Method, device, arrangement and software for determining the angle of arrival (AOA) for locating objects

Abstract

A method measures an angle of arrival (AOA) of an incoming signal using m separate antennas coupled via a switch with a single receiving device. The switch sequentially supplies the incoming signal to the receiver. A sampling of the incoming signal as received at the antennas has a sampling rate and cycle time performed in repetitive cycles. The receiver generates baseband signals with in-phase and quadrature components from the incoming signal and forwarding to each analog-to-digital converter to provide digitized samples. A signal processor is coupled to the respective analog-to-digital converter to analyze the digitized signals and to determine the angle of arrival of the incoming signal. The resulting phase error is compensated by sampling and signal processing. A device operates according to the method and an arrangement with a mobile transmitter and a device and software for locating the mobile transmitter by the device.

Claims

1. Method of measuring an angle of arrival (AOA) of an incoming signal; the method comprising: providing m separate antennas, where m is an integer greater than one, and a single receiver and a switch, wherein the incoming signal as received by the antennas is fed into the single receiver via the switch, the switch comprising an electronic signaller for sequentially supplying the incoming signal, as received at the m antennas, to the receiver by switching between said m antennas, wherein a sampling of the incoming signal as received at the m antennas is performed in repetitive cycles with a sampling rate and cycle time, the receiver comprising a generator for generating a baseband signal having an in-phase component and a baseband signal having a quadrature component from the incoming signal and for forwarding each baseboard signal to an analog-to-digital converter to provide digitized samples for each of the m antennas during each cycle; providing a signal processor coupled to the respective analog-to-digital converter to analyze the digitized signals and to determine the angle of arrival of the incoming signal; wherein the sampling rate of the signal processor is smaller than the number of m antennas multiplied by a minimum sampling rate, which is necessary to reconstruct the incoming signals of the individual m antennas; wherein the incoming signal supplied to the receiver comprises a phase error; compensating for the phase error by multiple sampling of at least one antenna and signal processing by a statistical method; and wherein the statistical method comprises using a uniformly best unbiased estimator.

2. Method according to claim 1, wherein a phase unwrapping is performed in the signal processor.

3. Method according to claim 1, wherein the incoming signals comprise different frequencies, wherein the frequencies are outside coherence bandwidths.

4. Method according to claim 3, wherein the frequencies differ by at least a factor of 2, with the frequencies being outside the coherence bandwidths.

5. Method according to claim 1, wherein a distance d between at least two of the m antennas corresponds to at least half the wavelength of at least one incoming signal.

6. Method according to claim 1, wherein the electrical length of the m antennas differ from each other and wherein a compensation of the different electrical lengths of the m antennas is performed in the signal processor.

7. Method according to claim 1, wherein an estimate of the angle of arrival is provided for measuring an angle of arrival (AOA) for at least 2 of the m antennas.

8. Method according to claim 7, wherein the estimate of the angle of arrival comprises the least-squares method.

9. A device operated according to the method according to claim 1; the device comprising: m separate antennas, wherein m is an integer greater than one; a switch; and a receiver.

10. Device according to claim 9, wherein the device is operated by a self-sufficient energy source.

11. Device according to claim 9, wherein the device is part of a real-time localization system.

12. Device according to claim 9, wherein the device comprises a system-on-a-chip (SoC), which comprises the receiver and/or the signal processor.

13. Arrangement comprising the device according to claim 9, and a central data processing unit, the central processing unit evaluating the determined angles of arrival; wherein the arrangement is adapted for locating at least one mobile transmitter.

14. An arrangement comprising: the device according to claim 9; a central data processing unit evaluating the determined angles of arrival; and at least one mobile transmitter; wherein the arrangement is adapted for locating said at least one mobile transmitter.

Description

DESCRIPTION OF THE INVENTION ON THE BASIS OF EXEMPLARY EMBODIMENTS

(1) Advantageous embodiments of the present invention will be explained in more detail below on the basis of the drawings. The figures show the following:

(2) FIG. 1 shows an overview of an arrangement for locating a mobile transmitter;

(3) FIG. 2 shows a simplified schematic representation of n antennas with an incoming signal;

(4) FIG. 3 shows an example of the triangulation in two dimensions;

(5) FIG. 4 shows a very simplified schematic representation of the measure concept;

(6) FIG. 5 shows a very simplified schematic representation of the RF front ends;

(7) FIG. 6 shows a simplified schematic representation of the distances between the antennas and its neighboring antennas;

(8) FIG. 7 shows a block diagram of a direct-conversion receiver;

(9) FIG. 8 shows a block diagram of a superheterodyne receiver; and

(10) FIG. 9 shows a simplified schematic representation of the phase of a baseband signal without and with an unwrapped phase.

(11) FIG. 1 shows an overview of an arrangement for locating a mobile transmitter. This overview shows the concept of the present invention. In this embodiment, the arrangement comprises four devices 1, one mobile transmitter 2 and a central data processing system 3, which is additionally in communication with a server 4.

(12) All devices 1 communicate with each other via a radio connection. In addition, each device 1 is assigned a unique ID by which the respective device 1 can identify itself. The number of devices 1 that are necessary to locate a corresponding mobile transmitter 2 depends on the particular surroundings and must be evaluated empirically. It is therefore advantageous for determining the number of devices 1 to have a more accurate knowledge of the surroundings. Obstacles to the radio frequencies used may act as interferers, for example.

(13) The mobile transmitter 2 emits radio signals, which are received by the individual devices 1 as incoming signals. By means of the incoming signals, the devices 1 calculate the angle of arrival (AOA) Ψ on the basis of the method according to the invention. The calculation of the position of the mobile transmitter 2 in the space or relative to the installed devices 1 is carried out in a central data processing system 3. These calculations may also be carried out in one of the devices 1 itself so that no additional separate central data processing system 3 is required. If the calculation is carried out by one of the devices 1, one of the devices 1 can be automatically selected for this purpose, which, for example, is within range and at that time is not busy with performing measurements, making computing capacities available.

(14) To ensure that the calculations of the position of the mobile transmitter 2 are accurate, the exact positions of the devices 1 must be known. In this regard, the respective positions of the devices 1 with respect to a certain reference point may be known. A further possibility consists in the fact that the position of a first device 1 with respect to a reference point and the respective relative position of the other devices 1 to the first device 1 are known. Floor plans of the building may then, for example, be superimposed on the position of the mobile transmitter 2.

(15) Furthermore, a server 4, which communicates with the central data processing system 3 or with the device 1, which performs the calculations and receives and stores the measured positions of the mobile transmitter 2 for further evaluation, may be provided. A localization back end, for example, which allows access to the current and past locations of the mobile transmitter 2, could be operated.

(16) The system may be designed so that the position determination is triggered by the mobile transmitter 2, either at the request of the user, e.g. with a keystroke, or periodically at certain times.

(17) In order to allow for an accurate position calculation, the measurements of the phases and the angles of attack determined therefrom may be performed several times. In addition, to eliminate fading, shadowing and multipath propagation, measurements in two frequency bands may be performed consecutively.

(18) FIG. 2 shows a simplified schematic representation of n antennas with an incoming signal x.sub.HF. One way to measure the angle of arrival is phase interferometry. This technique measures the phase of an incoming signal on different antennas. It requires an arrangement of antennas, which are arranged at a known distance from each other. The angle of arrival Ψ of the incoming signal x.sub.HF can be calculated by the relationship sin

(19) $\psi =\frac{l}{\Delta d}.$
If the distance between two antennas Δd is smaller than the wavelength of the signal λ.sub.HF>Δd, the path difference l can be clearly determined by the phase difference Δφ of two signals from two antennas with

(20) $l=\frac{\mathrm{\Delta \phi }}{\pi }{\lambda }_{\mathrm{HF}}.$
The angle of arrival of the two antennas A1 and A2 can be calculated by

(21) $\psi =\arcsin \left(\frac{\mathrm{\Delta \phi }.Math.{\lambda }_{\mathrm{HF}}}{\pi .Math.\Delta d}\right)$
accordingly.

(22) In a three-dimensional space, it is not possible to determine a position (x, y, z) solely by an angle measurement in the φ direction corresponding to the spherical coordinates. Intersections of these angle measurements will always be independent of the z-axis. However, a position determination along the z-axis in closed rooms is usually not necessary since only small height differences are possible. However, one possibility would be to measure the θ direction according to the spherical coordinates when the devices 1 are mounted in different rotations. An example for a triangulation of a point or object in two dimensions is shown in FIG. 3. At least two angles φ.sub.1 and φ.sub.2 are necessary for the triangulation in two dimensions. The angle φ is a value between −90°<0°<90°, with 0° pointing in the direction of the x-axis. If the angle measurements φ are faulty, it may be necessary to perform further angle measurements with further devices 1, as indicated by the angle measurement φ.sub.3.

(23) FIG. 4 shows a very simplified schematic representation of the measurement concept. The embodiment shows a device 1 with six antennas A1 to A6, switching means 5 and further processing means, which may include the receiving device 6 and the signal processing means 7. The individual antennas A1 to A6 may be randomly selected by the switching means 5. A safety timer t.sub.start may also be provided prior to the actual measurement. During this time, all devices involved, for example further devices 1, may switch to a measurement mode. The mobile transmitter 2 emits a carrier wave at a predetermined frequency. After the delay t.sub.start, the device 1 starts the measuring process. In this process, each antenna is selected, for example, for a previously defined measurement interval t.sub.m: Antenna A1 is selected for the time 2.Math.t.sub.m and the other antennas A2 to A6 for the time t.sub.m. After the expiration of a time t.sub.stop, the measurement in the device 1 or in other devices 1 is stopped. The selected time t.sub.stop is much longer than 7.Math.t.sub.m in order to avoid problems with the synchronization. The mobile transmitter 2 then waits for a confirmation of the measurement by all devices 1 involved. If no or only partial confirmation by the devices 1 is received, the measurement is considered flawed.

(24) FIG. 5 shows a very simplified schematic representation of the RF front end. In this embodiment, six antennas A1 to A6 are shown, which are connected with the switching means 5. A first toggle switch 8a is connected downstream from the switching means 5. This toggle switch 8a is designed as a single-pole toggle switch (SPDT, single pole double throw). Subsequently, an impedance adjustment is performed for different frequency bands, for example an adjustment for two different frequency bands, such as 2.4 GHz and sub-1 GHz. A second toggle switch 8b is inserted after the impedance adjustment and before the system-on-a-chip 11, said switch being designed as a differential double-pole toggle switch (DPxDT, double pole double throw crossed). It is advantageous that all switches have a minimum insertion loss in order to avoid high attenuation and thus to keep the signal-to-noise ratio (SNR) high. The further data processing is carried out on the system-on-a-chip 11, which means that the system-on-a-chip 11 may comprise the receiving device 6 and the signal processing means 7.

(25) FIG. 6 shows a simplified schematic representation of the distances between the antennas and their neighboring antennas. In this embodiment, six antennas A1 to A6 are shown with the corresponding distances d.sub.ij, with i,j denoting the relevant antenna A1 to A6. PCB antennas may be used to keep costs down. The present embodiment uses the frequencies of 2.4 GHz and 868 MHz. The antennas are mounted so that clear measurements of the angle of arrival are possible in both frequency bands used. The low frequency band around 868 MHz has a wavelength of λ≈34.5 cm. The high frequency band around 2.4 GHz has a wavelength of λ≈12.2 cm. This means that the distances d.sub.ij can be chosen in such a way that multiple measurements in the frequency bands are possible. Thus, it is advantageous if a distance d.sub.ij between at least two of the antennas A1 to A6 corresponds to at least half the wavelength λ of at least one incoming signal. The distance between the antennas A5 and A6 can be selected, for example, with d.sub.56=17.25 cm, which corresponds to half the wavelength of the high frequency band around 2.4 GHz. The angle of arrival may correspondingly be calculated for 2 antennas by

(26) ${\psi }_{\mathrm{ij}}=\arcsin \left(\frac{{\mathrm{\Delta \phi }}_{\mathrm{ij}}.Math.\lambda }{\pi .Math.\Delta d}\right),$
with Δd=d.sub.ij.

(27) FIG. 7 shows a block diagram of a direct-conversion receiver as it is provided in the device 1. The direct-conversion receiver includes a band pass filter upstream from the IQ demodulator, which pre-selects the band, and a programmable amplifier. Two analog-to-digital converters (ADCs) are inserted downstream from the IQ demodulator, one each for the in-phase signal and the quadrature signal. The control unit 12 sets the receiver to a carrier frequency by setting the frequency of the local oscillator f.sub.0 accordingly.

(28) On systems configured as a system-on-a-chip, superheterodyne receivers as shown in FIG. 8 may be used. The x.sub.HF signal is first mixed down to a lower frequency f.sub.IF and is subsequently demodulated. The reason for this is that the maximum possible carrier frequency f.sub.0 is limited by the required accuracy of the IQ demodulator and may not be guaranteed at higher frequencies.

(29) FIG. 9 shows the phase of a baseband signal. An unwrapping algorithm converts the phase without unwrapping 14 to the phase with unwrapping 15. The conversion may, however, cause problems with discontinuities, such as those caused by the wrapping properties of the arctan 2-function. An unwrapping algorithm may therefore be used, which detects and eliminates the discontinuities in the phase. Phase jumps around −2π are thus detected and corrected accordingly by adding 2π to the following samples of the phase.

LIST OF REFERENCE SIGNS

(30) 1 Device 2 Mobile transmitter 3 Central processing unit 4 Server 5 Switching means 6 Receiving device 7 Signal processing means 8 Toggle switch 9 Impedance adjustment 10 Arrangement 11 System-on-a-chip 12 Control unit 13 Direct conversion receiver 14 Phase without unwrapping 15 Phase with unwrapping t.sub.z Cycle time A Antenna