WO2013108243A1 - Hybrid-based system and method for indoor localization - Google Patents

Hybrid-based system and method for indoor localization

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Publication number
WO2013108243A1
WO2013108243A1 PCT/IL2013/000005 IL2013000005W WO2013108243A1 WO 2013108243 A1 WO2013108243 A1 WO 2013108243A1 IL 2013000005 W IL2013000005 W IL 2013000005W WO 2013108243 A1 WO2013108243 A1 WO 2013108243A1
Authority
WO
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Application
Patent type
Prior art keywords
ultrasonic
mobile
time
device
system
Prior art date
Application number
PCT/IL2013/000005
Other languages
French (fr)
Inventor
Israel WEISMAN
Ilia ANSHELEVICH
Original Assignee
Weisman Israel
Anshelevich Ilia
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

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Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO 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
    • G01S1/00Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith
    • G01S1/72Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith using ultrasonic, sonic or infrasonic waves
    • G01S1/76Systems for determining direction or position line
    • G01S1/80Systems for determining direction or position line using a comparison of transit time of synchronised signals transmitted from non-directional transducers or transducer systems spaced apart, i.e. path-difference systems
    • G01S1/805Systems for determining direction or position line using a comparison of transit time of synchronised signals transmitted from non-directional transducers or transducer systems spaced apart, i.e. path-difference systems the synchronised signals being pulses or equivalent modulations on carrier waves and the transit times being compared by measuring the difference in arrival time of a significant part of the modulations
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO 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
    • G01S5/00Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
    • G01S5/18Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using ultrasonic, sonic, or infrasonic waves
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO 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
    • G01S5/00Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
    • G01S5/18Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using ultrasonic, sonic, or infrasonic waves
    • G01S5/26Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements

Abstract

A system for estimating position of a mobile electronic device that is located within a detection space, the mobile electronic device maintains a mobile device system time and includes an electroacoustic transducer, a mobile device processor coupled with the electroacoustic transducer, and a mobile device radio frequency (RF) communication module operative to receive a time-synchronization signal from a reference time provider maintaining a reference time, the mobile electronic device is provided with an ultrasonic transmission code and the reference time, the system comprising at least one ultrasonic transmitter that respectively maintains an ultrasonic transmitter system time and that is provided with said ultrasonic transmission code, said at least one ultrasonic transmitter comprising a processor; an RF communication module operative to receive said time-synchronization signal from said reference time provider, said processor synchronizes said ultrasonic transmitter system time with said reference time, by reception of said time-synchronization signal; and an ultrasonic electroacoustic emitter, said ultrasonic electroacoustic emitter emitting an ultrasonic transmission characterized by a particular sound emission signature, according to said ultrasonic transmission code, wherein said electroacoustic transducer detects at least part of said ultrasonic transmission, said mobile device processor calculates a mobile device system time difference between said mobile device system time and said reference time, said mobile device processor calculates distances of said mobile electronic device to each of said at least one ultrasonic transmitter by measuring respective propagation delays of each of said ultrasonic transmissions with respect to said ultrasonic transmission code and to said mobile device system time difference, so as to compute an estimated said position of said mobile electronic device.

Description

HYBRID-BASED SYSTEM AND METHOD FOR INDOOR

LOCALIZATION

FIELD OF THE DISCLOSED TECHNIQUE

The disclosed technique relates to localization of electronic devices, in general, and to a method and a system for estimating locations of a plurality of electronic devices that are substantially located indoors, in particular.

BACKGROUND OF THE DISCLOSED TECHNIQUE

Localization systems, location-sensing systems, positioning systems, and location systems are all terms that refer to systems that are employed to locate living beings (e.g., persons, domesticated animals) as well as objects. Localization systems, among the various types that exist, may be classified as those which are used primarily outdoors, and those which are primarily used indoors. Outdoor location systems that are based essentially on global navigation satellite systems (GNSSs), such as the global positioning system (GPS), rely on having an unobstructed line of sight (LOS) to at least four GPS satellites that continually transmit GPS signals in order to determine location of a GPS receiver on Earth. By determining the transit time of GPS signals, the GPS receiver calculates its position by computing the distance to each GPS satellite. The determination of position within an indoor environment, however, where GNSS signals are feeble or unavailable, necessitates reliance upon other localization techniques.

There is a diversity of indoor location systems that are known in the art, each relying on a particular localization technology. Among the indoor localization systems, there are those which are based on radio frequency (RF) techniques, such as radio direction finding (RDF), radio frequency identification (RFID), and RF wireless local area networks (LANs). Other indoor localization techniques include photonic-based systems that rely on light wave transmission and reception (including image acquisition via cameras and related image processing techniques), sonic wave (e.g., ultrasound) techniques, and the like.

Various types of ultrasonic indoor localization systems are known in the art. For example, the "Cricket" system, as described in a dissertation by Nissaka Bodhi Priyantha, entitled "The Cricket Indoor Location System" and published in 2005 by the Massachusetts Institute of Technology, employs both RF and ultrasound techniques for localization. The Cricket system includes a plurality of Cricket nodes each including a radio frequency (RF) transceiver, a microcontroller, an ultrasound transmitter and an ultrasound receiver. The Cricket system includes two types of Cricket nodes: location transmitters ("beacons") that are attached at fixed positions to ceilings and walls of a building, and receivers ("listeners") that are attached to mobile objects for which their location is to be determined. Each beacon periodically transmits an ultrasonic pulse (at a frequency of 40 kHz.) simultaneously with an RF message containing beacon specific information (an identifier) as well as its coordinates. The listeners receive the RF message along with the lagging ultrasonic pulse and measure the time-difference-of-arrival (TDOA) therebetween. The TDOA is used to compute the beacon-to-listener distances so as to determine the locations of the listeners.

The "Dolphin" localization system described in an article entitled "Broadband Ultrasonic Location Systems for Improved Indoor Positioning" by Mike Hazas and Andy Hopper published on May 2006 the in the journal of the Institute of Electrical and Electronics Engineers (IEEE) Transactions on Mobile Computing, Vol. 5, No. 5 is directed to two broadband ultrasonic indoor positioning systems that employ a plurality of transmitter and receiver units (collectively referred to as "Dolphin" units). According to one system, the positions of eight coplanar receivers that are affixed to a ceiling are surveyed. Four transmitters are placed at fixed positions in a room and an additional mobile unit transmitter is placed within a small office. The system employs direct sequence (DS) spread spectrum techniques as well as code division multiple access (CDMA) in order to achieve separation of overlapping signals transmitted by the ultrasonic transmitters. To reduce interference that occasionally occurs in CDMA systems due to simultaneous transmission of signals, the system further employs successive interference cancellation (SIC). According to SIC a receiver receiving signals from all of the transmitters (i.e., a received waveform) reconstructs a signal received from the transmitter having the largest signal power relative to the other transmitters, so that it is iteratively subtracted from the received waveform. The location of the mobile unit is estimated according to the following steps. The times-of-f light of a plurality of ranging messages from the mobile unit is measured by correlating the signals received by the receivers against a 50 kHz. carrier modulated expected signal. The times-of-f light are converted to transmitter-to-receiver distances by using the speed of sound in air. Lastly, by using the surveyed positions of the receivers and the transmitter-to-receiver distances, the location of the mobile device is estimated by employing a multilateration algorithm.

The "Bat" ultrasonic location system, as described in numerous published publications that may be found in the Internet address http://www.cl.cam.ac.uk/research/dtg/attarchive/bat/ of AT&T laboratories Cambridge, is directed to an ultrasonic localization system where a small unit (called "Bat") is attached to equipment that is carried by a user. The Bat system further includes a plurality of ultrasound receiver units and a base station. Each Bat unit has a globally unique identifier, and includes a radio transceiver, controlling logic, and an ultrasonic transducer. The ultrasound receiver units, connected by a wired daisy-chain network, are positioned at known locations on ceilings of rooms to be instrumented. The base station periodically transmits an RF message containing the identifier for the corresponding Bat to emit an ultrasonic pulse. To reduce reflections of the ultrasonic pulse from objects in the environment, the base station waits for reverberations of the ultrasonic pulse to subside before triggering another ultrasonic puise. The ultrasound receiver units monitor the incoming ultrasound pulse and record its time of arrival. The times-of-flight of the ultrasound pulse from the Bat to the receivers are converted into corresponding Bat-to-receiver distances. These distances from three or more non-coliinear ultrasonic receiver units are used to compute the 3-D position of the Bat unit by employing multilateration.

U.S. Patent No.: 7,916,577 B2 issued to Jeong et al. entitled "Method and System for Recognizing Location by Using Sound Sources With Different Frequencies" is directed to a method and a system for recognizing the locations of moving objects by calculating respective distances of these moving objects from a plurality of synchronized ultrasound sources. The system includes a reference time broadcasting device, a plurality of ultrasonic satellites each of which includes an ultrasonic transmitter, a plurality of location determination receivers, a server, wireless network. The location determination receivers are attached to the moving objects. The wireless network interconnects the server, the location determination receivers, and the ultrasonic satellites. The sever stores the coordinates of the ultrasonic satellites. The reference time broadcasting device generates RF synchronization signals. Both the location determination receivers and the ultrasonic satellites receive these RF synchronization signals. Upon reception of RF synchronization signals, each ultrasonic satellite transmits ultrasonic signals at a particular frequency. The location determination receivers receive these ultrasonic signals and calculate the transmission time for each signal. The transmission time is the time difference between reception of an RF synchronization signal and reception of an ultrasonic signal. Once the location determination device calculates the transmission times, it calculates the distance to the satellites that transmitted these ultrasonic signals by multiplying the transmission times by the velocity of sound. The location determination device calculates the coordinates of its own location by knowing its respective distances from four satellites as well as the coordinates of each of these satellites (transmitted to it by the server).

An article entitled "Investigating Ultrasonic Positioning on Mobile Phones" by Filonenko et al. published in 2010 by the IEEE is directed to an indoor ultrasound positioning system implemented by the use of mobile phones. The system employs the inbuilt speakers of the mobile phones to generate a simple sine tone, which is then received by at most four matched microphones that are located in one corner of a test laboratory. The sine tone ("audio stream") from the four microphones are analyzed in real time by digital signal processing (DSP) filters that are tuned to specific ultrasound frequencies. The arrival time of the audio streams at each microphone is used to calculate the position of the signal source using trilateration. The derived position is combined with accelerometer and magnetometer readings to obtain the position and orientation of the mobile phone.

An article entitled "3D Localization and Tracking of Objects Using Miniature Microphones" by lonescu et al. in Wireless Sensor Network, 2011, 3, pp. 147-157 is directed to a system for the localization and tracking of remote objects by ultrasound. The system includes a central processing unit (CPU), a data emission/acquisition board, four coplanar ultrasound transmitters {"tweeters") and a plurality of receivers (remote objects). The tweeters form a reference frame, each emitting ultrasonic pulses in the 17-40 kHz. band toward the remote objects. Each remote object is equipped with several miniature microphones mounted at selected positions thereon. The shape of the object and its 3D orientation is represented in a virtual context by knowing the coordinates of the miniature microphones and the geometry of the object. The data emission/acquisition board acquires the ultrasound pulses reaching the miniature microphones, as electrical signals. The CPU estimates the distance between each microphone and each of the tweeters from the time-of-f light of the ultrasound pulses reaching the microphones. By knowing the position of the tweeters, the CPU uses the obtained distances to compute the current position of the remote objects in the reference frame.

U.S. Patent Application Publication No.: 2009/0295639 A1 to Zhao et al., entitled "Autonomous Ultrasonic Indoor Location System, Apparatus and Method" is directed to an autonomous ultrasonic indoor location system for determining location of a beacon receiving apparatus based on the positions of a plurality of transmitters. The system includes an ultrasonic location beacon (ULB) transmitting apparatus and a ULB receiving apparatus. The ULB transmitting apparatus is installed on a ceiling whereas the ULB receiving apparatus is carried on a user. The ULB transmitting apparatus includes an RF transmitter, a structural ultrasound transmitter that includes a plurality of ultrasound transmitters, and a transmission timing controller. The timing controller includes a timing generation means and an ultrasound transmission controlling means. The ULB receiving apparatus includes an RF receiving unit, an ultrasound receiving unit, a synchronization unit, an order identification unit, a time-of-arrival (TOA) unit, and a position calculation unit.

The timing generation means generates RF transmission timing signals at a predetermined period, and outputs the generated RF transmission timing signals to the ultrasound transmission controlling means and to the RF transmitter. The RF transmitter transmits the RF signals according to the RF transmission timing signals received from the timing generation means. The RF transmitter transmits an RF signal containing synchronization information that is based on a predetermined transmission timing signal. The ULB transmitting apparatus sequentially transmits ultrasound signals at a predetermined order after transmission of the RF signal containing synchronization information by the RF transmitter. The ULB receiving apparatus detects the synchronization information transmitted from the ULB transmitting apparatus and synchronizes with the ULB transmitting apparatus using the detected synchronization information. The order identification unit of the ULB receiving apparatus sequentially receives ultrasonic signals from the ultrasound receiving unit. Ultrasound receiving unit determines the transmission order of received ultrasound signals based on the reception timings and the synchronization timing obtained by the synchronization unit. The TOA acquisition unit acquires a TOA information sequence and sends it to the position calculation unit. The position calculation unit obtains distances from the respective ultrasonic transmitters of the ULB receiving apparatus by multiplying the respective TOA information in the TOA information sequence by the speed of ultrasound signals and then calculates the location of the ULB receiving apparatus based on the values of the distances and positions of the respective ultrasound transmitters by triangulation and multilateration.

A survey of indoor localization systems known in the art may be found in an article entitled "A Survey of Indoor Positioning and Object Locating Systems" by Hakan Koyuncu, and Shuang Hua Yang published in May 2010 in the IJCSNS International Journal of Computer Science and Network Security, Vol. 10 No. 5, which is a study directed at the investigation of various indoor positioning techniques. Another general survey and taxonomy of a variety of location systems may be found in an article entitled "Location Systems for Ubiquitous Computing" by Jeffrey Hightower and Gaetano Borriello, published in August 2001 by IEEE. SUMMARY OF THE PRESENT DISCLOSED TECHNIQUE it is an object of the disclosed technique to provide a novel method and system for estimating position of a plurality of mobile electronic devices that are located within enclosed spaces (indoors, such as within a building), without utilizing global navigation satellite systems (GNSS), by employing a hybrid-based approach. This hybrid-based approach combines ultrasonic localization techniques with radio frequency (RF) communication techniques, (e.g., cellular communication, Wi-Fi, Bluetooth) for time synchronization and localization, and further integrates inertia! navigation, as well as the use of temperature monitoring of the detection space so as to minimize the effect of temperature variations on ultrasonic position estimation.

In accordance with the disclosed technique, there is thus provided a system for estimating position of a mobile electronic device that is located within a detection space. The mobile electronic device includes an electroacoustic transducer, a mobile device processor coupled with the electroacoustic transducer, and a mobile device radio frequency (RF) communication module that is operative to receive a time-synchronization signal from a reference time provider. The reference time provider maintains a reference time. The mobile electronic device maintains a mobile device system time. The mobile electronic device is provided with an ultrasonic transmission code and the reference time. The system comprises at least one ultrasonic transmitter (i.e., typically a plurality). The ultrasonic transmitter comprises a processor and an ultrasonic electroacoustic emitter. The ultrasonic transmitter is located within the detection space and distanced apart from the mobile electronic device. The ultrasonic transmitter is provided with the ultrasonic transmission code. Each ultrasonic transmitter respectively maintains an ultrasonic transmitter system time. The RF communication module is operative to receive the time-synchronization signal from the reference time provider. The RF communication module is coupled with the processor. The processor synchronizes the ultrasonic transmitter system time with the reference time, by reception of the time-synchronization signal. The ultrasonic electroacoustic emitter is coupled with the processor. The ultrasonic electroacoustic emitter emits an ultrasonic transmission within detection space according to the ultrasonic transmission code. The ultrasonic transmission is characterized by a particular sound emission signature. The electroacoustic transducer detects at least part of the ultrasonic transmission. The mobile device processor calculates a mobile device system time difference between the mobile device system time and the reference time. The mobile device processor calculates distances of the mobile electronic device to each ultrasonic transmitter whose ultrasonic transmissions is detected by mobile electronic device, by measuring respective propagation delays of each of the ultrasonic transmissions with respect to the ultrasonic transmission code and with respect to the mobile device system time difference, so as to compute an estimated position of mobile electronic device.

In accordance with a another aspect of the disclosed technique, there is thus provided a method for estimating position of a mobile electronic device that is located within a detection space, in relation to respective positions of at least one ultrasonic transmitter (i.e., typically a plurality). Each ultrasonic transmitter maintains a respective ultrasonic transmitter system time. The mobile electronic device is operative to receive a time-synchronization signal from a reference time provider. The reference time provider maintains a reference time. The mobile electronic device maintains a mobile electronic device time. The method comprises the procedures of providing an ultrasonic transmission code to the mobile electronic device and to the ultrasonic transmitter, synchronizing the ultrasonic transmitter system time of each respective ultrasonic transmitter with the reference time, providing the reference time to the mobile electronic device, emitting an ultrasonic transmission, detecting at least part of the ultrasonic transmission, and calculating distances between the mobile electronic device to each ultrasonic transmitter whose ultrasonic transmission are detected by the mobile electronic device. The mobile electronic device calculates a mobile device system time difference between the mobile device system time and the reference time. Each ultrasonic transmission is characterized by a particular sound emission signature according to the ultrasonic transmission code. Calculating the distances of the mobile electronic device to each ultrasonic transmitter is carried out by measuring respective propagation delays of each ultrasonic transmission with respect to the ultrasonic transmission code and with respect to the mobile device system time difference, so as to compute an estimated position of the mobile electronic device.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed technique will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:

Figure 1 is a schematic illustration of a system for determining position of a mobile electronic device located within a detection space, constructed and operative in accordance with an embodiment of the disclosed technique;

Figure 2 is a schematic illustration depicting the implementation of the system of Figure 1 within a setting in the detection space;

Figure 3 is a schematic illustration of a timing diagram of the an ultrasonic transmission code, time-synchronization signals, as well as transmission and reception times of ultrasonic transmissions;

Figure 4 is a schematic illustration of synchronization of the system time of an ultrasonic transmitter with a reference cellular network system time, and a cellular networks time table which is provided to a mobile electronic device;

Figure 5 is a schematic illustration of a system that includes a server station, constructed and operative in accordance with another embodiment of the disclosed technique;

Figure 6A is a schematic block diagram of a method for determining position of a mobile electronic device located within a detection space, according to an embodiment of the disclosed technique;

Figure 6B is a schematic block diagram of the continuation of the method from Figure 6A;

Figure 7 is a schematic illustration of a system for determining position of a mobile electronic device located within a detection space, constructed and operative in accordance with another embodiment of the disclosed technique; and

Figure 8 is a schematic block diagram of a method for determining position of a mobile electronic device located within a detection space, according to another embodiment of the disclosed technique.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The disclosed technique overcomes the disadvantages of the prior art by providing a system and a method for estimating position of a plurality of mobile electronic devices that are located within enclosed spaces (indoors, such as within a building), where there is no or limited reception of signals from a global navigation satellite system (GNSS), by employing a hybrid-based approach that utilizes ultrasonic, radio frequency (RF) communications (e.g., Wi-Fi, cellular ) as well as inertial navigation techniques. This hybrid-based approach combines ultrasonic localization techniques with wired and/or wireless (e.g., RF) communication techniques for time synchronization and localization, and further integrates inertial navigation, as well as the use of temperature monitoring of the detection space so as to minimize the effect of temperature variations on ultrasonic position estimation.

According to the disclosed technique a plurality of ultrasonic transmitters are installed at known, designated locations within an indoor space so as to form a network (e.g., ; a grid, an array) of ultrasonic transmitters. This deployed network ofj ultrasonic transmitters forms a detection space reference frame that ' facilitates detection of mobile electronic devices (e.g., cellular phones, tablet computers, and the like) that are within the detection space. The mobile electronic devices as well as the ultrasonic transmitters are operativ e to be in communication with at least one reference time provider (e.g., a network time protocol (NTP) server, by employing a Wi-Fi router, a cellular base station of a cellular communications network, Bluetooth, ZigBee®, and the like.).

According to an embodiment of the disclosed technique, the deployed network of ultrasonic transmitters all communicate with an RF communication server base station and mutually form a wireless local area network (WLAN). The ultrasonic transmitters each include a time keeping mechanism (e.g., an internal clock) and are all collectively synchronized to a common reference time that is kept by the reference time provider (e.g., the RF communication server base station). The RF communication server base station employs a network time protocol (NTP) for synchronizing the ultrasonic transmitter with the reference time. Likewise, each mobile electronic device includes a timekeeping mechanism that maintains a respective mobile device system time. When a mobile electronic device enters the detection space it is time-wise synchronized with the reference time kept by the RF communication server base station (i.e., via a mobile device program application, an "app", that the user may download). An ultrasonic transmission code that specifies transmission times of the ultrasonic transmissions is provided (e.g., uploaded) to the ultrasonic transmitters as well as to the mobile electronic devices.

Each ultrasonic transmitter emits ultrasonic transmissions that are characterized by a distinctive sound emission signature (e.g., a particular code, frequency, modulation, etc.). When a mobile electronic device within the detection space detects ultrasonic transmissions, it measures their respective time propagation delays in relation to their corresponding transmission times. In this manner, the mobile electronic device "knows" the specific time at which ultrasonic transmissions were emitted, thereby enabling measurement of their respective time propagation delays, so as to estimate respective distances of the mobile electronic device to each of the ultrasonic transmitters that emitted the respective ultrasonic transmissions. When the distances from the mobile electronic device to those ultrasonic transmitters, whose ultrasonic transmissions were detected, are known, its position within the detection space may be determined by employing trilateration techniques. The mobile electronic device is operative to employ inertial position estimation to supplement and refine ultrasonic positioning so as to enhance positional accuracy, especially at locations in detection space where there is no or limited reception of the ultrasonic transmissions. Furthermore, the mobile electronic device consolidates both an estimated inertial current position (i.e., yielded from an inertial measurement system) with an estimated position based on RF signal strength signal aggregation and trilateration (i.e., yielded from detected RF signal strength measurements) into the computation of the position of the mobile electronic device within the detection space.

According to another embodiment of the disclosed technique, the ultrasonic transmitters are operative to be time-wise synchronized with a system time of a cellular network. According to this approach, the ultrasonic transmitters (as well as the mobile electronic devices) are operative to be in communication with at least one cellular base station of a cellular communications network. The internal clock of each ultrasonic transmitter is time-wise synchronized to a common (preferably) cellular network system time of a respective one of the cellular communications networks. This common cellular network system time is referred to as a reference cellular system time. Likewise, each mobile device system time is synchronized with a cellular network system time of one of the respective cellular communications networks with which the mobile electronic device is registered to (i.e., as opposed to using GPS time for synchronization of a GPS receiver).

A cellular networks time table that specifies respective cellular network system time differences between respective system times of the cellular networks is provided to the mobile electronic devices (i.e., since cellular base stations might not necessarily be time-wise synchronized to each other). When a mobile electronic device within the detection space detects ultrasonic transmissions, it measures their respective time propagation delays in relation to their corresponding transmission times as well as taking into account the system time difference between the reference cellular system time and its own mobile device system time. Given the specific time at which the ultrasonic transmissions were emitted, the mobile electronic device estimates its position within the detection space by computing respective distances to the ultrasonic transmitters by measuring the time propagation delays of the detected ultrasonic transmissions. Further given these distances from the mobile electronic device to the ultrasonic transmitters, the position of the mobile electronic device within the detection space is determined by employing trilateration techniques.

The term "global navigation satellite system" (GNSS) used herein, refers to a space-based system for providing location and time information to a corresponding GNSS receiver on Earth (or in vicinity thereof, such as in low Earth orbit). The term GNSS is used herein interchangeably with implementations thereof, which include the U.S. "Global Positioning System" (GPS), the Russian "GLObal NAvigation Satellite System" (GLONASS), the European "Galileo positioning system", the Chinese "Compass navigation system", and the like. The terms "determining", "estimating", and "computing" used herein within the context of assessment of location of an entity, are interchangeable, and refer to the process of ascertaining the location of that entity to a certain degree (i.e., within an error range). The disclosed technique employs wireless RF communication techniques for time-synchronization between internal docks of the ultrasonic transmitters and an external reference clock. The term "RF communication" herein refers to communication between different entities by way of radio waves. Various RF communication protocols and standards may be employed, such as 3G, 4G, Wi-Fi, Bluetooth, ZigBee®, and the like. Time-synchronization between the internal clocks of the ultrasonic transmitters and the external reference clock may be achieved by way of wired communication (e.g., wired local area network (LAN), power line communication (PLC), etc.).

An embodiment of the disclosed technique employing cellular time-synchronization with the ultrasonic transmitters will now be described. Reference is now made to Figures 1 and 2. Figure 1 is a schematic illustration of a system, generally referenced 100, for determining position of a mobile electronic device located within a detection space, constructed and operative in accordance with an embodiment of the disclosed technique. Figure 2 is a schematic illustration depicting the implementation of the system of Figure 1 within a setting in the detection space. System 100 includes a plurality of ultrasonic transmitters 104-1 , 1042 to 104N (where N represents an integer) installed within a detection space 102 (Figures 1 & 2). System 100 (Figure 1 ) is operative to determine current positions of each of a plurality of mobile electronic devices 106^ 1062 to 106M (where M represents an integer) within detection space 102. Detection space 102 may be for example, part of the internal volume in a substantially closed architectural structure having an indoor environment (such as within a building, shopping mall, stadium with a retractable roof), where the position of the plurality of mobile electronic devices 106^ 1062 to 106M is to be determined. System 100 is typically implemented where there is limited or no reception of GNSS signals (i.e., when one's position cannot be determined solely on GNSS). Furthermore, system 100 may be implemented where high accuracy localization is required. Ultrasonic transmitters 104-1 , 1042 to 104N as well as mobile electronic devices 06 f 1062 to 106M are operative to be in radio frequency (RF) communication with at least one of cellular base stations 108^ 1082 to 108P (where P is an integer) of a respective cellular communications network 108! to 108Q (where Q is an integer). Without loss of generality in describing the disclosed technique, Figure 1 illustrates by way of example that cellular base stations '\ 08 and 1082 are part of cellular communications network 1 10i , while cellular base station 1083 and 108P are part of cellular communications network 110Q. Cellular base stations Q8 to 108P serve as wireless RF receiver-transmitter stations employed as part of a wireless telephone communications system, such as the global system for mobile communications (GSM), cellular code division multiple access (CDMA) systems, and the like. Detection space 102 may include cellular repeaters (not shown) for enhancing communications (i.e., extending the range of transmission and reception of signals) between the cellular base stations and ultrasonic transmitters 104-1 , 1042 to 104N as well as with mobile electronic devices 1061 r 1062 to 106M, situated within detection space 02.

Each ultrasonic transmitter includes a processor 112, an RF communication module, an internal clock 118, a digital-to-analog converter (DAC) 120, an amplifier 122, an ultrasonic electroacoustic emitter 124, an RF antenna 126, and a memory unit 128. RF antenna 126 is coupled with RF communication module 114. Processor 112 is coupled with RF communication module 114, internal clock 118, DAC 120, and with memory unit 128. DAC 120 is coupled with amplifier 122, which in turn is coupled with ultrasonic electroacoustic emitter 124. Each ultrasonic transmitter may further include a thermometer 130, coupled with processor 112. Alternatively, either one or both internal clock 118 and DAC 120 are integrated into processor 112. Each ultrasonic transmitter is distinguishable from the other ultrasonic transmitters by possessing a unique electronic identification number.

Each mobile electronic device includes a mobile device processor 132, a mobile device RF communication module 134, a mobile device internal clock 136, an inertial navigation system (INS) 138, a memory unit 140, an analog-to-digital converter (ADC) 142, an electroacoustic transducer 144, a mobile device antenna 146, and an input/output (I/O) interface 148 (that includes a display). Mobile device antenna 146 is coupled with mobile device RF communication module 134. Mobile device processor 132 is coupled with mobile device RF communication module 134, mobile device internal clock 136, INS 138, memory unit 140, ADC 142 and with I/O interface 148. Electroacoustic transducer 144 is coupled with ADC 142. Alternatively, either one or both mobile device internal clock 136 and ADC 142 are integrated into the circuitry of mobile device processor 132. Internal clock 136 maintains a mobile device system time. Mobile device RF communication module 134 typically further includes a dedicated wireless communication module (not shown) that is operative to communicate with other devices as well as to the Internet via Wi-Fi, Worldwide Interoperability for Microwave Access (WiMAX), Bluetooth, and the like. Mobile electronic devices 106-t, 1062 to 106M may be implemented as cellular telephones (e.g., smartphones, such as the Apple iPhone®, the Nokia Lumia®, the Samsung Galaxy®, and the like), digital personal assistants (PDAs), tablet computers, laptop computers, and the like (where applicable).

RF communication module 114 is operative to receive time-synchronization signals (i.e., via RF antenna 126) from a plurality of cellular base stations. The base stations may be part of a single cellular communications network or part of different cellular communications networks. Each cellular communications network maintains, as part of its operating framework, a respective cellular communications network system time. With reference to Figure 1 , RF antenna 126 receives a time-synchronization signal 150 (e.g., a synchronization burst) from cellular base station 1082 and another time-synchronization signal 152 from cellular base station 1083. A time-synchronization signal may generally include a data payload (not shown) that carries a base station identity code (BSIC), a training sequence code, and frame number (FN) information (e.g., of time division multiple access (TDMA)). RF communication module 114 relays data pertaining to each of time-synchronization signals 150 and 152 to processor 112.

Internal clock 118 is a time keeping mechanism (i.e., a clock) that maintains an ultrasonic transmitter system time. Upon reception of time-synchronization signals 150 and 152, processor 112 records their respective system times and further determines whether the cellular communications network system times of cellular base station 1082 and that of cellular base station 1083 coincide (i.e., have the same time), otherwise processor 112 calculates their respective time differences, in general, processor 112 of each ultrasonic transmitter (e.g., ultrasonic transmitter 104i) keeps a record of ail cellular communications network system times of the respective cellular base stations (i.e., and their respective time differences) that are within communications range. Alternatively, processor 112 always calculates the cellular communications network system time differences of the cellular base stations, even if the result of which may be equal to zero. Processor 112 of each respective ultrasonic transmitter synchronizes its respective mobile device system time with a common cellular communications network system time belonging to one of the respective cellular communication networks. This cellular communication network is referred herein to as a reference cellular communication network. For example, processor 2 synchronizes the ultrasonic transmitter system time of ultrasonic transmitter 1041 with the cellular communications network system time of cellular base station 1082 (i.e., that which is kept, by cellular base station 1082 or cellular base station 1083). As the cellular communications network system time of cellular base station 1083 is known, processor 1 2 calculates and records the time differences between the ultrasonic transmitter system time of ultrasonic transmitter 1041 and that of the cellular communications network system times belonging to the other respective cellular base stations.

Processor 2 generates a plurality of emission signals {not shown) at specific times, as specified in an ultrasonic transmission code. The emission signals are provided to DAC 120, which converts them from digital form to analog form (i.e., as analog emission signals). These analog emission signals are amplified by amplifier 122 and subsequently provided to electroacoustic emitter 124, which in turn produces ultrasonic transmissions (diagrammatically depicted in Figure 1 as a plurality of wavefronts 149). The ultrasonic transmissions of each respective ultrasonic transmitter 104^ 1042, to 04N propagate through the medium of detection space 102 in accordance with nominal operating parameters, such as the maximum transmission range of ultrasonic transmissions and the transmission coverage area to which each respective ultrasonic transmitter it is configured. Reference is now further made to Figure 3, which is a schematic illustration of a timing diagram, generally referenced 200, of an ultrasonic transmission code, time-synchronization signals, as well as transmission and reception times of ultrasonic transmissions. Timing diagram 200 illustrates time-synchronization signal 150, time-synchronization signal 152, ultrasonic transmission code 162 that includes a plurality of ultrasonic transmissions 154^ 1542 to 154R (where R is an integer) from ultrasonic transmitter 104i (Figure 2), a plurality of ultrasonic transmissions 1561 r 1562 to 156s (where S is an integer) from ultrasonic transmitter 1042 (Figure 2), a plurality of ultrasonic transmissions 158^ 1582 to 58T (where T is an integer) from ultrasonic transmitter 104N (Figure 2), as well as corresponding receptions 160-1 , 1602 to 160w (where W represents an integer) of these ultrasonic transmissions by mobile electronic device 106^ Each point along the horizontal span of timing diagram 200 represents a particular instance in time. Time-synchronization signal 150 comprises of a plurality of time-synchronization bursts 150^ 1502 to 150u (where U is an integer). Likewise, time-synchronization signal 152 comprises of a plurality of time-synchronization bursts 152^ 1522 to 152v (where V is an integer).

Ultrasonic transmitters 104-,, 1042, to 104N emit ultrasonic transmissions according to ultrasonic transmission code 162, which specifies the transmission times of the ultrasonic transmissions. Ultrasonic transmission code 162 is stored memory unit 128 (Figure 1 ). Alternatively, ultrasonic transmission code 162 is stored in a separate memory unit (e.g., a memory card, hard disc drive (HDD), optical drive, etc.).

Generally, each ultrasonic transmitter emits ultrasonic transmissions that have a particular sound emission signature (i.e., a distinctive, identifiable sound emission characteristic and/or pattern, and/or combinations thereof). A particular sound emission signature of an ultrasonic transmission may be defined according to a plurality of sound emission characteristics and patterns that are exhibited by that ultrasonic transmission. Particularly, one of such sound emission characteristic or pattern, for example, is the timing sequence of the emissions. Detected ultrasonic emissions that are emitted by different ultrasonic transmitters may be distinguishable according to the different respective timing sequence of their emissions. Each ultrasonic transmitter emits a coded ultrasonic transmission (not shown) according to a unique timing sequence. Such an ultrasonic transmission may include an intermittent series of ultrasonic chirps, each of which may be selected from various types of chirps (e.g., 'up-chirp', 'down-chirp', exponential chirp, etc.). Hence, each distinctly coded ultrasonic transmission emitted from an ultrasonic transmitter may exhibit a distinct ultrasonic emission time sequence code (i.e., defined by the time intervals between successive chirps) as well as a pattern sequence code (e.g., a distinct chirp type code, defined by the types of chirps utilized in a particular sequence). Employment of both ultrasonic emission time sequence code as well as chirp type code provides redundancy in prevention of false detection (e.g., due to reflections, etc.) as well as in enhanced detection accuracy. System 100 is nonetheless operational if either one of the ultrasonic emission time sequence code or the chirp type code is employed. Typical attributes of an 'up-chirp' are for example, a 50 msec, in duration, 20-21 KHz signal. Typical attributes of a chirp type code is two 'up-chirps', followed by one 'down-chirp", followed by two 'up-chirps', where the time interval between successive chirps is 150 msec.

Alternatively, another sound emission characteristic that may be employed so as to differentiate between different ultrasonic sources is the frequency of ultrasonic emissions. Each ultrasonic transmitter emits ultrasonic transmissions (e.g., pulses) on a particular carrier transmission frequency fe that typically lies within an operational frequency range of 20 kHz to 24 kHz (i.e., the detectable frequency bandwidth). An ultrasonic transmission comprises a carrier signal that is varied (i.e., modulated) according to a baseband signal (i.e., a modulating signal). For example, an ultrasonic transmission signal emitted from an ultrasonic transmitter may employ frequency modulation (FM), expressed by the following equation:

f

s{t) = A sin(2/r + $ϊη(2π fm · )) ( 1 )

J m

where s{t) represents the time-dependent ultrasonic transmission signal, fa represents the frequency deviation, fm represents modulation frequency and A represents the amplitude of the ultrasonic transmission signal. The quotient of fa and /Js referred to as the modulation index (denoted herein by ϊ ), which represents the phase deviation of the angle of the signal:

θ(β) = 2π . /ε - ί + β ' *ίη(2π - /ΙΗ . ί) (2) from the angle 2 - fc - t of the unmodulated carrier signal. Alternatively, other modulation techniques may be employed, for example, amplitude modulation (AM), phase modulation (PM), chirp modulation, as well as digital modulation techniques such as phase-shift keying (PSK), frequency-shift keying (FSK), amplitude-shift keying (ASK), and the like.

Ultrasonic transmitter 104i produces a plurality of ultrasonic transmissions 154-1 , 1542 to 154R (on a carrier frequency fc ) whose transmission times are respectively t2 , t9 , and tl5 (Figure 3), according to ultrasonic transmission code 162. Ultrasonic transmission code 162 specifies transmission times of ultrasonic transmissions emitted from the ultrasonic transmitters. Likewise, ultrasonic transmitter 1042 produces a plurality of ultrasonic transmissions 156i, 1562 to 156s (on a carrier frequency ¾ ) whose transmission times are respectively, tA , tn , and t„.

Ultrasonic transmitter 104N produces a plurality of ultrasonic transmissions 158^ 1582 to 158T (on a carrier frequency ) whose transmission times are respectively, t3 , t]Q , and tl6 .

As stated above, each mobile electronic device includes a mobile device internal clock for maintaining its respective system time. In particular, mobile device internal clock 136 is a time keeping mechanism (i.e., a clock) that maintains a mobile device system time. Mobile electronic devices, such as cellular telephones are typically associated (e.g., registered) with one cellular subscription of a particular cellular communications network, at one particular instance. This time keeping mechanism of the mobile electronic device is synchronized with the system time of a particular cellular communications network. The cellular communications network to which a particular mobile electronic device is registered with is referred herein as a registered celiuiar network. The disclosed technique is applicable to mobile electronic devices that are simultaneously registered with a plurality of cellular subscriptions, corresponding to a plurality of respective cellular communications networks (e.g., mobile cellular phones with dual subscriber identification modules (SIMs)). Generally, mobile electronic devices 106 5 1062 to 106M are each operative to be in RF communication with at least one of cellular base stations 1081 ( 1082 to 108P. Suppose mobile electronic device 106-, is registered with cellular network 110Q. Figure 1 illustrates transmission of time-synchronization signal 152 by cellular base station 1083 (part of cellular network 110Q). Mobile device RF communication module 134 of mobile electronic device 106i receives the transmitted time-synchronization signal 152, via mobile device antenna 146. Upon reception of time-synchronization signal 152, mobile device processor 132 records the cellular communications network system time of cellular communication network 110Q. For mobile electronic devices that are registered with more than one cellular communications network, mobile device processor 132 keeps a record of all cellular communications network system times of the respective cellular base stations (i.e., and their respective time differences) that are within their respective communications range. In this case, mobile device processor 132 synchronizes the mobile device system time of mobile electronic device 106! with either one of the cellular communications network system times (e.g., that which is kept, by cellular base station 1082 and 1083). For example, mobile device processor 132 synchronizes mobile device system time of mobile electronic device 106·] with cellular communications network system time of cellular base station 1083. As the cellular communications network system time of cellular base station 1082 is known, mobile device processor 132 calculates and records the time differences between the mobile device system time of mobile electronic device 106i and that of cellular communications network system times belonging to the other respective cellular base stations.

Reference in now further made to Figure 4, which is a schematic illustration of synchronization of the system time of an ultrasonic transmitter with a reference cellular network system time, and a cellular networks time table that is provided to a mobile electronic device. Figure 4 illustrates three different cellular networks 110 t 1102, and 110Q respectively designated for brevity as "A", "B" and "C". Each cellular network maintains its respective cellular network system time, which is recorded in a cellular networks system time table 201. Particularly, cellular networks A, B, C each respectively maintain cellular network system times 202^ 2022, and 202Q. Cellular networks system time table 201 is a record of the cellular network system times of different cellular networks (particularly, that of cellular networks A, B and C). Cellular networks system time table 201 specifies that the cellular network system time of cellular network A is 00:00, whereas that of cellular networks B and C it is respectively 00:01 and 00:02 (i.e., in time units, represented for example in a minutes:seconds format). It can therefore be known, from cellular networks system time table 201 , for example, that the cellular network system time of cellular network B (i.e., 2022) lags one second behind that of cellular network A (i.e., 202!), which in turn is two seconds ahead of that of cellular network C (i.e., 202Q). In accordance with the supposition that mobile electronic device 106! is registered with cellular network 1 10Q, mobile device RF communication module 134 relays data pertaining to time-synchronization signal 152 to mobile device processor 132, which registers the received time-synchronization signal with mobile device interna! clock 136. Based upon the received time-synchronization signal 152, mobile device processor 132 synchronizes cellular network system time 202Q, of cellular network C with a mobile device system time 206i of mobile electronic device 106i (maintained by mobile device internal clock 136).

The ultrasonic transmitters (e.g., ultrasonic transmitter 104^ select a common (e.g., according to an algorithm, by default, etc.) reference cellular network system time of a respective cellular network (i.e., associated with one of cellular networks A, B and C) for which their respective system times would be synchronized with. For example, cellular networks system time table 201 specifies (Figure 4) that the cellular network system time 202-] of cellular network A is selected as the reference cellular network system time (indicated in Figure 4 as "REF."). Consequently, an ultrasonic transmitter system time 204-I of ultrasonic transmitter 04 (i.e., maintained by internal clock 118) is synchronized with the reference cellular network system time (i.e., cellular network system time 202^. Mobile device processor 132 calculates the respective cellular network system time differences according to cellular networks system time table 201 upon reception thereof by mobile electronic device 106^ Each mobile electronic device (e.g., 106!), by employing cellular networks system time table 20 , calculates a cellular network system time difference defined to be the time difference between its own system time and the reference cellular network system time. In Figure 4 for example, the cellular network system time difference between the mobile device system time 206! and the reference cellular network system time (i.e., 202^ is a two second time lag. In such a manner, different mobile electronic devices, registered with different cellular networks, are able to correlate their respective cellular network system time differences with respect to the reference cellular network system time of the ultrasonic transmitters. Thus, mobile electronic device 06 has the exact time when an ultrasonic transmission was emitted by an ultrasonic transmitter.

The ultrasonic transmitters (e.g., ultrasonic transmitter 104 provide cellular networks system time table 201 to the mobile electronic devices (e.g., mobile electronic device 106-t) (illustratively represented by following a route indicated by arrows 210 and 212 in Figure 4) via coded data in the ultrasonic transmissions. Alternatively, cellular networks system time table 201 is provided to the mobile electronic devices via an SMS message sent by the ultrasonic transmitters. Further alternatively, an external server 214 (detailed in accordance with another embodiment of the disclosed technique, described hereinbelow in conjunction with Figure 5) provides (i.e., transmits) cellular network system time table 201 to the mobile electronic devices (e.g., 106!) (illustratively represented by following a route indicated by arrows 216 and 218 in Figure 4). Further alternatively, cellular networks system time table 201 may be downloaded from the Internet.

Mobile electronic devices 106^ 1062 to 106M located within detection space 102 (Figure 2) are operative to detect the plurality of ultrasonic transmissions produced by the ultrasonic transmitters. Specifically, mobile electronic devices 106^ 1062 to 106M receive ultrasonic transmissions 154 t 1542 to 154R from ultrasonic transmitter 104i, ultrasonic transmissions 156^ 1562 to 156s from ultrasonic transmitter 1042 and ultrasonic transmissions 1581 f 1582 to 158T from ultrasonic transmitter 104N (Figure 2). For the purpose of elucidating the disclosed technique, with no loss of generality, the following description details the reception of ultrasonic transmissions by mobile electronic device 1 06·, (Figure 1 ).

Mobile electronic device 106τ is operative to detect at least part of the ultrasonic transmissions emitted from the ultrasonic transmitters, depending, to an extent, on its current relative location with respect to the respective positions of the ultrasonic transmitters as well as the prevailing environmental factors that affect the detection space 102 (e.g., such as when there are moving obstacles therein, etc.). Since ultrasonic transmissions emitted from each ultrasonic transmitter is distinctive, mobile electronic device 106! attributes each detected ultrasonic transmission to the ultrasonic transmitter source (i.e., recognition of the source of an ultrasonic transmission).

With reference to Figure 3, mobile electronic device 106 receives, via electroacoustic transducer 144, ultrasonic transmission 154i from ultrasonic transmitter 104! at time t6 (reception 160^ ), ultrasonic transmission 156τ from ultrasonic transmitter 1042 at timetg (reception

1602), and ultrasonic transmission 158-j from ultrasonic transmitter 1043 at ti me tn { reception 160w)- Electroacoustic transducer 144 (typically embodied in form of a microphone) converts these ultrasonic transmissions into corresponding electrical signals (not shown). ADC 142 converts the analog electrical signals, detected by electroacoustic transducer 144, into digital form and relays them to mobile device processor 132. Signals received by electroacoustic transducer 144 are typically amplified by an amplifier (not shown). Alternatively, the amplifier is integrated into mobile device processor 132.

Once the ultrasonic transmitters are time-wise-synchronized with the mobile electronic devices, the propagation delay of ultrasonic transmissions (i.e., the duration of time that ultrasonic signals travel from the ultrasonic transmitters to the destination mobile electronic device) are calculated. Mobile device processor 132 measures the propagation delay of the ultrasonic transmissions by calculating the difference between the reception time of the ultrasonic transmissions and their respective transmission times (as specified in ultrasonic transmission code 162). In particular, mobile device processor 132 measures the propagation delay of ultrasonic transmission 154·) (ί.β.,Δί, = t6-t2), the propagation delay of ultrasonic transmission 156τ (i.e., At2 =t -t4) and the propagation delay of ultrasonic transmission 158i (i.e., =tn-t3). Given the speed of sound, c, within detection space 102, mobile device processor 32 determines the three-dimensional (3-D) position of mobile electronic device 106!, denoted by the variables (x,y,z), by solving the following system of N linear equations:

{x-xxf +{y-yf +{z-zxf = c2-At2

(x - x2 f + (y - y2 f + (z - z2 f = c2■ At2

: (3)

(x - xN f + {y - yN† + (z- zN f =c2- ΔίΝ 2

where (^,^,,ζ,), (x2,y2,z2) , and (xN,yN,zN) represent known respective coordinate positions of ultrasonic transmitter 104-1, ultrasonic transmitter 1042 and ultrasonic transmitter 104N. Based on the measured propagation delays and the speed of sound in detection space 102, mobile device processor 132 calculates the respective distances from mobile electronic device 106^ to the ultrasonic transmitters, whose ultrasonic transmissions are detected (by mobile electronic device 106^, according to system of linear equations (3). Hence, the position of mobile electronic device 106! is determined in relation to its distance from each of the ultrasonic transmitters having their position in detection space 102 known. The ultrasonic transmitters are installed in such an alignment and orientation {e.g., on walls, ceilings, and the like) that substantially every location within detection space 102 is covered by overlapping transmission coverage areas of least three ultrasonic transmitters (with the exception of certain blind spots that may be present in detection space 102). In this manner, there are at least three equations for the three position variables to be solved. Generally, the more there are ultrasonic transmissions from different ultrasonic transmitters that are detectable by a mobile electronic device at a given location (i.e., the more there are equations), the more accurate the determined position of the mobile electronic device would be.

Mobile device processor 132 measures the phase difference between the received signals and the transmitted signals. The propagation delay of a received ultrasonic transmission is associated with the difference thereof. Mobile device processor 132 correlates the propagation delay of each of the received signals with their respective phase differences so as to facilitate calculation of distances between the respective ultrasonic transmitters and the mobile electronic device. This correlation further contributes in reducing the adverse effects of ultrasonic reflections on position estimation. Since the propagation-delay-to-phase-shift correlation of reflected ultrasonic transmissions is different to that of non-reflected ultrasonic transmissions, mobile device processor 132 may process only those ultrasonic transmissions that are within bounds of a predetermined correlation range (i.e., in effect, filtering out reflected ultrasonic transmissions).

The inherent time delay due to propagation of signals through the internal circuitry (not shown) of the components of system 100 may also be taken into consideration. The precision of position estimation is typically within a few centimeters.

In a simpler case, where determination of the two-dimensional (2-D) position of the mobile electronic device is sufficient, (when determination of the 3-D position is unnecessary), as for example in the case of a moving person (carrying the mobile electronic device) on a particular floor of a building, the reception of ultrasonic transmissions of only two ultrasonic transmitters are required (although, more than two are typically employed). In this case, system of linear equations (3) for N ultrasonic transmitters reduces to:

(x - x, )2 + (y - y] f + z 2 = c2 - At 2

(x - x2)2 + (y - y2)2 + z2 2 = c2 - At2 2

; ( )

(x - xN† + (y - yN f + z 2 = c2■ AtN 2

where (x^y^ , (¾,½) , to (½, v) represent known coordinate positions of ultrasonic transmitter 104-1 , ultrasonic transmitter 1042 and ultrasonic transmitter 104N, respectively, and constants z,2 , ∑2 2 to ∑N 2 are the respective known distances (i.e., vertical heights, along a Z-axis) of ultrasonic transmitters 104^ 04^ to 104N from the detection plane (X-Y plane). The 2-D position of mobile electronic device 10^ to be solved is denoted by the variables 0, j>) . In the system of linear equations (4) at least two equations for the two position variables are to be solved by mobile device processor 132, thereby determining the 2-D position of mobile electronic device 106-t within detection space 102.

The determination of position of a mobile electronic device (e.g., 106!) in the one-dimensional (1-D) case, such as along a narrow passageway (e.g., a corridor, an isle of a store, and the like), reception of ultrasonic transmissions of only one ultrasonic transmitter is required (although, more than one may be typically employed). In such a setting, at least one ultrasonic transmitter is installed along the narrow passageway, so that localization of a mobile electronic device along the narrow passageway would require determination of only one variable. In this case, mobile device processor determines (i.e., estimates) the position of mobile electronic device 106i by solving the following system of N linear equations for N ultrasonic transmitters: (x - j j ) + z, = c · Δί,

(x - , ) + z2 = c - Ai2

: (5)

where , x2 , and xN represent known positions of ultrasonic transmitter 104-1, ultrasonic transmitter 1042 and ultrasonic transmitter 104N, respectively, along the narrow passageway, and constants z, , z2 to zN are the respective known distances (i.e., vertical heights, along a

Z-axis) of ultrasonic transmitters 104-|, 104-1 , to 104N from the 1-D detection line (X line). The 1-D position of mobile electronic device 06-1 along the narrow passageway to be solved is denoted by the variable x . The position of mobile electronic device 06! would be known in relation to its respective distances from each of the N ultrasonic transmitters (i.e. x- xj , — JC2 IJ and as determined according to the system of linear equations (5). As in the 3-D and 2-D cases, generally, the more there are ultrasonic transmissions from different ultrasonic transmitters that are detectable by mobile electronic device 106 along the narrow passageway, the more accurate the determined (i.e., estimated) position would be. If in this case for example, we suppose that there are more than two ultrasonic transmitters employed ( N> 2), mobile device processor 132 may average these determined distances to yield an estimated position of mobile electronic device 106-1 with respect to the ultrasonic transmitters. Moreover, given that there are more equations than variables, mobile device processor 132 may further determine the speed of sound of the ultrasonic transmissions within detection space 102 (by the systems of linear equations (3), (4) and (5)), as the speed of sound may vary for it is not universally constant, but dependent upon the propagating medium through which the sound waves propagate. Generally, the speed of sound of a sound wave (e.g., an ultrasonic transmission) is dependent (among other factors) on the square root of the temperature of the medium (e.g., air within detection space 102) through which it propagates. For example, the speed of sound in dry air at a temperature of 20 °C (68 °F) is 343.2 meters per second (1 ,126 ft s), whereas at a temperature of 30 °C (86 °F) it is 349 meters per second (1 ,145 ft s). Given the temperature of a medium and its composition (as well as other parameters, such as the ratio of specific heats, i.e., the adiabatic index - its value for air is 1.4)), it is possible to calculate the speed of sound in that medium. For facilitating calculation of the speed of sound in detection space 102, each ultrasonic transmitter is equipped with thermometer 130 (Figure 1) that measures the ambient temperature in its respective surroundings and provides the measured temperature to processor 112, which in turn calculates the speed of sound in the respective surrounding medium. Each of ultrasonic transmitters 104-1 , 1042 and 104N transmits (e.g., ultrasonically) the calculated speed of sound in its respective surroundings c, , c2 andc^ , respectively to mobile electronic device 106^ The speed of sound information may be coded into the ultrasonic transmissions. Alternatively, given an initial calculation, any change in speed of sound information is transmitted as a separate transmission (not shown). Based on received values of c, , c2 and cN , by mobile electronic device 106!, mobile device processor 132 may calculate sound speed gradients in order to produce a sound speed gradient map (not shown) according to a temperature map (not shown) of detection space 102. Consequently, systems of linear equations (3), (4) and (5) may be refined by using the calculated values ofc, , c2 andc^ . Mobile device processor 132 uses the calculated speed of sound values, from measured temperatures at respective locations within detection space 102 to fine-tune position estimation of mobile electronic device 106^ According to the disclosed technique, the mobile electronic device further employ inertial navigation to supplement ultrasonic positioning so as to enhance positional accuracy, especially at locations in detection space 102 where there is no or limited line-of-sight (LOS) between the mobile electronic device and the ultrasonic transmitters. INS 138 continuously measures changes in displacement of mobile electronic device 106 relative to a previous known position, (i.e., via dead reckoning), its orientation and its acceleration and generates an estimated inertial current position and auxiliary inertial state (e.g., mobile electronic device user step count, state of no movement, etc.) of mobile electronic device 106^ INS 138 typically includes accelerometers (for detecting change in velocity, i.e., acceleration/deceleration), and gyroscopes (for detecting change in orientation, i.e., via angular velocity). INS 138 derives an updated estimation of position (and velocity) of mobile electronic device 10Q-i by integrating changes in the displacements and orientations thereof. Mobile device processor 132 consolidates the estimated inertial current position with the estimated position generated from ultrasonic trilateration in the computation of the position of mobile electronic device 106-t in detection space.

Typical situations where the use of inertial navigation positioning may be advantageous to supplement ultrasonic positioning is when there is, for example, a blind spot, an obstruction in the communication of ultrasonic transmissions to mobile electronic device 106-1 , a malfunction to one or more of the ultrasonic transmitters, and the like. Mobile device processor 132 uses the estimated position of the mobile electronic device 106-1 as determined by use of ultrasonic positioning together with the estimated position as determined by INS 138 to obtain, in effect, enhanced position estimation. In particular circumstances, position estimation might be based exclusively on inertial navigation, which is rather known to experience from integration drift errors that are cumulative over time (in relation to an initial position). The rate at which such errors increase is approximately proportional to the time since the last ultrasonically determined position and in such circumstances mobile device processor 132 accounts for this time-dependent cumulative error by calculating the time-dependent position error range for each estimated position.

The disclosed technique is further operative to account for the Doppler shift of the detected ultrasonic transmissions caused by the movement of the mobile electronic devices with respect to the ultrasonic transmitters. According to the Doppler effect, there is a change in the frequency of a wave (i.e., the detected ultrasound transmissions) for a moving observer (i.e., a moving user carrying the mobile electronic device), relative to the source (i.e., an ultrasonic transmitter) of the wave. As a result, the detected frequency of the ultrasonic transmissions is either greater than or less than the frequency of the source of the ultrasonic transmissions, depending on whether the user is moving toward or receding (respectively) from the source of ultrasonic transmissions (i.e., the ultrasonic transmitter). For example, if we assume that the speed of sound is 343.2 m/s and the user is moving at a typical walking speed of 5 km/h toward the an ultrasonic transmitter that emits ultrasonic transmissions at a frequency of 20 kHz, the detected frequency of the ultrasonic transmissions would be 20,080.9 Hz. Such a shift (i.e., 80.9 Hz.) in the detected frequency of ultrasonic transmissions from ultrasonic transmitters may be used by mobile device processor 132 to calculate the velocity (i.e., speed and direction) of mobile electronic device 106-i with respect to the ultrasonic transmitters. Mobile device processor 132 processes this information together with the estimated position generated from ultrasonic trilateration and inertial navigation information in order to yield enhanced localization estimation. It is noted that the size of the transmission frequency sub-range that is allocated to each ultrasonic transmitter (e.g., via server station 170) is selected such that it wide enough to encompass variability of frequency shifts due to the Doppler effect. To preclude overlapping frequency sub-ranges (i.e., even at the mutual boundary frequency of neighboring sub-ranges), at least part of the allocated frequency sub-ranges may each be separated by respective frequency separation ranges.

A typical application of the disclosed technique involves localization of a plurality of moving individuals (i.e., users), each carrying a mobile electronic device in a detection space that may be, for example the interior spaces of a museum, a library, a supermarket, a mail, a warehouse, an exhibition hall, an indoor fair, an office, a store, and the like. At such places it may be advantageous to know one's (i.e., of a user) position with respect to known geographical references (i.e., the geolocation). For example, knowing one's location with respect to a floor plan of a museum, knowing where a particular consumable product is located in a supermarket with respect to one's current location, knowing where a particular store is located in a mall with respect to a one's current location in the mall, and the like. The disclosed technique is operative to provide an indoor geographical map of detection space 102 to mobile electronic devices 106^ 1062, and 106M, so that each of their respective current detected positions is superimposed on such a map. The indoor geographical map specifies various places of interest within detection space 102 and provides geographical reference points with respect to the location of a user as well as navigational cues (e.g., waypoints).

Reference is now further made to Figure 5, which is a schematic illustration of a system generally referenced 300 that includes a server station (i.e., a base station), constructed and operative in accordance with another embodiment of the disclosed technique. The embodiment of Figure 5 illustrates a centralized management configuration (i.e., in comparison to the decentralized configuration shown in Figure 1 ), whereby the each ultrasonic transmitter is in communication with a centralized management station.

System 300 of Figure 5 illustrates identical elements to those shown in Figure 1 (system 100), except for the added server station 170 (i.e., implemented as the centralized management station). Server station

170 includes an RF 171 communication module, a server processor 174, a server memory unit 176, a server internal clock 178, communication module an I/O interface 182, and a server station antenna array 184. RF

171 communication module includes a cellular communication module 172 and a wireless communication module 180 (e.g., Wi-Fi based). Server processor 174 is coupled with cellular communication module 172, server memory unit 176, server internal clock 178, I/O interface 182, and with wireless communication module 180. Cellular communication module 172 and wireless communication module 180 are part of RF communication module 171. Server station antenna array 184 is coupled with communication module RF communication module 171. Server station 170 is typically located in the general neighborhood of detection space 102, such that it is in communication range of cellular base stations 108^ 1082 to 108P. Figure 5 illustrates that server station 170 is located exteriorly to detection space 102. Alternatively, server station 170 is located within detection space 102 (not shown). Cellular communication module 172 is operative to receive (via server station antenna array 184) time-synchronization signals (not shown) from cellular base stations 1081 t 1082 to 108p that are within communications range and to relay information pertaining to each of the time-synchronization signals to server processor 174. Server processor 174 records (i.e., in server memory unit 176) system times of each of the cellular base stations 108^ 082 to 108P, according to respective received time-synchronization signals, with respect to a server system time that is maintained by server internal clock 178. Server station 170 may be further connected to the Internet. Server station 170 may typically be implemented as an industry-standard Internet server.

An indoor geographical map (not shown) of detection space 102 is stored in server memory unit 176, as well as the location of each of ultrasonic transmitters 1041 f 1042, and 104N. Alternatively, the indoor geographical map is stored on a remote server (not shown) connected to the Internet. Server memory unit 176 further stores the electronic identification numbers associated with each of the ultrasonic transmitters and their respective carrier transmission frequencies (i.e., , fCi , f^ , etc.), as well as the ultrasonic transmission code 162. Wireless communication module 180 is operative to provide wireless data connection between server station 170 and the mobile electronic devices via for example, Wi-Fi, WiMAX, Bluetooth, and the like. Users carrying mobile electronic devices 106i, 1062, and 106M, desiring to know their respective geolocation in detection space 102 download the indoor geographic map from server station 170. Alternatively, server station may send a short message service (SMS) message detailing an Internet address from which the indoor geographic map may be downloaded to those mobile electronic devices that enter detection space 102 (e.g., via registration of the mobile electronic device with one of the celiuiar base stations in the mobile communication coverage area thereof). Further alternatively, application software (an "app") that includes the indoor geographic map may be integrated into or downloaded to a mobile electronic device. Execution of the application software on the mobile electronic device determines its geolocation in detection space 102 and further allows a user to submit queries for finding locations of interest in detection space 102.

Server processor 174 (Figure 5) of server station 170 calculates the cellular network system time differences, and records them in cellular networks time table 201 , stored within server memory unit 176. Server station 170 provides (e.g., transfers, transmits via an SMS message, via information encoded in the "app", via Wi-Fi, etc.) cellular networks time table 201 as well as ultrasonic transmission code 162 to mobile electronic devices 1061 t 1062, and 106M. This transfer is illustrated in Figure 4, whereby server station 170 (Figure 5), represented as external server 214 (Figure 4), transmits cellular system time table 201 to mobile electronic device 106<i (via the route indicated by arrows 216 and 2 8).

Firstly, server station 170 controls various operational aspects of the ultrasonic transmitters. I/O interface 182 allows a user (e.g., an administrator, "superuse , operator) to control and configure system 100. Server station 170 can activate and deactivate a particular ultrasonic transmitter by sending commands contained in an SMS message, via the cellular network. Once an ultrasonic transmitter is activated it registers with server station 170 by sending its unique electronic identification number along with its operational status via an SMS message to server station 170. In this manner, only those ultrasonic transmitters, which have their respective unique identification numbers stored in server memory unit 176, are operational.

Secondly, server station 170 assigns to each ultrasonic transmitter 104^ 1042 and 104N its respective ultrasonic transmission code. The ultrasonic transmission code may include the ultrasonic emission time sequence code, the chirp type code, the carrier transmission frequencies of each ultrasonic transmitter, combinations thereof, and the like. The ultrasonic emission time sequence code defines the time intervals between successive chirps. The chirp type code defines the types of chirps utilized in a particular sequence of chirps. The carrier transmission frequencies q , fCi and , are assigned such that each carrier transmission frequency lies within a respective allocated (and substantially non-overlapping) transmission frequency sub-range within the detectable frequency bandwidth. For example, server station 170 allots a transmission frequency sub-range of 20 kHz to 20.1 KHz. to ultrasonic transmitter 10A^ and further assigns to it a carrier transmission frequency of 20,050 Hz. Server station 170 may change the allotted frequency sub-ranges and their associated carrier transmission frequencies of the ultrasonic transmitters (e.g., by multiplexing according to a particular algorithm).

Thirdly, server station 170 controls other parameters associated with the ultrasonic transmission code of the ultrasonic transmitters, such as the modulation frequency ( fm ) and the amplitude { A ) of the ultrasonic transmission signal. Server station 170 may, for example, limit the ultrasonic transmission range of the signals of a particular ultrasonic transmitter (i.e., by reducing it respective ultrasonic transmission signal amplitude) in order to reduce ineffectual ultrasonic wave reflections from obstacles and reflective surfaces (e.g., windows) that may be present in detection space 102. In this manner, the volumetric ultrasonic transmission coverage area (i.e., the area where ultrasonic transmissions can be received for the purpose of localization) is adapted to the geometrical infrastructure of detection space 102. Optionally, the ultrasonic transmitters are mounted on motorized mechanisms (not shown) that allow adjustment of their orientation (i.e., the direction at which the ultrasonic transmissions are directed) via server station 170.

Fourthly, server station 170 may perform the computational task (i.e., solving equations (3), (4), and (5)) of position estimation so as to reduce the computational load on mobile electronic devices 106 τ 1062, and 106 for which their respective position in detection space 102 is to be estimated. The mobile electronic device (e.g., 106-i ) for which this case is implemented on (e.g., as a voluntary feature) transmits (e.g., via an SMS message) the measured propagation delays At , At2 , and AtN to server station 170 for processing. In response, server station 170 transmits the calculated estimated position of mobile electronic device 106! thereto, thereby reducing computational load on mobile electronic device 106^

Fifthly, server station 170 aggregates statistical information pertaining to the measured ambient temperatures in the respective surroundings of ultrasonic transmitters 104!, 1042, to 104Nl so as to produce a temperature map of detection space. The temperature map is consequently used to produce a corresponding sound speed gradient map, according to the calculated values ofc, , c2 andc^ . By continuously updating refined values c: , c2 and ¾ into systems of linear equations (3),

(4) and (5), the accuracies of previously estimated positions of the mobile electronic devices are enhanced accordingly.

Sixthly, system 300 is operative to generate an indoor map of the interior of detection space 102. The indoor map is generated such that each ultrasonic transmitter measures its distance to other ultrasonic transmitters (i.e., inter-transmitter distances) that are within its LOS. Given the measured distances between ultrasonic transmitters, an indoor map may be generated. For the purpose of indoor map generation, each ultrasonic transmitter 1041,... ,104N emits distinct ultrasonic emissions (e.g., 149), directed at other ultrasonic transmitters within its respective LOS. For the detection of these distinct ultrasonic transmissions, each ultrasonic transmitter 104 ,.., ,104N may further include an electroacoustic transducer (not shown) operative to detect at least part of the ultrasonic transmissions and to relay data pertaining to the detected ultrasonic transmissions to processor 112. Processor 112 calculates the distances of the particular ultrasonic transmitter (e.g., 104-i) to other ultrasonic transmitters, within its respective LOS, whose ultrasonic transmissions were detected, by measuring propagation delays of each of ultrasonic transmissions with respect to ultrasonic transmission code and with respect to reference time (i.e., time difference of arrival (TDOA) of ultrasonic transmissions), so as to generate an inter-distance indoor map between the different ultrasonic transmitters. Alternatively, data pertaining to the detected ultrasonic transmissions is transmitted to server station 170 via communication module 114. Server station 170 compiles a list of inter-distance measurements between different ultrasonic transmitters so as to generate an indoor map of detection space 102. Seventhly, system 300 may employ RF localization techniques to supplement ultrasonic localization and inertial navigation. For the purpose of elucidating the disclosed technique, and with no loss of generality, an RF localization technique that employs Wi-Fi will now described. It is pointed out that the principles of disclosed technique likewise apply to other types of RF communication standards, such as Bluetooth, ZigBee®, and the like.

Each ultrasonic transmitter 1 04<i 1 04N scans for wireless access points (not shown) that are available in its surroundings, and uploads the scan results to server station 1 70 (i.e., via its respective communication module 1 1 4). Common wireless access points include wireless routers. Each wireless router is characterized by a unique identifier (i.e., a basic service set identification (BSSID), such as media access control (MAC) address) and received signal strength indication (RSSI), as detected by an RF (Wi-Fi compatible) communication module. Additionally, a wireless access point may be identified by (typically a user-defined) service set identifier (SSID). Essentially, RF communication module 1 1 4 receives an RF signal (not shown) having corresponding identification. Basically, RF communication module 1 14 measures RSSI with its corresponding SSID and transmits these to server station 1 70. Server station 70 complies a list (not shown) of the respective wireless access points, as detected (if applicable) by each ultrasonic transmitter 1 041 , . .. , 1 04N. Such a list may typically include BSSID, SSID and RSSI data as detected by each of ultrasonic transmitters 104L . .. .1 04M in its respective effective detection area. Essentially, since RSSI measures signal strength of radio waves propagating from a source, the distance from that source may be roughly estimated according to the relationship between the strength of the detected signal and that of the transmitted signal. Given that the location of ultrasonic transmitters 1041 ? .. . , 1 04Ν are known in detection space 1 02 , as well as the estimated distances of the wireless access points to the ultrasonic transmitters 1 04 , . .. , 1 04N, server station 170 generates a map (i.e., via server processor 174) of the wireless access point locations in detection space 102. The estimated location of the wireless access points are transmitted to mobile electronic devices Ι Οδ^., . ,Ι ΟθΜ (e.g., through the mobile device application platform), thereby serving to further enhance localization of electronic devices ^ 06^... ,^ 0QM in detection space 102.

The mobile device application ("app") that is installed on the mobile electronic device may further perform a scan of ali wireless access points within its surroundings and provide the data (i.e., SSIDs' and RSSIs' via server station 170) to other electronic devices (e.g., "crowdsourcing"), so as to enhance localization for other users of other mobile electronic devices. Particularly, mobile device RF communication module 134 receives an RF signal of known transmitted signal strength and identification (e.g., SSID) from a respective RF source (e.g., a Wi-Fi router). Mobile electronic device 106i measures the RSSI with corresponding SSID information of each received RF signal and compiles a list. Mobile device processor 32 compares the received signal strength of the respective RF signal (for each corresponding SSID) with the respective transmitted signal strength, thereby generating an estimated RF current position of mobile electronic device 106! in relation to the distance from the RF source. Mobile device processor 132 then consolidates the estimated RF current position into the computation of the position of mobile electronic device 106^ Each mobile device processor 132 may typically further consolidate the estimated location of the wireless access points, transmitted to mobile electronic devices 106 ,... , 06M, via server station 170, into the computation of their respective positions in detection space 102.

Combining the estimated location results (i.e., fusion) that are attained by the different localization techniques (i.e., ultrasonic, inertial, RF) may be achieved by employing a weighted average of the results (i.e., whereby the weights are determined by the projected error size), by use, for example, of a Kaiman filter.

System 300 thus supplements ultrasonic localization and inertial navigation with RF localization by performing continuous estimation of position that is based on RSSI so as to enhance localization of mobile electronic devices 106! 106M within detection space 102. This combined hybrid approach affords greater robustness, redundancy, and accuracy in comparison to methods that employ only a single localization modality.

Reference is now made to Figures 6A and 6B. Figure 6A is a schematic block diagram of a method, generally referenced 400, for determining position of a mobile electronic device located within a detection space, according to an embodiment of the disclosed technique. Figure 6B is a schematic block diagram of the continuation of the method from Figure 6A. In procedure 402, a network of ultrasonic transmitters is established, installed within a detection space. Each ultrasonic transmitter maintains a respective ultrasonic transmitter system time. With reference to Figures 1 and 2, a network of ultrasonic transmitters 104-t , 1042 to 104N is established and installed within detection space 102 (Figure 2). Each of ultrasonic transmitters 104-1 , 1042 to 104N maintains a respective ultrasonic system time, kept by its respective internal clock 118 (Figure 1).

In procedure 404, an ultrasonic transmission code is provided to the ultrasonic transmitters and to the mobile electronic device, for which its location within the detection space is to be determined in relation to respective positions of the ultrasonic transmitters. The mobile electronic device maintains a mobile device system time and is registered with a particular cellular network in a plurality of cellular networks. Each cellular network maintains its respective cellular network system time. The mobile device system time is synchronized with the particular cellular network system time by reception of a synchronization signal therefrom. With reference to Figures 1 , 2, 3, 4 and 5, server station 170 (Figure 5) provides (e.g., transmits) ultrasonic transmission code 162 (Figure 3) to ultrasonic transmitters 10^ (Figure 1 ), 1042 to 104N (Figure 2) and to mobile electronic devices 106-1 , 1062 to 106N (Figure 2), for which the respective locations of the latter within detection space 102 is to be determined, in relation to known respective positions (Figure 2} of ultrasonic transmitters 104^ 1042 to 104N. Mobile electronic device 061 (Figure 1 ) maintains a mobile device system time, kept by mobile device internal clock 136. Mobile electronic device 106! is registered with cellular network 1 10Q (Figure 1 ) via cellular base station 1083. Each cellular network maintains its respective cellular network system time. Mobile device system time 206i (Figure 4) is synchronized with cellular network system time 202Q by reception of synchronization signal 152 (Figure 1 ) therefrom.

In procedure 406, the system times of the ultrasonic transmitters are synchronized with a reference cellular network system time, by reception of a respective synchronization signal, of a respective cellular network. With reference to Figures 1 and 4, system time 204i (Figure 4) of ultrasonic transmitter 104^ is synchronized with cellular network system time 202 of cellular network A (i.e., 0^, by reception of synchronization signal 150 (Figure 1 ).

In procedure 408, cellular network system time differences of other cellular networks with respect to the system time of the reference cellular network are calculated and recorded in a cellular networks time table, by reception of respective synchronization signals from the other cellular networks. With reference to Figures 1 , 4 and 5, processor 1 12 (Figure 1 ) of ultrasonic transmitter 10A^ calculates cellular network system time differences of cellular networks A (110^, B (1 102), and C (110Q) in with respect system time 202i (Figure 4) of the reference cellular network (i.e., 202^) in cellular networks time table 201 (Figure 4), recorded in memory unit 128 (Figure 1 ), by reception of respective synchronization signals 150 (from cellular network 1 10^ and 152 (from cellular network 1 10Q ) (The Synchronization signal from cellular network 1 102 is not shown). Alternatively, server processor 174 (Figure 5) of server station 170 calculates the cellular network system time differences, and records them in cellular networks time table 201 , stored within server memory unit 176.

In procedure 410, the cellular time differences are provided to the mobile electronic device. The mobile electronic device calculates a cellular network system time difference between its system time and the reference cellular network system time, according to the cellular network time differences. With reference to Figures 1 , 4 and 5, the cellular network system time differences, calculated by ultrasonic transmitter 04-i (Figure 1 ), as specified in a cellular networks system time table 201 (Figure 4) is provided (e.g., transmitted) to mobile electronic device 06i (Figure 1). Alternatively, server station 170 (Figure 5) provides (e.g., transmits via an SMS message) the cellular network system time differences to mobile electronic device 06^ Mobile device processor 132 (Figure 1 ) calculates a cellular network system time difference between mobile device system time (Figure 4), and reference cellular network system time 202 ? according to the calculated cellular network time differences.

In procedure 412, ultrasonic transmissions are emitted by the ultrasonic transmitters within the detection space, according to the ultrasonic transmission code. Each ultrasonic transmission from a respective ultrasonic transmitter exhibits a particular sound emission signature. With reference to Figures 1 , 2 and 3 ultrasonic transmitters 104 f 1042 to 104|M each respectively emit ultrasonic emissions 1541 . R, 1561....S, to 158·) j (Figure 2) within detection space 102, according to ultrasonic transmission code 162 (Figure 3). Each of the ultrasonic transmissions 154 ( ,iR, 156 t . s, to 158<i ..iT is characterized by a respective sound emission signature (e.g., a respective carrier frequency , , and , Figure 2). In procedure 414, at least part of the ultrasonic transmissions is detected by the mobile electronic device. With reference to Figures 1 , 2 and 3, mobile electronic device 106-1 (Figure 1 ) detects ultrasonic transmissions 154-1 , 154-1 and 56^ (Figure 2), respectively received as corresponding receptions 160^ 1602 to 160w (Figure 3).

In procedure 416, the distances of the mobile electronic device from the respective ultrasonic transmitters, whose ultrasonic transmissions are detected by the mobile electronic device, are calculated by measuring the respective propagation delays of each of the ultrasonic transmissions with respect to the ultrasonic transmission code and the cellular network system time difference, so as to compute an estimated position of the mobile electronic device within the detection space in relation to respective positions of the ultrasonic transmitters. With reference to Figures 1 , 2, 3 and 4, mobile device processor 132 (Figure 1 ) calculates the distances of mobile electronic device 106i from ultrasonic transmitters 104-1 , 1042 to 104N (Figure 2), by measuring the respective propagation delays Δί, , At2 , and AtN (Figure 3) of each of respective ultrasonic transmissions 154-1 ,

156i , and 158-, with respect to ultrasonic transmission code 162 (Figure 3) and the calculated cellular network system time difference (derived from cellular networks system time table 201 of Figure 4), so as to compute an estimated position of mobile electronic device 06! within detection space 102 in relation to respective known positions of ultrasonic transmitters 1041 ( 1042 to 104N (Figure 2).

According to another embodiment of the disclosed technique, the deployed network of ultrasonic transmitters communicate with an RF communication server base station and form a wireless local area network (WLAN), to which they are time-synchronized with. The RF communication server base station functions as the reference time provider, which in turn maintains a reference time. A network time protocol (NTP) is used to synchronize each of the internal clocks of the ultrasonic transmitters with the reference time. RF communication between the ultrasonic transmitters and the RF communication server base station may employ various protocols, such as, for example, Wi-Fi (IEEE 802.11 ), Bluetooth (IEEE 802.15.1 ), ZigBee® (IEEE 802.15.4), ultra-wideband (UWB - IEEE 802.12.3), and the like. Alternatively, at least part or all of the ultrasonic transmitters are time-synchronized to the reference time by way of wired communication (e.g., a wired local area network (LAN), via power line communication (PLC), etc.) to the RF communication server base station.

Reference is now made to Figure 7, which is a schematic illustration of a system, generally referenced 301 , for determining position of a mobile electronic device located within a detection space, constructed and operative in accordance with another embodiment of the disclosed technique. System 301 is substantially similar to system 300 except that time-synchronization between the internal clocks of the ultrasonic transmitters and the reference time is achieved via a NTP in a WLAN (e.g., Wi-Fi). Apart from the omitted cellular base stations 108i,..,108P, system 301 , as illustrated in Figure 7, includes substantially identical elements to those of system 300, shown in Figure 5. More specifically, system 301 includes a server station 370 (i.e., also denoted "RF communication server base station", similar to server station 170). Server station 370 includes an RF communication module 371 , a server processor 374, a server memory unit 376, a server internal clock 378, an I/O interface 382, and a server station antenna array 384. RF communication module 371 may typically include a cellular communication module and a wireless communication module (not shown - e.g., for Wi-Fi communication). Server processor 374 is coupled with communication module 371 , server memory unit 376, server internal clock 378, and with I/O interface 382. Server station antenna array 384 is coupled with RF communication module 371. Server station 370 is typically located in the general neighborhood of detection space 102, such that it is in communication range of ultrasonic transmitters 104i,..,104N. Server station 370 is located in a detection space 102, as shown in Figure 7. Clock 378 maintains a reference time. RF communication module 371 is operative to be in communication with RF communication module 1 14 as well as with mobile device RF communication module 134. RF communication module 1 14 of each of ultrasonic transmitters l OA^ 104N is operative to receive a time-synchronization signal 350 from the reference time provider {i.e., server station 370). RF communication module 1 14 of ultrasonic transmitter 104i receives time-synchronization signal 350 via antenna 126 and relays to processor 1 12 information pertaining thereto. Consequently, processor 1 12 synchronizes clock 1 18 with the reference time kept by clock 378 of server station 378 according to NTP clock synchronization algorithm. Thus, all respective clocks 1 18 of ultrasonic transmitters 104! 104N maintain the same reference time.

Alternatively, ultrasonic transmitters 104! 104N are time-wise synchronized to the reference time either during fabrication thereof, or prior to installation in detection space 102. Further alternatively, ultrasonic transmitters 1041,...,104N are time-wise synchronized to the reference time by way of wired communication to the reference time provider.

Similarly, internal clocks 136 of mobile electronic devices 106Ϊ,... ,106μ are also synchronized with the reference time. A time-synchronization signal 352 (typically a plurality thereof) is transmitted by RF communication module 371 of server station 370 via antenna array 384. RF communication module 114 of mobile electronic device 106! receives this time-synchronization signal via antenna 146 and relays to mobile device processor 132 information pertaining thereto. Based on this information, mobile device processor 32 synchronizes clock 136 with the reference time maintained by clock 378, according to NTP clock synchronization algorithm. Alternatively, other clock synchronization algorithms may be employed, such as precision time protocol (PTP), daytime protocol, clock sampling mutual network synchronization, reference broadcast time synchronization, and the like. It is noted that time-synchronization signal 350 may be identical to or substantially similar to time-synchronization signal 352.

In practice, users carrying mobile electronic devices Ι Οβ^.,. ,Ι ΟβΜ (e.g., a smartphone, a tablet computer) into detection space 102 (e.g., store, mall, warehouse, parking lot, exhibition, etc.) may download (beforehand, at their own discretion, or be prompted (e.g., via an SMS message, a QR (quick response) code advertisement, etc.)) to their mobile electronic device a computer-executable file (a program, application, "app") that includes searchable points of interest of the venue superimposed on an indoor geographic map of the premises (detection space 102). Display 148 is operative to display the geolocation of mobile electronic device 106 based on the computed estimated position of mobile electronic device 106! within detection space 102.

Reference is now made to Figure 8, which is a schematic block diagram of a method, generally referenced 450, for determining position of a mobile electronic device located within a detection space, according to another embodiment of the disclosed technique. In procedure 452, a network of ultrasonic transmitters is established, installed within a detection space. Each ultrasonic transmitter maintains a respective ultrasonic transmitter system time. With reference to Figures 7 and 2, a network of ultrasonic transmitters 104 1042 to 104N is established and installed within detection space 102 (Figure 2). Each of ultrasonic transmitters 1041 ; 1042 to 104N maintains a respective ultrasonic system time, kept by its respective internal clock 118 (Figure 7).

In procedure 454, an ultrasonic transmission code is provided to the ultrasonic transmitters and to the mobile electronic device, for which its location within the detection space is to be determined in relation to respective positions of the ultrasonic transmitters. The mobile electronic device maintains a mobile device system time. With reference to Figures 7, 2 and 3, server station 370 (Figure 7) provides (e.g., transmits) ultrasonic transmission code 162 (Figure 3) to ultrasonic transmitters 104i (Figure 7), 1042 to 104N (Figure 2) and to mobile electronic devices 106·,, 1062 to 106N (Figure 2), for which the respective locations of the latter within detection space 102 is to be determined, in relation to known respective positions (Figure 2) of ultrasonic transmitters 104^ 1042 to 104N. Mobile electronic device 06-\ (Figure 7) maintains a mobile device system time, kept by mobile device internal clock 136. The system time of mobile electronic device 106i is maintained by clock 136 (Figure 7).

In procedure 456, the system times of the ultrasonic transmitters are synchronized with a reference time, by reception of a respective synchronization signal, from a reference time provider. With reference to Figure 7, the system time of ultrasonic transmitter 104-1 , which is maintained by clock 118, is synchronized with the reference time, by reception of synchronization signal 350 from the reference time provider (i.e., server station 370).

In procedure 458, the reference time is provided to the mobile electronic device. The mobile electronic device calculates a mobile device system time difference between the mobile device system time and the reference time. With reference to Figure 7, RF communication module 134 receives via mobile device antenna 146 information pertaining to the reference time from sever station 370. Mobile device processor 132 calculates the mobile device system time difference between the mobile device system time and the reference time. Alternatively, information pertaining to the reference time may be maintained by a mobile device application, which is downloaded to mobile electronic device 106^ (e.g., from the Internet, from server memory 376, etc.).

In procedure 460, ultrasonic transmissions are emitted by the ultrasonic transmitters within the detection space, according to the ultrasonic transmission code. Each ultrasonic transmission from a respective ultrasonic transmitter exhibits a particular sound emission signature. With reference to Figures 7, 2 and 3 ultrasonic transmitters 104-1 , 1042 to 104N each respectively emit ultrasonic emissions 154! . Rl 156! s, to 158i ,,.,τ (Figure 2) within detection space 102, according to ultrasonic transmission code 162 (Figure 3). Each of the ultrasonic transmissions 54 t..iR) 56I i iS. to 58i, T is characterized by a respective sound emission signature (e.g., a distinct time sequence code, a distinct chirp type code, a respective carrier frequency fCi , ¾ , and f , Figure 2).

In procedure 462, at least part of the ultrasonic transmissions is detected by the mobile electronic device. With reference to Figures 7, 2 and 3, mobile electronic device 106! (Figure 1 ) detects ultrasonic transmissions 1541 r 154i and "ϊ δβϊ (Figure 2), respectively received as corresponding receptions 160i, 1602 to 160w (Figure 3).

In procedure 464, the distances of the mobile electronic device from the respective ultrasonic transmitters, whose ultrasonic transmissions are detected by the mobile electronic device, are calculated by measuring the respective propagation delays of each of the ultrasonic transmissions with respect to the ultrasonic transmission code and the reference time, so as to compute an estimated position of the mobile electronic device within the detection space in relation to respective positions of the ultrasonic transmitters. With reference to Figures 7, 2 and 3, mobile device processor 132 (Figure 7) calculates the distances of mobile electronic device 106! from ultrasonic transmitters 1041 r 1042 to 104N (Figure 2), by measuring the respective propagation delays At, , At2 , and AtN (Figure 3) of each of respective ultrasonic transmissions 154-1 , 156i, and 158i with respect to ultrasonic transmission code 162 (Figure 3) and the reference time as maintained by server station 370 (Figure 7), so as to compute an estimated position of mobile electronic device 106! within detection space 102 in relation to respective known positions of ultrasonic transmitters 104! , 1042 to 104N (Figure 2).

It will be appreciated by persons skilled in the art that the disclosed technique is not limited to what has been particularly shown and described hereinabove. Rather the scope of the disclosed technique is defined only by the claims, which follow.

Claims

1. A system for estimating position of a mobile electronic device that is located within a detection space, the mobile electronic device includes an electroacoustic transducer, a mobile device processor coupled with the electroacoustic transducer, and a mobile device radio frequency (RF) communication module operative to receive a time-synchronization signal from a reference time provider, the reference time provider maintains a reference time, the mobile electronic device maintains a mobile device system time, the mobile electronic device is provided with an ultrasonic transmission code and the reference time, the system comprising:
at least one ultrasonic transmitter located within said detection space and distanced apart from said mobile electronic device, said at least one ultrasonic transmitter is provided with said ultrasonic transmission code, each of said at least one ultrasonic transmitter respectively maintains an ultrasonic transmitter system time, said at least one ultrasonic transmitter comprising:
a processor;
an RF communication module operative to receive said time-synchronization signal from said reference time provider, said RF communication module is coupled with said processor, said processor synchronizes said ultrasonic transmitter system time with said reference time, by reception of said time-synchronization signal; and
an ultrasonic electroacoustic emitter, coupled with said processor, said ultrasonic electroacoustic emitter emits an ultrasonic transmission within said detection space according to said ultrasonic transmission code, said ultrasonic transmission characterized by a particular sound emission signature; wherein said electroacoustic transducer detects at least part of said ultrasonic transmission, said mobile device processor calculates a mobile device system time difference between said mobile device system time and said reference time, said mobile device processor calculates distances of said mobile electronic device to each of said at least one ultrasonic transmitter whose ultrasonic transmissions are detected by said mobile electronic device, by measuring respective propagation delays of each of said ultrasonic transmissions with respect to said ultrasonic transmission code and to said mobile device system time difference, so as to compute an estimated said position of said mobile electronic device.
2. The system according to claim 1 , wherein said reference time provider is selected from at least one cellular network, each of said at least one cellular network respectively maintains a cellular network system time.
3. The system according to claim 2, wherein said reference time to which each of said at least one ultrasonic transmitter is said synchronized with, corresponds to one of said at least one cellular network, denoted a reference cellular network system time.
4. The system according to claim 3, wherein said mobile electronic device is registered with one of said at least one cellular network, denoted a registered cellular network, said mobile device system time is synchronized with respective said cellular network system time, by reception of said time-synchronization signal.
5. The system according to claim 4, wherein said mobile electronic device is provided with a cellular networks time table that specifies respective time differences between said reference cellular network system time and each one of said cellular network system time.
6. The system according to claim 5, wherein said mobile device processor calculates said distances, by measuring respective said propagation delays further with respect to a cellular network system time difference between said reference cellular network system time and said respective network system time of said registered cellular network, according to said cellular networks time table.
7. The system according to claim 1 , wherein said ultrasonic transmission code specifies at least one transmission time of said ultrasonic transmission.
8. The system according to claim 1 , wherein said particular sound emission signature is defined by at least one selected from a list consisting of:
frequency of said ultrasonic transmission;
modulation of said ultrasonic transmission;
timing sequence of a plurality of said ultrasonic transmission; frequency deviation of said ultrasonic transmission;
pattern sequence of a plurality of said ultrasonic transmission; and
amplitude of said ultrasonic transmission.
9. The system according to claim 1 , further comprising an inertial navigation system (INS) coupled with said mobile device processor, said INS generates an estimated inertial current position and an auxiliary inertial state of said mobile electronic device, said mobile device processor consolidates said estimated inertial current position into computation of said position of said mobile electronic device.
10. The system according to claim 1 , further comprising a server, which includes a server processor, a server RF communication module, and a server memory unit, said server RF communication module and said server memory unit are coupled with said server processor, said server RF communication module is operative to be in communication with said RF communication module and said mobile device RF communication module.
11. The system according to claim 10, wherein said server RF communication module transmits said ultrasonic transmission code to said RF communication module and to said mobile device RF communication module.
12. The system according to claim 1 , wherein said reference time provider employs at least one time synchronization method, selected from the list consisting of:
network time protocol (NTP);
precision time protocol (PTP);
daytime protocol;
clock sampling mutual network synchronization; and
reference broadcast time synchronization.
13. The system according to claim 12, wherein said reference time provider is said server.
14. The system according to claim 1 , further comprising a display for displaying a geolocation of said mobile electronic device in said detection space, based on said estimated said position.
15. The system according to claim 1 , wherein said mobile device RF communication module receives at least one RF signal of known transmitted signal strength and identification transmitted respectively, from a respective RF source, said mobile device processor compares received signal strength of said respective RF signal with respective said transmitted signal strength, so as to generate an estimated RF current position of said mobile electronic device in relation to distance to said RF source, said processor consolidates said estimated RF current position into computation of said position of said mobile electronic device.
16. The system according to claim 13, wherein said RF communication module receives at least one RF signal having corresponding identification, said RF communication module measures received signal strength, transmitted respectively from an RF source, said RF communication module transmits said received signal strength with said corresponding identification to said server, said server generates a list of said received signal strength with said corresponding identification and transmits said list to said mobile electronic device, said mobile electronic device receives said at least one RF signal having said corresponding identification and further measures received signal strength thereof so as to generate a mobile list, said mobile electronic device consolidates said list and said mobile list into computation of said position of said mobile electronic device.
17. The system according to claim 12, wherein said at least one ultrasonic transmitter further includes an electroacoustic transducer for detecting said ultrasonic transmission emitted from another one of said at least one ultrasonic transmitter, so as to measure respective inter-transmitter distances between each of said at least one ultrasonic transmitter, whose said uftrasonic transmission is detected, and respective said at least one ultrasonic transmitter whose said ultrasonic transmission is said emitted, whereby said respective inter-transmitter distances are transmitted via said RF communication module to said server so as to generate an inter-transmitter distance map.
18. A method for estimating position of a mobile electronic device that is located within a detection space, in relation to respective positions of at least one ultrasonic transmitter, each of at least one ultrasonic transmitter maintains a respective ultrasonic transmitter system time, said mobile electronic device is operative to receive a time-synchronization signal from a reference time provider, said reference time provider maintains a reference time, said mobile electronic device maintains a mobile electronic device time, the method comprising the procedures of:
providing an ultrasonic transmission code to said mobile electronic device and to said at least one ultrasonic transmitter; synchronizing said ultrasonic transmitter system time of each respective one of said at least one ultrasonic transmitter, with said reference time;
providing said reference time to said mobile electronic device, where said mobile electronic device calculates a mobile device system time difference between said mobile device system time and said reference time;
emitting an ultrasonic transmission, characterized by a particular sound emission signature, according to said ultrasonic transmission code;
detecting at least part of said ultrasonic transmission; and calculating distances of said mobile electronic device to each of said at least one ultrasonic transmitter, whose ultrasonic transmissions are detected by said mobile electronic device, by measuring respective propagation delays of each of said ultrasonic transmissions with respect to said ultrasonic transmission code and with respect to said mobile device system time difference, so as to compute an estimated said position of said mobile electronic device.
19. The method according to claim 18, wherein said reference time provider is selected from at least one cellular network, each of said at least one cellular network respectively maintains a cellular network system time.
20. The method according to claim 19, wherein said reference time to which each of said at least one ultrasonic transmitter is said synchronized with corresponds to one of said at least one cellular network, denoted a reference cellular network system time.
21. The method according to claim 20, wherein said mobile electronic device is registered with one of said at least one cellular network, denoted a registered cellular network, said mobile device system time is synchronized with respective said cellular network system time, by reception of said time-synchronization signal.
22. The method according to claim 21 , further comprising a procedure of providing to said mobile electronic device, a cellular networks time table that specifies respective time differences between said reference cellular network system time and each one of said cellular network system time.
23. The system according to claim 22, further comprising a procedure of calculating said distances, by measuring respective said propagation delays further with respect to a cellular network system time difference between said reference cellular network system time and said respective network system time of said registered cellular network, according to said cellular networks time table.
24. The method according to claim 18, wherein said ultrasonic transmission code specifies at least one transmission time of said ultrasonic transmission.
25. The method system according to claim 18, wherein said particular sound emission signature is defined by at least one selected from a list consisting of:
frequency of said ultrasonic transmission;
modulation of said ultrasonic transmission;
timing sequence of a plurality of said ultrasonic transmission; frequency deviation of said ultrasonic transmission;
pattern sequence of a plurality of said ultrasonic transmission; and
amplitude of said ultrasonic transmission.
26. The method to claim 18, further comprising a procedure of consolidating an estimated inertial current position and an auxiliary inertial state of said mobile electronic device into computation of said position of said mobile electronic device.
27. The method according to claim 18, further comprising a procedure of providing communication between a server with said at least one ultrasonic transmitter and with said electronic mobile device.
28. The method according to claim 27, further comprising a procedure of transmitting said ultrasonic transmission code to said at least one ultrasonic transmitter and to said mobile electronic device, by said server.
29. The method according to claim 18, wherein said reference time provider employs at least one time synchronization method, selected from the list consisting of:
network time protocol (NTP);
precision time protocol (PTP);
daytime protocol;
clock sampling mutual network synchronization; and
reference broadcast time synchronization.
30. The method according to claim 29, wherein said reference time provider is said server.
31. The method according to claim 18, further comprising a procedure of displaying a geolocation of said mobile electronic device in said detection space, based on said estimated said position.
32. The method according to claim 18, further comprising a procedure of consolidating an estimated RF current position of said mobile electronic device into computation of said position of said mobile electronic device, comprising the sub-procedures of:
receiving at least one RF signal of known transmitted signal strength and identification, transmitted from a respective RF source; comparing received signal strength of said respective RF signal with respective said transmitted signal strength; and
generating an estimated RF current position of said mobile electronic device in relation to distance to respective said RF source.
33. The method according to claim 30, further comprising a procedure of consolidating:
a list of received signal strength with corresponding identification of respective at least one RF signal, received by respective at least one ultrasonic transmitter; and
a mobile list of received signal strength with corresponding identification of respective said at least one RF signal, received by respective said mobile electronic device;
into said computation of said position of said mobile electronic device, the procedure comprising the sub-procedures of:
measuring said received signal strength by said at least one ultrasonic transmitter so as to compile a measurement list; measuring said received signal strength by said mobile electronic device so as to generate said mobile list;
providing said measurement list to said server so as to generate said list; and
providing said list to said mobile electronic device from said server.
34. The method according to claim 29, further comprising a procedure of generating a map of distances between at least two of said at least one ultrasonic transmitter, the procedure comprising the sub-procedures of:
detecting said ultrasonic transmission by said at least one ultrasonic transmitter;
detecting said ultrasonic transmission, emitted from another one of said at least one ultrasonic transmitter;
measuring respective distances between each of said at least one ultrasonic transmitter, whose said ultrasonic transmission is detected, and respective said at least one ultrasonic transmitter whose said ultrasonic transmission is said emitted ;
providing measured said respective distances between each of said at least one ultrasonic transmitter to said either one of said server and said mobile electronic device; and
generating said map of distances, based on said sub-procedure of providing measured said respective distances, by either one of said server and said mobile electronic device.
PCT/IL2013/000005 2012-01-18 2013-01-17 Hybrid-based system and method for indoor localization WO2013108243A1 (en)

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