(12) United States Patent
`Gerten et al.
`
`111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US006760319Bl
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 6,760,319 Bl
`Jul. 6, 2004
`
`(54) FIXED FREQUENCY INTERFERENCE
`AVOIDANCE ENHANCEMENT
`
`(75)
`
`Inventors: Leo Joseph Gerten, Hoffman Estates,
`IL (US); Kevin Alan Harnist,
`Arlington Heights, IL (US); Mark
`Robert Mahoney, Schaumburg, IL
`(US); Chuck Bromley Harmke,
`Rolling Meadows, IL (US)
`
`(73) Assignee: Motorola, Inc., Schaumburg, IL (US)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 707 days.
`
`(21) Appl. No.: 09/610,022
`
`(22) Filed:
`
`Jul. 5, 2000
`
`Int. Cl? ................................................. H04J 13/06
`(51)
`(52) U.S. Cl. ....................... 370/335; 370/342; 370/441;
`375/132
`(58) Field of Search ................................. 370/320, 329,
`370/332, 335, 441; 375/132
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`4,556,982 A * 12/1985 Dunn ......................... 375/224
`
`5,715,295 A * 2/1998 Yamashita .................. 455!455
`5,737,359 A * 4/1998 Koivu ........................ 375/133
`5,937,002 A * 8/1999 Andersson et a!.
`......... 375/131
`
`* cited by examiner
`
`Primary Examiner-Kenneth Vanderpuye
`Assistant Examiner-Joshua Kading
`
`(57)
`
`ABSTRACT
`
`A system and method is provided for removing channels in
`a frequency hopping scheme having strong interference or
`interferers in a wireless communication system. The present
`invention employs signal strength measurements on N num(cid:173)
`ber channels of the frequency hopping scheme to determine
`M number of channels to be avoided. The system and/or
`method then modifies the frequency hopping scheme to
`avoid transmission over the M channels. The M channels to
`avoid can be communicated to wireless units involved in the
`communication system, so that the members of the wireless
`communication system can frequency hop together over the
`modified frequency hopping scheme.
`
`7 Claims, 8 Drawing Sheets
`
`SCAN COMPLETE
`
`0001
`
`Marvell Semiconductor, Inc.
`MediaTek Inc.
`MediaTek USA, Inc.
`Exh. 1003
`IPR of U.S. Pat. No. 7,477,624
`
`

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`

`
`U.S. Patent
`
`Jul. 6, 2004
`
`Sheet 3 of 8
`
`US 6, 760,319 Bl
`
`100
`
`PERFORM SERVICE
`DISCOVERY
`
`115
`NO
`
`COMMENCE
`NORMAL
`OPERATION
`
`CHANNEL SCAN AT END
`OF TRANSMISSION
`
`DETERMINE CHANNELS
`TO BE A VOIDED
`
`CREATE LINK TO
`COMMUNICATE CHANNELS
`TO BE AVOIDED
`
`COMMUNICATE CHANNELS
`TO BE AVOIDED
`
`MODIFY HOPPING SEQUENCE
`
`120
`
`130
`
`140
`
`150
`
`160
`
`170
`
`USE MODIFIED HOPPING
`SEQUENCE TO TRANSMIT DATA
`
`F'IG. 3
`
`0004
`
`

`
`U.S. Patent
`
`Jul. 6, 2004
`
`Sheet 4 of 8
`
`US 6, 760,319 Bl
`
`200
`
`GET NEXT CHANNEL ---------------.
`
`COMPLETE
`
`READ SIGNAL STRENGTH
`
`WAIT PREDETERMINED
`TIME THEN READ
`SIGNAL STRENGTH
`
`YES
`
`PLACE
`CHANNEL
`ON LEVEL
`ONE LIST
`
`PLACE CHANNEL ON
`LEVEL TWO LIST
`
`I?IG. 4
`
`SCAN COMPLETE
`
`0005
`
`

`
`U.S. Patent
`
`Jul. 6, 2004
`
`Sheet 5 of 8
`
`US 6, 760,319 Bl
`
`3 00"'-.
`
`IDENTIFY M CHANNELS TO
`BE A VOIDED OF N
`TOTAL CHANNELS
`
`310" DEFINE AN ALTERNATE
`REGISTER BANK OF N-M
`CHANNELS
`
`320 " REMOVE SYNTHESIZER CODE FOR
`
`M CHANNELS TO BE AVOIDED
`
`33 0"
`
`LOAD ALTERNATE REGISTER
`BANK WITH N-M SYNTHESIZER
`CODES FOR N-M CHANNELS
`
`'
`3 40" RECONFIGURE ADDRESSING
`SCHEME TO ADDRESS
`ALTERNATE REGISTER BANK
`WITH N-M SYNTHESIZER
`CODES FOR N-M CHANNELS
`
`FIG. 5
`
`0006
`
`

`
`U.S. Patent
`
`Jul. 6, 2004
`
`Sheet 6 of 8
`
`US 6, 760,319 Bl
`
`A
`
`B
`
`C
`
`D
`
`E F
`
`X
`
`Y2
`
`FIG. 6
`
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`
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`
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`
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`
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`
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`
`FIG. 7
`
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`•
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`1
`3
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`77
`
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`
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`•
`•
`•
`78
`1
`3
`•
`•
`•
`77
`
`0007
`
`

`
`U.S. Patent
`
`Jul. 6, 2004
`
`Sheet 7 of 8
`
`US 6, 760,319 Bl
`
`400
`
`PROVIDE ALTERNATE CODE
`WORD BANK OF REGISTERS
`
`410
`LOAD ALTERNATE CODE WORD
`BANK WITH N CODE WORDS
`
`REPLACE LEVEL 2 LIST
`~-.~ CHANNELS WITH GUARDBAND
`CHANNELS
`
`PLACE CHANNELS ADJACENT
`LEVEL 2 CHANNELS ON
`LEVEL 2 LIST
`
`PLACE LEVEL 1 CHANNELS ON
`LEVEL 2 LIST UNTIL M TOTAL
`CHANNELS REPLACED OR
`UNTIL NO MORE LEVEL 1
`CHANNELS ARE LEFT
`
`FIG. B
`
`0008
`
`

`
`U.S. Patent
`
`Jul. 6, 2004
`
`Sheet 8 of 8
`
`US 6, 760,319 Bl
`
`500
`
`PROVIDE ALTERNATE CODE
`WORD BANK OF REGISTERS
`
`510
`LOAD ALTERNATE CODE WORD
`BANK WITH N CODE WORDS
`
`520
`
`REPLACE CHANNELS ON LEVEL
`2 LIST WITH CHANNELS
`FROM GUARDBAND
`
`REMOVE SYNTHESIZER CODE
`FOR REMAINING LEVEL 2
`CHANNELS TO BE AVOIDED
`UP TO M CHANNELS
`
`550
`
`REDUCE ALTERNATE CODE
`BANK REGISTER TO N-M
`CHANNELS
`
`560
`
`RECONFIGURE ADDRESSING
`SCHEME TO ADDRESS REGISTER
`BANK WITH N-M
`SYNTHESIZER CODES FOR
`N-M CHANNELS
`
`FIG. 9
`
`NO
`570
`
`BEGIN DATA
`TRANSMISSION
`
`0009
`
`

`
`US 6,760,319 Bl
`
`1
`FIXED FREQUENCY INTERFERENCE
`AVOIDANCE ENHANCEMENT
`
`TECHNICAL FIELD
`
`The present invention generally relates to communication
`systems, and in particular to a system and method for
`improving noise and interference immunity in a wireless
`communication system.
`
`BACKGROUND OF THE INVENTION
`
`10
`
`2
`FIG. 2 illustrates a block schematic diagram of a mobile
`communication unit in accordance with the present inven(cid:173)
`tion;
`FIG. 3 is a flow diagram illustrating a methodology for
`5 determining and communicating channels to be avoided to a
`remote device in accordance with the present invention;
`FIG. 4 is a flow diagram illustrating a methodology for
`determining channels with interferers above a certain thresh(cid:173)
`old in accordance with the present invention;
`FIG. 5 is a flow diagram illustrating a methodology for
`modifying the hopping sequence in a wireless communica(cid:173)
`tion system in accordance with the present invention;
`FIG. 6 is a block schematic diagram of a hop selection
`15 kernel having a modulo of 79 for a wireless communication
`device employing the Bluetooth standard in accordance with
`the present invention;
`FIG. 7 is a block schematic diagram of a modified hop
`selection kernel having a modulo of 75 for a wireless
`20 communication device employing the Bluetooth standard in
`accordance with the present invention;
`FIG. 8 is a flow diagram illustrating another methodology
`for modifying the hopping sequence in a wireless commu(cid:173)
`nication system in accordance with the present invention;
`25 and
`FIG. 9 is a flow diagram illustrating yet another method(cid:173)
`ology for modifying the hopping sequence in a wireless
`communication system in accordance with the present
`invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`Recently a standard for short range wireless communica(cid:173)
`tion has evolved known as the Bluetooth standard (see
`www.bluetooth.com). Bluetooth is a Radio Frequency (RF)
`specification for short range, point to multi -point voice and
`data transfers. Bluetooth can transmit through solid, non(cid:173)
`metal objects. It has a nominal link range from 10 centime(cid:173)
`ters to 10 meters, but can be extended to 100 meters by
`increasing the transmit power. It is based on short-range
`radio links and facilitates ad hoc connections for stationary
`and mobile communication environments. The Bluetooth
`standard is a low-cost short range wireless communication
`standard that typically operates in the 2,400-2,483.5 MHz
`industrial, scientific and medical (ISM) band. The ISM band
`is available worldwide and allows unlicensed operation of
`spread spectrum systems. The Bluetooth standard is often
`employed for short-distance connections and can be
`employed to replace cables used today that, for example,
`connect laptops to cellular telephones, printers, desktops, 30
`fax machined, joysticks and many other digital device that
`can be part of the Bluetooth system. Bluetooth can also
`provide a bridge to existing data networks. Bluetooth is
`specifically designed to provide low-cost, robust, efficient,
`high capacity, ad hoc voice and data networking.
`Bluetooth technology has been designed to operate in
`noisy radio frequency environments and uses a fast
`acknowledgment and frequency hopping scheme to make a
`robust communications link. Bluetooth radio modules
`attempt to avoid interference from other signals by hopping
`to a new frequency after transmitting or receiving a packet
`as compared to other systems operating at the same fre(cid:173)
`quency band. The implementations of faster hops and
`shorter packets limit impact of microwave and other sources
`of interference. Bluetooth uses forward error correction to 45
`limit impact of random noise on longer distance link.
`In Bluetooth Synchronous Connection Oriented (SCO)
`links there is no provision for re-sending lost data; and each
`time a receiver hops to a blocked channel, up to 3.75
`milliseconds of sequential audio may be unrecoverable. The 50
`lost packets due to fixed interferers are compounded with
`lost packets from FHSS (Frequency Hopped Spread
`Spectrum) interference from other FCC (Federal Commu(cid:173)
`nications Commission) devices operating in the vicinity to
`produce noticeably degraded audio for the user. For Blue- 55
`tooth Asynchronous Connection-Less (ACL) links, different
`levels of error correction and detection can be put in place
`to protect against lost or bad data. However, in any case, the
`error correction or detection often results in reduced bit rate.
`Other standards in the ISM band also have similar problems 60
`associated with channels with strong interference or noisy
`fixed interferers.
`
`The present invention relates to a system and method for
`35 removing channels in a frequency hopping scheme having
`strong interference or interferers in a wireless communica(cid:173)
`tion system. The present invention employs signal strength
`measurements on N number of channels (N being an integer)
`of the frequency hopping scheme to determine M number of
`40 channels (M being an integer less than or equal to N) to
`avoid. The system and/or method then modify the frequency
`hopping scheme to avoid transmission over the M channels.
`The M channels to avoid can be communicated to wireless
`units involved in the communication system, so that the
`members of the wireless communication system can fre(cid:173)
`quency hop together over the modified frequency hopping
`scheme. The frequency hopping scheme can be modified by
`providing a first register bank storing synthesizer codes for
`generating frequency hopping over the N total channels in
`normal mode with an alternate register bank storing synthe(cid:173)
`sizer codes for generating frequency hopping over N-M
`channels for interference avoidance mode. Alternatively, the
`frequency hopping scheme can be modified by substituting
`guardband channels for channels with strong interference or
`interferers. A combination of the substitution of guardband
`channels arid a reduced alternate register bank can also be
`employed to provide the modified frequency hopping
`scheme.
`The present invention will be described with reference to
`a system and method for removal of channels having strong
`interference or interferers on certain channels employed by
`a frequency hopping scheme in a wireless radio communi(cid:173)
`cation system. An example of a system and method will also
`be provided directed to a wireless communication system
`employing the Bluetooth standard in at least one piconet. It
`is to be appreciated that the system and/or method of the
`present invention may be employed in wireless radio com-
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 illustrates a system diagram of a scatternet employ- 65
`ing the Bluetooth standard in accordance with the present
`invention;
`
`0010
`
`

`
`US 6,760,319 Bl
`
`3
`munication systems that utilize other communication stan(cid:173)
`dards (e.g., IEEE 802.11). It is also to be appreciated that by
`removing channels with interferers from the hop sequence
`where it is known that a packet would be lost or degraded,
`effectively increases the number of devices that may operate
`in a given area or the range that devices operate at to still
`achieve a desired audio quality.
`FIG.1 illustrates operation of three piconets 10, 12 and 14
`forming a scatternet. Each piconet contains a plurality of
`wireless mobile communication units. A piconet is a collec(cid:173)
`tions of devices that can be connected via Bluetooth tech(cid:173)
`nology in an ad hoc fashion. A piconet can start with two
`connected devices, such as a portable PC and cellular phone,
`and may grow to eight connected devices. Each Bluetooth
`device is a peer unit and has substantially identical imple(cid:173)
`mentations. However, when establishing a piconet, one unit
`will act as a master for synchronization purposes and the
`other as a slave for the duration of the piconet connection.
`Two or more independent non-synchronized piconets that
`communicate with each other are known as a scatternet. A
`slave as well as a master unit in one piconet can establish a
`connection by becoming a slave in another piconet. A master
`unit is a device in a piconet whose clock and hopping
`sequence are employed to synchronize other devices in the
`piconet-devices in a piconet that are not the master are
`typically slaves.
`A first piconet 10 is formed with a plurality of mobile
`units 20 each wirelessly communicating with one another
`through an antenna 21. The first piconent 10 includes a
`master mobile unit and a slave mobile unit that is also a slave
`of a second piconet 12. The second piconet 12 includes a
`number of mobile units 22 wireless communicating with one
`another through an antenna 23. The second piconet 12
`includes a master mobile unit that is also a slave unit of a
`third piconet 14. The third piconet 14 includes a number of
`mobile units 24 wireless communicating with one another
`through an antenna 25. The present invention may be
`employed in other radio networking connections based on
`the particular standard being employed.
`Referring now to FIG. 2, a schematic representation of the
`mobile communication unit 20 is shown according to one
`particular aspect of the present invention, wherein a central
`control system 30 is responsible for controlling general
`operations of the mobile communication unit 20. The central
`control system 30 can include a processor or the like that is
`programmed to control and operate various components
`within the mobile communication unit 20 in order to carry
`out various functions described herein. The manner in which
`the processor can be programmed to carry out the functions
`relating to the present invention will be readily apparent to
`those having ordinary skill in the art based on the description
`provided herein.
`The mobile communication unit 20 includes a transceiver
`32 having transmitting circuitry 34 and receiving circuitry
`36 that are both coupled to an antenna 38. The receiver 36
`receives transmissions through the antenna 38, which is
`converted by a mixer 40, filtered by an intermediate fre(cid:173)
`quency (IF) filter 42 and demodulated by a demodulator 44.
`The transmission is then digitized through an ND converter
`46 for processing by the central control system 30. Trans(cid:173)
`missions are transmitted from the central control system 30
`through a D/Aconverter 48 to a modulator 50 and a filter 52
`to the transmitter 34 out through the antenna 38. A frequency
`synthesizer component 60 contains a memory component
`62. The frequency synthesizer component 60 cooperates
`with the central control system 30 and a device clock 64 to
`provide frequency hopping for the mobile communication
`
`5
`
`10
`
`4
`unit 20. The memory component 62 may include a plurality
`of register banks for storing synthesizer codes that are
`employed to facilitate frequency hopping. Alternatively, the
`register banks may reside in the central control system 30
`(e.g., in a memory component, onboard registers or memory
`in a processor or in separate register components). The
`frequency synthesizer component 60 is also operatively
`coupled to the modulator 50, the demodulator 44 and the
`mixer 40 to provide a frequency oscillation component for
`transmitting and receiving communications. A power mea(cid:173)
`surement component 66 is operatively coupled to the
`receiver 34 and provides transmission power measurement
`information to the central control system 30. Power is
`provided to the central control system 30 and other compo(cid:173)
`nents forming the mobile communication unit 20 by a power
`15 component 70, such as a battery power module, line power
`or the like, for example.
`The present invention provides for elimination of M
`channels with high interference of N total channels being
`transmitted in a frequency hopping scheme in a wireless
`20 communication system, such as a piconent or the like.
`Presently, the Bluetooth standard and the IEEE 802.11
`standard provide for frequency hopping between seventy
`nine channels, while the FCC requires frequency hopping
`with at least seventy five channels. The present invention
`25 will be described by example with respect to elimination of
`transmissions over channels having four worst interferers
`amongst seventy nine channels in a Bluetooth piconet.
`However, it is to be appreciated that the number of channels
`for different standards may vary as well as the number of
`30 channels in the above standards being subject to change.
`Therefore, the invention is not limited to the example(s)
`discussed herein and many variations with respect to elimi(cid:173)
`nation of transmissions over channels having strong inter(cid:173)
`ferers over different or modified standards in a wireless
`35 communication system are contemplated by the present
`invention, and are intended to fall within the scope of the
`hereto appended claims.
`FIG. 3 is a flow diagram illustrating one particular meth(cid:173)
`odology for communicating channels to be avoided in
`40 accordance with the present invention. In step 100, a master
`device performs a service discovery request to determine if
`a remote device has interference avoidance capabilities. In
`step 110, the master device determines if the remote device
`has interference avoidance capabilities. If the remote device
`45 does not have interference avoidance capabilities (NO), the
`master device and the remote device commence normal
`operation in step 115. If the remote device does have
`interference avoidance capabilities (YES), the master device
`performs a channel scan at completion of its last transmis-
`50 sian (step 120) and determines which channels have stron(cid:173)
`gest interference in step 130. The master device establishes
`a link to communicate channels to be avoided in step 140.
`The master device then communicates the channels to be
`avoided to the remote device at step 150. In step 160, the
`55 master device and the remote device modify their respective
`hopping sequences. In step 170, the master device and the
`remote device begin transmitting data at the modified hop(cid:173)
`ping sequences. In step 180, the master device periodically
`updates the channels to be avoided. If the master does not
`60 update the channels to be avoided (NO), the master device
`and the remote device continue transmitting data at the
`modified hopping sequences in step 170. If the master does
`update the channels to be avoided (YES), the master device
`returns to step 140 to create another link and communicate
`65 the new channels to the remote device.
`The above process can be applied to a Bluetooth example
`and includes identification of a Bluetooth device's ability to
`
`0011
`
`

`
`US 6,760,319 Bl
`
`5
`support interference avoidance, the measurements of signal
`strength on all channels and identification of which channel
`should not be used without violating the FCC rules, a
`method of modifying the Bluetooth hop sequence so that it
`will avoid channels containing strong or fixed interferers 5
`while still supporting standard Bluetooth hopping with other
`non-enabled members of the piconet and a method of
`relating necessary interference avoidance information to the
`remote Bluetooth devices.
`Once a connection is made between a master and slave in
`a piconet, a Bluetooth service discovery protocol (SDP) can
`be used to relay capability of the slave device to participate
`in interference avoidance. This is accomplished by one
`device querying service records of another device to deter(cid:173)
`mine if the remote device supports interference avoidance. 15
`Interference avoidance capable devices will create a service
`record identifying the service and store that record in an SDP
`server database.
`In order to identify channels with fixed interferers in step
`130, an identification algorithm may be employed. The 20
`identification algorithm can use hardware (e.g., measure(cid:173)
`ment power component 66) and software (e.g., residing in
`central control system 30) to read signal strength of channels
`and determine which channels to avoid. FIG. 4 is a flow
`diagram illustrating one particular methodology for deter(cid:173)
`mining channels with interferers above a certain threshold
`according to step 130 of FIG. 3. In step 200, a master device
`obtains a next channel in a list of channels to determine
`signal strength of that channel. In step 210, the master device
`determines if there are any additional channels to scan. If the
`master device does not have additional channels to scan
`(NO), the scan is completed as illustrated in step 215. If the
`master device does have additional channels to scan (YES),
`the master device advances to step 220 where the master
`device determines signal strength of the channel. In step
`230, the master device determines if the signal strength of
`the channel is above a level one threshold. If the signal
`strength of the channel is not above a level one threshold
`(NO), the process/algorithm returns to step 200 to obtain the
`next channel. If the signal strength of the channel is above
`a level one threshold (YES), the process/algorithm advances
`to step 240. In step 240, the master device waits a prede(cid:173)
`termined period and then determines signal strength of the
`channel a second time. In step 245, the master device
`determines if the signal strength of the channel is above a
`level one threshold. If the signal strength of the channel is
`not above a level one threshold (NO), the process/algorithm
`returns to step 200 to obtain the next channel. If the signal
`strength of the channel is above a level one threshold (YES),
`the process/algorithm advances to step 250. In step 250, the 50
`master device determines if the signal strength of the chan(cid:173)
`nel is above a level two threshold. If the signal strength of
`the channel is not above a level two threshold (NO), the
`channel is placed on the level one list in step 260 and the
`process/algorithm returns to step 200 to obtain the next
`channel. If the signal strength of the channel is above a level
`two threshold (YES), the process/algorithm advances to step
`255. In step 255, the process/algorithm determines if the
`level two list is full. If the level two list is full (YES), the
`scan is complete in step 270. If the level two list is not full 60
`(YES), the channel is placed on the level two list in step 265
`and the process/algorithm returns to step 200 to obtain the
`next channel.
`In the Blue tooth example, an exemplary channel scanning
`algorithm can include reading signal strength of all 79
`Bluetooth available channels. In an alternate aspect of the
`invention, the signal strength is read from all 79 Bluetooth
`
`6
`available channels plus guardbands around the 79 Bluetooth
`channels so as to cover the full 2.4 GHz ISM band. The
`guardbands around the 79 Bluetooth channels are channels
`that are still within the ISM band but not employed by the
`Blue tooth standard. For the Bluetooth standard, this includes
`a first guardband at a frequency of 2.401 GHZ before a
`bottom frequency of the Bluetooth standard and three addi(cid:173)
`tional guardbands at frequencies of 2.481 GHZ, 2.482 GHZ
`and 2.483 GHZ above a top frequency of the Bluetooth
`10 standard. It is to be appreciated that other standards also
`include guardband frequencies, such as the IEEE 802.11
`standard.
`For example, in a two-way radio implementation during
`transmission of a voice audio signal from a device such as
`a microphone pin coupled to the two-way radio or a remote
`device, a manner in which to identify channels that should
`be avoided is to leave the two-way radio keyed for an
`additional fraction of a second (typically on the order of 0.1
`second) at the end of a transmission. When a call is initiated
`from the microphone pin, which is a remote Blue tooth audio
`device (REA), the REA keys the two-way radio for the
`duration of the audio transmission across the Bluetooth
`channel. The digital Bluetooth audio from the remote device
`is decoded and enters the two-way radio as analog audio via
`25 the accessory microphone pin. The only change to this
`normal procedure is that at the end of the Bluetooth audio
`transmission, the REA will leave the radio keyed for an
`additional fraction of a second. During this time the REA's
`receiver is free to sweep the ISM band for interferers and
`30 determine which are fixed. In this manner, the following
`channel scanning algorithm will include ISM band interfer(cid:173)
`ers generated by the two-way radio during transmit.
`The order in which channels can be scanned is equivalent
`to stepping through a code word bank of registers starting at
`35 index zero and proceeding to index seventy-eight (channels
`0, 2, 4, ... 74, 76, 78, 1, 3, 5, ... 73, 75, 77). Optionally,
`the guardbands then can be scanned. If the signal strength of
`a particular channel does not exceed a certain threshold,
`which is referred to as Levell, then it may be concluded that
`40 the channel in question will not significantly interfere with
`normal transmissions. If the signal strength does surpass the
`Level 1 threshold then the signal strength of that channel
`will be measured again 3.125 milliseconds later (the longest
`Bluetooth packet will take 3.125 milliseconds to transmit).
`45 If the signal strength does not exceed the Levell threshold
`on the second measurement then the channel does not
`contain a fixed interferer and the channel scanning algorithm
`will move on to the next channel to be scanned, thus
`avoiding identifying a hopping signal from another device as
`a candidate for removal. If on the second measurement the
`signal strength is above a different, higher threshold, which
`will is referred to as Level 2, then it is placed on an index
`of the channel on a list of Level 2 interferers called Level_
`2_List, otherwise it will be placed on a list of Level 1
`55 interferers called Level_l_List. Entries into the Level_l_
`List may be overwritten by other interferers if the Level_
`l_List becomes full. This procedure can be repeated until
`all the channels have been considered or the Level_2_List
`is full.
`In the Bluetooth example, additional channels can be
`added to the list of interferers if the appropriate number of
`interferers above a certain threshold is not identified. For
`example, if there were not four channels listed in the
`Level_2_List after the scan is complete, then the remaining
`65 slots available in the Level_2_List will be filled with the
`channel immediately before and after a channel already on
`the Level_2_List (the adjacent channel C/1 is 0 dB for a
`
`0012
`
`

`
`US 6,760,319 Bl
`
`7
`Blue tooth radio). If there are not four indices in the Level_
`2_List after the addition of the adjacent channels, then the
`remaining Level_2_List can be replaced with channels in
`the Level_1_List until there are no more channels in the
`Level_1_List.
`
`5
`
`8
`
`TABLE 1-continued
`
`Page scan/
`Inquiry scan
`
`Page/
`Inquiry
`
`Page response Connection
`(master/slave)
`state
`
`A A27-23
`
`B A22-19
`c As, 6, 4, 2, o
`
`A27-23
`
`A27-23
`
`A22-19
`As, 6, 4, 2, o
`
`A22-19
`As, 6, 4, 2, o
`
`A27-23
`._l CLK25-2r
`A22-19
`As, 6, 4, 2, o.-J
`CLK20-ro
`A18-1o ._1 CLKls-7
`D A18-1o
`A18-1o
`A1s-1o
`E A13, 11, 9, 7, s, 3, 1A13, 11, 9, 7, s, 3, 1A13, 11, 9, 7, s, 3, 1A13, 11, 9, 7, s, 3, 1
`F 0
`0
`0
`16 X CLK27-3
`mod 79
`
`FIG. 5 is a flow diagram illustrating one particular meth(cid:173)
`odology for modifying the hopping sequence of the master
`and slave device as illustrated in step 160 of FIG. 3. In step
`300, the master device and the slave device identify M 10
`channels to be avoided among N total channels. In step 310,
`both the master device and the slave device define an
`alternate register bank of N-M channels. In step 320, the
`synthesizer code words for the M channels to be avoided are
`removed. In step 330, the alternate register bank is loaded 15
`with N-M synthesizer code words for the N-M channels with
`the synthesizer code words for the M channels to be avoided
`removed. In step 340, the address scheme is reconfigured for
`addressing the alternate register bank with N-M synthesizer
`codes for N-M channels.
`
`In the Bluetooth example, the above methodology can
`seek to reduce the level of interference in a Blue tooth system
`by identifying the 4 strongest interferers, removing these
`synthesizer code words from a length-79 register bank,
`creating a new length-75 register bank. The synthesizer code
`words within the length-75 register bank can be ordered so
`that a length-32 segment still spans 64 MHz as is conven(cid:173)
`tional in a length-79 register bank. It is to be appreciated that
`the above reconfigured addressing scheme can be employed,
`so as to skip addressing of the 4 strongest interferers in the
`length-79 register bank. However, a simpler and less time
`consuming methodology would be to reduce the length
`79-register bank to a length 75-register bank.
`
`FIG. 6 illustrates a hop selection kernel370 for a 79-hop
`system as illustrated in the Bluetooth specification, while
`Table 1 below illustrates how each of the control signals
`used by the selection kernel is determined for a 79-hop
`system. During the connection state the control signals (X,
`Y1, Y2, A, B, C, D, E, F) are derived from the 27 MSB's
`(Most Significant Bits) of the CLK signal and the 28-bit
`address of the master as per Table 1. The control signals are
`used to determine addresses to a bank of 79 registers in
`segments of 32. However, after the 4 worst interferers have
`been identified the register bank will have been shortened to
`length-75, meaning that the hop selection kernel must be
`modified so that it generated addresses to a bank of 75
`registers, instead of 79, still in segments of 32. Referring to
`Table 1, the first change (of two changes) is to generate
`control signal F modulo 75 instead of modulo 79 as shown
`in Table 1. The second change (of two changes) is to change
`the modulo of the final add operation from 79 as shown in
`FIG. 6 to 75 as shown in FIG. 7 to generate a modified hop
`selection kernel 380 illustrated in FIG. 7. The modulo
`operation is well known to those skilled in the art and
`implementation of the hop selection kernel and the modulo
`operation can be employed via hardware and/or software.
`
`TABLE 1
`
`Page scan/
`Inquiry scan
`
`X CLKN16-12
`
`Y1 0
`Y2 0
`
`Page/
`Inquiry
`
`Page response Connection
`(master/slave)
`state
`Xprm4-D <79) I CL~2
`Xp4-D(79)/
`(79)
`(79)
`Xprs4--0
`Xi4--0
`CLKE1/CLKN1 CLKE1/CLKN1 CLK1
`32 x CLK1/
`32 x CLKE1/
`32 x CLK1
`32 x CLKN1
`32 x CLKN1
`
`The hop selection kernel in FIG. 7 starts by adding X and
`A modulo 32. The 4 LSB's (Least Significant Bits) of the
`result are then exc