| WV AP DO AR R O
`US 20050058181A1
`a9 United States
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`a2 Patent Application Publication o) Pub. No.: US 2005/0058181 A1
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`Lyle et al. 3) Pub. Date: Mar. 17, 2005
`(599 APPARATUS AND METHOD EMPLOYING (21) Appl. No.: 10/650,385
`DYNAMIC HOP SEQUENCE ADJUSTMENT
`IN FHSS NETWORKS (22) Filed: Aug. 28, 2003
`(75) Inventors: Ruthie D. Lyle, Durham, NC (US); Publication Classification
`Jamel Pleasant Lynch JR., Carrboro, .
`NC (US); Mcgill Quinn, Durham, NC (51 Int. CL7 e HO04B 1/713
`(US); William J. Vigilante JR., (52) US. Cl e 375/133
`Scranton, PA (US)
`Correspondence Address: 7 ABSTRACT
`IBM CORPORATION
`PO BOX 12195 A frequency hopping spread spectrum apparatus and method
`DEPT 9CCA, BLDG 002 is disclosed which mitigates interference from adjacent
`RESEARCH TRIANGLE PARK, NC 27709 frequency hopping spread spectrum devices. The apparatus
`(US) and method are adapted to detect the information related to
`the hop sequence of an adjacent interfering network device
`(73) Assignee: International Business Machines Cor- and alter its own hop sequence based on the information
`poration;, Armonk, NY relating to the interfering hop sequence.
`Foreach 1 1 the following
`frequency used in frequencies are
`the interferinghop 2 2 used in the altered
`sequence, hop sequence.
`3 3
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`“ >< ”
`23 23 Samsung v. Zophonos
`IPR2026-00083
`Exhibit 1012 Exhibit 1012
`Page 01 of 11
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`Patent Application Publication Mar. 17,2005 Sheet 1 of 3 US 2005/0058181 A1
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`Exhibit 1012
`Page 02 of 11
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`Patent Application Publication Mar. 17,2005 Sheet 2 of 3 US 2005/0058181 A1
`Processor(s) PAF
`205 206
`Interference
`Memory Detector Hop Sequencer
`204 201 202
`Memory Processor(s) PAF
`304 305 306
`. Interference
`Mode Switch Detector Hop Sequencer
`303 301 302
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`Exhibit 1012
`Page 03 of 11
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`Patent Application Publication Mar. 17,2005 Sheet 3 of 3
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`a
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`frequency used in
`the interfering hop
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`Exhibit 1012
`Page 04 of 11
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`sequence,
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`the following
`frequencies are
`used in the altered
`hop sequence.
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`APPARATUS AND METHOD EMPLOYING
`DYNAMIC HOP SEQUENCE ADJUSTMENT IN
`FHSS NETWORKS
`
`BACKGROUND OF THE INVENTION
`
`[0001] This invention pertains to apparatus and methods
`which communicate through frequency hopping spread
`spectrtum (FHSS) networks and, more particularly, to an
`apparatus having wired or wireless communication capa-
`bilities over a frequency hopping spread spectrum network.
`The apparatus and methods perform a hop sequence alter-
`ation based on a neighboring frequency hopping spread
`spectrum network’s hop sequence.
`
`[0002] Bluetooth®' technology defines a specific wireless
`frequency hopping spread spectrum communication link
`operating in the unlicensed ISM band at 2.4 GHz using a
`frequency hopping tranceiver. It allows real-time voice and
`data communications between Bluetooth® devices. The
`communication range of Bluetooth® devices is between 10
`and 100 meters, but more commonly is limited to between
`10 and 20 meters due to channel noise and power limitations
`of typical devices. At the present time, the communication
`bandwidth of Bluetooth® devices is limited to 1 Mbps.
`
`The Bluetooth word mark is owned by the Bluetooth SIG, Inc.
`
`[0003] A “physical channel” or “channel” is defined in the
`Bluetooth® specification as a synchronized sequence of
`randomized hops between various of 79 or 23 RF channels.
`Each RF channel occupies 1 Mhz of bandwidth in the
`2400-2483.5 MHz RF range. Whether the channel com-
`prises 79 or 23 RF channels is predetermined and depends
`on the country in which the devices operate.
`
`[0004] Bluetooth® devices within communicating range
`can set up ad-hoc networks by sharing a common physical
`channel and thereby forming what is known as a “piconet.”
`A piconet consists of one and only one master device which
`controls the piconet and a maximum of 7 slave devices.
`Typically, the master communicates to the slave in a 625 us
`time-slot and the slave replies to the master in the very next
`time-slot. This technique is known as Time Division
`Duplexing (TDD). The two consecutive slots are referred to
`as a frame. Each frame can be thought of as a call and
`response between the master device and the corresponding
`slave device.
`
`[0005] Piconets are formed in an ad hoc fashion by having
`all devices continuously scan for inquiries in the area where
`they are operating. Any device, at any time, can initiate an
`inquiry. The device that initiates the inquiry takes on the role
`of the master device in the piconet. Devices in the range of
`the master’s inquiry reply to the inquiry. These replying
`devices assume the role of a slave device in the piconet. All
`devices can have the capacity to fulfill both the master role
`and the slave role. The distinction between master and slave
`allows easier synchronization over the frequency hopping
`spread spectrum communications link. All slaves synchro-
`nize to the master and the master sets the frequency hopping
`sequence.
`
`[0006] A Bluetooth® device can participate in more than
`one piconet by applying time multiplexing. To participate on
`a selected one of several channels/piconets, the device uses
`the associated master device address and the master clock
`value of the selected channel, and locally applies a proper
`time shift to obtain the correct phasing therefore.
`
`Exhibit 1012
`Page 05 of 11
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`Mar. 17, 2005
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`[0007] A Bluetooth® unit can act as a slave in several
`piconets, but only as a master in a single piconet. Thus, what
`might be considered as two separate piconets having a
`common master would, by definition, be synchronized and
`would use the same hopping sequence and would therefore
`actually constitute one and the same piconet.
`
`[0008] A limited number of overlapping piconets can
`autonomously operate because of Bluetooth’s frequency-
`hopping mechanism in which each piconet uses a different
`pseudo-random frequency hopping sequence wherein each
`pseudo-random sequence is seeded by the master’s device
`address and is therefore a unique sequence. However, col-
`lisions are inevitable. Moreover, as the number of overlap-
`ping piconets are increased, collisions become increasingly
`likely and are problematic.
`
`[0009] The IDC forecasts that by 2004 roughly 103.1
`million Bluetooth® devices will be enabled in the US and
`451.9 million devices world wide. Consequently, the prob-
`ability of interference resulting from neighboring piconets
`become increasingly probable. In the event of co-channel
`and adjacent interference, collisions occur which cause data
`packet retransmissions. The collisions and retransmissions
`result in a undesirable reduction in the data rate. Depending
`on the number, range, and comparable signal strength of
`neighboring piconets mitigating this interference is impor-
`tant. In many applications, such as voice over IP, even the
`smallest degradation in the signal is highly undesirable
`because it degrades the quality of the signal to an unusable
`degree. Moreover, in a typical office environment, the simul-
`taneous operation of multiple Bluetooth® piconets will
`crowd the spectrum and increase the probability of signal
`degradation due to increased collision frequency.
`
`SUMMARY OF THE INVENTION
`
`[0010] A novel technology is introduced herein which
`addresses the aforementioned problems and which is appli-
`cable to frequency hopping spread spectrum devices and
`methods in general and more specifically to both current and
`future Bluetooth® devices and methods. The invention
`includes dynamically adjusting the hop sequence of a pico-
`net based upon the hop sequence of neighboring piconets to
`mitigate interference. This invention addresses both single
`and multislot interference.
`
`[0011] Embodiments of the invention include embodi-
`ments as an apparatus and a method for performing the
`functions programmed or hardwired to execute in the appa-
`ratus herein described. The apparatus includes a processor,
`a memory, an interference detector, and a hop sequencer.
`The interference detector detects interference from an inter-
`fering network and determines the characteristics of the
`interfering network. The characteristics can include the hop
`sequence of the interfering network or data relating thereto.
`The hop sequencer controls the hop sequence of the device
`and alters the hop sequence of a second frequency hopping
`spread spectrum network based upon the characteristics of
`the interfering network.
`
`[0012] In one embodiment, logic is included which pro-
`vides the capability to join the interfering network to obtain
`the characteristics which relate to the interfering network.
`Logic is also included to rejoin the original network such
`that the characteristics of the interfering network are made
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`available on the original network. Optionally, the interfering
`network characteristics can be transferred over the original
`network.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0013] Some of the purposes of the invention having been
`stated, others will appear as the description proceeds, when
`taken in connection with the accompanying drawings, in
`which:
`
`[0014] FIG. 1 illustrates a variety of devices configured in
`accordance with the present invention;
`
`[0015] FIG. 2 is a block diagram of a device configured in
`accordance with an embodiment of the present invention;
`
`[0016] FIG. 3 is a block diagram of a device configured in
`accordance with an embodiment of the present invention;
`and
`
`[0017] FIG. 4 depicts a mapping in accordance with an
`embodiment of the present invention between hop frequen-
`cies used in an interfering network and the hop frequencies
`used in another network.
`
`DETAILED DESCRIPTION OF THE
`ILLUSTRATIVE EMBODIMENTS
`
`[0018] While the present invention will be described more
`fully hereinafter with reference to the accompanying draw-
`ings, in which a preferred embodiment of the present inven-
`tion is shown, it is to be understood at the outset of the
`description which follows that persons of skill in the appro-
`priate arts may modify the invention here described while
`still achieving the favorable results of this invention.
`Accordingly, the description which follows is to be under-
`stood as being a broad, teaching disclosure directed to
`persons of skill in the appropriate arts, and not as limiting
`upon the present invention.
`
`[0019] Although the illustrative embodiments will be
`described as modifications to existing Bluetooth devices and
`methods, the invention here described is applicable to fre-
`quency hopping spread spectrum devices and methods in
`general. For the most part, details concerning frequency
`hopping spread spectrum networks in general, and Bluetooth
`networks in particular, have been omitted in as much as such
`details are not necessary to obtain a complete understanding
`of the present invention and are within the skills of persons
`of ordinary skill in the relevant art. Details concerning
`Bluetooth networks can be obtained from Volume I of the
`Bluetooth Core Specification which is available through the
`Bluetooth SIG, Inc. The core specification is entitled Speci-
`fication of the Bluetooth System. At the time of this writing,
`version 1.0 B dated Dec. 1, 1999 had been listed as the
`current version.
`
`[0020] The ease and reliability in which various devices
`are able to wirelessly communicate over Bluetooth Piconets
`has led to a proliferation of these devices since its inception
`in the early 1990s. Bluetooth’s unique protocol, including
`the ability for devices to instigate communications autono-
`mously in addition to conventional operator control, allows
`devices of disparate function to interact over a shared
`network.
`
`[0021] Referring now more particularly to the accompa-
`nying drawings, FIG. 1 illustrates a variety of devices
`Exhibit 1012
`Page 06 of 11
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`Mar. 17, 2005
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`configured in accordance with the present invention. There
`shown are a scanner 101, an automobile 102, a fax machine
`103, a PDA 104, a microwave oven 105, a printer 106, a
`laptop computer 107, a desktop computer 108, and a tooth-
`brush 109. Each of the devices shown comprises logic which
`performs the functions here described to mitigate inter-
`piconet interference and are able to communicate with each
`other, though they provide widely differing functionality. In
`accordance with the present invention, as will be explained
`in more detail as the description proceeds, if devices 106,
`107, 108 and 109 are operating on a first Piconet and devices
`101, 102, 103, 104 and 105 are operating on a second, each
`of devices on one Piconet or the other are able hop on an
`altered sequence, as required, should interference be
`detected from the neighboring Piconet.
`
`[0022] Although not shown, it is assumed that each of the
`embodiments here presented includes a frequency hopping
`spread spectrum transceiver. Details concerning frequency
`hopping spread spectrum transceivers are well known in the
`art and are omitted so as to not obfuscate the present
`disclosure in unnecessary detail.
`
`[0023] FIG.?2 is a block diagram of a device configured in
`accordance with an embodiment of the present invention.
`The device can be any of the devices shown in FIG. 1 and
`the like. The device includes a processor 205 which controls
`a processor aided function or functions (PAF) 206. PAF 206
`varies according to the function of the device and includes
`the communication of data over the frequency hopping
`spread spectrum network. For example, for scanner 101, the
`PAF 206 can include the functions for contolling the scanner
`light source, including its light emission and movement, the
`functions for communicating the scanned data to a computer
`requesting the scanned data, and the functions for accepting
`user input via buttons on the front panel. For automobile
`102, the PAF 206 can include the functions for controlling
`the ignition of fuel, the security system of the automobile,
`the display of information via the instrument panel, and can
`include functions for diagnosing or troubleshooting the
`vehicle. Processor 205 assists with the functions of PAF 206
`to varying degrees. For example, processor 205 can be
`involved with the enablement and/or disablement of any of
`the PAF’s 206 which are self-controlled or are controlled by
`a self-contained processor within a particular PAF sub-
`system. The processor can also be involved with very low
`level PAF detail. In the preferred embodiment, however,
`processor 205 controls the principal functionality of the
`device. That is, in scanner 101, processor 205 is involved in
`the scanning operation; in PDA 104 processor 205 is that
`processor responsible for displaying information on the
`display and for accepting touchpad input on a touch sensi-
`tive display and operating on such input. In addition, pro-
`cessor 205 can comprise various sub processors, each of
`which capable of performing lower-level functions and
`communicating results to other processors.
`
`[0024] The device includes a memory 204 which is acces-
`sible to the processor 205. Memory 204 stores code which
`is to be executed on processor 205, and provides routine data
`storage for the computational needs of processor 205.
`Memory 204 also functions to temporarily or permanently
`store data which is to be transferred over the frequency
`hopping spread spectrum network. Processor 205 normally
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`aids in the communication of the network data stored in
`memory 204 over the frequency hopping spread spectrum
`network.
`
`[0025] The device also includes interference detector 201
`and hop sequencer 202 to assist with the local functions of
`the frequency hopping spread spectrum network. Interfer-
`ence detector 201 and hop sequencer 202 can be coupled
`directly or can be coupled indirectly via processor 205. The
`interference detector 201 detects interference from a neigh-
`boring piconet. The interference detection itself can be in the
`form of detecting a degradation in data throughput on the
`piconet in which the device is currently operating. Alterna-
`tively, the interference detection can simply be the detection
`of a second piconet operating within the same area. Inter-
`ference detector 201 also determines interfering hop
`sequence data or characteristics relating to the interfering
`network. This can be done by obtaining the data through a
`nearby access point or hub to which the interfering network
`shares common functionality. However, in the preferred
`embodiment, the interference detector 201 contains logic
`which joins the interfering network and thereby obtains and
`stores the hopping sequence of the interfering network and
`or data or parameters associated with the hopping sequence
`of the interfering network. As part of data retained by
`interference detector 201 which pertains to the interfering
`network, the device optionally retains a correlated time
`stamp which correlates the sequence of the interfering
`network to any other sequence. Alternatively, any other
`means of correlating the interfering sequence to the
`sequences of other networks is usable. For example, since
`the sequences are deterministic, logic on board the device
`can be implemented such that the correlation can be made.
`This is accomplished by recording portions of the interfering
`sequence using, for example, spare processor 205 bandwidth
`on board the device wherein a simulation can be enacted to
`reverse engineer and identify the sequence and its state
`relative to another hop sequence. Logic within interference
`detector 201 would follow both Piconets simultaneously
`when making the correlation. In this way a time stamp is not
`necessarily needed.
`
`[0026] The interfering hop sequence data obtained by
`interference detector 201 can additionally be obtained from
`another device on the Piconet having a configuration similar
`to the device herein described, that device having at least an
`interference detector 201.
`
`[0027] Hop sequencer 202 gains access to the interfering
`hop sequence data relating to the interfering network as
`obtained by interference detector 201. This access can be
`direct or indirect as previously described. Hop sequencer
`202 contains logic which alters the hop sequence of its own
`network based upon the interfering hop sequence data
`determined by the interference detector. As with Bluetooth
`networks, it is desirable in the preferred embodiment to hop
`on all 79 channels in the spectrum since maintaining the
`usage of all 79 channels minimizes the overall chances of
`experiencing collisions. The altered hop sequence is selected
`by any heuristic or deterministic method, specific examples
`of which are given in the embodiments which follow.
`
`[0028] FIG. 3 is a block diagram of a device configured in
`accordance with another embodiment of the present inven-
`tion. Memory 304, processor 305, and processor aided
`function or functions (PAF) 306 operate as do the corre-
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`Exhibit 1012
`Page 07 of 11
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`Mar. 17, 2005
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`sponding structures of FIG. 2, specifically memory 204,
`processor 205, and PAF 206 of FIG. 2. Unless otherwise
`stated or where details conflict, the embodiment given in
`FIG. 3 operates in the same manner as described with
`respect to the embodiment of FIG. 2. In this embodiment, it
`is also desirable to hop on all available channels since the
`usage of all available channels provides a more robust
`connection. Where the embodiment is implemented as a
`Bluetooth network, the entire set of RF channels available is
`either 79 or 23. The number of RF channels can change
`depending on the country in which operation occurs. In
`some countries the number of RF channels available is 79,
`in other countries only 23 RF channels are available. In the
`case that only 23 channels are available in any given
`country, all 23 channels are used for hopping.
`
`[0029] Mode switch 303 contains logic which selects the
`hopping mode from at least two modes of operation. The
`first mode is a mode which dictates the hopping sequence for
`a given network; in the case of a Bluetooth network, this
`mode is referred to as the master mode. The second mode is
`a mode which follows the hopping sequence set elsewhere
`on the network; this second mode is referred to as the slave
`mode in Bluetooth networks. However, no distinction as to
`master or slave is given according to the present embodi-
`ment since it is foreseeable that masters can become slaves
`and slaves become masters within a given piconet. Typically,
`only one device on a network sets the hopping frequency and
`all other devices follow. However, it is possible to allow
`different devices on the network to take over the task of
`setting the hopping sequence for the network. This capabil-
`ity allows a master to become a slave on the current network
`in order to become a master on another network or to
`otherwise join another network without collapsing the cur-
`rent network.
`
`[0030] Mode switch 303 is capable of selecting an oper-
`ating mode for the device as would be done in the promis-
`cuous mode of a Bluetooth piconet session. However the
`coupling between processor 305 and mode switch 303
`allows for processor 305 to initiate a piconet session as
`would any Bluetooth device.
`
`[0031] Interference detector 301 is coupled to processor
`305 and performs lower-level network functions here below
`described. Interface detector 301 operates in accordance to
`the mode of operation indicated by mode switch 303. The
`operating mode indicated by mode switch 303 may be
`accessed directly from mode switch 303 or indirectly from
`processor 305. Interference detector 301 includes logic
`which detects interference from a nearby network operating
`within its range. Interference detector 301 also includes
`logic to detector otherwise determine the interfering hop
`sequence of the interfering frequency hopping spread spec-
`trum network. If the frequency hopping spread spectrum
`network is of the Bluetooth variety, the hopping sequences
`are deterministic and therefore the only data needed is that
`data which defines the hopping sequence of the interfering
`network. Since it is possible for some devices on a network
`to experience interference while others experience none or
`little, the device detecting the interference via interference
`detector 301 is likely to be positioned so as to favorably
`detect the interfering hop sequence data from the nearby
`interfering network. Although any one device on a network
`is able to detect the interference, that one device need not be
`charged with the responsibility to obtain the interfering hop
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`sequence data; another device can be charged with the
`responsibility. While not required, in the preferred embodi-
`ment, the device which detects interference is also the device
`which determines the interfering hop sequence data of the
`interfering network. If the device is to operate in a Bluetooth
`style network, the preferred method of obtaining the inter-
`fering hop sequence data is by joining the interfering net-
`work and recording the interfering hop sequence parameters
`and thereafter rejoining the original network and reporting
`the interfering hop sequence parameters to the original
`network. This reportage can be to the master device or in
`general to the device which is operating in the mode which
`sets the hopping sequence for the original network as
`selected by the mode switch 303. However, if it is the master
`device itself which detects the interference and desires to
`join the interfering network in order to attain the interfering
`hop sequence data, then no reportage is necessary over the
`network since the master device itself retains the interfering
`hop sequence data in local memory. As mapped to the
`current Bluetooth technology, the master device is the device
`which operates in the mode which sets the hopping sequence
`of the original network as selected by mode switch 303.
`When the master rejoins the original network, it does so with
`knowledge of the interfering hop sequence as stored in its
`own local memory. Whether it is the slave or the master
`which ventures out and joins the interfering network and
`comes back and rejoins the original network is arbitrary and
`is set by mode switch 303. However, in the preferred
`embodiment, it is the slave mode device or the device
`operating in the mode which follows the hopping sequence
`which temporarily leaves the original network and joins the
`interfering network to obtain the interfering hop sequence
`data. In the preferred embodiment, slave mode venturing is
`preferred because a master would have to collapse the
`network in order to join the interfering network according to
`current Bluetooth designs. However, other embodiments
`may be devised in which it is possible for a master to pass
`the responsibility of maintaining the current network to
`another device on the network such that a network need not
`collapse in order for a master to temporarily join another
`network.
`
`[0032] In an alternative embodiment, no original network
`need exist. A device which is about to instigate a network
`can first check for the existence of other networks which
`could interfere with a network which is about to be initiated.
`The device could join the interfering network, obtain the
`interfering hop sequence data, and then proceed to instigate
`an ad-hoc network having knowledge of the interfering
`network’s hop sequence in such a way that the initiated hop
`sequence tends to not coincide statistically with the inter-
`fering network’s hop sequence using any of the methods
`described hereinbelow. In this alternative embodiment, since
`it is the master device which detects the interference and
`joins the interfering network, interference detector 301 is set
`to perform this function when mode switch 303 indicates
`that the device is to operate in the mode which sets the
`hopping sequence (master).
`
`[0033] Referring again to the embodiment of FIG. 3, hop
`sequencer 302 includes logic which either dictates the
`hopping sequence for the network in which it operates, or
`follows the hopping sequence set by another device on the
`network as a function of mode switch 303. In either mode,
`the hop sequencer comprises a pseudo-random number
`generator or the like to set or follow the pseudo-random hop
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`Exhibit 1012
`Page 08 of 11
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`Mar. 17, 2005
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`sequence. Hop sequencer 302 is coupled to processor 305
`and performs lower-level network functions here below
`described. Hop sequencer 302 operates in accordance with
`the mode of operation indicated by mode switch 303 and the
`data obtained by interference detector 301. The operating
`mode indicated by mode switch 303 and the data obtained by
`interference detector 301 may be accessed directly from
`mode switch 303 and interference detector 301 or indirectly
`from processor 305. In addition, hop sequencer 302 includes
`logic which obtains the interfering hop sequence data of a
`nearby interfering network by either accepting the interfer-
`ing hop sequence data over the network—when the data is
`reported by another device over the network—, or by
`reading the interfering hop sequence data from local stor-
`age—when the data was obtained by the same device and is
`therefore available locally. The local storage can reside in
`either the memory 304, hop sequencer 302, or the interfer-
`ence detector 301. Alternatively, the local storage can reside
`in a register anywhere within the device or within any
`memory accessible from the device of the present embodi-
`ment.
`
`[0034] Hop sequencer 302 additionally includes logic
`which alters its dictated hop sequence while operating in the
`mode which dictates the hopping sequence as indicated by
`the mode switch 303. This however, does not preclude a
`device which had been operating in the mode which follows
`the hopping sequence to switch its mode to a mode which
`dictates the hop sequence as would be the case when a slave
`detects the interference and rejoins the network. In other
`embodiments, it is possible that the slave when rejoining the
`original network negotiates with the existing master and
`takes over the responsibility of master in the original net-
`work. This would be the case when limited processing is
`available on typical devices and the time required to devise
`a new hopping sequence is extensive and perhaps beyond
`the capability of the processor while a device is in full
`master mode operation. The alteration of the hop sequence
`is based upon the obtained interfering hop sequence data and
`is calculated so as to minimize collisions between the two
`networks. The altered-hop-sequence calculation can be by
`heuristic methods when enough processing power and
`memory is available within the device. The processing can
`be performed either in processor 305 or a sub processor
`within hop sequencer 302. Alternatively, the altered hop
`sequence can be calculated by deterministic methods; sev-
`eral examples of which are given hereinbelow. In any case,
`the altered hop sequence comprises the same number of RF
`channels as are available. That is, the altered hop sequence
`contains all 79 or all 23 available RF channels, over the long
`run, depending on the country in which the device operates.
`
`[0035] The heuristic and deterministic methods can
`involve seeding the pseudo-random number generator with
`candidate-alternative values and comparing the resulting
`sequence to the interfering sequence. In all cases, the
`heuristic and deterministic methods can be either simulated
`or actually attempted in real time. The heuristic and deter-
`ministic methods can also involve using alternate pseudo-
`random number generator circuits rather than alternate seed-
`ing; in this case the circuit to be used for any particular
`sequence is communicated over the network for all devices
`on the network. However, alternate seeding is preferred over
`alternate circuitry/logic because embodiments can be imple-
`mented using mostly or entirely existing hardware. On the
`other hand, when pseudo-random number generator circuits
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`US 2005/0058181 Al
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`are implemented in software onboard the device, embodi-
`ments which utilize alternate circuitry are feasible.
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`[0036] One example of an altered hop sequence using a
`heuristic method, as calculated by the hop sequencer 302, is
`to iteratively offset the existing hop sequence by a constant
`number of slots and determine if the offset altered sequence
`would produce (or produces) fewer collisions than the
`existing sequence. If several offset altered sequences are
`found to produce fewer collisions, the offset altered
`sequence which is found to produce the fewest collisions is
`the sequence selected for the alteration. Weights can be
`assigned such that the decision is made based on whether
`fewer collisions occur in the short-term or whether fewer
`occur over the long-term.
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`[0037] Note that the term -offset-, as used herein, differs
`from its meaning in the Bluetooth® specification. As used in
`the Bluetooth® specification, -clock offset- and -offset- refer
`to that number us which must be added or taken away from
`a local slave clock to bring it into alignment with a master
`clock on the same piconet, usually 625 us or less. Con-
`versely, as used herein, the term -offset- refers to an offset in
`the pseudo-random sequence of an unassociated piconet
`which hops on an altogether different sequence, in which
`case alignment is neither possible nor desired. In embodi-
`ments where the sequence is selected to be the sequence of
`the neighboring piconet, the offset is large (preferably >6
`ms) and is in a direction which causes an intentional
`misalignment of the hop sequences. In other words, where
`an embodiment utilizes a sequence offset, there is no attempt
`to align phases with the neighboring piconets; phase align-
`ment, or “clock offset” as referred to in the Bluetooth®
`specification, still applies to masters and slaves within the
`piconets of this invention which, in addition, have a
`sequence offset as disclosed herein. Therefore, as used
`herein, the term -offset- refers to the relatively larger-scale
`extra-piconet offset to sequences and not to the microscale
`intra-piconet phase alignments which still occur.
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`[0038] An example of an altered hop sequence using a
`deterministic method, as calculated by the hop sequencer
`302, is to adopt a variation of the interfering hop sequence
`which tends to produce fewer collisions than a random
`sequence. One such method is to introduce a translation to
`the interfering hop sequence. The resulting altered hop
`sequence of this example is produced by the method previ-
`ously described requiring an alternate circuit. Thus, in this
`example, it is preferable that the pseudo-random number
`generator circuitry be implemented in software. One such
`translation is show