Device for determining a position of a transmitter and corresponding method

Abstract

What is disclosed is a device for determining a piece of information on a position of a transmitter, comprising an antenna device, a signal processing device and a data processing device. Thus, the antenna device comprises several different directional characteristics, the directional characteristics each relating to at least a set of spatially different receive sensitivities of the antenna device. The antenna device receives signals from the transmitter with different directional characteristics, the signal processing device processing the signals received and establishing a respective amplitude value of a field strength. The data processing device establishes the information on the position of the transmitter based on the directional characteristics and the amplitude values having been established for the associated signals received. Additionally, a corresponding method is disclosed.

Claims

1. A device for determining at least one piece of information on a position of at least one transmitter, comprising an antenna device, a signal processing device and a data processing device, wherein the antenna device comprises a feed network having a plurality of antenna inputs and a plurality of signal inputs, wherein the antenna device comprises a multibeam antenna device comprising a plurality of antenna elements, wherein each of the antenna inputs is connected to one of the antenna elements, wherein the antenna device comprises several different directional characteristics, wherein the directional characteristics each relate to at least a set of spatially different receive sensitivities of the antenna device, wherein the antenna device is configured to receive for each of a plurality of the directional characteristics at least one signal from the transmitter, wherein the several different directional characteristics are selected for receiving the at least one signal from the transmitter for each of the plurality of the directional characteristics one after another by connecting the signal processing device to different signal inputs of the plurality of signal inputs, wherein the signal processing device is configured to process the signals received by the antenna device and to establish for each of the signals an amplitude value of a field strength of the respective signal, and wherein the data processing device is configured to establish the information on the position of the transmitter based on the plurality of the directional characteristics and based on the amplitude values established from the signals associated with one of the plurality of the directional characteristics.

2. The device in accordance with claim 1, the device comprising a control device, wherein the control device is configured to switch different directional characteristics for receiving signals emanating from the transmitter, and wherein the data processing device is configured to establish the information on the position of the transmitter based on the switched directional characteristics and the associated amplitude values established.

3. The device in accordance with claim 1, wherein the data processing device is configured to establish a statement on a direction of the transmitter relative to the antenna device as information on the position of the transmitter from the amplitude values established in a vector form and data on the directional characteristics.

4. The device in accordance with claim 1, wherein the antenna device is configured such that the directional characteristics each comprise a global maximum which is located each in a certain sector, determined by a pair of an azimuth angle and a co-elevation angle, in an irradiation region associated to the antenna device.

5. The device in accordance with claim 4, wherein the antenna device is configured such that the directional characteristics each comprise a side maximum which is located each in a sector differing from that sector where the global maximum is located, and which comprises a predeterminable level distance to a level of the global maximum.

6. The device in accordance with claim 4, wherein the antenna device is configured such that the directional characteristics each comprise a side maximum which is located each in the same sector as the global maximum and which comprises a predeterminable level distance to a level of the global maximum.

7. The device in accordance with claim 1, wherein the signal processing device is an RFID reader which generates a “received signal strength indication” (RSSI) value as an amplitude value of the field strength of the signals received.

8. The device in accordance with claim 1, wherein the signal processing device is configured to identify the transmitter.

9. The device in accordance with claim 2, the device comprising a signal source, wherein the signal source is configured to generate an excitation signal, and wherein the control device is configured to switch a respective directional characteristic for radiating the excitation signal.

10. The device in accordance with claim 9, wherein the control device is configured to switch the directional characteristic switched for radiating the excitation signal as a directional characteristic for receiving the signal emanating from the transmitter.

11. The device in accordance with claim 1, wherein the antenna device comprises several antenna elements.

12. The device in accordance with claim 1, wherein the antenna device comprises a feed network, and wherein the feed network causes different directional characteristics of the antenna device.

13. The device in accordance with claim 12, wherein the feed network is configured to output the signals received from the antenna device for each of the plurality of the directional characteristics separately.

14. The device in accordance with claim 1, wherein the antenna device is implemented as a multibeam antenna.

15. A method for determining at least one piece of information on a position of at least one transmitter using an antenna device, a control device, a signal processing device and a data processing device, wherein the antenna device comprises a feed network having a plurality of antenna inputs and a plurality of signal inputs, wherein the antenna device comprises a multibeam antenna device comprising a plurality of antenna elements, and wherein each of the antenna inputs is connected to one of the antenna elements, the method comprising the steps of: using an antenna device comprising several different directional characteristics for receiving for each of a plurality of the directional characteristics at least one signal from the transmitter, wherein the directional characteristics each relate to at least a set of spatially different receive sensitivities of the antenna device, wherein the several different directional characteristics are selected for receiving the at least one signal for each of the plurality of the directional characteristics from the transmitter one after another by connecting the signal processing device to different signal inputs of the plurality of signal inputs, using a signal processing device for processing the signals received by the antenna device and to establish for each of the signals an amplitude value of a field strength of the respective signal, and using a data processing device for establishing the information on the position of the transmitter based on the plurality of the directional characteristics and based on the amplitude values established from the signals associated with one of the plurality of the directional characteristics.

16. A device for determining at least one piece of information on a position of at least one transmitter, comprising an antenna device, a control device, a signal processing device and a data processing device, wherein the antenna device comprises a feed network having a plurality of antenna inputs and a plurality of signal inputs, wherein the antenna device comprises a multibeam antenna device comprising a plurality of antenna elements, wherein each of the antenna inputs is connected to one of the antenna elements, wherein the antenna device comprises several different directional characteristics, wherein the directional characteristics each relate to at least a set of spatially different receive sensitivities of the antenna device, wherein the antenna device is configured to receive for each of a plurality of the directional characteristics at least one signal from the transmitter, wherein the antenna device comprises a feed network, wherein the several different directional characteristics are selected for receiving the at least one signal from the transmitter for each of the plurality of the directional characteristics one after another by connecting the signal processing device to different signal inputs of the plurality of signal inputs, the feed network causing different directional characteristics of the antenna device, wherein the feed network is configured to output signals received from the antenna device for each of the plurality of the directional characteristics separately, wherein the antenna device is configured such that the directional characteristics each comprise a global maximum which is located each in a certain sector, determined by a pair of an azimuth angle and a co-elevation angle, in an irradiation region associated to the antenna device, wherein the antenna device is configured such that the directional characteristics each comprise a side maximum which is located each in a sector differing from that sector where the global maximum is located, and which comprises a predeterminable level distance to a level of the global maximum, wherein the control device is configured to switch the different directional characteristics caused by the feed network for receiving signals emanating from the transmitter, wherein the signal processing device is configured to process the signals received by the antenna device and to establish for each of the signals an amplitude value of a field strength of the respective signal, wherein the data processing device is configured to establish the information on the position of the transmitter based on the plurality of the directional characteristics and based on the amplitude values established from the signals associated with one of the plurality of the directional characteristics, and wherein the data processing device is configured to establish a statement on a direction of the transmitter relative to the antenna device as information on the position of the transmitter from the amplitude values established in a vector form and data on the directional characteristics.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiment of the present invention will be detailed subsequently referring to the appended drawings, in which:

(2) FIG. 1 shows a rough illustration of an inventive device in combination with a transmitter;

(3) FIG. 2 shows a drawing of an irradiation region and the decomposition thereof into 16 sectors;

(4) FIG. 3 shows a drawing of the association of directional characteristics to sectors of the irradiation region; and

(5) FIG. 4 shows a schematic illustration of an alternative implementation of the device.

DETAILED DESCRIPTION OF THE INVENTION

(6) FIG. 1 shows an application of the inventive device 1 which in this case is used for establishing the position of a transmitter 2.

(7) For this purpose, the device 1 comprises an antenna device 3 comprising several antenna elements 8, a control device 4, a signal processing device 5, and a data processing device 6. The antenna device 3 in this case is a multibeam antenna.

(8) The control device 4 acts on the antenna device 3 in order to decide which directional characteristic 7 is to be switched so that the signal received via this directional characteristic is fed to the signal processing device 5. The signals received from the antenna device 3 here are output by the feed network 9 in association to the individual directional characteristics 7. A directional characteristic 7 here is associated to each of the n antenna elements 8 of the antenna device 3 and in turn to one of the n antenna inputs 21 (output port would be an alternative term) of the feed network 9. The m signal inputs 20 of the feed network 9 are each connected individually to the signal processing device 5 via the switch 12 illustrated so that only the signal received of this one directional characteristics will be processed further. This allows selecting and/or switching a certain directional characteristic {right arrow over (C)}.sub.k.

(9) Alternatively, there are several signal processing devices 5—which are not illustrated here—each evaluating a signal received with a directional characteristic. Such an implementation allows parallel evaluation of signals connected to several directional characteristics. For this implementation, it is particularly provided for the feed network 9 to be implemented as a Butler matrix, for example. Put generally: The feed network 9 makes available the respective separate signals for each directional characteristic with which the antenna device 3 has received signals. In this implementation, the feed network 9 outputs the signals received via an associated directional characteristic 7, at the m signal inputs 20. The n antenna elements 8 here are connected to n antenna inputs 21 of the feed network 9.

(10) In the implementation illustrated, however, a single signal processing device 5 for which a respective directional characteristic 7 is switched is sufficient by providing a connection between the signal input 20 of the respective desired directional characteristic 7 and the signal processing device 5. Here, the signal inputs 20 serve for outputting the signals received. The characteristic as a signal input 20 results since it serves as an input for the excitation signals.

(11) The signal processing device 5 establishes a respective amplitude value of the field strength of the signals from the signals received. This means that a measure of the signal strength is generated. At the same time, only a single value results per measurement or per switched directional characteristic.

(12) In one implementation, the signal processing device 5 is particularly configured to extract from the respective signal received a piece of information which the transmitter has impressed on the signal emanating from it. The information may, for example, be measuring values which the transmitter 2 transmits or, for example, at least a symbol of identification of the transmitter 2.

(13) In particular, the signal processing device 5 reduces the signals received to only the amplitude value so that the complex signals—including magnitude and phase—are reduced to a measuring value. The information transmitted with the signal is to be considered separately from the physical characteristics.

(14) Using control logic 10 which in this case is part of the antenna device 3—several directional characteristics 7 are switched and the respective amplitude value is established. The position of the transmitter 2 is subsequently established based on the amplitude values established and the knowledge of the distribution of sensitivity of the directional characteristics 7. The data processing device 6 serves for this which may also comprise a data storage, like for storing the data on the directional characteristics.

(15) The directional characteristics 7 each comprise a main direction due to their beam shape. Thus, signals from different directions and regions are received by the different directional characteristics 7 so that, in the end, the position of the transmitter 2 can be determined using the amplitude values and the associated distributions of receive sensitivities of the directional characteristics—i.e. the data associated to the directional characteristics and describing these in relation to their receive sensitivities.

(16) An example is to be considered where the transmitter 2 is located within a region from which signals can be received only with a directional characteristic 7. Thus, a signal can be received only with this directional characteristic and an amplitude value unequaling zero will result only with this directional characteristic. Thus, the direction where the transmitter is located relative to the antenna device 3 can be deduced from the amplitude values.

(17) When additionally a measure of the field strength to be expected from the transmitter 2 is known, in one implementation, the amplitude value established also allows drawing conclusions as to the distance to the antenna device since the receive sensitivity, for example, decreases with an increasing distance.

(18) Additionally, the device 1 here comprises a signal source for transmitting excitation signals towards the transmitter 2 using the different directional characteristics. Here, the transmitter 2 may be of a purely passive nature, for example, like an RFID tag which reacts to the excitation signal with a response signal. The transmitter may, for example, also be a radar device where the signals emanating from the transmitter 2 are reflection signals. In one implementation—not illustrated here—the signal source 11 is a component of the signal processing device 5 which may, for example, be an RFID reader.

(19) In the case of an application with an RFID tag as a transmitter 2, the signal processing device 5 particularly is a conventional RFID reader. Such an RFID reading device 5 evaluates a signal originating from an RFID tag by extracting data which the RFID tag transfers, for example, like identification data, on the one hand and by generating a so-called “received signal strength indicator” (RSSI) value being an indicator of the field strength of the signals received on the other hand.

(20) The technical bases of the invention will be discussed again below.

(21) An overall spatial region is assumed where the transmitter 2 can be located and which is covered by the directional characteristics of the antenna device 3.

(22) The overall spatial region or irradiation region Ω is defined as follows:

(23) $\begin{array}{cc}\Omega =\left\{\stackrel{.fwdarw.}{\omega }=\left(\begin{array}{c}\varphi \\ \theta \end{array}\right):{\varphi }_1\le \varphi \le {\varphi }_u\&{\theta }_1\le \theta \le {\theta }_u\right\}& \left(1\right)\end{array}$

(24) Thus, φ is the azimuth angle and θ the co-elevation angle. The angles each comprise a lower threshold φ.sub.l and θ.sub.l and an upper threshold φ.sub.u and θ.sub.u. Respective spatial sectors Ω.sub.i,j are formed which a respective directional characteristic {right arrow over (C)}.sub.k of the antenna device corresponds with.

(25) The directional characteristics {right arrow over (C)}.sub.k in one implementation are characterized by the fact that they comprise their global maximum in an associated sector. In addition, there are no further maximums in any of the remaining sectors up to a certain predeterminable level distance below the global maximum.

(26) The sector Ω.sub.i,j is given by the following definition:

(27) $\begin{array}{cc}{\Omega }_{\mathrm{ij}}=\left\{\stackrel{.fwdarw.}{\omega }=\left(\begin{array}{c}\varphi \\ \theta \end{array}\right):{\varphi }_{1,i}\le \varphi \le {\varphi }_{u,i}\&{\theta }_{1,j}\le \theta \le {\theta }_{u,j}\right\}\subset \Omega & \left(2\right)\end{array}$
with i=1, . . . μ and j=1, . . . v  . (3)

(28) Here, the following applies:

(29) $\begin{array}{cc}\Omega =\underset{\left(i\right)}{.Math.}\underset{\left(j\right)}{.Math.}{\Omega }_{\mathrm{ij}}& \left(4\right)\end{array}$

(30) The number of sectors results from formula (3) as μ*v.

(31) FIG. 2 exemplarily shows the partitioning of the irradiation region Ω (in accordance with definition (1)) into 16 sectors Ω.sub.ij (in accordance with the definition in (2)), with μ=v=4.

(32) The following directional characteristic is associated to the sector Ω.sub.ij:

(33) $\begin{array}{cc}{\stackrel{.fwdarw.}{C}}_k={\stackrel{.fwdarw.}{C}}_k\left(\stackrel{.fwdarw.}{\omega }\right)={\stackrel{.fwdarw.}{C}}_k\left(\varphi ,\theta \right)=\left(\begin{array}{c}{C}_k^{\left(\mathrm{co}\right))}\\ C_k^{\left(\mathrm{cross}\right)}\end{array}\right)\mathrm{with}k=v*\left(j-1\right)+i,& \left(5\right)\end{array}$
with the co-polarizing C.sub.k.sup.(co) component and the cross-polarizing component C.sub.k.sup.(cross).

(34) The directional characteristic comprises its global magnitude maximum in the interval φ.sub.1, i≤φ≤φ.sub.u, i and θ.sub.1, j≤θ≤θ.sub.u, j.

(35) The association between (i, j) and k in formula (5) can be selected as desired as long as the following applies: max{k}=μ*v. An alternative association is: k=μ*(i−1)+j.

(36) The directional characteristics are set by a corresponding feed network 9. Every signal input (alternative term: input port) 20 of the feed network 9 here corresponds with a certain directional characteristic 7, as is outlined in FIG. 1 for a multibeam antenna.

(37) The directional characteristics {right arrow over (C)}.sub.k particularly are so-called port directional characteristics. In one implementation, the feed network 9 is an eigenmode network (see, for example, [6].) In a further implementation, the feed network 9 is realized as a Butler matrix (see, for example, [7]) the signal inputs 20 of which correspond with mutually orthogonal feed vectors. Alternatively, the network 9 may generate feed vectors oriented to one another in any way.

(38) In FIG. 3, each port at the input (i.e. each signal input) 20 of the antenna device 3 or the feed network 9 corresponds with a directional characteristic {right arrow over (C)}.sub.k in accordance with equation (5), resulting in a radiation maximum in the sector Ω.sub.ij (in accordance with equation (2)).

(39) Here, the multibeam antenna, for example, as an antenna device 3 comprises n antenna elements which are connected to the n antenna inputs 21 of the feed network 9 and using which m signal inputs 20 are excited or switched.

(40) Sending out signals via the antenna device or the antenna elements 8 thereof will be described in connection with FIG. 3 (see both vectors on the left-hand side with the arrow pointing upwards).

(41) The following is assumed:

(42) $\begin{array}{cc}{\stackrel{.fwdarw.}{a}}_{1,k}=\left(\begin{array}{c}0\\ .Math.\\ 1\\ .Math.\\ 0\end{array}\right)& \left(6\right)\end{array}$
be the input vector which will excite only the k-th input port 20 (bottom level of the feed network 9). Using the scattering matrix of the feed network 9:

(43) $\begin{array}{cc}\tilde{S}=\left(\begin{array}{cc}{\tilde{S}}_{11}& {\tilde{S}}_{12}\\ {\tilde{S}}_{21}& {\tilde{S}}_{22}\end{array}\right)& \left(7\right)\end{array}$
the result will be the excitation vector at the output of the network (top level with the antenna elements 8):
{right arrow over (b)}.sub.2,k={right arrow over (q)}.sub.k={tilde over (S)}.sub.21{right arrow over (a)}.sub.1,k  (8)
with the vector {right arrow over (q)}.sub.k causing the directional characteristic {right arrow over (C)}.sub.k.

(44) When several signal inputs 20 (an alternative term would be ports) are fed at the same time, weighted superpositioning of the directional characteristics associated to the ports 20 will take place. The directional characteristics are combined with one another for emitting the excitation signals.

(45) In the example of FIG. 3 (left side), the input vector {right arrow over (a)}.sub.1 of formula (8) as the vector of the excitation signal is partitioned proportionately to the feed vectors {right arrow over (q)}.sub.i.

(46) The receive case will be discussed using the vectors on the right-hand side (connected by the schematic arrow pointing downwards) of FIG. 3, wherein the input vector {right arrow over (a)}.sub.2 will be decomposed in correspondence with equation (9) into its portions of the individual directional characteristics 7.

(47) When a signal is received from a certain direction, the vector {right arrow over (a)}.sub.2 will be present at the top level of the feed network 9.

(48) Since the network 9 in the implementation described here is a passive one, the following applies:
{tilde over (S)}.sub.12={tilde over (S)}.sub.21.sup.T.

(49) Consequently, {right arrow over (a)}.sub.2 will transform to the bottom level of the feed network 9 as follows:

(50) $\begin{array}{cc}{\stackrel{.fwdarw.}{b}}_1={\tilde{S}}_{12}{\stackrel{.fwdarw.}{a}}_2={\tilde{S}}_{21}^T{\stackrel{.fwdarw.}{a}}_2=\left(\begin{array}{c}{\stackrel{.fwdarw.}{q}}_1^T\\ .Math.\\ {\stackrel{.fwdarw.}{q}}_k^T\\ .Math.\\ {\stackrel{.fwdarw.}{q}}_m^T\end{array}\right)& \left(9\right)\end{array}$

(51) The term {right arrow over (q)}.sub.k.sup.T{right arrow over (a)}.sub.2 thus corresponds to the projection of the vector of the receive signals of the antenna elements 8 onto the vector {right arrow over (q)}.sub.k resulting in the directional characteristic {right arrow over (C)}.sub.k. {right arrow over (a)}.sub.2 is thus decomposed into the portions occurring in the individual {right arrow over (C)}.sub.k.

(52) It is assumed that the vectors {right arrow over (q)}.sub.k and {right arrow over (q)}.sub.l with (k, l)=1, . . . m and k unequaling l are orthogonal in pairs. In addition, a signal is to be received from the main radiating direction of the characteristic {right arrow over (C)}.sub.k. Thus, {right arrow over (a)}.sub.2=c{right arrow over (q)}*.sub.k applies with any real constant c>0, which is to be understood to be a measure of the receive amplitude.

(53) Then, {right arrow over (b)}.sub.1=c{right arrow over (a)}.sub.1,k will result. This means that only at the antenna input 21 there is a signal applied, corresponding to the directional characteristic {right arrow over (C)}.sub.k. In the remaining characteristics {right arrow over (C)}.sub.l (l≠k), there are no signal portions contained.

(54) Consequently, using the signal {right arrow over (b)}.sub.1 which describes the receive signal {right arrow over (a)}.sub.2 subdivided in correspondence with the individual directional characteristics, the direction of incidence of the respective signal received can be deduced.

(55) The method for identifying in one implementation is as follows: A directional characteristic {right arrow over (C)}.sub.k is switched. Here, in one implementation, particularly one of the input ports 20 of the feed network 9 is selected and connected to the signal processing device 5 or the signal source 11. The antenna device 3 sends out an excitation or request signal via the directional characteristic selected. The transponders 2 (or RFID tags as examples of the transmitters described here) reached, or excited, or woken-up with the directional characteristics returns a response signal which contains, among other things, the identification of the transponder. The response signal is received via the antenna device and that part of the signal corresponding with the selected directional characteristic {right arrow over (C)}.sub.k is available for the reader as an implementation of the signal processing device 5. The reader 5 evaluates the response signal and makes available the identification of the transponder and a measure of the strength of the signal (RSSI value) received.

(56) Thus, the transponder (generally the transmitter) can be associated to the currently selected (or switched) directional characteristic.

(57) This process is performed for several directional characteristics 7. This means that the signal portions in the individual {right arrow over (C)}.sub.k are read out one after the other and the transponder signals or amplitude magnitudes can be associated to the directional characteristics. In total, a vector for the position of the transmitter is setup. The values of the inputs result from the magnitudes of the field strengths of the respective signals received and the basic vectors result from the associated directional characteristics, for example the respective direction of the beam.

(58) FIG. 4 shows an alternative implementation of the device 1. The antenna device 3 here is also implemented as a multibeam antenna and comprises the control logic 10 and the data processing device 6 (alternatively also referred to as computing unit).

(59) What follows is a consideration of evaluating the signals received or establishing the information on the position of the transmitter 2.

(60) In order to be able to determine the direction of the transponders (or generally transmitters, irrespective of whether they are active or passive transmitters), it would be easier for the response signals (or generally the signals received) to be present in a complex form, i.e. including magnitude and phase. A conventional RFID reader (or RFID receiver), however, only makes available amplitudes in the form of RSSI values. When using the inventive device and partitioning of the irradiation region Ω into the individual sectors Ω.sub.ij in accordance with equations (2) and (4), the complex signals at the antenna elements 8 can be deduced, as will be discussed below.

(61) Instead of the complex signals {right arrow over (b)}.sub.1 (cf. equation (9) and FIG. 3), in correspondence with the identification of the transmitter or RFID tag as described above, there are the amplitudes of the individual components of {right arrow over (b)}.sub.1. The following vector is obtained:

(62) $\begin{array}{cc}\widehat{{\stackrel{.fwdarw.}{b}}_1}=\left(\begin{array}{c}{\hat{b}}_{1,1}\\ .Math.\\ {\hat{b}}_{1,k}\\ .Math.\\ {\hat{b}}_{1,m}\end{array}\right)=\left(\begin{array}{c}.Math.{\stackrel{.fwdarw.}{q}}_1^T{\stackrel{.fwdarw.}{a}}_2.Math.\\ .Math.\\ .Math.{\stackrel{.fwdarw.}{q}}_k^T{\stackrel{.fwdarw.}{a}}_2.Math.\\ .Math.\\ .Math.{\stackrel{.fwdarw.}{q}}_m^T{\stackrel{.fwdarw.}{a}}_2.Math.\end{array}\right){\stackrel{.fwdarw.}{a}}_2.& \left(10\right)\end{array}$

(63) Like {right arrow over (b)}.sub.1, the vector {right arrow over (b)}.sub.1 is also dependent on the direction of incidence of the receive signal. Due to the unambiguous association of a directional characteristic {right arrow over (C)}.sub.k to a certain irradiation region Ω.sub.ij, however, an unambiguous vector of RSSI values {circumflex over ({right arrow over (b)})}.sub.1 is to be associated to each direction of incidence.

(64) For a certain direction of incidence {right arrow over (ω)}.sub.0, {circumflex over ({right arrow over (b)})}.sub.1({right arrow over (ω)}.sub.0) will result only for {right arrow over (ω)}={right arrow over (ω)}.sub.0, but for no other directions of incidence. The phase of the signals thus is hidden inherently in the individual directional characteristics. This means that a representation can be defined as follows:
f:{circumflex over ({right arrow over (b)})}.sub.1({right arrow over (ω)}){right arrow over (b)}.sub.1({right arrow over (ω)})  (11)
and
f:{circumflex over ({right arrow over (b)})}.sub.1({right arrow over (ω)}){right arrow over (a)}.sub.2({right arrow over (ω)})  (12)

(65) In order to be able to make the association between {circumflex over ({right arrow over (b)})}.sub.1({right arrow over (ω)}) and {right arrow over (b)}({right arrow over (ω)}) or {right arrow over (a)}.sub.2({right arrow over (ω)}), the possible complex vectors for different angles of incidence have to be established at first. This means that the directional characteristic and the spatial distribution of the receive sensitivity (or usually also the transmit sensitivity thereof) has to be established. This may be done by simulating or measuring the array where the vectors for all the angles of incidence are recorded over the irradiation region Ω—in accordance with the definition in (1). The irradiation region here is passed in a discrete manner so that the final result is a countable (finite) set of known angles of incidence {right arrow over (ω)}.sub.l and, thus, vectors {right arrow over (b)}.sub.1.sup.(s)({right arrow over (ω)}.sub.l) and {right arrow over (a)}.sub.2.sup.(s)(ω.sub.l). The superscript (s) indicates that vectors established for discrete angles of incidence are concerned. In principle, these are steering vectors.

(66) The association to the complex vector corresponds to a search where the complex vector {right arrow over (b)}′.sub.1.sup.(s)={tilde over (S)}.sup.T{right arrow over (a)}′.sub.2.sup.(s) is established in a least square error way, for which the norm:
∥{circumflex over ({right arrow over (b)})}.sub.1−{circumflex over ({right arrow over (b)})}.sub.1.sup.(s)({right arrow over (ω)}.sub.l)∥  (13)
with the following vector:

(67) $\begin{array}{cc}\widehat{{\stackrel{.fwdarw.}{b}}_1^{\left(s\right)}}\left({\stackrel{.fwdarw.}{\omega }}_l\right)=\left(\begin{array}{c}.Math.b_{1,1}^{\left(s\right)}\left({\stackrel{.fwdarw.}{\omega }}_l\right).Math.\\ .Math.\\ .Math.b_{1,k}^{\left(s\right)}\left({\stackrel{.fwdarw.}{\omega }}_l\right).Math.\\ .Math.\\ .Math.b_{1,m}^{\left(s\right)}\left({\stackrel{.fwdarw.}{\omega }}_l\right).Math.\end{array}\right)=\left(\begin{array}{c}.Math.{\stackrel{.fwdarw.}{q}}_1^T{\stackrel{.fwdarw.}{a}}_2^{\left(s\right)}\left({\stackrel{.fwdarw.}{\omega }}_l\right).Math.\\ .Math.\\ .Math.{\stackrel{.fwdarw.}{q}}_k^T{\stackrel{.fwdarw.}{a}}_2^{\left(s\right)}\left({\stackrel{.fwdarw.}{\omega }}_l\right).Math.\\ .Math.\\ .Math.{\stackrel{.fwdarw.}{q}}_m^T{\stackrel{.fwdarw.}{a}}_2^{\left(s\right)}\left({\stackrel{.fwdarw.}{\omega }}_l\right).Math.\end{array}\right)& \left(14\right)\end{array}$
becomes minimal.

(68) This implies:

(69) 0$\begin{array}{cc}.Math.\widehat{{\stackrel{.fwdarw.}{b}}_1}-\hat{{\stackrel{.fwdarw.}{b^{\prime }}}_1^{\left(s\right)}}.Math.=\underset{l}{\min }.Math.\widehat{{\stackrel{.fwdarw.}{b}}_1}-\widehat{{\stackrel{.fwdarw.}{b}}_1^{\left(s\right)}}\left({\stackrel{.fwdarw.}{\omega }}_l\right).Math.& \left(15\right)\end{array}$

(70) As can be seen from equation (14), the vectors {right arrow over (a)}.sub.2.sup.(s)({right arrow over (ω)}.sub.l) at the antenna foot points can be measured on the one hand and the vectors {right arrow over (b)}.sub.1.sup.(s)({right arrow over (ω)}.sub.l) be established using the scattering matrix {tilde over (S)}.sub.21.sup.T by means of computation. Consequently, it is sufficient to determine the directional characteristics of the individual antenna elements in the array, with no feed network. On the other hand, the port directional characteristics of the array, i.e. including the feed network, can be measured and the vectors {right arrow over (b)}.sub.1.sup.(s)({right arrow over (ω)}.sub.l) be established directly.

(71) The angle of incidence {right arrow over (ω)}∈{{right arrow over (w)}.sub.l} results directly from the complex vector {right arrow over (b)}′.sub.1.sup.(s) or {right arrow over (a)}′.sub.2.sup.(s) or from any direction estimation algorithm applied to the vector. It is also possible to determine a temporal mean value across several successive angles of incidence which are established over several switching cycles. Thus, the variance of the estimated angle and, consequently, the measuring uncertainty decrease. In practice, side maximums of the directional characteristics present are usually to be limited to a certain maximum level relative to the level of the main maximum in order to be robust to possible uncertainties caused by superimposed noise. Otherwise, there may be ambiguities when determining the direction.

(72) In order to make functions (11) and (12) unambiguous, in one implementation, it is provided for to use a multibeam antenna the directional characteristics of which comprise an unambiguous global maximum and, across all the sectors, no symmetry in the form of another global maximum within the irradiation region. The combination of a typical or conventional RFID reader with a corresponding multibeam antenna allows drawing conclusions as to the complex-value receive signals, without having to interfere in the reader.

(73) FIG. 4 shows an exemplary architecture of a corresponding setup of the device 1 by means of which the available directional characteristics {right arrow over (C)}.sub.k can be read out in accordance with the procedure described before and the angle of incidence of the identified tags (or transmitter) 2 can be determined. Apart from the antenna elements 8 and feed network 9, the multibeam antenna 3 comprises a radio-frequency switch (RF switch) 12 and control logic 10. Using the control logic 10, the desired port directional characteristic {right arrow over (C)}.sub.k (cf. definition (5)) is adjusted using the RF switch 12. The RF signal to be transmitted as an excitation signal is provided by the external RFID reader 5 (which consequently comprises the signal source 11 of the implementation of FIG. 1) via an RF signal connection, and the receive signal for the RFID reader 5 is provided. A, relative to the antenna device 3, external control device 4 allows controlling the reader 5 and the multibeam antenna 3. The data processing device 6 as part of the antenna device 3 determines the direction of incidence of the transponder signals in accordance with equation (13). The RSSI values and the transponder identification are obtained from the RFID reader 5. In typical installations of RFID readers 5 with a control unit, the illustrated implementation is of advantage in that only the antenna present has to be replaced by the antenna device 3 comprising control logic 10 and the data processing device 6—no other additional components are required.

(74) The invention is to be described below in other words:

(75) In one implementation, the invention allows establishing information on a position of the transmitter, the information being at least a statement on the direction of the transmitter. This is done based on RSSI values (or, generally, only with amplitude values of the signals received) in combination with a multibeam antenna.

(76) The following advantages result, among others:

(77) When using a computing unit or data processing device which is accommodated in one implementation in the multibeam antenna, in one implementation a single RF path between multibeam antenna and RFID reader is sufficient for estimating the direction.

(78) This means that, in one implementation, only a single RFID reader comprising a single port is used. Such a reader generally is cheaper than an RFID reader having several ports. In addition, in one implementation, no additional infrastructure components for switching and computing are necessary since switching and estimating the direction are covered functionally by the multibeam antenna itself.

(79) The number of antenna elements or directional characteristics and the partitioning of the irradiation region may be selected as desired. With an increasing number of elements and sectors, the precision of estimating the direction can be increased. This means that it can be adapted to the respective case of application.

(80) Any conventional (commercial) standard RFID reader can be used as the signal processing device. These provide an RSSI value for each transponder identified.

(81) In accordance with the invention, using an antenna device with different switchable or selectable directional characteristics (in one implementation, the multibeam antenna) and corresponding partitioning of the irradiation region, it is possible to dispense with measuring complex signals. A part of the signal processing is performed by the antenna device and the directional characteristics thereof so that the RSSI values (or, generally, the amplitude values) are sufficient for determining the position or at least estimating the direction.

(82) All in all, the following advantages result: The precision of the results does no longer, or only to a limited extent, depend on the directional effect of the individual antenna elements. This is based on the fact that the signals received with the individual directional characteristics and, thus, the individual antenna elements are processed altogether to form a vector for the position of the transmitter. Compared to solutions of mechanical tracking of directional antennas, the invention allows a more compact realization with low response times, in addition without mechanical expenditure or wear. This particularly applies to the implementation where the antenna device is a patch antenna. Compared to solutions where several receive nodes are distributed in space, a single receive node is sufficient. A signal processing device, like an RFID reader, for example, is consequently sufficient. The precision is not determined exclusively by the number of nodes, but by the number of antenna elements in the array and the number of sectors.

(83) Technical fields of application of the invention are, for example, logistics, production, gate passage and others, including bulk reading (detecting many transponders within a short time), automized stock taking or identity checks in persons (like in healthcare).

(84) Although some aspects have been described in the context of a device, it is clear that these aspects also represent a description of the corresponding method, such that a block or element of a device also corresponds to a respective method step or a feature of a method step. Analogously, aspects described in the context of or as a method step also represent a description of a corresponding block or item or feature of a corresponding device. Some or all of the method steps may be executed by (or using) a hardware apparatus, like, for example, a microprocessor, a programmable computer or an electronic circuit. In some embodiments, some or several of the most important method steps may be executed by such an apparatus.

(85) Depending on certain implementation requirements, embodiments of the invention can be implemented in hardware or in software or at least partly in hardware or at least partly in software. The implementation can be performed using a digital storage medium, for example a floppy disk, a DVD, a Blu-Ray disc, a CD, an ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, a hard drive or another magnetic or optical memory having electronically readable control signals stored thereon, which cooperate or are capable of cooperating with a programmable computer system such that the respective method is performed. Therefore, the digital storage medium may be computer-readable.

(86) Some embodiments according to the invention include a data carrier comprising electronically readable control signals, which are capable of cooperating with a programmable computer system such that one of the methods described herein is performed.

(87) Generally, embodiments of the present invention can be implemented as a computer program product with program code, the program code being operative for performing one of the methods when the computer program product runs on a computer.

(88) The program code may, for example, be stored on a machine-readable carrier.

(89) Other embodiments comprise the computer program for performing one of the methods described herein, wherein the computer program is stored on a machine-readable carrier. In other words, an embodiment of the inventive method is, therefore, a computer program comprising program code for performing one of the methods described herein, when the computer program runs on a computer.

(90) A further embodiment of the inventive methods is, therefore, a data carrier (or a digital storage medium or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein. The data carrier or the digital storage medium or the computer-readable medium is typically tangible and/or non-volatile.

(91) A further embodiment of the inventive method is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals may, for example, be configured to be transferred via a data communication connection, for example via the Internet.

(92) A further embodiment comprises processing means, for example a computer, or a programmable logic device, configured to or adapted to perform one of the methods described herein.

(93) A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein.

(94) A further embodiment according to the invention comprises a device or a system configured to transfer a computer program for performing one of the methods described herein to a receiver. The transmission can be performed electronically or optically. The receiver may, for example, be a computer, a mobile device, a memory device or the like. The device or system may, for example, comprise a file server for transferring the computer program to the receiver.

(95) In some embodiments, a programmable logic device (for example a field-programmable gate array, FPGA) may be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field-programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, in some embodiments, the methods are performed by any hardware apparatus. This can be a universally applicable hardware, such as a computer processor (CPU), or hardware specific for the method, such as ASIC, or a microprocessor, like in the form of an ARM architecture.

(96) While this invention has been described in terms of several embodiments, there are alterations, permutations, and equivalents which will be apparent to others skilled in the art and which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and compositions of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.

REFERENCES

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