111111111111111111111111111111111111111111111111111111111111111
`
`United States Patent
`Dingsor
`
`[19]
`
`nil Patent Number:
`[45] Date of Patent:
`
`5,742,641
`Apr. 21, 1998
`
`[54] APPARATUS, METHOD AND ARTICLE OF
`MANUFACTURE FOR THE DYNAMIC
`COMPENSATION OF FM DEVIATION IN A
`FM RADIO RECEIVER
`
`[75]
`
`Inventor: Andrew Dwight Dingsor, Durham,
`N.C.
`
`[73] Assignee: International Business Machines
`Corporation, Armonk, N.Y.
`
`[21] Appl. No.: 683,478
`
`[22] Filed:
`
`Jul. 18, 1996
`
`[51] Int. C1.6
`[52] U.S. Cl.
`[58] Field of Search
`
` HO4B 1/38; HO4L 5/16
` 375/222; 455/557; 455/75
`375/222; 329/315,
`329/123; 455/557. 558. 75
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5/1974 Gross et al.
`3,810,188
`5/1978 Rogers, Jr.
`4,087,756
`4,293,818 10/1981 Jarger
`4,355,414 10/1982 Inoue
`8/1984 Couvillon
`4,466,128
`4,484,154 11/1984 Pavin
`6/1985 Marshall
`4,523,324
`2/1986 Curtis et al.
`4,573,026
`9/1989 Gamer et al.
`4,870,699
`2/1990 Gamer et al.
`4,905,305
`7/1991 Owen
`5,034,695
`1/1994 Vannatta et al.
`5,280,644
`4/1994 Arens et al.
`5,301,364
`5,365,546 11/1994 Koenck et al.
`
` 346/33
` 329/50
` 329/50
` 455/184
` 455/208
` 331/23
` 375/91
` 332/18
` 455/76
` 455/183
` 329/325
` 455/265
` 455/69
` 375/9
`
`3/1995 Schuermann
`5,396,251
`4/1995 Dorr
`5,408,695
`5,438,699 8/1995 Coveley
`9/1995 Lindell
`5,453,748
`2/1996 Takahara et al.
`5,493,710
`5,497,402
`3/1996 Pyo et al.
`5,517,491
`5/1996 Nanni et al.
`
`342/51
`455/226.1
`455/67.4
`342/51
`455/192.2
`375/344
`370/29
`
`Primary Examiner—Stephen Chin
`Assistant Examiner—Mohammad Ghayour
`Attorney, Agent, or Firm John D. Flynn
`
`[57]
`
`ABSTRACT
`
`Described is a method, apparatus, and article of manufacture
`to minimize radio data modem receive errors when a base
`station keys up. It applies to an intermittently keyed, mul-
`tiple base station, single frequency reuse, FM modulated,
`radio data network such as the ARDIS network. Compen-
`sation is provided for the fact that each base station in the
`network may have a different transmit FM deviation level.
`Since these networks typically use the same base station to
`transmit to any one radio data modem over periods of time,
`and since the modem receiver can measure and remember
`the FM deviation level of each base station, a modem can
`compensate by using the FM deviation value of its "present"
`base station as the starting value for its automatic deviation
`control algorithm. By seeding the algorithm with the actual
`value for the "present" base station, receive data errors are
`reduced during the critical time when the base station is
`keying up. As the geographical position of the modem
`changes, or as radio conditions vary, the network may select
`a different base station to transmit to a modem. The modem
`will detect this change, and dynamically change its com-
`pensation to match the new "present" base station.
`
`19 Claims, 10 Drawing Sheets
`
`401
`
`403
`
`/ 4°'
`
`405
`
`'I
`
`FRAMING
`
`FEC
`
`FILTERS
`
`411
`
`D/A
`
`ENCODER
`
`DATA
`IN
`
`I
`
`DECODER
`429
`
`431
`
`/
`
`419
`
`SYMBOL
`CLOCK
`
`421
`
`FEC &
`FRAMING
`
`411--• DETECTOR
`
`DATA
`OUT
`
`RX ACQUIRE &
`STEADY STATE
`425
`427
`DC
`H FILTERS fo-1 ESTIMATOR lot-
`
`RX
`
`ND
`
`415
`
`440
`
`441
`
`FM DEVIATION
`COMPENSATION
`
`443
`
`FM DEVIATION
`FACTOR
`A
`
`445
`FM DEVIATION
`ADJUSTMENT
`CONTROL
`
`LG Ex. 1015
`LG Electronics Inc. v. ParkerVision, Inc.
`IPR2022-00245
`Page 00001
`
`

`

`DEVICE
`MOBILE
`
`129
`
`FIG. 1
`
`OT JO 1 WEIS
`
`00
`
`11
`
`Waled *S11
`
`DEVICE
`MOBILE
`
`131
`
`101
`
`DEVICE
`MOBILE
`
`125
`
`111
`
`CONTROLLER
`
`NETWORK
`
`DEVICE
`MOBILE
`
`123
`
`DEVICE
`
`129MOBILE
`
`103
`
`105
`
`DEVICE
`MOBILE
`
`121
`
`IPR2022-00245 Page 00002
`
`

`

`*-k
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`IN)
`
`Ui
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`1:111 JO Z laatiS
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`4
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`‘,
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`FIG. 2
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`I
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`I
`I
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`I
`
`RECEIVER
`
`I
`I
`I
`I
`I
`
`I
`
`I ANTENNA
`
`209
`
`DSP
`
`MICROPROCESSOR
`
`COMPUTER
`
`TRANSMITTER
`
`205
`
`,,-- 203
`
`RADIO
`
`207
`
`201
`
`200
`
`IPR2022-00245 Page 00003
`
`

`

`polud °S11
`
`8661 `It *AV
`
`01 JO £ PatiS
`
`FIG. 3
`
`FMDCF
`
`BS ID
`
`FM DEVIATION TABLE
`
`211
`
`A
`
`INJ
`
`X
`
`,
`
`20,9
`
`207--N_
`RECEIVER
`
`A
`
`DSP
`
`41111-------
`
`y4 PROCESSOR
`
`--.
`
`205
`
`203.-. \
`
`IPR2022-00245 Page 00004
`
`

`

`0I JO 17 PaqS
`
`00
`VZ
`
`jualud •Sil
`
`415
`
`44411--
`
`ND
`
`ADJUSTMENT
`FM DEVIATION
`
`CONTROL
`
`445
`
`FM DEVIATION
`
`FACTOR
`
`44
`
`COMPENSATION
`FM DEVIATION
`
`44
`
`440
`
`FIG. 4
`
`DC 14_
`425
`
`ESTIMATOR
`
`F I LTE RS .0--
`
`427
`
`22
`
` :
`
`STEADY STATE
`RX ACQUIRE &
`
`421
`
`CLOCK
`SYMBOL
`
`419
`
`DETECTOR
`
`.11111--
`
`FRAMING
`
`FEC &
`
`429
`DECODER
`
`431
`
` TX
`
`
`
`D/A
`
`411
`
`ENCODER
`
`FILTERS
`
`FEC
`
`FRAMING -110,
`
`405
`
`40
`0
`
`Z
`
`403
`
`401
`
`OUT
`DATA
`
`IN
`DATA
`
`IPR2022-00245 Page 00005
`
`

`

`0I JO S WEIS
`
`00
`
`et
`
`FIG. 5
`
`TRANSMITTER
`
`PORTION
`
`SYNTHESIZER
`GENERATOR
`FREQUENCY
`
`OSCILLATOR
`
`CRYSTAL
`
`I/F LOGIC
`PCMCIAS-
`
`CONNECTOR
`
`PCMCIA
`
`ANTENNA
`
`DUPLEXOR
`
`DSP
`
`Ae P
`
`PORTION
`RECEIVER
`
`MEMORY
`
`- -
`
`IPR2022-00245 Page 00006
`
`

`

`U.S. Patent
`
`Apr. 21, 1998
`
`Sheet 6 of 10
`
`5,742,641
`
`DEMODULATE FM SIGNAL TO PRODUCE BASEBAND SIGNAL
`
`CONVERT THE BASEBAND SIGNAL INTO DIGITAL SAMPLES
`
`601
`
`603
`
`605
`
`COMPENSATING EACH SAMPLE WITH AN FM DEVIATION FACTOR
`
`DECODING THE COMPENSATED DIGITAL SAMPLES
`
`EXTRACTING BASE STATION IDENTIFIER
`
`UPDATING THE FM DEVIATION TABLE WITH CURRENT FM
`DEVIATION FACTOR
`
`RESET THE FM DEVIATION FACTOR WITH VALUE
`ASSOCIATED W/ EXPECTED BASE STATION IDENTIFIER
`
`OUTPUTTING THE DIGITIAL DATA SHOWN IF MESSAGE
`IS ADDRESSED TO MODEM
`
`FIG. 6
`
`607
`
`609
`
`611
`
`613
`
`615
`
`IPR2022-00245 Page 00007
`
`

`

`illaWd eSsa
`
`OT JO L loNS
`
`VC
`
`FREQUENCY
`
`VA
`
`VB
`
`FC F LO
`
`FIG. 7
`
`BWB
`
`BWA
`
`BWC
`
`FC
`
`S
`V MIN
`
`V MAX
`
`•
`
`VOLTAGE
`
`VB
`
`IPR2022-00245 Page 00008
`
`

`

`U.S. Patent
`
`Apr. 21, 1998
`
`Sheet 8 of 10
`
`5,742,641
`
`801
`
`DETERMINE MAX & MIN VALUES OVER A GIVEN
`TIME PERIOD OR NUMBER OF SAMPLES
`
`COMPARE TO EXPECTED OR DESIRED MAX & MIN
`VALUES
`
`803
`
`ADJUST FM DEVIATION FACTOR ACCORDINGLY
`
`805
`
`FIG. 8
`
`IPR2022-00245 Page 00009
`
`

`

`"'mind *S'fl
`
`OT JO 6 WEIS
`
`FM DEVIATION TABLE
`211
`
`901
`
`DIGITAL DATA STREAM
`
`TABLE ACCESS
`927
`
`ID
`STATION
`BASE
`EXPECTED
`
`905
`
`1
`
`DSP
`
`205
`
`DATA
`CONTROL
`
`146
`
`I/F
`DSP
`
`925
`203
`
`PROCESSING
`
`MESSAGE
`
`923
`
`HOST
`921
`
`I/F
`
`MESSAGE TO HOST
`
`FMDCF
`FACTORY
`
`MODEM/HOST
`ADDRESS OF
`
`903
`
`909
`
`907
`
`IPR2022-00245 Page 00010
`
`

`

`lualud 'S'fl
`
`OT JO OT WIN
`
`FIG. 10
`
`0.9876
`
`1.0371
`
`1.1059
`
`1.2369
`
`A2467D3201
`
`656437CE51
`
`A13579BD709
`
`C547621F1
`
`FM DEVIATION FACTOR
`
`BASE STATION ID
`
`IPR2022-00245 Page 00011
`
`

`

`5,742,641
`
`1
`APPARATUS, METHOD AND ARTICLE OF
`MANUFACTURE FOR THE DYNAMIC
`COMPENSATION OF FM DEVIATION IN A
`FM RADIO RECEIVER
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention is related to digitally controlled
`radio communications devices and more particularly, to FM
`deviation control in a FM radio receiver.
`2. Description of the Prior Art
`In an intermittently keyed single frequency reuse radio
`data network, multiple base stations transmit data to mul-
`tiple radio data modems at different times on the same radio
`frequency. Each radio data modem can listen for transmis-
`sions from multiple base stations. To communicate with
`each radio data modem, the network controller selects the
`base station with the "best" signal path to the particular
`modem. Single frequency reuse networks like ARDIS use
`frequency modulation to convey messages to modems.
`Frequency modulation (FM) changes the carrier
`frequency, or an intermediate frequency if channels are
`multiplexed, in proportion to the instantaneous average
`value of a baseband signal. With FM the carrier frequency
`is modulated with the baseband signal. In the ARDIS
`network, associated with each base station transmitter are
`errors or drifts in the FM deviation level. These drifts or
`errors are caused by components changing over time. The
`transmitter components are tuned periodically but, can drift
`or change between tunings. The deviation level may increase
`the modulation voltage range (i.e., amplify the modulation
`voltage) or decrease the modulation voltage range (i.e.,
`attenuate the modulation voltage). FM deviation causes the
`modulating signal to be amplified outside a specified range
`or attenuated within a specified range. Thus, FM deviation
`is caused by changes in the range or magnitude (i.e., VA44,
`of the modulating signal of the transmitter. In an
`to
`FM system this causes the transmitted FM signal to occupy
`more bandwidth (i.e., the carver frequency is varied over a
`wider bandwidth due to larger voltage range of modulating
`signal) or less bandwidth (i.e., the carrier frequency is varied
`over a smaller bandwidth due to smaller voltage range of the
`modulating signal).
`In FM receivers, the FM deviation error of the transmitter
`is manifested as an error in the amplitude level of the
`demodulated baseband signal. This amplitude deviation is
`due to the transmitted FM signal occupying a bandwidth that
`is larger or smaller than that allocated to the transmitter. FM
`deviation causes a change in the amplitude of the demodu-
`lated baseband signal which if uncompensated can cause
`errors, loss of data error margin, higher bit error rates which
`results in more data frames being transmitted in error, more
`re-tries, and slower perceived throughput for the user of the
`radio-data modem. This loss of error margin is particularly
`significant in 4-level data encoding systems like RD-LAP.
`RD-LAP uses four level symbols and associated levels are
`commonly referred to as +3, +1, —1, —3. Because the
`symbols are level sensitive, changes in the received base-
`band voltage range can cause errors in the symbol recovery
`and thus in resulting data. In a four-level system such as
`RD-LAP the distance between adjacent symbol levels is
`one-third of the total range from maximum to minimum
`levels (+3 to —3). A receiver can receive these levels without
`ambiguity when the received symbol falls within half the
`inter-level distance, or only one-sixth the total range. As
`error in the transmitted signal deviation increases, reception
`by the modem becomes more and more difficult.
`
`5
`
`35
`
`40
`
`2
`FM deviation is particular a problem in intermittently
`keyed single frequency reuse networks where multiple base
`stations time multiplex the same frequency spectrum. Each
`base station transmitter may have a different FM deviation
`level. Because a receiver in the network must be capable of
`receiving message from any base stations it must be capable
`of handling a wide variety of FM deviation levels. This
`problem is unique to intermittently keyed single frequency
`reuse networks, like ARDIS. Using multiple base stations on
`10 the same frequency helps provide the benefit of increased
`"building penetration" since the modem has a better chance
`of receiving one of multiple base stations. However, the
`modem must be able to adapt to the characteristics of each
`of these base stations. This problem is not present in other
`network architectures, where base stations are continuously
`15 keyed and only one base station transmits on that frequency
`(in each geographical area). In those networks, the modem
`receives from only one base station over long periods of
`time.
`This problem has traditionally been reduced by imple-
`20 menting a type of automatic gain control in the receiver.
`These techniques analyze the content of a received signal
`over a significant period of time, and then adjust the receiver
`to compensate. These techniques work well for continuously
`keyed networks where the receiver hears one base station
`25 over long periods of time. However, these techniques do not
`eliminate the problem completely in intermittently keyed
`networks because during data at the beginning of a trans-
`mitter key-up can be received in error or not at all, while the
`AGC is attempting to lock or settle onto the desired ampli-
`30 fication or attenuation level. In an intermittently keyed
`network, base stations key up only to send information
`frames, and these are the first frames sent when the base
`station keys up. Thus, the important initial data frames are
`lost resulting in less data throughput.
`These unresolved problems and deficiencies are clearly
`felt in the art and are solved by the invention in the manner
`described below.
`SUMMARY OF THE INVENTION
`The above-mentioned needs have been met in accordance
`with the present invention by providing for a method,
`apparatus and article of manufacture that satisfies these
`needs. Accordingly, it is an object of the present invention to
`provide FM data communications that are less error prone.
`It is a further object of the present invention to provide
`FM data communications that reduces the number of trans-
`mission retries.
`It is an object of the present invention to provide FM data
`communications with higher throughput.
`It is a further object of the present invention to provide
`FM data communications with a minimum impact on the
`communications time line.
`It is yet another object of the present invention to provide
`55 dynamic compensation wherein a receiver maintains a table
`of deviation levels for base stations from which it can listen.
`It is yet another object of the present invention to provide
`compensation for FM deviation with less dependency on an
`automatic gain control mechanism such that data at the
`60 beginning of a transmission from a base station is received
`with fewer errors.
`It is yet another object of the present invention to provide
`compensation for FM deviation with less dependency on
`expensive radio components.
`It is yet another object of the present invention to provide
`compensation for FM deviation where the compensation can
`be changed and updated easily.
`
`45
`
`50
`
`65
`
`IPR2022-00245 Page 00012
`
`

`

`5,742,641
`
`3
`Briefly described the present invention provides a
`method, apparatus, and article of manufacture to minimize
`radio data modem receive errors when a base station keys
`up. A modem used with an intermittently keyed, multiple
`base station, single frequency reuse, FM modulated, radio
`data network such as the ARDIS network is provided with
`compensation for the fact that each base station in the
`network may have a different transmit FM deviation level.
`Since these networks typically use the same base station to
`transmit to any one radio data modem over periods of time,
`and since the modem can measure and remember the FM
`deviation level of each base station, a modem can compen-
`sate by using the FM deviation value of its "present" base
`station as the starting value for its automatic deviation
`control algorithm. By seeding the algorithm with the actual
`value for the "present" base station, receive data errors are
`reduced during the critical time when the base station is
`keying up. As the geographical position of the modem
`changes, or as radio conditions vary, the network may select
`a different base station to transmit to a modem. The modem
`will detect this change, and dynamically change its com-
`pensation to match the new "present" base station.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The foregoing and other objects, aspects and advantages
`of the invention will be better understood from the following
`detailed description with reference to the drawings, in
`which:
`FIG. 1 depicts an architecture of a single frequency reuse
`radio data network.
`FIG. 2 depicts an overview of an FM radio modem.
`FIG. 3 depicts reception of FM signal providing for FM
`deviation compensation
`FIG. 4 depicts a more detailed look at the digital signal
`processing in a generic DSP having FM deviation compen-
`sation
`FIG. 5 depicts an PCMCIA FM radio modem.
`FIG. 6 depicts a method of receiving FM signals in
`accordance with the present invention.
`FIG. 7 depicts the relationship between FM deviation and
`bandwidth utilization.
`FIG. 8 is a simple FM deviation control algorithm.
`FIG. 9 depicts data stream processing in the micropro-
`cessor.
`FIG. 10 is a sample FM deviation table.
`
`DETAILED DESCRIPTION
`An overview of a single frequency reuse network such as
`ARDIS is shown in FIG. 1. Note base stations 101, 103 and
`105 are coupled by land lines to a network controller 111.
`Several mobile users are depicted in the area shown as 121,
`123, 125, 127, 129 and 131. All these mobile users are
`locked onto the single frequency used in the network.
`Frequency-agile mobile devices have scanned to find the
`network, and fixed frequency devices are programmed there
`permanently. Throughout the business day, the mobile users
`stay locked on this same frequency. Although the throughput
`requirements in some large cities may require the network to
`operate additional network "layers" on additional
`frequencies, the mobile users will typically operate on the
`same frequency for long periods of time (days/months).
`The network controller chooses the best base station to
`transmit to each mobile user, and keys up that base station
`when it has a data message for a particular mobile user.
`
`15
`
`30
`
`4
`When the network controller has a data message to be
`transmitted to another mobile user, if the presently keyed up
`base station is also serving that mobile user, it will keep that
`base station keyed up and enqueue the message for trans-
`5 mission by that base station. However, if another base
`station is serving the other mobile user, the network con-
`troller will key down the present base station (when the first
`message is completed) and then key up the correct base
`station to transmit the message.
`10 Mobile users in a "good" coverage area are able to receive
`signals from several of the base stations. For example, in
`FIG. 1, mobile user 125 might hear base stations 101 and
`103, but not 105. Since in practice, the base stations are
`keyed on and off rapidly (within seconds), with one or two
`information messages being sent to users per key up, mobile
`user 125 might hear transmissions from base station 101,
`followed by silence while 105 is transmitting, and then
`would hear from 101 again, and then from 103.
`An overview of a mobile device is shown in FIG. 2. FIG.
`20 2 depicts a host device 200 and wireless modem 201. A
`wireless modem 201 is similar to a wired modem in that it
`permits a computer or other device to send and receive data
`from external sources. The host device 200 can be a com-
`puter such as a laptop, palm top, personal digital assistant
`25 (PDA), PC, mainframe, base station, switch, pager or other
`processing device. The wireless modem 201 may be
`installed as an adapter card or slot such as a PCMCIA slot
`or may be packaged in a standalone housing or fully
`integrated into the host device.
`The present invention provides FM deviation compensa-
`tion to a FM signal used in wireless communication. The FM
`deviation compensation is applied when the radio modem is
`receiving FM signals from an FM transmitter. The present
`invention may be used with any FM radio system including
`35 but not limited too the following: Radio Data Link Access
`Protocol (RDLAP) and Motorola Data Communication
`(MDC).
`In the preferred embodiment, the radio modem consists of
`three major components: a microprocessor 203, a digital
`ao signal processor (DSP) 205 and radio 207 including an
`antenna. The microprocessor 203 including memory (i.e., in
`the preferred embodiment static random access memory
`RAM (SRAM) and/or flash memory and/or DRAM) and
`associated circuitry is responsible for interfacing with the
`45 host computer 200 or other device wishing to send and
`receive data. It may provide other functions such as buffer-
`ing; modem management functions; DSP configuration and
`booting or startup; and radio configuration and booting or
`start up; and Messaging and protocol management. The
`50 microprocessor may also control channel and frequency
`assignment and control of the frequency synthesizer or
`frequency generator that makes use of the crystal to provide
`signals at frequencies necessary for modulation and
`demodulation of RF signals. The microprocessor may also
`55 provide additional layers of protocol stack, such as the
`RD-LAP Service Sublayer. The microprocessor interface
`permits the modem to receive data and commands from the
`host device and provide data and status information to the
`host device. The three major components may all be embod-
`60 ied only in a single semiconductor device.
`The DSP 205 may provide transmit functions including
`encoding of signals that are transmitted. The DSP 205
`provides receive functions including decoding and FM
`deviation compensation to signals that are received. In the
`65 preferred embodiment the DSP 205 provides processing for
`FM deviation compensation for received signals. The DSP
`205 functions are discussed in detail below.
`
`IPR2022-00245 Page 00013
`
`

`

`5,742,641
`
`5
`In the preferred embodiment the radio 207 consists of a
`transmitter for modulating signals and a receiver for
`demodulating signals. The transmitter and receiver may
`share a common antenna 209 via a duplexer. The transmitter
`is responsible for generating an FM signal at a carrier
`frequency using a baseband signal and a local oscillator
`signal (i.e., modulating the carrier frequency in accordance
`with the baseband signal). The receiver is responsible for
`producing a baseband signal from an FM signal using a local
`oscillator signal (i.e., demodulating the FM signal using the
`changing carrier frequency to provide the baseband signal).
`The radio 207 or communications circuitry provides physi-
`cal access to a network or connection (i.e., the wireless or
`ARDIS network of the preferred embodiment). The radio
`207, as is common among wireless modems, may have its
`own battery. An antenna is used for transmitting and receiv-
`ing the electromagnetic communications signals from the air
`interface.
`In the preferred embodiment the radio modem fits into a
`PCMCIA slot of a host device. Thus, the wireless modem
`comprises a PCMCIA connector and PCMCIA interface
`logic for providing the modem with an external interface.
`This is depicted in FIG. 5. Note that various components of
`the modem may be located eternally from the PCMCIA card
`(i.e., the battery, antenna, radio). Note that in both the
`Receiver and Transmitter a local oscillator signal at a
`designated frequency is shown. Note however that a single
`crystal may be utilized to produce the local oscillator signal
`for multiple frequencies and channels. As shown in FIG. 5
`a programmable frequency synthesizer may also be utilized
`in the modem for providing a plurality of frequencies so that
`multiple channels and full duplex operation are supported.
`The modem may also provide support for a plurality of
`protocols including those used in ARDIS. Also note that
`although the present invention is depicted with only a single
`receive/transmit stages, multiple stages can be used, as is
`common for instance in super-heterodyne receivers. Thus,
`IF stages and filters and amplifiers are not shown or dis-
`cussed. All or any subset of the above functions can be
`provided in a single semiconductor device.
`FIG. 7 depicts FM deviation level in a transmitter. As
`shown in FIG. 7, the desired or expected FM modulation
`level or modulation range is VA. In the preferred
`embodiment, VA is an encoded base band analog signal that
`represents digital information to be transmitted. VA is used
`to frequency modulate the carrier frequency of a transmitted
`signal. Thus, as VA changes so does the carrier frequency of
`the transmitted signal. VA is the voltage range expected by
`the transmitter. The transmitter expects a base band signal
`that varies in amplitude between VmAx and V Aim in accor-
`dance with digital information encoded into the base band
`signal. If the encoder is tuned properly then the FM devia-
`tion level is VA and the transmitted signal occupies a
`bandwidth BWA. At a receiver, VA is recovered, as modified
`by noise and interference during transmission, by demodu-
`lating the received FM modulated signal. The receiver then
`decodes VA to obtain the digital data stream.
`However, if the transmitter or encoder components drift
`or vary over time or are coal-adjusted then the analog base
`band signal can be amplified as shown by VB or attenuated
`as shown by Vc. Accordingly, the FM signal transmitted
`occupies frequency bandwidth BWB or BW,„ respectively.
`In the receiver the amplified analog baseband voltage VB 5or
`the attenuated baseband voltage V, is recovered. Without
`compensation, the scaling of the demodulated baseband
`signal can cause errors in the decoded digital data stream.
`Automatic Gain Control (AGC) circuitry can scale (amplify
`
`6
`or attenuate) the baseband signal by continuously monitor-
`ing the baseband voltage levels and adjusting a gain accord-
`ingly. However, automatic gain control circuitry when
`implemented in the radio portion makes changes, improve-
`s meats and updates difficult and expensive, while adding to
`the cost of the radio portion of the wireless modem. Also
`AGC circuitry requires tracking and measurement over a
`relatively long period of time before the appropriate gain is
`determined. Thus, data received from an intermittently
`10 keyed single frequency reuse network while the AGC is
`attempting to determine an appropriate gain can be lost or
`error prone resulting in more retries and retransmission
`which degrade the effective bandwidth of the RF channel.
`The right hand side of FIG. 7 depicts sample voltage
`15 ranges representing the same digital information. Note that
`ranges correspond to VA, VB and V,.
`
`FM Deviation Compensation for Received Signals
`
`20
`
`In an intermittently keyed single frequency reuse network
`each modem is capable of hearing all messages from base
`stations radiating in a given geographical vicinity. The
`network controller is able to determine the best base station
`for communication with a particular modem in the network
`25 Each base station in the network is assigned a unique
`identifier. In RD-LAP and MDC networks this ID consists of
`a country code, network ID, subnetwork ID, and base station
`ID. Each base station transmits its identifier whenever it
`transmits a data message, either immediately preceding the
`30 data message, or immediately following it. Each modem
`hears the base station IDs and correlates the messages it has
`received with the ID of the base station which sent it. The
`modem therefore knows which base station has been chosen
`by the network controller to send it messages, and which
`35 base station is most likely to send it future messages. Since
`the base station from which the modem is to receive future
`messages is known and since the modem can hear messages
`from other base stations the modem can dynamically main-
`tain a table of FM deviation factors that can be used by the
`40 wireless modem and applied when that particular base
`station becomes the most likely base station from which the
`wireless modem will receive messages.
`FIG. 3 illustrates the signal path for the reception of FM
`signals. Messages in the form of FM signals are radiated by
`45 base stations in the ARDIS network. The wireless modem
`thus receives a stream of messages represented by FM
`signals. An FM signal is received from an antenna 209 and
`the received FM signal is provided to receiver 207. The
`receiver 207 takes the FM signal mixes it with a local
`50 oscillator signal to produce an analog baseband signal. This
`baseband signal is then processed by the DSP 205 to produce
`a digital data stream that the microprocessor 203 provides to
`the host device. Note that other techniques may be utilized
`to produce the analog baseband signal from the received FM
`55 modulated signal. Thus, multiple mixer stages may be used
`with intermediate frequency (IF) processing that can pro-
`duce one or more baseband signals. The IF stage and
`amplifiers and filters are omitted for clarity.
`In the preferred embodiment, the DSP performs FM
`60 deviation compensation. The pipelined nature of a DSP
`makes it ideally suited for FM deviation control functions
`and for decoding functions associated with wireless modem
`operations. The DSP 205 makes use of a FM deviation table
`211 which is created dynamically. The DSP 205 may access
`65 the FM deviation table 211 directly or indirectly via the
`microprocessor 203. The DSP 205 contains an FM deviation
`compensation (FMDC) function which applies a FM devia-
`
`IPR2022-00245 Page 00014
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`

`5,742,641
`
`7
`tion compensation factor (FMDCF) to each sample of the
`digitized analog baseband signal. The FMDC uses a default
`or starting or seed FMDCF and then adjusts the FMDCF in
`accordance with a control algorithm. The starting FMDCF is
`usually associated with the base station identifier of the base
`station that messages are expected to be received from.
`Thus, after each message with the base identifier extracted
`from the message, the adjusted FMDCF is stored in the FM
`Deviation Factor (FMDF) table with the extracted base
`station identifier. In the event that a message is received
`from other than the expected base station then the FMDCF
`is reset to a value obtained from the FMDF table associated
`with the expected base station.
`FIG. 4 depicts DSP functions for transmitting and receiv-
`ing FM signals. As shown in FIG. 4, the received analog
`baseband signal is converted to digital samples by A/D
`converter 415. Note that each sample represents a voltage
`level (e.g., positive and/or negative voltage levels) of the
`received baseband signal at a certain point in time. The
`digital samples, which may be any bit length but, are
`typically 8 or 16 bits may be represented in any binary form
`(i.e., short real, long real, floating point, integer, one's
`complement, two complement etc.). In the preferred
`embodiment a 2's complement form is used. The FM
`deviation control 440 applies FM deviation compensation to
`each sample in FM deviation compensation (FMDC) func-
`tion 441 using the FMDCF 443. The FM deviation control
`440 also provides for dynamic tracking of the FM deviation
`level and for adjusting the FMDCF 443 as it tracks or
`monitors the sample stream as shown in FM Deviation
`Adjustment Control (FMDAC) function 445.
`Each sample is provided to the FM deviation compensa-
`tion (FMDC) function 441. The FMDC applies the FM
`Deviation Compensation Factor (FMDCF) 443 to each
`sample. Each sample is scaled by the FMDCF to produce
`compensated samples. Note that any form of binary arith-
`metic may used to perform the scaling such as multiplication
`or division or normalization. The scaling operation can be
`thought of as amplifying or attenuating the baseband signal
`to the desired voltage range (i.e, VA of FIG. 7) in the digital
`domain. In the preferred embodiment, the FMDCF is
`applied by multiplying each sample by the FMDCF which is
`a real number. If the FMDCF is less than 1.0 the digitized
`samples are attenuated (i.e., scaled down) and if the FMDCF
`is greater than 1.0 the digitized samples are amplified (i.e.,
`scaled up).
`The compensated digital samples are then decoded using
`standard decode functions as shown in the decoder 419 of
`FIG. 4. The Symbol Clock 421 and Rx Acquire & Steady
`State 423 work together to synchronize the device's symbol
`clock with the base station's (transmitter's) symbol clock.
`The DC Estimator 425 tracks the received signal and pro-
`vides the average dc bias level over time. The detector 429
`outputs the digital data which is then processed to remove
`any transmission errors and the forward error correction
`encoding and framing information that was added for wire-
`less transmission. The data, if addressed to the host device
`is then provide to the host device by the microprocessor.
`Note the microprocessor or DSP extracts the base station
`identifier and determines whether the message is addressed
`to the wireless modem or associated host device. The data is
`then provided to the host device by the microprocessor.
`As shown in FIG. 4, while the FMDCF is applied to each
`sample the FM Deviation Adjustment control (FMDAC)
`function 445 continuously monitors the sample stream to
`determine the MAX and MINT of the sample values (i.e.,
`Vm„ and VMJN) over some period of time and adjusts the
`
`8
`FMDCF, accordingly. The FMDAC function 445 measures
`the MAX and MIN values over a plurality of samples and
`determines what type of adjustment, if any, is needed to the
`FMDCF. A control algorithm is used to determine the
`5 amount of adjustment such as Least Mean Square. Typically
`the adjustment is proportional to the difference between the
`currentm„ and currentmiN values and a desired or