United States Patent (19)
`Heiman et al.
`
`54) POWER-SAVING ARRANGEMENT AND
`METHOD FOR MOBILE UNITS IN
`COMMUNICATIONS NETWORK
`
`75 Inventors: Frederic Heiman, Los Gatos; Patrick
`Pinard, Santa Clara; Andrew
`Werback; Michael Shiba, both of San
`Jose, all of Calif.
`73 Assignee: Symbol Technologies, Inc., Holtsville,
`N.Y.
`
`US006002918A
`Patent Number:
`11
`(45) Date of Patent:
`
`6,002,918
`Dec. 14, 1999
`
`5,519,762 5/1996 Bartlett ................................... 455/38.3
`5,568,513 10/1996 Croft et al. .
`... 455/38.3
`5,584,048 12/1996 Wieczorek .....
`... 455/38.3
`5,630,207 5/1997 Gitlin et al. ...
`... 455/38.4
`5,649.289 7/1997 Wang et al.
`... 455/31.3
`5,793,303 8/1998 Koga...........
`... 455/38.4
`5,815,811 9/1998 Pinard et al. ........................... 455/434
`
`OTHER PUBLICATIONS
`
`Wireless LAND Medium Access Control (MAC) and Physi
`cal Layer (PHY) Specifications, The Editors of IEEE, p.
`802.11, May 20, 1996.
`
`Primary Examiner Willis R. Wolfe
`Attorney, Agent, or Firm Kirschstein, et al.
`
`21 Appl. No.: 08/747,034
`22 Filed:
`Nov. 8, 1996
`O
`O
`Related U.S. Application Dat
`pplication Uata
`eae
`63 Continuation-in-part of application No. 08/549,051, Oct. 27,
`ABSTRACT
`57
`1995, Pat. No. 5,815,811, which is a continuation-in-part of
`application No. 08/044,648, Apr. 8, 1993, Pat. No. 5,528,
`A communications network comprising a cellular local area
`621, which is a continuation-in-part of application No.
`wireleSS network includes a plurality of access points con
`07/799,172, Nov. 27, 1991, Pat. No. 5,280,498, which is a
`graising:SENSE nected to a housed computer and each other, and a plurality
`application No. 67/374,452, Jun. 29, 1989, Pat. SF O29
`of mobile units each mobile unit being arranged for asso
`183.
`ciation with an acceSS point. The mobile units are arranged
`51 Int. CI.
`to periodically Scan for and identify the most eligible access
`
`H04Q 7/32; H04B 1/16;
`
`O
`
`-1 - O
`
`- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
`
`H04B 700
`
`point for association on the basis of the criteria of best
`
`52 U.S. CI
`
`455/38.3; 455/38.4; 455/566;
`
`quality signal Strength and loading factor. In order to identify
`
`O X
`
`O
`
`-- O
`
`- - - - - - - - - - - - - - - - - - - - - - - -
`
`eas 455574:455/3 43
`
`when mobile units are being removed from a predetermined
`
`455412 414
`58 Field of Search
`455312,313,383,384. 466.503. 507.
`57 536 566 434 343 574 500
`s
`s
`s
`s
`s
`s
`References Cited
`U.S. PATENT DOCUMENTS
`5,465,401 11/1995 Thompson .............................. 455/566
`
`56)
`
`area, access points having directional antennae are situated
`adjacent exit points to detect when mobile units are in a
`vicinity. Each mobile unit may include paging facilities,
`including the capability of transmitting information in a
`coded form known both to the unit and to a host, and
`power-saving facilities.
`
`
`
`
`
`32
`
`MESSAGE:
`PLEASE CONFIRM
`MEETING TIME:
`
`29 Claims, 7 Drawing Sheets
`
`58
`
`scANMEcH-68
`70
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`-52
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`U.S. Patent
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`Dec. 14, 1999
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`Sheet 1 of 7
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`6,002,918
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`- 38
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`42
`u-80
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`MEETING TIME:
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`34
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`6PM 7PM 8PM
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`R-49
`e
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`32
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`
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`44
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`
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`PLEASE CONFIRM
`MEETING TIME:
`
`49
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`Ex. 1013 / Page 2 of 17
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`U.S. Patent
`US. Patent
`
`Dec. 14, 1999
`Dec. 14, 1999
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`Sheet 2 of 7
`Sheet 2 0f 7
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`6,002,918
`6,002,918
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`3.wt
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`ON
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`02
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`03
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`Ex.1013/Page 30f17
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`Rzo._.__.rwoz_._.m_m__>_m__.:m___
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`U.S. Patent
`US. Patent
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`Dec. 14, 1999
`Dec. 14,1999
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`Sheet 3 of 7
`Sheet 3 0f7
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`6,002,918
`6,002,918
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`FIG. 2B
`FIG. 23
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`U.S. Patent
`US. Patent
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`Dec. 14, 1999
`Dec. 14,1999
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`Sheet 4 of 7
`Sheet 4 0f7
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`6,002,918
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`FIG. 3
`FIG. 3
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`EX. 1013 / Page 5 of 17
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`U.S. Patent
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`Dec. 14, 1999
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`Sheet 5 of 7
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`6,002,918
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`ØNIOWOT
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`|-JET EW||
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`NI
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`TENNWHO
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`d\/
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`SSERHOCIW
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`U.S. Patent
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`Dec. 14, 1999
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`Sheet 6 of 7
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`6,002,918
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`RECEIVE PPR
`
`10
`
`DETERMINE RSS
`
`11
`
`SELECT ELIGIBLE
`GROUP
`
`DETERMINE LOAD
`FACTORS
`
`CHOOSE LOWEST
`LOAD FACTOR
`
`12
`
`13
`
`14
`
`FIG. 5
`
`
`
`
`
`DAP
`WITH SAME LOAD
`FACTOR2
`
`
`
`YES SELECT AP WITH
`HIGHESTRSS
`
`ASSOCATE
`WITH AP
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`Ex. 1013 / Page 7 of 17
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`U.S. Patent
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`Dec. 14, 1999
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`Sheet 7 of 7
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`EXIT
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`6,002,918
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`1
`POWER-SAVING ARRANGEMENT AND
`METHOD FOR MOBILE UNITS IN
`COMMUNICATIONS NETWORK
`
`REFERENCE TO RELATED APPLICATIONS
`This application is a continuation-in part of application
`Ser. No. 08/549,051 filed Oct. 27, 1995, now U.S. Pat. No.
`5,815,811, which is a CIP of Ser. No. 08/044,648, filed Apr.
`8, 1993 now U.S. Pat. No. 5,528,621, which was a
`continuation-in part of Ser. No. 07/799,172, filed Nov. 27,
`1991, now U.S. Pat. No. 5,280,498, which was a
`continuation-in-part of application Ser. No. 07/635,859,
`filed Dec. 28, 1990, now U.S. Pat. No. 5,142.550, which was
`a continuation-in-part of application Ser. No. 07/374,452,
`filed Jun. 29, 1989, now U.S. Pat. No. 5,029,183, issued Jul.
`2, 1991. This application is related to application Ser. No.
`08/344,737, filed Nov. 23, 1994 and Ser. No. 08/193,069,
`filed Jan. 18, 1994, now U.S. Pat. No. 5,479,441.
`
`5
`
`15
`
`BACKGROUND OF THE INVENTION
`
`2
`Specification the mobile unit determines the acceSS point
`with which it will associate and the access point must accept
`the mobile unit unless it is defective or certain alarm
`conditions exist, Such as memory full. There is, however, no
`Suggestion of how, or by what criteria, other than those
`mentioned above, the mobile unit might Select an appropri
`ate access point, or the optimum access point.
`U.S. Pat. No. 5,276,680 relates to a communication
`System including a plurality of portable units and a plurality
`of controllers wired to a network. Each portable unit polls all
`of the controllers to establish whether it can associate with
`any controller and receives a response from any controller
`having less than a predetermined number of portable units
`already associated there with.
`SUMMARY OF THE INVENTION
`1. Objects of the Invention
`It is an object of the represent invention to reduce the
`amount of data that need to be transmitted by wireless
`telegraphy.
`It is a further object of the present invention to provide a
`communication System allowing improved Selection by a
`mobile unit of an access point for association.
`It is a further object of the present invention to provide a
`communication System allowing Selection by a mobile unit
`of an acceSS point to provide optimum operation of the
`System.
`It is a further object of the present invention to provide a
`communication System providing information concerning
`the physical location of a mobile unit.
`It is a further object of the present invention to provide a
`communication system adapted to prevent mobile units from
`being taken outside a given physical area.
`It is yet a further object of the present invention to reduce
`the power required by mobile units, and to improve battery
`life.
`2. Features of the Invention
`According to the present invention, there is provided a
`wireleSS communications network comprising a mobile unit
`and a base unit, a first one of Said units being arranged to
`transmit a message to a Second one of Said units, Said
`message having associated with it a coded portion repre
`Sentative of possible responses to the message, and Said
`Second unit being arranged to decode Said coded portion and
`to offer to a user a plurality of options corresponding to Said
`possible responses.
`Typically, the network will include a central base Station
`or house computer which is in communication with a
`number of hand-held units, Such as portable computer ter
`minals or bar code Scanners. In the preferred embodiment,
`messages may be transmitted from the central computer to
`one of the mobile units by transmitting an addressed mes
`Sage by wireleSS telegraphy. That message may include text
`and/or graphics, along with a coded portion defining Several
`possible answers to the message. The receiving mobile unit
`decodes the coded portion, and displays not only the mes
`Sage but also the possible options on a Screen. The user may
`then Select the option, for example by touching a touch
`Sensitive Screen, to reply. The response then goes back to the
`base unit in coded form, thereby reducing the amount of data
`that has to be transmitted acroSS the wireleSS portion of the
`network.
`Both the base unit and the mobile unit preferably include
`an information Store, Such as a hard disk and/or a random
`acceSS memory. The Stores contain common information
`
`25
`
`40
`
`1. Field of the Invention
`The invention relates generally to cellular networks. In
`particular the invention relates to a local area wireleSS
`network including a plurality of mobile units and a plurality
`of access points.
`2. Description of the Related Art
`Wireless local area networks (LANS) are used in busi
`neSS applications Such as inventory, price verification mark
`down, portable point of Sale, order entry, Shipping, receiving
`and package tracking. Such Systems are often proprietary
`Systems wherein the operator carries a mobile unit Such as
`a hand-held computer communicating with a house com
`puter via one of a plurality of access points connected to the
`35
`house computer and to one another, each access point
`interacting with the house computer to create a wireleSS cell.
`In order to achieve inter-operability of the various pro
`prietary systems a draft standard IEEE 802.11 has been
`proposed (the IEEE 802.11 draft specification is available
`for public inspection).
`The draft standard includes features such as 1 Mbps and
`2 Mbps data rates, carrier Sense multiple access/collision
`avoidance (CSMA/CA), a power-save mode for battery
`operated mobile Stations, Seamless roaming in a full cellular
`network, high throughput operation, diverse antenna SyS
`tems designed to eliminate "dead spots”, and an easy inter
`face to existing network infrastructures.
`The term "roaming relates to the Scanning by each
`mobile unit of all access points to identify and asSociate with
`an eligible access point. Roaming between cells provides
`great flexibility and is particularly advantageous in locations
`that are difficult to wire, for simple relocation of work
`stations, and for portable work stations. The IEE 802.11
`protocol Supports either direct-Sequence or frequency
`55
`hopping spread-spectrum Systems, as well as infrared com
`munications. Each access point executes a unique hopping
`pattern acroSS 79 non-overlapping frequencies at a rate of
`one hop every 100 milliseconds, 66 hopping patterns being
`specified in the IEEE 802.11 draft standard and being
`selected to minimize the possibility of interference. Fre
`quency hopping spread-spectrum Systems are preferred by
`the majority of users as they allow increased capacity and
`decreased interference.
`Although the IEEE 802.11 draft specification provides the
`basic packet types which can enable roaming it does not
`actually Set the roaming algorithm. According to the draft
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`3
`enabling coded messages to be sent and decoded in a
`previously-agreed way. In addition to the encoded informa
`tion representing possible responses to messages, it may also
`represent textual data records which are present in both the
`store of the mobile and the store of the base unit.
`In addition, in a further preferred embodiment, messages
`may be transmitted using a tree-like data Structure. Encoded
`portions of the message, understood both by the mobile unit
`and the base unit, may define the manner in which the tree
`is built up. When the mobile unit decodes these portions, it
`may display to the user, for example on a Screen, the full
`Structure of the message. This may conveniently be done by
`displaying to the user a nested Sequence of menus, each
`menu having Several user-Selectable options. Some or all of
`these options may not only allow the user to Select a
`Sub-menu, but may also activate a coded response back from
`the mobile unit to the base unit, thereby providing the base
`unit with information on which options have been selected
`by the user.
`The common information stored within the base unit and
`within the mobile unit may be user-definable and updatable.
`One way of achieving this is to provide a cradle, attached to
`the base unit, into which the mobile unit may be placed when
`it is not in use. Electrical connections on the mobile unit and
`one the cradle allow information within the mobile unit to be
`downloaded into the base unit. Similarly, information may
`be uploaded from the base unit to the mobile unit.
`Alternatively, the information store within the mobile unit
`may be removable (for example a removable read-only
`memory). The read-only memory containing one particular
`Set of encoding information may then be replaced, at will,
`with another read-only memory containing another Set. In
`that way, the mobile unit may easily be re-programmed for
`a variety of different applications.
`There may be several mobile units on the network, each
`having a different Set of encoding information. All of the
`various Sets may be maintained simultaneously at the base
`unit, and the communication between the base unit and any
`given mobile unit is then encoded according to its own
`individual information Set.
`According to a further aspect of the invention there is
`provided a mobile unit for use with a wireleSS communica
`tions network, Said unit including a radio transmitter/
`receiver and a timer for instructing Said radio to enter a
`power-saving mode after a period of no message traffic; Said
`radio automatically reverting to normal powered operation
`when a radio signal is received or is to be sent by Said radio.
`The invention also extends to a corresponding method of
`operating a mobile unit within a wireleSS communications
`network.
`According to the invention there is also provided a data
`communications network including a plurality of Stationary
`access points and a plurality of mobile units, a mobile unit
`being capable of communicating with at least two acceSS
`points in a predetermined range therefrom, comprising:
`means in the mobile unit to Scan for and associate the
`mobile unit with the most eligible access point at predeter
`mined intervals, the most eligible access point being
`Selected according to each of the following criteria:
`(a) received access point Signal quality; and
`(b) loading factor at the access point.
`Accordingly, a simple and reliable arrangement is pro
`Vided enabling preemptive roaming and optimum Selection
`of an access point for association with a mobile unit.
`Each mobile unit may Select a group of eligible acceSS
`points and Select the most eligible access point from that
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`group. The received access point Signal quality may be
`represented by the received signal Strength indication
`(RSSI). The loading factor may be defined by the number of
`mobile units associated with a given access point. The
`cellular communications network may comprise a 1 Mbps
`frequency-hopping spread-spectrum wireleSS LAN con
`forming to the IEEE 802.11 draft specification.
`Each mobile unit may send out a probe message packet to
`all access points wherein the probe packet has no destination
`address but a mobile unit Specific Source address. The probe
`packet may include an identification of the acceSS point with
`which the mobile unit is currently associated. Each acceSS
`point that detects the probe packet may send a probe
`response packet containing the following information:
`access point address,
`acceSS point frequency hopping pattern;
`access point present channel;
`time remaining in present channel;
`loading factor.
`The mobile unit may carry out its selection on the basis of
`the Signal quality of, and information contained in the
`received probe response packets or the access point Signal
`quality may be determined from a beacon Signal Sent by the
`access point independently of a probe response packet.
`Each mobile unit may store the RSSI value for each
`access point and calculate an average value over a prede
`termined period, and RSSI values outside a predetermined
`range may be omitted from the averaging calculation.
`Each mobile unit may carry out a full scan of all available
`frequency channels on power-up and thereafter at regular
`intervals. The full Scan may be carried out at approximately
`thirty Second intervals. Each mobile unit may carry out a
`partial Scan of known acceSS points at regular intervals more
`frequently than a full Scan is carried out, for example at
`approximately five Second intervals.
`Each mobile unit not associated with an access point may
`identify on Scanning all access points with Signal quality
`equal to or above a threshold value and Select for association
`the access point having the lowest loading factor; when two
`or more access points have an equal lowest loading factor
`the access point having the highest RSSI value may be
`selected. The threshold value may be set at six counts below
`the highest detected RSSI value.
`A mobile unit associated with an access point and expe
`riencing an unacceptably low communication level may
`roam excluding the current access point from Selection. The
`unacceptably low communication level may be achieved
`when more than 50% retries, CRC errors or missed beacons
`are experienced. The excluded access point may be
`re-included for selection when its RSSI value has increased
`by a predetermined limit. If not eligible access points are
`identified for re-association the mobile unit may continue to
`asSociate with the current access point.
`A mobile unit associated with an access point and achiev
`ing a Satisfactory level of communication may make a
`Scanning decision at predetermined intervals. A Satisfactory
`communication level may be achieved when 50% or less
`retries, CRC errors or missed beacons are experienced. An
`eligible groups may be selected comprising all access points
`with Signal quality above a predetermined threshold, the
`group including the current access point when its signal
`quality is above a further predetermined threshold, and the
`access point may be Selected having the lowest loading
`factor, access points having a loading factor of more than a
`given proportion of the current access point loading factor
`may be excluded and where two or more access points have
`
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`25
`
`S
`the same loading factor, the access point having the highest
`Signal quality may be Selected. The eligible group threshold
`value may be six counts below the highest received RSSI
`value, the current access point further threshold value may
`be eleven counts below the RSSI value, and access points
`having a loading factor of more than 75% of the current
`access point loading factor may be excluded.
`Each mobile unit may carry out a partial Scan of known
`access points at predetermined intervals and may carry out
`the roaming decision immediately after the partial Scan.
`The communications network may be included in one of
`an inventory, price verification, mark-down, portable point
`of Sale, order entry, Shipping, receiving and package tracking
`Systems.
`According to the invention there if further provided a
`mobile unit for use in a cellular communications network
`comprising a plurality of access points, the mobile unit
`including a communications System for association with an
`access point and a Selection System for Scanning all acceSS
`points, Selecting a group of eligible access points for asso
`ciation and Selecting from that group a most eligible acceSS
`point, Selection being carried out according to the following
`criteria:
`a received acceSS point signal quality; and
`loading factor.
`According to the invention there is further provided a
`cellular communications network comprising a plurality of
`mobile units and a plurality of access points, the mobile unit
`being arranged to roam and associate with a Selected acceSS
`point, the mobile unit including a Selection System for
`Selecting a group of eligible access points for association
`and Selecting form that group the most eligible access point,
`Selection being carried out according to the following cri
`teria:
`received access point Signal quality; and
`loading factor.
`According to the invention there is further provided a
`method of operation of a cellular communications network,
`the network including a plurality of access points in com
`munication with each other and a plurality of mobile units
`40
`wherein:
`each mobile unit Scans for and asSociates with the most
`eligible access point at predetermined intervals, each mobile
`unit Selecting a group of eligible access points and, from that
`group, Selecting the most eligible access point according to
`the following criteria:
`received access point Signal quality; and
`loading factor.
`According to the invention there is yet further provided a
`data communications network including a plurality of Sta
`tionary acceSS points and a plurality of mobile units wherein:
`each mobile unit Scans for and Selects as eligible acceSS
`point for association there with on the basis of received
`access point Signal quality and loading factor at the acceSS
`point and wherein:
`a physical area is defined within which all mobile units
`must be kept and access points are provided adjacent the or
`each exit point from the physical area.
`The access point at the exit point may include a direc
`tional (horn) antenna providing a strong signal in the vicinity
`of the exit point.
`The novel features which are considered as characteristic
`of the invention are Set forth in particular in the appended
`claims. The invention itself, however, both as to its con
`Struction and its method of operation, together with addi
`tional objects and advantages thereof, will best be under
`stood from the following description of a Specific
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`embodiment, when read in conjunction with the accompa
`nying drawings. It is to be understood that the invention may
`be carried into practice in a number of ways, and the
`described embodiment is not intended to be limiting.
`BRIEF DESCRIPTION OF THE DRAWING(S)
`FIG. 1 is a schematic view of a radio terminal Suitable for
`use in a preferred embodiment of the present invention;
`FIG. 1A shows an exemplary Structured message that may
`be received by the unit of FIG. 1;
`FIG. 1B shows one preferred form in which the message
`of FIG. 1A may be transmitted over the wireless link;
`FIG. 2 shows an alternative embodiment to that shown in
`FIG. 1;
`FIG. 2B shows, schematically, the functional elements
`that make up the radio terminals shown in FIGS. 1 and 2;
`FIG. 3 is a Schematic illustration showing the communi
`cation System of the preferred embodiment in operation;
`FIG. 4 is a block diagram illustrating the Steps carried out
`by a mobile unit during the roaming process,
`FIG. 5 is a flow chart illustrating the steps carried out by
`a mobile unit for Selection of the most eligible access point;
`FIG. 6 shows a probe response message typically Sent by
`an acceSS point according to the present invention; and
`FIG. 7 is a schematic illustration showing a further
`embodiment of the communication System of the present
`invention.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`Turning first to FIG. 1, there is shown a portable radio
`terminal Suitable for use as a mobile unit in a preferred
`embodiment of the invention. The radio terminal or mobile
`unit 30 has a housing 32 of a suitable size either to be
`hand-held, or to be attached to a user's wrist or forearm by
`means of a rear Strap (not shown). The front of the housing
`has a touch Sensitive Screen 34 which is used not only to
`display information, but also to input data, for example by
`preSSure of the user's finger or of a pen on the Screen Surface.
`The unit includes a radio transmitter/receiver 35 and a
`laser-based optical Scanning mechanism, both contained
`within a generally spherical rotational housing 36. The
`optical Scanning mechanism produces a one-dimensional or
`two-dimensional pattern of Scanning laser light, which
`leaves the housing 36 via an aperture 38. The laser light
`impinges upon an indicia to be read (not shown), for
`example a bar code, and is reflected back to the mobile unit
`30 where it is detected. The radio transmitter/receiver is
`arranged to communicate with a base unit or backbone
`house computer 4, shown schematically in FIG. 3. The
`house computer 4 may include one or more data entry
`terminals or Screens 4a, and a hard disk or other data Storage
`device 4b.
`The mobile unit 30 remains in wireless communication
`with the house computer 4 via the radio-transmitter/receiver
`35. This may receive and transmit not only textual data,
`entered via the touch-Sensitive Screen 34, but also data
`representing a bar code which has been Scanned by the
`optical Scanning mechanism 37.
`In the preferred embodiment of the invention, the mobile
`unit 30 includes a fixed or removable memory 49; if the
`memory is designed to be removable, a slot 48 in the housing
`is provided for that purpose. The unit also includes an
`electrical connection 46 allowing the information in the
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`Ex. 1013 / Page 11 of 17
`ERICSSON v. UNILOC
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`memory 49 to be downloaded to the house computer 4 when
`the unit is returned to a docking station 4c (FIG. 3).
`Additionally, the information stored in the memory 49 may
`at that State be updated under control of the house computer
`4
`
`In addition, the mobile unit 30 includes an LED 40, and
`a miniature Speaker 42.
`FIG. 2 shows an alternative embodiment which differs
`from the embodiment of FIG. 1 merely by having a series of
`true buttons, or a keyboard 44'.
`FIG. 2B shows, in purely schematic form, the major
`Structural elements that go to making up a mobile unit of the
`type shown in FIG. 1 or FIG. 2. Each of the elements is
`known per Se, and it will be evident to a skilled man in the
`art how to link them into a unit which operates as described.
`As shown in FIG. 2B, the mobile unit has two basic
`portions, a radio Section generally indicated at 50 and a
`terminal Section generally indicated at 52. These two Sec
`tions communicate with each other via an interface 54.
`The radio section 50 incorporates a radio transmitter/
`receiver 56 and an aerial 58 for communicating with a
`remote access point 5 (FIG. 3).
`The terminal Section 52 includes a random acceSS
`memory 60, a screen 62, a CPU 64 and an optional keyboard
`66. In addition, for Scanning operations, the Section is
`provided with a Scanning mechanism 68 and a laser and
`optics assembly 70 for producing an outgoing Scanning laser
`beam 72. The reflector beam is detected by a photodiode 74.
`All of these devices are operated by a main battery 76.
`The CPU 64 includes a clock 78. A further CMOS clock
`80 is also provided, which has its own battery 82.
`Accordingly, the unit is capable of keeping track of the time
`even when the CPU 64 is powered down.
`In the preferred embodiment, the mobile unit 30 may
`double as a personal pager, with messages and other infor
`mation being transmitted to and from the house computer 4.
`In a typical prior art pager, messages are transmitted in
`textual form, both to and (if the pager has the capability)
`from the remote unit. The embodiment shown in FIG. 1
`however, has an additional capability which may signifi
`cantly reduce the amount of information that has to be
`transmitted acroSS the wireleSS link.
`In the preferred embodiment, common coded information
`is stored both within the memory 49 of the mobile unit, and
`centrally on the house computer 4, for example on the hard
`disk 4c. This enables textual information to be transmitted b
`way of Short codes, with both the transmitting unit and the
`receiving unit being party to the same code protocol.
`For example, if a user wishes to Send a message from the
`house computer 4 to a mobile unit 30, he simply types the
`message to be sent on the terminal 4a. Attached to the
`message may be a Series of codes A,B,C which represent
`possible responses to the message. In the example shown in
`FIG. 1, the message is "please confirm meeting time', with
`the possible responses being A-6 pm; B-7pm, C-8 pm. On
`receipt of the codes A,B,C, the mobile unit decodes them
`using information stored within the memory 49, and dis
`plays the corresponding text on the Screen 34. In addition,
`the screen may also display virtual “buttons' 44 that the user
`may press to respond to the message. For instance, if the user
`wishes to confirm that the meeting time is 6 pm, he simply
`presses the Screen at the position shown by the virtual
`“button’ A, which instructs the radio-transmitter/receiver 35
`to Send a coded A Signal back to the house computer 4.
`It will of course be understood that in a practical
`embodiment, the codes A,B,C will be encoded bit-wise for
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`35
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`40
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`6,002,918
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`wireleSS transmission. The three buttons shown accordingly
`require the transmission of just two bits of information
`acroSS the wireleSS link. It is of course envisaged that there
`may be more or fewer than three buttons, and that the
`number of buttons may be selected by the perSon Sending the
`message. In a further development, the message Sent may be
`represented by a tree-like data Structure; this is shown in
`FIG. 1A. In that example, the message appearing on the
`user's Screen is “is the meeting Still on?', along with two
`options: A-YES and B-NO. If the user selects A, a further
`message appears-“please confirm time'-along with three
`further options: C-7 pm, D-8 pm and E-9 pm. The user then
`Selects either C, D or E and a coded message is Sent back to
`the house computer which is there decoded according to the
`information stored on the hard disk 4b. On the other hand,
`the user may select option B, in which case the coded
`message is sent back informing the house computer that the
`meeting has been cancelled.
`FIG. 1B shows one form in which the message structure
`shown in FIG. 1A may be transmitted from the house
`computer 4 to the mobile unit 30. The message 100 starts
`with a header 101, an identifier 102 which identifies the
`particular mobile unit that the message is directed to, fol
`lowed by the first textual part of the message 103. Linking
`information 104 follows, which defines where the textual
`part 103 is linked to the options to be presented to the user
`at that point. That is followed by coded information A 105
`and B 106, representing respectively “YES” and “NO”.
`Further linking information 107 follows, which indicates
`how the next textual message 108 is to linked to the data
`Structure previously defined. Further linking information
`follows, specifying how the textual information 108 is to be
`linked to the Subsequent codes C 110, D 111 and E 112.
`Other equivalent message Structures could of course be
`devised by those skilled in the art.
`In a practical embodiment, there will of course be Several
`individual mobile units 30, each with its owe identifier.
`Messages transmitted by the wireleSS System may be
`addressed to a particular unit by means of the ID 102 (FIG.
`1b). Since each unit decodes only messages which are
`intended for it, it is possible for different units to use a
`different Series of codes A,B,C and So on when communi
`cating with the house computer 4. The house computer 4 in
`that event maintains information Simultaneously on Several
`different encoding protocols, and chooses the appropriate
`protocol according to the particular mobile unit that is to be
`addressed, or from which a message has been received.
`FIG. 2 shows an alternative mobile unit 30', which is
`identical with the unit of FIG. 1 except that the user responds
`by pressing one of a Series of true buttons 44 on the housing
`32. In this embodiment, the screen 34 needs to indicate
`Specifically to the user which button represents which
`response the buttons 44 may be in addition to or may
`comprise a form of the numeric keyboard.
`Referring now to FIG. 3, there is shown a further appli
`cation of a cellular