Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
  • G01S13/87—Combinations of radar systems, e.g. primary radar and secondary radar
  • G01S13/878—Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
  • G01S13/74—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
  • G01S13/82—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein continuous-type signals are transmitted
  • G01S13/825—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein continuous-type signals are transmitted with exchange of information between interrogator and responder
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
  • G06K7/0008—General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer

Definitions

• the invention relates to tracking systems and, more particularly, to systems designed to track articles and personnel.
• Global positioning systems and local positioning systems are examples that may be used depending on the particular
• the hardware may be used, for example, to collect data about the various entities being tracked or located.
• these tags may be e usually low-powered, for example, emitting in the range of 1 - 10 mW.
• read ranges up to about 100 meters can be realized. Alterntatively, in a more cluttered indoor environment, read ranges more like 25 meters is typical. As a practical
• the system includes a radio
• the antenna moduel is used in transmitting and receiving signals from the radio
• the antenna module is also used in transmitting and receiving signals used in the wireless communication system.
• the controller is coupled to the antenna module. The controller is used in communications with the radio frequency identification tag and the wireless communication system.
• Signals are transmitted and received using an
• antenna module from the radio frequency identification tag and from the wireless communication
• N controller is coupled to the antenna module and used in communications with the radio frequency identification tag and the wireless communication system.
• Figure 1 shows an overview of a positioning system
• Figure 2 shows several cell controllers deployed in a multi-story building
• FIG. 3 is a block diagram of a tag RF design
• Figure 4 is a block diagram of an alternative embodiment of a tag
• Figures 5N-5G are diagrams of a signal as it passes through various stages of the system
• Figure 6 is a block diagram of the cell controller RF design
• Figure 7 is a block diagram of a cell controller active antenna module
• Figure 8 is a block diagram of a modulator RF design
• Figure 9 is a block diagram of a cell controller cable extender module
• Figure 10 is a block diagram of a cell controller
• Figure 11 illustrates extraction of tag data from a series of correlations
• Figures 12N-C are diagrams of tag datagrams
• Figure 13 shows a tag incorporating a delay element
• Figure 14 shows several cell controller receive chains operating in parallel
• Figure 15N is a block diagram of an embodiment of the signal processing hardware of Figure 10.
• Figure 15B is a flowchart depicting method steps of one embodiment of the Signal
• Figure 16 is a block diagram of an embodiment of a signal filtering technique
• Figure 17 is a block diagram of an embodiment of the transversal filter of Figure 16.
• FIG 18 is a flowchart depicting method steps of one embodiment of the recursive-least squares (RLS) technique as used in a method step of Figure 15B;
• RLS recursive-least squares
• Figures 19A-19E are diagrams of sample waveforms in embodiments of the system of Figure 1 ;
• Figure 20 is a flowchart depicting method steps of one embodiment of approximating a
• Figure 21 is an example of an embodiment of a block diagram of a cell controller
• Figure 22 is an example of an embodiment of a block diagram of a cell controller active
• Figure 23 is an example of an embodiment of a block diagram of a tag
• Figure 24 is an example of an embodiment of tag specifications
• Figure 25 is an example of another embodiment of a position system
• Figure 26 is an example of an architecture of a local positioning system (LPS) cell
• Figure 27 is an example of an embodiment of a "fixed" portion of a digital enhanced cordless telecommunications (DECT) installation
• Figure 28 is an example of an embodiment of a single base station supporting DECT and
• Figure 29 is an example of the Second LF Carrier Recovery, Demodulator, and NGC
• Figure 30 is an example of another embodiment of a system including integration of LPS
• This system may be used, for example, to track and locate objects indoors. This system may be
• radio-frequency identification system characterized as a radio-frequency identification system.
• a radio-frequency identification system may also be
• Radio Frequency Identification (RFLD) products typically have three components: (1) a tag (the item being identified), (2) an interrogator (a device which detects the presence of a RFID (RFLD) tag), (2) an interrogator (a device which detects the presence of a RFID (RFLD) tag, and (3) an interrogator (a device which detects the presence of
• RFLD products are typically designed to detect
• RFLD systems are usually deployed as high-end replacement technology for bar coding.
• RFLD and related systems include passive RFLD systems, active RFLD systems, infrared LD
• the tags in a passive RFLD system do not carry on-board power.
• the interrogator in such a passive RFLD system do not carry on-board power.
• Such systems transmits operating power for the tags. Such systems generally have a detection range of a meter or less, although somewhat longer ranges have been achieved. Typically, these
• a coil in the tag is powered by the electromagnetic
• tags used in other passive RFLD systems have a limited ability to accept
• Passive RFLD tags have been employed in conjunction with access control, smart cards,
• NBI vehicle identification
• waste management item tracking
• animal identification animal identification
• manufacturing control materials handling
• materials handling materials handling
• Circuitry in the tag receives a carrier from the interrogator, translates
• the signal to another frequency, and emits a response modulated onto that second frequency.
• the tag modulates its antenna cross section to identify itself to
• SAW Surface acoustic wave
• interrogator's carrier after a delay.
• the tag's identity is indicated by time variations in the delayed
• Active RFLD systems require battery-powered tags.
• the battery permits a longer
• Active tags tend to enable multiple tags to be within range of an interrogator
• Some active RFLD tags "chirp” (transmit) a signal spontaneously at
• a tag's chirped signal is detected by the interrogator if the tag is in range of the interrogator.
• Infrared systems While not RFLD systems, also endeavor to detect and identify
• a typical IRLD system includes a tag that chirps its identity at randomized intervals. Infrared readers located in the ceiling detect these transmissions, and
• the transmission rate from the tag to reader is typically about 600 baud.
• Motion detectors in the tags enable the tags to transmit more frequently when in motion.
• tags are typically about the size of dominos.
• ENS systems are intended to deter theft in retail environments. ENS tags are fairly
• ENS tags are not generally considered to be identification products, because ENS tags are uncoded and cannot be distinguished from one another.
• an article tracking system 100 contains the following general
• Inexpensive miniature radio frequency transponding tags lOla-c are attached to
• Tags lOla-c "wake up” periodically, and "chirp” (transmit)
• the tags 101 a-c are designed so that their range is 50- 100 meters in a typical indoor environment, the range mostly being limited by a need to conserve
• Cell controllers 102a-c detect the chirps of tags 101 a-c and calculate
• Each antenna module preferably has a transmit antenna and a receive
• the antenna modules connected to cell controllers 102b and 102c are
• a cell controller 102a is typically contained in a case and is mounted behind a hung ceiling.
• the cell controller 102a can receive power from a conventional wall
• the cell controller 102a is attached through coaxial cables 103a-d to the antenna modules 104a-d, respectively, which provide coverage of an area of the indoor
• a tag signal 107, transmitted by a tag 101a, is received by one or more antenna modules 104a-d, and is processed by chips in the cell controller 102a, such as digital signal
• DSP digital signal processing
• Host Computer Cell controllers 102a-c are in data communication with a host computer
• client workstations 120a-c communicate with
• the client workstations 120a-c can access the SQL Server and presents the data in a way that
• the tag 101a does not generate its own radio signal. Rather, an antenna module, for
• example antenna module 104a continuously transmits a direct sequence spread spectrum
• the interrogator signal 106 at a first frequency, for example 2440-megahertz.
• the tag 101a receives
• this signal 106 modulates its ULD code onto the signal 106, and immediately transmits back a
• frequency-shifted signal 107 at, for example, 5800-megahertz to, for example, antenna 104a.
• the distance from the antenna module 104a to the tag 101a can then be determined by the cell
• the cell controller 102a can quickly switch among antenna modules 104a-d to obtain the distance from the tag 101a to each of antenna modules 104a-d
• the system 100 is designed to be scaleable, allowing addition of cell controllers to
• Figure 2 shows how a collection
• cell controllers 102a-c can be deployed in the large multistory building 110. As shown in
• multiple cell controllers 102a-c feed data to a single host computer 105, typically through a TCP/IP communications network.
• a single host computer 105 typically through a TCP/IP communications network.
• connection to the host can be accomplished via RS485, RS232, RS422, power line modem, or
• Each of the cell controllers 102a-c can be installed to cover a separate floor 130a-c,
• cell controller 102a On floor 130a, cell controller 102a, with its collection of antenna modules 104a-d, is installed in the
• Antenna modules 104a-d are designed to provide good gain downwardly and horizontally, and
• a ground plane is placed behind each antenna to reflect signals downward.
• the horizontal location of the tag 101a with respect to an antenna module 104a can be determined more precisely by estimating the distance from the tag 101a to each antenna module 104a-d, based on the combined time of flight of the
• each cell operates independently, enabling more cells to be added without affecting the performance of
• wishing to triangulate upon the location of a tag 101a may install enough antenna modules such
• the tag 101a will be in range of at least two or three of the antenna modules, depending on
• antenna type may be based on a variety of
• a tag RF circuitry 300 receives signal 106 at a tag receive antenna
• the circuitry 300 is to transpond the incoming spread spectrum signal 106 by frequency translation.
• the secondary function of the tag RF circuitry 300 is to modulate tag data onto the emitted tag
• 107 includes, in a preferred embodiment of the invention, the serial number of the tag, datagram
• tag data 309 such as that derived from a motion indicator or a low power indicator.
• the incoming signal 106 is preferably a direct sequence spread spectrum signal, biphase or quadrature modulated from the cell controller 102a, in the 2440 megahertz band.
• the tag receive antenna 301 which collects the signal 106 and feeds it into the
• filter 302 ensures that the tag is receiving signals only in the 2440 megahertz ISM band, rejecting
• the filter 302 is configured to filter the filter 302
• the signal 106 is implemented as an etched coupled stripline filter embedded in the circuit board.
• the signal 106 is then amplified by an amplifier 303 to ensure that the received signal can be mixed, in a
• the frequency mixer 304 translates or shifts the carrier frequency from 2440 megahertz
• the incoming signal with a center frequency of 2440 megahertz, is mixed
• phase locked oscillator (PLO) 305 with a center frequency of 3340
• the PLO 305 consists of a phase locked loop (PLL) chip with three inputs: (1) a sampled output from a voltage controlled oscillator (VCO); (2) a reference tone from a 10
• VCO voltage controlled oscillator
• the PLO 305 outputs a 1670-megahertz tone, which is then doubled to give the desired 3340-megahertz result.
• the next element of the tag RF circuitry 300 is a biphase modulator 307 which, under
• control of the microprocessor 308, can either pass the 5800-megahertz signal unaltered, or change the phase of the signal by 180 degrees.
• the modulator 307 is implemented as a single
• pole double throw RF switch 801 that feeds a 180 degree hybrid, as shown in Figure 8.
• modulation forms of modulation can be used, including on-off keyed (OOK) modulation, binary phase-shift
• BPSK BPSK modulation
• MPK multiple phase-shift keyed
• modulator 307 is fed into an amplifier 310, then is filtered by a transmitter bandpass filter 311,
• the amplifier 310 operates at high frequency, it consumes significant power, and alternative embodiments (such as that shown in Figure 4) that make this amplifier 310 unnecessary are
• the Tx Filter 31 implemented as a 5-pole filter, is necessary to ensure tag
• the tag RF circuitry 300 shown in Figure 3 is intended to illustrate the general functions
• Figure 4 shows an alternative embodiment 400 which fulfills the same basic functions as that shown in Figure 3, but with fewer components and using less power.
• the essential difference between the circuitry 400 shown in Figure 4 and the circuitry 300 shown in Figure 3 is that the modulator 404 in Figure 4 is placed before the frequency mixer 406 in order to reduce the
• the amplifier 310 is eliminated
• a tag such as the tag 101 a, can transpond using backscatter, frequency translation by
• timing is an important, if not critical, feature of the system, enabling the cell controllers 102a-c
• PLO 407 and in the microprocessor 405 clock timing allows the cell controller 102a to accurately calibrate the source by measuring phase shifts in the received signal (as described hereinafter),
• transmit antenna 409 and receive antenna 401 are combined into a single element, and which
• tags 101 a-c are powered depends on the application. (Note that Figure 3 and 4 omit the tag power source.) Typically, a tag 101a will be battery powered, with
• the RF stage turned on and off under control of the microprocessor 405.
• the microprocessor 405 goes into a low power state, where it merely waits until it
• all tag circuitry 400 cycles on and off under analog control, using an RC time constant in the circuit 400 as the timing
• the cell controllers 102a-c and those cell controllers are sending pseudonoise with low cross
• the tag 101a will correctly transpond both signals simultaneously.
• Tags 101 a-c require a period of time, on the order of a millisecond, to charge up and
• the tags 101 a-c will not be stable enough to use, but will nonetheless emit RF into the radio channel through the transmit antenna 409.
• the tag RF circuitry 300, 400 shown in Figure 3 and 4 can be used in conjunction with
• Spread spectrum operation is not required; two licensed narrow bands can be used. However, spread spectrum operation in the 2440 and 5800 megahertz bands is assumed for the remainder of the discussion.
• the tag RF circuitry 300, 400 shown in Figures 3 and 4 use frequency division multiple
• the tag circuitry 300, 400 receives and emits signals on different frequencies.
• alternative embodiment 1500 uses time division multiple access, as shown in Figure 13.
• tag circuitry 1500 shown in Figure 13 takes as an input at
• a receive antenna 1501 a signal at one frequency, such as 915mHz, and emits the same signal
• a cell controller such as cell controller 102a, transmits an interrogation signal 106 in bursts
• a tag such as tag 101a, takes this signal as an input through the receive
• delay element 1505 is then used to delay for a microsecond.
• the signal then passes through a
• N SAW device can be used as the time delay element 1505. During the period of the delay, the cell controller ceases
• the delay-based tag is capable of modulating the response signal by a 180-degree
• tag design 1500 shown in Figure 13 is similar to those shown
• Figure 6 shows the radio stage of a cell controller 102a.
• the architecture of an antenna module, such as the antenna module 104, is shown in Figure 7. Together, the cell controller 102a
• Figure 10 shows the main components of the cell controller digital subsystem 650.
• the digital subsystem 650 provides a baseband input signal 601, and some number of
• microprocessor nanoseconds later receives a demodulated response 107 from a tag 102a.
• 1001 can change the behavior of the radio system by (a) modifying the baseband
• pseudonoise sequence code (c) modifying the transmit frequency 610 of radio transmitter 1002 and the receive frequency of radio receiver 1003 within a narrow range; (d) modifying the transmit gain of radio transmitter 1002 and the receive gain of radio receiver 1003; and (e) by
• the demodulated response 107 from the tag 102a is split into I (Inphase) and Q
• processing hardware 1004 for example a combination of DSP and FPGA components, reduces
• each channel must be correlated twice, once with each sequence.
• the correlated data from the signal processing hardware 1004 is processed by a microprocessor 1001, such as a Pentium processor.
• Ethernet being preferred.
• the data that is input to the transmit chain is a baseband input signal 601 which is a
• pseudonoise spreading sequence The length of the sequence and the code encoded in the
• a cell controller microprocessor 1001 sets a cell controller microprocessor 1001 and can be varied depending on signal processing requirements. Thirty-one or 127 bit sequences are typical, giving about 15 dB and
• the 2440 megahertz and 5780 megahertz bands can support a 40 megahertz baseband input signal 601, and the cell controller 102a is designed to
• Figures 5A-5G show an interrogation signal 106 as it passes through various stages of
• Figure 5A shows a square wave baseband input to the
• FIG. 5B shows this baseband input digitally correlated 510.
• Figure 5C shows an output 520 from a-modulator 602, viewed through a spectrum analyzer centered at 2440
• Figure 5D shows a spectrum analyzer view 530 of the tag signal 107, centered at
• Figure 5E shows the demodulated response from tag 107, separated into its I
• Figure 5G shows the negative of the second derivative of the correlated
• the modulator 602 ( Figure 6) modulates the baseband input 601 onto a 2440 megahertz carrier.
• Various forms of modulation are available and well-known to those skilled in the art.
• the modulator 602 is implemented as a single pole double throw RF switch 801 that feeds a 180-degree hybrid combiner 803, as shown in Figure 8.
• 602 is preferably implemented as a QPSK modulator, which duplicates the BPSK modulator with one channel offset by 90 degrees from the other, each channel driven by a different
• Modulation by the modulator 602 results in sidelobes extending for hundreds
• a SAW filter 607 that combines wide passbands with tight stopbands.
• a wider passband supports a faster chipping rate in the baseband input signal
• the modulator 602 is configured to avoid jammers and/or support advanced signal processing techniques.
• the modulator 602 is configured to avoid jammers and/or support advanced signal processing techniques.
• a preamplifier 606 is necessary prior to the SAW LF filter 607, and
• the 10 megahertz source 603 needs to be
• the output from the LF filter 607 (from amplifier 608) is then mixed by a mixer 609 with
• phase locked oscillator (PLO) 611 and is converted to a carrier frequency of 2440 megahertz.
• the frequency of the PLO 611 can be modified within a narrow range under
• microprocessor control 610 in order to provide the frequency diversity needed to avoid jammers and/or for various advanced signal processing techniques.
• a driver amplifier 612 which raises the power level of the
• the RF bandpass filter 613 which buffers the output of the mixer 609 for a bandpass filter 613.
• An attenuator 614 under microprocessor control 615 allows the signal processing
• the signal is then fed into a diplexer 618, which combines the transmitted 106 and
• the diplexer 618 is a highpass/lowpass filter
• bandpass filters 613, 624, the specifications of the diplexer 618 are not very stringent.
• the cell controller RF stage 600 shown in Figure 6 supports one remote antenna module 104a-d at a time. In order to support multiple antennas from the same cell controller, the system
• the switch 619 needs a switch 619, which enables a microprocessor control 620 to rapidly switch from one antenna to the next.
• the switch 619 takes RF and passes it into one of n cables, where n is, for
• the switch 619 also provides DC power to the selected line.
• the RF switch 619 also provides DC power to the selected line.
• the DC power is coupled into the cables with RF chokes to provide RF isolation.
• the DC power is coupled into the cables with RF chokes to provide RF isolation.
• the rise time of the DC in an antenna is in the range of 20 microseconds, limited by the
• an antenna is preloaded before the RF is switched.
• the DC signal 712 is sent to Tx/Rx power
• control logic 702 which, in the simplest embodiment is a filter to remove noise from the line and provide a clean 5 volt power source.
• the RF output 710 from the bias tee 701 is fed into a
• diplexer 715 which is identical to the diplexer 618 in the cell controller 102a. This is then
• the transmit antenna 705 and receive antenna 706 are, in this embodiment, wall mounted
• the 5780-megahertz response 107 from the tag 101a is filtered by a filter 707, amplified by an amplifier 708, and sent back down the cable 103a to the cell controller 102a.
• the system is designed to use cables 103a-d of a standard length, for example, 20 meters.
• a cable extender module 900 connects two lengths of cable and supports an extended cable
• the elements of the module 900 use the DC power 910 from the
• Bias tees 906, 907 separate the DC power 910 from the RF signals, and
• diplexers 908, 909 operate to separate the transmit signal 106 from the receive signal 107.
• controller 102a passes through the switch elements 621, 619 and diplexer 618 to the cell
• controller receive RF chain 622.
• the signal passes through a combination of a preamplifier 623
• bandpass filter 624 the exact arrangement of which varies based on the parts selected.
• the signal then enters an I-Q zero LF demodulator circuitry 627-633. As noted
• microprocessor Rx frequency control 635 must be set in tandem with its
• controller can send and receive from only one antenna at a given time. Improved performance can be achieved by selecting send and receive antennas independently of each other. Software in the cell controller determines which antenna module receives the best signal from the tag. For
• the antenna 104 will receive a strong signal from the tag 101a.
• the cell controller 102a can then
• the design 1600 shown in Figure 14 provides multiple receive chains 1610a-1610n
• Each of the receive chains 1610a-1610n includes an IQ demodulator, a digitizer, and a correlating element, shown as integer DSPs, for example, integer DSP 1620.
• processing software to employ spatial processing techniques to isolate multipath effects. These techniques take advantage of the fact that the multipath-corrupted response will have different
• a simple triangular correlation peak can be derived from a
• Figure 11 shows how tag data is extracted from a series of correlations. In the left half of the chart 1110 shown in Figure 11, the tag is transmitting a "one.” This is
• the tag flips the phase of the modulator by 180
• 1120d is corrupted, and is best ignored.
• the fifth and sixth correlation peaks 1120e-f cleanly reflect the 180-degree shift.
• Pseudonoise sequences can be varied under microprocessor control at the cell controller.
• the 10-megahertz sources in the cell controller 102a and the tag 101a will differ typically by a
• This factor can be calibrated by noting the phase difference between contiguous
• Each tag is a stand-alone unit that is unaware in any way of the outside world.
• ULD Unique Identifying Code
• the tag does not explicitly respond to an interrogation signal, but merely transponds
• any incoming signal 106 in the 2440-megahertz band which may or may not include a
• tags "wake up" and chi ⁇ their ULDs at randomized times, which can be calculated (by both the tag and the cell
• controller based on a pseudorandom number generator which inco ⁇ orates the tag's ULD.
• the tag For a tag which chi ⁇ s approximately every 5 seconds, the tag generates pseudorandom
• analog inputs such as an input from an internal clock or the delay of
• a typical pseudorandom number generator has the form:
• the resulting N is used as the seed for the next pseudorandom number in the
• pseudorandom number sequence When using a pseudorandom number generator of this kind,
• Delay Xor(N, BitRotate (ULD, AND(N, 1111 2 )) Formula 3
• N Xor(Delay, BitRotate(ULD, And(N,l 111 2 )).
• one embodiment of the tag datagram 1400 contains a header
• the header 1401 can be of zero length.
• the identifier preamble 1402 can be implemented, for example, as a validity check such as a cyclic redundancy check (CRC). Given a sufficiently simple Delay function and high clock stability, the cell controller can infer the tag's chi ⁇ ing sequence by noting the timing of a series of chi ⁇ s of the
• the tag adds
• Delay information 1414 thus enabling the cell controller to forecast the transmission time of the tag's next and subsequent chi ⁇ s of the datagram 1410.
• the tag will next chi ⁇ its datagram 1420, even if the cell controller does not have enough time
• the cell controller can then anticipate this next chi ⁇ and ascertain the identity of the tag at that time. Once the tag is identified, the cell controller can duplicate the tag's pseudorandom number
• 5 1423 must be defined so that it does not include the synchronization sequence or its inverse.
• Figures 12a, 12b, and 12c include optional data sections 1404, 1415, 1426, which allow
• These sections 1404, 1415, 1426 can include data
• An identifier preamble related to the tag ULD, precedes the tag ULD. This identifier preamble enables the cell controller to quickly verify that a tag is chi ⁇ ing as expected, without
• the identifier preamble
• the ULD of a tag may be hardcoded into the tag (e.g., as a serial number).
• Tags may be
• Each cell controller contains information (received from another source) about
• the cell controller can extract the ULD information from the tag signal to determine
• 1414, 1425 and data fields 1404, 1415, 1426 can also include error correction bits.
• data can be reduced to a stream of half-bytes.
• the tag can look up the half-byte's value in a table which
• a single cell controller can handle all three types of datagrams 1400,
• the amount of time it takes for a cell controller to detect the presence of a tag may vary depending on the nature of the cell controller design. For example, a 100-microsecond time to
• switch antennas may be significant when the cell controller is cycling among 16 antennas.
• the tag datagram header must be long enough to give the cell controller time to try all
• the cell controller can collect
• tag datagram in order to be reasonably certain that it is receiving a signal from the correct tag.
• a correct identifier preamble arriving exactly on schedule is almost certain to be from the expected tag. This provides an opportunity for the cell controller to try a variety of antennas that
• the tag can be any suitable tag. If it is necessary to track tags between the tag datagram transmissions, the tag can be any suitable tag.
• the cell controller can anticipate the exact timing of each such transmission, thus matching each
• Error correction codes can be arranged such that long chi ⁇ s from one tag will not typically be corrupted by quick chi ⁇ s
• the cell controller has the data to forecast most of such collisions.
• the cell controller can select an antenna such that the signal the antenna receives from one tag
• the cell controller has a means for sending information
• Such instructions can include commands to be passed on to a device attached to the tag.
• the cell controller is capable of downloading such information, most simply by on-off
• a single cell controller can support read-only tags, read/write
• Timing of transmission from tag to cell controller depends on the item being tagged. Inventory and equipment can be set to transmit relatively infrequently, such as once per minute.
• motion detectors may be placed in a tag to decrease the time between
• a tag might transmit more
• a tag might inco ⁇ orate a slightly modified Electronic Article Surveillance (EAS) device, which
• transmission interval can be modified under the control of that device.
• Tag Power Tags 101 a-c transmit a low RF power level in order to increase their portability and
• tag signal transmissions 107 are designed to be only a few milliseconds in
• a motion detector can be inco ⁇ orated into the tag so that, for example,
• battery replacement may be accomplished by inco ⁇ orating the
• re-usable tag electronics may be attached to a disposable patient bracelet, with the battery included in the bracelet.
• a battery may be inco ⁇ orated into the clip of an LD bracelet. More generally, a battery may be
• the tag could tap into that
• a tag signal 107 is received at a time that is the sum of (1) known fixed delays in the cell
• controller 102a that transmitted the interrogator signal 106, due to its circuitry and the wiring to
• the cell controller 102a can derive a simple triangular correlation peak from the received
• Tag signal 107 As shown in Figure 5B. But in most indoor environments, the actual received tag signal looks more like that shown in Figures 5D-5G. Indoor radio signals are subject to substantial multipath effects, due to reflection from a variety of surfaces, such as whiteboards, fluorescent lights, file cabinets, elevator shafts, steel beams, and the like.
• a 40-megahertz chip rate results in a correlation peak with a rise time of 25 nanoseconds
• Approximate location of a tag can be calculated by noting when correlated signal-to-noise
• the MUSIC algorithm known to those in this field, can be used, for which
• MUSIC requires frequency diversity
• motion detectors can be inco ⁇ orated into the tag, which would then
• Story-by-story discrimination in a building can be accomplished by mounting antennas in the
• antennas mounted sideways on horizontal partitions can determine location relative to those partitions. Relatively narrow beamwidth antennas, which are less sensitive to multipath
• a cell controller antenna 104a can be mounted near a computer screen, with coverage
• a single antenna module can include three separate antennas placed in a triangle. By comparing phase difference using the Inphase and Quadrature components of the returning signal, an indication of the tag's angle can be determined. In high frequency embodiments, such
• such antennas could be within inches of each other and be quite effective.
• Heuristic techniques can be used to analyze the correlation profile to estimate the time at which the correlation began, that is, the time at which the correlation peak begins to be
• Frequency diversity can provide a variety of samples, the best of which can be chosen. Improved estimates can be achieved by pattern matching the
• tags can be placed at known fixed locations, and tags passing near those
• Antenna diversity is the most important tool for improving the accuracy of tag location
• antennas can be placed so that only one antenna is in range of a given tag. In this case there is insufficient data for triangulation, and only enough
• bearing of a tag can be estimated from the signal strength of antennas designed for the pu ⁇ ose
• Antenna diversity also provides system scaleability. For facilities or sections within facilities, that do not require calculation of tag location with high accuracy, substantially omnidirectional and/or ceiling mounted antennas can be installed relatively far from each other, for a relatively low cost per square foot of coverage. For facilities, or sections within facilities,
• a diversity of closely-spaced and/or directional antennas can provide high accuracy at an increased cost.
• the tag's transmission interval varies according to an algorithm
• the tag may for example, include an element, such as a
• a photo LD with an inco ⁇ orated tag might be reprogrammed each time the person wearing the photo LD
• multiple cell controllers can be installed, covering
• each cell controller will be operating according to a
• codes with known cross-correlation characteristics such as Gold Codes
• cell controllers can switch choice of pseudonoise codes on a randomized
• each cell controller reports the tag's
• the central host 105 assembles this data to calculate the distances from its antenna modules.
• the cell controller can choose another code.
• the tag being in essence a transponder, does not need to know the
• center frequency can be adjusted somewhat if another user
• the signal processing hardware 1004 performs operations
• the signal processing hardware 1004 generally functions to perform operations upon the signal from digitizer 636 such as, for example, the previously
• signal processing hardware 1004 may perform a filtering
• the signal processing hardware may include one or more hardware components that collectively perform digital signal processing of the received signals. Recall that the signal processing hardware 1004 was previously described in
• a correlator unit 1800 connected to other DSP
• DSP hardware components 1802 vary with the type of processing done in each particular
• connections 1804a and 1804b may be controlled by the microprocessor 1001, such as by using connections 1804a and 1804b.
• signal processing hardware 1004 uses only the correlator 1800.
• data is directly output by the correlation unit, as indicated by the path 1804a.
• Nt step 2000 a number of samples of received signals are taken. The number of samples to be taken varies with each
• the sampling rate is typically twice the transmission rate. For example,
• 254 points or received signals are sampled where each of the 254 signals is
• the system has a chipping rate of 40 megahertz.
• the signal transmitter rate is 127
• a first range of the sample received signals is determined. The first range
• One factor that may be considered is the anticipated arrival time of a signal returned by a tag. This relates to, for example, anticipated delays in the transmission circuitry and may be used in determining a starting point of the first
• Another factor that may be considered relates to the tag transmission range and the
• the first range as well as the size of the first range. For example, if objects in one system are
• the earliest possible time which a signal may be received by an antenna of a cell controller is earlier than a time of a different tag in another
• the actual span or size of the first range is 26 which was determined in accordance
• Nt step 2004 auto-correlation is performed for the first range of samples producing a
• One preferred embodiment implements the auto-correlation portion using
• FPGN field programmable gate array
• sample waveform 254 consecutive samples of received data (“sample waveform") are compared with an idealized version of the same data (“reference waveform"). If a coherent demodulation is available, then a real correlation may be
• Autocorrelation may generally
• An autocorrelation function is a plot of autocorrelation over all phase shifts (t-r) of the
• this number of calculations may cause a "bottleneck"
• a correlator implemented in hardware can generally make a quick estimate of tag
• the reference waveform generally includes l's and -l's, 2's complement arithmetic
• FPGA field programmable array
• custom or custom ASICs enabling operations to take place in parallel and with generally high
• the tag's radio has a maximum range of 100 meters, there is no reason to perform the autocorrelation function with phase shifts corresponding to the
• half-chip intervals may be used to search for the signal, and then half-chip intervals may be used.
• a subset of the 254 autocorrelation offsets may be used in the search for the peak or
• heuristics are used to select a sample point which approximates where in
• step 2006 produces a
• One heuristic or technique which may be used to approximate the location in the first range of the received tag signal is related to the strength or magnitude of
• corresponding signal may be used in approximating where the received tag signal may be
• the rising or leading edge detection technique is a second heuristic that may be used to determine the rising or leading edge detection technique.
• One technique used with the rising or leading edge detection may include using
• the rising edge detection technique is based upon the assumption that the first peak is the line-of-
• a threshold value is determined
• the threshold value chosen varies with environmental and
• Running trials of the system is one suggested method for choosing a threshold
• a second range of samples is determined which is a subset of the first range
• step 2008 the precise starting and end point as well as the size or span of the
• ending points of the second range may be related to or dependent upon the heuristic used to
• One preferred embodiment may use the rising edge detection technique
• a range is determined having a
• the second factor to be considered is the actual size of the second range. It
• the size of the second range in one particular embodiment is 12. The reasons and factors that may be considered when choosing the size of the second range will be considered.
• step 2010 the recursive least squares (RLS) technique using the second range of
• the RLS technique used in step 2010 is used to filter out the noise component of received signals.
• the RLS technique is used to filter out the
• this vector contains values which correspond to filtered received signals.
• the approximate peak co ⁇ esponding to the filtered received tag signal is determined using the values included in the vector. Detail is described in the paragraphs that
• step 2016, the tag distance is determined using the time of the filtered received tag
• One of the functions of the signal processing hardware 1004 is to filter the noise component out of a received signal.
• Figure 16 depicts a feedback control system
• transversal filter 2022 which includes a transversal filter 2022 and an adaptive weight control mechanism 2024.
• the transversal filter 2022 operates upon an input signal u and represented as an input
• the transversal filter produces an output
• This estimation e ⁇ or (n) is the difference between the desired response signal d(n)
• the adaptive weight control mechanism 2024 is a mechanism for performing the adaptive
• control process by varying certain parameters which feed back into the transversal filter 2022.
• the transversal filter 2022 may also be referred to as a tap delay line filter.
• transversal filter such that, given the least squares estimate of the tap weight vector, w(n-l) of the filter at time n-1, the updated estimate of this vector at time n may be computed.
• estimated signal E(n) 2026 is denoted as w H (n-1) u(n). The precise notation of this will be
• transversal filter 2022 Generally, a transversal filter includes three basic elements: unit delay
• unit delay operator 2031a operates on input u(n)
• the resulting output is u(n)
• the role of the multiplier 2032a in the filter is to multiply the tap input 2030a by a filter coefficient refe ⁇ ed to as a tap weight denoted w * 0 (n). It should be noted that the asterisk in
• Figure 17 denotes complex conjugation which assumes that the tap inputs, and therefore the tap
• weights are all complex values.
• the combined function of the adders in the filter is to sum the
• multipliers 2032b-2032m-l operate similarly to the multiplier 2032a.
• the input signal u(n), and the tap weights denoted w(n) are represented as vectors with each element of the vectors co ⁇ esponding to various components.
• the recursive least squares or RLS technique attempts to choose a tap vector
• the e ⁇ or is determined as the sum of the
• the adaptive weight control mechanism 2024 of Figure 17 is used to determine the weighting
• weighting factor allows additional weight to be given to the e ⁇ or values which are most recent
• the adaptive weight control mechanism 2024 provides a co ⁇ ection factor
• co ⁇ ection factor determined at time n is applied to the tap weight at a time of n+1.
• correction factor which is applied to the tap weights.
• the error factor provides for adjustment or co ⁇ ection of the various tap weights. This is the nature of the feed back mechanism of the system 2018 of Figure 16.
• step 2034 variables are initialized to initial
• control variable n Some of the variables used in Figure 18 processing steps are initialized to a
• n is initialized to one in the method described in Figure
• the tap weight vector w and the tap input vector u may be initialized to 0.
• the co ⁇ elation matrix denoted P(0) may be initialized to the inverse of a small positive constant time the identity matrix denoted I.
• the recommended choice of the small positive constant A is
• ⁇ is a small positive constant which may be refe ⁇ ed to as the "forgetting
• ⁇ should generally be chosen such that:
• the former condition generally reflects the fact that the RLS technique provides a converged
• a starting value for P(0) a starting value should be chosen which assures the non-singularity of the co ⁇ elation matrix.
• control proceeds to step 236 where a determination is made whether or not the loop control variable n is less than or equal to the number of desired iterations. If the
• n is greater than the number of desired iterations, meaning that execution of the method steps of Figure 18 is complete, control proceeds to step 238 where the
• step 2036 If a determination is made at step 2036 that n is less than
• step 2040 the gain denoted k(n) is computed as:
• ⁇ (n) is computed as:
• step 2044 the tap weight vector for a particular instance in time
• w(n) is computed as:
• Control proceeds to step 2046 where the inverse of the co ⁇ elation matrix denoted P(n) is
• Control then proceeds to step 2048 where the loop control variable n is incremented by 1.
• Control proceeds to the top of the loop at step 2036 where a determination again is made whether or not the loop formed by steps 236-248 has been performed the desired number of iterations.
• step 2044 describes the adaptive operation of this
• (n) represents the a priori estimation error.
• the a priori estimation e ⁇ or refers to an
• ⁇ is a positive constant close to but less than 1.
• ⁇ is used in determining
• w(n) is computed as being dependent upon the value w(n-l). It should also be noted that in the flowchart of Figure 18, the asterisk denotes the complex conjugate of a number. Additionally, the superscript of H, as depicted in step 2042 when associated with the tap weight
• a complex valued matrix such as the tap weight vector w(n) is Hermitian if it is equal to its conjugate transpose, as known to those skilled in the art.
• step 2010 performs the RLS technique just described using the second range of sample receive signals. Also recall that a note was made that the size or span
• the RLS technique performs matrix operations which are generally expensive in terms of computing time and
• the noise component of the receive signal includes tonal frequencies or jammers
• the model may follow the peaks of the jammer signals rather than properly fit a curve identifying the filtered received signal. Additionally, if the size of the second range is too small,
• the RLS technique used in this embodiment assumes that the observed sequence includes a linear combination of a known number of the data sequence. Generally, the RLS technique
• the RLS technique assumes a wide-sense stationary process. Generally, the RLS technique also presumes the presence of random additive noise which is uncorrelated with the data sequence. With the presence of "white noise", the sum process
• the sum process is no longer wide-sense stationary.
• corrective technique that may be considered is in choosing the number of coefficients or taps.
• the noise input to the co ⁇ elator may be modeled as the
• the number of coefficients or taps should generally span the main peak of the impulse response magnitude. However, the number of taps
• the number of taps may vary with embodiment and application. For each
• the observed process should be modeled to take into account all
• the size of the second range varies with the environment in which this application will be used. If there will be tonal frequencies, such as a microwave oven within an indoor environment, this should be considered when choosing an appropriate value for the second range. In one preferred
• a value of 12 was used for the size of the second range for an indoor article
• This indoor system may possibly have tonal frequencies
• one data set of 254 received signals was recorded. Rather than perform the method
• the number of iterations of the RLS algorithm should be as large as possible in order to meet the
• each element in this vector co ⁇ esponds to a component of a received signal which represents a filtered signal.
• each element of the vector co ⁇ esponds to a filtered signal with the noise portion removed.
• the vector produced in step 2012 is a vector
• step 2010 removes the noise component and returns a
• step 2014 is set forth in paragraphs that follow in connection with Figure
• Figure 19B shows a waveform with a low degree of indoor
• Figure 19C illustrates a
• Each of the waveforms shown in Figures 19B-D are waveforms that may
• model in Figure 19E, is an example of a waveform resulting from graphing the 12 points included in the second range of samples which is output from the RLS technique in one
• this vector may be produced in step 2012 after performing the RLS technique in step 2010.
• the peak of the actual waveform for example, may be approximated in step 2014, as the 4 th data point of the "model" waveform of Figure 19E.
• the transmission rate is 127 chips per data bit.
• bit pattern of the transmitted signal repeats itself every 127 bits. N lesser number bit
• sequence such as 31 chips, may also be used in a particular implementation which requires less
• a longer bit sequence generally allows for
• a longer sequence generally enables a stronger signal at the output of the co ⁇ elator than that produced by a shorter sequence.
• the processing gain indicates this signal strength enhancement and refers to the number of bits
• co ⁇ elation is required. For example, in an embodiment where one is required to detect or reduce
• sequence length as well as the various properties of the sequence sent in the transmission signals may vary with application and each particular implementation.
• processing may be performed using the techniques previously described. Since it is the atypical
• the system may devote
• correlation function performed in step 2004 on a first range of samples is implemented in a
• the same data set was used when performing multiple iterations of the RLS algorithm of Figure 18.
• a single data set set may be "reused" on subsequent iterations
• step 2100 if the first or last element of the
• a threshold value is determined which, in one embodiment
• step 2100 is equal to 62.5 percent of this largest magnitude previously determined in step 2100.
• threshold is refe ⁇ ed to as the X. It should be noted that in one prefe ⁇ ed embodiment, if the
• Xth element is the second to last vector element.
• the actual received tag signal is determined based on the expected shape of the received signal as being a co ⁇ elated signal with a triangular peak.
• weight v[j] MNX(0, magnitude(vector element j) - (largest magnitude of all vector elements/4) )
• Received signal [X+l - (weightv[X]/Total) /** if element X+2 is not used and is the second to last element of the vector **/
• the autocorrelation (step 2004) is performed by the correlator 1800.
• a first heurisitic determines the received tag signal to be the signal in the first range with the maximum magnitude of all the signals in the first range.
• a second or alternate heurisitic that may be included in an embodiment is to choose a threshold value. The first signal included in the first range having a magnitude equal
• choosing the threshold value may vary with environmental and other factors particular to each
• this threshold value is selected in accordance with trial test runs of
• received tag signal is then used (step 2016) in determining the tag distance.
• signal processing hardware 1004 may include other hardware
• Each particular embodiment may be implemented in using a variety of
• code may be executed on a computer system, such as the microprocessor 1001 or the host computer 105 or yet another computer component included in the signal processing hardware
• the components may vary with application and design choices associated with a particular implementation.
• Another embodiment of the signal processing hardware includes hardware and/or
• This embodiment may perform, for example, all the
• chassis RF subsystem consists of three of the five major cell controller components:

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