` (43) International Publication Date:©26 November 1992 (26.11.92)
`
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`
`(51) International Patent Classification 5 ;
`
`H04Q 7/00
`
`(11) International Publication Number:
`
`WO 92/21214
`
`PCT
`
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`International Bureau
`
`
`
`(21) International Application Number: PCT/US92/02536|(74) Agents: NICHOLS, Daniel, K. et al.; Motorola, Inc., In-
`tellectual Property Department, 8000 West Sunrise
`Boulevard, Ft. Lauderdale, FL 33322 (US).
`
`(22) International Filing Date:
`
`30 March 1992 (30.03.92)
`
`(30) Priority data:
`2
`
`17 May 1991 (17.05.91)
`
`US
`
`(71) Applicant: MOTOROLA, INC. [US/US]; 1303 E. Algon-
`quin Road, Schaumburg, IL 60196 (US).
`
`; 9324 N.W. 18th Street,
`(72) Inventors: PATSIOKAS,Stelios, J.
`Plantation, FL 33322 (US). D'AMICO, Thomas, V.
`;
`2707 North Ocean Boulevard #302, Boca Raton, FL}
`33431 (US). SUTER, Charles, D.
`; 4408 Main Street,
`Lake Worth, FL 33461 (US). POMBO,Raul, A. ; 8361-D
`Trent Court, Boca Raton, FL 33433 (US).
`
`
`
`(81) Designated States: AT (European patent), AU, BE (Euro-
`pean patent), BR, CA, CH (European patent), DE, DE
`(European patent), DK (European patent), ES (Euro-
`pean patent), FI, FR (European patent), GB (European
`patent), GR (European patent), HU, IT (European pa-
`tent), KR, LU (European patent), MC (European pa-
`tent), NL (European patent), NO, SE (Europeanpatent).
`
`Published
`With international search report.
`
`(54) Title: CHANNEL ACQUISITION METHOD AND APPARATUS FOR A COMMUNICATION SYSTEM
`
`
`
`
`
`BSi
`
`<A
` COVERAGE
`
`COVERAGE
`AREA
`AREA
`OF BS1
`OF BS2
`
`
`(57) Abstract
`
`A method and apparatus whereby a communication unit (10) transmits a communication channel request and the nearest
`base site (12) makes the communication channel grantor allocation. A basesite receives the channel request signal, measures the
`received signal strength (RSSI) level of the received signal, and if that level is above a thresholdlevel, a communication channel
`is allocated to the requesting communication unit, thus establishing a communication link. If the channel request signal does not
`have an RSSIlevel above the threshold, the base site delays the grant of a communication channel for a period inversely propor-
`tional to the measured RSSI level to allow other base sites the opportunity to grant a communication channel to the requesting
`communication unit. If the base site determines that another basesite has granted a communication channel to the requesting
`communication unit, the allocation process is stopped, and the base site continues scanning for channel request signals.
`
`1
`
`APPLE 1007
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`1
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`APPLE 1007
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`

`FOR THE PURPOSES OF INFORMATION ONLY
`
`Codes used to identify States party to the PCT on the front pages of p
`applications under the PCT.
`
`amphlets publishing international
`
`United States of America
`
`finland
`France
`Gabon
`United Kingdon
`Guinea
`Greece
`Hungary
`ireland
`aly
`Japan
`Democrauc People’s Republic
`of Korea
`Republic of Korea
`Licehtenstein
`Sri Lanka
`Luacmbourg
`Monaro
`Madagastar
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`AT
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`88
`BE
`BF
`BG
`BJ
`BR
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`Austria
`Australia
`Barbados
`Belgium
`Buckina Fase
`Bulgaria
`Benin
`Brasil
`Canada
`Centeal Afeican Republic
`Congo
`Switeerland
`C6te dane
`Cameroon
`Crcchoslovakia
`Geacmany
`Denmark
`Spats
`
`Mali
`Atangolia
`Mauritania
`Malawi
`Netherlands
`Norway
`Pulaund
`Romania
`Russian Federation
`Sudan
`Sweden
`Senegal
`Soviet Union
`Chad
`Togo
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`WO 92/21214
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`PCT/US92/02536
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`10
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`CHANNEL ACQUISITION METHOD AND APPARATUS
`FOR A COMMUNICATION SYSTEM
`
`hnical
`
`Fi
`
`15
`
`This invention relates generally to communication systems
`and more specifically to radio telephone communication sysiems .
`
`Background
`Radio telephone communication systems (such as second
`generation cordless telephone, or Digital European Cordless
`Telephone) comprise a plurality of base sites (also known as
`telepoints) and a plurality of radio telephones (also known as
`handsets). Taking second generation cordless telephone (CT2)
`as an example, the users of the CT2 radio telephones
`communicate with users of other radio telephones or subscribers
`in a public switched telephone network (PSTN) via the base
`points. A large numberof base points is desirable in certain
`areas (such as shopping malls) where many personsare likely to
`place radio telephone calls because that eliminates gapsin
`coverage by the base site network. However, these basesites
`are not synchronized with each other. When a radio telephone
`user wishesto place a call, he or she causesthe radio telephone
`unit to transmit a channel request signal. Since each basesite is
`monitoring the channels of the CT2 system independently, the
`basesite that grants the channel request is not necessarily the
`one closest to the radio telephone unit transmitting the channel
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`request signal. That may be a problem because the user may
`moveout of range of the basesite, thus causing the
`communication link to be dropped. On the other hand,if the
`nearest base station had made the channel grant, the radio
`telephone user would have been able to continue the
`communication while moving in a greater area. Accordingly, a
`need exists for a method and apparatus for acquiring a
`communication channelthat overcomes the above problem.
`
`10
`
`Summary_of the Invention
`Briefly, according to the invention, a method and apparatus
`are provided whereby a communication unit transmits a
`communication channel request and the nearest basesite makes
`the communication channel grant. A basesite receives the
`channel request signal, measures the received signal strength
`15
`(RSS)levelof the received signal, and if that level is aboveafirst
`threshold level, a communication channelis granted to the
`requesting unit, thus establishing a communication link. Then,
`the base site maintains the communication link as long as RSSI
`level does not drop below a second threshold level that is
`substantially lower than thefirst threshold level.
`
`20
`
`Brief Description of the Drawings
`FIG. 1 is a simplified block diagram of a communication
`system in accordance with the invention.
`FIG. 2 is a simplified block diagram of a basesite in
`accordance with the invention.
`FIG. 3 is a flow chart of a channelacquisition methodin
`accordance with the invention.
`FIG. 4 is a flow chart of another channel acquisition method
`in accordance with the invention.
`
`Detailed Description of the Preferred Embodiment
`Referring to FIG. 1, there is shown a simplified block
`diagram of a communication system in accordance with the
`invention. A communication unit 10 (preferably, a radio
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`telephone) operates in a CT2 communication system that
`comprises at least first and second base sites, 12 and 14,
`respectively. The system may also comprise several other base
`sites, communication units, and a public switched telephone
`network (PSTN) 16. The communication unit 10 is closer to the
`first base site 12 than to the second basesite 14. When the user
`
`In
`
`of the communication unit 10 wishes to make a call, he or she
`causes the communication unit to transmit a channel request
`signal (which includes the unit's identification number) requesting
`a communication channel. The communication unit 10 is within
`the coverage areas(i.e., ranges) of both the first base site 12 and
`the second basesite 14. Thus, in a conventional CT2 system,
`either of the base sites could grant a communication channel to
`the communication device, establishing a communication link.
`the event that the second basesite 14 is the first to receive the
`channelrequestsignal, it would grant the channelto the
`communication unit 10. That would create a problem for the user
`of the communication unit 10 because if the user moves any
`further away from the second basesite 14, the unit would move
`out of the range of the second basesite 14 and consequently the
`communication link would be lost. However, in accordance with
`the invention the first base station 12 would be the one granting
`the communication channel to the communication unit 10, thus
`solving the problem that would have been caused by a more
`distant base site granting the communication channel.
`Referring to Figure 2, a public basesite (or wireless
`phonebooth) 20, in accordance with the invention, is shownin
`block diagram form. Each of the componentsof the base site 20
`represented by a block is conventional. The basesite 20, which
`is coupled to a network controller 38, comprises a radio
`transceiver 30, an RSSI detector 32, and a memory 36for storing
`information (including the identification numbers corresponding to
`communication units sending channel request signals, and
`memory templates containing information relating to subscribers).
`The RSSI detector 32 is used to determine the RSSI level of
`signals received by the base site 20. The basesite 20 also
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`
`includes a controller 38 (e.g., a conventional microprocessor)
`which is capable of scanning the CT2 channels to searchfor
`channel request signals. The controller 38 also includesthe
`capability for determining whether received signals have received
`signal levels (or strengths) at predetermined thresholds and may
`also include digital signal processing (DSP) capabilities for
`turning voice signals into digital form and processing those
`signals using well-known DSP methods. A module 40 provides
`call authentication andstatistic functions for the base station 20,
`and a service command module processes requests for services
`and informs the network controller 18 what services are required.
`A PSTNinterface module 34 provides an interface with the public
`switched telephone network 16 (shownin FIG.1).
`The base station 20 enables a communication unit to
`communicate with other communication units within the same or
`other communication networks, and to acquire access to anyof
`the information and services available through the network
`controller. Moreover, since the base station 20 has its own
`memory, memory templatesrelating to a subscriber may be
`transferredtoit, thus allowing the base station 20 to provide the
`requested services and/or information to the requesting
`subscriber without a continuous coupling to the network
`controller.
`Referring to FIG. 3, there is shown a flow chart of a channel
`acquisition method in accordance with the invention.
`In step 100,
`a basesite (e.g., base site 20) scans the CT2 channels for
`channelrequest signals.
`In decision 102, the base site
`determines whether a channelrequest signalis detected. The
`base site detects channel request signals having an RSS!level at
`or aboveafirst threshold. Thefirst threshold correspondsto the
`30
`full sensitivity of the base site.
`If the base site detecis a channel
`requestsignal in decision 102, then a further decision 104 is
`made ia determine whetherthe RSSIlevel of the channelrequest
`signal is above a predetermined threshold level. The
`predeterminedthresholdlevel is a predetermined value of
`decibels above the maximum sensitivity level of the basesite.
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`That value is selected in accordance with the desired distance
`
`from the base site on which the communication channel is
`granted. For example, a cistance of 15 meters orless from the
`granting base station may be desired.
`If the base site determines,
`in decision 104, that the RSSI level is at or above the second
`threshold,in step 106 it grants a channel to the requesting
`communication unit, thus establishing a communication link
`between the base site and the communication unit. The
`communication link is maintained as long as the signals received
`from the communication unit do not drop belowthefirst threshold.
`The basesite then continues scanning at full sensitivity.
`Referring to FIG. 4 there is showna flow chart of another
`channel acquisition method in accordance with the invention.
`In
`step 200 the base site scans for channel request signals. A
`decision 202 is then made as to whethera valid channel request
`is detected (i.e., one containing the appropriate digital
`information). The base site continues to scan until a valid
`channel request signal is detected .
`In step 204, when the base
`site receives a channel request on a specific channel, it reads the
`RSS! of the received channel request signal. A decision 206 is
`then made as to whether the RSSI level measuredin step 204is
`below a predetermined threshold level. The predetermined
`threshold correspondsto the maximum distance from the base
`site required for establishing a communication link with that base
`site.
`If the RSSI is not below the threshold (i.e., it is at or above
`the threshold), a channel is granted to the requesting
`communication unit (step 208).
`If the measured RSSI is below
`the threshold, a decision 210 is made as to whether the
`identification number of the requesting communication unit has
`been stored. The identification number is included in the channel
`request signal.
`!f the communication unit's identification number
`is not stored in the base site memory,the controller in the base
`calculates a delay time in step 212. The delay time is inversely
`proportional to the measured RSSI level. Thus, the higher the
`RSSI level, the shorter the delay.
`In decision 218 it is determined
`whether the delay time period has expired.
`If it has expired, the
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`identification number(ID) of the requesting communication unit is
`stored in the base site memory in step 222, and the channel
`allocation process returns to step 200.
`If the delay time period
`has not expired, a decision 220 is made to determine whether a
`communication channel has been granted to the requesting unit
`by another base site or by another transceiver within the same
`base site. The basesite may dothis by detecting the
`synchronization data(i.e., the handshakeinformation) transmitted
`by the communication unit when a channel has been grantedioit.
`In decision 210,if it is determined that the ID of the
`communication unit has been stored, then a decision 214 is made
`to determine whether a communication channel has been
`granted to the requesting communication unit by a second base
`site unit.
`If the channel was not granted, a channel grant is sent
`(224) to the communication unit.
`lf decision 214 determines that
`the channel was granted, the communication unit ID is cleared
`from memory, and the channelallocation process returns to step
`200.
`,
`Similarly, other base sites close enough to receive the
`channel request signals perform the above method. When one
`base site is closer to the requesting communication device than
`another, the closer base site has a shorter delay so thatit will
`establish the communication link earlier than the more distant
`base. Oncethefarther base site detects the communication link
`between the communication unit and the closer basesite (e.g., by
`detecting synchronization signals)it will not attempt to grant a
`communication channelto the communication unit. Therefore,
`the longerdelay of the secondbasesite allows the first base site
`to establish the desired communication link, and the problems
`arising from a moredistant base site granting the channel request
`have been solved.
`
`Whatis claimedis:
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`Claims
`1.
`In a communication system having a plurality of base sites
`capable of allocating a communication channel for use by a
`communication unit in response to a request from the
`communication unit, and any of the base sites receiving the
`request being capable of allocating the communication channel
`without regard to the availability of a base site closer to the
`requesting communication unit, a method facilitating the use of a
`particular base site comprising the stepof:
`allocating a communication channel to the communication
`unit requesting the communication channel after determining that
`other basesites have not allocated the communication channel to
`
`the communication unit requesting the communication channel.
`
`10
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`2. In acommunication system havingaplurality of base sites
`
`capableof allocating a communication channel for useby a
`communication unit in response to a request from the
`communication unit, and any of the basesites receiving the
`request being capable ofallocating the communication channel
`without regard to the availability of a basesite closerto the
`requesting communication unit, a methodfacilitating the use of a
`particular base site comprising the steps of:
`(a) determining whether a communication channelis
`available for allocation to a communication unit requesting the
`communication channel; and
`(b) allocating the communication channelto the
`communication unit requesting the communication channel after
`determining that other base sites have not allocated the
`communication channelto the communication unit requesting the
`communication channel whenit is determined that the
`communication channel is available.
`
`15
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`9
`
`10
`
`In a communication system comprising a plurality of
`3.
`communication units and base sites, a methodforallocating
`communication channels comprising the steps of:
`with one of the communication units:
`(a) transmitting a channel request signal requesting a
`communication channel;
`,
`with one of the basesites:
`(b) receiving the channel request signal, the channel
`request signal having a received signal strength level;
`(c) measuring the received signal strength level of the
`channel request signal;
`(d) granting a communication channel to the
`communication unit that transmitted the channel request signal
`when the received signal level is aboveafirst threshold to
`15
`establish a communication link with the communication unit;
`(e) measuring the received signallevel of signals received
`from the communication unit; and
`(f) maintaining the communication link as long as the
`received signal level of signals received from the communication
`unit is above a second threshold level having a value
`substantially lower than the value of thefirst threshold level.
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`4, Inacommunication system comprising a plurality of
`communication units and basesites, a method for allocating
`communication channels comprising the steps of:
`-
`"
`with one of the base sites:
`(a) scanning for channel request signals;
`(b) detecting a channel request signal from a
`communication unit, the channel request signal having a received
`signal strength level;
`(c) measuring the received signal strength level of the
`channelrequestsignal received from the communication unit;
`and
`
`(d) granting a channelto the communication unit, and
`establishing a communication link with the communication unit,
`whenthe received signallevel is above a predetermined
`threshold level.
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`5. The method forallocating communication channels of
`claim 4, comprising the step of:
`.
`,
`(e) continuing scanning for channel request signals.
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`6. Ina communication system comprising a plurality of
`communication units and basesites, a methodfor allocating
`communication channels comprising the steps of:
`-
`"
`with one of the basesites:
`(a) scanning for channel request signals;
`(b) detecting a channel requestsignal having a received
`signal strength level, from a communication unit, the channel
`request signal including an identification number corresponding
`to the communication unit;
`,
`(c) measuring the received signal strength level of the
`channel requestsignal;
`(d) determining whether the channel request signal has a
`received signal strength level above a predetermined threshold;
`(e) granting a communication channel to the
`communication unit, when the channel request signal has a
`received signal level above the predetermined threshold;
`(f) determining whetherthe identification number has been
`stored;.
`(g) calculating a delay time interval whenthe identification
`numberhas not been stored;
`(h) determining whetherthe delay time period has expired;
`(i) storing the identification number, whenthe time period
`expires;
`(j) determining whether a communication channel has
`beenallocated to the communication unit;
`(k) returning to step (a) whenit is determined in step (j) that
`a communication channel has been allocated to the
`communication unit; and
`(l) returning to step (h) when a communication channel
`has not been allocated to the communication unit.
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`7. The methodfor allocating communication channels of
`claim 6, further comprising the following steps following step(f):
`(f1) determining whether a communication channel has
`been allocated to the communication unit, when the identification
`
`number has beenstored;
`(f2) allocating a communication channel to the
`communication unit, when it is determined in step (f1) that a
`communication channel has not been allocated to the
`
`communication unit.
`
`8. The methodfor allocating communication channels of
`claim 7, further comprising the steps of:
`(f3) clearing the identification number that wasstored,
`whenit is determined in step (f1) that a communication channel
`has been allocated to the communication unit; and
`(f4) returning to step (a).
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`9, Abasesite, for establishing communication links with
`communication units, comprising:
`means for scanning for channel request signals;
`meansfor detecting a channel request signal from a
`communication unit, the channel request signal having a received
`signal strength level;
`°
`means for measuring the received signal strength level of
`the channel request signal received from the communication unit;
`and
`
`meansfor granting a channel to the communication unit,
`and establishing a communication link with the communication
`unit, when the received signal level is above a predetermined
`threshold level.
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`Ae
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`COVERAGE
`AREA
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`OF BS1
`
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`COVERAGE
`AREA
`OF BS2
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`RF eo PSTN 7 TO
`
`INTERFACE
`MODULE
`
`PSTN
`16
`
`PUBLIC BASE SITE
`
`TRANSCEIVER
`
`CALL
`AUTHENTICATION
`AND
`STATISTICS
`
`CONTROLLER
`
`SERVICE
`COMMAND
`MODULE
`
`20
`
`LIG.2
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`100
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`106
`
`SCAN FOR CHANNEL
`REQUEST SIGNALS
`
`102
`
`
`RSSI_ AT
`
`PREDETERMINED
`LEVEL
`
`
`
`
` CH. REQ.
`DETECTED
`
`
`
`
`GRANT COMMUNICATION
`LINK AND CONTINUE
`OPERATION AT FULL
`SENSITIVITY
`
`
`
`
`
`FTG. 3
`
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`200
`
`SCANNING FOR
`CHANNEL REQ.
`SIGNALS
`
`SIGNAL
` 216
`
`214
`YES
`
`/
`
`
`202
`€H. REQ™<
`
`20
`
`20
`
`

`

`
`..wermational application No.
`INTERNATIONAL SEARCH REPORT
`PCT/US92/02536
`
`
`
`A.
`CLASSIFICATION OF SUBJECT MATTER
`IPC(S)
`:H04Q 7/00-*
`US CL :455/34t ~
`
`Accordingto International Patent Classification (IPC) or to both nationalclassification and IPC
`
`Minimum documentation searched (classification system followed byclassification symbols)
`
`
`U.S.
`:
`455/33.1,33.2,33.454.1,54.2,56.1; 379/59,60
`
` Documentation searched other than minimum documentationto the extentthat such documents are included in the fields searched
`
`
`
`
`Electronic data base consulted during the international search (name of data base and, where practicable, search terms used)
`
`DOCUMENTS CONSIDERED TO BE RELEVANT
`
`US, A, 5,050,234 (OHTERU) 17 September 1991, See Abstract, col. 2, lines 20-60.
`
`
`
`US, A, 4,881,271 (YAMAUCHI ETAL.) 14 November 1989, See col. 6, lines 4-47.
`
`
`
`
`
`
`
`
`
`
`
`Y,P
`
`Y Y Y
`
`CT]
`
`"0"
`
`
`
`| See patent family annex. Specialcategories ofcited documents:
`
`US, A, 4,485,486 (WEBB ET AL.) 27 November 1984, See Abstract.
`
`US, A, 4,783,780 (ALEXIS) 08 November 1988, See col. 11, lines 27-61.
`
`Further documents are listed in the continuation of Box C.
`
`
`
`
`sys
`
`Interdocumentpubtebedsit the international filing date or pricrity
`not in conflictwith the application but cited to understand the
`documentdefiningthe generalsate ofthe art which is notconsidered
`“A
`incipie
`underlying
`the i
`‘
`
`
`to be part of underlyingtheinventionprinciple or theory
`ere
`:
`.
`.
`document of particular relevance; the claimed invention cannot be
`“x°
`E
`earlier documentpublished on or after the international filing date
`considerednovel or cannotbe considered to involve an inventivestep
`od
`document which may throw doubts on priority claim(s) or which is
`when the document
`taken alone
`Cited to establish the
`publication date of another citation or othe:
`resist reason (ne specified)
`7
`document of particular relevance; the claimed invention cannot be
`considered to involve an inventive step when the document is
`document referring to an oral disclosure, use, exhibition or other
`combined with one ot more other such documents, such combination
`means
`being obvious to a person skilled in the art
`
`*P’ documentpublished prior to the international filing date but laerthan=-g,* document member of the same patent fumily
`
`
`
`
`the priority date claimed
`
`
`
`Date ofthe actual completion of the international search
`Date of mailing of the international search report
`SUG IE
`
`
`16 JULY 1992
`
`Authorized officer
`
`Name and mailing address of the ISA/
`Box PCT
`. oun: HES
`
`er
`Commissioner of Patenu and Trademarks
`w
`Ry
`Wathingwon, D.C. 20231
`fy EDWARD URBAN
`INTERNSTIONALBEVESY
`
`
`
`
`Facsimile No. NOT APPLICABLE Telephone No._(703) 305-4385
`
`
`
`
`Form PCT/ISA/210 (second sheet)(July 1992)x
`
`21
`
`21
`
`