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`川川川 B
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7，280，580 Bl
`Oct. 9，2007
`
`ーー
`
`(12) United States Patent
`Haartsen
`
`5，832，026 A 1111998 Li
`5，848，095 A 12/1998 Deutsch
`5，870，391 A 2/1999 Nago
`5，898，733 A 4/1999 Satyanarayana
`6，480，721 Bl * 11/2002 Sydon et al. ...・ H ・H ・H ・..455/464
`
`FOREIGN PATENT DOCUMENTS
`
`5/1986
`2/1999
`4/1999
`
`0182762 Al
`W099109671
`W099/19993
`* cited by examiner
`
`》 O O
`H W W
`
`Primary Examinerー-CurtisOdom
`(74) Attorneぁ Agent，or Firm-Potomac Patent Group
`PLLC
`
`(57)
`
`ABSTRACT
`
`A hop channel is selected for use in a channel hopping
`communication system that includes a sequence of hop
`channels， wherein the sequence comprises a set offorbidden
`hop channels and a remaining set of allowable hop channels.
`Selection involves selecting a hop channel from the
`sequence as a function of a present phase. If the selected hop
`channel is an allowable hop channel， then the selected hop
`channel is used for communication during the present phase.
`If the selected hop channel is a forbidden hop channel， then
`a time-varying parameter is used to select a substitute hop
`channel from the set of allowable hop channels. The sub-
`stitute hop channel is then used for communication during
`the present phase. The time-varying parameter may， for
`example， be a clock value. With this strategy， the resultant
`hopping sequence is identical to the original hopping
`sequence whenever the original sequence calls for an allow-
`able hop channel. In all other cases， a substitute hop channel
`is dynamically selected from the set of allowable hop
`channels.
`
`42 Claims， 15 Drawing Sheets
`
`(54) HOP SEQUENCE ADAPTATION IN A
`FREQUENCY-HOPPING COMMUNICATIONS
`SYSTEM
`
`(75) Inventor: Jacobus C. Haartsen， Hardenberg (NL)
`
`(73) Assignee: Telefonaktlebolaget L M Ericsson
`(pub1.)， Stockholm (SE)
`
`( *) Notice: Subject to any disclaimer， the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/418，562
`
`(22) Filed:
`
`Oct. 15， 1999
`
`(51) Int. C1.
`(2006.01)
`H04B 1/00
`(52) Uふ C1........................................ 375/138; 375/132
`(58) Field of Classification Search ...・ H ・H ・H ・... 375/200，
`375/202，130-153，267; 455/450，464; 370/338，
`370/333， 330
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4，023，103 A
`5/1977 Malm
`4，476，566 A *
`10/1984 Dent .......................... 375/132
`4，606，040 A
`8/1986 David et al.
`4，716，573 A *
`12/1987 Bergstrom et al. ...・ H ・...375/132
`4，780，885 A *
`1011988 Paul et al. •••••••••••••••••• 375/267
`5，307，348 A
`4/1994 Buchholz et al
`5，323，447 A *
`6/1994 Gillis et al. ...・ H ・.....・ H ・.455/464
`5，408，496 A
`4/1995 Ritz et al
`5，515，369 A
`5/1996 Flanuner， III et al
`5，619，493 A
`4/1997 Ritz et al.
`5，737，358 A
`4/1998 Ritz et al.
`5，809，059 A
`9/1998 Souissi et al
`
`DETERMINE PRESET HOP
`CHANNEL AS FUNCTION OF PHASE
`
`901
`
`903
`
`905
`
`907
`
`909
`
`PRESENT HOP CHANNEL=TABLE(INDEX)
`
`USE PRESENT HOP CHANNEL
`
`0001
`
`Marvell Semiconductor, Inc.
`MediaTek Inc.
`MediaTek USA, Inc.
`Exh. 1006
`IPR of U.S. Pat. No. 7,477,624
`
`

`
`u.s. Patent
`
`Oct. 9，2007
`
`Sheet 1 of 15
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`US 7，280，580 Bl
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`u.s. Patent
`
`Oct. 9，2007
`
`Sheet 9 of 15
`
`US 7，280，580 Bl
`
`DETERMINE PRESET HOP
`CHANNEL AS FUNCTION OF PHASE
`
`901
`
`903
`
`INDEX=MOD(CLOCK，N2)+BASE VALUE
`
`PRESENT HOP CHANNEL=TABLE(INDEX)
`
`USE PRESENT HOP CHANNEL
`
`905
`
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`
`0010
`
`

`
`u.s. Patent
`
`Oct. 9，2007
`
`Sheet 10 of 15
`
`US 7，280，580 Bl
`
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`

`
`u.s. Patent
`
`Oct. 9，2007
`
`Sheet 11 of 15
`
`US 7，280，580 Bl
`
`1107
`
`N2 = NUMBER OF ALLOWABLE
`HOPS
`
`1101
`
`PRESENT HOP CHANNEL =
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`
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`FIG. 11
`
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`
`

`
`u.s. Patent
`
`Oct. 9， 2007
`
`Sheet 12 of 15
`
`US 7，280，580 Bl
`
`1201 _、
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`

`
`u.s. Patent
`
`Oct. 9，2007
`
`Sheet 13 of 15
`
`US 7，280，580 Bl
`
`1307
`
`N2 = NUMBER OF ALLOWABLE
`HOPS
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`1301
`
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`
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`GAP COUNT(OFFSET + LAST GAP COUNT)
`
`FIG. 13
`
`0014
`
`

`
`u.s. Patent
`
`Oct. 9，2007
`
`Sheet 14 of 15
`
`US 7，280，580 Bl
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`u.s. Patent
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`Oct. 9，2007
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`Sheet 15 of 15
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`US 7，280，580 Bl
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`US 7，280，580 B1
`
`1
`HOP SEQUENCE ADAPTATION IN A
`FREQUENCY-HOPPING COMMUNICATIONS
`SYSTEM
`
`2
`signature sequence. At the receiver， the same unique signa-
`印 resequence is used to recover the underlying informa-
`tional data stream signal.
`In frequency hopping systems， the spreading is achieved
`5 by transmitting the informational data stream over ever-
`changing radio frequencies. For each communication， the
`Ihe invention relates tO COHmlullcat1011systems where particular frequenciesused by both the transmitter and
`receiver are determined by a predefined frequency hop
`trans111ltter a11d recelver make 118e of a hop sequence to sequalce.The use oftkeq11encyhoPPIng is attract1ve for the
`remain in contact. More particularlぁthei~v:ntion r
`to 10 radio ~pplications ~e~ti~~ed ;b~~~ rb~;ause it more readily
`techniques for dynamically skipping certain hops ofthe hop allows ~the use of cost effective radios.
`A system called Bluetooth was recently introduced to
`sequence.
`In the last several decades， progress in radio and Very provide pervasive connectivity especially between portable
`Large Scale Integrated circuit (VLSI) technology has fos- devices like mobile phones， laptops， personal digital assis-
`tered widespread use of radio communications in consumer 15 tants (PDAs)， and other nomadic devices. This system
`applications. Portable devices， such as mobile radios， can applies frequency hopping to enable the construction of
`now be produced having acceptable cost， size and power low-power， low-cost radios with a small footprint. The
`consumption.
`system supports both data and voice. The latter is optimized
`b~ ap?lyi~g fast !requ~cy ~o~p~ng in combination with a
`Although wireless technology is today focused mainly on
`voice communications(e.g.，with respect to handheldmrobust voice coding-The fast frequency hopping has a
`radios)， this field will likely expand in the near 印 刷reto nominal rate of 800 hops per second (hops/s) through the
`entire 2.4 GHz ISM band. Devices based on the Bluetooth
`provide greater information flow to and from other types of
`nomadIC deVIceS EU1daxed devicesMore speclacany，1t is system concept cmcreate SO called piconets，which com-
`orise a master device and one or more slave devices con-
`likely that further advances in technology will provide very _ _ l'
`inexpensive radio equipment that can easily be integrated 25nected via the FH piconet channel-The FH sequence used
`into many devices. 百;is--~iil r~duce the ~;mber of ~~bles for the piconet channel is completely determined by the
`C11rrently used-For instance rad10 communication Can address or identity of the device actmg as the master TIle
`th~~~~~~b~r~~f~~abk;:~~~U;;~~;:t system clock of the master d白ev吋lC印ed必耐eteぽrmm
`eliminate or redl悶
`maωst匂erde，町Vl叩ce凶s(伊e.g.，peぽTSωona札1c∞om甲pu凶lteぽrs吋)with their r閃es叩pe氏c- the hopping sequence (i.e.， the designation ofwhich one of
`tive peripherals (e.g.， printers)・
`30 the possible hops in the sequence is the“cu汀 ent"hop). In the
`Bluetooth system， each device has a free-running system
`~l~~k~ E~~hJ ;ith~ s-l~~~ d~vi~~s -~dd~ a-~~汀esponding time
`百leaforementioned radio communications will require
`an unlicensed band with suflicient capacity to allow for high of志向tto its clock that enables it to become aligned with the
`data rate transmissions. A suitable band is the Industrial clock of the master device. By using the master address to
`Sc制cα1陀悶len臼n凶1
`globa札llyavailable. The band provides 83.5 MHz of radio -- of志向tto align to the master clock， each slave device keeps
`in hop synchrony to the master device; that is， master a~d
`spectrum.
`To allow different radio networks to share the same radio slave -de~ices re~ain in contact by hopping synchronously to
`medium without coordination， 時I叫 spr回 dingis usually the制 nehop企eque即 yor hop carrier. For more details，
`applied. In fact， the Federal Communications Commission 40 reference is made to U.S. patent -application Ser. No. 08/932，
`(FCC) in the United States cu汀 entlyrequires radio equip- 911， filed on Sep. 18， 1997 in the name ofJ. C. Haartsen and
`ment operating in the 2.4 GHz band to apply some form of entitled“Frequency Hopping Piconets in an Uncoordinated
`spectrum spreading technique when the transmit power Wireless MuI1:i-user System，" which is hereby incorporated
`exceeds about 0 dBm. Spread spectrum communication herein by reference in its entirety.
`techniques， which have been around since the days of World 45 The hop sequences used in the Bluetooth system are
`War II， are of interest in today's commercial applications generated -thro~gh a hop selection mechanism as described
`because they provide robustness against interference， and in U.S. patent applicati~n Ser. No. 08/950，068， filed on Oct.
`allow for multiple signals to occupy the same radio band at 24， 1997 in the name of J. C. Haartsen and entitled“Method
`the same time.
`and Apparatus for the Generation of Frequency Hopping
`Spreading can either be at the symbol level by applying 50 Sequences，" which is hereby incorporated herein by refer-
`direct-sequence (DS) spread spectrum techniques or at the ence in its entirety. With this method， hop carriers are
`channel level by applying frequency hopping (FH) spread generated“on the fly". The mechanism has no inherent
`spectrum techniques. In DS spread spectrum， the informa- memory: address and clock information instantaneously
`tional data stream to be transmitted is impressed upon a determine the sequence and phase and therefore directly
`much higher rate data stream known as a signature sequence. 55 determine the desired hop carrier. The advantages of such a
`Typically， the signature sequence data are binary， thereby selection scheme are numerous. By changing address and
`providing a bit stream. One way to generate this signature clock， a device can jump from one FH piconet channel
`sequence is with a pseudo-noise (PN) process that appears controlled by one address/clock combination to another
`random， but can be replicated by an authorized receiver. The piconet controlled by another address/clock combination. In
`informational data stream and the high bit rate signature 60 this regard， reference is also made to the aforementioned
`sequence stream are combined to generate a stream of application U.S. Ser. No. 08/932，911 describing FH piconets
`so-called “chips" by multiplying the two bit streams in an uncoordinated wireless multi-user system.
`together， assuming the binary values of the two bit streams
`Radio communications intended for local connectivity
`are represe凶 edby +1 or -1. This combination ofthe 1首位er between consumer applications require the use of a free and
`bit rate signal with the lower bit rate data stream is called 65 unlicensed band. As mentioned before， the ISM band at 2.45
`spreading the informational data stream signal. Each infor- GHz is a suitable band because it is available globally
`mational data stream or channel is allocated a unique (although the specific part ofthe ISM band that may be used
`
`pel，ates
`
`BACKGROUND
`
`0017
`
`

`
`US 7，280，580 B1
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`0018
`
`

`
`US 7，280，580 B1
`
`5
`6
`frequencies in the first sequence in their remaining order. calls for an allowable hop channel. In all other cases， a
`Other hop sequences are similarly derived by using different substitute hop channel is dynamically selected from the set
`decimation numbers.
`of allowable hop channels.
`U.S. Pat. No. 5，809，059， which issued to Souissi et al. on
`In another aspect of the invention， the time-varying
`Sep. 15， 1998， discloses a method and apparatus for spread 5 parameter may be a clock value. In some embodiments， the
`spectrum channel assignment. The technique includes com- time-varying parameter and the present phase may be
`puting average noise and interference levels for different derived from a same clock value. In altemative embodi-
`sequences of channels， and then selecting that one of the ments， the time-varying parameter may be a random value
`sequences of channels having the lowest average noise and or a pseudo-random value.
`interference level for a next transmission of information. 10 In yet another aspect of the invention， hop selection
`U.S. Pat. No. 4，606，040， which issued to David et al. on further comprises forming a sequence of allowable hop
`Aug. 12， 1986， discloses a transmitting-receiving station for channels from the set of allowable hop channels. In this case，
`a system for transmitting data by frequency hopping. In the operation of using a time-varying parameter to select a
`order to facilitate synchronization between two units when substitute hop channel from the set of allowable hop chan-
`one is in a standby mode， a code gene凶 ordefines the use 15 nels comprises forming an index value from the time-
`of a plurality of channels in accordance with a so-called varying parameter; using the index value to select one ofthe
`high-speed skip law for a transmitting-receiving station in allowable hop channels from the sequence of allowable hop
`
`either of the transmitting or recei、ringmodes， and in accor- channels; and using the selected allowable hop channel as
`
`index value=mo的 ime-varyingpararneter， N2)+
`BASE VALUE，
`
`dance with a so-called low-speed skip law for a transmitting- the substitute hop channel.
`receiving station in the stand-by mode. The high叩 eedskip 20 In still another aspect of the invention， the operation of
`law consists ofthe use of each ofthe channels during a time forming the index value from the time-varying parameter
`' while the low-speed 汰 iplaw governs the char創n昭1ge凶soぱft白he c∞omp戸戸n附 deteぽTmm凶nm廿山m昭19the expre 凶 m ・
`Tp
`listening channels employed during NxTp， each correspond-
`ing to a center channel of a sequence of N channels of the
`25
`high-speed skip law.
`U.S. Pat. No. 4，023，103， which issued to Malm on May where mod G，k) denotes j modulo k， N2 is the number of
`10， 1977， discloses a synchronizer for synchronizing a allowable hop channels in the sequence of allowable chop
`frequency hopping receiver with a companion frequency channels and BASE VALUE represents an index value ofthe
`hopping transmitter. The synchronizer includes an electronic O A first allowable hop channel in the sequence of allowable hop
`30
`clock that provides timing pulses for activating a pseudo- J V channels.
`random sequence generator at the frequency hopping rate， In yet another aspect of the invention， the operation of
`and means that cause the clock to skip one activating pulse using a time-varying parameter to select a substitute hop
`every N successive frequency hopping periods， until a channel from the set of allowable hop channels comprises
`frequency hopping local signal and a frequency hopping35determill1ng alIndex value，I，as a fullct1011of the t1mb
`signal from the companion receiver are out of sync by less J J varying parameter; designating one of the allowable hop
`than one frequency hopping period.
`channels in the sequence of hop channels as a first hop
`Each of the above-cited documents discloses a technique channel; starting at the first hop channel， processing the
`for skipping certain hops that has drawbacks， including the sequence ofhop channels to determine an ith allowable hop
`fact that each requires changes to the hop sequence genera- 40 channel in the sequence of hop channels; and selecting the
`tor.
`ith allowable hop channel for use as the substitute hop
`百lereis therefore a need for methods and appara印 sesfor channel.
`In some embodiments， the first hop channel may be the
`removing specific hop frequencies from an arbitrary hopping
`sequence. There is also a need for accomplishing this first hop channel in the sequence of hop channels. In
`without requiring off-line processing. It is also desirable to 45 altemative embodiments， the first hop channel may be a first
`be able to adapt hop sequences dynamically， and to apply hop channel after a last forbidden hop ch制 限1in the
`this adaptation to any existing hop selection scheme or sequence of hop channels. In this case， the operation of
`existing hop sequence.
`processing the sequence ofhop channels to determine an ith
`allowable hop channel in the sequence of hop channels
`50 wraps around to the start of the sequence of hop channels
`when i is greater than the number of hop channels following
`the last forbidden hop channel in the sequence of hop
`In accordance with the present invention， a hop channel is
`channels
`selected for use in a channel hopping communication system
`In still another aspect of the invention， the operation of
`that includes a sequence of hop channels， wherein the
`sequence comprises a set of forbidden hop channels and a 55 processing the sequence ofhop channels to determine an ith
`remaining set of allowable hop channels. In accordance with allowable hop channel in the sequence of hop channels may
`one aspect of the invention， selection involves selecting a altematively comprise， starting at the first hop channel and
`hop channel from the sequence as a function of a present continuing with each successive hop channel in the sequence
`phase. If the selected hop channel is an allowable hop ofhop channels， determining whether the hop channel is an
`channel， then the selected hop channel is used for commu- 60 allowable hop channel; and stopping when an ith allowable
`nication during the present phase. If the selected hop channel hop channel has been identified in the sequence of hop
`is a forbidden hop channel， then a time-varying parameter is channels
`In yet another aspect of the invention， the technique
`used to select a substitute hop channel from the set of
`allowable hop channels. The substitute hop channel is then further comprises determining a gap count for each of the
`used for communication during the present phase. With this 65 hop channels in the sequence of hop channels， wherein the
`strategy， the resultant hopping sequence is identical to the gap count represents how many forbidden hop channels are
`original hopping sequence whenever the original sequence in the sequence of hop channels from the first hop channel
`
`SUMMARY
`
`0019
`
`

`
`US 7，280，580 B1
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`8
`7
`up to and including said each of the hop channels. In these selection mechanism visits a “forbidden" hop， an offset may
`embodiments， the operation of processing the sequence of be temporarily added to the phase such that an allowed hop
`hop channels to determine an ith allowable hop channel in is instead selected. The offset is only applied when a
`the sequence ofhop channels comprises (a) using the index forbidden hop is selected. When an allowed hop is selected，
`value plus a previous gap count to select one of the hop 5 no adjustment is made. As used throughout this disclosure，
`channels from the sequence of hop channels; and (b) using the term “forbidden" refers to a hop channel that should be
`the selected hop channel as the substitute hop channel if the avoided during communication for any of a number of
`selected hop channel is associated with a present gap count reasons. For example， the detection of a substantial amount
`that is equal to the previous gap count， otherwise setting the of interference on a hop channel may make it desirable to
`previous gap count equal to the present gap count and 10 avoid use of that hop channel， at least until the interference
`subsides. It may also be the case that one or more hop
`rep回 tingoperations (a) and (b).
`channels are known to be “reserved" for use by another
`system， so that a present system can avoid experiencing
`interference by avoiding these channels. Similarly， a nearby
`The 0句ectsand advantages of the invention will be 15 system may be 印 刷redto provide a high priority/high
`understood by reading the following detailed description in quality service via one or more hop channels. In this case， a
`conjunction with the drawings in which:
`present system can avoid causing interference on these
`FIG. 1 is a graph depicting an exemplary hop carrier channels (and thereby avoid disturbing the nearby system)
`definition in the ISM band;
`by avoiding the use of these hop channels. These are but
`FIGS.2(α) and 2(b) are graphs depicting examples ofhop 20 mere examples of reasons why one or more hop channels
`carrier definitions in the ISM band in case of thr民 individual may be denoted as “forbidden" hop channels. Those having
`narrowband interferers;
`ordinary skill in the art will recognize that other reasons
`FIGS.3(α) and 3(b) are graphs depicting examples ofhop exist as well， and all such reasons are considered within the
`carrier definitions in the ISM band in case of a single scope of the invention. It will also be recogniz疋dthat the
`wideband interferer;
`25 designation of a hop channel as altematively“forbidden" or
`FIGS. 4(α) and 4(b) illustrate a hop carrier selection “allowed" need not be static， but can instead be determined
`and changed dynamically. For example， an allowed hop
`technique that utilizes a pre-stored sequence;
`FIG. 5 is a block diagram of an exemplary hop carrier channel may become“forbidden" in response to the detec-
`tion of interference on that hop channel， and may later be
`selector for the case of on-the-fly sequence generation;
`FIG. 6 is a block diagram illustrating the general concept 30 again designated as “allowed" when it is detected that the
`of a hop avoidance scheme in accordance with the invention; interference has sufliciently abated.
`In another aspect of the invention， for each phase value
`FIG. 7 is a diagram of a hop sequence having a total ofNl
`associated with a forbidden hop， the transformation of the
`hop channels;
`FIG. 8 is a block diagram illustrating a set of N2 remain- forbidden hop into an allowed hop may be evenly distributed
`ing allowable hop channels in accordance with one aspect of 35 over the allowed hops by using a time-varying parameter as
`the basis for making a selection， such as using a time-
`the invention;
`FIG. 9 is a flow chart of operations in accordance with one varying parameter to form the offset amount described
`above. For example， selection (eιvia the offset amount)
`embodiment of the invention;
`FIG. 10 is a diagram of a table that may be stored in a may be varied as a function of the system clock. Altema-
`memory for use in determining a substitute hop channel in 40 tively， selection may be made on the basis of a random or
`pseudo-random parameter. As a result， the randonmess that
`accordance with an embodiment of the invention;
`FIG. 11 is a flow chart of operations for determining a characterizes the initial FH sequence (which uses all hop
`suitable hop channel in accordance with one embodiment of frequencies) is preserved in the final， revised FH sequence
`the invention;
`(which has the same sequence length as the initial FH
`FIG. 12 is a diagram of a table that may be stored in a 45 sequence， but which uses only the allowed hop frequencies).
`memory for use in determining a substitute hop channel in In addition， each hop carrier in the revised FH sequence may
`accordance with an altemative embodiment ofthe invention; be visited with equal probability. Because of the feature
`FIG. 13 is a flow chart of operations for determining a whereby allowed hops continue to be used during their
`suitable hop channel in accordance with an alternative originally-scheduled phase values， the original FH sequence
`50 is reflected in the revised FH sequence: Only during phase
`embodiment of the invention;
`FIG. 14 is a block diagram of a frequency hop generator values associated with forbidden hops are substitute (al-
`for use in a Bluetooth system， in accordance with an lowed) hops utilized. This allows slave units participating on
`embodiment of invention; and
`the hopping channel to remain synchronized even if once in
`FIGS. 15(α) and 15(b) depict a comparison between an a while， they miss a hop (i.e.， when the forbidden hop is
`original and a corresponding revised hopping scheme， in 55 replaced by an allowed hop).
`accordance with the invention.
`These and other aspects of the invention will now be
`further described in greater detail.
`In general a hop selection scheme includes thr民 compo-
`nents: a白xedset of carriers to hop over (0武enrefer汀Tedto
`I百1t記e various features of the invention will now be 60 heぽ:relnas “hop chann記lels"
`described wi抗thr閃es叩pe氏cttωo the白gur閃es臥， inwhiにichlike parts are carriers that is followed as hopping progresses， and a phase
`identified with the same reference characters.
`that points to a particular place in the hop sequence. As the
`百letechniques described herein achieve the skipping of phase progresses， the system hops from one hop channel in
`certain hops in a hop sequence without having to change the the FH sequence to the next according to the defined
`hop sequence generator. Instead， a transformation operation 65 sequence， thereby operating at each of the carriers at one
`is performed in which a “forbidden" hop serves as the basis time or another. Most FH systems that use the ISM band at
`for determining an“allowed" hop. For example， if the hop 2.45 GHz have a carrier definition as shown in FIG. 1. The
`
`DETAILED DESCRIPTION
`
`0020
`
`

`
`US 7，280，580 B1
`
`10
`9
`83.5 MHz available radio spectrum at this ISM band is random properties of the FH sequence. If one were to use a
`divided into 79 carriers equally spaced by 1 MHz. The first fixed replacement of occupied carrier A by a clean carrier K，
`carrier is at 2402 MHz and the last carrier is at 2480 MHz. then K would be visited twice as often as the carriers not
`No hops are defined at the edges of the ISM band in order used for replacement， and this would violate the uniform
`to satisfシtherequirements on out-of-band spurious signals 5 probability requirement.
`In conventional FH systems， the sequences are pre-stored.
`using relaxed radio transmitter design.
`百lese79 carriers form the set of carriers that FH systems At the time of counection 印 刷p，one of the sequences， X， is
`such as IEEE 802.11 and Bluetooth hop over. The sequence selected which designates both the particular set offrequen-
`determines the order in which the hops are utilized (0自己n cies to be used and the ordering of those frequencies. During
`referred to herein as“visited"). To allow fair access to this 10 operation， the phase value determines the hop position ofthe
`ISM band， regulatory bodies like the FCC in the U.S. and the connection within the sequence. The rate of change of the
`Conference of European Posts and Telecommunications phase value determines the hop rate. A conventional hop
`(CEPT) in Europe have defined certain rules to which FH selection scheme is shown in FIGS. 4(α) and 4(b). In FIG.
`radios using the ISM band have to conform. For example， 4(α)， the original sequence X is stored in an addressable
`the FCC requires that at least 75 hop carriers be used， and 15 memory 403. In operation， an address selector 401 receives
`that， on average， each hop carrier be visited with equal a phase value， and converts this into an address for retrieving
`probability. In addition， in a 30 second period， the accumu- the frequency to be used for a next hop.
`In FIG. 4(b)， another sequence， Y， is stored in the memory
`lated dwell time on a single hop should not be gr回 terthan
`400 ms. In the IEEE 802.11 standard， the sequence length is 403. The sequence Y is similar to the original sequence X，
`exactly 79 and each hop carrier is visited only once in the 20 but has one or more carriers removed. (In the example of
`sequence. The sequence has a repetition interval of79 hops. FIG. 4(b)， the hops at 2465 MHz and 2478 MHz have been
`The sequence does not have to have a length identical to removed.) In operation， the addr出 selectoruses the input
`the number ofhop carriers in order to satisfシtheFCC rules， phase value to select a next hop frequency from the reduced
`however. For example， in Bluetooth， the sequence length is set of hop frequencies. In this marmer， hop avoidance can
`very long， consisting of 2^27 hops. Still， each hop carrier is 25 easily be accomplished.
`visited with equal probabi