Patent ID: 12222434

EMBODIMENTS

In many known positioning methods, clock signal inaccuracies in a master base station and non-master base stations have all contributed to a positioning error. Positioning methods disclosed herein enable the determining of a position of a wireless node, such as a wireless tag, using TDOA positioning in a system where only a single master base station need have access to an accurate, precise clock signal. A master base station acts as a TDOA reference device in the determination of duration of at least one accurate time period.

FIG.1illustrates an example system in accordance with at least some embodiments of the present invention. The example system ofFIG.1comprises master base station150and non-master base stations160and170. Locations of the base stations are known, wherefore also distances between the base stations are known. Since distances between the base stations are known, also the time of flight of radio signals, propagating at light speed, between the base stations are known. In case sound signals are used, the time of flight takes place at the speed of sound. One master and two non-master base stations is one numerical example to which the present invention is not limited, rather, the principles of the present invention are usable with one master and two, four or indeed another number of non-master base stations, for example. In some cases, a larger number of non-master base stations results in a more accurate location estimate. In general, the set of base stations may comprise one master base station and at least one non-master base station. In general, the set of base stations may be comprised in or as an indoor wireless network, for example based on ultra wide band, UWB, or wireless local area network, WLAN, technology.

The expression “base station” is used herein as a terminological choice, by which it is not intended to limit the scope of the disclosure. In cellular technologies the expression “base station” is common, while in non-cellular technologies the expression “access point” may be used. Examples of cellular technologies include long term evolution, LTE, and wideband code division multiple access, WCDMA. Examples of non-cellular technologies include WLAN, and worldwide interoperability for microwave access, WiMAX. However, the meaning is essentially the same, that being a fixed node with which a user device may communicate using a wireless communication interface. This fixed node transmits in the downlink and receives in the uplink. The term “base station” herein covers also nodes which may be referred to as access points, or indeed by other terms, as long as the node transmits in the downlink and receives in the uplink.

As noted, the base stations may be configured to operate in accordance with a suitable radio technology, such as, for example, ultra wide band, UWB. UWB is a technology for transmitting using a large bandwidth, for example wider than 500 megahertz or wider than 700 megahertz. UWB communications may be based on an impulse radio, which may employ a combination of burst position modulation, BPM, and binary phase shift keying, BPSK, for example. IEEE standard 802.15.4-2011 contains an example of such a UWB communication technology. Other impulse radio technologies may alternatively or in addition be used, which enable a sufficiently accurate signal transmit and reception time determination for example, to effectively make use of the wide frequency range. Other example technologies include cellular and non-cellular technologies. In some embodiments, the base stations may be configured to operate a wireless communication technology that based on an optical signal or sound signal. Also such technologies enable signal transmission and reception time determination.

The system illustrated inFIG.1further comprises tag110. The tag, or more generally, user device, may be configured to communicate wirelessly with the base stations to receive service from them, for example. For example, tag110may access network resources and/or obtain positioning service from the base stations to determine the geographic position of tag110. The tag may comprise a device enabled to receive wireless messages transmitted by the base stations, such as master base station150and non-master base stations160and170, and to perform mathematical operations. To enable this, each tag may comprise a wireless receiver, at least one processing core and memory. Tag110is configured to transmit a signal, such as a low-energy electromagnetic blink signal, for example. The signal may be an UWB signal with a spectral width of at least 500 MHz, for example. The signal may be an impulse radio signal of at least 500 MHz spectral width.

InFIG.1, master base station150transmits an initial message100A. Initial message100A may be transmitted from master base station150in a non-directed manner, that is, omnidirectionally or to a broad set of directions in the sense that the message is not transmitted only to a specific, single direction. This enables reception of the initial message100A by plural nodes, such as by the non-master base stations. The master base station may record a first timestamp100A_TX, indicating a point in time, when the master base station transmits the initial message. The master base station may, for example, obtain a current time from an internal clock of the master base station, compile the initial message using the current time and send the initial message without waiting. In some embodiments, the master base station may augment the current time obtained from the internal clock with a delay value which corresponds to the time it takes the master base station to transmit the message, such that the timestamp more accurately reflects the moment in time the initial message issues from antennas of the master base station. Delay values for different base stations may be configured during system setup or calibration, or at manufacture of the base stations, for example. The delay values are useful, for example, where the master base station and the non-master base stations have different electronics.

Initial message100A may be sent by the master base station more than once, for example, master base station150may transmit two copies of initial message100A upon request, or master base station150may transmit initial message100A periodically with a fixed periodicity, that is, a constant length of time between two consecutive initial messages100A. A second timestamp may have been recorded by master base station100A concerning transmission of the immediately preceding initial message100A. The length of time between the transmissions of the two initial messages would thus be limited by the first and second timestamps.

The initial messages100A are received in the non-master base stations160,170, which record timestamps indicating when the initial messages100A are received. As the non-master base stations are not necessarily required to have very accurate internal clocks, these non-master base stations determine length of time between consecutive receptions of initial messages100A.

FIG.2illustrates an example system in accordance with at least some embodiments of the present invention. The system ofFIG.2corresponds to that ofFIG.1. In the situation ofFIG.1, an initial message100A has been sent from master base station150and received in non-master base stations160,170. The tag110transmits the signal100B described above, for example omnidirectionally, such that the base stations are enabled to receive it. This signal is received in non-master base stations, which record a time of receipt of the signal at the non-master base station. The master base station receives signal100B and records a receipt timestamp indicating a time of receipt of signal100B in the master base station.

The master base station and the base stations each have time counters. The time counters may have a maximum value 0xffffffffff in hexadecimal, for example. The time counters may keep track of time, for example using a clock which has a 64 GHz clock frequency. Once a time counter reaches its maximum value, it may loop back to zero. The time counters may be employed in generating sending and receiving timestamps as described herein. The master base station and non-master base stations may start in an unsynchronized manner, and these clocks may have frequency offsets, dynamic noise and static noise. Each radio device has an antenna delay which, strictly speaking, is specific to the radio device. Further, signal power levels at receipt may introduce timing errors. Communicating a duration of a time period provides the effect that it overcomes issues from starting the clocks in an unsynchronized manner.

Non-master base stations obtain lengths of time limited by receipt in the non-master base station of the signal from tag110and receipt in the non-master base station of the immediately preceding initial message100A. The non-master base stations therefore may record two lengths of time: a first length of time from receipt of the most recent initial message100A to receipt of the signal100B from the tag, and a second length of time from receipt of the most recent initial message100A to the next initial message100A. The non-master base stations may report these lengths of time to the master base station, or to another node tasked with positioning the wireless tag110. The node tasked with positioning wireless tag110may thus be the master base station, or another entity. The non-master base stations160,170may provide the lengths of time to the node tasked with positioning wireless tag110directly, or via master base station150, for example. The determination of the time difference of arrival, TDOA, of the signal from wireless tag110in non-master base stations160,170will be described with reference toFIG.3.

Alternatively to reporting lengths of time to the master base station or to the other node tasked with positioning wireless tag110, the non-master base stations may report their timestamps of receipt of the100A and100B messages, enabling the master base station or other node to calculate the lengths of time. The effect is the same, namely that the master base station or other node obtains the lengths of time. Likewise, when the other node determines the position of wireless tag110, the master base station may report either lengths of time or of the timestamps. Wireless communication, either of lengths of time or of timestamps, may be based on UWB, Bluetooth low energy, BLE, WLAN or the long range, LoRa, spread spectrum wireless technology. Also wire-line communication may be used in the communicating of the timestamps and/or lengths of time.

In the overall determination of the location of wireless tag110, plural systems may be used, such that overall plural master base stations may be involved. The eventual location estimate of wireless tag110may be the average of estimates obtained using the involved systems, for example. An overall positioning system with plural master base stations controlling non-master base stations, wherein some of the non-master base stations may be shared between at least two of the master base stations, may be used to determine a location of a wireless tag. As noted above, a master base station may be configured to determine the location of wireless tag110, or another node may be configured to do this. When the other node is so configured, the other node may comprise an on-site computer, a gateway device or a cloud computing server, for example.

FIG.3illustrates TDOA determination in accordance with a first set of embodiments. The horizonta1axes correspond to master base station150, non-master base stations160,170, and to wireless tag110, as labelled in the figure. Time advances from the left toward the right.

Solid vertical arrows denote transmission of signals, and dashed vertical arrows denote reception of signals. First timestamp T1corresponds to transmission of an initial message100A from master base station, and second timestamp T1oldcorresponds to transmission of an immediately preceding initial message100A from the master base station. Time interval tb is the length of time between transmissions of the two initial messages100A from master base station150. Time interval tb may be referred to overall as a fifth length of time. Time interval tb may be obtained by subtracting T1−T1old. Similarly, the first, second, third and fourth lengths of time may be obtained as a difference between two counter values, a single counter value acting as a timestamp.

Timestamp T2(1) corresponds to reception of the initial message100A sent at the first timestamp T1at non-master base station160, and timestamp T2(2) corresponds to reception of the initial message100A sent at the first timestamp T1at non-master base station170. Likewise, timestamp T2old(1) corresponds to reception of the initial message100A sent at the second timestamp T1oldat non-master base station160, and timestamp T2old(2) corresponds to reception of the initial message100A sent at the second timestamp T1oldat non-master base station170. The time-of-flight from master base station150to non-master base station160is R1, and the time-of-flight from master base station150to non-master base station170is R2.

TX is the transmission of the signal from wireless tag110. This signal is received at non-master base station160at timestamp T4(1), and the same signal is received in non-master base station170at timestamp T4(2). The TDOA of this signal between these two non-master base stations160,170is denoted “TDOA” in the figure.

Non-master base station160thus obtains a first length of time ta1(1) from receipt T2old(1) of the most recent initial message100A to receipt T4(1) of the signal100B from the tag, and a second length of time tb1(1) from receipt T2old(1) of the most recent initial message100A to receipt T2(1) of the next initial message100A.

Non-master base station170thus obtains a third length of time ta1(2) from receipt T2old(2) of the most recent initial message100A to receipt T4(2) of the signal100B from the tag, and a fourth length of time tb1(2) from receipt T2old(2) of the most recent initial message100A to receipt T2(2) of the next initial message100A.

The TDOA of signal TX between non-master base stations160and170may then be obtained as:
TDOA(160,170)=ta1(1)×tb/tb1(1)+R1−(ta1(2)×tb/tb1(2)+R2),
or alternatively as
TDOA(160,170)=ta1(2)×tb/tb1(2)+R2−(ta1(1)×tb/tb1(1)+R1).

Plural ones of such TDOAs (obtained from plural pairs of non-master base stations) may be used to solve the geographic position of wireless tag110. As the system may comprise more than two non-master base stations, the number of TDOAs obtained from a single signal TX from wireless tag100may be fairly large. When there are more TDOAs than strictly needed to solve the position of wireless tag110, the increasing number of TDOAs have the effect that positioning error is reduced.

FIG.4illustrates TDOA determination in accordance with a second set of embodiments. In these embodiments, the TDOA is determined between the master base station and a non-master base station.

As inFIG.3, the master base station transmits initial messages100A at times T1and T1old. These messages are received by non-master base station160at times T2and T2old, respectively. The wireless tag110transmits its wireless signal TX, which is received by master base station150at time instant T3, and by non-master base station160at time instant T4. The time difference between T3and T4is the TDOA of this signal between master base station150and non-master base station160.

Four lengths of time may be defined: a first length of time ta limited by T3and T1old, a second length of time tb limited by T1oldand T1, a third length of time ta1limited by T4and T2old, and a fourth length of time tb1limited by T2and T2old.

The TDOA of signal TX between master base station150and non-master base station160may be obtained as:
TDOA(150,160)=ta1(1)×SYNC(1)−ta+R1,
or alternatively as
TDOA(150,160)=(ta−ta1(1)×SYNC(1)−R1, where SYNC(1)=tb/tb1(1).

Plural ones of such TDOAs may be used to solve the geographic position of wireless tag110. As the system may comprise more than two non-master base stations, the number of TDOAs obtained from a single signal TX from wireless tag100may be fairly large. When there are more TDOAs than strictly needed to solve the position of wireless tag110, the increasing number of TDOAs have the effect that positioning error is reduced. In some embodiments, both time differences of arrival between two non-master base stations and between master- and non-master base stations may be used together.

In both theFIG.3andFIG.4embodiments, the TDOA may be scaled by multiplying it with a time unit, such as a time unit equal to 1/64 GHz or 1/128 GHz, for example.

A technical effect and benefit of the methods disclosed herein is that wireless tag110may be positioned in a network of one master and plural non-master base stations using three messages, wherein the master base station transmits two messages100A and the wireless tag transmits a single message100B. TDOA values may be determined between all base stations within range of wireless tag110, wherefore as the number of base stations may be large, the number of TDOA values obtained from these three messages may be high, enabling accurate positioning of wireless tag110. This mechanism enables a positioning system with in principle unlimited range using an overall system where plural master base stations control non-master base stations, wherein some of the non-master base stations may be shared between at least two of the master base stations.

The methods disclosed herein overcome the technical problem of antenna delays being specific to individual radio devices, owing to manufacturing differences in individual parts, since lengths of time are determined from timestamps expressed as counter values in the individual base stations. The base station-specific antenna/RF delay is cancelled out from the computation of the length of time since it is identical in the receipt of all signals in this base station.

FIG.5illustrates an example apparatus capable of supporting at least some embodiments of the present invention. Illustrated is device500, which may comprise, for example, an electronic device such as a base station or tag ofFIG.1orFIG.2. Comprised in device500is processor510, which may comprise, for example, a single- or multi-core processor wherein a single-core processor comprises one processing core and a multi-core processor comprises more than one processing core. Processor510may comprise, in general, a control device. Processor510may comprise more than one processor. Processor510may be a control device. A processing core may comprise, for example, a Cortex-A8 processing core manufactured by ARM Holdings or a Zen processing core designed by Advanced Micro Devices Corporation. Processor510may comprise at least one Qualcomm Snapdragon and/or Intel Atom processor. Processor510may comprise at least one application-specific integrated circuit, ASIC. Processor510may comprise at least one field-programmable gate array, FPGA. Processor510may be means for performing method steps in device500. Processor510may be configured, at least in part by computer instructions, to perform actions.

Device500may comprise memory520. Memory520may comprise random-access memory and/or permanent memory. Memory520may comprise at least one RAM chip. Memory520may comprise solid-state, magnetic, optical and/or holographic memory, for example. Memory520may be at least in part accessible to processor510. Memory520may be at least in part comprised in processor510. Memory520may be means for storing information. Memory520may comprise computer instructions that processor510is configured to execute. When computer instructions configured to cause processor510to perform certain actions are stored in memory520, and device500overall is configured to run under the direction of processor510using computer instructions from memory520, processor510and/or its at least one processing core may be considered to be configured to perform said certain actions. Memory520may be at least in part comprised in processor510. Memory520may be at least in part external to device500but accessible to device500.

Device500may comprise a transmitter530. Device500may comprise a receiver540. Transmitter530and receiver540may be configured to transmit and receive, respectively, information in accordance with at least one cellular or non-cellular standard. Transmitter530and receiver540may be comprised in a single transceiver. Transmitter530may comprise more than one transmitter. Receiver540may comprise more than one receiver. Transmitter530and/or receiver540may be configured to operate in accordance with global system for mobile communication, GSM, wideband code division multiple access, WCDMA, 5G, long term evolution, LTE, UWB, UWB, wireless local area network, WLAN, Ethernet and/or worldwide interoperability for microwave access, WiMAX, standards, for example.

Device500may comprise a near-field communication, NFC, transceiver550. NFC transceiver550may support at least one NFC technology, such as NFC, Bluetooth, Wibree or similar technologies.

Device500may comprise user interface, UI,560. UI560may comprise at least one of a display, a keyboard, a touchscreen, a vibrator arranged to signal to a user by causing device500to vibrate, a speaker and a microphone. A user may be able to operate device500via UI560, for example to configure positioning parameters.

Processor510may be furnished with a transmitter arranged to output information from processor510, via electrical leads internal to device500, to other devices comprised in device500. Such a transmitter may comprise a serial bus transmitter arranged to, for example, output information via at least one electrical lead to memory520for storage therein. Alternatively to a serial bus, the transmitter may comprise a parallel bus transmitter. Likewise processor510may comprise a receiver arranged to receive information in processor510, via electrical leads internal to device500, from other devices comprised in device500. Such a receiver may comprise a serial bus receiver arranged to, for example, receive information via at least one electrical lead from receiver540for processing in processor510. Alternatively to a serial bus, the receiver may comprise a parallel bus receiver. Device500may comprise further devices not illustrated inFIG.5.

Processor510, memory520, transmitter530, receiver540, NFC transceiver550and/or UI560may be interconnected by electrical leads internal to device500in a multitude of different ways. For example, each of the aforementioned devices may be separately connected to a master bus internal to device500, to allow for the devices to exchange information. However, as the skilled person will appreciate, this is only one example and depending on the embodiment various ways of interconnecting at least two of the aforementioned devices may be selected without departing from the scope of the present invention.

FIG.6is a flow graph of a method in accordance with at least some embodiments of the present invention. The phases of the illustrated method may be performed in the node tasked with positioning wireless tag110. As described above, this node may be the master base station or a further entity. As noted above, this further entity may comprise a node such as an on-site computer, gateway device or cloud computing server, for example.

Phase610comprises obtaining the first and second lengths of time. Phase620comprises obtaining the third, fourth and fifth lengths of time. These lengths of time have been discussed herein above.

Phase630comprises determining a time difference of arrival of the signal from the wireless tag between the first and second non-master base stations as the first length of time multiplied by a ratio of the fifth length of time and the second length of time, to which is added a time of flight at light speed from the master base station to the first non-master base station and from which is subtracted a product of the third length of time and a ratio of the fifth length of time and the fourth length of time, and from which is subtracted a time of flight at light speed from the master base station to the second non-master base station.

FIG.7is a flow graph of a method in accordance with at least some embodiments of the present invention. The phases of the illustrated method may be performed in the node tasked with positioning wireless tag110. As described above, this node may be the master base station or a further entity.

Phase710comprises obtaining a first length of time and a second length of time. Phase720comprises obtaining a third length of time, a fourth length of time and a ratio between the second length of time and the fourth length of time.

Phase730comprises determining a time difference of arrival of the signal from the wireless tag between the master base station and the non-master base station as the third length of time multiplied by the ratio, from which the first length of time is subtracted and to which a time of flight at light speed from the master base station to the non-master base station is added.

It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the preceding description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, that is, a singular form, throughout this document does not exclude a plurality.

INDUSTRIAL APPLICABILITY

At least some embodiments of the present invention find industrial application in wireless positioning.

ACRONYMS LIST

TDOA time difference of arrival locationUWB ultra wide band

REFERENCE SIGNS LIST110tag150master base station160, 170non-master base station100Ainitial message100Bsignal from tag 110500-560structure of the device of FIG. 5610-630phases of the method of FIG. 6710-730phases of the method of FIG. 6