(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property Organization
`International Bureau
`
`7 June 2001 (07.06.2001) ||||||IlllIIIlIlllIllllIlIl||||Illlll|l||||l||||l||l||||l|||l|||||l||||l|||l||||
`
`(43) International Publication Date
`
`(10) International Publication Number
`WO 01/41371 A1
`
`
`(51) International Patent Classification7:
`H04Q 7/22
`
`H04L 12/28,
`
`(21) International Application Number:
`
`PCT/SE00/02450
`
`(22) International Filing Date: 6 December 2000 (06.12.2000)
`(25) Filing Language:
`English
`
`(26) Publication Language:
`
`English
`
`(74)
`
`81
`
`(
`
`)
`
`(30) Priority Data:
`998501936
`
`6 December 1999 (06.12.1999)
`
`EP
`
`(71) Applicant: TELEFONAKTIEBOLAGET LM ERICS-
`SON (publ) [SE/SET; 8-126 25 Stockholm (SE).
`
`(72) Inventors: RUNE, Johan; Terrarigvagen 5, 8-181 39
`Lidingo (SE). JOHANSSON, Per, X.; Dymlingsgrand
`
`10, S-129 30 Hagersten (SE). GEHRMANN, Christian;
`Sankt Mainsgatan 17 A, 57222 29 Lund (SE). SORENSEN,
`Johan; Ostra Str'o' 25 l-lolma, S—241 91 Esldv (SE). LARS-
`SON, Tony; Kungsholms strand 139,
`3 tr, S-l 12 48
`Stockholm (SE).
`
`Agents: BJELKSTAM, Peter ct al.; Bergenstrahle &
`Lindvall AB, Box 17704, 3-118 93 Stockholm (SE).
`
`Designated States (national): AE, AG, AL, AM, AT, AU,
`AZ, BA, BB, BG, BR, BY, BZ, CA, CH, CN, CR, CU, CZ,
`DE, DK, DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR,
`HU, ID, IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR,
`LS, LT, LU. LV, MA, MD, MG, MK, MN, MW, MX, MZ,
`NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ. TM,
`TR, T1", TZ, UA, UG, UZ, VN, YU, ZA, ZW.
`
`(84)
`
`Designated States (regional): ARIPO patent (GI-I, GM,
`KE, LS, MW, MZ, SD, SL, SZ, TZ, UG, ZW), Eurasian
`patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), European
`
`[Continued on next page]
`
`
`(54) Title: INTELLIGENT PICONET FORMING
`
`A first BT unit
`, ~ ———————— '>
`sends INEIJIRY messaget
`302
`600
`
`la
`l
`
`-—--—a
`
`An INQUIRY message is
`received in a second
`BT unit
`An lNQUIRY_message is
`fimuwinamnd
`
`<— —-
`
`
`ET unit
` An lNQUIRYmessage is
`
`received in a forth
`BT unit
`
`INQUIRY RESPONSE message indicating
`
`608
`tha it is a slave unit
`
`B
`INQUIRY RESPONSE message indicating
`rhat it is a master unit
`
`
`
`he fourth BT Llnit sen-s an
`
`INQUIRY RESPONSE message indicating
`
`
`816
`that it is a slave unit
`
`
`
`(57) Abstract: When connecting a unit to one or
`more existing ad hoc wireless networks comprising
`several units, the units e.g. adapted to communicate
`according to the Bluetooth specification and the net-
`work then being formed according to the same spec-
`ification to comprise one or more piconets, a unit
`can discover the units which are the masters in the
`networks, and then connect as a slave to those mas—
`ters. Specifically it does not have to use the mas-
`ter-slave switch according to the Bluetooth specifi-
`cation. In the first stage of the unit trying to make
`a connection it establishes contact with at least one
`unit in an existing ad hoc network and then addi—
`tional information on the status, in particular the role
`of master or slave, of the unit already connected in
`the network is transferred to the not yet connected
`unit. This information facilitates the decision of the
`unconnected unit as to which unit in the network that
`is should try to connect to, Then, in the actual con-
`necting of the unit to the network, the roles of the
`unit and of the already connected unit can be chosen
`by the unit wanting to be connected. In particular,
`the initially inquiring and paging unit may become a
`slave unit in a newly formed piconet or in an already
`existing piconet.
`
`APPLE 1015
`
`e -- —
`
`820
`
`822
`— — —- — — —>
`
`821+
`528
`6 — — — ,
`826
`
`The third BT unit responds
`to_thE_PAGE mass 5 [3
`sand
`on its DAC
`‘9
`y
`
`— -*
`832
`
`'840
`
`
`
`
`
`830
`The first B unit sendsan FHS
`packet to the third Bl unit reques—
`tin- a reversal of the gaging
`
`The first B Lnit receives
`-836
`
`_he third ET unit reverses the
`
`the FHS packet frdn
`(— _ _ _
`aglng direction bygsending an FH
`the third E unit
`834
`
`The third 8T unit recei~
`535
`The first 5 unit responc
`ves the response fran
`
`
`tn the FHS packet by sendind — - - —- >
`
`the first BT unit
`'
`< I:
`BL?
`
`
`,
`,
`.
` :dn—
`The third BT uni: lS
`The first B unit is cone
`544
`nected to the first BT uni
`
`nectad id [‘18 third Bl
`as a master unit
`unit as a s ave unit
`
`In " '- 'l
`A first
`message is receivad in
`the
`'
`t Bi unit
`81“
`A second ‘
`'. 1L
`
`message is racer/ed i
`6 - 7 ,
`
`
`the first B unit
`818
`
`
`
`
`
`A third INQLIRYVRESPQNSE
`message is received in
`I'
`r
`:
`n
`The first B unit c doses
`to connect
`to the third
`BT unit as a slave unit
`he
`irst : unit
`sends a PAGE message t3
`
`the third B unit
`The first B unit_recei—
`ves the response from
`he third E unit
`
`
`
`||||||llllllllll|||l||||||||||||lllll||||||l|||lllll|||||||||I|||||||||||||HI||
`WO01/41371A1
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`1
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`WO 01/41371 A1
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`|||||||||||l|l||||||||||l||||||||l|l|||||l||||||l|l||||||I||1|||||||l||||||ll|||
`
`patent (AT, BE. CH. CY. DE, DK. ES, FI, FR, GB, GR, IE,
`IT, LU. MC, NL, PT, SE, TR), OAPI patent (BF, BJ, CF,
`CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG).
`
`For two~letter codes and other abbreviations, refer to the ”Guidv
`ance Notes on Codes andAbbreviatt‘ons ” appearing at the begin-
`hing ofeach regular issue ofthe PCT Gazette,
`
`Published:
`7 With international search report,
`
`2
`
`

`

`WO 01/41371
`
`PCT/SE00/02450
`
`Intelligent piconet forming
`
`1
`
`forming ad hoc wireless networks, more
`to
`invention relates
`The present
`particularly to ad hoc networks formed according to the Bluetooth specification, and
`connecting a unit to an already existing ad hoc network.
`BACKGROUND
`
`Bluetooth (ET) is a relatively new specification for wireless communication of data
`and voice based on .a low—cost short-range radio link.
`It can be built
`into a 9x9 mm
`microchip, what
`facilitates
`ad hoc
`connections
`for both stationary
`and mobile
`communication environments.
`Information in this application is in part based on the
`Bluetooth specification,
`"Specification of the Bluetooth System", July 26th 1999,
`the
`entirety of which is hereby incorporated by reference.
`
`The original
`intention in making the specification of Bluetooth was to eliminate
`cables between telephones, PC-cards (Personal Computer cards), wireless headsets, etc.,
`but
`today the Bluetooth specification is used for establishing true ad hoc wireless
`networks intended for both synchronous traffic, e. g. voice, and asynchronous traffic, e. g.
`data traffic based on the IF (the Internet Protocol). Now the intention of the Bluetooth
`specification comprises that any commodity device such as telephones, personal digital
`assistants
`(PDAs),
`laptop computers, digital cameras, video monitors, printers,
`fax
`machines, etc. should be capable of communicating over a radio interface,
`i.e. any of
`these devices could contain a radio chip made according to the Bluetooth specification
`and having the software specified therefor.
`
`In addition to merely replacing the cables between various devices,
`the use of the
`Bluetooth specification in various device provides a bridge to existing data networks and
`their peripheral devices, and a mechanism to form small private ad hoc groupings for
`connected devices away from fixed network structures or connected to a fixed network
`
`the Bluetooth specification the wireless
`a gateway. According to
`structure via
`communication uses a fast acknowledgement and frequency hopping scheme to make the
`radio links between devices
`adapted to communicate
`according to the Bluetooth
`specification robust. The devices avoid interference with one another by hopping to a new
`frequency or channel after transmitting or receiving a packet. Compared to other systems
`operating in the same frequency band,
`in the Wireless communication according to the
`Bluetooth specification typically frequency hops are made faster and shorter packets are
`used. The radio band used by devices adapted to communicate according to the Bluetooth
`specification is the unlicensed 2.4 GHz Industrial—Scientific—Medical
`(ISM) band with a
`
`channel spacing of 1 MHz.
`
`A device adapted to communicate according to the Bluetooth specification includes a
`radio unit, a link control unit and a support unit for link management and host terminal
`interface function. According to the specification a point—to—point connection can be
`provided in the case, where only two units adapted to communicate according to the
`Bluetooth specification are involved, or a point-to-multipoint connection in the case of
`more than tWO units. For a nniTit—tn-mnltirmi1'1?3 nnnnpr‘tinn
`the marlin hand in thrprl lm
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`
`several units adapted to communicate according to the Bluetooth specification. Two or
`
`more units adapted to communicate according to the Bluetooth specification form a small
`
`network called a piconet,
`
`see Figs.
`
`1a _ 1c. Within a piconet, a unit adapted to
`
`communicate according to the Bluetooth specification can have either of two roles: it can
`
`be a master or a slave. Within each piconet there may be only one master and one slave,
`
`see Fig. 1a, or more than one up to seven active slaves, see Fig.
`
`lb. Any unit adapted to
`
`communicate according to the Bluetooth specification can become a master in a piconet.
`
`Furthermore,
`
`two or more piconets can be interconnected,
`
`forming a composite
`
`network called a scatternet, see Fig. 1c. The connection point between two piconets
`
`consists of a unit C adapted to communicate according to the Bluetooth specification that
`
`is a member of both piconets. A unit adapted to communicate according to the Bluetooth
`
`specification can simultaneously be a slave member of multiple piconets, but only a
`
`master in one piconet, and thus a unit adapted to communicate according to the Bluetooth
`
`specification and acting as a master in one piconet can participate in other piconets only
`
`as a slave. A unit adapted to communicate according to the Bluetooth specification can
`
`only transmit and receive data in one piconet at a time, and therefore participation in
`
`multiple piconets is made on a time division multiplex basis.
`
`The Bluetooth specification provides full—duplex transmission built on slotted Time
`
`Division Duplex (TDD), where each slor is 0.625 ms long. The time slots are numbered
`
`sequentially using a large number range, which is cyclic with a cycle length of 227.
`
`Master-to-slave
`
`transmission
`
`always
`
`starts
`
`in an even—numbered
`
`time
`
`slot while
`
`slave-to—master transmission always starts in an odd—numbered time slot. The combination
`
`of an even—numbered time slot and its subsequent odd—numbered time slot
`
`is called a
`
`frame,
`
`the frame thus including a master—to-slave time slot and a slave—to—master
`
`time
`
`slot, except
`
`in the case where multi—slot packets are used and longer frames are used.
`
`There is no direct transmission between slaves, neither within a piconet or between two
`
`different piconets.
`
`The communication within a piconet
`
`is organised such that
`
`the master polls each
`
`slave according to some polling schedule. With one exception, a slave is only allowed to
`
`transmit after having been polled by the masrer. The slave will then start its transmission
`
`in the slave-to—master
`
`time slot
`
`immediately following the packet
`
`received from the
`
`master. The master may or may not include data in the packet used to poll a slave. The
`
`only exception to the above principle is that when a slave is connected by an established
`
`Synchronous Connection Oriented (SCO)
`
`link it
`
`is always allowed to transmit
`
`in the
`
`pre—allocated slave-to—master time slot, even if not explicitly polled by the master in the
`preceding master—to—slave time slot.
`V
`
`Each unit adapted to communicate according to the Bluetooth specification has a
`
`globally unique 48—bit IEEE 802 address. This address, called the Bluetooth unit Address
`
`(BD_ADDR),
`
`is assigned at
`
`the time when the unit
`
`is manufactured and it
`
`is never
`
`changed.
`
`In addition thereto the master of a piconet assigns a local Active Member
`
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`
`Address (AM_ADDR)
`
`to each active slave member of the piconet. The AM_ADDR,
`
`which is only three bits long,
`
`is dynamically assigned and de—assigned and is unique only
`
`within a single piconet. The master uses the AM_ADDR when polling a slave in a
`
`piconet. However, when the slave, triggered by a packet from the master addressed using
`
`5 the AM_ADDR of the slave,
`
`transmits a packet
`
`to the master,
`
`it
`
`includes its own
`
`AM_ADDR and not
`
`the AM_ADDR of the master
`
`in the packet header since an
`
`AM_ADDR of the master does not exist. Thus, the master of a piconet never assigns an
`
`AM_ADDR to itself.
`
`Although all data are transmitted in packets, the packets can carry both synchronous
`
`10 data, on the mentioned Synchronous Connection Oriented links, mainly intended for voice
`
`traffic, and asynchronous data, on Asynchronous ConnectionLess (ACL) links. An SCO
`
`link is a symmetric point—to—point link between the master and a specific slave. The SCO
`link reserves slots and can therefore be considered as a circuit-switched connection
`
`between the master and the slave. An ACL link is a point-to-multipoint
`
`link between the
`
`15 master and all
`
`the slaves participating in the piconet. Slots may be reserved for SCO
`
`links, as indicated above, and in slots not reserved for such links the master can establish
`
`an ACL link on a per slot basis to any slave. The ACL link provides a packet-switched
`
`connection between the master and all active slaves participating in the piconet.
`
`Depending on the type of packet used, an acknowledgement and retransmission
`
`20 scheme is used to ensure reliable transfer of data, such a scheme not being used for
`
`packets on SCO links transferring synchronous data. Forward error correction (FEC) in
`
`the form of channel coding is also used which limits the impact of random noise on
`
`long—distance links.
`
`The standard format of a packet used for transmission according to the Bluetooth
`
`25 specification is illustrated in Fig. 2, this format not being used for some types of control
`
`packets. A standard packet has a field for an access code having the length of 72 bits and
`
`a header field of a length of 54 bits. There is a field for the payload which has a length
`
`that can range from zero to a maximum of 2745 bits. The AM_ADDR is located in the
`
`packet
`
`header
`
`followed
`
`by
`
`some
`
`control
`
`parameters,
`
`e. g.
`
`a
`
`bit
`
`indicating
`
`30 acknowledgement or retransmission request of the previous packet, when applicable, and
`
`a header error check (HEC).
`
`The access code used in a packet can be one of three different
`
`types: Channel
`
`Access Code (CAC), Device Access Code (DAC), and Inquiry Access Code (IAC):
`
`— The Channel Access Code identifies a channel
`
`that
`
`is used in a certain piconet.
`
`i.e.
`
`35 essentially the CAC identifies the piconet. All packets exchanged within a piconet carry
`
`the same the CAC. The CAC is derived from the BD_ADDR of the master unit of the
`
`piconet.
`
`- The Device Access Code is derived from a BD_ADDR of a particular unit adapted to
`
`communicate according to the Bluetooth specification.
`
`It
`
`is used for special signalling
`
`40 procedures, e. g. the PAGE procedure.
`
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`
`- The Inquiry Access Code appears in two variants:
`
`the General Inquiry Access Code
`
`(GIAC) and the Dedicated Inquiry Access Code (DIAC). Both are used in the INQUIRY
`
`procedure, that Will be explained in more detail below.
`
`The format of the payload depends on the type of packet. The payload of an ACL
`
`packet consists of a header, a data field and, with the exception of AUXl type packets, a
`
`cyclic redundancy check (CRC). The payload of a Synchronous Connection Oriented
`
`(SCO) packet consists of a single data field.
`
`In addition,
`
`there are hybrid packets
`
`including two data fields, one for synchronous data and one for asynchronous data.
`
`Packets in which the payload does not
`retransmitted.
`
`10
`
`include a CRC are neither acknowledged nor
`
`The protocol layers of a network formed by units adapted to communicate according
`
`to the Bluetooth specification are illustrated in Fig. 3. The Baseband, LMP and L2CAP
`
`represent existing Bluetooth specific protocols. The "High level protocol or application"
`
`layer represents protocols that may or may not be Bluetooth specific while the Network
`
`layer is not defined in the Bluetooth specification.
`
`A limitation of the Bluetooth specification is that
`
`therein no method is explicitly
`
`provided to address and route packets from one piconet
`
`to another. Thus,
`
`inter—piconet
`
`communication performed in a scatternet is not specified, although there are proposals for
`how to achieve this.
`
`An important capability in any ad hoc networking method is
`
`the neighbour
`
`discovery feature. Such a feature is also defined in the Bluetooth specification. Without a
`
`neighbour discovery capability, a unit adapted to communicate according to the Bluetooth
`
`specification would not be capable of finding any other units adapted to communicate
`
`according to
`
`the Bluetooth specification with which it
`
`could communicate
`
`and
`
`consequently no ad hoc network could be formed. The neighbour discovery procedure
`
`according to the Bluetooth specification consists of the INQUIRY message and the
`
`INQUIRY RESPONSE message. An "inquiry" procedure is defined which is used in
`
`applications where the device address of the destination is unknown to the source. For
`
`example,
`
`public
`
`facilities
`
`like printers or
`
`facsimile machines
`
`can be considered.
`
`Alternatively,
`
`the inquiry procedure can be used to discover other units adapted to
`
`communicate according to the Bluetooth specification which are located within the range
`
`of the transceiver of a considered unit adapted to communicate according to the Bluetooth
`
`specification.
`
`A unit adapted to communicate according to the Bluetooth specification and wanting
`
`to discover neighbouring units also adapted to communicate according to the Bluetooth
`
`specification, neighbouring meaning within radio coverage of
`
`the
`
`first unit, will
`
`repeatedly transmit
`
`according to well
`
`specified timing and frequency sequences,
`
`INQUIRY messages and listen for INQUIRY RESPONSE messages, which are optional.
`
`An INQUIRY message consists of only an Inquiry Access Code (IAC).
`
`It does not
`
`contain any information about the source but may indicate the class of devices which
`
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`
`Inquiry Access Code
`should respond. The Inquiry Access Code can be a General
`(GIAC), which is sent
`to discover any unit adapted to communicate according to the
`
`Bluetooth specification in the neighbourhood, or a Dedicated Inquiry Access Code
`(DLAC), which is sent to discover only a certain type of units adapted to communicate
`
`according to the Bluetooth specification, for which a particular DIAC is dedicated.
`A unit adapted to communicate according to the Bluetooth Specification receiving an
`INQUIRY message, including a GIAC or an appropriate DIAC, may respond by sending
`an INQUIRY RESPONSE message. The INQUIRY RESPONSE message is actually an
`Frequency Hop Synchronisation (FHS) packet, see Fig. 4. The FHS packet
`is a special
`control packet revealing, among other things,
`the transmitting unit and the clock of the
`transmitting unit. The payload field in such a packet includes eleven fields. All fields in
`the packet, except the AM_ADDR field, and of course the "Undefined" field,
`indicate
`properties or parameters of the unit that sends the FHS packet. The Lower Address Part
`(LAP), Upper Address Part
`(UAP)
`and Non—significant Address Part
`(NAP)
`fields
`together form the BD_ADDR. The "class of device" field indicates the class of device of
`the unit. The CLK field contains the current value of the internal clock of the unit. The
`
`SR, SP and "Page scan mode" fields all contain control parameters concerning the PAGE
`
`procedure. The contents of the AMgADDR field can be used to assign an AM_ADDR to
`a unit which will become a slave in a piconet, and otherwise these three bits should all be
`
`set to zero. The "Undefined" field is reserved for future use and includes two bits. which
`
`should be set
`to zero. By listening for INQUIRY RESPONSE messages the unit
`that
`initiated the INQUIRY procedure can collect the BD_ADDR and internal clock values of
`the neighbouring units
`also adapted to
`communicate
`according to the Bluetooth
`
`specification.
`is also used for other purposes according to the Bluetooth
`An FHS packet
`specification,
`in addition to the use as the INQUIRY RESPONSE message. e.g.
`for
`synchronising the frequency hop channel sequence, a paged master response and in the
`master-slave switch.
`
`Related to the INQUIRY procedure is
`
`the PAGE procedure, which is used to
`
`establish an actual connection between two units adapted to communicate according to the
`
`Bluetooth specification. Once the BDgADDR of a neighbouring unit is known to a unit.
`the paging unit. as a result of an INQUIRY procedure,
`the neighbouring unit can be
`paged by sending a PAGE message. Also the knowledge of the internal clock value of the
`unit to be paged will potentially speed up the PAGE procedure. since it makes it possible
`for
`the paging unit
`to estimate when and on which frequency hop channel
`the
`
`10
`
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`
`20
`
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`
`neighbouring unit will listen for PAGE messages.
`A PAGE message consists of the Device Access Code (DAC), derived from the
`BD_ADDR of the paged unit. A unit adapted to communicate according to the Bluetooth
`specification and receiving 3 PAGE message including its own DAC responds by sending
`an identical packet.
`i.e.
`including only the DAC of the paged unit. The paging unit then
`
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`
`replies by sending an FHS packet,
`
`including the BD__ADDR of the paging unit,
`
`the
`
`current value of the internal clt ck of the paging unit,
`
`the AM_ADDR assigned to the
`
`paged unit and some other parameters, see Fig. 4. The paged unit then responds once
`
`again by transmitting its DAC and thereby the connection between the two units is
`established.
`
`(7‘
`
`If the paging unit already was the master of a piconet,
`
`the paged unit has now
`
`joined this piconet as a new slave unit. Otherwise,
`
`the two units have just formed a new
`
`piconet having the paging unit as the master unit. Since the INQUIRY message does not
`
`include any information on the sender thereof,
`
`in particular not its BDWADDR,
`
`the unit
`
`10 that
`
`initiated the INQUIRY procedure is the only unit
`
`that can initiate a subsequent
`
`PAGE procedure. Thus,
`
`the unit
`
`initiating an INQUIRY procedure will also be the
`
`master of any new piconet that is formed as a result of a subsequent PAGE procedure. If
`
`considered necessary, however,
`
`the roles of master and slave can be switched using the
`
`master—slave—switch mechanism defined in the Bluetooth specification. This is a complex
`
`15 and extensive procedure resulting in a redefinition of the entire piconet,
`
`involving all
`
`other slave units in the piconet.
`
`.
`
`The
`
`INQUIRY and PAGE procedures
`
`are well
`
`specified in the Bluetooth
`
`specification. They are the only tools that are needed to form a new piconet or to join an
`
`existing one. Although the tools as
`
`such are well specified,
`
`there are no rules or
`
`20 guidelines as to how to use them. When neighbours are discovered there is no way of
`
`knowing to which thereof a connection should be made to in order to form an appropriate
`
`piconet. Even if the master—slave—switch mechanism exists, using it
`
`is an extensive
`
`procedure and it
`
`is difficult to know when to use it in order to improve the efficiency of
`
`a piconet. Hence, piconets will be more or less established at random. often resulting in
`
`25 far from optimal piconet and scatternet strucrures.
`
`An exception exists in the case where the unit wanting to establish a connection
`
`already knows the BD_ADDR of the unit to which it wants to connect. The use of the
`
`Dedicated Inquiry Access Code in the INQUIRY messages and the class of device field in
`
`the FHS packet, indicating the class of device of the unit that sends the FHS packet, can
`
`30 also be used to impose a certain control of the establishment of piconets. Nevertheless.
`
`units adapted to communicate according to the Bluetooth specification and forming a
`
`piconet or a scatternet generally result in less than optimal networks being formed.
`
`The information exchanged during the INQUIRY and PAGE procedures is not
`
`sufficient to determine how to establish connections in order to form an efficient piconet.
`
`35 Furthermore,
`
`the fact that the unit that initiates an INQUIRY procedure will have to be
`
`the master of any new piconet that is formed as a result of a subsequent PAGE procedure
`makes the forming of piconets and scatternets inflexible. The complex and extensive
`
`master—slave-switch mechanism is too inefficient to compensate for this inflexibility.
`
`Consider, for instance, a scenario in which a number of people have gathered in a
`
`40 conference room for a meeting. They turn on their
`
`laptops. which have circuits to
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`communicate according to the Bluetooth specification and at
`
`random start
`
`to send
`
`INQUIRY messages and listen for INQUIRY messages from other units. Some other
`
`people may also later join the meeting resulting in more INQUIRY procedures. The
`
`followed by PAGE procedures and the
`result of these random INQUIRY procedures,
`5 forming of piconets, may well be something like the interconnected networks shown in
`Fig. 5, whereas an optimal piconet structure could be similar to the network shown in
`
`Fig. 6.
`
`When a new unit moves into the neighbourhood of an existing piconet, e. g. as could
`
`be the case in this meeting scenario,
`
`it may want
`
`to communicate with the units
`
`10 connected to that piconet. The unit would then obviously like to join the piconet as a new
`
`slave unit. However,
`
`the means by which to achieve this as provided by the Bluetooth
`
`specification are few and inefficient. The unit would have to wait and hope to be
`
`discovered by the master unit of the piconet, by receiving an INQUIRY message from
`
`the master unit, and to be subsequently paged and connected. However, when receiving
`
`15 an INQUIRY message,
`
`it does not provide any information about
`
`the sender of the
`
`message. Therefore, an INQUIRY message received by the unit may also be transmitted
`
`by a slave unit, which is actually more likely, since there are usually more slave units
`than master units.
`
`Waiting and hoping constitute no efficient method, but the Bluetooth specification
`
`20 allows an alternative way. The unit can itself send INQUIRY messages and hope to
`
`receive a response from the master unit of a piconet. However,
`
`the
`
`INQUIRY
`
`RESPONSE message, an FHS message, does not
`
`include any information on the fact
`
`whether the sender is a master or a slave of a piconet. Therefore, the unit has to take a
`
`chance and page and connect to a responding unit, hoping that the responding unit turns
`
`25 out to be the master of the piconet. If the unit is lucky. and actually manages to connect
`
`to the master unit of an existing piconet, a new piconet is formed having the inquiring
`
`and paging unit as the master unit and the paged master unit of the already existing
`
`piconet as a slave unit.
`
`To join the old piconet the newly arrived unit has to request a master—slave switch.
`
`30 This master-slave switch will make the master unit of the old piconet, which is also a
`
`slave unit of the new piconet, a master also in the new piconet. Then, the two piconets
`
`will merge into one piconet making the new unit a slave unit
`
`in the merged piconet.
`
`Hence, joining an existing piconet as a slave unit requires first of all luck, and possibly
`also a master—slave switch.
`
`35
`
`SUMMARY OF THE INVENTION
`
`The procedures for establishing piconets and scatternets and connecting new units to
`
`already existing piconets according to the Bluetooth specification would be facilitated and
`
`better piconet and scatternet topologies would be possible to achieve, if more information
`
`about
`
`the involved units could be exchanged before the piconets and scatternets are
`
`40 actually established and if the connection procedure could be made more flexible.
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`For this purpose procedures can be used for exchanging small, but valuable, pieces
`
`of information during the INQUIRY and PAGE procedures and a procedure can be used
`
`to increase the control of the forming of piconets and scatternets, based on the exchanged
`information.
`
`The present invention relates to a method of forming ad hoc wireless networks, and
`
`more particularly,
`
`to forming wireless networks according to the Bluetooth specification
`
`and how a unit adapted to communicate according to the Bluetooth specification may best
`
`discover masters in existing piconets and be connected as a slave to those masters without
`
`having to use the master—slave switch.
`
`An object of the present invention is to provide a method of more easily finding out
`
`the roles, master or slave. of units located in the neighbourhood of a considered unit, i.e.
`
`whether the neighbouring units are masters or slaves in already existing piconets.
`
`Another object of the present invention is to allow the unit to connect to a master as
`
`a slave without using the complicated master-slave switching.
`
`Generally, the method can be divided into two basic parts.
`
`First,
`
`in the INQUIRY procedure, a few additional pieces of information are
`
`exchanged between two units adapted to communicate
`
`according to the Bluetooth
`
`specification. The additional
`
`information informs on the status of the responding unit in
`
`an existing piconet or existing piconets, what facilitates the decision of the unit. which
`
`sends the INQUIRY message, on which unit to attempt
`
`to be connected to. A similar
`
`improvement of the INQUIRY procedure can be achieved in an alternative way, by using
`
`a modified INQUIRY message. These two alternatives, which together constitute the first
`
`basic part of the method, are described in further detail below.
`
`In the second basic part of the method. a procedure is provided by which the initial
`
`inquiring and paging unit can become a slave unit
`
`in a new formed piconet or in an
`
`already existing piconet. This new mechanism is used during the PAGE procedure and
`
`hence the use of the complex and extensive master~slave—switch mechanism is avoided,
`
`although there may be other situations in which the master—slave—switch mechanism is still
`
`needed. This second basic part of the method is also described in further detail below.
`
`Some merits of
`
`the proposed method include providing means
`
`to impose an
`
`intelligent control of the forming of piconets in general. Efficient procedures are provided
`
`allowing a unit to join an existing piconet. In addition,
`
`the method allows exchange of
`
`piconet related information during the INQUIRY procedure and enhances the INQUIRY
`
`procedure so that
`
`the master units of existing piconets can be discovered. The second
`
`basic part of the method provides a procedure by which the initially inquiring and paging
`
`unit can become a slave unit
`
`in a now formed or previously existing piconet without
`
`going through the master—slave switch procedure. Furthermore,
`
`the method as proposed
`
`can be used to facilitate reforming scattemet structures.
`
`The preferred procedures of the proposed method do not imply modifications of any
`
`of the existing message formats according to the Bluetooth specification although some of
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`the alternative procedures require modifications of existing message formats.
`
`Although the preferred embodiments of the proposed are directed to a system of
`
`0|
`
`10
`
`units adapted to communicate according to the Bluetooth specification,
`
`the disclosed
`
`method is also applicable to general ad hoc networks which have features similar to those
`
`formed according to the Bluetooth specification. The proposed method provides means to
`
`impose an intelligent control of the forming of ad hoc networks in general and allows
`
`exchange of ad hoc network related information during a neighbour discovery procedure.
`
`A procedure is provided for the unit initiating the establishment of an ad hoc network to
`
`transfer the specific role of the initiator to another unit during the establishment phase.
`
`Additional objects and advantages of the invention will be set
`
`forth in the
`
`description which follows, and in part will be obvious from the description, or may be
`
`learned by practice of the invention. The objects and advantages of the invention may be
`
`realized and obtained by means of
`
`the methods, processes,
`
`instrumentalities
`
`and
`
`combinations particularly pointed out in the appended claim