US007039358B1
`
`(12) United States Patent
`US 7,039,358 B1
`(10) Patent N0.:
`
`Shellhammer et al.
`(45) Date of Patent:
`May 2, 2006
`
`(54) COEXISTENCE TECHNIQUES IN WIRELESS
`NETWORKS
`
`(75)
`
`InVemOISI Stephen J- Shellhammers Lake GIOVes
`NY (US); Jacob Sharony, Dix Hills,
`NY (US); Anthony D- Bluso, South
`Setauket, NY (US); Sean A. Connolly,
`Stony Brook, NY (US); William
`Sackett, Rocky Point, NY (US); Joseph
`Cabana, Centereach, NY (US); Patrick
`Tilleya Corarna NY (US); Robert
`Bead" L05 Altos’ CA (Us)
`(73) Assignee: Symbol Technologies, Inc., Holtsville,
`NY (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 499 days.
`
`(21) Appl. No.: 09/714,803
`
`2/2000 Clapper ................. 342/357.13
`6,023,241 A *
`4/2000 Wright et al.
`.............. 455/66.1
`6,047,165 A *
`6,326,926 B1* 12/2001 Shoobridge et al.
`........ 343/702
`6,377,608 B1*
`4/2002 Zyren .................. 375/132
`
`...... 343/702
`6,414,643 B1*
`7/2002 Cheng et al.
`9/2002 Vij et 31. .............. 370/310
`6,452,910 B1*
`
`6,477,378 B1* 11/2002 Halminen ......
`455/450
`........ 455/84
`6,526,264 B1*
`2/2003 Sugar et al.
`
`6,529,584 B1*
`3/2003 Ravago et al.
`..... 379/671
`..
`
`
`6,531,985 B1*
`3/2003 Jones et al. .............. 343/702
`.............. 455/73
`6,560,443 B1*
`5/2003 Vaisanen et al.
`FOREIGN PATENT DOCUMENTS
`
`EP
`
`1119137
`
`*
`
`7/2001
`
`* cited by examiner
`
`Primary Examiner%harles Craver
`(74) Attorney, Agent, or FirmiBaker Botts LLP
`
`(22)
`
`Filed:
`
`Nov. 16, 2000
`
`(57)
`
`ABSTRACT
`
`Related US. Application Data
`
`(60) Provisional application No. 60/175 262 filed on Jan.
`10 2000 provisional application, No, 60/196 979
`filed on Apr 13 2000
`i
`’
`i
`’
`
`’
`
`i
`
`(51)
`
`(2006.01)
`
`Int. Cl.
`H043 7/00
`455/41 2, 455/426 1
`(52) U S Cl
`455;41 141 3
`(58) Field of Classification Search
`455/561 4141 414 4 4'5'4' 462 463 554'1’
`’
`’
`'
`’
`’
`’
`'
`’
`’
`45455/31/25442505312661S 562815554621691313534372501a
`’
`’
`’
`’
`'
`’
`'
`’
`343/702’
`lication file for com lete search histo
`p
`References Cited
`U.S. PATENT DOCUMENTS
`
`See a
`
`pp
`
`(56)
`
`ry.
`
`Techniques are provided for frequency coordination among
`two different wireless network protocols, such as the IEEE
`802.11 and Bluetooth protocols, operating in proximity with
`one another. Coordination is accomplished by the use of a
`first radio transceiver operating in accordance with a first
`communication protocol (which may be the 802.11 protocol)
`and using a frequency band (which may be the 2.4 GHZ
`band), a base station connected to a wired network and
`operlating in acicordiance with the first communicationipro-
`toco, a secon ra 10 transcelver operatmg 1n accor ance
`with a second communication protocol (which may be the
`Bluetooth protocol) and using the frequency band, and a
`coordinator associated with the base station for,
`in turn,
`activating the first radio transceiver, deactivating the first
`radio transceiver, activating the second radio transceiver,
`and deactivating the second radio transceiver.
`
`5,610,386 A *
`
`3/1997
`
`Ball et al.
`
`.............. 235/462.44
`
`31 Claims, 4 Drawing Sheets
`
`
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`BT
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`I~ figs—7
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`U.S. Patent
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`May 2, 2006
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`Sheet 1 0f 4
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`US 7,039,358 B1
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`
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`FIG. 1
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`FIG. 2
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`U.S. Patent
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`May 2, 2006
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`Sheet 2 0f 4
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`US 7,039,358 B1
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`,_J_T_.
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`320
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`U.S. Patent
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`May 2, 2006
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`Sheet 3 0f 4
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`US 7,039,358 B1
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`T[f(n-2])
`
`Rmmn
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`T(f(n]]
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`R(f(n+1l) T(f(n+2))
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`tuning
`
`data
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`60 usec
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`tune to f(n+2)
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`tune to f[n+1]
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`U.S. Patent
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`May 2, 2006
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`Sheet 4 0f 4
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`US 7,039,358 B1
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`521
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`210
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`_,__e——e——»—-522
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`110
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`26
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`530
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`
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`US 7,039,358 B1
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`1
`COEXISTENCE TECHNIQUES IN WIRELESS
`NETWORKS
`
`BACKGROUND OF THE INVENTION
`
`This application claims the benefit of provisional appli-
`cation Ser. No. 60/175,262, filed Jan. 10, 2000 and Ser. No.
`60/196,979, filed Apr. 13, 2000. This invention relates to
`wireless data communications networks, and in particular to
`arrangements for ensuring coexistence between wireless
`networks that share the same frequency band with different
`operating protocols.
`Wireless devices communicate with one another using
`agreed-upon protocols that are transmitted in predefined
`frequency bands. Often, devices using one or more wireless
`protocols may operate by transmission within the same
`frequency band. It is therefore necessary to develop coor-
`dination techniques in order for devices using one or more
`wireless protocols to efficiently operate in the same band of
`frequencies at the same time.
`For example, the assignee of the present invention sup-
`plies wireless data communications systems known as the
`Spectrum 24® System that follows the communications
`protocol of IEEE 802.11 Standard (802.11), which is hereby
`incorporated by reference. In the system as implemented,
`mobile units (MUs) are in data communication with a
`central computer through one or more access points (APs).
`The APs may communicate with a computer directly or over
`an Ethernet wired network. Each of the MUs associates itself
`with one of the APs. As defined in 802.11, this communi-
`cations protocol uses the 2.4 GHz ISM frequency band.
`As currently designed, 802.11 devices may use several
`predefined methods for transmission within the 2.4 GHz
`band to perform as a wireless local area network. One
`method is to use a frequency hopping spread spectrum
`(FHSS) mechanism wherein data is transmitted for a certain
`period of time in a particular channel and, following a
`pseudorandom sequence, continues transmission at a differ-
`ent channel for the same predetermined length of time. As
`currently designed, 802.11 devices operate at a frequency
`hopping rate of 10 hops/second. Another method is to use a
`direct
`sequence
`spread spectrum (DSSS) mechanism
`wherein the data is transmitted in a predetermined frequency
`channel and is multiplied by a pseudorandom chipping
`sequence during transmission.
`As all 802.11 devices use the same ISM frequency band,
`interference among these devices is minimized by use of a
`Carrier Sense Multiple Access/Collision Avoidance (CSMA/
`CA) protocol. Under CSMA/CA, an 8021.11 device listens
`for another’s devices transmission prior to initiating its own
`transmission. If no other transmission is detected, the device
`transmits its information and waits for an acknowledgment
`(ACK) from the receiving device. If no acknowledgment of
`receipt is received after a pre-determined time interval, the
`device will retransmit after waiting for a randomly chosen
`interval of time. Thus, if two or more devices began trans-
`mitting coincidentally at the same time and the resulting
`interference blocks all of the transmissions, each device will
`wait a random amount of time to attempt a retransmission.
`This allows the devices to transmit at different times.
`
`Another example of a wireless specification that also uses
`the 2.4 GHz ISM frequency band is BluetoothTM, which is
`designed for communication among devices within a short
`range transmitting at a lower power level. The Bluetooth
`specification, version 1.1, which would be known to one of
`ordinary skill
`in the art,
`is fully incorporated herein by
`reference. As currently designed, Bluetooth operates using a
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`frequency hopping spread spectrum mechanism at a rate of
`1600 hops/second. Bluetooth uses a master/slave system of
`communication. One example of a Bluetooth network may
`be a mobile device attached to the user’s belt that commu-
`
`nicates with a cordless scanner for reading bar codes and
`worn by the user as a ring. In this case, the mobile device
`would operate as the master and the cordless ring scanner
`would operate as the slave. In this system for data trans-
`mission, the master and slave only communicate at pre-
`defined intervals. At
`the first
`interval,
`the master may
`communicate to a first slave device, which may only respond
`during the second interval. At the third interval, a master
`may communicate to a second slave device, which may only
`respond during a fourth interval. By using this system, it is
`ensured that only one device within a particular Bluetooth
`“piconet” is transmitting at any particular time. Thus, inter-
`ference is minimized.
`
`Additionally, it is desirable for one Bluetooth piconet to
`operate in close proximity with another, separate Bluetooth
`piconet. Because there are 79 different frequency channels
`used by Bluetooth, different Bluetooth networks are unlikely
`to be operating on the same frequency at the same time.
`Interference between the separate Bluetooth piconets is thus
`minimized. This allows, for example, multiple individuals
`working in close proximity with one another to each have his
`or her own mobile unit along with a cordless ring scanner.
`Along with the need to operate multiple networks of the
`same protocol in close proximity, there is also a recognized
`need in the art to coordinate the transmissions of devices
`
`operating under different protocols that use the same fre-
`quency band. For example,
`it may be desirable to use a
`cordless ring scanner that communicates with belt-mounted
`terminal using the Bluetooth protocol while the same belt
`mounted terminal communicates with an access point using
`the 802.11 protocol. For example, once the user scans a bar
`code using the cordless ring scanner, the bar code informa-
`tion may be sent to the belt-mounted terminal. That bar code
`information may then be transmitted to the 802.11 AP. Then
`an acknowledgment, and possibly a message, may need to
`be sent from the AP back to the belt-mounted terminal. The
`
`terminal may also need to communicate with other Blue-
`tooth enabled peripherals like a printer or a headset.
`Although communication protocols such as 802.11 and
`Bluetooth are designed to ensure that devices using the same
`protocol may operate in the same frequency band with a
`minimum of interference,
`there has heretofore been no
`method of coordination for the use of these wireless devices
`
`in the same frequency operating under different communi-
`cation protocols.
`It is additionally desirable to provide voice service using
`the Bluetooth communications protocol,
`for example,
`between a belt-mounted terminal and a headset worn by the
`user. Bluetooth supports voice communications using Syn-
`chronous Connection Oriented (SCO) voice packets which
`are transmitted every 3.75 ms. The requirement for such
`frequent Bluetooth packet transmission makes it difficult to
`coordinate voice transmission using the Bluetooth SCO
`packets with 802.11 communications.
`It is therefore an object of this invention to utilize coor-
`dination techniques to ensure that, for example, both Blue-
`tooth and 802.11 enabled devices, may operate robustly in
`the same frequency band at the same time.
`
`SUMMARY OF THE INVENTION
`
`An embodiment of the present invention includes a first
`radio transceiver operating in accordance with a first com-
`
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`US 7,039,358 B1
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`3
`munication protocol (which may be the 802.11 protocol) and
`using a frequency band (which may be the 2.4 GHZ ISM
`band), a base station operating in accordance with the first
`communication protocol, a second radio transceiver operat-
`ing in accordance with a second communication protocol
`(which may be the Bluetooth protocol) and using the fre-
`quency band, and a coordinator associated with the base
`station for,
`in turn, activating the first radio transceiver,
`deactivating the first radio transceiver, activating the second
`radio transceiver, and deactivating the second radio trans-
`ceiver.
`The first radio transceiver and the second radio trans-
`
`ceiver may be mounted together in a housing, which may be
`suitable for wearing on a belt or a laptop computer or a PDA.
`One or more slave devices may be associated with the
`second transceiver and operate in accordance with the
`second communication protocol. The slave devices may
`include a scanner, worn on a user’s finger and capable of
`transmitting bar code information to the second transceiver,
`a printer, or a personal data managing device.
`In one arrangement wherein the first and second trans-
`ceivers are mounted together in a housing, they may include
`orthogonally polarized antennas. In another arrangement a
`Bluetooth protocol transceiver transmits at power level of
`about 0 dBm. In still another arrangement, two or more sub
`bands within the frequency band are provided and the 802.1 1
`protocol transceiver uses one of the two or more sub-bands
`and the Bluetooth protocol transceiver uses another of the
`two or more sub-bands. In still another arrangement in the
`second radio transceiver is equipped with a look-ahead
`function for determining whether two or more sub-bands are
`being used by the first radio transceiver that will also be used
`by the second transceiver. In still another arrangement, a
`coordinator is associated with the first radio transceiver for
`
`deactivating the second radio transceiver while the first radio
`transceiver is in use.
`
`According to the invention, there is provided a method for
`operating a portable data communications device using first
`and second wireless data communications protocol. The data
`communications device is operated in a power saving mode
`of the first communication protocol, whereby the device has
`active time periods for transmitting and receiving data
`communications signals using the first communications pro-
`tocol and dormant time periods during which the device
`neither transmits nor receives data communications signals
`using the first protocol. The data communications device is
`operated as a master device according to the second com-
`munications protocol whereby the data communication
`device controls operation of slave devices communicating
`therewith. The operation according to the second data com-
`munications protocol is controlled to operate only during the
`dormant time periods of the first protocols.
`In one embodiment, a signal indicating that the active
`time period will commence following a predetermined time
`interval is provided to terminate operation according to the
`second data communication protocol during the predeter-
`mined time interval. The first wireless data communications
`
`protocol may be the 802.11 protocol. The second wireless
`communication protocol may be Bluetooth.
`In another aspect of the invention, there is provided a
`method for operating a wireless data communications sys-
`tem having an access point and at least one mobile unit
`associated with said access point using a first wireless
`protocol (which may be 802.11), wherein said mobile unit is
`arranged to conduct wireless data communications with
`other units using a second wireless protocol (which may be
`Bluetooth). Periodic beacon signals are transmitted from the
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`access point according to the first wireless protocol. Global
`clear to send signals are transmitted from the access point
`according to the first wireless protocol, whereby the global
`clear to send signals prevent mobile units from transmitting
`signals using the first data communications protocol during
`an allocated time interval within the beacon signal period.
`The access point is controlled to avoid transmissions during
`the allocated time interval, and the mobile unit is operated
`in response to the global clear to send signal to conduct
`wireless communications acting as a master unit using the
`second wireless protocol during the allocated time interval.
`In one embodiment, the beacon signal period is divided
`into three time intervals, wherein the access point conducts
`power saving mode data communications during a first time
`interval, wherein the access point conducts data communi-
`cations using the second communications protocol during
`the second time interval and wherein the access point
`conducts data communications using the first wireless pro-
`tocol during a third time interval. The first time interval may
`immediately following the beacon signal.
`In another
`embodiment, the first time interval may not be utilized.
`In accordance with another aspect of the invention, there
`is provided a method of operating a data communications
`system using a master-slave protocol (such a Bluetooth),
`wherein a master transceiver transmits to slave units during
`first even time slots and wherein slave units transmit to the
`master unit during odd time slots, and wherein the trans-
`missions follow a predetermined frequency hop pattern at a
`hop rate corresponding to the time slots. The master unit is
`operated during a first time period of each time slot to detect
`interfering signals at a frequency corresponding to the
`following time slot. Transmission by the master transceiver
`is inhibited during even time slots if interfering signals have
`been detected during either of the current or previous time
`slots.
`
`In a preferred practice, the operating step includes tuning
`the master unit
`to receive signals corresponding to the
`frequency allocated to the next following time slot; detecting
`the strength of signals received and retuning the master unit
`to send or receive signals corresponding to the frequency
`allocated to the current time slot.
`
`In another aspect of the invention, there is provided a
`method for providing voice communications in a wireless
`data communications system having a mobile unit arranged
`to communicate with an access point using a first data
`communications protocol (such as 802.11) and arranged to
`communicate with other devices using a second data com-
`munications protocol (such as Bluetooth). Data correspond-
`ing to the voice communication is communicated between
`the access point and the mobile unit using the first data
`communications protocol. The data corresponding to the
`voice communications is communicated between the mobile
`unit and a portable device using the second data communi-
`cation protocol. The communication is arranged at time
`intervals which avoid interference with the communicating
`using the first data communications protocol. Voice signals
`are converted to data corresponding to the voice signals and
`data signals corresponding to voice signal are converted into
`voice signals in the portable device.
`In a preferred arrangement,
`the data corresponding to
`voice signals comprises compressed voice signal data. The
`communication between the mobile unit and the portable
`device preferably uses a Bluetooth ACL link.
`According to a further aspect of the invention, there is
`provided a method for operating a mobile unit arranged to
`communicate using first and second data communication
`protocols operating in the same frequency band (such as
`802.11 and Bluetooth) wherein the mobile unit associates
`with an access point and receives therefrom beacon signals
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`US 7,039,358 B1
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`5
`demarcating time intervals according to the first communi-
`cations protocol. Signals are received from the access point
`(such as CTS signals) designating a portion of one of the
`time intervals during which mobile units associated with the
`access point refrain from transmissions using said first data
`communications protocol. The mobile unit is operated as a
`master unit using the second data communications protocol
`to communicate with slave units during the designated
`portion of the time interval.
`According to a further aspect of the invention, there is
`provided a method for operating a wireless data communi-
`cations network having at least one access point and at least
`one mobile unit, including a mobile unit arranged to com-
`municate with the access point using a first wireless data
`communication protocol (such as 802.11) in a first frequency
`band and to communicate with other devices using a second
`wireless data communication protocol (such as Bluetooth) in
`the first frequency band. Signals (such as CTS) as sent from
`the access point in the first communications protocol, which
`designate a time period wherein mobile units associated with
`the access point refrain from transmitting using the first data
`communications protocol. The mobile units operate as a
`master unit to conduct wireless data communications with
`
`the other devices operating as slave units using the second
`data communications protocol during the designated time
`period.
`According to still another aspect of the invention, a
`method is provided for operating a mobile unit arranged to
`communicate using first and second data communications
`protocols operating in the same frequency band (such as
`802.11 and Bluetooth), wherein the mobile unit associates
`with an access point. The mobile unit receives first and
`second control signals using the first data communications
`protocol. The mobile units are operated in response to the
`first control signals to act as a master unit and conduct data
`communications with slave units using the second data
`communications protocol. Communications by the mobile
`unit using the second data communications protocol
`is
`discontinued in response to the second control signal.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram of a wireless communications
`system using 802.11 and Bluetooth devices.
`FIG. 2 is a block diagram of a wireless communications
`system using 802.11 and Bluetooth devices at the same time
`along with a connect button switch and connected indica-
`tors.
`
`FIG. 3 is a schematic diagram of an embodiment of the
`present
`invention illustrating a coordinated time line
`between the operation of 802.11 and Bluetooth devices.
`FIG. 4 is a schematic diagram of an embodiment of the
`present invention illustrating another coordinated time line
`between the operation of 802.11 and Bluetooth devices.
`FIG. 5 is a diagram showing a modified Bluetooth oper-
`ating method for avoiding interference.
`FIG. 6 is a drawing showing one example of orthogonally
`polarized antennas.
`FIG. 7 is a drawing of a wireless headset arranged for
`voice communications.
`
`FIG. 8 is a block diagram of the headset of FIG. 7.
`
`DESCRIPTION OF THE INVENTION
`
`Turning to FIG. 1, shown are a plurality of base stations
`or Access Points (APs) 20, 30 that are physically connected
`40, 50 to a wired network 10. While a wired network with
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`multiple access points connected to a CPU 12 is a typical
`installation, the system may use a single computer and single
`AP. Each AP contains apparatus 60, 70 for the transmission
`and reception of radio frequency (RF) signals under the
`802.11 protocol. Also using the 802.11 protocol, a plurality
`of radio transceivers or mobile units (MUs) 120, 140 com-
`municate using apparatus 80, 90 for the transmission and
`reception of RF signals. Each MU 120, 140 may also be
`associated with a radio transceiver which is a Bluetooth
`
`Master (BTM) device 130, 150, which together make up a
`dual mode devices 100, 110. The association between the
`MU and BTM may be, for example, by way of being
`physically housed in the same unit. An example of a dual
`mode device 100, 110 may be portable terminal worn on a
`belt.
`
`Each BTM 130, 150 communicates with one or more
`Bluetooth Slave (BTS) devices 160, 170, 180, 190, 200, 210
`via the Bluetooth protocol. The Bluetooth protocol is estab-
`lished such that each BTS is uniquely associated with a
`BTM. Thus, as illustrated, BTSIA 160, BTSlB 170, and
`BTSlC 180 communicate using RF signals 220, 230, 240
`only with BTMl 130. This forms a piconet 280. Corre-
`spondingly, BTSZA 190, BTSZB 200, and BTSZC 210
`communicate using RF signals 250, 260, 270 with BTM2
`150. This forms a piconet 290. An example of a BTS may
`be a cordless ring scanner, a printer, or personal data
`managing device.
`With no coordination, there will be times when the BTM
`130, 150 and the associated MU 120, 140 attempt to operate
`at the exact same time. Since the two devices operate in the
`same 2.4 GHz ISM frequency band the BTM 130, 150 and
`the MU 120, 140 may severely interfere with one another,
`especially if they are housed in a dual mode device 100, 110.
`Therefore, there is a need for coordination between the two
`devices. One such coordination scheme is primarily based
`on time multiplexing of the 802.11 and BT radios, which is
`especially suitable for a controlled environment (e.g., the
`802.11 and BT radios are housed in the same terminal or
`
`the Bluetooth
`In one embodiment,
`dual mode device).
`systems are enabled or disabled according to a global/central
`signal from the 802.11 AP as described herein. The central
`signal may also be coordinated among the two devices
`without coordinating with the AP.
`In a further embodiment, the dual mode devices 100, 110
`may be designed such that the 802.11 antennas 80, 90 have
`orthogonal polarization with respect to the Bluetooth anten-
`nas used to generate RF signals 220, 230, 240, 250, 260,
`270. This technique may provide additional protection from
`802.11 Bluetooth interference and does not require the need
`for centralized control.
`
`FIG. 6 shows one example of orthogonally polarized
`antennas that can be used to reduce interference. The
`
`antenna structure of FIG. 6 includes a vertically polarized
`monopole antenna 502, which is connected to a transmitter/
`receiver by an unbalanced transmission line 510. The struc-
`ture also includes a horizontally polarized dipole antenna
`having dipole arms 504, 506 which are connected to a
`transmitter/receiver by balanced transmission line 508.
`Those skilled in the art will recognize that many other
`orthogonal-polarized antenna configurations may be used. In
`a further embodiment, the BTMs 130, 150 may be designed
`to transmit at a relatively low power level such as lower than
`0 dBm. This technique may provide additional protection
`from 802.11 Bluetooth interference and may be used with
`other antenna or frequency coordination methods discussed
`herein.
`
`Ex. 1006 / Page 8 of 12
`ERICSSON v. UNILOC
`
`Ex. 1006 / Page 8 of 12
`ERICSSON v. UNILOC
`
`

`

`US 7,039,358 B1
`
`7
`In a further embodiment, the 802.11 APs 20, 30 and MUs
`120, 140 may be designed to operate in one portion of the
`2.4 GHz spectrum, while the BTMs 130, 150 and BTSs 160,
`170, 180, 190, 200, 210 may be designed to operate in
`another portion of the 2.4 GHz spectrum.
`In a further embodiment, the BTMs 130, 150 may be
`equipped with a look-ahead function to determine which
`frequencies within the 2.4 GHz band will be used for two or
`more future Bluetooth frequency hops to occur. If the BTM
`130, 150 determines that one of the next two or more
`frequency hops will use the same frequency that the 802.11
`system is using, the BTMs 130, 150 will blank their output,
`thus reducing the effect of the interference on the 802.11
`transmissions. By using this method, interference between
`Bluetooth and 802.11 could be reduced or eliminated at the
`
`expense of dropping a couple of packets when channel
`overlap occurs. This approach may also be expanded to
`include the blanking of adjacent channels that may also
`interfere with the 802.11 transmissions.
`
`Bluetooth uses a Frequency Hopping Spread Spectrum
`(FHSS) radio, which hops much faster than most IEEE
`802.11 radios. Bluetooth sends a short packet as it dwells on
`a given frequency. Most IEEE 802.11 radios hop much
`slower and send much longer packets. Also there are ver-
`sions of IEEE 802.11 WLANs that use Direct Sequence
`Spread Spectrum (DSSS) which do not hop and occupy a
`wide band.
`
`As a result, during the transmission of an IEEE 802.11
`packet the Bluetooth radio hops across many frequencies
`and potentially sends a packet on each frequency. These
`Bluetooth packets can interfere with the IEEE 802.11 pack-
`ets and cause the IEEE 802.11 packet to be in error. The
`IEEE 802.11 packet needs to be retransmitted, and once
`again may be destroyed by the signal from the Bluetooth
`radio.
`
`This technique shown in FIG. 5 can be used in any
`Bluetooth radio and in any device that will operate in an
`IEEE 802.11 WLAN environment. Since it detects devices
`
`radiating in the 2.4 GHz ISM band it could also be used to
`prevent interference with other devices in that band.
`A Bluetooth network consists of up to eight Bluetooth
`devices operating in a piconet. The piconet has one master
`and up to seven slaves. All the Bluetooth devices in the
`piconet hop in unison, at a rate of 1600 hops/second. The
`time that the frequency hopper dwells on a given frequency
`is called the slot time. At this hop rate the slot time is 625
`microseconds. Typically packets are completed within one
`slot time, however, it is also possible to have 3 and 5 slot
`packets. The master and the slaves take turns transmitting,
`with the master transmitting on even slots and the slaves
`transmitting on odd slots. See also Bluetooth Specification,
`version 1.0, Dec. 1, 1999, which is hereby incorporated by
`reference in full.
`
`There are two types of links between the master and each
`of the slave devices in a Bluetooth piconet. There is an
`asynchronous connection-less link (ACL) which is used to
`transfer data. There is also a synchronous connection ori-
`ented link (SCO) that is used to transfer voice data. The
`master in the picolink determines when data on an ACL link
`is transferred. Data is transferred when the master has data
`to send to a slave or the master wants to receive data from
`a slave.
`
`Each Bluetooth device within a piconet frequency hops in
`unison, according to a pseudo random sequence. FIG. 5
`illustrates a device hopping along its sequence of frequen-
`cies: f(1), f(2), .
`.
`. f(n) .
`.
`. The figure also shows how the
`625-microsecond slot
`time includes a 220-microsecond
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`period for tuning the frequency synthesizer in the radio to a
`new frequency and a 405-microsecond data transmission
`period.
`As stated above during even slots T(f) the master trans-
`mits to a slave and during odd slots R(f) the slave transmits
`back to the master. The master can transmit on any even time
`slot. The slave can only transmit to the master in a time slot
`if the master sent the slave a packet in the previous time slot.
`If the master does not send data to any slave in slot 11 then
`no slave can transmit in slot (n+1). The exception to this rule
`is for SCO link packets in which data is always transmitted
`in predefined periodic intervals. So for ACL links if the
`master does not transmit any data, the slaves do not send any
`data.
`
`Currently the piconet master does not attempt to deter-
`mine if any other devices are using the spectrum before it
`transmits. As a result, if there is an IEEE 802.11 packet
`currently being transmitted the Bluetooth master will not
`bother to check to see if this other system is transmitting and
`will itself transmit at the same time, and possibly on the
`same frequency. As a result it will interfere with the IEEE
`802.11 packet possibly causing the packet to be received
`incorrectly.
`It is proposed to subdivide the 220 microsecond tuning
`time interval into several subintervals and to spend some of
`that time looking ahead into subsequent frequencies to see if
`there is any other devices transmitting in those channels. The
`reason to look ahead is that if the a master sends a message
`to slave #1 on frequency f(n), then the master has cleared
`slave #1 to transmit during the next time slot on frequency
`f(n+1). Therefore, the master needs to look ahead to the
`frequency that corresponds to the next slot. The 220 micro-
`second timing interval can be subdivided as follows. In the
`first 80 microseconds the frequency synthesizer in the mas-
`ter retunes to f(n+1), then in the next 60 microseconds the
`master listens for any signal in that band. This can be done
`using a standard Receive Strength Signal Indicator (RSSI) in
`the radio. Then in the next 80 microseconds the frequency
`synthesizer then retunes the radio to f(n). FIG. 5 illustrates
`the new proposed time slot subdivision.
`Just prior to receiving on frequency f(n—1) the master
`checks to see that the frequency band at f(n) is clear. Also,
`prior to transmitting on frequency f(n) the master also makes
`sure that the frequency band f(n) is clear. If frequenc