US-12625229-B2 - Method and arrangement for evaluating a distance between at least two antenna units

US12625229B2US 12625229 B2US12625229 B2US 12625229B2US-12625229-B2

Abstract

A method for evaluating a distance between at least a first antenna unit and a second antenna unit by two-way transmission of at least two signals having different circular polarizations between the antenna units. Phase information is determined and used to determine at least a first phase sum and a second phase sum, where the phase sums are further utilized in determination of at least one distance indicator that is indicative of the distance between the first antenna unit and the second antenna unit.

Inventors

Kari Leppänen
Jussi Salmi

Assignees

KOHERENT OY

Dates

Publication Date: 20260512
Application Date: 20220525
Priority Date: 20210611

Claims (13)

1 . A method for evaluating a distance between at least a first antenna unit and a second antenna unit, the method comprising at least transmitting a first signal via the first antenna unit, said first signal comprising a first circular polarization, receiving the first signal at the second antenna unit, determining first phase information, said first phase information being indicative of a phase of the received first signal with respect to a local oscillator of a radio unit with which the second antenna unit is associated, transmitting a first response signal via the second antenna unit, said first response signal essentially corresponding to said first signal, receiving the first response signal at the first antenna unit, determining first response phase information, said first response phase information being indicative of a phase of the received first response signal with respect to a local oscillator of a radio unit with which the first antenna unit is associated, determining a first phase sum being indicative of a sum of the first phase information and the first response phase information, transmitting a second signal via one of the first or second antenna units, said second signal comprising a second circular polarization, the second circular polarization being opposite to the first circular polarization, receiving the second signal at the other of the first or second antenna unit, determining second phase information, said second phase information being indicative of a phase of the received second signal with respect to a local oscillator of the radio unit with which the receiving antenna unit is associated, transmitting a second response signal via the other of the first or second antenna units which has not transmitted the second signal, said second response signal essentially corresponding to said second signal, receiving the second response signal at the antenna unit that has transmitted the second signal, determining second response phase information, said second response phase information being indicative of a phase of the received second response signal with respect to the local oscillator of a radio unit with which the receiving antenna unit is associated, determining a second phase sum being indicative of a sum of the second phase information and the second response phase information, and determining at least one distance indicator that is indicative of the distance between the first antenna unit and the second antenna unit based on at least the first phase sum and second phase sum.
2 . The method of claim 1 , wherein the at least one distance indicator comprises a first distance variable indicative of a sum of the first phase sum and second phase sum.
3 . The method of claim 1 , comprising obtaining direction of signal data with respect to the coordinate system of each of the first and second antenna unit and utilizing said direction of signal data in the determination of the at least one distance indicator, optionally by obtaining antenna phase pattern calibration data and interpolating an antenna phase response.
4 . The method of claim 3 , wherein the method comprises receiving the transmitted signals at at least three separate antenna elements comprised in the first antenna unit and/or second antenna unit to determine said direction of signal data.
5 . The method of claim 1 , wherein the phase information, phase sums and/or distance indicator is determined with respect to a reference point of the first antenna unit and/or second antenna unit, said reference point optionally being a geometric center on the antenna unit plane with respect to positions of two or more antenna elements comprised in each antenna unit.
6 . The method of claim 1 , wherein the method comprises determining self-measurement data indicative of a phase of a self-measurement signal, for the first and second polarizations, received at a transmitting antenna unit during transmission of a signal and utilizing said self-measurement data in determining the at least one distance indicator.
7 . The method of claim 1 , wherein the at least one distance indicator comprises a rotation variable indicative of a difference between the first phase sum and the second phase sum, and the method optionally comprises determining a rotation angle between the first antenna unit and the second antenna unit based on the rotation variable.
8 . The method of claim 7 , wherein the rotation variable is determined at least once and utilized in tracking of the rotation angle between the first antenna unit and the second antenna unit, the method comprising transmitting subsequent first signals and first response signals to determine subsequent first phase sums, where the rotation variable is used to compensate for the rotation angle between the first antenna unit and the second antenna unit, to track the distance between the first antenna unit and second antenna unit.
9 . The method of claim 1 , wherein each of the at least first and second antenna units transmits at least one signal within a predetermined time slot and in predetermined order.
10 . The method of claim 9 , wherein the first antenna unit is a master unit and the remaining at least second antenna unit is a slave unit, the master unit being configured to transmit the first signal, wherein the master unit is configured to check before transmission of the first signal at each measurement cycle whether a radio channel is free for transmission and if the channel is free, the at least first signal is transmitted, said transmitting not being executed if the channel is not free.
11 . The method of claim 9 , wherein the slave unit(s) are configured to determine, before transmitting of a signal in a given measurement cycle, if a previous antenna unit in the predetermined order of antenna units has transmitted a signal in the measurement cycle, and if yes, transmit their respective signal, while the signal is not transmitted if it is determined that the previous antenna unit has not transmitted a signal.
12 . The method of claim 1 , wherein the method comprises evaluating at least two distances between a plurality of antenna units by additionally at least receiving the first signal at at least a third antenna unit, transmitting a first response signal via the third antenna unit and receiving the first response signal at at least the first antenna unit, receiving the second signal at at least the third antenna unit, and transmitting a second response signal via the third antenna unit and receiving the second response signal at at least the first antenna unit to obtain at least two pairs of antenna units that have performed two-way transmission of at least a signal comprising the first polarization and a signal comprising the second polarization and determining respective phase information for each pair of antenna units, determining respective first and second phase sums for each pair of antenna units, and determining at least one distance indicator being indicative of the distance between the antenna units, for each pair of antenna units.
13 . An arrangement for evaluating a distance between at least a first antenna unit and a second antenna unit, the arrangement comprising at least a first antenna unit associated with a first radio unit, a second antenna unit associated with a second radio unit, and a processor, wherein the arrangement is configured to transmit a first signal via the first antenna unit, said first signal comprising a first circular polarization, receive the first signal at the second antenna unit, determine first phase information, said first phase information being indicative of a phase of the received first signal with respect to a local oscillator of a radio unit with which the second antenna unit is associated, transmit a first response signal via the second antenna unit, said first response signal essentially corresponding to said first signal, receive the first response signal at the first antenna unit, determine first response phase information, said first response phase information being indicative of a phase of the received first response signal with respect to a local oscillator of a radio unit with which the first antenna unit is associated, determine a first phase sum being indicative of a sum of the first phase information and the first response phase information, transmit a second signal via one of the first antenna unit or second antenna unit, said second signal comprising a second circular polarization, the second circular polarization being opposite to the first circular polarization receive the second signal at the other of the first or second antenna unit, determine second phase information, said second phase information being indicative of a phase of the received second signal with respect to a local oscillator of the radio unit with which the receiving antenna unit is associated, transmit a second response signal via the other of the first or second antenna units, which has not transmitted the second signal, said second response signal essentially corresponding to said second signal, receive the second response signal at the antenna unit that has transmitted the second signal, determine second response phase information, said second response phase information being indicative of a phase of the received second response signal with respect to the local oscillator of a radio unit with which the receiving antenna unit is associated, determine a second phase sum being indicative of a sum of the second phase information and the second response phase information, and determine at least one distance indicator that is indicative of the distance between the first antenna unit and the second antenna unit based on at least the first phase sum and second phase sum.

Description

TECHNICAL FIELD OF THE INVENTION The invention relates to radio communication and localization in general. More specifically, the invention relates to evaluating a distance between at least a first antenna unit and a second antenna unit by two-way transmission of at least two signals having different circular polarizations between the antenna units. BACKGROUND OF THE INVENTION Systems and methods involving transmission of signals, such as radio signals, from a first (transmitter) device to a second (receiver) device are used in many applications, e.g. in tracking or other purposes where distance measurements are utilized. In some systems, it may be possible to evaluate the distance between two devices by alternately using the first and second devices as transmitter and receiver. Here, the phases of one or more transmitted signals that are received by the receiving device may be determined and used in distance measurements. There are, however, many complications involved with such measurements, and obtaining accurate results regarding the distance between the devices may be laborious or unfeasible. One problem is associated with reflections of the signals. Reflections of the transmitted signal from other objects that reach the receiver device may be impossible to distinguish from the signal received directly from the transmitter device. When determining a distance or phase length (from the determined phase of the received signal with respect to a local oscillator of the receiver device), the determined distance or phase length will then be affected by the reflected signal and may be erroneous. Distinguishing the original transmitted signal from a reflected signal is especially difficult in cases where the reflection occurs in a direction close to the direction of the original signal. In such a case the reflected signal has approximately the same delay as the original signal which makes the reflected signal practically indistinguishable from the original one in spatial or temporal signal processing. Still, in applications where extremely high distance measurement accuracy is desired, such distortion of the signal phase is detrimental. To reduce or eliminate the effect of reflections, polarized signals may be employed in the transmissions. Circularly polarized signals are known as especially advantageous in being able to reduce the effect of reflected signals from metal surfaces, which may be the most problematic reflection surfaces if linearly polarized signals are used. Reflections from metal surfaces (or other surfaces with similar reflection coefficients) will essentially change the polarization of the signal, such that if the receiving antenna is adapted to receive essentially only signals with circular polarization of the original signal, the reflected signal may not be received or at least will be strongly attenuated. Circularly polarized signals may also reduce the effect of reflections due to other types of surfaces, even if the polarization of the reflected signal is not perfectly circular. There are, however, also some problems associated with the use of circularly polarized signals. Rotation along the line-of-sight (LOS) axis between the antenna units will affect phase measurements and thus the determination of distance between the antenna units. In e.g. geodetic GNSS, the problem of rotation along the LOS axis between transmitter and receiver may be eliminated by using a joint solution of the rotation angle and the position coordinates as well as differentiation with respect to a reference station in proximity. This requires a large number of satellites in the solution, making such a solution impractical for a terrestrial system where only a small number of antenna units are available for tracking the position of a moving radio device. Also, a reference antenna may be impractical for terrestrial navigation. SUMMARY OF THE INVENTION An object of the invention is to alleviate at least some of the problems in the prior art. In accordance with one aspect of the present invention, a method is provided for evaluating a distance between at least a first antenna unit and a second antenna unit, the method comprising at least transmitting a first signal via the first antenna unit, said first signal comprising a first circular polarization,receiving the first signal at the second antenna unit,determining first phase information, said first phase information being indicative of a phase of the received first signal with respect to a local oscillator of a radio unit with which the second antenna unit is associated,transmitting a first response signal via the second antenna unit, said first response signal essentially corresponding to said first signal,receiving the first response signal at the first antenna unit,determining first response phase information, said first response phase information being indicative of a phase of the received first response signal with respect to a local oscillator of a radio unit w