USOO7587207B2
`
`(12) United States Patent
`(10) Patent No.:
`US 7,587,207 B2
`
`Davies et al.
`(45) Date of Patent:
`Sep. 8, 2009
`
`(54) DATA DELIVERY THROUGH BEACONS
`
`(75)
`
`Inventors: Robert J. Davies, Horley (GB); Saul R.
`Dooley, Reigate (GB)
`
`(73) Assignee:
`
`IPG Electronics 503 Limited, St. Peter
`Port (GG)
`
`*
`
`Notice:
`
`J
`y
`Sub'ect to an disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 1859 days.
`
`(21) Appl.No.: 09/876,515
`
`(22)
`
`Filed:
`
`Jun. 7, 2001
`
`(65)
`
`(30)
`
`Prior Publication Data
`
`US 2002/0002034 A1
`
`Jan. 3, 2002
`
`Foreign Application Priority Data
`
`Jun. 26, 2000
`Aug. 15, 2000
`
`(GB)
`(GB)
`
`................................. 00154542
`................................. 00200733
`
`(51)
`
`Int. Cl.
`(2006.01)
`H04 W 24/00
`(52) U.S. Cl.
`.................. 455/456.1; 455/456.5; 455/457
`(58) Field of Classification Search ................. 455/457,
`455/456.1, 456.5
`See application file for complete search history.
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`1/2001 King 6111.
`6,169,498 B1*
`6,311,060 B1* 10/2001 Evans et al.
`6,782,253 B1 *
`8/2004 Shteyn et a1.
`
`............... 340/6861
`.............. 455/426.1
`............ 455/414.1
`
`FOREIGN PATENT DOCUMENTS
`
`EP
`EP
`
`0752793 A2
`1006684 A2
`
`8/1997
`7/2000
`
`* cited by examiner
`
`Primary ExamineriQuoc D Tran
`Assistant ExamineriKaren L Le
`
`(74) Attorney, Agent, or FirmiVolpe and Koenig, PC.
`
`(57)
`
`ABSTRACT
`
`A communications system comprises at least one beacon
`device capable of wireless message transmission and at least
`one portable device capable of receiving such a message
`transmission. The beacon is arranged to broadcast a series of
`inquiry messages each in the form of a plurality of predeter-
`mined data fields arranged according to a first communica-
`tions protocol, such as Bluetooth. For the delivery of addi-
`tional data via broadcast, and in particular data including
`location information, the beacon adds to each inquiry mes-
`sage prior to transmission an additional data field carrying
`broadcast data, with the portable device receiving the trans-
`mitted inquiry messages including the location data and read-
`ing the broadcast data from the additional data field.
`
`5,835,861 A * 11/1998 Whiteside ................... 455/466
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`11 Claims, 3 Drawing Sheets
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`I. FILT
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`APPLE 1001
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`ID packet
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`Slot boundary
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`US 7,587,207 B2
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`1
`DATA DELIVERY THROUGH BEACONS
`
`The present invention relates to services offered to users of
`electronic equipment, especially but not exclusively to users
`of mobile communications devices such as portable tele-
`phones and suitably equipped PDA’s (personal digital assis-
`tants). The invention further relates to means for delivery of
`such services, and to portable devices for receiving them.
`Recent years have seen a great increase in subscribers
`world-wide to mobile telephone networks and,
`through
`advances in technology and the addition of functionalities,
`cellular telephones have become personal, trusted devices. A
`result of this is that a mobile information society is develop-
`ing, with personalised and localised services becoming
`increasingly more important. Such “Context-Aware” (CA)
`mobile telephones are used with low power, short range base
`stations in places like shopping malls to provide location-
`specific information. This information might include local
`maps, information on nearby shops and restaurants and so on.
`The user’s CA terminal may be equipped to filter the infor-
`mation received according to pre-stored user preferences and
`the user is only alerted if an item of data of particular interest
`has been received.
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`An example of a CA terminal is given in US. Pat. No.
`5,835,861 which discloses the use of wireless telephones
`within the context of advertisement billboards. The user of a
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`such as staying close to a beacon whilst contact is established
`between portable device and beacon, nor having to specifi-
`cally initiate interaction (as is the case with the above-men-
`tioned system in US. Pat. No. 5,835,861). A further require-
`ment is that the portable device should be kept relatively
`simple insofar as the data gathering from beacons is con-
`cerned:
`in the Cooltown system, a full web browser and
`display capability is required to support user navigation
`within the web page indicated by the URL being broadcast.
`It is therefore an object ofthe invention to provide a system
`for the delivery of data via beacons whereby the amount of
`dedicated circuitry and operating procedure are kept to low
`levels.
`
`In accordance with a first aspect of the present invention
`there is provided a communications system comprising at
`least one beacon device capable of wireless message trans-
`mission and at least one portable device capable of receiving
`such a message transmission, wherein the beacon is arranged
`to broadcast a series of inquiry messages each in the form of
`a plurality of predetermined data fields arranged according to
`a first communications protocol, wherein the beacon is fur-
`ther arranged to add to each inquiry message prior to trans-
`mission an additional data field, and wherein the at least one
`portable device is arranged to receive the transmitted inquiry
`messages and read data from said additional data field, the
`additional data field including location information. By add-
`ing the additional field (suitably at the end of a respective
`inquiry message), data broadcast may be carried on top of an
`existing inquiry process, such that the usual delays while such
`a process is carried out prior to data transfer are avoided.
`Furthermore, by placing the additional field at the end of
`those sent according to the communications protocol (pref-
`erably but not essentially Bluetooth), those protocol-compat-
`ible devices not intended for reception of beacon signals can
`simply ignore the additional data without compromising
`operation according to protocol.
`Where the protocol is Bluetooth (or a similar frequency
`hopping arrangement) the beacon may be configured to
`broadcast a series of inquiry messages on a predetermined
`clocked succession or sequence of frequencies, with clock
`information for the beacon being carried by the additional
`data field. In one arrangement, the additional data field may
`carry at least 64 bits of data. As will be described in greater
`detail hereinafter with respect to embodiments of the inven-
`tion, this can improve the inquiry performance of a Bluetooth
`system, shortening the time to establish a connection for data
`exchange.
`The beacon may be arranged to include an indication in one
`of said predetermined data fields (suitably in a currently
`unused or unassigned field), said indication denoting the pres-
`ence of said additional data field, such that devices configured
`for reception ofbeacon data may be triggered to read from the
`additional data field.
`
`Where the first communications protocol comprises Blue-
`tooth messaging, a special Dedicated Enquiry Access Code
`(DIAC) may be used to indicate the presence of location
`information in the additional data field.
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`wireless telephone obtains the telephone number of a vendor
`by activating his/her wireless telephone to transmit a prompt
`signal to an active advertisement source and to receive from
`the advertisement source a response signal containing the
`telephone number of the advertising vendor. The telephone
`number can then be used to automatically place a call to that
`vendor via the public switched telephone network. Alterna-
`tively, the telephone number can be stored for use later on.
`This arrangement can be used to place a call to a vendor
`without having to either memori se the telephone number or to
`write it down. The signals between the billboard and the caller
`can be transmitted as modulated infrared (IR) signals.
`In another example, Hewlett-Packard has posted a publi-
`cation on the Web at <http://www.cooltown.hp.com/papers/
`webpres/WebPresence.htm> about their “Cooltown” project.
`The convergence of Web technology, wireless networks and
`portable client devices provides design opportunities for
`computer/communications systems. In the Cooltown project,
`systems that are location-aware can be created using URL’s
`for addressing, physical URL’s for delivery via beacons and
`sensing ofURL’s for discovery, and localised web servers for
`directories. The systems are ubiquitous to support nomadic
`users. On top of this infrastructure the Internet connectivity
`can be leveraged to support communications services. Web
`presence bridges the World Wide Web and the physical world
`inhabited by the users, providing a model for supporting
`nomadic users without a central control point.
`The Cooltown Museum and Bookstore offers visitors a
`
`Web -enhanced experience. As visitors tour the museum, their
`portable digital assistant (PDA) can receive Web URLs from
`wireless “beacons”. These beacons are small infrared trans-
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`ceivers located close to pictures or sculptures; the URLs link
`into a Web of information about the items. Using the PDA’s
`Web browser, visitors can read or hear about the artist or the
`work and about related art works in the museum. The URLs
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`can also be stored as bookmarks for further study or they can
`be used to select reproductions ofthe artwork from the muse-
`um’s online store.
`
`It will be recognised that an important requirement for CA
`devices is that they quickly and efficiently gather data from
`beacons such that the user is not required to undertake actions
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`The presence of location information in the additional data
`field may be indicated by header information appearing in the
`additional data field.
`
`60
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`The communications system may perform wireless mes-
`sage transmission and reception using a scheme which
`employs frequency hopping. In this case, location data may
`be sent on each frequency used for inquiry message broad-
`casts.
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`65
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`The beacon may be arranged to include in a message first
`comparison data, with the portable device further comprising
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`US 7,587,207 B2
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`3
`storage means holding second comparison data and compara-
`tor means arranged to identify when there is a match between
`the first and second comparison data and present the data read
`from the additional data field, otherwise to not present the
`data. Such second comparison data may be predetermined
`and/or pre-stored, or it may be determined adaptively from
`user profiling of the portable device user.
`That is, means may be provided for generating said second
`comparison data from user profiling of the portable device
`user.
`
`The comparator means may be a programmable device
`operable to perform, in synchronous or overlapping manner,
`comparisons between respective sets of first and second com-
`parison data.
`Also in accordance with the present invention there is
`provided a mobile communication device for use in the sys-
`tem recited above, the device comprising a receiver capable of
`receiving a short-range wireless inquiry message including a
`plurality of data fields according to a first communications
`protocol, means for determining when an additional data field
`including location information has been added to said plural-
`ity of data fields, and means for reading the location informa-
`tion data from such an additional data field.
`
`Further in accordance with the present invention, there is
`provided a beacon device capable of wireless message trans-
`mission and for use in a communications system comprising
`said beacon device and at least one portable device capable of
`receiving such a message transmission, wherein the beacon is
`configured to broadcast a series of inquiry messages each in
`the form of a plurality of predetermined data fields arranged
`according to a first communications protocol, and to add to
`each inquiry message prior to transmission an additional data
`field, such as to enable the at least one portable device
`arranged to receive the transmitted inquiry messages to read
`data from said additional data field, the additional data field
`including location information. As described in relation to the
`system as a whole, the beacon device may be arranged to add
`said additional data field at the end of a respective inquiry
`message; it may be arranged to include an indication in one of
`said predetermined data fields, said indication denoting the
`presence of said additional data field; the first communica-
`tions protocol may comprise Bluetooth messaging; and the
`device may be configured to broadcast a series of inquiry
`messages on a predetermined clocked succession of frequen-
`cies, with clock information for said beacon being included in
`data carried by said additional data field.
`Still further in accordance with the present invention, there
`is provided a method for enabling the user of a portable
`communications device to receive broadcast messages
`wherein at least one beacon device broadcasts a series of
`
`inquiry messages each in the form of a plurality of predeter-
`mined data fields arranged according to a first communica-
`tions protocol, wherein the beacon adds to each inquiry mes-
`sage prior to transmission an additional data field carrying
`broadcast message data, including location information, and
`wherein the portable device receives the transmitted inquiry
`messages, including the location information, and reads the
`broadcast data from said additional data field.
`
`These and other aspects and optional features ofthe present
`invention appear in the appended claims, to which reference
`should now be made and the disclosure of which is incorpo-
`rated herein by reference or will become apparent from read-
`ing the following description ofthe preferred embodiments of
`the invention.
`Preferred embodiments of the invention will now be
`
`described, by way of example only, and with reference to the
`accompanying drawings, in which:
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`FIG. 1 is a block schematic diagram of a beacon and
`portable device embodying the invention;
`FIG. 2 is a schematic diagram of a series of devices in a
`linked beacon infrastructure;
`FIG. 3 is a chart illustrating a portion ofthe transmission of
`a train of inquiry access codes centred on a given frequency;
`FIG. 4 illustrates alternation between trains ofinquiry mes-
`sages over the duration of an inquiry broadcast;
`FIG. 5 illustrates the insertion of a packet of broadcast data
`within an existing transmission slot;
`FIG. 6 illustrates a first arrangement for sending beacon
`clock data in a sequence of inquiry message trains; and
`FIG. 7 illustrates an alternate arrangement to that of FIG. 6
`for the sending of beacon clock data.
`In the following description we consider particularly a CA
`application which utilises Bluetooth protocols for communi-
`cation of messages from beacon to portable device (whether
`telephone, PDA or other). As will be recognised, the general
`invention concept of including a broadcast channel as part of
`the inquiry procedure is not restricted to Bluetooth devices,
`and is applicable to other communications arrangements, in
`particular frequency hopping systems.
`FIG. 1 is a block schematic diagram of a CA mobile tele-
`phone 10 in use with one or more low power, short range base
`stations or beacons 12, 14. As mentioned previously, and
`discussed in greater detail below, such an arrangement may be
`used in places like shopping malls to provide location-spe-
`cific information such as local maps, information on nearby
`shops and restaurants and so on, with the beacon download-
`ing information keys to a mobile device. As will be discussed
`in greater detail below, the arrangement may also be used to
`provide location information itself, for example mapping co-
`ordinates or the like. An information key is a small data object
`that provides a reference to a source of full information, and
`it is in the form of a number of predetermined fields, one of
`which may contain a short piece of descriptive text presented
`to a user. Another field will be a pointer or address of some
`form, for example a URL or telephone number. Other supple-
`mentary fields may control how the data is presented to a user
`and how the address may be exploited. The beacon will gen-
`erally broadcast cyclically a number of these keys, each typi-
`cally relating to a different service.
`Issues relating to the beacon construction and configura-
`tion include the beacons range which will be dependent on
`output power (typical range being 1 mW to 100 mW), levels
`of local interference, and receiver sensitivity.
`The user’s CA terminal 10 comprises an aerial 16 coupled
`with transceiver stage 18 for the reception and transmission of
`messages. Outgoing messages result from user input to the
`telephone, either audio input via microphone 20 and A/D
`converter 22 or other data input via the keypad or other input
`means 24. These inputs are processed to message data format
`by signal and data processing stage 26 and converted to trans-
`mission format by encoder 28 before being supplied to the
`transceiver stage 18.
`Messages received via the aerial 16 and transceiver 18 are
`passed via a decoding stage 30 to a filtering and signal pro-
`cessing stage 32. If the data carried by the message is for
`presentation on a display screen 34 of the telephone, the data
`will be passed to a display driver 36, optionally after buffering
`38, with the driver formatting the display image. As will be
`recognised, the display 34 may be a relatively simple low-
`resolution device, and the conversion of received data to
`display data may be carried out as a subset of the processing
`stage 32 functionality, without the requirement for a dedi-
`cated display driver stage.
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`US 7,587,207 B2
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`5
`Where the message is carrying data from one or other ofthe
`beacons 12, 14, the telephone has the ability to filter the
`information received according to pre-stored 40 user prefer-
`ences and the user is only alerted (i.e. the information will
`only be retained in buffer 38 and/or presented on screen 34) if
`comparison of stored preference data and subject matter indi-
`cators in the mes sage indicate that an item ofdata ofparticular
`interest has been received.
`
`For conventional audio messages, the audio data is output
`by the filter and processing stage 32, Via D/A converter 42 and
`amplifier 44 to an earphone or speaker 46. Receipt of such
`messages from the telephone network 48 is indicated by
`arrow 50: the telephone network 48 also provides the link
`from the telephone 10 to a wide-area network (WAN) server
`52 and, via the WAN 54 (which may be the internet), to one or
`more remote service providers 56 providing a source of data
`for the telephone 10.
`Communication between the CA terminal (telephone 10)
`and the CA base station (beacon 12) takes two forms: ‘push’
`and ‘pull’. In ‘push’ mode, information is broadcast by the
`beacons 12, 14, to all portable terminals 10 in the form of
`short ‘keys’ indicated at 60. The keys will take various forms
`according to the application but will generally include a con-
`cise description of the information being sent and a pointer to
`fuller information, e.g. a URL identifying one of the service
`providers 56.
`Keys are received by the terminal 10 ‘unconsciously’, that
`is, without direct intervention by the user, and automatically
`filtered according to the user’s pre-set preferences. This fil-
`tering may be done by a comparator function applied in
`processing stage 32. Suitably, the processing stage is operable
`to apply the comparator function in multiple simultaneous or
`overlapping copies such as to process in parallel the relatively
`large number of keys that may be received. Some will be
`discarded, some kept for further study, others might cause the
`user to be alerted immediately. By way of example, shops
`might choose to push details of special offers into passing
`terminals in the knowledge that users who have interest and
`have therefore set their filters 32 accordingly will be alerted
`by their terminal.
`Sometimes the user will wish to obtain more information
`
`than is contained in the keys. Here, ‘pull’ mode allows a user
`to set up a connection with a server 56 (which need not
`necessarily be specially configured for CA use) and actively
`request information to pull down into the terminal 10. This
`mode is therefore typically interactive.
`Whilst base stations or beacons will typically be indepen-
`dent of one another (in a shopping mall set up, each shop
`provides and maintains its own beacon without reference to
`any beacons provided by neighbouring shops), the beacons
`may be wholly or partially networked with at least some
`coordination as to their broadcast messages.
`FIG. 2 is a diagram of such a system 100 of linked beacons
`embodying the invention and providing an implementation of
`an infrastructure for use in, for example, department stores,
`shopping malls, theme parks, etc. The system 100 comprises
`a plurality of beacons 102, 104, 106, 108 distributed over a
`series of locales. Each ofthe beacons 102-108 broadcasts one
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`or more short-range inquiry signals in a time-slot format as
`described in greater detail hereinafter. The beacons 102-108
`are controlled by a beacon infrastructure server (BIS) 110,
`with one or more terminals 112, 114, 116, 118 being con-
`nected to the server 110. The terminals 112-118 enable ser-
`
`vice providers, i.e., the users ofbeacons 102-108, to author or
`edit allocated service slots in the form of added data piggy
`backed on inquiry facilitation signals transmitted by beacons
`102-108. A service provider may lease a beacon or one of the
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`beacon’s service slots from the infrastructure provider. To this
`end, server 110 provides simple HTML templates for filling
`out by the user via one ofterminals 112-118. Having filled out
`the template with, for example, a description of the service
`and other information for the data to be carried via the beacon
`
`broadcast, the template is returned to server 110, preferably
`via a secure link using, e. g., Secure HTTP (S-HTTP) or
`Secure Sockets Layer (SSL). SSL creates a secure link
`between a client and a server, over which any amount of data
`can be sent securely. S-HTTP is designed to transmit indi-
`vidual messages securely. Server 110 then creates the appro-
`priate additional data package for appending to the inquiry
`signal of a relevant one of the beacons 102-108 based on the
`information submitted with the template. The system 100
`may further comprise an application server 120 to assist in
`carrying out various functions, as will be readily understood
`by the skilled reader.
`Referring back to FIG. 1, a strong candidate technology for
`the wireless link necessary for at least the ‘push’ mode of the
`above-described CA system is Bluetooth, on the grounds that
`it is expected to become a component part of a large number
`of mobile telephones 10. In analysing the Bluetooth protocol
`for CA broadcast or ‘push’ mode utilisation, a problem may
`be seen. In the ideal case, the terminal 10 will detect fixed
`beacons 12, 14 and extract basic information from them with-
`out the terminal 10 needing to transmit at all. However, this
`type of broadcast operation is not supported by the current
`Bluetooth specification.
`In part, the incompatibility follows the frequency hopping
`nature of Bluetooth beacon systems which means that, in
`order for broadcast messages (or, indeed, any messages) to be
`received by a passing terminal, the terminal has to be syn-
`chronised to the beacon in both time and frequency. The
`portable device 10 has to synchronise its clock to the beacon
`clock and, from the beacons identity, deduce which of several
`hopping sequences is being employed.
`To make this deduction, the portable device has conven-
`tionally been required to joinias a slaveithe piconet
`administered by the beacon as piconet master. Two sets of
`procedures are used, namely “inquiry” and “page”. Inquiry
`allows a would-be slave to find a base station and issue a
`
`request to join the piconet. Page allows a base station to invite
`slaves of its choice to join the net. Analysis of these proce-
`dures indicates that the time taken to join a piconet and then
`be in a position to receive information from the master could
`be several tens of seconds, which is much too long for CA
`applications, where a user may move out of range of a beacon
`before joining could be completed.
`The difficulty of receiving broadcast data from beacons is
`caused at least partially by the frequency-hopping nature of
`Bluetooth and similar systems. The Bluetooth inquiry proce-
`dure has been proposed specifically to solve the problem of
`bringing together master and slave: the applicants have rec-
`ognised that it is possible to piggy-back a broadcast channel
`on the inquiry messages issued by the master. Only CA ter-
`minals need read the broadcast channel messages and only
`CA base stations or beacons send them. In consequence, at the
`air interface, the mechanism is entirely compatible with con-
`ventional (non-CA) Bluetooth systems.
`To illustrate how this is implemented, we first consider how
`the Inquiry procedures themselves operate, with reference to
`FIGS. 3 and 4. When a Bluetooth unit wants to discover other
`
`Bluetooth devices, it enters a so-called inquiry substate. In
`this mode, it issues an inquiry message containing a General
`Inquiry Access Code (GIAC) or a number of optional Dedi-
`cated Inquiry Access Codes (DIAC). This message transmis-
`sion is repeated at several levels; first, it is transmitted on 16
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`US 7,587,207 B2
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`7
`frequencies from a total of 32 making up the inquiry hopping
`sequence. The message is sent twice on two frequencies in
`even timeslots with the following, odd timeslots used to listen
`for replies on the two corresponding inquiry response hop-
`ping frequencies. Sixteen frequencies and their response
`counterparts can therefore be covered in 16 timeslots, or 10
`ms. The chart of FIG. 3 illustrates the transmission sequence
`on sixteen frequencies centred around f{k}, where f{k} rep-
`resents the inquiry hopping sequence.
`The next step is the repetition of the transmission sequence
`at least Ninqmw times. At the very least, this requires 256
`repetitions of the entire sequence which constitutes a train of
`transmissions which we will refer to as inquiry transmission
`train A. Next, inquiry transmission train A is swapped for
`inquiry transmission train B consisting of a transmission
`sequence on the remaining 16 frequencies. Again, the train B
`is made up of 256 repetitions of the transmission sequence.
`Overall the inquiry transmissions cycle between transmis-
`sions of train A and train B. As shown by FIG. 4, the specifi-
`cation states that this switch between trains must occur at least
`
`three times to ensure the collection of all responses in an
`error-free environment. This means that an inquiry broadcast
`could take at least 10.24 seconds.
`
`One way to reduce this would be for the switch between
`inquiry transmission trains to be made more rapidly, i.e. with-
`out waiting until the 2.56 seconds for 256 repetitions ofthe 10
`ms to cover the 16 timeslots is up. This may suitably be
`accomplished by setting the systems to switch over if no
`inquiry message is detected after say 50 ms, on the under-
`standing that no such message will be detected in the remain-
`der of the present train.
`A portable device that wants to be discovered by a beacon
`enters the inquiry scan substate. Here, it listens for a message
`containing the GIAC or DIAC’s of interest. It, too, operates in
`a cyclic way. It listens on a single hop frequency for an inquiry
`scan period ofTwiinquiry_scan. This must be long enough to
`cover the 16 inquiry frequencies used by the inquiry. The
`interval between the beginning of successive scans must be no
`greater than 1.28 seconds. The frequency chosen comes from
`the list of 32 making up the inquiry hopping sequence.
`On hearing an inquiry containing an appropriate IAC, the
`portable device enters a so-called inquiry response substate
`and issues a number of inquiry response messages to the
`beacon. The beacon will then page the portable device, invit-
`ing it to join the piconet.
`As mentioned above and shown in FIG. 5, the applicants
`propose that the inquiry messages issued by the base station
`have an extra field appended to them, capable of carrying a
`user-defined payload (CA DATA). In the CA scenario, this
`payload is used to carry broadcast information, or keys, to CA
`terminals during the inquiry procedure. By adding the field to
`the end of the inquiry message, it will be appreciated that
`non-CA receivers can ignore it without modification. In addi-
`tion, by using a CA-specific DIAC, CA receivers can be
`alerted to the presence of the extra information field.
`The presence of the extra data field means that the guard
`space conventionally allowed at the end of a Bluetooth
`inquiry packet is reduced. However, this spaceiprovided to
`give a frequency synthesiser time to change to a new hop
`frequencyiwill be generally unused otherwise, as current
`frequency synthesisers are capable of switching at speeds
`which do not need extension into the extra guard space. The
`standard inquiry packet is an ID packet of length 68 bits.
`Since it is sent in a half-slot, the guard space allocated is
`(625/2—68):244.5 us (625 us slot period, 1 Mbit/s signalling
`rate). Modern synthesisers can switch in much less time with
`figures of 100 us or lower considered routine by experts in the
`
`8
`field. Applicants therefore propose allocation of 100 bits as a
`suitable size for this new field, although it will be readily
`understood that other field sizes are, of course, possible.
`CA handsets can receive the broadcast data quickly with-
`out being required to run through a lengthy procedure to join
`a piconet. In addition, since there is no need for the handset to
`transmit any information whatsoever, there is a consequent
`power saving that will be particularly important in dense
`environments where many CA base stations may be present.
`Nevertheless, when the handset is in interactive mode and
`wishes to join a piconet in order to obtain more information,
`it may employ the default inquiry procedures as normal.
`There is no loss of functionality through supporting the addi-
`tional data field.
`
`In a typical embodiment, four of our 100 bits will be lost as
`trailer bits for the ID field; this is a consequence of it being
`read by a correlator. Of the 96 bits remaining, applicants
`preferred allocation is that 64 be used as data and 32 as a 2/3
`FEC (forward error correction) checksum, although the
`checksum, any headers included, and other overheads may
`greatly reduce the number of bits available for data, perhaps
`to 10 bits or fewer in some circumstances. Each inquiry burst
`thus contains 8 bytes of broadcast data. In a most common
`scenario, by the second group of A and B trains the portable
`device has found the base station, understood it to be a CA
`beacon and is awaiting the broadcast data. Since it will be
`listening specifically, the portable device will at least be able
`to read 256 bursts of data twice (A and B), giving us two lots
`of 2 Kbytes, or 4 Kbytes in total.
`At this stage, the portable device does not know the phase
`of the beacons clock because this information is not been
`
`transmitted. To assist the portable device, clock information
`is transmitted in at least some of the trains in the firstA and B
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`groups, as shown in FIG. 6, together with some auxiliary
`information indicating when the next switches betweenA and
`B will occur. This clock information will be transmitted in
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`place of the CA broadcast data so means are provided to
`discriminate between the two data channels. Use of separate
`DIAC’s is one possible method.
`In the case where the portable device knows the timing of
`the beacon, the portable devices also knows how it will hop,
`which gives the ability to track all transmissions of a train.
`Since there are 16 transmissions in a frame, then the resultant
`CA channel has 16 times as much capacity and can convey 64
`Kbytes of i