(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2003/0100328A1
`(43) Pub. Date:
`May 29, 2003
`Klein et al.
`
`US 2003O100328A1
`
`(54) TRANSMIT POWER CONTROL FOR
`MOBILE UNIT
`(76) Inventors: John Klein, Morgan Hill, CA (US);
`Richard Montgomery, Saratoga, CA
`(US); Dong Nguyen, Sunnyvale, CA
`(US); Andrew Werback, San Jose, CA
`(US); William Kellogg, San Jose, CA
`(US); Wayne Ouchida, Mountain View,
`CA (US); Graham Melville, Morgan
`Hill, CA (US)
`Correspondence Address:
`BAKER & BOTTS
`30 ROCKEFELLER PLAZA
`NEW YORK, NY 10112
`
`(21) Appl. No.:
`(22) Filed:
`
`09/996,514
`Nov. 28, 2001
`Publication Classification
`
`(51) Int. Cl." ....................................................... H04B 7/00
`(52) U.S. Cl. .............................................. 455/522; 455/69
`
`(57)
`ABSTRACT
`In a wireleSS local area network which includes access point
`having variable transmitter power levels, transmitter power
`data is Sent from the access points to the mobile units and
`used by the mobile units in order to provide a corresponding
`variation in the transmitter power of the mobile unit.
`
`MU
`
`ROAMING DECISION
`
`RECEIVE BEACONS
`AND SELECTAP
`
`
`
`SET POWER LEWEL
`SING BEACON DAT
`
`
`
`
`
`AP
`
`TRANSMIT BEACON WITH
`POWER DATA
`
`
`
`
`
`REQUESTASSOCATION
`
`
`
`PROCESS ASSOCATION
`REQUEST
`
`Hewlett Packard Exhibit 1009, Page 1 of 6
`Hewlett Packard Enterprise Company v. Intellectual Ventures II LLC
`IPR2021-01377
`
`

`

`Patent Application Publication May 29, 2003. Sheet 1 of 2
`
`US 2003/0100328A1
`
`al OA
`
`GD
`
`AP
`
`B
`
`OC
`
`4B
`
`C
`
`1.
`
`1E
`
`F
`
`GD-
`
`OD
`
`
`
`Hewlett Packard Exhibit 1009, Page 2 of 6
`Hewlett Packard Enterprise Company v. Intellectual Ventures II LLC
`IPR2021-01377
`
`

`

`Patent Application Publication May 29, 2003 Sheet 2 of 2
`
`US 2003/0100328A1
`
`3)
`
`MOBILE
`DEWICE
`
`
`
`FIG. 3
`
`MU
`
`ROAMING DECISION
`
`
`
`
`
`
`
`RECEIVE BEACONS
`AND SELECTAP
`
`SET POWER LEWEL
`SING BEACON DATA
`
`
`
`REQUESTASSOCATION
`
`FIG. 4
`
`AP
`
`TRANSMIT BEACON WITH
`POWER DATA
`
`PROCESS ASSOCATION
`REQUEST
`
`Hewlett Packard Exhibit 1009, Page 3 of 6
`Hewlett Packard Enterprise Company v. Intellectual Ventures II LLC
`IPR2021-01377
`
`

`

`US 2003/0100328A1
`
`May 29, 2003
`
`TRANSMIT POWER CONTROL FOR MOBILE
`UNIT
`
`BACKGROUND OF THE INVENTION
`0001. This invention relates to wireless local area net
`works (WLAN) and particularly, to avoidance of radio
`interference in Such networks. AS data rates of WLAN
`Systems increase, more access points are required and the
`effective range of a higher data rate Signals between the
`access point and mobile units is reduced. In order to provide
`sufficient high bandwidth connectivity for mobile units, the
`density of access point population is increased, particularly,
`in areas in which a high number of mobile units are
`anticipated. The close distribution of access points is Some
`times referred to as micro-cell distribution. AS the distance
`between access points is reduced, RF interference between
`access points can increase. One technique for controlling
`Such interference is reduce the transmit power output of the
`access points, to thereby reduce their range and reduce
`interference.
`0002 Interference can also exist between transmissions
`of mobile units. It is difficult, however, to generally reduce
`the power output of mobile units, because the mobile unit
`may Sometimes be used in an area where there is a high
`density of access points, and accordingly, only a lower
`transmittal power is required, and also the Same mobile units
`may roam into an area in which acceSS points are spaced at
`further distances, and the full power of the mobile unit is
`required to effectively transmit to the access points.
`0003. It is an object of the present invention to provide a
`method and apparatus for controlling the transmit power
`level of a mobile unit in accordance with the environment
`encountered by the multiple unit.
`
`SUMMARY OF THE INVENTION
`In accordance with the invention, there is provided
`0004.
`a method for use in a wireless local area network, wherein
`mobile units receive beacon Signals from access points and
`asSociate with access points for data communication there
`with. The method is for controlling transmitter power level
`of a mobile unit. Data representing transmitter power level
`for an access point is transmitted from the acceSS point to the
`mobile unit. The mobile unit receives the access point
`transmitter power level data and adjusts the power level of
`the mobile unit transmitter in accordance with the value of
`the access point transmitter power level.
`0005 The power adjustment of the made mobile unit,
`may comprise Setting the mobile unit power level to a power
`level corresponding to the power level of the access point as
`represented by the access point power level data. Alterna
`tively, the power level of the mobile unit may be set to a
`level which is a Selected amount greater than the acceSS
`power level data. In one arrangement, the acceSS point
`power level data is transmitted as part of the beacon Signal.
`The adjustment of the power level of the mobile unit is
`advantageously performed when the mobile unit associates
`with an acceSS point.
`0006. In accordance with the invention, there is provided
`a mobile unit for use in a wireless local area network having
`access points transmitting at different power levels. The
`mobile unit includes a receiver for receiving data Signals
`from the acceSS point and a transmitter responsive to trans
`mitter power level Signals to transmit at a Selected power
`level corresponding to the power level Signals. The mobile
`
`unit further includes a processor coupled to receive data
`Signals from the receiver and programmed to derive power
`level data from Signals received from the access points and
`to provide corresponding power level Signals to the trans
`mitter.
`0007. In a preferred arrangement, the processor is further
`programmed to provide maximum power level Signals to the
`transmitter when it fails to derive power level data from the
`received AP Signals.
`0008. In accordance with the invention, there is provided
`a method for controlling interference in a wireless local area
`network having access points and mobile units. Access
`points are provided with adjustable transmitter power level
`and distributed over an area with varying spacing between
`access point. The transmitter power of the access points is
`manually adjusted according to the access point spacing,
`wherein access points with greater spacing have greater
`transmitter power. Power level data representing transmitter
`power of the acceSS points is transmitted from each of the
`points in every 802.11 beacon. Mobile units are provided
`having transmitters responsive to power level Signals for
`adjusting transmitter power of the mobile units. Power level
`data transmitted by the acceSS points is received by the
`mobile units which provide power level Signals correspond
`ing thereto to the mobile unit transmitters.
`0009. In a preferred arrangement, the power level data
`Signals from the AP represent the same power level as the
`power level data for the MU, or alternatively, a power level
`incrementally greater than the power level represented by
`the power level data. In a System wherein, the access points
`transmit beacon signals for use by mobile units to associate
`with the acceSS points, the power level data can be trans
`mitted within the beacon signals. Preferably the power level
`Signals are providing to the mobile unit transmitter while the
`mobile unit is within range of the associated access point.
`Where the mobile unit does not receive power level data
`from the associated access point, a maximum power level
`data Signals can be provided to the mobile unit transmitter.
`0010 For a better understanding of the present invention,
`together with other and further objects, reference is made to
`the following description, taken in conjunction with the
`accompanying drawings, and its Scope will be pointed out in
`the appended claims.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0011 FIG. 1 is an area map showing the distribution of
`access points having fixed and/or variable transmitter power
`and mobile units for communicating therewith.
`0012 FIG. 2 is a block diagram of a variable transmitter
`power access point.
`0013 FIG. 3 is a block diagram of a variable transmitter
`power mobile unit in accordance with the present invention.
`0014 FIG. 4 is a flow diagram illustrating one embodi
`ment of the method of the present invention.
`
`DESCRIPTION OF THE INVENTION
`0015 Referring to FIG. 1, there is shown a map illus
`trating exemplary locations of fixed power acceSS points
`10A through 10E, variable power access points 12A through
`12G and mobile units 14A through 14E in a wireless local
`area network. In the network illustrated in FIG. 1, access
`points 10A through 10E may have fixed transmitter power
`and are arranged at a wider Spacing between adjacent access
`
`Hewlett Packard Exhibit 1009, Page 4 of 6
`Hewlett Packard Enterprise Company v. Intellectual Ventures II LLC
`IPR2021-01377
`
`

`

`US 2003/0100328A1
`
`May 29, 2003
`
`points, which is Selected according to the transmitter power,
`and hence the range of each acceSS point 10. Variable power
`access points 12A through 12G are provided in a central
`area, wherein a greater Volume of data traffic may be
`anticipated. For example, variable power acceSS points 12A
`through 12G may be provided for servicing mobile units
`within a central laboratory area of an industrial complex,
`wherein a high Volume of data transmission might be
`anticipated, while access points 10A through 10E may be
`provided in peripheral areas, wherein a Smaller number of
`mobile units, and hence a lower Volume of data traffic may
`be anticipated.
`0016. In the system illustrated in FIG. 1, since variable
`power access points 12 are arranged with a closer spacing
`between acceSS points, and hence a greater acceSS points
`population, it can be anticipated that signals from acceSS
`points, Such as access point 12A, may interfere with Signals
`from the adjacent and Second adjacent access points, Some
`of which may be operating in the same frequency band. In
`order to reduce Such radio interference, or the existence of
`radio frequency noise in the communication channel, the
`transmitter power of access points 12 is variable Such that
`the power level of the access points 12 can be set at a value
`that is reduced according to the reduced Spacing of the
`access points. Fixed transmitter power acceSS points 10,
`which may also be variable power acceSS points Set at
`maximum power, transmit a greater power level because of
`the greater distance between access points and the likelihood
`that reduced transmitter power will cause coverage gaps in
`the wireleSS local area network.
`0017 While it is clearly possible to vary the transmitter
`power of the variable power access points 12, according to
`the Spacing between access points to provide effective local
`area network coverage, the fact that mobile units 14 can
`roam within any area of the wireless local area network, and
`hence be at a position which is widely Spaced from the
`nearest acceSS point with which it associates, it is not
`possible to adjust the transmitter power of the mobile units
`based their location, Since their location is not fixed.
`0.018. In accordance with the method of the present
`invention, the variable power acceSS points 12 transmit
`power level data to their associated mobile units, which
`indicates to the associated or potentially associated mobile
`units, the power level at which the acceSS point is transmit
`ting. Mobile units 14 receive the power level data from the
`access points and are arranged to adjust the power level of
`their own transmitters to correspond to the power level being
`transmitted by the access point with which the mobile unit
`is or becomes associated. In the event, the mobile unit, Such
`as mobile unit 14E is associated or becomes associated with
`a fixed power acceSS point 10E, of conventional design, it
`does not receive a power level data from the access point. In
`this event, the transmitter of mobile unit 14E is set to the
`maximum power level Setting.
`0.019
`FIG. 2 is a block diagram of an exemplary embodi
`ment of a variable access point 12. Access point 12 includes
`an asynchronous interface controller 18 which Sends and
`receives signals over cable 16 which is connected to, for
`example, a central computer or a wired data communications
`network. A central processing unit 20 in acceSS point 12
`controls the operation of the access point to transmit and
`receive signals and to control the operation of access point
`12 in connection with association of mobile units therewith.
`A transmitter/receiver 22 is provided for Sending and receiv
`ing wireleSS data communications Signals using antenna 24.
`
`In connection with the variable power access point 12, the
`transmitter power level of the access point is controlled, for
`example, by providing power level data 26 in an allocated
`memory location of CPU 20. The power level data 26 is
`transferred to a register 28 in the transmitter/receiver 22
`whereat it is used to control the power level of the acceSS
`point during transmission. When the wireless local area
`network illustrated, for example, in FIG. 1 is installed and
`tested, the power level data 26 can be provided at each
`access point 12 in accordance with the spacing of the access
`points and the Signal level of the access points as observed
`by testing instruments within the area covered. The variation
`of power level 26 may be affected, for example, by a control
`Signal provided by a central processor over the wired
`network cable 16, or alternately the power level can be set
`by connecting a control unit to the access point directly and
`providing the power level as a control signal for CPU20, for
`example, through a Serial port thereof. In connection with
`the testing of the operation of the WLAN, the power level
`data 26 maybe changed or adjusted, as appropriate, for
`propagation conditions that are observed. In accordance
`with the method of the present invention, the transmitter
`power level of mobile units 14 is adjusted in accordance
`with the power level set by the power level data 26 of the
`access point transmitters with which the mobile units are
`asSociated or about to become associated. For example, if
`the WLAN of FIG. 1 is a network operating in accordance
`with IEEE standard 802.11, the access points 10 and 12
`transmit beacon Signals which are used by mobile units 14
`to request association. The mobile units 14 receive beacon
`Signals from nearby acceSS points and observe Signal level
`thereof. The beacon Signals optionally include data signals
`which can be used by the mobile units in connection with the
`association process. Assuming mobile unit 14C of FIG. 1
`receives the Strongest beacon Signal from variable power
`access point 12E, mobile unit 14C additionally receives
`within the beacon Signal, data representing the power level
`26 at which variable power access point 12E has been set.
`CPU20 adds this power level data to the transmitted beacon
`signal. Referring to FIG.3, mobile unit 14 includes a mobile
`device 30, such as a PDA, a notebook computer or a
`telephone, a communication controller 32, which may be a
`digital Signal processor or a microcomputer, and a transmit
`ter/receiver 34, which transmits and receives radio fre
`quency data communication Signals via antenna 36. Trans
`mitter/receiver 34 is arranged to transmit a transmitter power
`level which is set forth in a register 40 within the transmitter
`receiver.
`0020 Mobile unit 14 receives a beacon signal from an
`access point 12 which includes transmitter power data
`transmitted by the access point 12 as part of the beacon. The
`transmitter power level data is extracted from the received
`signal in CPU 32 and set forth in a register 38 in CPU 32.
`This power level data is used to provide transmitter power
`level signals to a reister 40 in transmitter/receiver 34 in the
`mobile unit 14. In one example, the transmitter power level
`Signals may represent the same transmitter power which is
`represented by the power level data Signals received from
`the access point. Alternately, Since the mobile units 14
`experience a variety of environmental or multipath condi
`tions, the power level Signals provided to the transmitter 34
`of the mobile unit 14 may represent a transmitted power
`level that is greater, for example, 1 or 2 incremental values
`greater, than the transmitter power represented by the power
`level data Signal received from the access point 12.
`0021. In a preferred arrangement, CPU 32 is arranged to
`set the power level signals 40 provided to transmitter 34 at
`
`Hewlett Packard Exhibit 1009, Page 5 of 6
`Hewlett Packard Enterprise Company v. Intellectual Ventures II LLC
`IPR2021-01377
`
`

`

`US 2003/0100328A1
`
`May 29, 2003
`
`a maximum value when no power level data is received from
`the access point, for example, when the access point is not
`a variable power access point Such, as access point 10C of
`FIG. 1.
`0022 FIG. 4 is a flow diagram illustrating the method of
`controlling power of the mobile units 14 in accordance with
`one embodiment of the present invention. As shown in FIG.
`4, when the mobile unit makes a decision for roaming, Such
`as upon initial initiation of operation, or when Signal levels
`received from an associated acceSS point vary on account of
`movement of the mobile unit, the mobile unit receives
`beacon Signals and Selects an access point with which to
`attempt association. The access point Sends the beacon
`Signal with power data which is thereafter extracted from the
`beacon data by the mobile unit. The power level of the
`mobile unit is set using the power level data received as part
`of the beacon Signals, and provided as a power level Signal
`to the transmitter 34 of the mobile unit. The mobile unit 14
`thereafter requests association with the access point and the
`access point processes the association request. Thereafter,
`during data communication between the mobile unit and the
`asSociated access point, the transmitted power of the mobile
`unit is set by the power level Signal provided to transmitter
`34 by CPU 32 and corresponds to the power level data sent
`by the access point to the mobile unit. This power level is set
`to the Same or slightly greater power level than the power
`level represented by the power level data previously been Set
`by the access point, as described above.
`0023) While there have been described what are believed
`to be the preferred embodiments of the present invention,
`those skilled in the art will recognize that other and further
`modifications and changes may be made thereto without
`departing from the Spirit of the invention and it is intended
`to claim all Such changes and modifications as fall within the
`true Scope of the invention.
`We claim:
`1. In a wireless local area network wherein mobile units
`receive beacon Signals from access points and asSociate with
`access points for data communications therewith, a method
`for controlling transmitter power level of a mobile unit,
`comprising transmitting from an acceSS point to Said mobile
`unit data representing transmitter power level for Said acceSS
`point, receiving at Said mobile unit Said access point trans
`mitter power level data; and adjusting transmitter power
`level of said mobile unit in accordance with the value of said
`access point transmitter power level data.
`2. A method according to claim 1 wherein adjusting power
`level of Said mobile unit comprises Setting Said mobile unit
`to a power level corresponding to Said acceSS point trans
`mitter power level data.
`3. A method according to claim 1 wherein adjusting power
`level of Said mobile unit comprises Setting Said mobile unit
`to a power levela Selected amount greater than a power level
`corresponding to Said acceSS point transmitter power level
`data.
`4. A method according to claim 1 wherein Said acceSS
`point transmitter power level data is transmitted as part of
`Said beacon Signal.
`5. A method according to claim 1 wherein Said adjusting
`power level of said mobile unit is performed when said
`mobile unit associates with an access point.
`
`6. A mobile unit for use in a wireless local area network
`having acceSS points transmitting at different power levels,
`comprising:
`a receiver for receiving data Signals from Said access
`points;
`a transmitter responsive to transmitter power level signals
`to transmit at a Selected power level corresponding to
`Said Signals, and
`a processor, coupled to receive data Signals from Said
`receiver and programmed to derive power level data
`from Signals received from Said access points and to
`provide corresponding power level Signals to Said
`transmitter.
`7. A mobile unit as specified in claim 6 wherein said
`processor is further programmed to provide maximum
`power level Signals to Said transmitter when Said processor
`fails to derive said power level data from said received
`Signals.
`8. A method for controlling interference in a wireless local
`area network having access points and mobile units, com
`prising:
`providing acceSS points including access points with
`adjustable transmitter power level and distributing Said
`access points over an area with varying spacing
`between access points;
`adjusting the transmitter power of Said adjustable trans
`mitter power level acceSS points according to Said
`access point Spacing, wherein access points with
`greater spacing have greater transmitter power;
`providing power level data representing transmitter power
`of Said adjustable power level access points, and trans
`mitting Said power level data from each of Said adjust
`able power level acceSS points,
`providing mobile units having transmitters responsive to
`power level Signals for adjusting transmitter power of
`Said mobile units,
`receiving Said power level data at Said mobile units and
`providing power level Signal corresponding thereto to
`Said mobile unit transmitters.
`9. A method to claim 8 wherein said power level data
`Signals represent the same power level as Said power level
`data
`10. A method according to claim 8 wherein said power
`level data Signals represent a power level greater than the
`power level represented by Said power level data.
`11. A method according to claim 8 wherein Said access
`points transmit beacon Signals for use by mobile units to
`asSociate with one of Said acceSS points, and wherein Said
`power level data is transmitted with Said beacon Signals.
`12. A method according to claim 11 wherein Said power
`level Signals are provided to Said mobile unit transmitter
`while Said mobile unit is associating with an access point.
`13. A method according to claim 8 comprising the further
`Step of providing maximum power level Signals to Said
`mobile unit transmitter when said mobile unit does not
`receive Said power level data.
`
`k
`
`k
`
`k
`
`k
`
`k
`
`Hewlett Packard Exhibit 1009, Page 6 of 6
`Hewlett Packard Enterprise Company v. Intellectual Ventures II LLC
`IPR2021-01377
`
`