EXHIBIT
`
`DSS—2 001
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`

`
`Umted States Patent
`
`[191
`
`[11] Patent Number:
`
`5,699,357
`
`Carvey
`
`[45] Date of Patent:
`
`Dec. 16, 1997
`
`US005699357A
`
`[54] PERSONAL DATA NETWORK
`
`[75]
`
`Inventor: Philip P. Carvey,Bedford, Mass.
`_
`.
`[73] Assigneez BBN Corporation, Cambridge. Mass.
`
`[21] Appl. No.: 611,695
`[22] Filed:
`Mar. 6’ 1996
`Cl 6
`HMJ 3/06
`[51]
`Int.
`........................................................
`.
`[52] U.S. Cl.
`.......................... 370/347; 370/350; 370/442;
`370/509; 455/89; 364/708.1
`[58] Field of Search ..................................... 370/310. 311,
`370/312, 313, 365, 367, 348. 349, 350,
`431, 433, 442, 443, 445_ 449_ 453_ 452_
`465. 468. 503. 509, 510, 512, 511, 514,
`522; 455/39» 100. 54-1. 66. 33.3; 375/222;
`354770501. 705-05. 703-1; 395/200-01~
`200-02~ 209-171 20(?-19- 230~ 823s 335~
`882’ 551’ 341/22’ 345/156‘ 157’ 169
`References Cited
`U.S. PATENT DOCUMENTS
`
`[56]
`
`......................... 370/461
`3/1994 Paggeotetal.
`5,297,142
`4/1994 Iguchi eta]. ......................... 364/708.1
`5,307,297
`5371,734 12/1994 Fischel-_
`5,481,265
`1/1996 Russell.
`
`Primary Examiner—We].lington Chin
`Assistant Examiner—l1uy D. Vu
`Attomey Agent, or Fmn—Henry D. Pahl, Jr.
`[57]
`ABSTRACT
`
`The CW‘ "°‘W°fk diS°1°5‘=d ‘min “Wes 1°W d“tY CY°1°
`pulsed radio frequency energy to effect bidirectional wire-
`less data communication between a server microcomputer
`unit and a plurality of peripheral units, each of which is
`intended to be carried 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 consump-
`tion and avoidance of interference between nearby similar
`systems is obtained.
`
`5,247,285
`
`9/1993 Yokota et al.
`
`....................... 364/708.1
`
`18 Claims. 6 Drawing Sheets
`
` Personal
`
`.2 ..__
`
`Digital
`Assistant
`
`(FDA)
`
`
`
`
`RF Links
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`DSS-2001
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`IPR ofU.S. Patent No. 6,128,290
`Page 1 of15
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`

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`U.S. Patent
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`Dec. 16, 1997
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`Sheet 1 of 6
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`5,699,357
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`U.S. Patent
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`Dec. 16, 1997
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`Sheet 2 of 6
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`5,699,357
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`43
`
`40
`
`Sensor/
`Actuator
`
`Interface
`
`
`
`
`
`42
`
`Local
`
`Oscillator
`
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`U.S. Patent
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`Dec. 16, 1997
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`Sheet 3 of 6
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`5,699,357
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`52
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`Sheet 4 of 6
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`Sheet 5 of 6
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`5,699,357
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`1
`PERSONAL DATA NETWORK
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates to a data network and more
`particularly to a data network which can etfect 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 elect:ronic
`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-
`pling of peripheral devices or accessories to the main
`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, all of
`which are adapted to be carried on the person of an user; 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-
`tems; 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
`units which are to be linked are all
`in close physical
`proximity, e.g.. under two meters separation. to establish,
`with very high accuracy. at common time base or synchro-
`nization. The short distances involved means that accuracy
`of synchronization is not appreciably affected by transit time
`delays. Using the common time base. code sequences are
`generated which control the 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 interfer-
`ing 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
`for realistic games. Likewise. so called virtual keyboards are
`
`5,699,357
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`2
`
`being developed which use inertial or magnetic sensors
`attached to a users fingers in the manner of rings. Further,
`apart fi'orn 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, monitoring 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 peripheral units collec-
`tively as personal electronic accessories (PEAs).
`Briefly stated, a data network system according to the
`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 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 powered and portable and which provide input
`information from the user or output information to the user.
`The server microcomputer incorporates an RF transmitter
`for sending commands and synchronizing information to the
`peripheral units. The peripheral units, in turn, each include
`an RF receiver for detecting those commands and synchro-
`nizing information and include also respective RF transmit-
`ters for sending information from the peripheral unit to the
`server microcomputer. The server microcomputer includes a
`receiver for receiving that information transmitted from the
`peripheral units.
`
`35
`
`The servm 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-
`nizing information initially transmitted from the server
`microcomputer. Preferably. the input and output information
`is carried by frequency modulation of the respective trans-
`mitters.
`
`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;
`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
`are transmitted between the server microcomputer and the
`various peripheral units;
`
`FIG. 7 is a block diagram of the controller employed in
`the PEA modern; and
`
`FIG. 8 is a block diagram of the digital matched filter
`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
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`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 is adapted to be carried on the person of the user, e.g.
`in his hand or on a belt hook. Such PDAs typically accept
`options which are physically configured as an industry
`standard PCMCIA card. In accordance with the present
`invention such a card. designated by reference character 13
`is implemented which includes a PCMCIA interface and
`PDA modern.
`
`As is described in greater detail hereinafter. the network
`system of the present invention establishes wireless com-
`munication 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
`are referred to herein as an “ensemble". The present inven-
`tion allows the creation of a data network linking 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
`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 prefaably incor-
`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-
`zation of impedance matching networks which in turn
`facilitates the operation at very low power.
`Referring now to FIG. 2. the PDA modem illustrated there
`comprises five major components. a transrnitter 40. a
`receiver 41, a local oscillator 42 which is shared by the
`transmitta and the receiver, a controller 43 which times and
`coordinates the operations of the transmitter. receiver.
`microprocessor and. finally. a voltage cont.ro1led crystal
`oscillator oscillator 44 which is utilized in maintaining a
`common time base with the host microcomputer. The oscil-
`lator 44 utilizes a crystal which operates at 4 Mhz.
`As is described in greater detail hereinafter. the controller
`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-
`mation from receiver 41 to a sensor/actuator interface,
`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 commacially available general purpose microproces-
`sor such as the PICl6C64. together with a special purpose
`logic integrated circuit (IC). The special purpose IC imple-
`ments those functions which cannot be efiiciently executed
`on the general purpose microprocessor. For example. 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 form of time
`division multiple access (TDMA). This TDMA access is
`characterized by a frame interval. common to the host and
`all PEAS of 32.768 milliseconds, segmented into 16.384
`time slots. Each time slot is further partitioned 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-
`quency shift keying (FSK). well known to those skilled in
`digital radio transmission. However. as is explained in
`
`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 TDMA 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 now to. FIG. 3. the PEA modem illust:rated
`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 oscillator
`18 which is utilized in maintaining the network time base.
`The oscillator 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 controller 14 ditlers 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 sensorltransducer 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 efl"ected using the
`local oscillator 45 to drive the transmit antenna amplifier 50
`whose output drives 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
`nanoseconds before the start of transmission.
`the local
`oscillator 45 is powered up. During this period and during all
`receive intervals. frequency selection varactor switchs 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 switchs 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. This 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 input signal from the
`Referring now to FIG. 5.
`receiving antenna 38 is applied.
`through an impedance
`matching 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 Irn and combined with
`the local oscillator shifted -45 degrees in phase in mixer 66
`to produce signal Qm. Irn and Qm are the so-called “in-
`phase” and “quadrature-phase” signals commonly known to
`radio engineers. Both 1111 and Qm are centered at zero hm'tz
`rather than at an intermediate frequency. This 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-
`verted to baseband. Direct conversion reduces power
`consumption. 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 1m and Qm respectively.
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`The filtered output signals If and Qf passed through
`blocking amplifiers 69 and 70 to fonn signals I and Q. The
`supply currents of amplifiers 69 and 70 are adjusted so that
`the parasitic output capacitance of these amplifiers elfec-
`tively form a bandpass filter with gain. These amplifiers
`block frequencies below 100 KHz and above two MHz. This
`filtering adds to the overall selectivity and blocks any
`unwanted DC mixer byproduct common to direct conversion
`schemes.
`
`Some conventional frequency discriminators create the
`signal V=I*dQ/dt—Q*dI/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
`totally insensitive to both amplitude and phase errors
`between in I and Q mixer stages. Its disadvantage is that it
`requires the creation of the time derivatives of I and Q. As
`is well lmown. precise derivative forming circuits is difiicu-
`ult and power consumptive.
`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, Qa. Qb and
`Qc respectively. Multipliers 75 and 76 together with adder
`77 then form the signal U=Ia*Qb—Ib*Qa. The advantage is
`that U has the same desirable properties of a discriminator
`based on I*dQ/dt—Q*d.I/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 efiect
`this phase separation. These
`networks produce an accurate 90 degree phase sepmation
`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 controlla 43 in
`both establishing the common time base and in recovering
`the data transmitted as described in greater detail hereinafter.
`
`FRAME STRUCTURE
`
`As indicated previously, the basic scheme for allowing
`multiple Personal Electronic Assessocies (PEAs) to com-
`municate with the common server 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
`embodiement. 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 ofl’. thus effecting a substantial power reduction. As
`is described in greater detail hereinafter. some slots are used
`to establish synchronization between PEA and PDA and
`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
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`25
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`30
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`35
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`45
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`55
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`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 than one virtual channel can be established
`between the PDA and a single PEA. If one channel is
`outgoing from PDA to PEA whfle the other channel is
`incoming from the PEA to the PDA. an elfectively full
`duplex communication link is constructed. It is possible for
`each virtual channel to dilferent bandwidths. Another pos-
`sible operational mode is for the data transfer direction of a
`single virtual channel can be changed dynamically. A control
`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 atfected at the
`frame 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
`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
`may preclude establishment of a reliable radio link. There-
`fore PEA to PEA links are not present in the preferred
`embodiment. While all
`these operational modes appear
`dilferent. 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 same carrier frequency. it is possible for the RF bursts of
`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
`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 stronger transmitter is part of the home ensemble.
`there are circumstances 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 RF bursts and
`home 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 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=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 efliciency decreases. As a general rule. as the
`channel’s error rate increase. the channel bandwdith eth-
`ciency (needed to achieve a certain corrected error rate)
`decreases and the minimum wordsize increases. In one of
`the simplest error correction scheme. called majority coding.
`where data bit is transmitted three time (M=1. C=2). channel
`bandwidth is reduced to 33%.
`
`In channels where errors occur in bursts. single error
`correction codes. even though they have high channel
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`efficiency. will yield poor after correction error rates. In
`interleaving. a well known scheme to handle bmst errors.
`data is segmented into words which are then interleaved
`onto the channel. Ifthe 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 packetize the
`data and retransmit on detection of a checksum error. For
`virtual channels not requiring low latency. the highest chan-
`nel efliciencies are possible. Hybrid schemes where error
`correction codes are employed together with retransmission
`of packets on checksum 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.
`One assignment scheme that has desirable properties
`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 RF 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 codewrrds 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. Acodeword/rotation combination is selected for
`the second section such that 1) the last RF burst postion of
`the last sector codeword and the two RF 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
`RF burst position of the new codeword do not form a
`codewords. and 3) the codeword/rotation has not been
`selected before. Each sector consists of three identical RF
`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 will become aligned. Every
`possible correlation between the two frames will thus even-
`tually occur. Assuming each ensemble is using 100% of its
`bandwidth. then it is highly likely that at some time a
`codeword in each ensemble will be aligned. When code-
`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 anotha 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
`unccrrectible error rate is sufliciently low that, by employing
`packetinizing and retransmitting on checksum errors. an
`effectively error free channel can be obtained.
`As will be understood by those skilled in the art. the
`TDMA 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 RF 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
`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
`bit pattern of each SB will be identical. Between two
`different ensembles, however, the SB data bit pattun. 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. each of
`the eight SBs 100-108 is immediately followed by a sector
`assigned to the common Communication and Control Chan-
`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
`110-118 in FIG. 6 while the Attention Channels are desig-
`nated by reference characters 120-127. As will be explained
`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-
`ler could be implemented in a single custom integrated
`circuit, the present embodiment partitions the controller into
`a commercially available microprocessor 90. a P'IC16C64, a
`special purpose logic integrated circuit IC 91. voltage con-
`trolled crystal oscillator 44. and a charge pump voltage
`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 arxivating charge pump. Varying the control
`voltage Vc from 0 to -6 volts changes the oscillator fre-
`quency by 50 parts per million. VCXO 44 is powered
`continuously and serves as the time base for all aaivities.
`The microprocessor chip 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
`for all activities. It contains registers. counters. Finite State
`Machines (FSMS), and as will be explained in more detail
`later. a Digital Matched Filter (DMF) used to detect syn-
`chronization and attachment beacons. and a l(D4><l6-bit
`SRAM used to store the usage sector assignments in the
`PEAs TDMA plan. While some of the activites are imple-
`mented without microprocessor intervention. most activities
`involve the microprocessor execution of short instruction
`sequences. Normally, the microprocessor clock. sourced by
`controller IC 91 is inactive, thus reducing power consump-
`tion. When rnicroprocessor 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 mieroprocesscx is to perform When the micro-
`processor has completed its program sequence. issues a code
`to controller IC 91 indicating completion. Controller IC 91
`then inactivates the rnicrorxocessor clock returning the
`micrprocessor into its minimum power consumption state.
`To reduce power consumption by the controller IC 91.
`only a very small percentage of the logic is clocked con-
`tinuously. Clocks to all remaining sections of controller IC
`91 are enabled only when required. As is common practice
`
`10
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`DSS