System, method and computer program for positioning animal tags

Abstract

A system and method applicable for determining the positions of radio tags based on triangulation and respective radio tag signals transmitted from each radio tag, where each of a set of base stations is configured to transmit a radio base signal including an identifier that uniquely identifies the base station, and other base stations of the set of base stations receive the radio base signal and forward received base station messages to a central control unit which determines a position for any added base station using triangulation and known positions for base stations already included in the system, in order to facilitate expanding the number of base stations in the system.

Claims

1. A system for determining positions of radio tags (T), the system comprising: a central control unit (110); and a set of base stations (121, 122, 123, 124), each base station in said set of base stations being configured to receive a global time reference (CLK) and radio tag signals (S.sub.T) transmitted from said radio tags (T), each of the radio tag signals (S.sub.T) comprising a tag identifier uniquely identifying a respective radio tag of said radio tags (T), and each base station in said set of base stations being configured to forward a respective tag message describing each of any received radio tag signals (S.sub.T) to the central control unit (110), the central control unit (110) being configured to receive the tag messages, and based thereon determine a respective position for each radio tag (T) from which a radio tag signal (S.sub.T) has been received by at least three base stations in said set of base stations, wherein each base station in said set of base stations is further configured to: transmit a radio base signal comprising a base station identifier uniquely identifying the base station, receive radio base signals from other base stations in said set of base stations, and forward a base station message describing any received radio base signal to the central control unit (110), wherein the central control unit (110) is further configured to: receive at least three base station messages from respective at least three base stations in said set of base stations describing a first radio base signal from a first base station in said set of base stations, and determine a position for said first base station (121) using the received at least three base station messages, triangulation, and respective known positions of said respective base stations, wherein said set of base stations comprises: anchor base stations arranged in a frame around an area in which positions for radio tags (T) are to be determined, the anchor base stations being located in a common plane, and one or more intermediate base stations arranged between two of said anchor base stations, and wherein the central control unit (110) is configured to: calculate a first sub distance between a first anchor base station and an intermediate base station of said one or more intermediate base stations where, in a projection onto the common plane, the intermediate base station is located on a straight line between the first anchor base station and a second anchor base station, calculate a second sub distance between the second anchor base station and the intermediate base station, obtain an overall distance between said first and second anchor base stations, and determine that the intermediate base station is located outside the common plane if a sum of the first and second sub distances is larger than the overall distance.

2. A method of determining positions of radio tags (T) via a set of base stations (121, 122, 123, 124) and a central control unit (110), the method comprising: receiving, in each base station in the set of base stations, a global time reference (CLK); receiving, in at least three base stations in said set of base stations, a radio tag signal (S.sub.T) transmitted from a radio tag (T), the radio tag signal (S.sub.T) comprising an identifier uniquely identifying the radio tag (T); forwarding, from each of the at least three base stations, a respective tag message describing the received radio tag signal (S.sub.T) to the central control unit (110); receiving in the central control unit (110) the respective tag messages forwarded by the at least three base stations, and based thereon determining a position of the radio tag (T); transmitting, from each base station in said set of base stations, a respective radio base signal comprising an identifier uniquely identifying the base station; checking if a radio base signal having been received from any other base station of said base stations in said set of base stations, and forwarding a base station message describing any received radio base signal received from said any other base station to the central control unit (110); and in response to receiving in the central control unit (110) at least three base station messages describing a first radio base signal of a first base station in said set of base stations, determining a position for the first base station (121) using the received at least three base station messages, triangulation, and respective known positions of respective base stations in said set of base stations from which the at least three base station messages were received, wherein said set of base stations comprises: anchor base stations arranged in a frame around an area in which positions for the radio tags (T) are to be determined, the anchor base stations being located in a common plane, and one or more intermediate base stations arranged between two of said anchor base stations, wherein the method further comprises, in the central control unit (110): calculating a first sub distance between a first base station and an intermediate base station where, in a projection onto the common plane, the intermediate base station is located on a straight line between the first anchor base station and a second anchor base station, calculating a second sub distance between the second anchor base station and the intermediate base station, obtaining an overall distance between said first and second anchor base stations, and determining that the intermediate base station is located outside the common plane if a sum of the first and second sub distances is larger than the overall distance, the overall distance, the first sub distance and the second sub distance being calculated based on respective radio base signals from the intermediate base station, the first anchor base station, and the second anchor base station.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is now to be explained more closely by means of preferred embodiments, which are disclosed as examples, and with reference to the attached drawings.

(2) FIG. 1 Illustrates schematically how an animal tag is positioned according to the invention;

(3) FIG. 2 Illustrates schematically how a base station is positioned according to the invention;

(4) FIG. 3 shows an example of how anchor base stations and intermediate base stations can be arranged according to one embodiment of the invention;

(5) FIGS. 4-6 exemplify different elevation relationships between the anchor base stations and the intermediate base stations according to embodiments of the invention;

(6) FIG. 7 illustrates, by means of a flow diagram, the general method performed in the central control unit for positioning animal tags; and

(7) FIG. 8 illustrates, by means of a flow diagram, the general method performed in the central control unit for positioning base stations.

DETAILED DESCRIPTION

(8) In FIG. 1, we see a schematic illustration of a system for positioning animal tags T according to one embodiment of the invention.

(9) The system includes a central control unit 110 and a set of base stations 122, 123 and 124 respectively. Each base station in the set of base stations is configured to receive a global time reference CLK, for example in the form of a clock signal from the central control unit 110. Thereby, all base stations share a common time basis that enables determining propagation delays in radio signals that have been received by two or more of the base stations.

(10) Each base station in the set of base stations 122, 123 and 124 is also configured to receive a respective radio tag signal S.sub.T that has been transmitted from at least one animal tag T. Each of these radio tag signals S.sub.T contains an identifier uniquely identifying the respective animal tag T. Thereby, the radio tag signals S.sub.T can be distinguished from one another upon receipt in the base stations.

(11) Each base station in the set of base stations 122, 123 and 124 is also configured to forward a respective tag message M.sub.T(t.sub.2), M.sub.T(t.sub.3) and M.sub.T(t.sub.4) to the central control unit 110. The tag messages M.sub.T(t.sub.2), M.sub.T(t.sub.3) and M.sub.T(t.sub.4) describe each of any received radio tag signals S.sub.T. In the example illustrated in FIG. 1, the animal tag T is located a relatively short distance from a base station 122, a relatively long distance from a base station 124 and at an intermediate distance from a base station 123. Consequently, the radio tag signals S.sub.T will reach the base station 122 at a first point in time t.sub.1, the base station 123 at a second point in time t.sub.2, and the base station 124 at a third point in time t.sub.3, where the first, second and third points in time occur in the temporal order t.sub.1, t.sub.2 and t.sub.3. The tag messages M.sub.T(t.sub.2), M.sub.T(t.sub.3) and M.sub.T(t.sub.4) reflect the first, second and third points in time t.sub.1, t.sub.2 and t.sub.3 respectively.

(12) The central control unit 110 is configured to receive the tag messages M.sub.T(t.sub.2), M.sub.T(t.sub.3) and M.sub.T(t.sub.4), and based thereon determine a position P[T] for the animal tag T. This determination is made by analyzing the radio tag signal S.sub.T having been received by at least three base stations, here 122, 123 and 124.

(13) Preferably, the central control unit 110 is configured to determine the position of the animal tag T based on triangulation by using the tag messages M.sub.T(t.sub.2), M.sub.T(t.sub.3) and M.sub.T(t.sub.4). Namely, each tag message M.sub.T(t.sub.2), M.sub.T(t.sub.3) and M.sub.T(t.sub.4) contains an indication of the propagation delay radio tag signal S.sub.T to the base station in question, and thus a distance measure between the animal tag T and this base station. Assuming that the respective position of each of said base stations 122, 123 and 124 is known, it is straightforward to determine the position P[T] for the animal tag T.

(14) Referring now to FIG. 2, we will explain how a base station is positioned according to the invention. Here, a base station 121 is also included in addition to the base stations 122, 123 and 124 of FIG. 1. Analogous to above, we assume that the respective positions of the base stations 122, 123 and 124 are known. However, the base station 121 is newly added resource whose position is to be determined. To this aim, each base station 121, 122, 123 and 124 is configured to transmit a respective radio base signal containing an identifier uniquely identifying the base station. FIG. 2 shows one such radio base signal S.sub.B1 transmitted from the base station 121, and thus containing an identifier uniquely identifying the base station 121.

(15) Each base station is configured to receive radio base signals from other base stations in the system, i.e. here the base station 122 is configured to receive radio base signals from the base stations 121, 123 and 124; the base station 123 is configured to receive radio base signals from the base stations 121, 122 and 124; the base station 124 is configured to receive radio base signals from the base stations 121, 122 and 123; the base station 121 is configured to receive radio base signals from the base stations 122, 123 and 124. Moreover, each base station is configured to forward a base station message describing any received radio base signal to the central control unit 110. In the example shown in FIG. 2, the base station messages M.sub.B1(t.sub.2), M.sub.B1(t.sub.3) and M.sub.B1(t.sub.4) describing the radio base signal S.sub.B1 are forwarded from the base stations 122, 123 and 124 to the central control unit 110.

(16) The central control unit 110, in turn, is configured to receive base station messages describing radio base signals, and based thereon determine positions for the base stations concerned. A condition for this is that base station messages from a given base station, say 121, have been received by at least three other base stations. In FIG. 2, the central control unit 110 receives the base station messages M.sub.B1(t.sub.1), M.sub.B1(t.sub.2) and M.sub.B1(t.sub.3) describing the radio base signal S.sub.B1 from the base station 121. Based thereon, the central control unit 110 determines a position P[B1] for the base station 121 using triangulation and a respective known position for each of said at least three base stations 122, 123 and 124 analogous to what is described above referring to determining the position P[T] for the animal tag T.

(17) According to one embodiment of the invention, the base stations 121, 122, 123 and 124 are configured to transmit the radio base signals repeatedly, i.e. not only when a new base station is added to the system.

(18) The central control unit 110 is further configured to determine a respective updated position P[B1] for a particular base station, e.g. 121, in response to receiving a new radio base signal SB.sub.1 from that base station 121. Analogous to the above, a condition for this is that the new radio base signal SB.sub.1 has been received by at least three other base stations in the system, such as 122, 123 and 124.

(19) According to embodiments of the invention, the system contains base stations of at least two different categories, namely anchor base stations and at least one intermediate base station. FIG. 3 shows an example configuration, where a subset of anchor base stations BSA1, BSA2 and BSA3, BSA4 are arranged in a frame around an area in which positions for animal tags T are to be determined. The subset of anchor base stations BSA1, BSA2, BSA3 and BSA4 are located in a common plane. Typically, this means that they all have the same elevation relative to a reference plane, e.g. the ground.

(20) In FIG. 3, the at least one intermediate base station is represented by BSI1, BSI2, BSI3, BSI4 and BSI5. An intermediate base station is defined as a base station being arranged between two base stations in the set of anchor base stations, i.e. here BSA1, BSA2, BSA3 and BSA4. An intermediate base station may either be located in the common plane of the anchor base stations, or outside this plane. For instance, BSI1 and BSI4 may be located in the common plane while BSI2, BSI3 and BSI5 are located outside the common plane as will be discussed below.

(21) FIG. 4 shows the anchor base stations BSA1 and BSA3 and the intermediate base station BSI5 seen from a view perpendicular to the view represented in FIG. 3. The anchor base stations BSA1 and BSA3 have a known, and here equal, elevation relative to the reference level. Namely, we presume that the elevation level of the common plane is known.

(22) The intermediate base station BSI3, however, is located outside the common plane. In FIG. 4, this is indicated by a deviation Δe.sub.BSI5 from the common plane. In order to determine a position in three dimensions for the intermediate base station BSI3, i.e. effectively calculating the deviation Δe.sub.BSI5, the central control unit 110 is configured to receive an elevation indicator for the intermediate base station BSI1. The elevation indicator is merely a symbol reflecting whether the intermediate base station is located above or below the common plane. For example, a binary “1” may symbolize above and a binary “0” may symbolize below.

(23) The central control unit 110 is further configured to determine a respective distance d.sub.BSA1-BSI5 and d.sub.BSA3-BSI5 between the intermediate base station BSI1 and each of said anchor base stations BSA1 and BSA3. The distances d.sub.BSA1-BSI5 and d.sub.BSA3-BSI5 are determined as described above by receiving base station messages from the intermediate base station BSI1 in base stations whose locations are already known with respect to position as well as elevation.

(24) According to one embodiment of the invention, it is presumed that, in a projection onto the common plane, the intermediate base station BSI5 is located on a straight line between the anchor base stations BSA1 and BSA3 respectively.

(25) The central control unit 110 is configured to obtain an overall distance d.sub.BSA1-BSA3 between the anchor base stations BSA1 and BSA3, either from a database or by calculation as described above. The central control unit 110 is further configured to calculate a first sub distance d.sub.BSA1-BSI5 between the first anchor base station BSA3 and the intermediate base station BSI5; and calculate a second sub distance d.sub.BSA3-BSI5 between the second anchor base BSA3 station and the intermediate base station BSI5. The first and second sub distances d.sub.BSA1-BSI5 and d.sub.BSA3-BSI5 are likewise calculated by receiving base station messages from the intermediate base station BSI1 in base stations whose locations are already known.

(26) Then, by applying Pythagoras Theorem and by using the elevation indicator, central control unit 110 is configured to determine the specific elevation the intermediate base station BSI5, i.e. calculating the deviation Δe.sub.BSI5 and applying an adequate sign relative to the common plane.

(27) The central control unit 110 is preferably configured determine whether or not the intermediate base station BSI5 is located in the common plane as follows. If a sum of the first and second sub distances d.sub.BSA1-BSI5 and d.sub.BSA3-BSI5 is larger than the overall distance d.sub.BSA1-BSA3 between the anchor nodes BSA1 and BSA3, then the intermediate base station BSI5 is not located in the common plane.

(28) FIG. 5 shows another example illustrating that the intermediate base station BSI2 is located a deviation Δe.sub.BSI2 below the common plane in which the anchor nodes BSA2 and BSA3 are located. The anchor nodes BSA2 and BSA3 are separated from one another by an overall distance d.sub.BSA2-BSA3, a first sub distance between the anchor node BSA2 and the intermediate node BSI2 is d.sub.BSA2-BSI2 and a second sub distance between the anchor node BSA3 and the intermediate node BSI2 is d.sub.BSA3-BSI2.

(29) FIG. 6 shows yet another example of an intermediate node BSI3 being located below the common plane, namely the one including the anchor nodes BSA3 and BSA4 respectively. Here, the anchor nodes BSA3 and BSA4 are separated from one another by an overall distance d.sub.BSA3-BSA4, a first sub distance between the anchor node BSA3 and the intermediate node BSI3 is d.sub.BSA3-BSI3 and a second sub distances between the anchor node BSA4 and the intermediate node BSI3 is d.sub.BSA4-BSI3.

(30) It is generally advantageous if the processing unit 120 is configured to effect the above-mentioned procedure in an automatic manner by executing a computer program 135. Therefore, the processing unit 120 may include a memory unit, i.e. non-volatile data carrier 130, storing the computer program 135, which, in turn, contains software for making processing circuitry in the form of at least one processor in the processing unit 120 execute the above-described actions when the computer program 135 is run on the at least one processor.

(31) In order to sum up, and with reference to the flow diagrams in FIGS. 7 and 8, we will now describe the general method according to the invention for positioning animal tags and base stations performed in the base stations and the central control unit respectively.

(32) In FIG. 7, in a first step 710, a global time reference is received. Thereafter, a step 720 checks if a tag signal has been received; if so, a step 730 follows, and otherwise the procedure loops back to step 710. In 730, a tag message is forwarded to the central control unit in response to the tag signal. Subsequently, the procedure loops back to step 710.

(33) In another step 740 following step 710, it is checked if a radio base signal has been received; if so, a step 750 follows, and otherwise the procedure loops back to step 710. In step 750, a base station message is forwarded to the central control unit in response to the radio base signal. Subsequently, the procedure loops back to step 710.

(34) In FIG. 8, in a first step 810, it is checked if a tag message has been received from a base station. If so, a step 820 follows; and otherwise, the procedure loops back to step 810.

(35) In step 820, it is checked if altogether at least three tag messages have been received from the same animal tag. If so, a step 830 follows; and otherwise, the procedure loops back to step 810. In step 830, a position is determined for the animal tag from which at least three tag messages have been received. Subsequently, the procedure loops back to step 810.

(36) In first step 840 of a procedure parallel to the above, it is checked if a base station message has been received. If so, a step 850 follows; and otherwise, the procedure loops back to step 840.

(37) In step 850, it is checked if altogether at least three base station messages have been received from the base station. If so, a step 860 follows; and otherwise, the procedure loops back to step 840. In step 860, a position is determined for the base station from which at least three base station messages have been received. Subsequently, the procedure loops back to step 840.

(38) All of the process steps, as well as any sub-sequence of steps, described with reference to FIGS. 7 and 8 may be controlled by means of a programmed processor. Moreover, although the embodiments of the invention described above with reference to the drawings comprise processor and processes performed in at least one processor, the invention thus also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other form suitable for use in the implementation of the process according to the invention. The program may either be a part of an operating system, or be a separate application. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a Flash memory, a ROM (Read Only Memory), for example a DVD (Digital Video/Versatile Disk), a CD (Compact Disc) or a semiconductor ROM, an EPROM (Erasable Programmable Read-Only Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), or a magnetic recording medium, for example a floppy disc or hard disc. Further, the carrier may be a transmissible carrier such as an electrical or optical signal, which may be conveyed via electrical or optical cable or by, radio or by other means. When the program is embodied in a signal, which may be conveyed, directly by a cable or other device or means, the carrier may be constituted by such cable or device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant processes.

(39) Although the invention is primarily intended to determine the positions of milk-producing animals, e.g. cows, the proposed solution is equally well applicable for any other kind of livestock or wild animals.

(40) The term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components. However, the term does not preclude the presence or addition of one or more additional features, integers, steps or components or groups thereof.

(41) The invention is not restricted to the described embodiments in the figures, but may be varied freely within the scope of the claims.