WO2018203326A1

WO2018203326A1 - System and method for use in positioning systems

Info

Publication number: WO2018203326A1
Application number: PCT/IL2018/050467
Authority: WO
Inventors: Yaron SHAVIT
Original assignee: Intraposition Ltd.
Priority date: 2017-04-30
Filing date: 2018-04-29
Publication date: 2018-11-08
Also published as: IL252030A0

Abstract

A system and method for use in time synchronization of a plurality of receiver units are described. The method comprising: providing a plurality of receiver units arranged in preselected locations within a region of interest and at least one reference transmitter unit, said reference transmitter unit is configured and operable for transmitting synchronization messages; receiving readout time of said at least one reference transmitter at time of transmission of a synchronization message, and readout time of one or more of the receiver units upon receiving said synchronization message; processing the received data on readout time and determining one or more synchronization functions for transformation between time provided by each of said plurality of receiver units to time as provided by the reference transmitter providing synchronization link between time readout of said one or more receiver units and time readout of said reference transmitter; and storing in a storage unit, data indicative of a plurality of synchronization functions for transformation of time readouts of the receiver units to time readout of said at least one reference transmitter, thereby enabling time synchronization with respect to readout time of said at least reference transmitter.

Description

SYSTEM AND METHOD FOR USE IN POSITIONING SYSTEMS

TECHNOLOGICAL FIELD

The present invention is in the field of positioning systems and is particularly relevant for clock synchronization for such systems, being indoor or outdoor positioning systems.

BACKGROUND

Indoor positioning systems provide data about exact location of one or more objects within a predefined area. Such location data may be used for various applications such as to locate specific items in a store or warehouse as well as various other applications.

Location data may be determined based on determining differences in time of arrival of signals transmitted from an object to be located. Using electromagnetic signals, such time differences may be in the range of nanoseconds, for determining location with accuracy of about 1 meter, and smaller for greater accuracy. To this end, accurate synchronization of time measurement by signal receiving elements is required.

Wireless communication technology (e.g. Wi-Fi, ultra-wide band, Bluetooth etc.) enables communication, and accordingly time synchronization, of a plurality of units within a selected region with reduced installation costs. Utilizing a plurality of receiver- transmitters units capable of communicating wirelessly between them enables employment of an indoor mapping/positioning system with reduced cost and effort while enabling time synchronization between them to maintain accuracy of positioning.

Various techniques are known capable of providing location and positioning data within a selected region using wireless communication techniques.

US 2001/0030625 describes an object tracking system for locating radio-tagged objects having a plurality of tag transmission readers that detect tag transmissions, and generate time-of-arrival output signals representative of the time-of-arrival of first-to- arrive tag transmissions based on clock signals generated by local clock generators at the tag reader sites. The tag reader sites may transmit time-of-arrival signals to an object location processor by way of a wireless local area network. Measurements made on transmissions from a fixed position reference tag are used to update a reader clock offset database employed by the processor to maintain that the reader clocks are effectively time aligned.

US 6,968,194 describes a method and system for synchronizing location finding measurements in a wireless local area network (WLAN) providing a low cost mechanism for correcting location measurements within a WLAN location finding system. Multiple location receivers compute the time-of-arrival (TOA) of a reference transmitter signal, which is generally a beacon signal. The TOAs are collected and reported to a master unit that contains stored predetermined position information for the location receivers. The master unit computes the time-differences-of-arrival (TDOA) between multiple receivers and computes differences between the measured TDOAs and theoretical TDOAs computed in conformity with the predetermined position of each location receiver. The deviations between theoretical and measured TDOAs are collected in a statistical sample set and Kalman filters are used to produce a model of location receiver timebase offset and drift over multiple received beacon signals. The filter outputs are used to then either correct subsequent TDOA measurements for each location receiver, improving the accuracy of subsequent and/or prior TDOA measurements, or commands are sent to the location receivers to calibrate the timebases within the location receivers in order to improve the accuracy of subsequent TOA measurements.

WO 2016/189526 describes a real-time wireless positioning system, comprising: a plurality of portable tag devices; a plurality of autonomous reference transmitters installed in a defined area housing said plurality of tag devices; a plurality of anchors installed in a defined area housing said plurality of tag devices and said plurality of autonomous reference transmitters; and at least one location engine unit in an area housing said plurality of tag devices, said plurality of autonomous reference transmitters and said plurality of anchors. GENERAL DESCRIPTION

As indicated above, there are various techniques providing indoor location data and positioning capabilities. A major challenge in positioning, relates to alignment/synchronization of time counted by different receiving/transmitting elements of the system. Generally, there are various techniques for time synchronization between different remote clocks. Synchronization of clocks of a plurality of elements of the system may generally be provided by determining a plurality of time synchronization functions. Each of the time synchronization functions provide a relation between time reading determined by one clock to that determined by one or more other clocks. Often, to provide a high accuracy positioning system, maintenance of a plurality of synchronization functions may require either the use of accurate, stable and costly clocks or powerful computation resources for highly frequent updates of the synchronization functions.

Thus, there is a need in the art for a novel configuration suitable for use in positioning systems that enables to determine high accuracy position data while using relatively low cost elements and reduced complexity in data processing. The present invention involves a system comprising a plurality of receiver units arranged in predetermined known locations in a region of interest, and at least one reference transmitter, which may generally be one of the receiver units operating as a reference transmitter according to a selected pattern, and a control system. The receiver units may generally be configured as radio frequency (RF) transmitter-receiver units and generally comprise an internal clock. Each of the receiver units is configured for being responsive to input signals in one or more selected transmission channels and/or frequency ranges, and transmits, in response, a corresponding output signal indicative of the received signals and time of reception based on the internal clock of the unit. Generally, the receiver units are configured for receiving RF signals from one or more reference transmitters and/or one or more portable transmitters which are abbreviated "tags" in this document. The receiver units may be configured to transmit corresponding indications to the control system using wired or wireless communication, which need not be similar to the RF frequency range used for transmission of synchronization or location signals. The control system is configured for receiving the output signals transmitted by the receiver units for analysis and processing as will be described in more detail further below.

Generally, in some preferred embodiments of the invention, the system is configured as a positioning system, wherein a central control system (server system) is configured and operable for determining location of one or more transmitting tag units that may be mobile within in the region of interest where the plurality of receiver units are employed. In such configurations, the tag units are configured for periodically transmitting location signals, each signal including at least tag identity. The receiver units that receive the location signal transmit corresponding data including time of reception to the control system. Utilizing data on location of the different receiver units, and data on reception time of the location signals, provided by three or more receiver units, the control system is capable of determining location of a tag.

To enable the control system to accurately determine location of the one or more tags, the reception time data provided by the different receiver units needs to be synchronized. To this end, the system utilizes one or more reference transmitters, located in predetermined known locations, and configured for periodically transmitting synchronization signals. The synchronization signals, also termed herein as synchronization messages include a signal/message identity, transmitter identity, and are associated with transmission readout time data as determined by the reference transmitter. The transmission readout time data is further transmitted by the reference transmitter as part of the signal or is directly transmitted to the control system or server system together with data on signal and transmitter identities. When one or more receiver units, of the plurality of receiver units, receive such synchronization messages, any receiver unit determines time of reception of the signal and provides corresponding data to the control system. More specifically, the receiver units transmit reception data to the control system. The reception data comprises receiver unit identity, reception time of signal, synchronization message identity, reference transmitter identity and transmission time as registered by the reference transmitter. In this connection the terms signal and message are used herein interchangeably and relate to one or more data pieces transmitted by a transmitter unit (being a tag or reference transmitter). The signals/messages may be digital or analog and typically contain certain information therein as described above.

Generally the term readout time as used herein relates to output data indicative of status of an internal clock of the receiver unit or reference transmitter at the time of reception or transmission of signal. It should be noted that each of these units generally includes and internal clock having certain time loop and time resolution. Synchronization between receiver unit and a reference transmitter and/or linking readout times of two or more receiver unit according to the present technique relates to transformation of time readout of the different units to be associated with a common clock enabling to compare the readout time data on a common time scale. Such transformation is generally required for determining time difference between readout of different units.

Based on the synchronization message data and the reception data, the control system determines synchronization functions linking readout time of different receiver units to time readout of the reference transmitter that transmitted the synchronization message. Enabling transformation between the corresponding clocks for comparing readout time based on common time count. Collecting synchronization data associated with at least one reference transmitter and a plurality of receiver units enables linking time data of each of the receiver units to the reference transmitter. Therefore, after collecting data about synchronization message from a plurality of receiver units, the control system operates to determine a plurality of synchronization functions linking time readout of each of the receiver units to that of a corresponding reference transmitter, each of the synchronization functions being indicative of time variation (drift and shift) between a receiver unit and a reference transmitter.

The use of time synchronization functions linking receiver units with corresponding one or more reference transmitters provides a novel time synchronization topology enabling to reduce the amount of calculations required for determining time synchronization between each two receiver units compared to conventional synchronization techniques. More specifically, according to certain conventional techniques, the time synchronization functions are based on reception time of a synchronization message by two different receiver units, thus linking the two receiver units to each other. Generally, linking a plurality of N receiver units between them requires a number of links corresponding to the binomial coefficient However, the

present technique linking N receiver units to corresponding K reference transmitter requires up to N-K links (or below when some receiver units are not in direct communication with certain reference transmitters). This simplifies processing and enables high accuracy time synchronization and positioning of tags utilizing low cost receiver and transmitter units, and reduced processing power. It should however be noted that the technique may comprise determining inverse time synchronization functions for one or more combinations of receiver unit and reference transmitter. In this connection, the number of N-K links relates to pairs of time synchronization function and inverse thereof counted as one link.

According to a broad aspect, the present invention provides a method for use in time synchronization of a plurality of receiver units, the method comprising:

providing a plurality of receiver units arranged in preselected locations within a region of interest and at least one reference transmitter unit, said reference transmitter unit is configured and operable for transmitting synchronization messages;

receiving readout time of said at least one reference transmitter at time of transmission of a synchronization message, and readout time of one or more of the receiver units upon receiving said synchronization message;

processing the received data on readout time and determining one or more synchronization functions for transformation between time provided by each of said plurality of receiver units to time as provided by the reference transmitter providing synchronization link between time readout of said one or more receiver units and time readout of said reference transmitter;

storing in a storage unit, data indicative of a plurality of synchronization functions for transformation of time readouts of the receiver units to time readout of said at least one reference transmitter, thereby enabling time synchronization with respect to readout time of said at least reference transmitter. As indicated above, the number of synchronization functions (links) may not exceed N-K, where N is the number of receiver units and K is the number of reference transmitters.

According to one other broad aspect, the present invention provides system comprising:

at least one reference transmitter located in a predetermined location in a region of interest and configured for periodically transmitting a time synchronization message and corresponding time of transmission of said time synchronization message;

a plurality of receiver units arranged in said region of interest in predetermined locations, said plurality of receiver unit are configured to receive said time synchronization message and transmit data indicative of reception time of said time synchronization message;

a control system comprising a communication module configured for communicating with said plurality of receiver units, and a processing utility, and is connectable to a storage utility comprising pre-stored location data comprising data on location of said plurality of receiver units and at least one reference transmitter; the processing utility is configured and operable for receiving data on transmission and reception times of one or more synchronization messages and for determining one or more time synchronization functions in accordance with said pre-stored location data;

each of said one or more synchronization functions being indicative of time variation between a receiver unit and a reference transmitter

According to yet another broad aspect, the present invention provides a system for use in determining location of one or more transmitting tag units within a region of interest, the system comprising:

a control system comprising at least a communication module and processing utility, and configured for occasionally determining location of said one or more transmitting tag units;

at least one reference transmitter located in a predetermined location in the region of interest and configured for transmitting time synchronization messages and corresponding readout time of transmission of said time synchronization messages; a plurality of receiver units arranged in said region of interest in predetermined locations, the receiver units are configured for receiving one or more messages comprising location messages and said time synchronization messages and for transmitting data indicative of the received input messages and corresponding reception time readout to the control system;

the control system is connectable to a storage utility comprising pre-stored location data comprising data on location of said plurality of receiver units and at least one reference transmitter; the processing utility is configured and operable for receiving data on transmission and reception readout times of one or more synchronization messages, determining one or more time synchronization functions in accordance with said pre-stored location data;

the one or more synchronization functions are indicative of time transformation between a receiver unit and reference transmitter, thereby enabling time synchronization with respect to time readout of said reference transmitter.

The processing utility may be configured for occasionally storing data on said one or more synchronization functions in said storage utility, and for retrieving said data on one or more synchronization functions for determining location of one or more transmitting tag units.

According to some embodiments, the said processing utility comprises a time synchronization module configured and operable for receiving data on transmission readout time of one or more time synchronization messages and corresponding reception readout time from at least some of said plurality of receiver units and for determining a plurality of time synchronization functions linking readout time of said receiver units to said at least one reference transmitter.

Generally, for a system comprising N receiver units and K reference transmitters, the number of synchronization functions may not exceed N-K. The number N-K may be determined by counting synchronization functions and inverse of function thereof as a common function.

According to some embodiments, the system comprises two or more reference transmitters, said control system further comprising a synchronization validation module configured and operable for analyzing time synchronization functions of said receiver units with respect to the two or more reference transmitters in accordance with said pre- stored data on location of said plurality of receiver units and said reference transmitters and to determine inconsistency in time synchronization for two or more receiver units; upon determining inconsistency of one or more time synchronization functions, such time synchronization functions are marked accordingly.

Generally, according to some embodiments, the at least one reference transmitter may be provided by at least one receiver unit being configured to periodically operate as a reference transmitter.

According to some embodiments, the system may be configured as an indoor positioning system. In such configurations, the system may further comprise one or more tag units portable within said region of interest; said one or more tag units are configured for periodically transmitting location signals comprising tag identity and signal identity, said location signals are received by at least some of said plurality of receiver units, which in response are configured to transmit to the control system data on the location signals and corresponding reception time.

Generally, the control system may further comprise a tag location module configured and operable for receiving, from a plurality of receiver units, data on a location signal transmitted by a tag, and for utilizing data on reception time, together with corresponding time synchronization functions and said pre-stored data on location of the receiver units.

According to some embodiments, the control system may comprise a receiver linking module configured and operable for obtaining synchronization function data associated with two or more synchronization functions linking a selected pair of receiver units to one or more reference transmitters and determining relative clock synchronization between said selected pair of receiver units in accordance with corresponding synchronization functions of said receiver units with respect to at least one reference transmitter. The receiver linking module may be utilized of determining time difference (in accordance with a common clock) between readout times of the different receiver units.

According to yet another other broad aspect, the present invention provides a server system for use in indoor positioning/mapping, the system comprising:

a communication unit configured for receiving communication signals from a plurality of receiver units;

a storage utility comprising pre-stored location data indicative of locations of said plurality of receiver units within a region of interest;

a processing utility comprising:

time synchronization module configured and operable for receiving input clock data indicative of clock synchronization communications from said plurality of receiver units, said input clock data comprises transmission readout time of synchronization messages transmitted from at least one reference transmitter located at a known location and reception readout time associated with reception of said one or more synchronization messages by said plurality of receiver units, and for determining, for each of said receiver units, a time synchronization function enabling transformation between readout time of said receiver unit to time of said at least one reference transmitter in accordance with said pre-stored location data; and

a positioning module configured and operable for receiving input location data indicative of positioning communication from at least two of said receiver units, and for determining location of one or more mobile transmitter unit in accordance with said pre- stored location data of said receiver units and corresponding time synchronization functions. The processing utility may be configured for occasionally storing data on said one or more synchronization functions in said storage utility, and for retrieving said data on one or more synchronization functions for determining location of one or more transmitting tag units.

Generally, for a system comprising N receiver units and K reference transmitters, the number of synchronization functions may not exceed N-K.

According to some embodiments, the processing utility may further comprise a synchronization validation module configured and operable for periodically processing time synchronization functions associated with two or more receiver units and generated with respect to two or more known locations, and for determining inconsistency between time synchronization functions for two or more receiver units; upon determining inconsistency, said synchronization validation module is configured to mark the corresponding time synchronization functions accordingly.

According to yet another broad aspect, the present invention provides a method for use in determining position of an unknown emitter; the method comprising:

receiving transmission data indicative of transmission of a time synchronization message from a reference transmitter, said transmission data comprises data on reference transmitter location, transmission time and signal identity;

receiving reception data corresponding to reception of said time synchronization messages by two or more receiver units, the reception data comprises data on receiver location, reception time and signal identity;

determining time synchronization functions for each of the two or more receiver units, said time synchronization functions linking between time of said receiver units to time of said reference transmitter; and

receiving location data indicative of reception, by the one or more receiver units, of one or more location signals transmitted by at least one tag and processing said location data utilizing said time synchronization functions for determining location of said at least one transmitting tag unit.

According to some embodiments, said utilizing of the time synchronization functions may comprise determining relative time between two or more receiver units in accordance with the corresponding time synchronization functions linking said receiver units with a reference transmitter. According to some embodiments, the method may further comprise validation of said time synchronization functions, said validating comprising: providing time synchronization functions for two or more receiver units determined in accordance with two or more different reference transmitter units, and determining time variations between said two or more receiver units when linked through said different reference transmitters; upon determining time variations exceeding a predetermined threshold, the corresponding time synchronization functions are marked accordingly.

Generally as indicated above, number of synchronization functions may not exceed N-K, where N is the number of the receiver units and K is number of reference transmitters configured for periodically transmitting synchronization messages.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Fig. 1 illustrates schematically a system according to some embodiments of the invention;

Fig. 2 illustrates block diagram configuration of a server system configured to provide controlling according to some embodiments of the invention;

Fig. 3 exemplifies a technique to determine time synchronization function for receiver units according to some embodiments of the invention;

Fig. 4 exemplifies a technique for use in time synchronization and positioning according to some embodiments of the invention; and

Figs. 5A and 5B illustrate a comparison between conventional synchronization techniques (Fig. 5A) and the technique of the present invention (Fig. 5B).

DETAILED DESCRIPTION OF EMBODIMENTS

As described above, an indoor positioning system generally provides location data on one or more transmitters within a region of interest. The use of wireless, or at least partially wireless communication, between different receiver units, enables to reduce the work and costs associated with employment of indoor positioning systems, thus expanding the use thereof. Further, to provide reliable location data, time counters (clocks) of different units of the system need to be sufficiently synchronized. Reference is made to Fig. 1 illustrating a system 1000 according to some embodiments of the present invention. System 1000 includes a plurality of receiver units, R1-R7 in this specific example, one or more reference transmitter units, two such reference transmitters are exemplified herein as RT1 and RT2, one or more moving tag T, and a control system 500. Generally system 1000 may be suitable for indoor positioning by utilizing the plurality of receiver units R1-R7 for receiving location signals sent from one or more tags (one such tag is shown as T) and providing the control system reception-time data. The control system 500 may utilize pre-stored data on locations of the receiver units together with data on time differences in receiving location signals by two or more (or three or more) of the receiver units, to determine location of the tags.

As known in the art, to accurately determine location of such tags, the tag T is configured to periodically transmit location signals. These location signals are received by at least some (generally at least three) of the receiver units R1-R7. The location of the Tag T can then be determined using the Time difference of Arrival technique (TDoA). To accurately determine time of arrival, and accordingly differences in arrival times, of such location signals to the different receiver units R1-R7, the internal clocks of the different receiver units need to be synchronized. To this end, the present technique utilizes one or more reference transmitters, e.g. RT1 and RT2, located in predetermined locations, which are pre-stored and accessible by the control system 500. The reference transmitters RT1 and RT2 generally include an internal time counter (clock) and transmission module, and are configured to periodically transmit synchronization messages in a predetermined channel (e.g. predetermined RF frequency range). The synchronization messages typically include transmitter identity (ID) and signal identity, and are associated with registration of transmission time. Such transmission time may be data pieces transmitted within the synchronization message, or transmitted separately to the control system 500 for registration. It should be noted, that the transmission time is determined by the time of the reference transmitter internal clock when the signal is transmitted. It should also be noted that generally, the one or more reference transmitters may be embedded within one or more of the receiver units. More specifically, the receiver units (e.g. R1-R7) may be configured to periodically switch operation scheme and transmit synchronization messages acting as reference transmitters (e.g. RT1 or RT2). Generally, as the electric path for reception and transmission might not be equal, the internal clock may be considered as a separate clock to avoid time variations.

Each of the receiver units (R1-R7 in this example) includes a communication module configured for receiving RF signals and for transmitting corresponding data to the control system 500 and an internal time counter (clock). The receiver units are configured for receiving signals in predetermined channels, and for transmitting corresponding data to the control system 500, together with data on time of reception of the signals. Thus, at least some of the receiver units may receive synchronization messages sent by one of the reference transmitters RTl or RT2 (or the one or more tags T). In response, the receiver units that receive the signal, register time of reception according to the internal clock thereof, and provide corresponding data, including signal identity, reference transmitter identity, receiver unit identity and time of reception, to the control system 500. In some embodiments, the receiver units may also provide data on time of transmission of the synchronization message, as registered by the reference transmitter generating the signals. In some other embodiments, the reference transmitter transmits data of transmission time to the control system 500.

The control system 500 typically includes a communication module 510, processing utility 550 and has access to one or more storage utilities (not specifically shown here). The communication utility 510 is configured for receiving, through wired or preferably wireless communication, data on signal reception from the receiver units, and data on transmission of synchronization messages (either from the receiver units or directly from the reference transmitter(s)). The processing utility 550 utilizes the data on transmission and reception of synchronization messages and pre-stored data on locations of the receiver units and reference transmitter(s) to determine time synchronization functions for the receiver units. The time synchronization functions link receiver units to reference transmitters and provide data on difference between time determined by clock of a receiver unit and that determined by the clock of a reference transmitter.

Generally, to determine time synchronization function, the processing utility utilizes data that include pre-stored location of the transmitting reference transmitter (e.g. RTl), time of transmission of the synchronization message, pre-stored location of the receiving receiver unit (e.g. Rl) and time of reception of the signal. Utilizing pre- stored data on location of reference transmitter and receiver unit, the processing utility may determine the distance required for the signal to propagate in order to reach the receiver unit. This distance, divided by the speed of light, provides the time of propagation in the form of d/c=t_p. Utilizing this information, the processing utility may determine that time reading of receiver unit Rl when receiving synchronization message j corresponds to time reading tRTi¹ of reference transmitter RT1 when transmitting signal j with an addition of propagation time t_p. Repeating transmission and reception of the synchronization messages enables the processing utility to determine a relation up to a selected order between time readout of the receiver unit to time readout of the reference transmitter, such as /. JJ → t^ , ¾_ri = as well as its inverse relation fi t_m -i t _ffy., , thus providing a link between receiver unit Rl and reference transmitter RT1. Similarly, the processing utility determined links between additional receiver units such as R2-R7 and reference transmitter RT1, providing a common clock suitable for use with the relevant receiver units. It should be noted that in some cases the inverse relation (inverse synchronization function) may be determined directly from a synchronization function. In some other cases such inverse relation may be determined separately and be stored as an inverse synchronization function including the relative coefficients.

Accordingly, the control system 500 is configured and operable to generate and maintain a set of time synchronization functions (typically in the form of a set of power series coefficients a_n) providing links between the different receiver units and the reference transmitters. Such a set of time synchronization functions may be in the form of a table, where for each reference transmitter the table includes data on the synchronization function (coefficients) linking the time reading of the different receiver units to that of the reference transmitter. It should however be noted that some of the receiver units might not receive synchronization messages from some of the reference transmitters due to limitations in signal transmission. This might result from physical arrangement of the receiver units and reference transmitters and geometry of the region of interest. As a result of limited reception, the set of time synchronization functions may include several empty entries, where some of the receiver units may not be directly linked to some of the reference transmitters. However, the receiver units and the reference transmitters are preferably arranged in the space to allow signal reception providing at least one, and preferably two or more links for each receiver unit, through at least two reference transmitters, as will be described further below. Reference is made to Fig. 2 schematically illustrating a configuration of the control system 500. It should generally be noted that the control system 500 may be a local control system, or utilize one or more remote components utilizing remote server, cloud processing or other suitable computing techniques. The control system 500 includes a communication module 510 configured for receiving data from the receiver units and reference transmitters in the region where the system is employed, and a processing utility 550 configured for utilizing the received data for determining time synchronization functions, and typically also location data of tags. Additionally, control system 500 may include, or be connectable to a storage utility 450. The storage utility 450, includes pre- stored data on arrangement of elements in the selected region location of the receiver units, and may be further used for temporal storing of data on transmission and reception of time synchronization messages and of the corresponding time synchronization functions determined by the processing utility 550.

The processing utility 550 is configured and operable for processing received data on signal communication between the receiver units, reference transmitters and, when used, tags of the system, and for determining corresponding time synchronization functions according to transmission and reception time data. Additionally, the processing utility 550 may be configured for utilizing the determined time synchronization functions for determining location data corresponding to the one or more portable tags when used. Generally, the processing utility 550 may be a software and/or hardware utility capable of performing data processing. The processing utility 550 may be implemented by a local processing module including one or more processing units, or at least partially via remote processing performed by one or more processing units accessible through a communication network.

The processing utility 550 includes several hardware or software modules configured for providing specific processing tasks including at least a time synchronization module 560 configured and operable for determining time synchronization functions between receiver units and reference transmitters in accordance with data on signal communication there between. Additionally, the processing utility 550 may also include one or more of receiver linking module 570, synchronization validations module 580 and tag location module 590 in accordance with specific embodiments of the invention. The time synchronization module 560 is configured and operable for receiving, through the communication module 510, transmission and reception time data of one or more synchronization messages. More specifically, such transmission-reception data typically include data on transmission of a time synchronization message from one of the reference transmitters, and corresponding data on reception of the signal by several (generally at least two) of the receiver units. Utilizing the pre-stored data on location of the receiver units and reference transmitters from the storage utility 450, the time synchronization module is configured to determine a correspondence between the time readings provided from the receiver units and reference transmitter. More specifically, based on the pre-stored location data, the distance between a transmitting reference transmitter (e.g. RT1) and a receiving receiver unit (e.g. Rl) is provided as dn. Accordingly, the time synchronization module is configured to determine that time reading of receiver unit Rl when receiving the synchronization message j corresponds to time reading tRTi¹ of reference transmitter RT1 when transmitting signal j with an addition of propagation time t_p. As indicated above, a determined time synchronization function, linking a receiver unit with a reference transmitter, may typically include one or more time synchronization coefficients a_n providing a relation between time reading t received from the receiver unit Ri, and the time reading tRn of a reference transmitter RTi being in the form t_ffri Generally, the time synchronization relation may be up to first order, i.e. Cl_n=0 for n>l, up to second order, i.e. a_n=0 for n>2, or to higher order.

To determine the coefficients a_n the time synchronization module typically utilizes transmission and reception data of two or more synchronization messages. The use of a plurality of synchronization messages provides data on shift of time reading as well as on drift, associated with variations in clock speed. Generally, in some embodiments, data associated with transmission and reception of each synchronization message is pre-processed and stored at the storage utility or in a local memory (e.g. RAM memory), and data associated with previous synchronization messages is extracted from the storage utility or memory to collectively be used for determining the time synchronization coefficients. The so-determined time synchronization functions or coefficients thereof are stored for update and/or use for operation of the system. As indicated, above, the so-determined time synchronization functions provide links between receiver units Rl-Rn and reference transmitters RTl-RTk in accordance with transmission-reception between them. As noted, the receiver units and reference transmitters are preferably arranged such that each receiver unit is located to be in proper communication with at least one, and preferably at least two, reference transmitters. However, in accordance with structure of the region of interest, some receiver units may not be connected to some reference transmitters, leaving the corresponding time synchronization function empty. It should be further noted that the total number of time synchronization functions does not exceed N-K, where N is the number of receiver units and K is the number of reference transmitters. Additionally, the actual number of time synchronization functions may be lower as some receiver units may be located such that no signal reception is provided with respect to some of the reference transmitters, e.g. in an L or U shaped region of interest.

The plurality of time synchronization functions generally provide data on time relation between receiver units and reference transmitters of the system. To determine corresponding links between receiver units, the processing utility may also include a receiver linking module 570. The receiver linking module 570 is configured and operable for following links formed by the time synchronization function to determine clock synchronization between pairs of receiver units. Thus, the receiver linking module 570 is configured for determining relative clock synchronization between selected pairs of receiver units in accordance with corresponding synchronization functions of said receiver units with respect to at least one reference transmitter. More specifically, given receiver units Rl and R2, the time synchronization function data may include synchronization data linking receiver Rl to reference transmitters RT1 and RT2, and similarly for receiver unit R2. This provides _._ri = ^β³¹ _κ ί* , t_STi =∑α^ί5 _¾ί ,, as well as £_sr, = and t_SJ2 =∑o.²² The receiver linking module 570 may be used for reducing computation complexity by determining a function linking ¾₇ and tR2 and storing corresponding relation in the storage utility 450 for use in location detection.

Generally as indicated above, the receiver linking module 570 may determine common time synchronization for two or more receiver units that may be linked between them by a one or more reference transmitters. The receiver linking module may also be configured for following additional links for determining common time synchronization between receiver units that are not linked by a single reference transmitter. For example, In Fig. 1 receiver units R3 and R5 are not directly linked by a common reference transmitter. To this end the receiver linking module may follow a selected path linking the receiver units via two or more reference transmitters and additional receiver units. More specifically, in this example, the receiver linking module may determine common time synchronization based on a path of the type: R3 RT1 R6 ->RT2 R5, thereby determining common time synchronization between receiver units R3 and R5.

The synchronization validation module 580 may be configured and operable for establishing/determining consistency of the time synchronization functions. To this end the synchronization validation module operates to compare time synchronization functions associated with two or more receiver units and establish that time reading data is following a direct, line-of-sight link when determined in accordance with two or more different reference transmitters. For example, the synchronization validation module may analyze time synchronization function linking receivers Rl and R2 through reference transmitters RT1 and RT2 as shown above as t_RT1 = f±± (t_R1) , t_RT1 = 2l (¾2) _> ^as well as t_RT2 ⁼ zC^_fll) ^and ^RT2 ⁼ f22 ^R2 - A double link with inconsistency is exemplified in Fig. 3 illustrating synchronization messages transmitted by reference transmitters RT1 and RT2 and received by receiver units Rl and R2, when a signal transmitted by reference transmitter RT2 has a longer path due to element 4 blocking its propagation, and element 6 reflecting the signal via a longer path. Generally, when the shortest path is established, the time synchronization functions may be validated by determining time consistency along double link routes. For example, the synchronization validation module may operate to establish that given time readings t and satisfy the conditions that t_R2 = fil ifll ipRl)) ^and ¾1 =

fe fe))- However, inconsistencies may occur, for example, due to a combination of blocking elements (4 in Fig. 3) limiting signal transmission and reception between a reference transmitter combined with reflection of the synchronization message by a reflecting element (6 in Fig. 3). Alternatively, such inconsistencies may occur due to errors in data registration or for other unknown reasons. Generally, when time synchronization inconsistency is detected to exceed a predetermined error threshold, e.g. associated with time difference above an error threshold, the corresponding links are marked as unusable. In some embodiments the control system 500 may provide suitable indication to an operator aiming at reducing inconsistencies. Such suitable indications may include identities of the receiver units and reference transmitters for which inconsistency is determined.

Generally, the processing utility 500 may also include a tag location module 590. The tag location module 590 is configured and operable for receiving, through the communication module 510, data on reception of location signals from a plurality of two or more receiver units. Generally, location signals are transmitted periodically or occasionally by one or more tags (as shown in Fig. 1) that may move around in the region of interest. Upon reception of such a location signal, the receiver units register tag identity and time of reception, and transmit corresponding data to the control system 500. The tag location module 590 is configured for receiving the location data provided from two or more receiver units, and utilizing the time synchronization functions and pre-stored location data of the receiver units, thus determining location of the corresponding tag. Generally the location of tags may be determined by the time difference of arrival (TDOA) technique in accordance with synchronized time of the receiver units. The tag location module 590 may utilize data on links between receiver units through one or more reference transmitters for determining a common clock linking the two or more receiver units for locating the tag.

It should be noted that time synchronization between the plurality of receiver units may generally be continuously updated. Thus, the set of time synchronization functions may be regularly updated, in response to periodic transmission of synchronization messages by the one or more reference transmitters and reception of these signals by receiver units. Accordingly, the technique of the invention maintains a reduced number of synchronization functions by linking the receiver units via one or more reference transmitters. This enables reducing computational complexity, which might be required for simultaneously determining location of tags and maintaining synchronization of the receiver units.

Reference is now made to Fig. 4 exemplifying an operation technique for determining synchronization within a plurality of receiver units. As shown, the present technique includes receiving transmission data 1010 from a reference transmitter (e.g. RT1) directly or indirectly (via one or more receiver units) on transmission of synchronization messages. Accordingly, the technique also includes receiving reception data 1020 from one or more (preferably two or more) receiver units providing data on reception of synchronization messages. In accordance with the transmission and reception data, the technique includes determining corresponding time synchronization functions 1030 linking a plurality of receiver units through one or more reference transmitters. Generally, according to some embodiments, the time synchronization functions may be validated to remove inconsistencies 1035 as described above. Utilizing the determined time synchronization functions, data on location signals from unknown/moving tags can be processed for determining location of the tag 1040 by difference times of signal arrival to the receiver units. Generally this may be provided by determining relative time (common clock) linking various receiver units 1045. Such common clocks can be determined by algebraic transformation of the time synchronization coefficients linking the receiver units through one or more reference transmitters. It should be noted that determining time synchronization functions 1030 between internal clocks of the different receiver units may generally be concurrent with utilizing stored time synchronization functions for determining location for determining location of tags 1040. Accordingly data on determined time synchronization functions may be stored in a storage utility, and/or in local memory (e.g. random access memory utility) and being updated in accordance with transmission of synchronization signals/messages from one or more reference transmitters. Further, the stored time synchronization functions are also used for determining location of tags in accordance with transmission of location signals/messages therefrom.

It should be noted that the above described method is generally operated almost simultaneously. More specifically, the reference transmitters employed in the region of interest may be configured for periodically transmitting time synchronization messages. Accordingly, the time synchronization functions determined in accordance with the present technique are periodically updated, while simultaneously allowing to determine location of tags.

Reference is made to Figs 5A and 5B exemplifying receiver linking topology according to conventional techniques and according to the present technique. As shown, receiver units R1-R7 are linked between them in Fig. 5A, in accordance with conventional techniques. In such a configuration, time synchronization is typically determined between the receiver units providing for i,j being between 1 to 7 in this example. Such linking topology requires a number of links corresponding to the binomial coefficient the example of N=7 provides 21 links.

The time synchronization topology according to the present technique is exemplified in Fig. 5B providing a reference transmitter RT linking the receiver units. As described above, the time synchronization functions, determined according to the present technique, provide relation between time reading of the different receiver units, e.g. R1-R7, and that of the reference transmitters (generally at RT). This technique reduces the number of links in the system topology, and accordingly reduces computation complexity required for determining location of one or more tags. As shown in Fig. 5B, for a system utilizing N receiver units and K reference transmitters, the number of time synchronization functions does not exceed NK. As exemplified, in the case of N=7 and K=l (one reference transmitter RT) the control system is required to maintain and determine data on 7 links. Addition of one or more additional reference transmitters may improve synchronization robustness; in this example, the use of a second reference transmitter results in 14 links and thus slightly increases complexity, while increasing robustness.

As indicated above, the present invention provides a system and technique suitable for use as a positioning system such as in indoor positioning. According to the present technique, a plurality of receiver units being employed in a region of interest are configured for receiving time synchronization messages and communicating corresponding data for processing. In accordance with timestamps of the synchronization messages and time of reception data of such messages, the technique provides for determining a set of time synchronization functions, thus establishing links between the receiver units through corresponding one or more reference transmitters (transmitting the synchronization messages). Such time synchronization functions enable determining efficient location data with reduced complexity. Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention as hereinbefore described without departing from its scope defined in and by the appended claims.

Claims

CLAIMS:

1. A method for use in time synchronization of a plurality of receiver units, the method comprising:

a) providing a plurality of receiver units arranged in preselected locations within a region of interest and at least one reference transmitter unit, said reference transmitter unit is configured and operable for transmitting synchronization messages;

b) receiving readout time of said at least one reference transmitter at time of transmission of a synchronization message, and readout time of one or more of the receiver units upon receiving said synchronization message; c) processing the received data on readout time and determining one or more synchronization functions for transformation between time provided by each of said plurality of receiver units to time as provided by the reference transmitter providing synchronization link between time readout of said one or more receiver units and time readout of said reference transmitter;

d) storing in a storage unit, data indicative of a plurality of synchronization functions for transformation of time readouts of the receiver units to time readout of said at least one reference transmitter, thereby enabling time synchronization with respect to readout time of said at least reference transmitter.

2. The method of claim 1, wherein for N receiver units and K reference transmitters, and wherein number of synchronization functions does not exceed N-K.

3. A system for use in determining location of one or more transmitting tag units within a region of interest, the system comprising:

a) a control system comprising at least a communication module and processing utility, and configured for occasionally determining location of said one or more transmitting tag units;

b) at least one reference transmitter located in a predetermined location in the region of interest and configured for transmitting time synchronization messages and corresponding readout time of transmission of said time synchronization messages;

c) a plurality of receiver units arranged in said region of interest in predetermined locations, the receiver units are configured for receiving one or more messages comprising location messages and said time synchronization messages and for transmitting data indicative of the received input messages and corresponding reception time readout to the control system;

said one or more synchronization functions being indicative of time transformation between a receiver unit and reference transmitter, thereby enabling time synchronization with respect to time readout of said reference transmitter.

4. The system of claim 3, wherein said processing utility is configured for occasionally storing data on said one or more synchronization functions in said storage utility, and for retrieving said data on one or more synchronization functions for determining location of one or more transmitting tag units.

5. The system of claim 3 or 4, wherein said processing utility comprises a time synchronization module configured and operable for receiving data on transmission readout time of one or more time synchronization messages and corresponding reception readout time from at least some of said plurality of receiver units and for determining a plurality of time synchronization functions linking readout time of said receiver units to said at least one reference transmitter.

6. The system of any one of claims 3 to 5, comprising N receiver units and K reference transmitters, and wherein number of synchronization functions does not exceed

N-K.

7. The system of any one of claims 3 to 6, wherein the system comprises two or more reference transmitters, said control system further comprises a synchronization validation module configured and operable for analyzing time synchronization functions of said receiver units with respect to the two or more reference transmitters in accordance with said pre-stored data on location of said plurality of receiver units and said reference transmitters and to determine inconsistency in time synchronization for two or more receiver units; upon determining inconsistency of one or more time synchronization functions, such time synchronization functions are marked accordingly.

8. The system of any one of claims 3 to 7, wherein said at least one reference transmitter is provided by at least one receiver unit being configured for occasionally

5 operating as a reference transmitter.

9. The system of any one of claims 3 to 8, wherein the system is configured as an indoor positioning system; said one or more transmitting tag units are portable within said region of interest; said one or more transmitting tag units being configured for periodically transmitting location signals comprising tag identity and signal identity, said

10 location signals are received by at least some of said plurality of receiver units, which in response are configured to transmit to the control system data on the location signals and corresponding reception time.

10. The system of claim 9, wherein the control system further comprises a tag location module configured and operable for receiving from a plurality of receiver units data on

15 location signals transmitted by a tag, and for utilizing data on reception time, together with corresponding time synchronization functions and said pre-stored data on location of the receiver units.

11. The system of any one of claims 3 to 10, wherein said control system comprises a receiver linking module configured and operable for obtaining synchronization function

20 data associated with two or more synchronization functions linking a selected pair of receiver units to one or more reference transmitters and determining relative clock synchronization between said selected pair of receiver units in accordance with corresponding synchronization functions of said receiver units with respect to at least one reference transmitter.

25 12. A server system for use in indoor positioning/mapping, the system comprising:

30 a processing utility comprising:

i) time synchronization module configured and operable for receiving input clock data indicative of clock synchronization communications from said plurality of receiver units, said input clock data comprises transmission readout time of synchronization messages transmitted from at least one reference transmitter located at a known location and reception readout time associated with reception of said one or more synchronization messages by said plurality of receiver units, and for 5 determining, for each of said receiver units, a time synchronization function enabling transformation between readout time of said receiver unit to time of said at least one reference transmitter in accordance with said pre-stored location data; and

ii) a positioning module configured and operable for receiving input 10 location data indicative of positioning communication from at least two of said receiver units, and for determining location of one or more mobile transmitter unit in accordance with said pre-stored location data of said receiver units and corresponding time synchronization functions.

15 13. The server system of claim 12, wherein said processing utility is configured for occasionally storing data on said one or more synchronization functions in said storage utility, and for retrieving said data on one or more synchronization functions for determining location of one or more transmitting tag units.

14. The server system of claim 12 or 13, wherein number of synchronization functions 20 does not exceed N-K, where N is the number of the receiver units and K is number of reference transmitters configured for transmitting synchronization messages.

15. The server system of any one of claims 12 to 14, wherein said processing utility further comprises a synchronization validation module configured and operable for periodically processing time synchronization functions associated with two or more

25 receiver units and generated with respect to two or more known locations, and for determining inconsistency between time synchronization functions for two or more receiver units; upon determining inconsistency, said synchronization validation module is configured to mark the corresponding time synchronization functions accordingly.

16. The server system of any one of claims 12 to 15, further comprising a receiver 30 linking module configured and operable for obtaining synchronization function data associated with two or more synchronization functions linking a selected pair of receiver units to one or more reference transmitters and determining relative clock synchronization between said selected pair of receiver units in accordance with corresponding synchronization functions of said receiver units with respect to at least one reference transmitter.

17. A method for use in determining position of at least one transmitting tag unit; the method comprising:

18. The method of claim 17, wherein said utilizing the time synchronization functions comprises determining relative time between two or more receiver units in accordance with the corresponding time synchronization functions linking said receiver units with a reference transmitter.

19. The method of claim 17 or 18, further comprising validating said time synchronization functions, said validating comprising: providing time synchronization functions for two or more receiver units determined in accordance with two or more different reference transmitter units, and determining time variations between said two or more receiver units when linked through said different reference transmitters; upon determining time variations exceeding a predetermined threshold, the corresponding time synchronization functions are marked accordingly.

20. The method of any one of claims 17 to 19, wherein number of synchronization functions does not exceed N-K, where N is the number of the receiver units and K is number of reference transmitters configured for periodically transmitting synchronization messages.