PCT
`WORLD INTELLECfUAL PROPERTY ORGANIZATION
`International Bureau
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`WO 97/31437
`(51) International Patent Classification 6 :
`H04B 11/00
`
`(43) International Publication Date:
`
`28 August 1997 (28.08.97)
`
`(11) International Publication Number:
`
`Al
`
`(81) Designated States: AL, AM, AT, AU, AZ, BA, BB, BG, BR,
`BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GE,
`HU, IL, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS,
`LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL,
`PT, RO, RU, SD, SE, SG, SI, SK, TJ, TM, TR, TT, UA,
`UG, US, UZ, VN, ARIPO patent (KE, LS, MW, SD, SZ,
`UG), Eurasian patent (AM, AZ, BY, KG, KZ, MD, RU, TJ,
`TM), European patent (AT, BE, CH, DE, DK, ES, FI, FR,
`GB, GR, IE, IT, LU, MC, NL, PT, SE), OAPI patent (BF,
`BJ, CF, CG, CI, CM, GA, GN, ML, MR, NE, SN, TD, TG).
`
`Published
`With international search report.
`
`(21) International Application Number:
`
`PCT/1897/00144
`
`(22) International Filing Date:
`
`19 February 1997 (19.02.97)
`
`(30) Priority Data:
`08/603,413
`08/653,899
`
`20 February 1996 (20.02.96)
`28 May 1996 (28.05.96)
`
`us
`us
`
`(71) Applicant (for all designated States except US): SONIC SYS(cid:173)
`TEMS [CA/CA]; 200-2386 East Mall, University of British
`Colwnbia, Vancouver, British Colwnbia V6T 123 (CA).
`
`(72) Inventors; and
`(75) Inventors/Applicants (for US only): McCONNELL, Peter,
`Robert, Henderson [CA/CA]; 5970 Empress Avenue, Burn(cid:173)
`aby, British Colwnbia V5E 2S2 (CA). STRAGG, Robert,
`Allan [CA/CA]; 5516 Cypress, Vancouver, British Colum(cid:173)
`bia V6M 3R6 (CA).
`
`(74) Agent: DEETH WILLIAMS WALL; National Bank Boiling,
`Suite 400, 150 York Street, Toronto, Ontario M5H 3S5
`(CA).
`
`(54) Title: DIGITAL SONIC AND ULTRASONIC COMMUNICATIONS NETWORKS
`
`503
`
`505
`
`507
`
`509
`
`Transducer
`
`DSP
`Based
`Logic
`Board
`
`Controller
`
`Coded
`Sound Generator
`
`(57) Abstract
`
`A digital communications network is provided using digital sonic and ultrasonic communications, i.e., communications using acoustic
`energy instead of RF energy. The "acoustic spectrum", as opposed to the RF spectrum, is uncluttered and unregulated, allowing for
`unfettered commercial development of equipment for ITS applications as well as a wide variety of other applications, including applications
`that currently employ RF communications. Exemplary applications include electronic toll boothing, controlled entry systems, border crossing
`systems, etc. Coding and processing techniques are employed that allow acoustic communications, including the communication of digital
`data, to be reliably transmitted and received even in noisy acoustic environments.
`
`Page 1 of 45
`
`GOOGLE EXHIBIT 1008
`
`

`

`FOR THE PURPOSES OF INFORMATION ONLY
`
`Codes used to identify States party to the PCT on the front pages of pamphlets publishing international
`applications under the PCT.
`
`AM
`AT
`AU
`BB
`BE
`BF
`BG
`BJ
`BR
`BY
`CA
`CF
`CG
`CH
`Cl
`CM
`CN
`cs
`CZ
`DE
`DK
`EE
`F.S
`FI
`FR
`GA
`
`Armenia
`Austria
`AUlltralia
`Barbados
`Belgium
`Burkina Faso
`Bulgaria
`Benin
`Brazil
`Belarus
`Canada
`Central African Republic
`Congo
`Swit:r.erland
`Cllte d'Ivoire
`Cameroon
`China
`C:r.echoslovakia
`C:r.ech Republic
`Gennany
`Denmark
`Estonia
`Spain
`Finland
`France
`Gabon
`
`GB
`GE
`GN
`GR
`HU
`IE
`IT
`JP
`KE
`KG
`KP
`
`KR
`KZ
`LI
`LK
`LR
`LT
`LU
`LV
`MC
`MD
`MG
`ML
`MN
`MR
`
`United Kingdom
`Georgia
`Guinea
`Greece
`Hungary
`Ireland
`Italy
`Japan
`Kenya
`Kyrgystan
`Democratic People• s Republic
`of Korea
`Republic of Korea
`Kazakhstan
`Liechtenstein
`Sri Lanka
`Liberia
`Lithuania
`Luxembourg
`Latvia
`Monaco
`Republic of Moldova
`Madaga.scar
`Mali
`Mongolia
`Mauritania
`
`MW
`MX
`NE
`NL
`NO
`NZ
`PL
`PT
`RO
`RU
`SD
`SE
`SG
`SJ
`SK
`SN
`sz
`TD
`TG
`TJ
`TI
`UA
`UG
`us
`uz
`VN
`
`Malawi
`Mexico
`Niger
`Netherlands
`Norway
`New Zealand
`Poland
`Portugal
`Romania
`Russian Federation
`Sudan
`Sweden
`Singapore
`Slovenia
`Slovakia
`Senegal
`Swaziland
`Chad
`Togo
`Tajikistan
`Trinidad and Tobago
`Ukraine
`Uganda
`United States of America
`Uzbekistan
`Viet Nam
`
`Page 2 of 45
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`

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`WO97/31437
`
`PCT/IB97 /00144
`
`DIGITAL SONIC AND ULTRASONIC
`COMMUNICATIONS NETWORKS
`
`1. Field of the Invention
`
`The present invention relates to digital communications networks, and to
`
`5
`
`communications using acoustic energy.
`2. State of the Art
`
`An industrial economy depends heavily on transportation infrastructure.
`
`The United States enjoys one of the most advanced highway systems in the
`
`world. Nevertheless, this system, designed principally in the 1950s, is
`
`10
`
`beginning to show signs of age. Furthermore, because of current budgetary
`
`pressures, very few new highways are being planned or built. Instead, attention
`
`has been focussed on maximizing the utilization of existing highways through
`
`the application of computer and communications technologies. This effort is
`
`referred to generally as the Intelligent Transit System (ITS).
`
`15
`
`The tacit underlying assumption concerning the application of
`
`communications technology to transit has been that Radio-Frequency (RF)
`
`communications will be used. The widespread use of RF communications in
`
`transit applications, however, suffers in concept from a number of
`
`disadvantages. The ITS initiative appears to have gained critical momentum
`
`20
`
`just at a time when the scarcity of RF bandwidth is being felt most acutely.
`
`The RF spectrum is, quite literally, "cluttered" with a wide variety of users all
`
`competing for scarce bandwidth. Federal regulatory approval is therefore
`
`required for most RF communications. Furthermore, a great deal of traffic is
`
`interstate and even international (particularly in Europe). The result is a
`
`25
`
`patchwork of rules, regulations and practices, from jurisdiction to jurisdiction,
`
`concerning RF communications.
`
`What is needed, then is additional bandwidth that may be applied within
`
`the context of the ITS and other similar transit applications. Preferably, such
`
`bandwidth should be "clutter-free" and unregulated so as to allow for the
`
`1
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`CONFIRMATION COPY
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`WO97/31437
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`PCT/IB97/00144
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`consistent commercial use of such bandwidth from jurisdiction to jurisdiction.
`
`The present invention addresses this need.
`
`SUMMARY OF THE INVENTION
`
`In accordance with the present invention, generally speaking, a digital
`
`5
`
`communications network is provided using digital sonic and ultrasonic
`
`communications-i.e., communications using acoustic energy instead of RF
`
`energy. The "acoustic spectrum," as opposed to the RF spectrum, is
`
`uncluttered and unregulated, allowing for unfettered commercial development of
`
`equipment for ITS applications as well as a wide variety of other applications,
`
`10
`
`including applications that currently employ RF communications. Exemplary
`
`applications include electronic toll boothing, controlled entry systems, border
`
`crossing systems, etc. Coding and processing techniques are employed that
`
`allow acoustic communications, including the communication of digital data, to
`
`be reliably transmitted and received even in noisy acoustic environments.
`
`15
`
`More particularly, in accordance with one embodiment of the invention,
`
`a digital acoustic communications apparatus includes one or more digital
`
`acoustic communications devices comprising a data processor; memory coupled
`
`to the data processor and storing digital data; and means for transmitting and/or
`
`receiving digital data acoustically; wherein the acoustic digital communications
`
`20
`
`apparatus, during operation, transmits and/or receives digital data acoustically.
`
`In accordance with further aspects of the this embodiment of invention, the
`
`memory stores at least one of an identifying code word and a command, and
`
`the means for transmitting and/or receiving transmits and/or receives at least
`
`one of said identifying code word and said command acoustically. The means
`
`25
`
`for transmitting and/or receiving may be an acoustic digital communications
`
`transmitter operating in the human audible range or may be an acoustic digital
`
`communications transmitter operating in the ultrasonic range. Alternatively, the
`
`means for transmitting and/or receiving may be an acoustic digital
`
`communications receiver comprising an analog-to-digital converter, wherein the
`
`30
`
`data processor comprises a digital signal processor coupled to the
`
`analog-to-digital converter for filtering a digital representation of a received
`
`2
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`Page 4 of 45
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`WO97/31437
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`PCT/IB97 /00144
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`acoustic signal and for recovering digital data symbols encoded therein. The
`
`acoustic digital communications receiver may operate in the human audible
`
`range or may further comprising a downconverter, whereby the acoustic digital
`
`communications receiver operates in the ultrasonic range. Still further, the
`
`5
`
`means for transmitting and/or receiving may be a digital acoustic transceiver
`
`comprising an input sound transducer, an analog-to-digital converter coupled to
`
`the input sound transducer, an output sound transducer, and a digital-to-analog
`
`converter coupled to the output sound transducer; in which case the data
`
`processor may be a digital signal processor coupled to the analog-to-digital
`
`10
`
`converter for filtering a digital representation of a received acoustic signal and
`
`for recovering digital data symbols encoded therein, and coupled to the memory
`
`and to the digital-to-analog converter for transmitting the identifying code word
`
`or the command stored in memory acoustically. The acoustic digital
`
`communications transceiver may operate in the human audible range or in the
`
`15
`
`ultrasonic range. A system in accordance with another aspect of the present
`
`invention comprises a plurality of digital acoustic communications devices
`
`including a plurality of acoustic digital transmitters and at least one acoustic
`
`digital receiver for, when one of said acoustic digital transmitters is within
`
`range and transmitting digital information, receiving said digital information.
`
`20
`
`The system preferably further comprises a computer and at least one wide area
`
`network communications link established between the acoustic digital receiver
`
`and the computer. More preferably, the system comprises multiple acoustic
`
`digital receivers and multiple wide area network communications links, one
`
`such link being established between each of a plurality of said acoustic digital
`
`25
`
`receivers and said computer.
`
`In accordance with another aspect of the present invention, a method of
`
`digital communications comprising the steps of generating a carrier signal;
`
`modulating the carrier signal in accordance with digital information to produce
`
`a modulated signal; and applying the modulated signal to an acoustic transducer
`
`30
`
`to produce a coded acoustic signal. The coded acoustic signal is propagated
`
`across a distance many times a wavelength of the coded acoustic signal.
`
`3
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`Further steps include receiving the coded acoustic signal and transducing the
`
`coded acoustic signal to produce a modulated signal; and demodulating the
`
`modulated signal to produce the digital information.
`
`Uses of the communications method are many and varied. One such use
`
`5
`
`comprising the steps of providing an acoustic digital communications transmitter
`
`to be carried with a moving object; providing an acoustic digital
`
`communications receiver in proximity to a controlled area; transmitting from
`
`the acoustic digital communications transmitter at least one of an identifying
`
`code word that identifies the acoustic digital communications transmitter and a
`
`10
`
`command; receiving at the acoustic digital communications receiver the
`
`identifying code word or command; and in response to at least one of the
`
`identifying code word or command, allowing physical access of the moving
`
`object to the controlled area. Another such use comprises the steps of
`
`providing an acoustic digital communications transmitter to be carried with a
`
`15
`
`moving object; providing an acoustic digital communications receiver within an
`
`area to be monitored; transmitting from the acoustic digital communications
`
`transmitter an identifying code word that identifies the acoustic digital
`
`communications transmitter; receiving at the acoustic digital communications
`
`receiver the identifying code word; and when the code word is not received
`
`20
`
`within a predetermined interval of time, producing an alarm indication. Still a
`
`further use comprises the steps of providing a first acoustic digital
`
`communications transceiver to be carried on an object; providing a second
`
`acoustic digital communications transceiver at a fixed location; transmitting
`
`from one of the first and second acoustic digital communications transceivers a
`
`25
`
`query message; receiving the query message at another of the first and second
`
`acoustic digital communications transceivers and transmitting a response
`
`message; determining a one-way propagation time between the first and second
`
`acoustic digital communications transceivers; and determining a distance
`
`between the first and second acoustic digital communications transceivers. The
`
`30
`
`location of the object may be intended to remain fixed for a time, in which case
`
`the foregoing steps are repeated multiple times; a determination is made
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`4
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`PCTIIB97/00144
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`whether the location of the object has changed; and if the location of the object
`
`has changed, an alarm indication is produced. Alternatively, the first acoustic
`
`digital communications transceiver may be a mobile acoustic digital
`
`communications transceiver carried on a moving object, and the second acoustic
`
`5
`
`digital communications transceiver may be a base acoustic digital
`
`communications transceiver, in which case the foregoing steps are repeated
`
`multiple times; and a rate of change of location of the object is determined.
`
`The foregoing steps may be repeated at multiple base acoustic digital
`
`transceivers and results communicated from the multiple base acoustic digital
`
`10
`
`transceivers to a common site. In this manner one or both of a location and a
`
`heading of the object may be determined.
`
`BRIEF DESCRIPTION OF THE DRAWING
`
`The present invention may be further understood from the following
`
`description in conjunction with the appended drawing. In the drawing:
`
`15
`
`Figure 1 is a timing diagram of a Coded Audio Signal transmitted at
`
`fixed intervals;
`
`Figure 2 is a block diagram of a Coded Audio Sound Generator;
`
`Figure 3 is a plot of a correlation output for a codeword UW 1 in no
`
`noise;
`
`20
`
`Figure 4 is a plot of a correlation output for codeword UWl in noise,
`
`with the noise level set at twice the signal level;
`
`Figure 5 is a block diagram of a Coded Detector Module System;
`
`Figure 6 is an equivalent functional block diagram of a portion of the
`
`Coded Detector Module of Figure 5 realized by the DSP;
`
`25
`
`Figure 7 is a timing diagram of a Coded Audio Signal transmitted at
`
`fixed intervals;
`
`Figure 8 is a diagram of an Audio Command Packet;
`
`Figure 9 is an equivalent functional block diagram of a portion of the
`
`Coded Detector Module realized by the DSP;
`
`30
`
`Figure 10 is a block diagram of an ultrasonic Transit Control Module;
`
`Figure 11 is a block diagram of a Coded Audio Transceiver Module;
`
`5
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`Page 7 of 45
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`PCT/IB97/00144
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`Figure 12 is a diagram illustrating a communications sequence allowing
`
`a distance ranging operation to be performed using acoustic energy;
`
`Figure 13 is a timing diagram illustrating the timing of query and
`
`response messages for purposes of performing a distance ranging calculation;
`
`5
`
`Figure 14 is a block diagram of an acoustic digital communications
`
`network, in particular a network for geolocation; and
`
`Figure 15 is a diagram of a portion of a dedicated short-range
`
`communications system.
`
`DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
`
`Building blocks of the present digital sonic and ultrasonic
`
`communications networks include sonic transmitters (sound generators), sonic
`
`receivers (detectors) and sonic transceivers (sound generators and detectors).
`
`Different embodiments of these building blocks may possess varying degrees of
`
`sophistication. Whereas the sound generators are relatively simple in their
`
`15
`
`construction, the sound detectors rely on Digital Signal Processing techniques to
`
`achieve accurate detection over moderate distances ( on the order of one mile).
`
`Three principal embodiments of a coded audio detector are described.
`
`The first embodiment provides the ability to uniquely detect a particular coded
`
`sound generator. The second embodiment adds to this unique detection
`
`20
`
`capability the further ability of a vehicle operator to have the detector take
`
`specific actions. In a third embodiment, an ultrasonic downconverter module is
`
`provided, allowing the coded sound detector to operate in the ultrasonic range.
`
`The invention will be described primarily in terms of transit
`
`applications. It should be understood, however, that the communications
`
`25
`
`techniques described, besides being applicable to vehicular communications, are
`
`equally application to personal communications, the tagging of goods, etc.
`
`In the first embodiment, a Coded Audio Detector Module is DSP-based.
`
`A vehicle is equipped with a special Coded Sound Generator which issues
`
`"codewords" at fixed intervals, or on command of the driver. Between the
`
`30
`
`transmission of these special codewords, the Coded Sound Generator need not
`
`emit any sound. The DSP-based Coded Audio Detector Module receives the
`
`6
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`Page 8 of 45
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`WO97/31437
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`foregoing codewords, decodes the codeword to determine if it is one of a
`
`pre-determined set of codewords recognized as being valid, and then issues a
`
`signal to a controller if the codeword assigned to that vehicle is valid.
`
`The Coded Audio Detector Module, or CADM, is used as part of a
`
`5
`
`two-part system. The first part is an audio-based transmitter system on each
`
`vehicle that is to control or interact with the system. Referring to Figure 1,
`
`when the vehicle operator enables the Coded Sound Generator, the transmitter
`
`sends a codeword at specific time intervals, say 5 seconds, using binary FSK
`
`modulation of the audio carrier for example.
`
`10
`
`Each vehicle is provided with a Coded Sound Generator. The Coded
`
`Sound Generator may be a simple audio generator the output of which is input
`
`to the microphone input of an amplifier. This Coded Sound Generator
`
`generates the appropriate codeword.
`
`Referring more particularly to Figure 2, a programmed microprocessor
`
`15
`
`201 is coupled to a Digital to Analog Converter (DAC) 203. An output of the
`
`DAC 203 is coupled to an amplifier 209, which is coupled to a speaker 211. A
`
`mode selection switch 213 and a manual signal switch 215 are also provided
`
`and are coupled to the microprocessor 201.
`
`The microprocessor 201 reads the mode selection switch 213 to
`
`20
`
`determine if the operator wants the Coded Sound Generator to be activated
`
`continuously at intervals or only upon user command. The microprocessor 201
`
`generates synthetic digital waveforms representing the desired codeword. These
`
`signals are converted to an analog voltage by the DAC 203 and then input to
`
`the amplifier 209. The manual signal switch 215 allows the operator to
`
`25
`
`generate codeword signals at will rather than at timed intervals.
`
`The CADM will only issue a control signal when a coded signal which
`
`meets specific conditions is detected. This feature allows for greater security
`
`and reliability of operation.
`
`In the first embodiment, the codewords used in the Coded Audio
`
`30
`
`Detector Module are binary patterns of a specific length. The patterns are
`
`chosen such that they have desirable autocorrelation function characteristics-
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`specifically low auto-correlation sidelobes. Furthermore, in choosing a family
`
`of codewords, attention should also be paid to the cross-correlation properties
`
`of the codewords. In particular, in addition to there being a low degree of
`
`correlation between the codewords, their cross-correlation functions should have
`
`5
`
`low sidelobes. For example, the following seven codewords represent a family
`
`of codewords which satisfy the foregoing requirements:
`UWl = 110111010100000
`UW2 = 101110110100000
`UW3 = 101111001100000
`UW4 = 110101101100000
`UW5 = 101111010010000
`UW6 = 111100101010000
`UW7 = 101011101000100
`The audio codeword may be transmitted using simple Frequency Shift
`
`15
`
`Keying (FSK) modulation at some carrier frequency, where fc is the center
`frequency, fc + of is the frequency for the transmission of a binary 1, and fc-of
`is the frequency for the transmission of a binary 0. The codeword consists of a
`
`stream of binary digits sent using one of these two tones.
`
`The CADM receives the codeword using a microphone system and then
`
`20
`
`demodulates the audio codeword. Demodulation is performed using an FSK
`
`demodulator. The CADM first synchronizes to the incoming bit stream by
`
`performing a symbol timing recovery operation on the codeword. Once
`
`synchronized, the FSK CADM searches for the codeword. The search may be
`
`done by binary correlation with threshold detection, using the stored reference
`
`25
`
`codewords (UWl to UW7) as a reference. If the codeword is received with
`
`more bits matching the stored reference pattern than the threshold value, it will
`
`be processed and the desired commands will be interpreted and issued to the
`
`controller. If the packet was received with an uncorrectable number of errors,
`
`the command will be rejected and no signals will be sent to the controller.
`
`30
`
`To test the performance of the detector in searching for the codeword,
`
`the 15-bit codeword UWl was used an example. The codeword was sent as a
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`15-bit sequence using the binary FSK modulation scheme discussed earlier, and
`
`was preceded and followed by silence. The signal was processed using a binary
`
`correlation algorithm, and the correlation output was plotted as a function of
`
`time as shown in Figure 3. In this case, the maximum in the correlation is seen
`
`5
`
`to occur at about sample 101, which marks the location of the codeword in
`
`time. The maximum of the correlation value is 60, since the 15-bit codeword
`
`was sampled at 4 samples per bit. If a threshold value of, say, 56 was taken as
`
`a detection threshold, then only correlation outputs in excess of 56 would cause
`
`the microphone system to indicate the presence of the codeword.
`
`10
`
`The real performance advantage of binary correlation with threshold
`
`detection using the foregoing codewords is obtained under noisy conditions.
`
`Consider the same 15-bit codeword in a noisy environment where the noise
`
`level is twice the level of the codeword sound received from the vehicle.
`
`Referring to Figure 4, it may be seen that the correlation peak is still quite
`
`15
`
`prominent and distinct from any correlation peaks generated by the noise itself.
`
`In this example, the correlation peak near bit 100 is still very prominent and the
`
`peaks resulting from the correlation of the stored reference with the noise are
`
`still very small.
`
`It is possible to use longer length codewords to achieve even better
`
`20
`
`performance in a noisy environment. Longer codewords also reduce the
`
`probability of false detection, i.e., the probability of the chance situation where
`
`received noise just happens to look like the stored reference signal and falsely
`
`causes the detection threshold of the binary correlator to be exceeded. The
`
`following table shows the probability of false detection and the probability of
`
`25
`
`missed detection (the probability that the codeword was in fact transmitted, but
`
`that noise corrupted a sufficiently large number of bits that the binary correlator
`
`missed the codeword), for codeword lengths of 15, 20 and 32 bits, where the
`
`correlator threshold is set to tolerate two bit errors (a 1 % bit error rate
`
`channel). It is readily seen that for the 32-bit codeword case tolerating two
`
`30
`
`errors, there will be very few cases of false detection. Assuming that events
`
`happen at the bit interval and that the bit rate is 20 bps, then there would be on
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`average one false detection approximately every 4. 7 days. This probability can
`
`be reduced even more by using the loudness of the received codeword to trigger
`
`a signal pre-emption event (i.e., the correlation output must exceed the
`
`threshold, and the sound level must exceed a sound level threshold, indicating
`
`5
`
`that the vehicle is in proximity to the microphone).
`
`Table 1. Binary Correlation with Threshold Detection
`For Various Codeword Lengths.
`
`Codeword
`Length
`(bits)
`
`Bit
`Errors
`Tolerated
`
`15
`
`20
`
`20
`
`32
`
`32
`
`1
`
`1
`
`2
`
`2
`
`3
`
`10
`
`15
`
`Praise
`
`p missed
`
`4.88 X 10·4
`
`2.00 X lQ·5
`
`2.01 X lQ·4
`
`1.23 X lQ·7
`
`1.28 X 10-6
`
`9.63 X lQ·4
`
`1.69 X 10-3
`
`1.00 X 10-2
`
`3.99 X J0·3
`
`2.87 X 1Q·4
`
`In a preferred embodiment, the functionality of the CADM as described
`
`is implemented using substantially the same hardware platform as the
`
`DSP-based siren detector of WO 95/24028 (McConnell et al), published
`
`September 8, 1995, incorporated herein by reference. Only the DSP software
`
`20
`
`is changed. The detection algorithm may be based on the limiter/discriminator
`
`approach of McConnell et al., but includes in addition a low-rate demodulator
`
`to perform symbol timing recovery and codeword detection.
`
`Referring more particularly to Figure 5, a Coded Sound Generator 501
`
`is coupled to a loudspeaker 503. At the receiver, the coded signal produced by
`
`25
`
`the Coded Sound Generator and 501 is picked up by a transducer 505 and input
`
`to a DSP-based logic board 507.
`
`The DSP-based logic board 507 processes the coded signal and outputs
`
`pre-empt signals to a controller 509 based on that processing. The DSP-based
`
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`PCT/IB97/00144
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`logic board 507 realizes a Coded Audio Detector Module that uses the same
`
`limiter discriminator operations as described in McConnell et al.
`
`to perform
`
`FSK demodulation of the FSK signal. The software is modified to incorporate
`
`the following additional functions:
`Symbol Timing Recovery - this may be based on a simple
`
`5
`
`early/late-gate symbol synchronizer.
`Codeword Search - this may be based on a binary correlation with
`
`threshold detection technique, using the pre-stored reference codewords as
`
`templates for the binary correlation.
`
`10
`
`In addition to these functions, the software is modified to include a
`
`command parser to determine which codeword was received and to then take
`
`appropriate action based on the command and data in the command packet.
`
`An equivalent functional block diagram of the CADM is shown in
`
`Figure 6. An output signal from a microphone 601 is filtered in a band-pass
`
`15
`
`filter 603. The filtered signal is then input to a combination of a discriminator
`
`605, a decimator 607 and a median filter 609. An output of the median filter
`
`609 is coupled to a symbol synchronization block 611, followed by a codeword
`
`search block 613. An output of the codeword search block is input to a block
`
`615 to control whether a signal is issued to the controller. Also input to the
`
`20
`
`block 615 is the output of the decimator 607, indicative of the received signal
`
`level.
`
`As compared to the DSP-based detector of McConnell et al., the
`
`discriminator, decimator, and median filter operations are the same, to ensure
`
`the highest sensitivity possible for the CADM based on the excellent signal
`
`25
`
`detection capability inherent in that technique. Signal detection is followed by
`
`the operations of blocks 611, 613 and 615, required to decode the codeword
`
`and then execute the command associated with that codeword.
`
`The CADM may be provided with a multiplicity of channels. Different
`
`channels are allocated to different approaches to an installation. In the vast
`
`30
`
`majority of cases, a four channel detector system will suffice. Cases with more
`
`than four approaches may be dealt with by assigning additional channels.
`
`11
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`In accordance with a second embodiment, the DSP-based Coded Audio
`
`Detector Module offers increased functionality, above and beyond that of the
`
`first embodiment. As in the first embodiment, the CADM is based on the DSP
`
`siren detector module of McConnell et al., with the following exceptions.
`
`5
`
`First, the vehicle which is to activate the control function is equipped with a
`
`special Coded Sound Generator which issues coded "frames" at fixed intervals
`
`or on command of the driver. Between the transmission of these special coded
`
`frames, the Coded Sound Generator need not emit any sounds. Second, the
`
`DSP-based siren detector is modified to receive the coded frames, decode the
`
`10
`
`frame content, and then issue a control signal if the unique address assigned to
`
`that vehicle matches one of a list of addresses that the detector recognizes as
`
`being valid.
`
`As before, the Coded Audio Detector Module, or CADM, is part of a
`
`two part system. The first part is an audio based transmitter system on each
`
`15
`
`vehicle that is to control or interact with the system. Referring to Figure 7,
`
`when the vehicle operator enables the Coded Sound Generator, the transmitter
`
`at specific time intervals, say 5 seconds, sends a packet frame, using binary
`
`FSK modulation of the audio carrier for example.
`
`Each vehicle is provided with a Coded Sound Generator. The Coded
`
`20
`
`Sound Generator may be a simple audio generator the output of which is input
`
`to the microphone input of an amplifier system. This Coded Sound Generator
`
`generates the appropriate packet frame.
`
`The physical hardware used to realized the Coded Sound Generator may
`
`be the same as previously described in relation to Figure 2. Referring again to
`
`25
`
`Figure 2, the microprocessor reads the mode selection switch to determine if
`
`the operator wants the sound generated at intervals or only upon user actuation
`
`of a switch, for example. The microprocessor generates synthetic digital
`
`waveforms representing the packet frame (as opposed to a singular codeword as
`
`in the previous embodiment). These signals are converted to an analog voltage
`
`30
`
`by the Digital to Analog Convenor (DAC) and then input to the amplifier. A
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`12
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`manual signal switch is also available to allow the operator to generate packet
`
`frame signals at will rather than at timed intervals.
`
`The CADM will only issue a control signal when a packet frame which
`
`meets specific conditions is detected. This feature allows for a greater security
`
`5
`
`and reliability of operation.
`
`The audio command packet is structured in a fashion similar to a
`
`standard X.25 packet frame, described for example in Kuo, Protocols and
`
`Techniques For Data Communications Networks, Prentice Hall, 1981,
`
`incorporated herein by reference. Referring more particularly to Figure 8, the
`
`10
`
`audio command packet is transmitted using a simple Frequency Shift Keying
`
`(FSK) modulation at some carrier frequency, where fc is the center frequency,
`
`fc +of is the frequency for the transmission of a binary 1, and fc-of is the
`
`frequency for the transmission of a binary 0. The packet consists of a stream
`
`of binary digits sent using one of these two tones. The purpose of the various
`
`15
`
`segments of the packet are as follows:
`
`Preamble - to allow the CADM to synchronize to the symbol centers of
`
`the binary data signal. The preamble is typically an alternating binary
`
`sequence, such as 1010101010.
`
`Frame Synch - to provide word alignment to the control, data, and
`
`20
`
`parity portions of the command packet. The frame synch is typically a short
`
`binary sequence such as a Barker code, Lindner Sequence, Maury-Styles
`
`Sequence, etc. One suitable frame synch word consists of the binary sequence
`
`0010 0000 0111 0101.
`
`Header - this field of the frame contains binary address information that
`
`25
`
`is unique to each vehicle in the fleet, as well as a packet type identifier, and
`
`control flags. The actual binary sequence depends on the values given to the
`
`elements of the header field. In an exemplary embodiment, the fiel