United States Patent (19)
`Tymes
`
`(11)
`(45)
`
`Patent Number:
`Date of Patent:
`
`5,029,183
`Jul. 2, 1991
`
`(54) PACKET DATA COMMUNICATION
`NETWORK
`75 Inventor: LaRoy Tymes, Palo Alto, Calif.
`73) Assignee: Symbol Technologies, Inc., Bohemia,
`N.Y.
`(21) Appl. No.: 374,452
`(22
`Filed:
`Jun. 29, 1989
`(sil Int. C. ................ H04B 15/00
`52 U.S.C. ........................................................ 375/1
`(58) Field of Search ............................................ 375/1
`(56)
`References Cited
`U.S. PATENT DOCUMENTS
`3,641,433 2/1972 Mifflin et al. ........................... 375/1
`4,247,908 1/1981 Lockart et al. ......
`364/900
`4,291,409 9/1981 Weinberg et al. ...................... 375/1
`4,409,470 10/1983 Shepard et al...
`... 235/472
`4,460,120 7/1984 Shepard et al. ..
`... 235/472
`4,475,208 10/1984 Ricketts .................................. 375/1
`4,639,914 1/1987 Winters ...............
`370/110.1
`4,672,658 6/1987 Kavehrad et al. .................... 379/63
`4,673,805 6/1987 Shepard et al......
`... 235/472
`4,736,095 4/1988 Shepard et al. ..................... 235/472
`4,740,792 4/1988 Sagey et al. ......................... 342/457
`4,758,717 7/1988 Shepard et al......
`... 235/472
`4,789,983 12/1988 Acampora et al. ................... 370/96
`4,829,540 5/1989 Waggener, Sr. et al. .............. 375/1
`4,850,009 7/1989 Zook et al. ............................ 379/96
`
`OTHER PUBLICATIONS
`MSI Data Corporation, Product Brochure, MSI PRT
`Portable Radio Terminal, 2 pages, 1988.
`Vectran Corporation, Product Brochures, VR1100,
`VR1120, VR1130 and VR1150 Systems for Radio Data
`Link.
`Freret et al., "Applications of Spread-Spectrum Radio
`to Wireless Terminal Communications', Conf. Record,
`Natl Telecom. Conf., Nov. 30-Dec. 4, '80.
`Primary Examiner-Thomas H. Tarcza
`Assistant Examiner-David Cain
`Attorney, Agent, or Firm-Arnold, White & Durkee
`(57)
`ABSTRACT
`A packet data transmission system is used to link a num
`ber of remote hand-held data-gathering units such as bar
`code readers to a central computer which maintains a
`database management system. Data packets are sent
`from the remote units by an RF link to intermediate
`base stations, then sent by the base stations to the central
`computer by a serial link. Direct sequence spread spec
`trum modulation is used for the RF link. The remote
`hand-held units initiate an exhange using RF transmis
`sion to and from the base stations, receiving only during
`a rigid time window following a transmission from the
`remote unit. The base stations cannot initiate communi
`cation to the remote units, but instead send data to the
`remote units only as part of the exchange.
`
`84 Claims, 6 Drawing Sheets
`
`
`
`HOST
`COMPUTER
`
`14 - BASE
`STATION
`
`.
`
`.
`
`.
`
`
`
`TZ
`
`
`
`BASE
`STATION
`
`N
`
`REMOTE
`TERMINALS
`
`5
`
`15
`
`1S
`
`5
`
`15
`
`Qualcomm Incorporated
`Exhibit 1004
`Page 1 of 29
`
`

`

`U.S. Patent
`
`July 2, 1991
`
`Sheet 1 of 6
`
`5,029,183
`
`A-7G.7
`
`HOS
`COMPUTER
`
`
`
`14 u BASE
`STATION
`
`12
`
`TZ
`
`/ Y
`
`/ N Y
`
`
`
`5
`
`t3
`
`AAG1.A.
`REMOTE
`- - - - - - - ?--
`
`15
`
`
`
`
`
`Page 2 of 29
`
`

`

`U.S. Patent
`
`July 2, 1991
`
`Sheet 2 of 6
`
`5,029,183
`
`72
`73
`78
`17
`HEADER DATA Z, 0 to 22 BYTE
`N
`
`na
`
`START
`SYMBOL
`
`79
`
`13-BIT
`DEVICE ID
`
`s-BIT
`76
`
`77
`
`A768
`
`
`
`A7Gaza (e)
`
`(c) A fel
`
`(c) A (s)
`
`(c.
`
`A
`
`2MHz SAMPLE RATE
`
`Page 3 of 29
`
`

`

`U.S. Patent
`
`July 2, 1991
`
`Sheet 3 of 6
`
`5,029,183
`
`Z
`
`G8
`
`
`
`
`
`1,6
`
`88
`
`96
`
`
`
`16
`
`DG7
`
`Q97
`
`Page 4 of 29
`
`

`

`U.S. Patent
`
`July 2, 1991
`
`Sheet 4 of 6
`
`5,029,183
`
`
`
`
`
`8300030
`
`
`
`WWE HIS VIVO
`
`
`
`
`
`C|GE
`DGE ·
`
`U98
`
`88
`
`06
`
`Page 5 of 29
`
`

`

`U.S. Patent
`
`July 2, 1991
`
`Sheet 5 of 6
`
`5,029,183
`
`
`
`129
`
`BAR CODE
`DATA TO
`MEMORY
`
`PACKET
`
`132
`
`SPREAD &
`ENCODE
`
`ACTIVATE
`133-1. Receiver
`
`134
`
`WAT
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`LOAD
`A,B,C
`SAMPLES
`TO MEM.
`
`DEACT WAE
`RECEIVER
`
`TESTA,B,C
`DATASREAM
`FORMATCH.
`GENERATE
`CORRELATE
`LEVEL
`
`FND MAX
`EVE
`
`A.
`
`142
`
`43
`
`DECODE
`ALL OF
`SELECTED
`DATASTREAM
`
`14.5
`
`
`
`DESPREAD
`
`146
`
`YES
`
`YES
`
`Page 6 of 29
`
`

`

`U.S. Patent
`
`July 2, 1991
`
`Sheet 6 of 6
`
`5,029,183
`
`
`
`A7G 77A
`
`DEACTIVATE
`RECEIVER
`
`ACVATE
`TRANSM
`
`BEGIN
`ME-OUT
`
`LOAD BYTE
`OF PACKET
`DATA TO
`TRANSMIT
`
`ACTIVATE
`RECEIVER
`
`LOAD
`CAL-BACK
`PACKET
`
`Page 7 of 29
`
`

`

`1.
`
`PACKET DATA COMMUNICATION NETWORK
`
`BACKGROUND OF THE INVENTION
`This invention relates to data communication sys
`tems, and more particularly to an RF packet communi
`cation system in which a number of remote units send
`data to a central computer via intermediate base sta
`tions.
`Bar code readers used in retail or commercial facili
`ties are usually connected to a central computer by
`physical wiring. This connection is quite suitable for
`permanently-mounted bar code readers as used in su
`permarket checkout counters, or for hand-held scanners
`15
`or wands used at similar fixed locations. However,
`when the bar code reader is to be used by a person who
`is moving about a building, or when temporary installa
`tions are employed, physical wiring is unsuitable, or is
`at least quite inconvenient. A radio frequency (RF) link
`20
`can be used to send data from the a hand-held bar code
`scanner to a central station, or to a local relay point, but
`the RF links that have previously been available for this
`purpose have had characteristics making them expen
`sive and inconvenient. These RF links typically have
`used RF bands requiring F.C.C. licensing for each in
`25
`stallation, adding to the cost and administrative burden.
`The RF components employed in this type of equip
`ment have to be of high precision so that frequency drift
`and bandwidth spillage are kept within F.C.C. toler
`ances. In addition, battery drain has required either
`large, heavy batteries, or frequent recharging, or both.
`The RF transmission methods previously used also
`have limited the number of portable terminals which
`could be used in a given area due to use of a relatively
`narrow bandwidth. Examples of bar code readers using
`35
`local RF data links include portable terminals commeri
`cally available from the following companies: MSI
`Data Corporation, Vectran Corporation, LXE Corpo
`ration, Norand Corporation, and Telxon Corporation.
`Portable bar code readers having long-distance RF
`links are available from Mobil Data International and
`from Motorola, Inc. (the KDX1000).
`Indoor RF communications networks of the voice
`type have been proposed, such as that of U.S. Pat. No.
`4,789,983 for “Wireless Network for Wideband Indoor
`45
`Communications', or U.S. Pat. No. 4,639,914 for
`“Wireless PBX/LAN System'.
`The remote terminals in these prior systems are ad
`dressable at any time, i.e., always activated, so the re
`quirements for power are dictated by this feature. In
`50
`addition, these prior systems have used RF frequency
`bands requiring F.C.C. licensing of individual users.
`For these reasons, prior systems of this type have been
`too costly and otherwise unsuitable for the present pur
`poses.
`55
`Spread spectrum wireless transmission is able to use a
`band that is designated as an "unlicensed' band by the
`F.C.C. and so licensing is not a factor, and the use of
`spread spectrum techniques allows the transmission to
`be accomplished in a reliable manner even though this
`band is subject to interference from the many diverse
`users. In U.S. Pat. No. 4,672,658 for "Spread Spectrum
`Wireless PBX", a system is shown in which each sepa
`rate user transceiver is matched with a separate trans
`ceiver at the central PBX, and each one of these
`matched pairs transmits with a unique direct sequence
`spread spectrum chipping pattern. A separate call set-up
`transceiver having a common direct sequence chipping
`
`5,029, 183
`2
`pattern is used for exchanging information involved in
`setting up a call. As above, this system requires continu
`ous monitoring of the RF bands by all of the transceiv
`ers, and is a voice oriented system requiring varying
`time periods of maintaining connections, as well as re
`quiring connection from user to user, rather than user to
`central station. Another example of use of spread spec
`trum in a local RF link is a utility meter reading system
`wherein a utility truck driving by a house activates a
`reader by a CW transmission then receives the data
`from the reader.
`Wireless data communications between a central
`computer and several remote terminals located within a
`building, using direct-sequence spread-spectrum tech
`niques to overcome multipath interference, is described
`by Freret et al, NTC Record, Nov., 1980, but again
`these types of systems rely upon continuous operation
`of the portable units, and impose burdens on the RF
`circuitry in the remote units which result in complex
`and expensive construction.
`In U.S. Pat. No. 4,740,792 a data transmission system.
`using spread spectrum RF is illustrated wherein vehi
`cles are provided with a transmitter, but no receiver,
`and the location of each vehicle is reported to a central
`station periodically by a transmitted packet. The trans
`mitter is powered up only for a very limited duty cycle,
`so battery drain is minimized. This system has no ability
`to send data from a central station to one of the vehicles,
`or to allow the transmitter at the vehicle to receive an
`acknowledge signal indicating receipt of the data trans
`mitted.
`It is an object of the present invention to provide an
`improved, low-cost, low-power, data communication
`network in which a number of remote terminals units
`are able to send packets od data to a central station, and,
`in most cases, to receive acknowledge signals and data
`from the central station, preferably a network using an
`RF link or the like so that the remote units may move
`about freely in an area to be covered by the network.
`Another object is to provide an improved packet trans
`mission network in which remote terminal units may be
`of low cost, low power and small size, yet provide
`reliable and fast response, as may be needed in a com
`mercial facility (usually indoor) using bar code scanners
`or the like for data gathering. Another object is to pro
`vide an improved protocol for use in a packet data
`transmission network which results in reliable opera
`tion, low power consumption and low cost implementa
`tion. A particular object is to provide an RF data link
`for portable terminals usable without site licensing
`under F.C.C. regulations, so that the expense and delays
`incident to such licensing ar eliminated or minimized.
`SUMMARY OF THE INVENTION
`In accordance with one embodiment of the invention,
`a packet data communication system includes a number
`of remote terminal units for gathering data, and a com
`munications link for sending packetized data to a central
`station and for receiving an acknowledge signal and
`data from the central station. A packet-exchange proto
`col is used for this communications link that provides
`reduced power dissipation at the remote unit by activat
`ing the receive function for only a short time, rather
`than requiring the remote unit to receive or "listen' at
`all times. To this end, the exchange protocol establishes
`a rigid time window keyed to a transmission by the
`remote unit, and the remote unit is responsive to a mes
`
`10
`
`30
`
`60
`
`Page 8 of 29
`
`

`

`10
`
`15
`
`35
`
`20
`
`5,029, 183
`4.
`3
`pseudo-random code used to generate the spread-spec
`sage form the central station only during this time win
`trum signals, and comparing this data with that received
`dow. The time window is defined to being at a fixed
`at other base stations, the best station can be selected
`time delay after a transmission from the remote unit to
`while communications continue uninterrupted.
`the central station; at all other times, the receiver is not
`powered up. In this protocol, the central station cannot
`BRIEF DESCRIPTION OF THE DRAWINGS
`initiate a packet transmission to a remote unit, but in
`The features believed charcteristic of the invention
`stead must wait until the remote unit has sent a transmit
`are set forth in the appended claims. The invention
`ted packet, then the central station can reply in the rigid
`time window, attaching to the acknowledge signal the
`itself, however, as well as other features and advantages
`thereof, may best be understood by reference to the
`data it wishes to send to this remote unit. The remote
`detailed description of a specific embodiment which
`units are low-cost, hand-held units in one embodiment,
`follows, when read in conjunction with the accompany
`and so will be of lesser computational capacity then the
`ing drawings, wherein:
`central station, and power dissipation must be mini
`mized. Accordingly, use of this protocol permits the
`FIG. 1 is an electrical diagram in block form of a
`packet data communication system according to one
`receive function, and the computation function needed
`embodiment of the invention;
`to decode received data, to be scheduled or managed by
`FIG. 2 is timing diagram showing events (RF trans
`the remote unit rather than being slaved to the central
`mission) vs. time for a data transmission sequence in the
`unit.
`system of FIG. 1;
`In an illustrative embodiment, the central station
`FIG. 3 is a more detailed electrical schematic dia
`includes a number of base stations located indifferent
`gram in block form of the host computer and one of the
`rooms or areas, with all of the base stations connected
`to a central computer, either by a wire connection or by
`base stations in the system of FIG. 1;
`FIG. 4 is a moe detailed electrical schematic diagram
`a similar RF link. At any given time, a remote unit is
`assigned to only one of these base stations, and as the
`in block form of one of the remote terminals in the
`remote unit moves about it is reassigned to another base
`system of FIG. 1;
`25
`station. A feature of the protocol is to include an ID
`FIG. 5 is a sectional view of a hand-held bar code
`scanner unit which may be used as the remote terminal
`number for the remote unit in the transmitted packet,
`according to one embodiment of the invention;
`and to include this same ID number in the reply packet,
`so acknowledgement by an assigned base station is con
`FIG. 5a is a pictorial view of another type of bar code
`reader which may be used as the remote terminal in
`firmed. But there need be no address or ID of the base
`30
`station included in the protocol for communicating with
`stead of the laser scanner of FIG. 5, according to an
`the remote units, since a remote unit is assigned to only
`other embodiment of the invention;
`FIG. 6 is a view of a part of a bar code symbol to be
`one base station, and the base station merely serves as a
`conduit for communicating with the central computer
`read by the remote unit of FIGS. 4 and 5, or of FIG.5a,
`and a timing diagram of the electrical signal produced
`in any event.
`thereby;
`The remote terminal units are, in one embodiment,
`FIG. 7 is an expanded view of part of the timing
`hand-held bar code readers, and these units are coupled
`diagram of FIG. 2;
`to the central station by an RF link so that the user is
`FIGS. 8a–8c are timing diagrams showing events vs.
`free to move about the area of the network. Ususally the
`time occurring in the system of FIGS. 1 and 3-6 using
`data packet being sent from the remote unit is the result
`of scanning a bar code symbol. The reply from the
`the protocol of FIGS. 2 and 7;
`FIG. 9 is an electrical schematic diagram of the cir
`central station in this case would be a validation of the
`cuitry of the transmitter/receiver in the remote unit of
`bar code information, or instructions to the user about
`what action to take regarding the package scanned by
`FIG. 4;
`FIG. 10 is an electrical schematic diagram of the
`the hand-held unit.
`45
`In a preferred embodiment the RF link employs a
`circuitry of the transmitter/receiver in a base station of
`spread spectrum modulation technique to send data
`the system of FIGS. 1 and 3;
`FIGS. 5a and 11b are a logic flow chart of an algo
`packets from the remote terminals to the base stations
`and return. Spread spectrum methods utilize a transmit
`rithm which may be executed by the CPU in a remote
`terminal unit of FIGS. 1, 4 and 9 for a system according
`ted bandwidth much wider than required for the data
`by adding some coded function to the data, then the
`to one embodiment of a invention.
`received signal is decoded and remapped into the origi
`DETAILED DESCRIPTION OF A SPECIFIC
`nal information bandwidth. A particular advantage of
`EMBODIMENT
`this type of RF data link is that a band may be used
`which does not require site licensing by the F.C.C., yet
`Referring to FIG. 1, a data communications network
`according to one embodiment of the invention is illus
`it provides reliable, low cost communication from a
`light-weight, hand-held, battery-operated unit.
`trated. A host processor 10 is connected by a communi
`An important feature in one embodiment is the use of
`cations link 11 to a number of base stations 12 and 13;
`the decode of an initial sync portion of the packet in the
`other base stations 14 can be coupled to the host
`direct-sequence spread spectrum transmission to pro
`through the base stations 12 or 13 by an RF link. Each
`60
`duce a quality factor for use in determining which base
`one of the base stations 12, 13 or 14 is coupled by an RF
`station should handle which remote unit. The spread
`link to a number of remote units 15. In one embodiment,
`spectrum transmission contains considerable redun
`the remote units 15 are laser-scan bar-code readers of
`the hand-held, battery-operated type as disclosed in
`dancy (eah bit is spread to produce a number of bits),
`and so a received packet can be used even if in a noisy
`U.S. Pat. Nos. 4,387,297, 4,409,470 or 4,760,248, all
`65
`assigned to Symbol Technologies, Inc., for example.
`environment where all decoded bits (before despread
`ing) are not valid. By recording the degree to which the
`Various other types of remote terminals may be advan
`tageously employed in a system having features of the
`incoming packets from a remote unit correlate with the
`
`50
`
`55
`
`Page 9 of 29
`
`

`

`O
`
`5,029, 183
`6
`5
`what data is included, if any, so a remote-to-base ex
`invention; these remote terminals ordinarily would in
`hange, including acknoledge, takes about 9.8 msec in
`clude data entry facilities such as a keyboard or the like,
`the example. The base stations 12, 13 and 14 cannot
`as well as a display (or printer) for indicating to a user
`initiate an exchange of FIG. 2, or initiate any other such
`information detected, transmitted and/or received by
`transmission to the remote units 15, but instead must
`this terminal 15. In this embodiment used as an illustra
`wait until a packet 17 is received from the remote unit
`tive example, there may be from one up to sixty-four of
`15 for which this base station has a message waiting,
`the base stations 12, 13 and 14 (three being shown in the
`then the data to be sent is included in the data portion of
`Figure), and up to several hundred of the remote units
`the return packet 18. For this reason, the remote units
`15; of course, the network may be expanded by merely
`15 are generally programmed to periodically, e.g.,
`changing the size of address fields and the like in the
`about every 500 msec or more, send a packet 17 to the
`digital system, as will appear, but a limiting factor is the
`base station with no data except its identifying code
`RF traffic and attendant delays in waiting for a quiet
`(traditionally called a NOP), so that the base station can
`channel. This communications network as seen in FIG.
`send any data it has waiting in its memory for relay to
`1 would ordinarily be used in a manufacturing facility,
`this remote unit 15. To prevent another remote unit 15
`office building complex, warehouse, retail establish
`15
`from starting one of the exchanges of FIG. 2 in the
`ment, or like commercial facility, or combination of
`interval just after the transmit packet 17 but before the
`these facilities, where the bar code readers or similar
`receive packet 18 has started, time to, the listening time,
`data-gathering terminals 15 would be used for inven
`is generally chosen to be longer than the time interval
`tory control in stockroom or receiving/shipping facili
`between transmit packet 17 and receive packet 18 (0.2
`ties, at checkout (point of sale) counters, for reading
`20
`msec in this example). If another remote unit 15 tries to
`forms or invoices or the like, for personnel security
`initiate its own exchange it will receive the RF trans
`checking at gates or other checkpoints, at time clocks,
`mission and will back off and try again at least about
`for manufacturing or process flow control, and many
`10-msec later. In the manner of CSMA protocols, the
`other such uses. Although hand-held, laser-scan type
`remote units 15 can be programmed to wait random
`bar-code readers are mentioned, the data terminals 15
`25
`time delays before retry, to thereby lessen the likelihood
`may also be bar-code readers of the wand type, and may
`of simultaneous retries.
`be stationary rather than hand-held. The device may be
`Referring to FIG.3, in a typical commercial or retail
`of the optical character recognition (OCR) type, as
`application of a network of FIG. 1, the host processor
`well. Other types of data gathering devices may use the
`10 maintains a database management system (employing
`features of the invention, such as temperature or pres
`suitable database management software similar to that
`sure measuring devices, event counters, voice or sound
`commercially available) to which the remote units 15
`activated devices, intrusion detectors, etc.
`make intries or inquiries via the base stations 12, 13 and
`According to an important feature of one embodi
`14. The host processor 10 has a CPU20 which may be
`ment of the invention, an RF packet communicatiohs
`a microprocessor device of the 80386 type manufac
`protocol between the remote units 15 and the base sta
`tured by Intel, for example, and the CPU accesses a
`tions 12, 13 and 14 includes a transmit/receive exhange,
`memory 21 via a main bus 22 to execute instructions.
`referred to hereinafter simply as an "exchange'. This
`Various I/O processors 23 are used to access peripher
`protocol is similar to collision-sense multiple-access
`als such as keyboard, video display,etc., as well as disk
`(CSMA) in that a unit first listens before transmitting,
`storage 24 for the database system and other computer
`and does not transmit if the channel is not free. As seen
`functions. A communications adapter 25 comples the
`in FIG. 2, this exchange always begins with a remote
`to-base transmitted packet 17, representing an RF trans
`CPU20 via main bus 22 to the link 11. This communica
`tions link 11 may be of the serial type such as RS232, or
`mission from a remote unit 15 to be received by the base
`in a system designed for higher performance the link 11
`stations within range. The transmitted packet 17 is fol
`may use one of the available local area network type of
`lowed after a fixed time interval by a base-to-remote
`45
`protocols such as Ethernet or token ring; in the example
`transmitted packet 18, representing reception by the
`embodiment, however, the standard local area network
`remote unit 15 of RF information transmitted by the
`protocols are needlessly complex and expensive, and a
`base station servicing this particular remote unit 15.
`more optimum solution is merely use of a serial port
`Each of these packets 17 and 18 is of fixed timing; a
`connected to a shared serial line 11, on a time-sharing
`transceiver in a remote unit-15 beings an exchange at its
`50
`basis (e.g., time slotted). The data rate on the link 11 is
`own initiative by first listening for other traffic for a
`rather modest compared to typical 4-Mbit or 16-Mbit/-
`brief interval to (typically 0.3 msec), and, if the RF
`sec LAN links of the token ring or Ethernet type; about
`channel is quiet, starting a transmission at a time of its
`160-Kbit/sec is adequate for the link 11, and so one of
`own selection (asynchronous to any clock period of the
`the various time-slot type of serial link methods may be
`base stations or host computer). This outgoing transmis
`55
`sion packet 17 lasts for a time t1 as seen in the Figure,
`used.
`The base stations 12, 13 and 14 each utilize a CPU 30
`and in an example embodiment this period is 4.8 milli
`which accesses a memory 31 via local bus 32, also seen
`seconds. Then at a precise time delay t2 after it started
`in FIG. 3. This data processing unit is coupled to the
`transmission (e.g., 5-msec after the beginning of t) the
`serial link 11 via a communications adapter 33. An RF
`transceiver begins listening for the return packet 18
`transceiver 34 is coupled to the CPU 30 in each base
`from the base station. The transceiver in the remote unit
`15 only responds to receipt of the packet beginning in a
`station via the local bus 32 and is connected to an an
`tenna 35 for RF transmission to and reception from the
`very rigid time window t3 of a few microseconds
`remote units 15 using the protocol of FIG. 2. An addi
`length, and if the packet 18 has not started during this
`tional RF transceiver 34a may be used, as well, as an RF
`window then anything to follow is ignored. The packet
`65
`link to and from other base stations, if necessary. An
`18 is an acknowledge signal, and also contains data if the
`example of a commercially-available microprocessor
`base station has any message waiting to be sent. The
`packet 18 also is 4.8 millisecond in length, regardless of
`device which may be used as the CPU 30 is a V-25
`
`35
`
`Page 10 of 29
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`10
`
`15
`
`25
`
`5,029, 183
`8
`7
`nications link 11 uses a protocol of adequate perfor
`device manufactured by NEC, which is the same device
`mance to allow each RF transmission (packet 17) from
`used in the remote units 15, as described below. An
`other microprocessor device which may be used as the
`a remote unit 15 to be decoded in the base station and
`relayed to the host processor 10 via the link 11, then a
`CPU 30 is the DSP56001 manufactured by Motorola,
`reply sent back from the host computer 10 via the link
`Inc. of Phoenix, Ariz. This DSP56001 microprocessor
`is primarily sold as a digital signal processor but also
`11 to the base station, so the base station can wait for
`another exchange for relay of the stored message to the
`functions as a high-performance, low-cost controller
`remote unit 15 in a packet 18. This sequence should
`device, capable of executing a 24-bit by 24-bit multiply
`operation in 100-nsec, and implementing interrupt rou
`appear to a user (a person carrying the bar code reader)
`as essentially "real time', even though the actual delay
`tines in 200-nsec. Examples of code used to execute
`typical I/O algorithms and code recognition are avail
`may be hundreds of milliseconds. This short cycle is
`maintained even when the network includes a large
`able from the manufacturer of th microprocessor de
`number of the remote units 15 operating sporadically.
`vices or associated vendors. The memory 31 includes
`Because of the RF protocol used, and the requirement
`ROM or EPROM for startup code executed by the
`that the RF link may be shared with a large number of
`CPU 30, as well as fast RAM for the program executed
`during normal operations and for buffering the digital
`remote units, the serial link 11 is much faster than an RF
`data incoming from or outgoing to the RF transceiver
`link via RF transceivers 34a and antennas 35 a from one
`base station to another base station, and so the serial link
`34. In addition, the CPU 30 includes a number of fast
`internal registers used for data manipulation in execut
`11 is used for messages between base stations whenever
`ing the code recognition algorithms. A particularly
`possible. The RF link is the example embodiment using
`20
`the protocol as described has a data rate of less than
`useful feature of the 56001 device is that a serial port is
`available for transmitting and receiving data via the
`one-tenth that of the serial link 11. Only when the physi
`cal layout, or the temporary nature of the network,
`serial communications link 11, so this function can be
`implemented with little added circuitry in the adapter
`demands this solution is the RF link from base to base
`employed.
`33. Likewise, the V-25 device has an analog input
`which may be used for this purpose; similarly, the
`Referring to FIG. 4, each remote unit 15 in the exam
`adapter 33 may buffer the incoming or outgoing serial
`ple embodiment is a data terminal (e.g., a hand-held bar
`code reader) having a CPU 40 executing instructions
`data so that parallel transfers on the bus 32 are used for
`from a program and data memory 41 which is coupled
`link data.
`to the CPU via a local bus 42. a peripheral bar code data
`The base stations 12, 13 and 14 are ordinarily located
`acquisition device 43 is coupled to the CPU via the bus
`in various rooms or bays of the commercial establish
`ment containing the network of FIG. 1, or located in
`42 and used to detect and/or covnert data from the bar
`other such places not readily accessible to an operator,
`code scanning section to be stored in the memory 41
`so usually a console with keyboard and display is not
`and processed by the CPU 40; other control devices
`interface with the keyboard and display. An RF trans
`used; if, however, a base station is configured for desk
`35
`ceiver 44 is coupled to and controlled by the CPU via
`top or wall mounting in an accessible location there
`the bus 42, and transmits the coded RF signal through
`maybe I/O devices coupled to the bus 32 to allow local
`data entry or display. The base stations are usually pow
`an antenna 45 or detects and converts RF received by
`the antenna, according to a protocol. In the example of
`ered by line current rather than being battery operated,
`and so there is less concern for power dissipation in
`the remote unit 15 being a laser-scan bar-code reader,
`the device 43 is used to input data from a photodetector
`these devices compared to that for the remote terminals
`device 46 which produces a serial electrical signal fed to
`15. The RF signal path in this environment is change
`a code recognition circuit 47 responding to the charac
`able in nature as equipment, fork-lift trucks, furniture,
`teristic patterns of bar code symbols and providing bar
`doors, etc., are moved about, or as the user moves from
`code data to the memory 41 via device 43 when a bar
`place to place and carries the hand-held remote unit
`45
`with him, or as the network is expanded or reduced in
`code is scanned. The bar code data is entered into the
`size; there is a high degree of multipathing in this type
`memory 41 by DMA if the CPU 40 includes this capa
`bility, or by move instructions executed by the CPU;
`of RF link. Thus, the particular one of th base stations
`alternatively, the memory 41 may be a video DRAM
`communicating at a given time with one of the remote
`device allowing serial data entry by a serial port sepa
`units 15 may change; to this end a "hand-off" protocol
`may be utilized, as will be described, to change the base
`rated from that used for CPU access. The CPU 40
`station which is designated to handle a remote unit. In
`within the remote unit checks the bar code data for
`validity and format, by executing code stored in the
`this manner, a remote unit 15 has a confirmed virtual
`memory 41, and, when the data packet has been pe
`RF link with only one base station at a time, although
`pared in the memory 41, the CPU initiates an RF trans
`others may be in range. The base station 12, 13 or 14 is
`55
`merely an intermediary; the remote unit is communicat
`mission by activating the RF transceiver 44 and trans
`ferring the encoded packet containing the bar code data
`ing with the host processor 10, and the function of a
`to the transceiver via bus 42. Usually the remote unit
`base station is merely to relay the data from a remote
`unit to the host computer, or from the host computer to
`has a manual data entry device such as a keyboard 48,
`and a visual display 49 such as an LCD device; the
`a remote unit. In a minimum-scale installation, there
`elements of the keyboard and display are scanned by
`may be only one base station, in which case the commu
`signals generated in the CPU 40, or generated in a key
`nication link 11 may be a direct connection via an RS
`232 serial port and calbe, or, if the building is such