US 6,643,278 B1
`(10) Patent N0.:
`(12) Umted States Patent
`
`Panasik et al.
`(45) Date of Patent:
`Nov. 4, 2003
`
`USOO6643278B1
`
`(54) WIRELESS NETWORK CIRCUITS,
`SYSTEMS, AND METHODS FOR
`FREQUENCY HOPPING WITH REDUCED
`PACKET INTERFERENCE
`.
`Inventors: Carl M. Panasik, Garland, TX (US);
`ThOmaS M- Slep, Garland, TX (Us)
`
`(75)
`
`.
`(73) Assignee: Texas Instruments Incorporated,
`Dallas, TX (US)
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`4,716,573 A
`12/1987 Bergstrém et a1.
`5,506,863 A *
`4/1996 Meidan et a1.
`.............. 375/134
`5,528,622 A
`6/1996 Cadd et a1.
`5,778,075 A *
`7/1998 Haartsen ..................... 375/138
`5,809,059 A
`9/1998 Souissi et a1.
`
`* cited by examiner
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`.
`.
`.
`Przmary Exammer—Dang Ton
`(74) Attorney, Agent, or Fer—Ronald O. Neerings; Wade
`James Brady, III; Frederick J. Telecky, Jr.
`
`(21) Appl. No.: 09/473,337
`
`(57)
`
`ABSTRACT
`
`(22)
`
`Filed:
`
`Dec. 28: 1999
`
`_
`_
`. .Related U..S. Appllcatlon Data
`PTOVlslonal aPphcatlon N0~ 60/125573: filed on Man 23:
`1999.
`
`(60)
`
`Int. Cl.7 .................................................. H04Q 7/00
`(51)
`(52) US. Cl.
`........................................ 370/330; 370/344
`(58) Field of Search ................................. 370/330, 480,
`370342, 441’ 442’ 241’ 252’ 254’ 389,
`392, 465, 394, 344, 345; 375/130, 131,
`132—134; 380/49, 9, 48, 59; 455/422, 436
`
`for determining a frequency hopping
`A method (10)
`sequence for a newly-entering network. The method com-
`prises the step of scanning (16) a plurality of frequency
`channels. For each of the plurality of frequency channels,
`.
`.
`.
`.
`the scanning step comprises detecting Whether a s1gnal (18,
`22) exists on the channel and recording information (20, 24)
`corresponding to each channel on which a signal is detected.
`Finally, and responsive to the recorded information,
`the
`method forms (30) the frequency hopping sequence.
`
`25 Claims, 2 Drawing Sheets
`
`12\
`
`CONNIENCE NEW HOPPING
`SEQUENCE DETERMINATION: START
`UP NEWLY—ENTERING NETWORK
`
`IO
`
`1‘
`
`
`
`I4\ DETERMINE FIRST CI—ANNEL FOR ANALYSIS
`4_—-——
`_.——'—
`SCAN SELEC ED CHANNEL
`FOR EXIST NC SIGNAL
`
`16\
`
`
`
`
`
`28
`
`NEXT C-IANNEL
`
`18
`FIXED
`
`20
`INTERFERENCE
`YES
`
`7
`RECORD [ME SLOT
`AND CHANNEL
`N0
`22
`PACKET
`
`
`
`INTERFERENCE
`
`RECORD USAGE
`NC
`CHARACTERISTICS
`
`
`
`
`
`
`
`YES
`26
`CREATE HOPP NC SEQUENCE
`FOR NEWLY—EN ERING NETWORK
`
`30
`
`
`
`MODIFY NEWLY—CREATED HOPPING
`
`32/ SEQUENCE TO AVOID FIXED INTERFERENCE
`
`
`NEW SEQUENCE
`w INCUMEENT
`
`SEQUENCE?
`WAIT AT LEAST TWO SLOTS
`34
`
`
`AFTER INCUMBENT USES FIRST
`CHANNEL IN ITS SEQUENCE
`
`38
`
`START FREQUENCY HOPP INC
`
`
`36
`
`EX. 1009 / Page 1 of11
`ERICSSON v. UNILOC
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`Ex. 1009 / Page 1 of 11
`ERICSSON v. UNILOC
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`

`

`US. Patent
`
`Nov. 4, 2003
`
`Sheet 1 0f 2
`
`US 6,643,278 B1
`
`P20
`
`
`
`l'
`
`
`
`
`:15
`
`
` '
`
`P17
`
`
`
`
`
`
`FREQUENCY
`CHANNEL
`
`LEGEND
`7
`
`FIRST NETWORK
`
`7A PACKET, P1n
`
`‘ SECOND NETWORK
`I
`' & PACKET, P2”
`
`FIXED
`M INTERFERENCE (Fl)
`
`
`
`
`
`
`
`RSSI
`
`PREAMBLE +
`DATA
`
`FREQUENCY
`
`SUBCHANNEL
`SCAN
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`
`
`
`
`PHYSICAL
`ENGINE
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`EX. 1009 / Page 2 of 11
`ERICSSON v. UNILOC
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`Ex. 1009 / Page 2 of 11
`ERICSSON v. UNILOC
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`

`

`US. Patent
`
`Nov. 4, 2003
`
`Sheet 2 0f 2
`
`US 6,643,278 B1
`
`FIG 2
`
`IO
`
`K
`
`12
`
`‘4
`
`16
`
`20
`
`RECORD TIME SLOT
`AND CHANNEL
`
`COMMENCE NEW HOPPING
`SEQUENCE DETERMINATION: START
`up NEWLY—ENTERING NETWORK
`
`DETERMINE FIRST CHANNEL FOR ANALYSIS
`
`
`
`SCAN SELECTED CHANNEL
`FOR EXISTING SIGNAL
`
`
`
`FIXED
`INTERFERENCE
`o
`
`YES
`
`
`
`
`PACKET
`INTERFERENCE
`
`?
`
`
` 28
`
`RECORD USAGE
`CHARACTERISTICS
`
`NEXT CHANNEL
`
`ALL
`
`CHANNELS
`
`SCANNED?
`
`
`YES
`
`26
`
`CREATE HOPPING SEQUENCE
`FOR NEWLY-ENTERING NETWORK
`
`MODIFY NEWLY—CREATED HOPPING
`SEQUENCE TO AVOID FIXED INTERFERENCE
`
`30
`
`32
`
`YES
`NEW SEQUENCE
`z INCUMBENT
`
`SEQUENCE?
`
`WAIT AT LEAST TWO SLOTS
`
`AFTER INCUMBENT USES FIRST
`
`CHANNEL IN ITS SEQUENCE
`
`
`
`NO
`
`.34
`
`38
`
`START FREQUENCY HOPPING
`
`36
`
`Ex. 1009 / Page 3 of 11
`ERICSSON v. UNILOC
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`Ex. 1009 / Page 3 of 11
`ERICSSON v. UNILOC
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`

`

`US 6,643,278 B1
`
`1
`
`WIRELESS NETWORK CIRCUITS,
`SYSTEMS, AND METHODS FOR
`FREQUENCY HOPPING WITH REDUCED
`PACKET INTERFERENCE
`
`This application claims the benefit of Provisional Appli-
`cation Ser. No. 60/125,573 filed Mar. 23, 1999.
`
`CROSS-REFERENCES TO RELATED
`APPLICATIONS
`
`Not Applicable.
`
`STATEMENT REGARDING FEDERALLY
`SPONSORED RESEARCH OR DEVELOPMENT
`
`Not Applicable.
`
`BACKGROUND OF THE INVENTION
`
`The present embodiments relate to wireless communica-
`tion systems, and are more particularly directed to such
`systems using frequency hopping.
`Wireless networks are becoming increasingly popular,
`and in this regard there has been improvement in many
`aspects of such networks. Some improvements relate to
`configurations that permit simultaneously operation of dif-
`ferent networks where there is minimal or no interference
`
`between communications belonging to each of the networks.
`In this respect, the term network is used, and is further used
`in the same manner for the remainder of this document, to
`describe a system consisting of an organized group of
`intercommunicating devices. Further in this respect,
`the
`different networks may be labeled according to a first
`network that is already transmitting in time followed by a
`second network in time seeking to transmit and thereby
`possibly communicating and causing interference due to a
`communication overlapping the pre-existing communica-
`tion of the first network. Accordingly,
`to facilitate the
`remaining discussion, such a first network is referred to as
`an incumbent network, while the network which seeks to
`communicate, or in fact does communicate, after the incum-
`bent network is referred to as the newly-entering network.
`Given this terminology, the present background and embodi-
`ments discussed below are directed to reducing interference
`between incumbent network communications and newly-
`entering network communications.
`One approach to reducing the above-introduced interfer-
`ence is known in the art as spread spectrum frequency
`hopping and is sometimes referred to more simply as
`frequency hopping. In frequency hopping, a newly-entering
`network transmitter transmits packets of information at
`different frequencies in an effort to reduce the chance that
`the packet will interfere or “collide” with a packet transmit-
`ted at a frequency by a transmitter in an incumbent network.
`The change between frequencies, that is, from one frequency
`to another, is said to be a “hop” between the frequencies.
`Moreover, the goal is such that each packet from a newly-
`entering network is transmitted at a frequency which neither
`overlaps nor is near enough to a frequency at which an
`incumbent network is transmitting. Further in this regard,
`some systems (e.g., using Bluetooth protocol) transmit each
`successive packet at a different frequency, that is, the trans-
`mitter is “hopping” to a different frequency for each packet.
`Alternatively, others systems (e.g., IEEE 802.11) transmit a
`first set of packets at a first frequency, and then hop to a
`second frequency to transmit a second set of packets, and so
`forth for numerous different sets of packets at numerous
`
`2
`different respective frequencies. Note further that if inter-
`ference or a collision does occur, it typically corrupts the
`data of both packets, that is, the data transmitted by both the
`newly-entering network and the incumbent network. As a
`result, both networks are then required to re-transmit the
`packets an additional time so as to replace the corrupted data
`resulting from the collision.
`In an effort to achieve minimal packet collision using
`frequency hopping, two prior art methods have arisen for
`determining the different frequencies to which a network
`will hop. In a first method, a frequency hopping network
`uses a pre-ordained hopping sequence. This first approach is
`used by way of example under the IEEE 802.11 standard. In
`a second method, a seed is provided to a pseudo-random
`generator which produces a corresponding pseudo-random
`series of frequencies along which the network hops. This
`second approach is used by way of example under the fairly
`recently developed Bluetooth protocol. Both of these
`approaches have achieved some level of success in reducing
`the amount of inter-network packet collision. Nevertheless,
`the present inventors have empirically determined that by
`locating two or more different networks in the same vicinity
`such that transmissions from each different network effec-
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`tively compete for airtime, there still arises a considerable
`amount of packet collisions, thereby reducing the effective
`transmission rate for each network.
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`Frequency hopping as described thus far reduces the
`chances of interference between a packet from newly-
`entering network and a packet from an incumbent network.
`Further in this regard and by way of additional background,
`FIG. 1 illustrates communications of such packets and, as
`detailed below,
`it also illustrates instances where packet
`collisions occur. Looking to FIG. 1 in greater detail, its
`horizontal axis illustrates time (or time slots), and its vertical
`axis indicates frequency. Additionally, FIG. 1 illustrates a
`number of blocks, where each block is intended to depict a
`packet as transmitted by either an incumbent network or a
`newly-entering network. Further in this regard, note that the
`term “packet” is used in this document to define a block of
`information sent in a finite period of time, where subsequent
`such packets are sent at other times. This block of informa-
`tion may take on various forms, and sometimes includes
`different information types such as a preamble or other type
`of control information, followed by user information which
`is sometimes also referred to as user data. Further,
`the
`overall packet also may be referred to in the art by other
`names, such as a frame, and thus these other information
`blocks are also intended as included within the term
`
`inventive
`“packet” for purposes of defining the present
`scope. In any event, returning to FIG. 1, for the sake of
`reference, each packet illustrated in FIG. 1 is labeled with an
`identifier using the letter “P” (i.e., for packet) and following
`after that letter is a number corresponding to the network
`which transmitted the packet. More particularly, packets
`transmitted by the first network (i.e.,
`the incumbent
`network) are labeled with an identifier P1 while packets
`transmitted by the second network (i.e., the newly-entering
`network) are labeled with an identifier P2. Further,
`the
`subscript for each packet identifies a time period encom-
`passed by the duration of the packet. For example, during a
`time to, the first network transmits a packet P1O while also
`during time t0 the second network transmits a packet P20.
`Further in this regard, in the prior art transmissions by the
`first network are asynchronous with respect to transmissions
`of the second network, both in start time and periodicity.
`Thus, time tO is only meant as a relative indication for the
`first packet from each network, and it is not intended to
`
`EX. 1009 / Page 4 of 11
`ERICSSON v. UNILOC
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`ERICSSON v. UNILOC
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`

`US 6,643,278 B1
`
`3
`suggest that the packets from both networks begin and end
`at the same time.
`
`the preceding
`to all packets in FIG. 1,
`With respect
`demonstrates that each packet begins at a certain time, ends
`at a later time, and fills a certain frequency range (where the
`range is referred to as a channel). As a result and as
`described below, interference may occur if the area in FIG.
`1 defined by a packet overlaps or is within a certain distance
`of a packet from another wireless link.
`Indeed and as
`discussed below, such interference may occur in one of four
`different ways.
`type of packet
`Time tl
`in FIG. 1 illustrates a first
`interference, where it may be seen that the first network
`transmits a packet P11 After packet P11 commences but also
`during time t1 the second network transmits a packet P21.
`The overlap of packets P11 and P21 is shown as a first
`collision C1. Note that the horizontal alignment of packets
`P11 and P21 graphically indicates that in the example of
`collision C1, both packets occupy the same frequency chan-
`nel. Thus, collision C1 represents an example where two
`different networks attempt to transmit packets during an
`overlapping time period and along the same channel.
`Before proceeding with other types of packet collisions,
`an additional discussion is noteworthy with respect to a
`methodology which has been used to further reduce the
`likelihood and impact of packet collisions such as collision
`C1. More particularly,
`this additional methodology is
`referred to in the art as listen-before-talk (“LBT”). In an
`LBT system,
`the system uses the hopping sequence
`described above, but prior to transmitting along a channel in
`the sequence the system monitors (or “listens”) at
`the
`channel
`to determine if there is another packet already
`occupying that channel during the current time. Returning to
`packet P11 by way of example,
`if the second network
`employed LBT, then it would listen at the desired channel at
`which it intended to transmit P21 and would therefore detect
`the presence of packet P11. As a result, the second network
`would avoid collision C1 by not transmitting packet P21 at
`the desired frequency, but instead it would delay a random
`period and then proceed to the next designated channel of its
`hopping sequence. Next, the second network would listen at
`that next designated channel
`to again determine if that
`channel was occupied by a packet from another network,
`and if no packet was detected then the second network
`would transmit its packet; however, if this next designated
`channel also was occupied, then the second network would
`continue to examine additional channels in this same manner
`
`until a channel was detected without being occupied by a
`packet from another network, at which time the second
`network would transmit its packet along the now unoccupied
`channel. Given this process, however, note that a delay
`arises in LBT systems, where the amount of delay depends
`on the number of times that the LBT network is forced to
`
`listen, detect, and advance from an occupied channel, and
`then delay an additional random period to listen, detect, and
`transmit along an unoccupied channel.
`While LBT as shown above reduces the possibility of
`collisions, it also has drawbacks. For example, LBT delays
`transmission by the network which was prepared to transmit
`along a channel but was prevented from doing so due to an
`already-transmitted packet
`in the desired channel. As
`another example, it adds an element of delay to each packet
`due to its listening aspect. Also, all
`the devices in an
`environment must utilize LBT to gain the most benefit
`(fairness) of the scheme. As still another example, some
`protocols (e.g., Bluetooth) utilized in the unlicensed bands
`do not support LBT, while such protocols may nonetheless
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`provide other beneficial aspects and, thus, the choice to use
`such a protocol is a tradeoff in that other aspects are obtained
`without the availability of LBT.
`Time t2 in FIG. 1 illustrates a second type of packet
`interference in connection with a collision C2 occurring
`between a first network packet P12 and a second network
`packet P22. For collision C2) the incumbent first network
`transmits packet P12 during a period including time t2 and at
`a first channel, and thereafter the second network transmits
`packet P22 also during a period including time t2 (i.e., the
`periods of the packets overlap). Packet P22 is transmitted at
`a second channel which, while different than the channel of
`packet P12, it is immediately adjacent the channel occupied
`by packet P12. Further in this regard, it is known in the art
`that while packets occupy a certain channel as shown by the
`vertical displacement of a packet in FIG. 1,
`there is an
`additional tendency for a packet to provide slight interfer-
`ence or “splatter” into adjacent frequency channels. As a
`result of this effect, even though packets P12 and P22 occupy
`different channels, they are still in adjacent channels and,
`thus, they are close enough to one another in frequency such
`that the splatter effect causes a collision between the packets.
`Indeed,
`in some networks the filters used are relatively
`inexpensive and, as a result, the concept illustrated with
`packets P12 and P22 may also apply to next-adj acent
`channels, that is, to the channels that are one more channel
`away from the channels adjacent to the channel in which a
`packet
`is transmitted. Thus, collision C2 represents an
`example where two different networks attempt to transmit
`packets during an overlapping time period and along adja-
`cent (or next-adjacent) frequency channels. Here, if neither
`network uses LBT,
`then both packets P12 and P22 will
`require retransmission due to the collision. If, however, the
`network that intended to transmit the second packet of the
`two uses LBT, then note first that LBT mechanisms are less
`likely to correctly discern an adjacent channel collision.
`However, if the LBT mechanism does recognize the poten-
`tial adjacent channel collision, then the second packet is not
`transmitted along the channel represented by P22 and instead
`that packet is delayed. This delay, while diminishing the
`effective transmission of the second network, avoids any
`disturbance to the first already-existing packet.
`In the
`example of time t2) therefore, if the second network uses
`LBT, then packet P12 will not be disturbed because the
`second network will move the transmission of packet P22 to
`a different channel.
`
`Time t4 in FIG. 1 illustrates a third type of packet
`interference in connection with a collision C4, which is
`comparable to collision C2 except that for collision C4 the
`networks transmit in opposite order. More particularly, for
`collision C4, the second network first transmits a packet P24
`and, thereafter, the first network transmits a packet P14. The
`duration of both of these packets overlaps time t4, and again
`their channels are adjacent to one another rather than being
`the same channel. Nonetheless,
`the splatter effect again
`causes sufficient reach of each packet
`into the adjacent
`channel such that a collision occurs. Here, if neither network
`uses LBT,
`then both packets P24 and P14 require
`re-transmission due to the collision; if, however, the network
`transmitting the second packet in time (i.e., P14) of the two
`which would otherwise collide uses LBT, then only that
`packet is delayed and the first already-existing packet (i.e.,
`P24) is not disturbed.
`Time t7 in FIG. 1 illustrates a fourth type of packet
`interference in connection with a collision C7, which is
`comparable to collision C1 except that for collision C7 the
`networks transmit in opposite order. More particularly, for
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`Ex. 1009 / Page 5 of 11
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`US 6,643,278 B1
`
`5
`collision C7, the second network first transmits a packet P27
`and, thereafter, the first network transmits a packet P17. The
`duration of both of these packets overlap time t7 and their
`channels are the same. As a result, collision C7 occurs
`(assuming the last network to transmit, which here is the first
`network, does not use LBT).
`FIG. 1 illustrates an additional type of potential interfer-
`ence by depicting a band of fixed interference FI. Fixed
`interference F1 is intended to represent a non-network source
`of radio frequency transmission that remains at the same
`frequency for numerous time slots. Such fixed interference
`may arise from various devices, such as a leaking micro-
`wave oven by way of example. In any event, note at time t5
`that the second network transmits a packet P25, and the
`channel along which that packet is transmitted overlaps
`fixed interference FI. As a result, fixed interference FI
`interferes with packet P25,
`thereby requiring it
`to be
`re-transmitted. Once more, however, if the second network
`were to implement LBT, then assuming fixed interference FI
`were detected during the listening operation of the LBT, then
`packet P25 would not be transmitted so as to avoid the
`otherwise imminent interference. Lastly, while the example
`of packet P25 demonstrates a data collision where the packet
`uses the same channel as the fixed interference, note further
`that fixed interference also may disturb packets in a channel
`that is adjacent to the channel including the fixed interfer-
`ence. Once more, because some networks use relatively
`inexpensive filters, the fixed interference may corrupt pack-
`ets which are either in a channel which is immediately
`adjacent to the fixed interference or which are in the next-
`adjacent channel (i.e., a channel which is next to the channel
`that is immediately adjacent to the fixed interference).
`In view of the above, one skilled in the art should
`appreciate there are various opportunities for packet colli-
`sion or packet interference to occur. Indeed, referring to FIG.
`1,
`the examples above demonstrate that an area may be
`described around each packet, where the packet is disturbed
`if another packet occurs within that area. Thus, this area,
`which may be perceived as a window or zone around the
`packet, is not only defined by the dimensions of the packet,
`but extends both before and after the packet by the width of
`another potentially-interfering packet, and extends above
`and below the packet channel through the height of at least
`the adjacent channel above and below the packet frequency
`channel. Still further, note that the packet sizes for both
`networks shown in FIG. 1 are the same size by way of
`example; however, in some contexts, an incumbent network
`may use packets of different dimension (i.e., either in
`frequency and/or time) relative to the newly-entering net-
`work. In these cases, the packet size for the incumbent as
`well as the packet size for the newly-entering network, in
`addition to the window-affecting factors described above, all
`further define a two-dimensional area relative to a newly-
`entering packet in which interference may occur. Given the
`size of the two-dimensional area, therefore, there remains a
`possibility of packet disturbance even given the pseudo
`random nature of hopping spread spectrum RF communi-
`cations.
`
`As an additional consideration relative to avoiding packet
`collisions, it is further noted that the Federal Communica-
`tions Commission (“FCC”) imposes a restriction on the art
`in the Industrial Scientific Medical
`(“ISM”) bands.
`Specifically,
`the FCC explicitly forbids independent net-
`works to expressly cooperate in allocation of the wireless
`medium.
`
`In view of the above, there arises a need to reduce the
`possibility of packet collision and interference, and prefer-
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`6
`ably to do so in a manner that may be used with protocols
`that do not support LBT. The preferred embodiment
`addresses these goals, as is explored below. In addition,
`there arises a need to achieve the above goals while com-
`plying the with the above-described FCC requirements. The
`preferred embodiments described below avoid these require-
`ments by not requiring the newly entering network to have
`knowledge of or cooperation with the incumbent network.
`
`BRIEF SUMMARY OF THE INVENTION
`
`there is a method for
`In the preferred embodiment,
`determining a frequency hopping sequence for a newly-
`entering network. The method comprises the step of scan-
`ning a plurality of frequency channels. For each of the
`plurality of frequency channels, the scanning step comprises
`detecting whether a signal exists on the channel and record-
`ing information corresponding to each channel on which a
`signal is detected. Finally, and responsive to the recorded
`information,
`the method forms the frequency hopping
`sequence. Other circuits, systems, and methods are also
`disclosed and claimed.
`
`BRIEF DESCRIPTION OF THE SEVERAL
`VIEWS OF THE DRAWING
`
`FIG. 1 illustrates various packets transmitted by a first and
`second network and demonstrates potential collisions
`between such packets as well as interference from a band of
`fixed interference.
`
`FIG. 2 illustrates a flow chart of the preferred embodiment
`as implemented in a method performed by a network trans-
`ceiver.
`
`FIG. 3 illustrates a block diagram of a network transceiver
`operable to perform the method shown in FIG. 2.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`FIG. 1 was described in the Background Of The Invention
`section of this document and the reader is assumed familiar
`
`with that description.
`FIG. 2 illustrates a flow chart of a method 10 according
`to the preferred embodiment and for operating a wireless
`network so as to reduce the drawbacks described above in
`
`connection with the prior art. By way of introduction to this
`preferred embodiment,
`the following discussion demon-
`strates that by the conclusion of method 10 an improved
`hopping sequence is generated for a wireless network. The
`hopping sequence is improved in two respects. First, the
`hopping sequence is such that packets may be communi-
`cated according to it and results in a reduced amount of
`packet collisions as compared to a prior art non-LBT wire-
`less frequency hopping system. Second,
`the hopping
`sequence is such that packets may be communicated accord-
`ing to it and results in a reduced incidence of conflict with
`fixed interference as compared to a prior art non-LBT
`wireless frequency hopping system. These benefits are illus-
`trated in greater detail after the following detailed discussion
`of method 10. Finally, it should be noted that method 10 may
`be implemented in connection with various types of wireless
`networks as may be ascertained by one skilled in the art and
`as further addressed later. Additionally, such a person also
`may determine various different circuits and software imple-
`mentations given the selected network, as is also explored
`later by way of example.
`Method 10 begins with a step 12 where the wireless
`network begins the determination of a new hopping
`
`Ex. 1009 / Page 6 of 11
`ERICSSON v. UNILOC
`
`Ex. 1009 / Page 6 of 11
`ERICSSON v. UNILOC
`
`

`

`US 6,643,278 B1
`
`7
`sequence to be used for intercommunications on the network
`(i.e., by all transmitters, receivers, and transceivers in the
`network). To facilitate the remaining discussion, the network
`which will use this new hopping sequence is referred to as
`the newly-entering network. This terminology is chosen
`because the newly-entering network’s communications are
`new with respect to any one or more incumbent networks
`that already may be communicating along the frequency
`band to be used by the newly-entering network. In the
`preferred embodiment, step 12 occurs at network start-up,
`such as when a first
`transceiver of the newly-entering
`network is turned on or is otherwise initialized. Next,
`method 10 continues to step 14.
`is selected for
`In step 14, a first frequency channel
`analysis. More particularly and as will become apparent
`given the remaining discussion of method 10, in the pre-
`ferred embodiment each channel along which the newly-
`entering network may transmit is individually analyzed by
`method 10 at least once. Accordingly, step 14 operates so
`that a first one of these channels is selected to be analyzed.
`This selection may be implemented in various fashions, such
`as by assigning a unique and ascending number to each
`increasing frequency channel which is available to the
`newly-entering network, and then step 14 may operate by
`initializing a counter to the first assigned number. Other
`implementations may be ascertained by one skilled in the
`art. In any event, once a first channel is selected for analysis,
`method 10 continues to step 16.
`In step 16, the channel selected by step 14 is scanned to
`determine if there is an existing signal in that channel. In the
`preferred embodiment, the known receive signal strength
`indicator (“RSSI”) is used as the scan technique. Note that
`an existing signal may be detected in the scanned channel
`due to various events as illustrated earlier in connection with
`
`FIG. 1. For example, an existing signal will be detected in
`step 16 if there is fixed interference in the scanned channel
`(or in a channel one or two adjacent channel locations from
`the scanned channel). As another example, an existing signal
`will be detected in step 16 if another network has transmitted
`a packet that, during the duration of the scan, is either in the
`scanned channel or in a channel that is adjacent the scanned
`channel. Each of these possibilities is responded to by one
`or more additional steps, as discussed below. Following the
`scan of step 16, method 10 continues to step 18.
`Step 18 directs the flow of method 10 if the interference,
`if any, detected in step 16 is fixed interference. The deter-
`mination of whether a particular detected interference is
`fixed interference (as opposed to packet interference) may
`be made in various fashions. Asimple approach is to wait on
`an occupied channel for a period of time which exceeds all
`known packet lengths (0.4 seconds by FCC part 15 rules). In
`a faster and preferred approach,
`the instance of a fixed
`interferer
`is determined by determining its occupied
`bandwidth, which is very small relative to data carrying
`modulated signals. More particularly, many scan circuits are
`available which can be configured according to the preferred
`embodiment to determine the bandwidth of a received signal
`by stepping through several sub-channels of the particular
`channel. In the process,
`the scanning circuit collects the
`RSSI as a function of each sub-channel and determines the
`
`half-power points, which is the bandwidth. Thus, once all
`sub-channels for the scanned channel are evaluated, and
`assuming that interference is detected on at least one of those
`sub-channels, then it may be further determined that the
`interference is fixed interference based on the bandwidth
`
`identified across all sub-channels. Specifically, fixed inter-
`ference typically occupies only ten percent or less of the
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`if ten same-sized sub-
`thus,
`entire channel bandwidth;
`channels are scanned for a given evaluated channel, and if
`the interference detected is only in one or two of those
`sub-channels,
`then the preferred embodiment determines
`that the detected interference is fixed interference; to the
`contrary, if interference is detected across most or all of
`those sub-channels, then the preferred embodiment deter-
`mines that the detected interference is packet interference. In
`any event, if fixed interference is detected, then step 18
`directs the flow to a step 20. To the contrary, if either no
`interference is detected, or if interference which is not fixed
`interference is detected, then method 10 continues from step
`18 to step 22. Each of these alternative paths is described
`below.
`
`In step 20, having been reached due to the detection of
`fixed interference existing in the scanned channel, method
`10 records an indication of the time slot and channel in
`which the fixed interference was detected. The use of this
`information is detailed later. Thereafter, method 10 contin-
`ues from step 20 to step 26, which is discussed following the
`discussion below concerning steps 22 and 24.
`Step 22 directs the flow of method 10 if the potential
`interference, if any, detected in step 16 is interference from
`another packet being transmitted in the same, or an adjacent,
`channel as the channel scanned in step 16. In the preferred
`embodiment,
`the determination of whether a particular
`detected interference is packet interference (as opposed to
`fixed interference) is again made by measuring bandwidth
`which may then be compared with the known packet
`bandwidth, such as in connection with the sub-channel
`evaluation described above. If packet
`interference is
`detected in the scanned channel, then step 22 directs the flow
`to a step 24. To the contrary, if no interference was detected
`and step 22 is reached, then method 10 continues from step
`22 to step 28. Each of these alternative paths is described
`below.
`
`In step 24, the usage characteristics of the packet inter-
`ference of the scanned channel are recorded. These charac-
`
`teristics preferably include the time slot and channel in
`which the packet was detected.
`In addition, when a
`potentially-interfering packet
`is detected in the scanned
`channel,
`there are two possible levels of information
`retrieval from that packet. As a first possibility, if the packet
`is detected in time to properly recover the header informa-
`tion from the packet, then that header information should
`include an indication of the hopping sequence of the incum-
`bent network which transmitted the packet. For example,
`this indication may be by way of a seed which is used by the
`incumbent ne