. How(cid:173)
`ever, the responses may be organized, as in the case of the
`first example, by information transmitted from the system
`controller.
`In the case of both examples, some generic parameters of
`the scheduled reverse channel transmissions are used by the
`fixed receivers for recovering the reverse channel informa(cid:173)
`tion from the transmissions made by the selective call
`transceivers. For example, predetermination of the modula(cid:173)
`tion and bit rate to be received in the reverse channel is 65
`typically needed by the fixed receivers to properly recover
`the reverse channel information. Also, in a half duplex
`
`SUMMARY OF THE INVENTION
`
`Accordingly, in a first aspect of the present invention, a
`method is used in a fixed system receiver for improving
`response reception in a radio communication system having
`a forward radio channel and a reverse radio channel. A
`command is transmitted in a forward channel radio signal by
`a fixed transmitter to a selective call transceiver. The fixed
`system receiver includes a forward receiver and a reverse
`receiver. The method includes the steps of receiving,
`demodulating, and decoding the command, determining a
`response period, and receiving and demodulating the reverse
`60 channel radio signal.
`In the step of receiving, demodulating, and decoding the
`command, which is performed in the forward receiver, the
`command, which includes an address of a selective call
`transceiver and a scheduled response time at which the
`selective call transceiver transmits a reverse channel radio
`signal including a data unit is received, demodulated, and
`decoded. The command includes a designated length of the
`
`IPR2020-00033 Page 00011
`
`

`

`3
`data unit. In the step of determining a response period, a
`response period is determined which begins substantially at
`the scheduled response time and has a duration which is
`substantial! y the designated length of the data unit. In the
`step of receiving and demodulating the reverse channel radio 5
`signal, the reverse channel radio signal transmitted by the
`selective call transceiver during the response period is
`received and demodulated.
`Accordingly, in a second aspect of the present invention,
`a fixed system receiver is for use in a radio communication
`system having a forward radio channel and a reverse radio
`channel. A command is transmitted in a forward channel
`radio signal by a fixed transmitter to a selective call trans(cid:173)
`ceiver. The fixed system receiver includes a forward
`receiver, a reverse receiver, and a response timer.
`The forward receiver is for receiving, demodulating, and
`decoding the command included in the forward channel
`radio signal. The command includes an address of a selec(cid:173)
`tive call transceiver and a scheduled response time at which
`the selective call transceiver transmits a reverse channel 20
`radio signal including a data unit. The command includes a
`designated length of the data unit.
`The reverse receiver is for receiving and demodulating the
`reverse channel radio signal.
`The response timer, which is coupled to the forward
`receiver and the reverse receiver, is for determining a
`response period beginning substantially at the scheduled
`response time and having a duration which is substantially
`the designated length of the data unit, and for generating a
`control signal which enables the reverse receiver during the
`response period.
`Accordingly, in a third aspect of the present invention, a
`fixed system receiver is for use in a radio communication
`system having a forward radio channel and a reverse radio
`channel. A command is transmitted in a forward channel
`radio signal by a fixed transmitter to a selective call trans(cid:173)
`ceiver. The fixed system receiver includes a combined
`receiver, a response timer, and a system controller.
`The combined receiver is for receiving, demodulating,
`and decoding the command. The command is included in the
`forward channel radio signal having a first radio carrier
`frequency. The command includes an address of a selective
`call transceiver and a scheduled response time at which the
`selective call transceiver transmits a reverse channel radio 45
`signal having the first radio carrier frequency. The reverse
`channel radio signal includes a data unit. The command
`includes a designated length of the data unit. The combined
`receiver is also for receiving and demodulating the reverse
`channel radio signal.
`The response timer, which is coupled to the combined
`receiver, is for determining a response period beginning
`substantially at the scheduled response time and having a
`duration which is substantially the designated length of the
`data unit. The response timer is also for generating a control 55
`signal which enables the combined receiver during the
`response period and disables the combined receiver at times
`which are not the response period.
`The system controller, which is coupled to the combined
`receiver, is for decoding a received data unit from the
`demodulated reverse channel radio signal received at the
`scheduled response time. The system controller is also for
`routing the received data unit to a system controller when the
`received data unit has the designated length of the data unit
`and when the received data unit includes a transceiver
`address which matches the address of the selective call
`transceiver, and is for terminating processing of the received
`
`50
`
`15
`
`25
`
`FIG. 1 is an electrical block diagram of a radio commu(cid:173)
`nication system, in accordance with the preferred embodi(cid:173)
`ment of the present invention.
`FIG. 2 is an electrical block diagram of a fixed receiver,
`in accordance with the preferred and first alternative
`embodiments of the present invention.
`FIG. 3 is an electrical block diagram of a fixed system
`receiver 107, in accordance with second and third alternative
`embodiments of the present invention.
`FIG. 4 is a timing diagram of forward and reverse channel
`radio signals for a first type of the radio communication
`system, in accordance with the preferred embodiment of the
`present invention.
`FIG. 5 is a timing diagram of forward and reverse channel
`30 radio signals for a second type of the radio communication
`system, in accordance with the preferred embodiment of the
`present invention.
`FIG. 6 is a timing diagram of forward and reverse channel
`radio signals for a third type of the radio communication
`35 system, in accordance with the second alternative embodi(cid:173)
`ment of the present invention.
`FIG. 7 is a flow chart for generating the control signal
`which enables reception of the reverse channel radio signal,
`in accordance with the preferred embodiment of the present
`invention.
`FIG. 8 is a flow chart for testing and routing received data
`units, in accordance with the preferred embodiment of the
`present invention.
`FIG. 9 is an electrical block diagram of a fixed system
`receiver in accordance with a fourth alternative embodiment
`of the present invention.
`
`40
`
`5,521,926
`
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`data unit when the received data unit does not have the
`designated length of the data unit or when the received data
`unit does not include a transceiver address which matches
`the address of the selective call transceiver.
`The forward radio channel has a plurality of forward
`channel frame boundaries and a reverse channel frame
`boundary, which is relative to one of the plurality of forward
`channel frame boundaries. The reverse channel frame
`boundary is included in the command. The scheduled
`10 response time is relative to the reverse channel frame
`boundary.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`Referring to FIG. 1, an electrical block diagram of a radio
`communication system 100 is shown in accordance with the
`preferred embodiment of the present invention. The radio
`communication system 100 comprises a message input
`device, such as a conventional telephone 101, connected by
`a conventional public switched telephone network (PSTN)
`108 to a system controller 102. The system controller 102
`oversees the operation of at least one radio frequency
`transmitter/receiver 103 and at least one fixed system
`60 receiver 107, and encodes and decodes inbound and out(cid:173)
`bound telephone addresses into formats that are compatible
`with land line message switch computers and personal radio
`telephone addressing requirements, such as cellular message
`protocols. The system controller 102 also functions to
`65 encode paging messages for transmission by the radio
`frequency transmitter/receiver 103. Telephony signals and
`data messages are transmitted from and received by a
`
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`conventional antenna 104 coupled to the radio frequency
`mined preferences, such as hours during which messages are
`transmitter/receiver 103, and are received by a conventional
`to be held back from delivery to the selective call trans(cid:173)
`antenna 109 coupled to the fixed system receiver 107, which
`ceiver.
`by a unique design recovers the data messages with
`The system controller 102 schedules transmissions of
`improved throughput and reduced falsing. The telephony 5
`messages and acknowledgments from the selective call
`signals are transmitted to and received from a conventional
`transceivers. These transmissions include demand type
`personal radio telephone 105. The radio frequency transmit(cid:173)
`transmissions from the selective call transceivers, such as
`ter/receiver 103 is also used to transmit data paging mes(cid:173)
`acknowledgments to messages which have been transmitted
`sages to a portable receiving device 106. Acknowledgments
`by the system controller 102 and responses to messages such
`and data messages are transmitted by the radio telephone
`as status inquiries transmitted from the system controller
`105 and the portable receiving device 106, received by the
`102. The scheduled transmissions can also include non-
`antennas 104 and 109, and coupled to the system controller
`demand transmissions from the selective call transceivers,
`102.
`such as messages being held by the selective call transceiv(cid:173)
`It should be noted that the system controller 102 is
`ers, about which the selective call transceivers have
`informed the system controller 102 within a previous mes-
`capable of operating in a distributed transmission control
`15 sage or acknowledgment transmitted to the system controller
`environment that allows mixing conventional cellular,
`102 by the selective call transceiver. The use of reverse
`simulcast, master/slave, or other coverage schemes involv(cid:173)
`ing a plurality of radio frequency transmitter/receivers 103,
`channel scheduling under certain circumstances improves
`the throughput of the reverse channel in comparison to that
`conventional antennas 104, fixed system receivers 107, and
`achievable for an unscheduled, random input reverse chan-
`conventional antennas 109, for providing reliable radio
`20 nel organization scheme such as that used in an ALOHA
`signals within a geographic area as large as a nationwide
`system, well known to one of ordinary skill in the art. As will
`network. Moreover, as one of ordinary skill in the art would
`be described in more detail below, a scheduled reverse
`recognize, the telephonic and selective call radio commu(cid:173)
`channel may be a portion of the total time available in a half
`nication system functions may reside in separate system
`duplex single frequency radio channel (a single radio carrier
`controllers 102 which operate either independently or in a
`frequency which is time shared for both forward and reverse
`networked fashion.
`channels). Alternatively, the scheduled reverse channel may
`It should also be noted that the radio frequency transmit(cid:173)
`be some portion of the time available, or all of the time
`ter/receiver 103 may comprise the fixed system receiver 107
`available, in a second radio carrier frequency which is
`coupled to a conventional radio frequency transmitter.
`different than the forward channel radio frequency. Methods
`30 for identifying scheduled times will be described below.
`It will be appreciated that other selective call radio
`The system controller 102 is preferably a model
`terminal devices (not shown in FIG. 1), such as conventional
`E09PED0552 PageBridge® paging terminal manufactured
`mobile cellular telephones, mobile radio data terminals,
`by Motorola, Inc., of Schaumburg Ill., modified with special
`mobile cellular telephones having attached data terminals, or
`firmware elements in accordance with the preferred embodi-
`mobile radios (trunked and non-trunked) having data termi(cid:173)
`35 ments of the present invention, as described herein. The
`nals attached, are also able to be used in the radio commu(cid:173)
`system controller alternatively could be implemented using
`nication system 100. In the following description, the term
`a MPS2000® paging terminal manufactured by Motorola,
`"selective call transceiver" will be used to refer to the
`Incorporated of Schaumburg, Ill. The subscriber data base
`personal radio telephone 105, or the portable transmitting/
`may alternatively be implemented as magnetic or optical
`receiving device 106, a mobile cellular telephone, a mobile
`40 disk memory, which may alternatively be external to the
`radio data terminal, a mobile cellular telephone having an
`system controller 102.
`attached data terminal, or a mobile radio (conventional or
`Referring to FIG. 2, an electrical block diagram of the
`trunked) having a data terminal attached. Each of the selec(cid:173)
`fixed receiver 107 is shown, in accordance with a preferred
`tive call transceivers assigned for use in the radio commu(cid:173)
`embodiment of the present invention. The fixed receiver 107
`nication system 100 has an address assigned thereto which
`45 comprises a combined receiver 205, which is a radio fre(cid:173)
`is a unique selective call address. The address enables the
`transmission of a message from the system controller 102
`quency receiver operating at a first radio carrier frequency
`only to the addressed selective call transceiver, and identifies
`for receiving forward and reverse radio channel signals, as
`will be described more fully below, a response timer 215, a
`messages and responses received at the system controller
`telephone interface 225, a routing controller 220, and the
`102 from the selective call transceiver. Furthermore, each of
`50 antenna 109. The antenna 109 is coupled to a first input of
`one or more of the selective call transceivers also has a
`the combined receiver 205. A first output 207 of the com(cid:173)
`unique telephone number assigned thereto, the telephone
`bined receiver 205 is coupled to the response timer 215 and
`number being unique within the PSTN 108. A list of the
`a second output 209 of the combined receiver 205 is coupled
`assigned selective call addresses and correlated telephone
`to the routing controller 220. A control signal is generated by
`numbers for the selective call transceivers is stored in the
`the response timer 215 and is coupled a second input 213 of
`system controller 102 in the form of a subscriber data base.
`the combined receiver 205. An output 211 of the combined
`The system controller 102 queues data and stored voice
`receiver 205 is coupled to the routing controller 220. The
`messages for transmission to the selective call transceivers,
`routing controller 220 has an output coupled to the telephone
`connects telephone calls for transmission to the selective call
`interface 225. The telephone interface 225 has an output
`transceivers,
`and
`receives
`acknowledgments,
`data
`60 which is coupled to the system controller 102, through a
`responses, data messages, and telephone calls from the
`private network or the PSTN 108. The fixed system receiver
`selective call transceivers. The subscriber data base in the
`107 includes unique functions which disable reception to
`system controller 102 stores information relevant to each
`reduce falsing and which test responses received from the
`subscriber's selective call transceiver, including a correla(cid:173)
`selective call transceivers to improve throughput, as will be
`tion between the unique address assigned to each selective
`65 more fully described below.
`call transceiver and the telephone number used within the
`PSTN 108 to route messages and telephone calls to each ,
`Referring again to FIG. 2, in a first alternative embodi(cid:173)
`ment of the present invention, the routing controller 220 is
`selective call transceiver, as well as other subscriber deter-
`
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`omitted and the output 211 of the combined receiver 205 is
`coupled directly to the telephone interface 225. The second
`output 209 of the combined receiver 205 is not used.
`The fixed system receiver 107 in accordance with the
`preferred and first alternative embodiments of the present
`invention preferably comprises a Nucleus® model receiver
`manufactured by Motorola, Inc. of Schaumburg, Ill., with
`unique functions added to the standard model. The unique
`functions are provided by firmware routines developed in
`accordance with techniques well known to one of ordinary
`skill in the art.
`The fixed system receiver 107, in accordance with the
`preferred and first alternative embodiment of the present
`invention, operates in a first type or a second type of radio
`communication system 100. In the first type of radio com(cid:173)
`munication system 100, a first radio carrier frequency is time
`shared by a forward channel, which is for transmitting
`information from the transmitter/receivers 103 in a forward
`channel radio signal to one or more identified selective call
`transceivers, and a reverse channel, which is for transmitting
`scheduled responses from the identified selective call trans(cid:173)
`ceivers in reverse channel radio signals to the transmitter/
`receivers 103. The antenna 109 intercepts the forward chan-
`nel radio signal, which includes telephony signals, digital
`messages, and commands. The combined receiver 205 25
`receives, demodulates and decodes the commands included
`in the forward channel radio signal. From information
`included in the commands, the response timer 215 generates
`the control signal, which enables and disables the combined
`receiver 205 during the reverse channel time of the first radio 30
`frequency. When the combined receiver 205 is enabled by
`the control signal, the combined receiver 205 receives and
`demodulates
`radio signals which contain scheduled
`responses transmitted by the selective call transceivers.
`In the preferred embodiment of the present invention, the
`scheduled responses are coupled to the routing controller
`220, wherein
`tests are performed on
`the scheduled
`responses. When tests results are successful, the scheduled
`responses are coupled to the telephone interface 225,
`wherein the scheduled responses are used to modulate
`signals, such as modem signals, which are transmitted to the
`system controller 102. When the tests are not successful, the
`scheduled responses are processed no further. In the first
`alternative embodiment of the present invention, the sched(cid:173)
`uled responses are not tested, and are coupled directly to the
`telephone interface 225. The scheduled responses include
`responses from the selective call transceivers such as mes(cid:173)
`sage and/or acknowledgment information.
`In the second type of radio communication system 100, 50
`the forward radio channel and reverse radio channel are at
`two different radio frequencies, and at least one of the
`transmitter/receivers 103 transmits the commands in two
`radio signals: a forward channel radio signal having a first
`radio carrier frequency which is a forward