0001
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`APL 1005
`IPR of U.S. Pat. No. 6,128,290
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`

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`-r
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`PATENT APPLICATION
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`08949999
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`CONTENTS
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`POSITION
`CLASSIFIER
`EXAMINER
`TYPIST
`VERIFIER
`CORPS CORR.
`SPEC. HAND
`FILE MAINT.
`DRAFTING
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`INDEX OF, CLAIMS
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`Claim
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`Date
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`9495------
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`971
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`SYMBOLS
`V ................ ..
`.Rejected
`.. Allowed
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`..... .............
`-(Through nuimbenal) Canceled
`.............. Retricte
`.+ .
`N.................... .. Non-elected
`.............. Inteference
`I . .....
`....... .. Appeal
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`Obecled
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`0004
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`t US GOVERNMENT PRINTING OFFICE 1999-456-878
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`STAPLE
`STPEA
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`AREA
`A
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`ORIGINAL CLASSIFICATION
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`CLASS32
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`USCASS
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`(ONE SUBCLASS PER BLOCK)
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`PATENT NUMBER
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`APPLICATION SERIAL NUMBER
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`l
`APPLFCANT'S NAME (PLEASE PRINT)
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`q
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`CA kvEY
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`IF REISSUE, ORIGINAL PATENT NUMBER
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`INTERNATIONAL CLASSIFICATION
`-7
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`2-
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`PTO ~~~~1
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`27
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`(REV. 5-91)
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`GROUP SSI
`ART UNIT
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`TEXAMINER (PLEA E STAMP OR PRINT FULL NAME)
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`i
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`2,133 PRIMARY EXAMINER (PLEASE STAMP OR PRINT FULL NAME)
`
`ISSU CLSIIAINSI
`(
`ISSUE CLASSIFICATION SLIP
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`U S DEPARTMENT OF COMMERCE
`PATENT AND TRADEMARK OFFICE
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`0005
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`

`
`United States Patent [191
`Carvey
`
`[54] PERSONAL DATA NETWORK
`
`[75]
`
`inventor: Philip F. Carvey, Bedford, Mass.
`
`[73] Assignee: BUN Corporation, Cambridge, Mass.
`
`[JNotice:
`
`This patent is subject to a terminal dis-
`claimer.
`
`[211 Appl. No.: 08/949,999
`
`[22] Filed:
`
`Oct. 14, 1997
`
`US006128290A
`[ill Patent Number:
`[45] Date of Patent:
`
`6,128,290
`*Oct. 3, 2000
`
`5,297,142
`5,307,297
`5,371,734
`5,481,265
`S,517,505
`5,598,419
`
`370/461
`Paggeot et a]l ..................
`.................. 364flO8.1
`Iguchi et al
`370/311
`Fischer..........................
`341/22
`Russell ........................
`370/350
`................
`Buchholz et atl
`................. 3?0/5 14
`Weigand et al
`
`Primary Exwnner--uy D. Va
`Assistant Examiner-4asper Kwoh
`Attorney, Agent, or Firm-4-conard Charles Suchyta; Floyd
`E. Anderson
`
`Related U.S. Application Data
`
`ABSTRACT
`
`[63] Continuation-in-part of applicationi No. 08/6tt,695, Mar. 6,
`1996, Pat. No. 5,699,357.
`H04B 7/212
`.....................................
`fInt. W
`[51]
`370W347; 370/350; 370/442;
`(52] US. CI ..................
`370/509; 455/89; 364/708. 1
`370/347, 350,
`[58] Field of Search...........................
`370/442, 509, 512; 455/89; 364/708.1
`
`References Cited
`U.S. PATENT DOCUMENT'S
`9/1993 Yokota0. ..................... 361/680
`
`5,247,285
`
`Thbe data network disclosed herein utilizes low duty cycle
`pulsed radio frequency energy to effect bidirectional wire-
`less data communication between a server microcomputer
`unit and a plurality of peripheral units located within short
`range of the server unit, e.g. within 20 meters. By estab-
`lishing a tightly synchronized common time base between
`the units and by the use of sparse codes, timed in relation to
`the common time base, low power consumption and avoid-
`ance of interference between nearby similar systems is
`obtained.
`
`11 Claims, 8 Drawing Sheets
`
`0006
`
`

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`U.S. Patent
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`Oct. 3, 2000
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`Sheet 1 of 8
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`6,128,290
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`U.S. Patent
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`Oct. 3, 2000
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`0008
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`U.S. PatentOc.3200
`Oct. 3, 2000
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`U.S. Patent
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`Oct. 3, 2000
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`U.S. Patent
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`Oct. 3, 2000
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`Sheet 5 of 8
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`U.S. Patent
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`Oct. 3, 2000
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`Sheet 6 of 8
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`U.S. Patent
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`Oct. 3, 2000
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`Sheet 7 of 8
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`U.S. Patent
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`Oct. 3, 2000
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`Sheet 8 of 8
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`691289290
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`0014
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`

`
`6,128,290
`
`1
`PERSONAL DATA NETWORK
`
`CROSS REFERENCE TO RELATED
`APPLICATION
`This application is a continuation-in-part of application
`Ser. No. 08/611,695 filed on Mar. 6, 1996 now U.S. Pat. No.
`5,699,357.
`
`BACKGROUND OF THE INVENTION
`'The present invention relates to a data network and more
`particularly to a data network which can effect bidirectional
`wireless data communications between a microcomputer
`unit and a plurality of peripheral units, all of which are
`adapted to be carried on the person of the user.
`The size and power consumption of digital electronic
`devices has been progressively reduced so that personal
`computers have evolved from lap tops through so-called
`notebooks, into hand held or belt carriable, devices com-
`monly referred to as personal digital assistants (PDAs). One
`area which has remained troublesome however, is the cou-
`to the main
`pling of peripheral devices or accessories
`processing unit. With rare exception, such coupling has
`typically been provided by means of connecting cables
`which place such restrictions on the handling of the units
`that many of the advantages of small size and light weight
`are lost.
`While it has been proposed to link a keyboard or a mouse
`to a main processing unit using infrared or radio frequency
`(RF) communications, such systems have been typically
`limited to a single peripheral unit with a dedicated channel
`of low capacity.
`Among the several objects of the present invention may
`be noted the provision of a novel data network which will
`provide wireless communication between a host or server
`microcomputer unit and a plurality of peripheral units; the
`provision of a data network which provides highly reliable
`bidirectional data communication between the peripheral
`units and the server; the provision of such a data network
`which requires extremely low power consumption, particu-
`larly for the peripheral units; the provision of such a network
`system which avoids interference from nearby similar sys-
`tem; and the provision of such a data network system which
`is highly reliable and which is of relatively simple and
`inexpensive construction. Other objects and features will be
`in part apparent and in part pointed out hereinafter.
`
`SUMMARY OF THE PRESENT INVENTION
`The data network of the present invention utilizes the fact
`that the server microcomputer unit and the several peripheral
`linked are all in close physical
`to be
`units which are
`proximity, e.g., within twenty meters, to establish, with very
`high accuracy, a common time base or synchronization. The
`short distances involved means that accuracy of synchroni-
`zation is not appreciably affected by transit time delays.
`Using the common time base, code sequences are generated
`which control the operation of the several transmitters in a
`low duty cycle pulsed mode of operation. The low duty cycle
`pulsed operation both substantially reduces power consump-
`tion and facilitates the rejection of interfering signals.
`In addition to conventional peripheral devices such as a
`keyboard or mouse, it should be understood that data com-
`munications in accordance with the present invention will
`also be useful for a wide variety of less conventional
`peripheral systems which can augment the usefulness of a
`microcomputer such as a PDA. For example, displays are
`
`being developed which project a private image directly into
`an user's eye using a device which is mounted on a head-
`band or eyeglasses. 'These displays are useful, for example,
`for providing combat information to military personnel and
`sfor realistic games. Likewise, so called virtual keyboards are
`being developed which use inertial or magnetic sensors
`attached to a users fingers in the manner of rings. Further,
`apart from wore usual business type computer applications,
`the data network system of the present invention may also be
`to useful for applications such as physiological monitoring
`where the peripheral units may be physiological sensors
`such as temperature, heartbeat and respiration rate sensors.
`As will be understood, such peripheral units may be useful
`for outpatient monitoring, monitoring for sudden infant
`is death syndrome, and for fitness training. it is convenient in
`the context of this present description to refer to such
`conventional and inconventional peripheral units collec-
`tively as personal electronic accessories (PEAs).
`Briefly stated, a data network system according to the
`20 present invention effects coordinating operation of a plural-
`ity of electronic devices carried on the person of the user.
`These devices include a server microcomputer and a plu-
`rality of peripheral units which are battery powered and
`portable and which provide input information from the user
`25 or output information to the user. The server microcomputer
`incorporates an RF transmitter for sending commands and
`the peripheral units, The
`information
`synchronizing
`to
`peripheral units, in turn, each include an RF receiver for
`detecting those commands and synchronizing information
`30 and include also respective RF transmitters for sending
`information from the peripheral unit to the server micro-
`computer. The server microcomputer includes a receiver for
`receiving that information transmitted from the peripheral
`units.
`The server and peripheral unit transmitters are energized
`in low duty cycle pulses at intervals which are determined by
`a code sequence which is timed in relation to the synchro-
`the server
`initially transmitted from
`nizing information
`microcomputer.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is an overall block diagram of a wireless data
`network system linking a personal digital assistant or server
`microcomputer with a plurality of peripheral units;
`FIG. 2 is a block diagram of a modem circuitry employed
`in one of the peripheral units of FIG. 1;
`FIG. 3 is a block diagram of a modem circuitry employed
`in the server microcomputer of FIG. 1;
`so FIG. 4 is a block diagram of the transmitter circuitry
`employed in the modem of FIG. 2;
`FIG. 5 is a circuit diagram of receiver circuitry employed
`in the modem of FIG. 2; and
`FIG. 6 is a diagram illustrating timing of RF signals which
`55 are transmitted between the server microcomputer and the
`various peripheral units;
`FIG. 7 is a block diagram of the controller employed in
`the PEA modem; and
`FIG. 8 is a block diagram of the digital matched filter
`60 employed in the PEA controller; and
`Corresponding reference characters indicate correspond-
`ing parts throughout the several view of the drawings.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`Referring now to FIG. 1, a server microcomputer of the
`type characterized as a personal digital assistant (PDA) is
`
`35
`
`40
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`45
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`65
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`6,128,290
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`3
`designated generally be reference character 11. The PDA
`may also be considered to be a HOST processor and the
`HUB of the local network. The PDA is powered by a battery
`12 and may be adapted to be cardied on the person of the
`user, e.g. in his hand or on a belt hook. Such PDAs. typically5
`accept options which are physically configured as an indus-
`try standard PCMCIA card. In accordance with tho present
`invention such a card, designated by reference character 13
`is implemented which includes a PCMCIA interface and
`PDA modem.
`As is described in greater detail hereinafter, the network
`system of the present invention establishes wireless com-
`munication between FDA 11 and a plurality of peripheral
`units or PEAs designated generally by reference characters
`21-29. A PDA and a collection of PEAs associated with it 1
`are referred to herein as an "ensemble". The present inven-
`lion allows the creation of a data network lining such an
`ensemble of elements with minimal likelihood of interfer-
`ence from similar ensembles located nearby. Each of the
`peripheral units, is powered by a respective battery 30) and 20
`incorporates a PEA modem 31. Further, each peripheral unit
`can incorporate a sensor 33, which responds to input from
`the user or an actuator 37 which provides output to the user.
`Some peripheral units might also employ both sensors and
`actuators. As illustrated, each PEA modem preferably incar- 25
`porates two antenna's, a dipole antenna 38 for reception and
`a loop antenna 39 for transmitting. The use of separate
`antennas for transmitting and receiving facilitates the utili-
`turn
`zation of impedance matching networks which in
`facilitates the operation at very low power.
`Referring now to FIG. 2, the PDA modem illustrated there
`comprises five major components, a transmitter 40, a
`receiver 41, a local oscillator 42 which is shared by the
`transmitter and the receiver, a controller 43 which times and
`coordinates the operations of the transmitter, receiver, 35
`microprocessor and, finally, a voltage controlled crystal
`oscillator oscillator 44 which is utilized in maintaining a
`common time base with the host microcomputer.1The oscil-
`lator 44 utilizes a crystal which operates at 4 Mhz.
`As is described in greater detail hereinafter, the controller 40
`43 sequences the operations necessary in establishing syn-
`chronization with the host system, adjusting the oscillator
`44, acquiring from the host appropriate code sequences to be
`used in data communications, in coupling received infor-
`to a sensr/actuator interface, 45
`mation from receiver 41
`designated by reference character 46, and in transmitting
`data from the interface 46 back to the host through trans-
`mitter 40. The controller in one embodiment is partitioned
`into a commercially available general purpose microproces-
`sor such as the P1C16C64, together with a special purpose so
`logic integrated circuit (IC). The special purpose IC imple-
`ments those functions which cannot be efficiently executed
`on the general purpose microprocessor. For example, the
`clock to the PIC16C64 is sourced by the special purpose IC
`the microprocessor's so-called "sleep" 55
`in
`because even
`mode, its power consumption is higher than acceptible.
`As is explained in greater detail hereinafter, the general
`scheme of data transmission and reception is a form of time
`division multiple access (TDMA). This TDMA access is
`characterized by a frame interval, common to the host and 60
`all PEAs of 32.768 milliseconds, segmented into 16,384
`time slots. Each time slot is further pantitioned into four data
`bit intervals during which the RF carrier is modulated either
`above the the nominal for a binary "one" or below the carrier
`for a binary "zero". The basic modulation scheme is fre- 65
`quency shift keying (FSK), well known to those skilled in
`in
`is explained
`digital radio transmission. However, as
`
`30
`
`greater detail hereinafter, the FSK tones are transmitted in
`only those slots indicated by a TDMA program. Both the
`host and all PEAs share a common TDMA program at one
`time. For each slot, this TO)MA program indicates that a PEA
`or host is to transmit, or not, and whether it will receive, or
`not. in the intervals between slots in which a PEA is to
`transmit or receive, all receive and transmit circuits are
`powered down.
`Referring nowto FIG. 3, the PElAmodem illustrated there
`comprises five major components, a transmitter 15, a
`receiver 17, a local oscillator 16 which is shared by the
`transmitter and the receiver, a controller 14 which times and
`coordinates the operations of the transmitter, receiver, and
`PCMCIA interface and, finally, a crystal oscillator 18 which
`is utilized in maintaining the network time base. The oscil-
`lator 18 utilizes a crystal which operates at 4 Mhz. There are
`no differences between the receiver, local oscillator, and
`transmitter in both the PEA and PDA modems. PDA con-
`troller 14 differs from the PEA modem in three ways. First
`it contains no synhronization capability as it serves as the
`network master. Secondly, it includes a PCMCIA interface
`rather than a sensor/transducer interface. Only the PEA
`modem is described in detail herein since it is includes all
`the novel capabilities of the PDA modem.
`Referring now to FIG. 4, transmission is effected using the
`local oscillator 45 to drive the transmit antenna amplifier 50
`whose output drivcs transmit antenna 51. The local oscillator
`45 is coupled to a tuning network 48 including a plurality of
`frequence adjusting varactors VR1-VR3. Operation of the
`varactors is controlled by switch pairs 52 and 53. 500
`local
`the start of transmission, the
`nanoseconds before
`oscillator 45 is powered up. During this period and during all
`receive intervals, frequency selection varactor switches 52
`and 53 are opened and closed respectively. This frequency
`selection state is employed for all periods except those in
`which the local oscillator is used to drive the antenna
`amplifier. To transmit a "one", both switches 52 and 53 are
`opened. This causes the oscillator to oscillate above its
`nominal value. To transmit a "zero", both switches 52 and 53
`are closed. Thbis causes the oscillator to oscillate below its
`nominal value. The local oscillator output then drives ampli-
`fier 50. In the preferred embodiment, the transmit antenna 51
`is loop of wire two centimeters in diameter. During short
`periods in which data is not being received nor is being
`transmitted, the oscillator is powered and the varactor con-
`trol voltage Vc is adjusted such that the oscillator frequency
`equals the carrier frequency.
`the
`Referring now to FIG. 5, the input signal from
`receiving antenna 38 is applied, through an impedance
`to a low noise amplifier 62 and
`matching network 61
`bandpass filter 63. The received and amplified signal is
`combined with the local oscillator shifted 45 degrees in
`phase in mixer 65 to produce signal Im and combined with
`the local oscillator shifted -45 degrees in phase in mixer 66
`to produce signal Qm. Im and Qm are the so-called "in-
`phase" and "quadrature-phase" signals commonly known to
`radio engineers. Both Im and Qm are centered at zero hertz
`rather than at an intermediate frequiency. Thbis scheme is
`commonly referred to as "direct conversion" because a
`direct conversion to baseband is effected rather than con-
`version to an intermediate frequency which is then con-
`to baseband. Direct conversion reduces power
`vented
`consumrption, as no intermediate frequency circuits are
`employed and it allows use of low pass filters to effect
`selectivity. Lowpass filters 67 and 68, preferably of the
`linear phase type, remove the unwanted mixing products and
`provide selectivity of signals Im and Qm respectively.
`
`0016
`
`

`
`6,128,290
`
`30
`
`5
`The filtered output signals If and Qf passed through
`blocking amplifiers 69 and 70 to form signals I and Q.,The
`supply currents of amplifiers 69 and 70 ame adjusted so that
`the parasitic output capacitance of these amplifiers effec-
`tively form a banidpass filter with gain. These amplifiers
`block frequencies below 100 ]CH& and above two MRz. This
`to the overall selectivity and blocks any
`filtering adds
`unwanted DC mixer byproduct common to direct conversion
`schemes.
`Some conventional frequency discriminators create the
`signal V-I*dQ/dt-Q*l/dt. When
`the frequency of the
`received signal is above the local oscillator frequency, V is
`greater than zero. Correspondingly, when the frequency of
`the received signal is below the local oscillator frequency, V
`is less than zero. This scheme has the advantages of being
`to both amplitude and phase errors
`totally insensitive
`between I and 0 mixer stages. Its disadvantage is that it
`requires the creation of the time derivatives of I and Q. As
`is well known, precise derivative forming circuits and and
`difficult to implement and power cronsumrptive.
`To circumvent the disadvantages of derivative forming
`networks and still keep the advantages of the frequency
`discrimination scheme, the receiver employs all pass phase
`shifters 71,72,73 and 74 to create the signals Ia, Qia, Qb and
`Qc respectively. Multipliers 75 and 76 together with adder
`77 then form the signal U-la*Qb-lb*Qa. The advantage is
`that U has the same desirable properties of a discriminator
`based on I*dQ/dt-Q*dl/dt without requiring differentiation.
`It is only required that Ia and lb be separated by 90 degrees
`and that Qa and Qb be separated by 90 degrees, As is well
`known, all pass networks consisting of a resistor and capaci -
`tor can be used
`to effect this phase separation. These
`networks produce an accurate 90 degree phase separation
`over a frequency range well in excess of the blocking
`amplifier bandpass and consume extremely low power con-
`sumption.
`Limiter 78 then amplifies U to form signal Lim. Limiter
`circuits which can generate these signals are well known and
`have been integrated into integrated receiver chips for many
`years. Limiter output Lim is utilized by the controller 43 in
`both establishing the common time base and in recovering
`the data transmitted as described in greater detail hereinafter.
`
`FRAME STRUCITURE
`As indicated previously, the basic scheme for allowing
`multiple Personal Electronic Assessocies (PEAs) to com-
`municate with the common sewver microcomputer (PDA)
`may be characterized as a form of time division multiple
`access (TDMA). A single virtual channel can be established
`between the PDA and any one PEA by assigning one or more
`slots within the 32.768 millisecond frame. In the preferred
`embodiment, four data bits are transmitted during each slot
`interval with the designation of a binary one or zero encoded
`by means of frequency modulation of the RF carrier as
`described previously. In slots where a PEA neither transmits
`nor receives, essentially all of the modem circuits are
`powered off, thus effecting a substantial power reduction. As
`is described in greater detail hereinafter, some slots are used
`to establish synchronization between PEA and PDA andi
`others are used to implement a control channel. These slots
`are not assigned to a particular PEA but are rather shared
`amongst all PEAs.
`In normal operation, each virtual channel is half duplex,
`transfering data either from PEA to PDA or from PDA to
`PEA. Assignment of a single slot per frame results in a
`virtual channel bandwidth of 122 bits per second. Virtual
`
`6
`channels requiring larger bandwidths are assigned a multi-
`plicity of slots. For example, when ten slots arc assigned, the
`virtual channel bandwidth is increased to 1220 bits per
`second. More than one virtual channel can be established
`5between the PDA and a single PEA. If one channel is
`outgoing from PDA to PEA while the other channel is
`incoming from the PEA to the PDA, an effectively full
`duplex communication link is constructed. It is possible for
`each virtual channel to differentiate bandwidths. Mnother
`10 possible operational mode is for the data transfer direction of
`a single virtual channel to be changed dynamically. Acontrol
`channel can be employed whose sole purpose is to indicate
`the data flow direction on the data channel. Changeover
`from one direction to another is typically affected at the
`15 frame boundary.
`A single virtual channel may be shared amongst several
`PEAs under control of the PDA- In this operational mode, a
`the
`to
`is employed to indicate
`control virtual channel
`ensemble of PEAs sharing the channel which is to transmit
`20 at any given time. Still another operational mode occurs
`when a single virtual channel is used to broadcast informa-
`tion from PDA to multiple PEAs. While it is possible to
`establish virtual channels between two PEAs, the increased
`worst case separation possible from one PEA to another PEA
`25 may preclude establishment of a reliable radio link. 'lthere-
`fore PEA to PEA links are not present in the preferred
`embodiment. While all these operational modes appear
`different, they are essentially well known variants to the
`underlying time division multiple access technique.
`TDMA allows an ensemble of PEAs and PDA to establish
`a wide assortment of non-conflicting, error free, virtual
`channels between PEAs and PDA. When two different
`ensembles of PEAs and PDA happen by chance to employ
`the sme carrier frequency, it is possible for the RF bursts of
`35 one ensemble to overlap those of the other ensemble. This
`overlap can cause errors. If during a particular bit period,
`two RF bursts are being simultaneously received, one from
`a transmitter in the home ensemble and the other from a
`foreign ensemble, the receiver will "capture' only the data
`40 received from the stronger of two transmitters. This well
`known aspect of FM modulation, results in an error free
`channel when the stronger transmitter is part of the home
`ensemble and can result in errors when the stronger trans-
`mitter is part of a foreign ensemble. While it is very likely
`that the stonger transmitter is part of the home ensemble,
`in normal operation where the
`there are circumstances
`stonger transmitter will part of a foreign ensemble. Note that
`even when a foreign transmitter is of much greater power
`than thehome transmitter, if the foreign RF bursts and home
`so RF burst do not overlap, no error occurs.
`As is well known, many channel errors can be corrected
`by employing Error Correction Codes (ECC).
`In this
`technique, data to be sent over a channel is segmented into
`words of length M. A checksumn of length C is computed as
`the word is being transmitted and also sent across the
`channel. For the M bits of data, a total of N-M+C bits of
`channel bandwidth are utilized. For a fixed word length, as
`the number of error bits which can be corrected increases,
`the channel efficiency decreases. As a general rule, as the
`60 channel's error rate increase, the channel bandwdith effi-
`ciency (needed to achieve a certain corrected error rate)
`decreases and the minimum wordsize increases. In one of
`the simplest error correction schemes, called majority
`coding, where data bit is transmitted three time (M=I, C-2),
`65 channel bandwidth is reduced tn 33%.
`In channels where errors occur in bursts, single err
`correction codes, even though they have high channel
`
`45
`
`55
`
`0017
`
`

`
`6,128,290
`
`10
`
`7
`efficiency, will yield poor after correction error rates. In
`interleaving, a well known scheme to handle burst errors,
`data is segmented into words which are then interleaved
`onto the channel. If the maximum error burst consists of four
`consecutive errors, then interleaving four words results in
`each burst occuring in a separate codeword. Since each
`codeword now has only one error after interleaving, it can be
`corrected.
`Yet another means for correcting errors is to packetime the
`data and retransmit on detection of a checksumn error. For
`virtual channels not requiring low latency, the highest chan-
`nel efficiencies are possible. Hybrid schemes where error
`correction codes are employed together with retransmission
`of packets on checksumn errors are also possible.
`Error rates caused by the
`interference of RF bursts
`between two different ensembles can be significantly
`reduced by judicious assignment of slots in each ensemble.
`that has desirable properties
`One assignment scheme
`employs majority encoding and the use of so-called Opti-
`cally Orthogonal Codes (OOCs). In this scheme, the 16384
`slots are equally segmented into 256 intervals called sectors.
`A maximum of three RFt bursts can occur in each section.
`The position of each burst is dictated by a one in an OOC
`codeword. Codewords have unity auto-correlation and
`cross-correlation with respect to rotation by an arbitrary
`number of slot positions within a sector. The codes are
`mostly zeros with three scattered ones representing
`the
`locations of the slots in which RF bursts are to be transmitted
`or received. There are ten OOC codewords with a sector
`length of 64 slots. In general, a sector can be assigned any
`one of the ten codewords with a rotation of from zero to 63
`slot positions.
`To assign slots in an ensemble, one of 640 different
`combinations of codeword and rotations is selected for the
`first sector A codeword/rotation combination is selected for
`the second section such that 1) the last RE burst postion of
`the last sector codeword and the two FP burst postions of the
`new codeword do not form a codeword and 2) the last two
`RF burst positions of the last sector codeword and the first
`FP burst position of the new codeword do not form a
`codewords, and 3) the codewordVrotation has not been
`selected before. Each sector consists of three identical FP
`bursts (i.e a majority error correcting code is chosen).
`At any instant of time, the frame structures of two
`ensembles will in general not be aligned. However, with
`their uncorrelated separate time bases, the frame structures
`will slip past one another and will become aligned. Every
`possible correlation between the two frames will thus even-
`tually occur. Assuming each ensemble is using 100% of its
`then it is highly likely that at some time a
`bandwidth,
`in each ensemble will be aligned. When code-
`codeword
`words from separate ensembles are aligned, a receiver
`captures data from the stronger transmitter. In this case, the
`error correction coding serves no value since it perfectly
`corrects
`the data of the foreign transmitter. When this
`condition occurs, the probability that another sector is also
`aligned is about 0.002. Thus one sees a worst case uncor-
`rectible error rate of about 0.001. As is well known, this
`uncorrectible error rate is sufficiently low that, by employing
`packetizing and retransmitting on checksumn errors, an effec-
`tively error free channel can be obtained.
`As will be understood by those skilled in the art, the
`TURA system is greatly facilitated by the establishment of
`a common frame time base between PEA and PDA. In
`establishing this common time base, the present invention
`employs timing or synchronization beacons (SBs) transmit-
`
`ted by the PDA. Each SB consists of eight FP bursts spread
`out over 252 slots. One of the SBs arbitrarily starts a frame.
`The positions of the remaining seven SBs are selected
`pseudo-randomly with two restrictions. First the maximum
`5 interval between two successive SBs is less than 6.144
`milliseconds. Secondly, the positions must allow a unique
`frame determination based on the intervals between SBs.
`Thus for example, equidistantly spaced SBs are not allowed.
`In accordance with one aspect of the present invention,
`the slot location of each RF burst within all SBs is identical
`for all ensembles. In a particular ensemble, the 32-bit data
`identical. Between two
`bit pattern of each SB will be
`different ensembles, however, the SB data bit pattern, cho-
`sen randomly, will be quasi-distinct. The combination of SB
`15 data bit pattern and SB locations allow every ensemble to be
`uniquely identified.
`In the preferred embodiment illustrated in FIG. 6, each of
`the eight SBs 100-107 is immediately followed by a sector
`assigned to the common Communication and Control Chan-
`20 nel (CCC). The sector immediately following the first seven
`CCC sectors is assigned to the Attention Channels (ACs).
`The CCC sectors are designated by reference characters
`110-117 in FIG. 6 while the Attention Channels are desig-
`nated by reference characters 120-127. As will be explained
`25 in greater detail later, the CCC and AC are used in main-
`taining the virtual channels between PDA and all PEAs.
`Referring now to FIG. 7, all PEA activities are activated
`and monitored by the PEA controller 43. While the control-
`3ler could bimlented in a single custom integrated
`circuit, the present embodiment partitions the controller into
`a commercially available microprocessor 90, a PIC16C64, a
`special purpose logic integrated circuit IC 91, voltage con-
`trolled crystal oscillator 44, and a charge pump voltage
`35 generator 93. Voltage controlled crystal oscillator (VCXO)
`44 is controlled by voltage Vc, sourced by charge pump 93.
`The controller IC 91 can cause the frequency of oscillation
`to change by activating charge pump. Varying the control
`voltage Vc from 0 to -6 volts changes the oscillator fre-
`40 quency by 50 parts per million. VCXO 44 is powered
`continuously and serves as the time base for all activities.
`The microprocessor chip includes 256 bytes of ROM which
`contains the program instmuctions needed for all activities
`and 256-bytes of SRAM