US007203500B2
`
`(12) United States Patent
`Leeper et al.
`
`(io) Patent No.:
`(45) Date of Patent:
`
`US 7,203,500 B2
`Apr. 10, 2007
`
`(54) APPARATUS AND ASSOCIATED METHODS
`FOR PRECISION RANGING
`MEASUREMENTS IN A WIRELESS
`COMMUNICATION ENVIRONMENT
`
`(75) Inventors: David G. Leeper, Scottsdale, AZ (US);
`David G. England, Chandler, AZ (US);
`Jeffrey D. Hoffman, Chandler, AZ (US)
`
`(73) Assignee: Intel Corporation, Santa Clara, CA
`(US)
`
`(*) Notice: Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 459 days.
`
`(21) Appl. No.: 10/633,269
`
`(22) Filed: Aug. 1, 2003
`
`(65) Prior Publication Data
`
`US 2005/0026563 Al Feb. 3, 2005
`
`6,011,974 A
`2002/0118723 Al
`
`1/2000 Cedervall et al.
`8/2002 McCrady et al.
`
`OTHER PUBLICATIONS
`
`Xinrong Li et al: Indoor Geolocation Using OFDM Signals in
`Hiperlan/2 Wireless LAN's IEEE vol. 2, Sep. 18, 2000.
`Porcino D et al: "Ultra-Wideband Radio Technology: Potential and
`Challenges Ahead" IEEE Communication S Magazine, IEEE Ser-
`vice Center, vol. 41 No. 7 Jul. 2003.
`Adams J C et al: "Ultra Wideband for Navigation and Communi-
`cations" IEEE vol. 2, Mar. 20, 2001.
`PCT Search Report.
`
`Primary Examiner•Lee Nguyen
`(74) Attorney, Agent, or Firm•Michael A. Proksch
`
`(57)
`
`ABSTRACT
`
`(51)
`
`(52)
`(58)
`
`Int. CI.
`H04Q 7/20 (2006.01)
`U.S. CI 455/456.1; 455/41.2; 342/458
`Field of Classification Search 455/456.1,
`455/456.5, 456.6, 41.2; 342/357.08, 357.09,
`342/357.1,458,463
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,919,708 A 11/1975 Pudsey
`
`An apparatus and associated methods to provide precision
`ranging measurements in an ultrawideband (UWB) wireless
`communication system are generally described. In this
`regard, according to one example embodiment, an innova-
`tive ranging agent is introduced that effectively computes
`one or more of the time of signal propagation, the difference
`in local clocks and frequency offsets to calculate an increas-
`ingly accurate estimate of the proximal distance between
`two or more devices in UWB communication.x.
`
`17 Claims, 4 Drawing Sheets
`
`102
`
`J
`
`Device
`
`112
`
`( Ranging Agent
`
`UWB Transceiver
`
`u
`
`100
`
`104
`
`Device
`
`110
`
`UWB Transceiver
`
`Ranging Agent j
`fsr
`
`114
`
`UNIFIED PATENTS EXHIBIT 1004
`Page 1 of 12
`
`

`

`U.S. Patent Apr. 10,2007 Sheet 1 of 4
`
`US 7,203,500 B2
`
`102
`
`Device J
`
`112
`
`Ranging Agent
`
`108
`
`UWB Transceiver
`
`FIG. 1
`
`u
`
`wo
`
`104
`
`Device
`
`no
`
`UWB Transceiver
`
`Ranging Agent )
`^=
`
`114
`
`200
`^
`
`FIG. 2
`
`Ranging Agent
`
`202 -^
`
`f Control Eleme
`Tt)
`
`/-204
`
`Memory
`
`Precision Timing
`Element
`
`1
`Frequency Offset
`Compensation
`
`'^-206
`
`Nv-208
`
`1
`Input/Output
`Interface(s)
`
`Nx-210
`
`UNIFIED PATENTS EXHIBIT 1004
`Page 2 of 12
`
`

`

`U.S. Patent Apr. 10, 2007 Sheet 2 of 4
`
`US 7,203,500 B2
`
`FIG. 3
`
`300
`
`Analog Signal In
`
`306
`
`Matched '
`Filter
`
`Strobe Signal
`
`Latch
`
`307
`-308
`Timing Data Out
`
`310
`
`305
`
`304
`
`Counter Reading
`Transfer
`x-302
`Clock
`
`Counter
`
`400
`
`( START)
`
`FIG. 4
`
`402
`
`RECEIVE THE ISSUED REQUEST,
`INITIALIZE TIMING ELEMENTS,
`AND ISSUE AN ACCEPTANCE
`
`ISSUE A REQUEST FOR RANGING EXCHANGE
`WITH ONE OR MORE TARGET RECEIVER(S),
`INITIALIZING TIMING ELEMENT(S)
`
`406
`
`408
`
`RECEIVE A RESPONSE FROM ONE OR
`MORE OF THE TARGETED RECEIVER(S)
`
`ISSUE A RANGING MESSAGE, RECORDING
`ITS TRANSMIT STROBE TIME
`
`412
`
`RECORD RECEIVE STROBE TIME AND
`N ISSUE ANOTHER RANGING MESSAGE,
`RECORDING THE TRANSMIT STROBE TIME
`
`414
`
`EXCHANGE RECORDED STROBE TIMES
`FROM WHICH RANGE IS CALCULATED
`
` ^
`( END ;
`
`UNIFIED PATENTS EXHIBIT 1004
`Page 3 of 12
`
`

`

`U.S. Patent Apr. 10, 2007 Sheet 3 of 4
`
`US 7,203,500 B2
`
`FIG. 5
`
`Core DLL
`
`500
`
`502
`
`504^
`
`Strobe Pulse
`
`•ww
`
`I 506
`
`ft
`
`600
`
`610
`
`FIG. 6
`
`RECEIVER CLOSES
`SYMBOL TIMING
`
`RECEIVER DETECTS
`START OF INFORMATION
`
`CORRELATION PATTERN
`
`INFORMATION ^
`
`MATCHED
`FILTER
`
`612
`
`614
`
`SYMBOL DETECT • •
`y /- 616
`
`618
`
`620
`
`ADC
`
`SLICER
`
`DEMOD
`
`UW
`DETECT
`
`SYMBOL PHASE
`
`UW DETECT
`626 ± ^r 622
`
`SYMBOL CLOCK
`
`SYMBOL COUNT
`
`624
`
`628
`
`SYMBOL
`COUNTER
`
`MESSAGE TIMESTAMP
`
`UNIFIED PATENTS EXHIBIT 1004
`Page 4 of 12
`
`

`

`U.S. Patent
`
`Apr. 10, 2007 Sheet 4 of 4
`
`US 7,203,500 B2
`
`FIG. 7
`
`00
`
`tB Device B
`
`Rev: null
`Record: T1 RB
`
`Send:T1RB
`Record: T2 TB
`
`Rcv:T1Ti)T2
`TA' ""RA
`Record: T3 RB
`
`Send:T2TR,T3
`TB' ' "RB
`Record: T4
`TB
`
`Rcv:T3TA,T4RA
`Record: T5RB
`
`704
`
`708
`
`Device A t.
`
`Send: null
`Record: T1
`TA
`
`Rcv:T1RB
`Record: T2
`RA
`
`Send:T1TA,T2RA
`Record: T3TA
`
`Rev: T2TB, T3RB
`Record: T4 RA
`
`Send:T3TA,T4RA
`Record: T5TA
`
`FIG. 8
`
`800
`
`STORAGE MEDIUM
`
`802
`
`CONTENT TO IMPLEMENT
`RANGING AGENT
`
`UNIFIED PATENTS EXHIBIT 1004
`Page 5 of 12
`
`

`

`US 7,203,500 B2
`1 2
`APPARATUS AND ASSOCIATED METHODS FIG. 6 is block diagram of precision timing element using
`FOR PRECISION RANGING elements of an ultrawideband transceiver and message time
`MEASUREMENTS IN A WIRELESS stamps, according to one example embodiment of the inven-
`COMMUNICATION ENVIRONMENT tion;
`5 FIG. 7 is communication flow diagram for a method for
`TECHNICAL FIELD clock frequency offset compensation, according to one
`example embodiment of the invention; and
`Embodiments of the present invention are generally FIG. 8 is a block diagram of an example article of
`directed to wireless communication technology and, more manufacture including content which, when executed by an
`particularly, to an apparatus and associated methods for 10 accessing machine, causes the machine to implement one or
`precision ranging measurements in a wireless communica- more aspects of embodiment(s) of the invention,
`tion environment.
`
`DETAILED DESCRIPTION
`
`BACKGROUND
`
`15 Embodiments of an apparatus and associated methods for
`Ultrawideband (UWB) wireless communication, in its precision ranging measurements in a wireless communica-
`most basic form, has been around since the beginning of tion environment are generally introduced herein. For ease
`wireless communication. According to one commonly held of description, and not limitation, the broader teachings of
`definition, a UWB signal is any signal wherein the band- the claimed invention will be developed in accordance with
`width divided by the center frequency is roughly 0.25, or 20 an implementation in an ultrawideband (UWB) wireless
`more. Recently (Feb. 14, 2002), the United States Federal communication environment. In this regard, according to but
`Communication Commission (FCC) approved the use of a one example embodiment of the teachings of the present
`pulsed-RF UWB technology for unlicensed operation. UWB invention, an innovative ranging agent is introduced which,
`offers the potential to communicate at very high data rates in cooperation with a wireless communication transceiver
`(hundreds of megabits per second) with very low radiated 25 (e-g-= ^ ultrawideband transceiver), exchanges messages
`power (200 microwatts or less) over short distances (10 with one or more remote (target) receiver(s), recording local
`meters or less). To date, this potential is yet to be realized, strobe times of transmission and reception of the exchanged
`as there is not yet a commercially available UWB solution messages. After (or, during) the exchange of multiple such
`for this unlicensed application messages, the devices exchange the locally recorded strobe
`The Institute of Electrical and Electronic Engineers 30 times from which the ranging agent in the device(s) may
`(IEEE) has established a standards task group, i.e., IEEE f cu ate one 0* mof of a sl^al Propagation time (or,
`802.15.3 TG3a, to study proposals for a standardized UWB ^^ tm•g offset' frequency offset and proximal distance
`wireless physical layer (PHY) representing the channel (-or' ran8e-) between the devices.
`characteristics above. In addition to the promise of high- Reference throughout this specification to "one embodi-
`speed communications, another goal of the standard is to 35 ment" or "an embodiment" means that a particular feature,
`enable ranging measurements between UWB-equipped structure or characteristic described in connection with the
`devices. While no specific accuracy/precision requirement embodiment is included in at least one embodiment of the
`has been set by TG3a, it has been generally assumed that Present invention. Thus, appearances of the phrases "in one
`with communications links of l-10meters, a measurement embodiment" or "in an embodiment" in vanous places
`accuracy/precision of 1 meter or better will be required. 40 throughout this specification are not necessarily all referring
`, ^ , , i. • JT i • ^ i ^ -i i i • ^ to the same embodiment. Furthermore, the particular fea-
`Just such a solution is offered in the detailed description, ^ ^ ^ , i.i. : ,...
`, , tures, structures or charactensties may be combined in any
`suitable manner in one or more embodiments.
`
`BRIEF DESCRIPTION OF THE DRAWINGS 45 Example Network Environment
`FIG. 1 illustrates a block diagram of a wireless commu-
`Embodiments of the present invention are illustrated by nication environment (e.g., an UWB communication envi-
`way of example, and not by way of limitation, in the figures ronment) within which the teachings of the present invention
`of the accompanying drawings in which like reference may be practiced. In accordance with the illustrated example
`numerals refer to similar elements and in which: 50 embodiment of FIG. 1, two or more electronic devices 102
`FIG. 1 is a block diagram of an example wireless com- and 104 are selectively coupled through an ultrawideband
`munication environment incorporating the teachings of the (UW8) wireless communication channel 106. To facilitate
`present invention, according to but one example embodi- such communication, electronic devices 102, 104 are
`ment. depicted comprising an ultrawideband (UWB) transceiver
`TT,^ -1 • 1 1 1 J- J- 1 • ^ 55 108, 110 with an associated one or more antenna(e) through
`FIG. 2 is a block diagram 01 an example ranging agent, , . , ^ ^ . . , i. J-TTTTTT-, • 1/ ( J-
`,. , 1 i- ^ OOOJ which the transmission/reception 01 UWB signal(s) 01 com-
`according to one example embodiment; . i. , , -•, . r
`rc ^ ,
`mumcation channel 106 is effected.
`FIG. 3 is a block diagram of a precision timing engine, ^ accordance with the teachings of the present invention:
`according to one example embodiment of the invention; one or both of devices 102 104 may ^^ a ranging agent
`FIG. 4 is a flow chart of an example method for providing 60 H2, 114, which may determine the proximal distance
`precision ranging measurements within a wireless commu- between the devices. As developed more fully below, rang-
`nication system, according to one example embodiment of ing agent 112, 114 initiates an exchange of messages
`the invention; between the devices 102,104 (or, ranging agents therein),
`FIG. 5 is a block diagram of a delay locked loop (DLL) wherein the devices log a strobe time of transmission/
`suitable for use as a counter within the precision timing 65 reception of such messages. The strobe times are selectively
`element, according to one example embodiment of the exchanged, and one or more of ranging agent 112, 114
`invention; computes one or more of the signal propagation time (t^,)
`
`UNIFIED PATENTS EXHIBIT 1004
`Page 6 of 12
`
`

`

`US 7,203,500 B2
`
`(i.e., distance/signal velocity), timing offset (t0), and fre-
`quency offset (f0) of the reference clocks between the
`devices. Given at least one or more of the signal propagation
`time, timing offset, and frequency offset, a ranging agent
`(e.g., 112) determines a proximal distance, or range, 5
`between its associated UWB transceiver (e.g., 108) and
`responding remote transceiver(s) (e.g., 110). For the deter-
`mination of frequency offset, two (2) or more measurement
`pairs may be required.
`In accordance with the illustrated example embodiment, 10
`different device implementations 102, 104 depict the rang-
`ing agent as coupled with (112) or integrated within (114) a
`UWB transceiver (108, 110, respectively), although the
`invention is not limited in this regard. That is, alternate
`implementations are envisioned wherein a remote ranging 15
`agent is communicatively coupled to one or more remote
`UWB transceivers to implement the teachings of the present
`invention to determine the proximal distance between one or
`more devices engaged in UWB communication. Thus,
`numerous alternate embodiments of the ranging agent, and 20
`its implementation within the communication environment
`are envisioned within the scope and spirit of the present
`invention.
`As used herein, electronic devices 102, 104 are intended
`to represent any of a broad range of electronic appliances, 25
`computing appliances, communication appliances, and the
`like. Moreover, in accordance with one example implemen-
`tation, devices 102, 104 may well represent one or more
`electronic components of (or, within) such appliances, such
`as, for example, chipsets, communication bridges, micro- 30
`processors, baseband processors, radio-frequency integrated
`circuits (RFICs), and the like to facilitate ultrawideband
`communication of content (audio, video, data, etc.) between
`such components within the appliances. It should be appre-
`ciated, based on the description to follow, that embodiments 35
`of the invention may well be implemented in hardware,
`software, firmware and/or any combination thereof within
`the scope and spirit of the present invention.
`In this regard, the communication environment depicted
`100 is intended to represent any of a broad range of 40
`communication environments. So, too, is the communica-
`tion channel 106 intended to represent any of a wide variety
`of communication channels. According to one example
`implementation, communication channel 106 is established
`by transceivers 108, 110 to comply with the pulsed-RF 45
`UWB channel characteristics described in the FCC approval
`for unlicensed UWB use introduced above, although the
`invention is not so limited.
`As introduced above and described more fully below,
`each ranging agent 112, 114 may work with an associated 50
`UWB transceiver 108, 110 to exchange messages (e.g.,
`ranging messages) between devices 102, 104, from which a
`proximal distance between the devices can be determined.
`As described below, ranging agent 112, 114 effectively
`computes one or more of the signal propagation (or, delay) 55
`time (t^,), the difference in local clocks, or timing offset (t0)
`and frequency offsets (f0) to calculate an increasingly accu-
`rate estimate of the proximal distance between devices 102,
`104. Those skilled in the art will appreciate that the deter-
`mination of the proximal distance may well be useful in 60
`support of a myriad of applications such as, for example,
`security/authentication applications, transmission control
`applications, effecting location-based services, and the like.
`
`Example Ranging Agent Architecture 65
`FIG. 2 is a block diagram of an example ranging agent,
`according to one example embodiment of the invention. In
`
`accordance with the illustrated example implementation of
`FIG. 2, ranging agent 200 is depicted comprising one or
`more of control element(s) 202, memory 204, a precision
`timing engine 206, frequency offset compensation element
`208, and input/output communication interface(s) 210
`although the invention is not limited in this regard. Accord-
`ing to one example embodiment, ranging agent 200 may
`well be implemented within environment 100 as one or more
`of ranging agent 112 and/or 114.
`It will be appreciated, given the discussion to follow, that
`although depicted as a number of disparate elements, one or
`more elements of ranging agent 200 may well be combined
`into multifunctional elements (e.g., precision timing engine
`206 and frequency offset compensation 208). Alternatively,
`one or more elements of ranging agent 200 may well
`represent elements physically located external to, yet uti-
`lized by, ranging agent 200, e.g., one or more elements of
`precision timing engine 206 may well be located within an
`associated UWB transceiver. In this regard, ranging agents
`of greater or lesser complexity are anticipated within the
`scope and spirit of the present invention.
`In accordance with the illustrated example embodiment,
`control element 202 controls the overall operation of ranging
`agent 202, although the invention is not so limited. In this
`regard, control element 202 selectively invokes one or more
`elements 204-210 of ranging agent 200 to determine the
`proximal distance between an associated transceiver and one
`or more remote transceiver(s). To perform the precision
`ranging measurements described herein, control element
`202 may communicate with and/or control at least an
`associated UWB transceiver through I/O communication
`interface(s) 210. As used herein control element 202 is
`intended to represent any of a broad range of control
`elements including, but not limited to, one or more micro-
`processors, microcontrollers, field-programmable gate
`arrays (FPGA), application specific integrated circuits
`(ASIC), special purpose controllers, executable content
`(e.g., software or firmware) to implement such control
`functions, or any combination thereof.
`As used herein, memory 204 is intended to represent any
`of a wide variety of storage media/mechanisms known in the
`art. In accordance with the illustrated embodiment, memory
`204 may be used by ranging agent 200 to store ranging
`information computed for one or more remote device(s).
`Precision timing engine 206 may be selectively invoked
`by, e.g., control element 202, to determine one or more of
`signal propagation time (t ), and timing offset (t0). Accord-
`ing to one example embodiment, precision timing engine
`206 generates and records strobe times from the transmis-
`sion and/or reception of an analog representation of ranging
`messages (i.e., at radio frequency (RF) or baseband). Con-
`trol element 202 may then compare such recorded times
`with transmission/reception strobe times exchanged with the
`one or more remote transceivers to compute such signal
`propagation and offset times.
`Turning to FIG. 3, a block diagram of an example of at
`least a subset of a precision timing engine architecture is
`presented, in accordance with but an example embodiment
`of the invention. In accordance with the illustrated example
`implementation, precision timing engine 300 is depicted
`comprising one or more of a clock 402, a counter 404, a
`matched filter and a latch 408, each coupled as depicted to
`providing timing data (410) upon the transmission or receipt
`of, e.g., ranging messages.
`In accordance with the illustrated example implementa-
`tion, clock 302 provides a reference signal (305) to counter
`304, the output of which is provided to latch element 308. At
`
`UNIFIED PATENTS EXHIBIT 1004
`Page 7 of 12
`
`

`

`US 7,203,500 B2
`
`the beginning of a ranging measurement, precision timing
`engine 206 initializes the counter 306. In certain implemen-
`tations, the clock elements of the devices in UWB commu-
`nication (e.g., clock 302 within precision timing engine 206)
`may be (a) frequency locked via communication messages 5
`(e.g., preamble calibration routines), or (b) are accurate
`enough that any frequency offset between the clocks in
`either device is negligible over the short period of the
`ranging measurement. Use of the frequency offset compen-
`sation element 208 of ranging agent 200, may even eliminate 10
`the need for assumption (b), as the frequency offset may be
`computed. As described more fully below, the clock ele-
`ments are used to record the strobe times associated with
`transmission/reception of two or more messages (e.g., dedi-
`cated ranging messages) between the devices, from which 15
`signal propagation and offset times are computed, as detailed
`more fully below.
`As shown, an analog representation (at radio frequency
`(RF) or baseband, e.g., from an associated UWB trans-
`ceiver) of the ranging message is provided to a matched filter 20
`306. Once the level of the received analog signal exceeds
`some threshold (set at the filter), a strobe signal is generated,
`which may cause the latch 308 to parallel transfer the
`contents of the counter 304 as the timing data 310 associated
`with, or representative of the strobe time. According to one 25
`example implementation, this timing data 310 is recorded
`e.g., in memory 204, for subsequent use in determining the
`ranging information.
`According to one embodiment, the strobe should be
`generated with minimal associated delays that could intro- 30
`duce variation in the time measurement. For this reason, a
`mechanism (e.g., the matched filter) that operates directly in
`response to the analog signal, or equivalent, is employed,
`although other mechanisms may well be used. In one
`embodiment, the process of exchanging messages between 35
`the devices may be repeated a number (N) of times and
`averaged to reduce the effect of any zero-mean random
`errors.
`For sub-nanosecond precision, the clock should prefer-
`ably be operating at 1 GHz or greater, and the counter should 40
`preferably have enough stages to cover the expected turn-
`around time (U):
`
`U~(TA-TA)~(TB-TB)
`(1)
`where: TA is the recorded time of transmission of message 45
`M at a first device (A)
`Tg is the recorded time of reception of message M at a
`second device (B)
`TB is the recorded time of transmission of message M'
`at device B 50
`TA is the recorded time of reception of message M' at
`device A.
`
`Thus, a 4 GHz clock and 24-stage counter/latch could cover
`turnaround time intervals of large as four milliseconds (4 55
`ms).
`Although depicted as a number of disparate elements,
`those skilled in the art will appreciate that one or more of
`such elements may well be combined into a common
`element. Moreover, it should be appreciated that one or more 60
`elements of the precision timing architecture 300 may well
`be reside external to the ranging agent, e.g., within the UWB
`transceiver and/or host device. In this regard, precision
`timing engine architectures of greater or lesser complexity
`that nonetheless generate a strobe upon the receipt of an 65
`analog signal, as described below, are anticipated within the
`scope and spirit of the present invention.
`
`Returning to FIG. 2, it was noted above that the accuracy
`of the calculated signal propagation time (t ) diminishes as
`the turnaround time (U) increases due to clock frequency
`offset between the two transceivers. As used herein, fre-
`quency offset compensation 208 is selectively invoked by,
`e.g., control element 202 to identify and compensate for a
`frequency offset between the clocks used in recording trans-
`mission/reception strobe times. More particularly, frequency
`offset compensation element 208 calculates the ratio of the
`clock frequency of one device (e.g., 102) with respect to
`another device (e.g., 104) through the exchange of a number
`of messages (e.g., five messages) denoting transmit and
`receive strobe times. An example of just such a method is
`presented below, with reference to FIG. 7.
`As denoted above, to determine the proximal distance
`between two devices, ranging agent 200 may interface with
`an UWB transceiver to facilitate the exchange of messages.
`According to one example implementation, the messages are
`dedicated "ranging" messages. In other instances, ranging
`agent 200 may record the transmit/receive strobe times
`associated with normal (i.e., non-dedicated) UWB trans-
`ceiver communication. In either case, ranging agent 200 is
`communicatively coupled to one or more elements a host
`device (e.g., 102) and/or an associated UWB transceiver
`(e.g., 108) through input/output (I/O) interface(s) 210. Such
`communication may be completed in accordance with any of
`a broad range of standard or proprietary, wired or wireless
`communication protocols. In this regard, I/O interface(s)
`210 is intended to represent any of a broad range of such
`wired or wireless interface(s) known in the art and, as such,
`need not be described further.
`Example Operation
`
`Ranging Measurement
`Having introduced an example embodiment of the archi-
`tecture and operating environment of the ranging agent 200,
`above, attention is now directed to FIG. 4, where a flow chart
`of an example method for performing precision ranging
`measurements in an UWB communication environment is
`presented, in accordance with but one example embodiment
`of the invention. For ease of illustration, and not limitation,
`the method of FIG. 4 is developed with continued reference
`to FIGS. 1 through 3, as appropriate. Nonetheless, it is to be
`appreciated that the teachings of FIG. 4 may well be
`implemented in alternate architectures/environments with-
`out deviating from the spirit and scope of the present
`invention.
`FIG. 4 is a flow chart of an example method for precision
`ranging measurements in an UWB communication environ-
`ment, according to one example embodiment of the inven-
`tion. In accordance with the illustrated example embodiment
`of FIG. 4, the method begins with block 402, wherein an
`initiating ranging agent (e.g., 112 associated with device
`102) is invoked to determine the proximal distance between
`an associated UWB transceiver (e.g., 108) and one or more
`remote target transceiver(s) (e.g., 110). More particularly,
`control element 202 invokes an instance of precision timing
`engine 206, which initializes the appropriate timing/counter
`elements (304) and issues a request for ranging exchange
`with one or more target receiver(s) (110) through UWB
`transceiver (108).
`In block 404 (at the remote device 104), the transceiver
`(110) receives the issued request, and ranging agent initial-
`izes one or more timing elements (e.g., counter 304), and
`issues an acceptance to the initiating device (102).
`Upon receipt of the acceptance via UWB transceiver
`(108), block 406, ranging agent 112 generates and issues a
`
`UNIFIED PATENTS EXHIBIT 1004
`Page 8 of 12
`
`

`

`US 7,203,500 B2
`
`ranging message, recording the transmit strobe time, block
`408. More particularly, as described in FIG. 3, an analog
`representation of the ranging message is received at matched
`filter 306. Once the analog representation reaches a thresh-
`old, the filter 306 generates a strobe signal 307, which causes 5
`latch 308 to parallel transfer the current output of counter
`304 as the transmit strobe time (T^).
`In block 410, the remote device (104) receives the ranging
`message and records the time of receipt. In the illustrated
`example embodiment of, e.g., FIG. 1, a precision timing 10
`engine 206 of the remote ranging agent (114) receives an
`analog representation of the received message at a matched
`filter 306. Once the analog representation of the received
`message reaches a threshold, the matched filter 306 gener-
`ates a strobe signal 307, which causes latch 308 to parallel 15
`transfer the current output of counter 304 as the receive
`strobe time (JB).
`Once the time of receipt (Tg) is recorded, remote ranging
`agent (114) generates a ranging message for transmission
`through an associated UWB transceiver (110) to device 102, 20
`block 410. As above, an analog representation of the ranging
`message is received at a matched filter 306 of ranging agent
`114 such that once the analog representation of the ranging
`message reaches a threshold, a transmit strobe 307 is gen-
`erated by the matched filter 306, which may cause the latch 25
`308 to parallel transfer the current output of counter 304 as
`the time of transmit (J'B).
`In block 412, ranging agent 112 of device 102 receives the
`ranging message from the remote device (104) and records
`the receive strobe time (T'^), using the elements of precision 30
`timing engine 300 described above. This process of
`exchanging ranging messages (blocks 408-412) may be
`performed a number (N) of times to reduce the impact of any
`zero-mean timing error in the process.
`In blocks 414 and 416, respectively, the ranging agents 35
`112, 114 of the devices 102, 104 exchange the recorded
`transmit and receive strobe times, from which signal propa-
`gation delay (t ) and timing offset (t0) may be calculated.
`According to one example embodiment, control element 202
`in a respective ranging agent (112, 114) calculates the 40
`propagation delay (t ) as:
`
`(T'A-TA)-(T'B-TB)
`
`distance
`signal_velocity
`
`(2)
`
`45
`
`where: TA is the recorded time of transmit of message M
`at a first device (A);
`Tg is the recorded time of reception of message M at a 50
`second device (B):
`
`7i=Z>^ (3)
`
`TB is the recorded time of transmit of message M' at a
`second device (B); 55
`TA is the recorded time of reception of message M' at
`the first device (A):
`
`T\=rn-t+t
`
`(4)
`
`FIG. 5 is a block diagram of an example counter imple- 60
`mentation, suitable for use in (or, by) the example precision
`timing engine 206, according to one example embodiment
`of the invention. In accordance with the illustrated example
`embodiment of FIG. 5, counter element 500 is depicted
`comprising a core delay locked loop (DLL) 502, coupled 65
`with a number of AND-gates 506. In addition to the output
`of DLL 502, another input of the AND-gates 506 are coupled
`
`8
`to receive a strobe pulse 504. In certain embodiments, the
`strobe pulse 504 may be the strobe pulse 307 as described in
`accordance with FIG. 3.
`The implementation of FIG. 5 recognizes that some
`implementations of an UWB transceiver (e.g., 108, 110)
`may comprise a delay locked loop (DLL) for high-frequency
`clock generation, timing and phase adjustment. In this
`regard, the DLL 502 of FIG. 5 may well reside in an
`associated UWB transceiver. Regardless, a composite tim-
`ing measurement may be derived by a frame counter, as
`described above, plus a derived delay based on the arrival of
`a generated strobe pulse (e.g., 307) in relation to the phasing
`in the DLL pulses (see, e.g., FIG. 5). It is noted that
`exchanging counter 304 (with it's multiple stages) with a
`series of AND-gates may save power and implementation
`space.
`FIG. 6 is a block diagram of an example counter imple-
`mentation, suitable for use in (or, by) the example precision
`timing engine 206, according to but one example embodi-
`ment of the invention. In accordance with the illustrated
`example embodiment of FIG. 6, precision timing element
`610 is depicted comprising a matched filter 612, an analog
`to digital converter 614, a sheer 616, demodulator 618,
`ultrawideband detector 620, a latch 622, a symbol counter
`624 and a summing element 626, each coupled as depicted.
`It will be appreciated that although depicted as a number of
`disparate elements, one or more of such elements 612-626
`may well be combined. As such, precision timing elements
`of greater or lesser complexity are anticipated within the
`spirit and scope of the present invention.
`In accordance with the illustrated example embodiment of
`FIG. 6, a message time stamp of high precision for a
`received message (e.g., 600) can be constructed from the
`combination of a symbol rate counter (624) plus (626) the
`receiver phase offset. As shown, the phase offset may be
`obtained from, e.g., a numerically controlled oscillator
`(NCO) located in the slicer 616 that is clocked at the symbol
`rate.
`
`Clock Frequency Offset Compensation
`As previously mentioned, the accuracy of the calculated
`propagation delay (t ) diminishes as the turnaround time
`increases due to clock frequency offset between the two
`radios. However, the clock frequency offset between the two
`radios can be calculated after a few (e.g., 5) message
`exchanges as provided in FIG. 7. In this regard, FIG. 7 is a
`communication flow diagram of an example method for
`determining frequency offset between the UWB transceivers
`to provide an improved level of ranging accuracy, according
`to yet another aspect of an embodiment of the invention.
`According to one example embodiment, the communica-
`tion flow diagram described herein is implemented by
`ranging agent 200, within communication environment 100
`and, as such, reference to such elements is made for pur-
`poses of illustration, and not limitati