0001
`
`APL 1006
`IPR of U.S. Pat. No. 6,128,290
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`

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`APPROVED:?
`FOR LIENE [7
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`INITIALS
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`PATENT NUMBER
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`,PPLucATION SERIAL NUMBER
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`CAV,VEGY
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`,PPLICANT'S NAME (PLEASE PRINT)
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`REISSUE. ORIGINAL PA'rENT NUMBER
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`INTERNATIONAL CLASSIIFICATIONC
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`Staple Issue Slip Here
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`POSITION
`CLASSIFIER-
`EXAMINER
`TYPIST
`VERIFIER
`CORPS CORR.
`SPEC.HAND
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`INDEX OF CLAIMS
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`Date
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`SYMBOLS
`.... ......Rected
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`- (hrtg nmb Wal.Cncle
`Reistricted
`..............
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`....... ........ Nan-elected
`N
`.................
`Inteiference
`Appul
`A.....................
`0...................... Objected
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`(LEFT INSIDE)
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`27
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`29
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`4
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`35
`36
`27
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`40
`41
`421
`433
`41
`45
`46
`47
`48
`49
`40
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`0005
`
`

`
`United States Patent (191
`Carvey
`
`INEhmhhhhEINI
`
`US005699357A
`[iij Patent Number:
`[45] Date of Patent:
`
`5f699%357
`Dec. 16, 1997
`
`[54] PERSONAL DATA NETWORK
`
`(75)
`
`Inventor Philip R. Camvy, Bedford, Mass.
`r73] Assignee: BEN Corpora"in Cambridge. Mass.
`
`5,297,142
`5M, 297
`5,371,734
`5,481.265
`
`3/1994 Fsgwt et al .
`....... 37QWI6
`.-......
`4/1994 I9achi et . ................. 364n7S. 1
`1211994 Fischer.
`1/1996 Russell .
`
`[21] Appl. No.: 611,695
`MM 6, 1996
`r22] Filed:
`
`[52] U.S. CL ..............
`
`3796347; 3701350; 370/442;
`370/509; 455/89; 364108.
`[58] Hld dSearch----.-..~.
`37(V310.311,
`3701312, 313, 365, 367, 348. 349, 350,
`431. 433. 442. 443,.445. 449, 458. 462,
`465. 468, 503, 509, 510, 512, 511, 514,
`522; 455/89. 100, 54.1. 66, 38.3 ; 375=22;
`3641705.01. 705.05, 708.1; 39-W200.01,
`200.02. 200.17, 200.19, 280, 1128, 835,
`882, 551; 341/22; 345/156. 157, 169
`References Cited
`U.S. PATENT DOCUMENTS
`SV1993 Yao"s@ at
`
`527,9
`
`.......
`.
`
`.- -. 364/01.1
`
`Ptimary ExaunsneWulington Chin
`Assfitant xaniner-Huy D. Vii
`Autorne; Agen4 or Finn-Hory D. Pahl, kr
`
`ABSTRACT
`
`The data network disclosed heen utilizes low duty cycle
`pulsed radio frequency energy to effect bidirectional wire-
`less data commiunication between a server microcomputer
`unit and a plurality of peripheral units, each of which is
`intended to be caried on the person of the microcomputer
`user. By establishing 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 consuamp-
`tion and avoidance of interference between nearby similar
`systems is obtained.
`
`18 Claims, 6 Drawing Sheets
`
`12
`
`Personal
`Digital
`Assistant
`( PDA)
`
`13
`
`I
`
`il
`
`RF Links
`
`Sensor
`33
`
`PEA
`Modem
`31
`
`30
`
`29
`
`Actuat
`
`39Jr
`
`PEA
`Modem
`31
`
`30
`
`0006
`
`

`
`U.S. Patent
`
`Dec. 16, 1997
`Dc 6 97
`
`Sheet I of 6
`Set1o
`
`,9,5
`59699r357
`
`.00
`
`-o
`
`JL p
`
`OD 0
`
`tOD
`
`c
`
`If)
`
`0007
`
`

`
`U.S. Patent
`
`Dec. 16, 1997
`Dc 6 97
`
`Sheet 2 of 6
`Set2o
`
`5fi99,357
`
`Sensor /
`Actuator
`Interface
`
`PC MC IA
`Interface
`
`FIG.?
`
`FIG. 3
`
`0008
`
`

`
`U.S. Patent
`
`Dec. 16, 1997
`Dc 6 97
`
`Sheet 3 of 6
`Set3o
`
`59699 357
`,9,5
`
`FIG. 4
`
`51
`
`5O--4
`
`To TX /RX
`
`ITo
`TX /RX
`}From TX /RX
`
`FIG.?7
`
`0009
`
`

`
`U.S. Patent
`
`Dec. 16, 1997
`
`Sheet 4 of 6
`
`59699,357
`
`0010
`
`

`
`U.S. Patent
`
`Dec. 16, 1997
`
`Sheet 5 of 6
`
`5,699,357
`
`r
`
`I
`
`0.
`
`0
`E
`
`01
`
`Uj
`tcnqW
`
`c
`0
`cU
`
`0011
`
`

`
`U.S. PatentDe16197
`Dec. 16, 1997
`
`Sheet 6 of 6
`Set6o65,937
`
`596"9,357
`
`E~
`
`0012
`
`

`
`5,699,357
`
`I
`PERSONAL DATA NETWORK
`
`2
`
`BACKGROUND OF THE INVENTION
`The present invention relates to a data network and more
`particularly to a data network which can effect bidirectional 5
`wireless data communications between a microcomputer
`unit and a plurality of peripheral units, all of which ame
`adapted to be carried on the person of die user
`Thke size and power onsumption of digital electronic
`devices has been progressively reduced so that persoal "'
`computers have evolved from lap tops through so-called
`notebooks. into hand held or belt carriable devices comn-
`monly referred to as personal digital assistants (PDAs). One
`area which has remained trouble some however, is the cou-
`to die main 15
`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 die 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
`(RP) communications, such systems have been typically
`limited to a single peripheral unit with a dedicated channel 2
`of low capacity.
`Among the several objects of die 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, all of 30
`which ame Adapted to be carried on the person of an user, die
`provision of a daa network which provides highly reliable
`bidirectional data communication between die peripheral
`units and the server, the provision of such a data network
`Which requires extremely low Power Consumption, pdiklU- 35
`Msry forthe 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 feasture will be 40
`in part apparent and in part pointed out hereinafter.
`SUMMARY OF THE PRESENT INWENTION
`The data network of the present invention utilizes die fadt
`diat the server microcomputer unitead the several per"pherl 45
`units which are to be linked are all in close physical
`proximity, e.g., under two meters separation, to establish.
`with very high accuracy, a common lime: base or syndiro-
`nization. The short distances Involved means that accuracy
`of synchronization is not appreciably affected by transit tm 5o
`delays. Using the common time base, code sequences; are
`generated which control die operation of the several trans-
`mitters in a low duty cycle pulsed mode of operation. The
`low duty cycle pulsed operation both substantially reduces
`power consumption and facilitates the rejection of intarfer- ss
`ig signals.
`In addition to conventional peripheral devices such as a
`keyboard or mouse, it should be understood! that data coo-
`munications in accordance with the present invention will
`als be useful for a wide variety of less conventional 6o
`peripheral systems which can augment the usefulness of a
`moicrocomputer such as a PDA. For example, displays are
`being developed which project a private image directly into
`an User's eye usingt a devic which is Mounted On a head-
`band at eyeglasses. These displays are usefuL for example, 65
`for providing combat Information to military personnel and
`for realistic gamnes. Likewise, so called virtual keyboards =r
`
`being developed which use inertial or magnetic sensors
`attached to a users fingers in die maer of rings. Frther,
`apart hum more usual business type computer applications.
`the data network system of the present invention may also be
`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, monitering for sudden infant
`death syndrome, and for fitness training, It is convenient in
`the context of this present description to refer to such
`conventional and inconventional pe4reral units collec-
`tively as personal electronic acces series (PEAs).
`Briefly stated, a data networls system according to the
`present Invention effects coordinating operation ofta plural-
`ity of electronic devices carried on the person of die user.
`These devices include a saver microcomputer which is
`battery powered and portable so as to be carried on the
`person of a user and a plurality of peripheral units which are
`also battery poowered and portable and which provide input
`information from the user or output information to the user.
`The sarver microcomputer incorporates an lRP transmitter
`for sending commands and synchronizing Information to the
`Peripheral units. The peripheral units, in turn, each include
`an RP receiver for detecting those commands and syndhro-
`niZzing Information and Include also respective RF transmnit-
`term for sending informatio
`from the peripheral unit to dhe
`server microcomputer. The server microcomputer includes a
`receiver for receiving that inforation transmitted from the
`peripheral units.
`Thie sarver 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 die syndhro-
`nizing information
`initially transmitted fromn the sarver
`microcomputer. Preferably. the input and output information
`is carried by frequency modulation of the respective trans-
`mitter.
`
`BRIEF DESCIPTION OP THE DRAWINGS
`PIG. 1 Is in overall block diagram of a wireless data
`network system linking a personal digital assistant or server
`micrcomputer 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;,
`P1G. 3 is a black diagram of a modem circuitry employed
`In die sarver microconmputer of FIG. 1;
`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. 6s adiagram. llustrating timing of RP signals which
`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
`employed in the PEA controller; and
`Corresponding reference characters indicate correspondi-
`ing parts throughout the several view of the drawings.
`DESCRWVrION OF THE PREFERRED
`EMBODIMNTU
`Referring now to FIG. 1. a server microcomputer of die
`type characterized as a personal digital assistant (PDA) is
`
`0013
`
`

`
`5,699,357
`
`3
`designated geneally be reference character U. The PDA
`may also be considered to be a HOST processor and the
`HUB of the local networkt The PDA Is powered by a battery
`12 and is adapted to be carried on the person of the user, e.g.
`in his hand or on a belt book. Such PDAs typically accept
`options which are physically configured as -n industry
`standard PCMCIA card. In accodance with the presnt
`invention such a card, designated by referenice character 13
`is implemented which includes a PCMCIA lantefooe ad
`PDA modem
`As is described in greater detail hereinafte, the network
`system of the present invention establishes wireless corn-
`andcation between PDA 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
`w~e referred to herein as an "ensemble. The present invcn-
`tion allows the creation of a data netwask linking such an
`ensemble Of elements with minimal likelihood of interfer-
`ence from similar ensembles looted nearby. Each of the
`peripheral units Is powered by a respective battery 30 and
`31. Frther, each peripheral unit
`incorporates a PEA muo
`can incorporate a sensor 33, which responds to input from
`the user &r a actuator 37 which provides output to the useL
`Some peripheral units mighit also employ both sensors and
`actuators. As Illustrated, each PEAmoademn preferably incor-
`poirates two antenna's, a dipole antenna 38 for reception and
`a loop antenna 39 for transmitting. The use of separate
`antennans for transmitting and receiving facilitaites the utili-
`zation of Impedlance matching networks 'which in turn
`facilitsas 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,
`finally, a voltage cintrolled crystal
`microprocessor and
`oscillator oscillator 44 which Is utilized in muantain a
`ime base with the host microcompute. The oscil-
`commtron
`lato 44 utilizes a crystal which operates at 41.MhL
`As is described in greater detail hereinafter, the controller
`43 sequences the operations necessary in establishing syn-
`chroctlzation 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-
`mation from receiver 41 to a scnriiactuawo
`interface,
`designated by reference character 46, and in transmitting
`data from the interface 46 back to the host bhough trans-
`inaer 40. The controller in one embodiment is partitioned
`into a commercially available general purpose icroproces-
`sor such as the PIC16C64, together with a special purpose
`logic integrated circuit (IC). The specia purpose IC imple-
`ments those functions which cannot be efficiently executed
`on the general purpose microprocessor. For eample, the
`clock to the PIC 16C64 is sourced by the special purpose IC
`because even In the microprocessor's so-called "sleep"
`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 fosir of time
`division multiple access (TDMA). 'Ibis TDMA access is
`chiaracrized by a framne interval, common to the host and
`all PEAs of 32,768 milliseconds, segmented into 16.384
`tinme slots. Each time; slot is further partitioned into four data
`bit intervals during which the RE carrier is modulated either
`above the t nominal for a binary "aC or below the cszricz
`for a binary "zero". The basic modulation scheme is fre-
`quency shift keying (PSK). well known to those skilled in
`digital radio transmission. However, as is explained in
`
`25
`
`4
`greater detail hereinafter, the PSK tones are transmitted in
`only those slots indicated by a TDM4A program. Both the
`host and all PEAs share a common TDMA progum at one
`time. For ech slot, thisTDMA program indicates that a PEA
`5or host Is to transmnit, 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
`poee- on
`Referring now to. FIG. 3. the PEA modem Illustrated
`10 there comprises five major components, a transmitter 15, a
`receiver 17, a local oscillator 16 which Is shaired by the
`transmitter and the receiver, a controller 14 'whih times and
`coordiates the operations of the tramsmitter, receiver and
`PCMCIA interface mad, finally, a crystal oscillao oscillator
`15 18 whih Is utilized in maintaining the network tim base.
`The oscillates 13 utilze a crystal which operates at 4 MhL.
`There are no differences between
`the receiver, local
`oscillator, and transititer in both the PEA and PDA
`modems. PDA controller 14 differs from the PEA modemn in
`20 tre Ways. Firs It Contains no #Ynlieonization capability AS
`it serves as the network master. Secondly. it includes a
`PCMCIA interface rather than a sensorrawsducer interface.
`Only the PEA modem is described in detail herein since it is
`Includes all the novel capabilities of the FDA modem
`Weaering now to IG. 4, transmission is afceddusing the
`local oscillator 45 to drive the transmit antenna amplifier 50
`whose output drives transmit antenna 51. Thle local oscilato
`45 is coupled to a tuning network 48 including a plurality of
`frequetice adjusting varctors VRl-VR3. Operation of the
`3o varmtors Is controlled by switch pairs 52 and 53. 500
`nanoseconds before the start of transmission, the local
`oscillator 45 Is powered up. During this period and during all
`receive Intervas. frequency selection varctcar gwitchs 52
`and 53 sim opened and closed respectively. This frequency
`as selection sate is employed for all periods except those in
`which the local oscillator is used to drive
`the antenna
`amplifier. To transmit a "one, both switcli 52 and 53Sae
`opened. This causes the oscillatocr to oscillate above its
`naminglvalue.lb transmit a"zero", both switches 52 and53
`40 are closed. This causes the oscillator to oscillate below its
`nominal value. The local oscillator output them drives amupli-
`fierSO0. In the preferred embodiment, the transmit antenna 51
`is loop of wire two centimeters in diameter. During short
`periods in whih data is no being received nor is being
`45 transmitted, the oscillto is powered and the vmco con-
`tro voltage Vc is adjusted such that the oscillator frequency
`equals the carrier frequency.
`Referring now to FIG. S, the Input signal from the
`receiving antenna 38 Is applid
`through an impedance
`so matcing network 61
`to a low noise amplifier 62 and
`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 Int and combined with
`the local oscillator shifted -45 degrees in phase in mixer 66
`55 to produce signal Qm. YIn and Qm. are the so-called "in-
`phase and "quadrature-phase signals commonly known to
`radio engineers. Both bin and Qm. are centered at zero hertz
`rather than at an intermediate frequency. This scheme is
`commonly referred to as "direct conversion" because a
`6o direct conversion to baselhand is effected rather than con-
`version to an intermediate frequency which is then con-
`verted to basrband. Direct conversion reduces power
`consumption, as no intermediate frequency cirutits are
`ernployod and it allows use of low pass filters to effect
`65 selectivity. Lawpass filters 67 and 68. preferably of the
`linear phase tipe. remove the unwanted mixing products and
`provide selectivity of signals Is and Qit respectively.
`
`0014
`
`

`
`5,699,357
`
`30
`
`5
`The liltered output signals If and Qf passed throug
`blocking amplifiers 69 and 70 to form Signals I and Q. The
`supply currents of amplifiers 69 and 70 Are adjusted sothas
`the parasitic output capacitance of these amplifiers cc
`tively form a bandpaus Ablte with gain. These amp91ien
`blockfrequencies below 100 KlHzand above twoM]Hz. TU
`fitering adds to the overall selectivity and blocks an)
`unwanted DC mixer byproduct common to direct cnversiom
`schemes.
`Some conventional frequency discriminators mrate the
`signal V-PdQ/&t-Q*dVdL When the frequency of the
`received signal is above the local oscillator frequency. V is
`greater than zero. Correspondingly, when the frequency ol
`the received signal is beow the local oscillator frequency. 'V
`is less than zero. This scheme has the advantages of being
`totally
`insensitive to both amplitude and phase ecrors
`between in I and Q mixe stages. Its disadvantage is that it
`requires the creation of the fiime derivatives of I and Q.As
`is well known, precise derivative forming circuits is difficu-
`uIt and power consumptive.
`To circumvent the disadvantages of derivative forming:
`networks and still keep the advantages of the frequency
`disarimination scheme, the receiver employs all pass phase
`shifters 71, 72.73 and 74 to create the signals In, Qa, Qb and
`Qc respectively. Multipliers 7S and 76 together with adder
`77 then form the signal U-na*Qb-lb*Qa. The advantage is
`that U has the sam desirable properties of a discriminator
`based on I*dQ/dt-Q*dVdt without requiring differentiation.
`htis only required that Is and lb be Separated by 90 degrees
`and that Qa and Qb be separated by 90 degrees. As is well
`knownL.all pass networks conuisting Of aresistor and capfil-
`tor ea 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-
`supon.
`Limiter 78 then amplifies U to form signal LUm. l1miter
`circuits which can generate these signals are well known and
`have been integrated into integrated receiver chips for many
`years. Limiter output Urn 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 STRUCTUE
`As indicated previously, the basic scheme for allowing
`multiple Personal Electonic Assessocies (PEAS) to com-
`municate with the common server naocompitrf (PDA)
`may be charactmrized as a form of dtie division multiple
`&aces (MDMA). 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. Ini the pre.ferrd
`crmbodiement, 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 trasmits
`nor receives, essentially all of the modem circuits arm
`powered off, thus effecting a substantial power reduction. As
`is described in greater detail hereinafter, some dlots are used
`to establish synchronization between PEA and PDA and
`others are used to implement a control chanweL 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 FDA to
`PEA. Assignment of a single slot Per fram results in A
`virtual channel bandwidth of 122 bits per second. NPIrtual
`
`channels requiring larger bandwidths are assigned a multi-
`plicity of slots. For example, when ten slots are assigned, the
`virtual channel bandwidth is increased to 1220 bits per
`second. More tha one virtual channel oan be established
`Sbetween the PDA and a Single PEA. If one channel is
`outgoing from PDA to PEA while the other channel is
`Pincoming from the PEA to the PDA, an effectively Mul
`duplex communication link is constructed. It is possible for
`each virtual channel to different bandwidths. Ansother pos-
`s0 ible operational mode Is for the dat transfer direction of a
`ingle virtual channel can be changod dynamdcally. Acontrol.
`channel can be employed whose sole purpose is to indicate
`the data flow direction on die data channel. Changeover
`frorn one direction to anothe IS typically affected at the
`15frame: boundary.
`A single, virtual channel may be shared amongst several
`PEAS under control of the PDA. In this operational mode, a
`control virtual channel Is employed to indicated to the
`ensemble of PEAs sharing the channel which is to transmit
`20at any given time. Still another opezational mode occurs
`when at single virtual channel is used to broadcast Informa-
`dion hrorn PDA to multiple PEAsL While It is possible to
`establish virtual diannels between two PEAS, the increased
`worst case separation possible from one PEA to another PEA
`25 may preclude establishment of a reliable radio lint There-
`fore PEA to PEA links are not present in the faefartri
`embodiment While all these operational modes appear
`diffieent, they are essentially Well known variants to the
`underlying time division multiple access technique.
`TD)MA&llows anensemblecofPEAS andPDAtc, establish
`a wide assortment of non-conflicting, eor free, virtal
`channels between PEAS and PDA. When two different
`ensembles of PEAS ad PDA happen by chance to employ
`the same carrier frequency, it Is possible for the RI' bursts of
`35one ensemble to overlap those of the other ensemble. This
`overlap can cause craors. If durin a particular bit period
`two RF bursts are being Simultaneously received. one from
`a transmitter in the home ensemble and the other from a
`fomvign 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 erro free
`channel when the stronger transmitter is part of the home
`ensemble and an result In arm when the stronger trans-
`miller is part of a foreign ensemble. While it is very likely
`45 that the stronger transmitter is part of the home ensemble,
`there are ciercumestances
`in normal operation where the
`stronger transmitter will part of a foreign ensemble. Note
`that even when a foreign transmitter is of much greater
`power than the home transmitter. If the foreign RW bursts and
`50 home RP burst do not overlap, no error occurs.
`As is well known, many channel arrors 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 checksum. 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=M4C bits of
`channel bandwidth are utilized. For a fixed word length, as
`the number of error bits which oan be cmrected increases.
`the channel efficiency decreases, As a general rule, as the
`6o channel's error rate increase, the channel bandwdith effi-
`ciency (needed to achieve a certain corrected error rate)
`decreases and the minimum woredize increases. In One Of
`the simplest eror correction scheme, called majority codiu&
`where data bit is transmitted three time (M1.1 Cr2). chanuel
`65 bandwidth is reduced to 33%.
`In channels where errors occur in bursts, single error
`correction codes, even though they have high channel
`
`is
`
`0015
`
`

`
`5,699,357
`
`7
`cEffciency, will yield poor after coneion new
`rates. in
`interleaving, a well konown scheme to handle burst enwos,
`data is segmented into words which are then interleaved
`onto the channel. TIthe maxfimfumn error burst consists of four
`consecutive eror, then interleaving four words results in s
`ach burst occuriag in a separate codeword. Since each
`oodeword now has only one error after interleaving, it can be
`corrected.
`Yet another means for correcting en ca Is to packetize the
`data and retransmit on detection of a checlumr arror. For 10
`virtual channels not requiring low lacy. the highest dum.
`nel efficiencies are possible. Hybrid schemes. where effo
`correction codes am employed together with retransmission
`of packets on checksumt errors are aimo possible.
`rates caused by the interference of RF bursts 15
`Err
`between two different ensembles can be significmntly
`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 (OCs). In this scheme,- the 16384 20
`slots are equally segmented into 256 intervals called sectors.
`A maximum of three RP bursts can occur in each sectionL
`The position of each burst is dictated by a one in a OOC
`codeword. Codewords have unity auto-correlation and
`cross-cosrelation with respect to rotation by an arbitrary 25
`number of slot positions within a sector. The codes are
`mostly zeros with three scattered Ones representing the
`loations ofithe slots In which RW bursts we to be transmitted
`or received. 7tere are ten OOC codewvords with a sector
`length of 64 slots. In general, a sector can be assigned any 3
`one of the ten codewords with a rotation of i1ron zero to 63
`Slot Positions.
`To assign slots in an ensemble, one of 640 different
`combinations of code:word and rotations is selected for the 3
`first sector A codewcrotation combination is selected fcr
`the second section such that 1) the last RW burst portion of
`the last sector codeword and the two RW burst portions of the
`new oodeword do not form a codeword and 2) die last two
`RF burst positions of the last sector codeword and the first4
`RF burs position of the new codeword do not form a
`codewords, and 3) the codeword6rotation has not been
`selected before. Bach sector consists of three identical RE
`bursts (Le a majority error correcting code Is chosen).
`At any instant of time, the framei
`stwutures Of two 45
`ensembles will in general not be aligned. However, with
`their unocarelated separate ine bases, the framec structures
`will slip past one another will become alipted. Every
`possible correlation between the two frames will thus even-
`tually occur. Assuming each ensemble is using 100% of its 50
`bandwidth. then it is highly likely
`that at some time a
`codeword in eachb ensemble will he aligned. When code-
`words from separate ensembles we aligned, a receiver
`captures data from the stronger transmaitter. In thi case, the
`arro correction coding serves no value danc It perfectly 55
`the data of the foreign transmitter. When this
`corrects
`cundition occurs, the probability that another sector is also
`aligned is about 0.002. Thus one sees a worst case uncor-
`medtible error rate of about 0.001. As is well known, this
`unconretable error rate Is sufficiently low that, by employing 60
`packetinizing and retransmitting on checksumn ernors, an
`effectively murr free channel cant be obtained.
`As will be understood by those skilled in die art, the
`TDMA system is greatly facilitated by the establishment of
`a common frame time base between PEA andA PDA. In 65
`establishing this common time; base, the present invention
`employs timing or synchronization beacons (SBs) transmit-
`
`ted by the PDA. Each SB consists of eight RW bursts spread
`out over 252 slots. One of the SBs arbitrarily starts a frame.
`The positions of the remnaining seven SBs are selected
`pseudo-randomly with two restrictions. Firt the maximum
`interval between two successive SBs is less than 6.144
`milliseconds. Secondly, the positions must allow a unique
`frame deteminwation based on the Intervals between SBt
`Thus for example, equidistantly spaced SBsarme not allowed
`In accordance with one aspect of the present invention,
`the slot location of each lRP burst within all SBs is identical
`for all ensembles. In a particular ensemble, the 32-bit data
`bit pattern of cad~ SB will be identical. Between two
`different ensembles, however, the SB data bit paen, cho-
`sen randomly, will be quasi-distinct. The combination of SB
`data Bit pattern and SB locations allow every ensemble to be
`uniquely identified.
`In the preferred embodiment Illustrated in FIG. 6, echb of
`the eight SBs l00-IN is ifmediately followed by a sector
`assigned to the common Communication and Control Chan-
`nel (CCCu T'he sector immediately following the first seven
`CCC sectors is assigned to the Attention Clunals (ACs).
`The COC sectors are designated by reficrence characters
`110-118 in FIG.L6 while the Attention Channels arm desig-
`nated by reftsence; characters 120-1N7. As will be explained
`in greater detail latw, 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 we activated
`and monitored by the PEA controller 43. While the control-
`ler could be iplenented In a single custom integrated
`circuit. the present embodimextmpartitions the cotoler into
`a commercially available microprocessor 90, a PHC16C64, a
`speia purpose logic Integrated circuit IC 91, voltage con-
`trolled crystal osdUlaW 44, and a charge piup voltage
`generator 93. Voltae controlled crystal oscillator (VCXO)
`44 is controlled by voltage Vc, sourced by charge pump 93.
`The controller rC 91 can cause the frequency of owcillation
`to change by activating charge pump. Vaerying the conro
`voltage Vc from 0 to -6 volts changes the oscillator fre-
`quency by 50 Paut per million. VaXO 44 is powered
`continuously and serves as the time base for all activities.
`The micoprocesor crip includes 256 bytes of ROM. which
`contains the program instructions needed for all activities
`and 256-bytes of SRAM used in program execution.
`The controller IC 91 serves as the primary control agent
`fordAl activities. It contains registers, counters, Finite State
`Machines (FSMs). and as will be explained in more detall
`syn-
`later, a Digital Matched Filter (DM1') used to detat
`chronization and attachment beacons, and a 10244 6-bit
`SR1AM used to store the usage sector assignments in dhe
`PEAS TDMA plan. While some of the activites are imple-
`mented without microprocessor intervention, most activities
`involve the micropocessor execution of short instruction
`sequences. Normally, the microprocessor clock. sourced by
`controller IC 91 is inactive, thus reducing power consump-
`tion. When microprocessor intervention is required, control-
`ler IC 91 activates the microprocessor clock and issues an
`8-bit code over the Interconnecting bus to indicate what
`activity the micropro