FI20215019A1

FI20215019A1 - A method and arrangement for evaluating at least one distance

Info

Publication number: FI20215019A1
Application number: FI20215019A
Authority: FI
Inventors: Kari Leppänen
Original assignee: Koherent Oy
Priority date: 2021-01-08
Filing date: 2021-01-08
Publication date: 2022-07-09
Also published as: WO2022148913A1

Abstract

A method for evaluating at least one distance between a first antenna unit and a second antenna unit, the method comprising at least resolving an integer ambiguity by sending one or more primary signals comprising frequencies in a first frequency range, and determining a set of one or more possible distance values being indicative of possible distances between the first antenna unit and second antenna unit. The method further comprises sending one or more auxiliary signals comprising frequencies in at least one second frequency range, and evaluating the distance between the between the first antenna unit and second antenna unit based on a selected likely distance value from the set of possible distance values.

Description

A METHOD AND ARRANGEMENT FOR EVALUATING AT LEAST ONE DISTANCE

TECHNICAL FIELD OF THE INVENTION The invention relates to measuring distance in general. More specifically, the invention relates to evaluating at least one distance by at least measurement of radio link phase and determination of an integer ambiguity in a distance between a first antenna unit and second antenna unit.

BACKGROUND OF THE INVENTION Methods for measuring distances where phase measurements between transmitter and receiver are carried out are burdened by the integer ambiguity (IA) problem. For instance, a measurement between a transmitter device and responder device can comprise measurement of a phase difference between a transmitted and response signal and this can be used to calculate a part (the length of a fractional part of a wavelength used) of the distance between the transmitter and responder. The determination of uncertainty in the number of full wavelengths — the integer ambiguity - between the transmitter and responder is also required in order to determine the total distance. The prior art discloses different methods for resolving the above discussed integer ambiguity problem. Carrier phase techniques with Global Navigation Satellite Systems (GNSS) solve the integer ambiguity problem by utilizing tens of simultaneous measurements of phase over radio links (pairs of radio units of which at least one transmits a signal and one receives a transmitted signal). The simultaneous phase measurements allow a joint solution for the N integer ambiguities. In terrestrial systems this would reguire tens of access a 25 points / base stations to be visible in line-of-sight simultaneously. This is not > practically possible. Also, strong radio reflections make this technigue 3 unreliable. E To solve the IA problem in terrestrial positioning or distance determination 2 systems, the IA for each radio link (or a very small number of radio links) has = 30 to be solved. One solution is to measure the distance of each link with a radio I pulse, but this suffers from poor accuracy with respect to the radio signal wavelength unless the instantaneous measurement bandwidth is very large. In addition, such a delay measurement suffers from radio reflections, making this technigue impractical.

There is a need for a method of accurate determination of a radio link distance enabled through phase measurement and reliable and simple determination of integer ambiguity in the link distance.

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 at least one distance between a first antenna unit and a second antenna unit, the method comprising at least resolving an integer ambiguity by: sending one or more primary signals comprising frequencies in a first frequency range, and determining a set of one or more possible distance values being indicative of possible distances between the first antenna unit and second antenna unit through: - sending at least a first primary signal having a first primary frequency via a first antenna unit - receiving the first primary signal at a second antenna unit, - determining at least first primary phase information related to the first primary signal, said first primary phase information being indicative of a phase of the received first primary signal with respect to a local oscillator of a radio unit with which the second antenna unit is associated with, - sending at least a first primary response signal having a primary response frequency via the second antenna unit, wherein the - primary response frequency essentially corresponds to the first O 25 primary freguency, = - receiving the first primary response signal at the first antenna 0 unit, 7 - determining at least first primary response phase information = related to the first primary response signal, said primary O 30 response phase information being indicative of a phase of the D received primary response signal with respect to a local oscillator N of the radio unit with which the at least one first antenna unit is N associated,

- determining at least a first primary phase sum being indicative of a sum of the first primary phase information and the first primary response phase information,

- determining the set of one or more possible distance values,

based at least on the first primary phase sum, a determined first distance variable, said distance variable being indicative of a first approximated distance between the first antenna unit and second antenna unit, and an estimated maximum error in the determined first distance variable, and sending one or more auxiliary signals comprising frequencies in at least one second frequency range, and determining the distance between the between the first antenna unit and second antenna unit by:

- sending at least one first auxiliary signal having a first auxiliary frequency via the first antenna unit,

- receiving the first auxiliary signal at the second antenna unit,

- determining at least first auxiliary phase information related to the first auxiliary signal, said first auxiliary phase information being indicative of a phase of the received first auxiliary signal with respect to a local oscillator of a radio unit with which the second antenna unit is associated with

- sending at least one first auxiliary response signal having an auxiliary response frequency via the second antenna unit, wherein the auxiliary response frequency essentially corresponds to the first auxiliary frequency, S - receiving the first auxiliary response signal at the first antenna i unit, > - determining at least first auxiliary response phase information 3 related to the first auxiliary response signal, said auxiliary E 30 response phase information being indicative of a phase of the o received auxiliary response signal with respect to a local 3 oscillator of the radio unit with which the at least one first antenna N unit is associated, S - determining at least a first auxiliary phase sum being indicative of a sum of the first auxiliary phase information and the first auxiliary response phase information, and

- determining the distance between the first antenna unit and second antenna unit based on a selected likely distance value from the set of possible distance values, the selecting of the likely distance value being based at least on the first primary phase sum, the first auxiliary phase sum, and estimated maximum error in the first primary phase sum and/or estimated maximum error in the auxiliary phase sum. The invention also relates to a computer program product according to independent claim 16 and an arrangement according to independent claim

17. The present invention may provide a method of determining an absolute distance for a single link between transceivers (a radio link between the first antenna unit and the second antenna unit) without the need for further transmitters or receivers in the determination of the distance between the two transceivers. Phase techniques in the prior art (e.g. Real Time Kinematic GNSS) require a high number of satellites transmitting signals to at least two receivers to resolve the IA problem. The present invention may be used in terrestrial systems, optionally also indoors to enable indoor positioning. This is because only one radio link between two antenna units may be required for accurate determination of a distance between the units. The arrangement may be utilized for accurate determination of a plurality of distances between different antenna units, and the distances may n advantageously be determined for each link/distance separately. S 25 The present invention may allow determination or evaluation of distance > between antenna units with narrow instantaneous bandwidth of used 3 frequencies in the transmitted signals (e.g. a bandwidth of 40 MHz). This is E opposed to other existing systems such as Ultra-Wide-Band (UWB) systems, o where a much larger instantaneous bandwidth must be used. The present 3 30 invention provides a method and arrangement which may be inexpensive to N implement, whereby inexpensive narrow band receivers may be utilized.

N Due to the narrow operating bandwidth of the present invention, the system may operate at freguency bands/ranges where high transmission powers are allowed, enabling better range and accuracy than e.g. UWB and Bluetooth-

based positioning systems, which operate at frequency bands where lower transmission powers must be used. Bands that are feasible with the present invention may be e.g. 5GHz RLAN (enabling transmission power of 100 mW or even 1W) or WIA band (enabling transmission power of 400 mW). 5 Therefore, the power used for transmission of one or more signals (e.g. primary and/or auxiliary signals) may be over tens of mW, such as over 20 mW, over 50 mW, or over 80 mW. In e.g. UWB techniques, the transmission powers are limited to levels that are several orders of magnitude smaller than with the present invention.

With the present invention, it may also be easier to fit the utilized narrow bands between e.g. wifi network channels.

In one embodiment, the method may comprise sending a plurality of primary signals and primary response signals. The method may additionally comprise sending a plurality of auxiliary signals and auxiliary response signals.

In the case of a plurality of primary or auxiliary signals, the frequency of at least consecutive primary signals and/or frequency of consecutive auxiliary signals may in an embodiment preferably be separated from each other by under 20 MHz, more preferably under 10 MHz, such as 5 MHz. Advantageously a difference between the first frequency range and the second frequency range is at least 150 MHz, preferably at least 200 MHz, most preferably at least 500 MHz. The frequency ranges may also be in completely different radio bands: for example, the higher range could be in the 5 GHz RLAN band whereas the lower range could be in 2.4 GHz ISM — band, allowing a freguency difference over 3 GHz. Thus, the first freguency O 25 range and second freguency range could be separated by e.g. 500 MHz- — 5GHz.

I 3 The first frequency range and/or the second frequency range may encompass E a maximum bandwidth of 100 Hz-100 kHz, preferably 10-100 kHz in the case o of only one signal transmitted in said range or 5-100 MHz, preferably 10-50 3 30 MHz, such as e.g. 40 MHz in the case of a plurality of signals being N transmitted in said range.

N In embodiments where only one first primary signal and one first primary response signal are used, e.g. a bandwidth of the first frequency range may be considered to essentially comprise only one freguency, still less expensive design and even coin battery operation are possible. The same applies to the second frequency range in cases where only one first auxiliary signal and one first auxiliary response signal are utilized. A first and/or second frequency range may in some embodiments of the invention be considered as having a selected bandwidth, yet it should be understood that one or more signals in said ranges do not necessarily have to span said bandwidths, but can exhibit separate frequencies which may be comprised in said ranges. It is also possible to use any number of auxiliary signals in various different frequency ranges (such as third, fourth etc. frequency ranges). For simplicity, the detailed description below focuses mainly on the case where only one frequency range (the second frequency range) for auxiliary signals is used. In one embodiment of the invention, at least a second primary signal and second primary response signal may be sent to determine respective phase information (second primary phase information, second primary response phase information) and a second primary phase sum. The distance variable may be determined by comparing at least the first primary phase sum and the second primary phase sum, optionally based on a difference between the first primary phase sum and second primary phase sum. First and subsequent primary signals (and corresponding response signals) may be transmitted to determine respective phase information to obtain a plurality of phase sums, while the difference between phase sums (such as difference between first and each subsequent phase sum) may be used to determine a distance variable that is indicative of an approximate distance between the first and = 25 second antenna unit.

O > The maximum error in the distance variable may, in embodiments where the 0 distance variable is dependent on the determined phase information or 7 sum(s), be determined based on at least the estimated maximum error in the = determined phase information. A maximum error in one or more determined O 30 phase sums may be determined based on one or more maximum errors in D determined phase information.

N S A maximum error in the distance variable may in some embodiments be determined based on other information or may e.g. be obtained as a previously determined parameter.

The set of possible distance values may in one embodiment be determined based at least on the first primary phase sum and variation of the integer ambiguity corresponding to distance variations of integer numbers of half wavelengths at the first primary frequency, said set of possible distance values being limited by the estimated maximum error in the distance variable.

When the maximum error of the distance variable is known, however, this may limit the possible distance values to ones which are within the maximum error values of the distance variable.

This may then be used to determine the set of possible distance values, which gives the possible distances between the antenna units in terms of distances that differ from each other in integer ambiguity.

The likely distance value may be selected by determining a second distance variable corresponding to a second approximate distance between the first and second antenna unit, the determining of the second distance variable being based on comparing at least the first primary phase sum and the first auxiliary phase sum, optionally based on a difference between the first primary phase sum and first auxiliary phase sum divided by the frequency difference of the first primary and first auxiliary signal.

A maximum error of the second distance variable may then limit the possible distance values.

Advantageously, when determining the second distance variable based on the first primary phase sum and first auxiliary phase sum, the maximum error of the second distance variable leaves only one possible distance value.

The likely distance value may then be selected as the distance value from the set of possible distance values fitting an error margin = 25 in the second distance variable, said error margin being determined by the N estimated maximum error in the first primary phase sum and/or the estimated 5 maximum error in the first auxiliary phase sum. 00 7 The likely distance value may be or correspond to the actual distance = between the first antenna unit and the second antenna unit or be indicative of O 30 said distance.

The determining of a distance between the first antenna unit D and the second antenna unit may herein refer to determining a value of N distance that is an approximation of the actual distance between the first N antenna unit and the second antenna unit based on the measurements carried out.

In one embodiment of the invention, one or more auxiliary signals comprising frequencies in a plurality of frequency ranges may be sent, said plurality of frequency ranges comprising at least the second frequency range, wherein auxiliary signals are sent in a subsequent frequency range if it is determined that the likely distance value cannot be uniquely selected based on the determined first or subsequent, previously determined auxiliary phase sum.

If it is determined, for instance after determining an auxiliary phase sum and a second distance variable, that possible distance values (corresponding to distance values within an error margin of the second distance variable corresponding to distance differences of integer half wavelengths at the first primary frequency) are not only limited to one possible value, and therefore that the likely distance value cannot be unambiguously selected, then a third frequency range may be selected, and subsequent auxiliary signals (and auxiliary response signals) may be transmitted and respective phase information determined, whereby the possible distance values are further limited, and it may be feasible to uniquely select the likely distance value.

In an embodiment of the invention, the second (or any subsequent) frequency range may be selected based on the estimated maximum error in the determined distance variable so that the difference between the first and second frequency range ensures that unaccounted phase rotations are avoided , optionally by determining a possible range for the distance variable based on its maximum error and selecting the second frequency range such that the expected minimum and maximum values of the first auxiliary phase sum corresponding to the minimum and maximum values of the first distance — variable do not differ more than a threshold value, such as 21. Using 21 or N smaller value for the threshold prevents phase ambiguity when first auxiliary a (or any subseguent) phase sum is used to further limit the set of possible > distance values. 00 z Some embodiments of the method additionally comprise tracking the distance - 30 between the first and second antenna unit by resolving the integer ambiguity 2 at least once and subsequently repeatedly sending subsequent primary = signals and primary response signals, determining subsequent primary I phases and primary response phases, and determining primary phase sums to repeatedly determine distance information being indicative of a change in distance between the first and second antenna unit.

Embodiments of the invention may thus provide an arrangement and method for continuous distance tracking or provision of location information, where integer ambiguity may be resolved/determined e.g. once or at predetermined intervals, while otherwise operating in a tracking mode, where only primary signals and primary response signals are sent (and received) to repeatedly determine a primary phase sum which may be used to repeatedly determine the distance between the antenna units without re-determination of an integer ambiguity. In continuous distance tracking or tracking mode, the subsequent primary — signals and primary response signals could be transmitted at predetermined adequately short time intervals such that it may be assumed that the integer ambiguity problem does not reappear, i.e. that the distance uncertainty between antenna units between times of sending subsequent signals increases less than an amount that would lead to a cycle slip that cannot be accounted for. Distance tracking may be used to track a position of a physical object, where e.g. a first or second antenna unit is associated with the physical object, such as coupled to the object. A maximum time interval between subsequent primary signals and primary response signals for tracking a physical object may be determined e.g. through a maximum uncertainty in the speed and/or acceleration of the physical object. In tracking of an object, the object's approximate location, speed and/or - acceleration may be estimated or an approximate (maximum) uncertainty in O 25 these may be determined. In some embodiments, an estimator may be used = for tracking/estimating the object's location. The object's location may be 0 tracked using e.g. simple interpolators, Kalman filters, extended Kalman 7 filters, or particle filters. The use of such estimators may make it possible to = measure the link phase (such as determined phase sums) with lower O 30 repetition rate (i.e. with using less and/or less frequent e.g. primary signals) D without a risk of uncounted 271 phase slips in the phase sum.

QA S The arrangement could be used for distance tracking such that most of the time, the transmitted signals only need to be in one narrow freguency band, e.g. a first frequency range.

In one embodiment, at least the first primary signal and the first auxiliary signal may be sent in succession. In one other embodiment, at least the first primary signal and the first auxiliary signal may be sent at least partially simultaneously. For instance, at least a first primary response signal and first auxiliary response signal may also be sent at least partially simultaneously. Also a plurality of e.g. primary signals and/or a plurality of auxiliary signals may be sent simultaneously. The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific example embodiments when read in connection with the accompanying drawings. The previously presented considerations concerning the various embodiments of the method may be flexibly applied to the embodiments of the arrangement mutatis mutandis, and vice versa, as being appreciated by a skilled person.

BRIEF DESCRIPTION OF THE DRAWINGS Next the invention will be described in greater detail with reference to exemplary embodiments in accordance with the accompanying drawings, in which: Figure 1 depicts one exemplary arrangement according to an embodiment = of the invention, & = Figure 2 shows one more exemplary arrangement according to an 0 25 embodiment of the invention,

O E Figure 3 shows exemplary first and second antenna units and radio units o that may be used in an arrangement,

O = Figure 4 shows other exemplary first and second antenna units and radio I units that may be used in an arrangement, Figure5 shows, on a graph of determined phase sum as a function of transmitted signal freguency, possible determined primary phase sums,

auxiliary phase sums, and integer ambiguity lines corresponding to a set of determined distance values in one use case scenario according to one embodiment of the invention, Figure 6 illustrates one possible radio unit that may be used in an arrangement, Figure 7 depicts allocation of time slots in measurement cycles, Figure 8 portrays a flow chart of a method according to one embodiment of the invention, and Figure 9 shows a flow chart of a method of selecting frequency ranges to be utilized in embodiments of the invention.

DETAILED DESCRIPTION Figure 1 shows an arrangement 100 according to one embodiment of the invention. The arrangement comprises at least a first antenna unit (AU) 104 and a second antenna unit 106. An arrangement 100 may also comprise some other number of antenna units, such as a third antenna unit and a fourth antenna unit etc. The number of antenna units may determine how many distances the arrangement 100 may possibly evaluate. Any number of distances between antenna units, such as the distance D between the fist antenna unit 104 and second antenna unit 106 may be evaluated. The first antenna unit 104 may be associated with a first radio unit 108 and the second antenna unit 106 may be associated with a second radio unit 110. — One radio unit 108, 110 could also be associated with two or more antenna O units 104, 106. An antenna unit 104, 106 may be comprised in a radio unit = 108, 110 or be coupled to a radio unit via e.g. cables. 3 25 The radio units 108, 110 are coupled to at least one processor 102. The E processor 102 may be a controller unit that is external to the radio units 108, o 110, and may be implemented as a microprocessor unit or provided as a part 3 of a larger computing unit such as a personal computer. Yet in some N embodiments, the processor 102 may be comprised in or be considered to N 30 be part of a radio unit 108, 110 The processor 102 may be configured to control the radio units and/or antenna units comprised in an arrangement 100. The processor 102 may additionally receive data from the antenna units 104, 106 or radio units 108,

110. The processor 102 may additionally or alternatively be configured to receive data from the antenna units and/or radio units comprised in an arrangement 100 in a wired (e.g. Ethernet) or wireless (e.g. WLAN) manner. Figure 2 shows an embodiment of an arrangement 100 where the processor 102 is wirelessly coupled to the radio units 108, 110. A processor 102 may be associated with a processor antenna unit 112. The processor 102 and radio units 108, 110 may be powered using for instance power-over-Ethernet (PoE), direct mains supply, batteries, solar panels, or mechanical generators (e.g. in wind turbine blades). In some embodiments, also a remote processor may be utilized in an arrangement 100, e.g. in addition to the processor 102 which may be a local processor or the processor 102 may be realized as a remote processor with no need for a local processor. A remote processor may receive any of the data obtained and could e.g. perform at least a portion of the determination of data that is carried out by the arrangement 100. A remote processor may refer to a processor which may be accessed through cloud computing or the remote processor may e.g. refer to a virtual processor comprised in a plurality of locations which may be configured to execute procedures presented herein through parallel processing means. The first antenna unit 104 is configured to send at least a first primary signal having a first primary frequency, which may be a radiofrequency (RF) signal. - The primary signal is preferably a sine wave, but can be any signal with a O 25 known modulation. The first antenna unit 104 may also transmit subseguent = primary signals, which will be discussed further below. 3 The first primary frequency (and possible subsequent primary signals) may E be comprised in a first frequency range. The first frequency range may for o instance encompass a maximum bandwidth of 100 Hz-100 kHz, preferably 3 30 10-100 kHz in the case of only one signal transmitted in said range or 5-100 N MHz, preferably 10-50 MHz, such as e.g. 40 MHz in the case of a plurality of N signals being transmitted in said range. The duration of the first primary signal (and any subseguent signals transmitted/sent by any of the antenna units of the arrangement) may for instance be between 10 and 10 000 us depending on e.g. the length of the distances that are to be evaluated, the time intervals between measurement cycles, and/or the guality of local oscillators comprised in the radio units 108,

110. A duration of a signal may for instance be about 100 js.

The first primary signal is then received at the second antenna unit 106. Based on the received first primary signal, at least first primary phase information related to the first primary signal is determined, said first primary phase information being indicative of a phase of the received first primary signal with respect to a local oscillator of the radio unit with which the at least one second antenna unit is associated, here the second radio unit 110.

To be precise, typically the signal freguency is higher than the local oscillator freguency and the phase measurement often occurs in digital baseband using e.g. fast fourier transform. Essentially, this is eguivalent to measuring the phase against the local oscillator that can, for simplicity, be understood to operate at the signal frequency.

If an arrangement 100 comprises further antenna units such as e.g. a third antenna unit, then the (first) primary signal may also be received at the third antenna unit and (first) primary phase information could be determined also at the third (and subseguent) antenna units.

The determination of phase information, such as the first primary phase information, may be carried out at the radio unit with which the receiving antenna unit is associated, such as the second radio unit 110 in the case of the second antenna unit 106 receiving the first primary signal.

N The second antenna unit 106 is configured to transmit at least a first primary a 25 response signal. The first primary response signal may be eguivalent to the > first primary signal or essentially correspond to the first primary signal at least 3 in frequency. The second antenna unit 106 may be configured to transmit E subseguent primary response signals. A second primary response signal may o essentially correspond to a second primary signal, a third primary response 3 30 signal may essentially correspond to a third primary signal, etc.

O The first primary response signal is received at the first antenna unit 104. Based on the received first primary response signal, at least first primary response phase information is determined, said first primary response phase information being indicative of a phase of the received first primary response signal with respect to a local oscillator of the radio unit with which the at least one first antenna unit is associated, here the first radio unit 108.

In addition to determining phase information, also amplitude information may be determined in some embodiments. For example, both phase information and amplitude information may be determined at a receiving radio unit upon receiving a signal.

The determined phase information (at least first primary phase information and first primary response phase information, phase information related to auxiliary signals discussed in more detail below, and/or amplitude information, for instance) may be received by the processor 102.

In some embodiments where amplitude information is determined, the amplitude information may be used to estimate the reliability of the determined data (e.g. a determined distance). For example, a temporary obstruction in the line of sight between the antenna units may be detected and any data marked invalid for the affected time period. The first primary phase information and first primary response phase information is then used to determine (by the processor 102) at least a first primary phase sum being indicative of a sum of the first primary phase information and the first primary response phase information. The first antenna unit 104 may be configured to send subsequent primary signals, e.g. at least a second primary signal, which differs in frequency from the first primary signal. The first and subsequent primary signals are yet preferably within the first frequency range and may be transmitted S simultaneously or seguentially. 5 25 The subsequent primary signal(s) may be received by the second antenna 2 unit 106, and subseguent primary phase information may be determined. E Subseguent primary response signals, such as at least a second primary O response signal, essentially corresponding to the second primary signal in D freguency, may then be sent by the second antenna unit 106. The subseguent S 30 primary response signal(s) are received at the first antenna unit 104. N Subsequent primary response phase information may be determined.

From subsequent primary phase information and subsequent primary response phase information, subsequent primary phase sums, e.g. at least a second primary phase sum may be determined.

If an arrangement 100 comprises more than two antenna units 104, 106, any one of them may transmit and receive the discussed signals, such that a distance between any two antenna units that have among themselves sent and received at least one signal can be evaluated.

A set of possible distance values is then determined based at least on the first primary phase sum, a determined first distance variable that is indicative of a first approximated distance between the antenna units, and an estimated maximum error in the determined first distance variable.

The distance variable could in some embodiments be based on an approximate distance between the antenna units.

Possible ways of determining the set of possible distance values will be discussed in more detail further below.

The first antenna unit 104 is also configured to send at least a first auxiliary signal having an auxiliary frequency.

Except for the frequency, the first auxiliary signal essentially corresponds to the first primary signal.

The first auxiliary frequency may exhibit a frequency that is in a second frequency range.

The second frequency range may encompass a maximum bandwidth of 100 Hz-100 kHz, preferably 10-100 kHz in the case of only one signal transmitted in said range or 5-100 MHz, preferably 10-50 MHz, such as e.g. 40 MHz in the case of a plurality of signals being transmitted in said range.

A difference between the first frequency range (a range of the first and possible subsequent primary signals and first and possible subsequent - primary response signals) and the second frequency range may be at least O 25 150 MHz, preferably at least 200 MHz, most preferably at least 500 MHz.

The = difference could even be over 3 GHz, for example, where the two freguency 0 ranges lie in completely different radio bands, such as the 2.4 GHz ISM and 7 5 GHz RLAN/ISM bands.

Ao > The frequency values of the first, second and/or any subsequent frequency 3 30 range may essentially comprise any frequency values.

More significant than N the freguency values comprised in the freguency ranges may be a selected N separation/distance or difference in freguency between the separate ranges or between the freguencies of at least the first primary signal and the first auxiliary signal.

The second antenna unit 106 receives the first auxiliary signal and first auxiliary phase information may be determined, where the first auxiliary phase information is indicative of a phase of the received first auxiliary signal with respect to a local oscillator of the second radio unit 110.

The second antenna unit 106 then transmits a first auxiliary response signal essentially corresponding in frequency to the first auxiliary signal. The first auxiliary response signal is received at the first antenna unit 104, and first auxiliary response phase information is determined, where the first auxiliary response phase information is indicative of a phase of the received first auxiliary response signal with respect to a local oscillator of the first radio unit 108.

The first auxiliary phase information and first auxiliary response phase information is then used to determine at least a first auxiliary phase sum being indicative of a sum of the first auxiliary phase information and the first auxiliary response phase information.

Processing of information may be conducted in different order than that which is proposed here. For instance, the aforementioned determination of a set of possible distance values may also be done e.g. after sending (and receiving) auxiliary signals and auxiliary response signals.

Subsequent auxiliary signals (and auxiliary response signals) may also be transmitted to determine subsequent auxiliary phase information, subsequent auxiliary response phase information, and subsequent auxiliary phase sums.

S Subseguent auxiliary signals may comprise freguencies in the second N freguency range, while the subseguent auxiliary response signal freguencies 5 25 may essentially correspond to those of the respective subsequent auxiliary 2 signals.

E If a plurality of auxiliary signals are transmitted, they may be transmitted O simultaneously or sequentially.

O

LO N Based at least on the determined first primary and first auxiliary phase sums, N 30 a likely distance value is determined/selected from the set of possible distance values (assuming that the difference between the first and second freguency range is sufficient for being able to carry out the selection unambiguously). The selection of the likely distance value will be discussed in more detail further below.

Figure 3 illustrates exemplary first and second antenna units 104, 106 and radio units 108, 110 that may be used in an arrangement. In the example of Fig. 3, the antenna units 104, 106 are provided separately from the radio units 108, 110. Fig. 3 exhibits schematically how phase information related to signals that are transmitted and received between two antenna units 104, 106 in a pair of antenna units that mutually transmit and receive at least one signal among each other may be used to evaluate a distance D between them.

As may be easily understood by the skilled person, distances may be defined in terms of phase lengths, i.e., phase shifts that occur in a signal (e.g. sine wave) as it traverses a certain length.

Assuming that the transmitting first antenna unit 104 transmits the at least one first primary signal with zero phase with respect to its local clock/oscillator (LO) the measured/determined phase 012 (or first primary phase information) of the primary signal received at the second antenna unit 106 may be determined by (as also seen from Figure 3): 012 = Oc1- Or1- Om - P12- Oa2- Or2- Oc. (1) Oc, and Oc are the phases of the local oscillators of the first and second radio units 108, 110, respectively (at the time of transmission for the first radio unit 108). P12 is the geometric phase corresponding to the distance or baseline or connecting geometric line between the first antenna unit 104 and the second antenna unit 106. Ori and Or, are the transmit and receive N branch phase lengths corresponding to the first antenna unit 104 and second a 25 antenna unit 106, respectively (with phase length referring here to the phase > shift that occurs in a signal traversing along a certain distance). ©a 1 and Oa? 3 are the phase lengths of the antenna feed cables of the first antenna unit 104 E and second antenna unit 106, respectively. 2 The transmit and receive branch phase lengths, e.g. Ori and Or2 comprise = 30 the phase lengths that are due to the physical lengths of the transmit and I receive branches of the associated radio units, comprising e.g. amplifiers and also possible cables in the radio units. For instance, the phase length Or, corresponds to the length of transmission branch from the digital-analog converter (DAC) to the antenna port of the first radio unit 108.

Accordingly, the second antenna unit 106 may transmit at least one primary response signal (possibly after determining that the first signal has been transmitted), and the first primary response signal may be received at the first antenna unit 104.

Yet, assuming that the second antenna unit 106 transmits the first primary response signal with zero phase with respect to its local clock/oscillator (LO), the measured/determined phase 2, (or first primary response phase information) of the primary response signal received at the first antenna unit 104 may be determined by: 021 = Oc,2- Or 2- Om - P21- Oao- Or1- Oc. (2) Oc,2 and Oc are the phases of the local oscillators of the second and first radio units 110, 108, respectively (at the time of transmission for the second radio unit 110). 92; is the geometric phase corresponding to the distance or baseline or connecting geometric line between the second antenna unit 106 and the first antenna unit 104. Oro and Ors are the transmit and receive branch phase lengths corresponding to the first antenna unit 104 and second antenna unit 106, respectively. The radio units may send the determined phase information (and possibly also other information, such as amplitude information) to a processor 102 (which may e.g. be incorporated with one of the radio units). The processor 102 may then determine at least a first primary phase sum. A phase sum may be determined as a sum of the phase information relating to a signal that has been sent by one antenna unit and received at one other N antenna unit and a corresponding response signal that has been sent by the a 25 one other antenna unit (e.g. second antenna unit 106) and received at the > one antenna unit (e.g. first antenna unit 104). In the example of Fig. 3 with a 3 first 104 and second antenna unit 106, a phase sum (e.g. first primary phase E sum) Pa may be determined as: 2 Da =@Qr2+ P21=-O11- Oa - P12- Oaz- Or2- O12- Ono - P21- Oa1- ORI 2 30 3 S (3) The LO terms Oc, and Oc cancel out, assuming that the LO phases have not drifted between the two transmissions (first signal and response signal).

The phase sum determined as described herein is thus advantageously not dependent on the phase of the local oscillators of the radio units involved. Possible frequency offset between local oscillators of radio units 108 and 110 can be easily measured from the determined phase information. The linear phase drift in Pa from such frequency offset can therefore be compensated for. If the instrumental terms in Equation 3 cannot be assumed to be stable, and their omission would lead to erroneous or inexact distance variables (which may be determined based on the phase sums, e.g. as demonstrated hereinlater), in one advantageous embodiment of the invention, calibration data may be determined in addition to the phase information for a pair of antenna units to perform self-calibration via self-measurements and subsequently essentially eliminate at least some of the instrumental terms in the phase sums. The calibration data may comprise calibration phase information being indicative of a phase of a self-measurement signal received at a transmitting antenna unit during transmission of a signal. Determining of calibration data according to an exemplary embodiment shown in Fig. 3 will be given below. An (attenuated) sample of for instance a first primary signal (or e.g. any subsequent primary signal or auxiliary signal) may be received at the first antenna unit 104 as a self-measurement signal and the phase pii of the received (first primary) signal as it reaches the antenna unit 104 may be determined by the first radio unit 108. The phase of the received signal may be determined/measured in the radio unit 108 with respect to the radio unit = 25 sampling clock or local oscillator of the radio unit 108.

O > According to Figure 3 it may be determined that first calibration phase 0 information indicative of the phase of the self-measurement signal may be 7 given by = N 011 =-Or1- Ora, (4). 3 30 Accordingly, a sample of the e.g. first primary response signal may be I received at the second antenna unit 106 as a self-measurement signal and the phase 022 of the received first primary response signal as it reaches the second antenna unit 106 may be determined by the second radio unit 110. The phase of the received signal may be determined/measured in the second radio unit 110 with respect to the radio unit sampling clock or local oscillator of the second radio unit 110. Response calibration phase information indicative of the phase of the self- measurement signal at the second antenna unit 106 may be given by (P22 = - OT2- Oro. (5) The radio units 108, 110 may send the determined calibration data (comprising the calibration phase information) to the processor 102, and the processor 102 may in some embodiments determine a phase sum as being indicative of a difference between a sum of the phase information relating to a signal that has been sent by one antenna unit and received at one other antenna unit and a corresponding response signal that has been sent by the one other antenna unit (e.g. second antenna unit 106) and received at the one antenna unit (e.g. first antenna unit 104) and the sum of the calibration data. Alternatively, the radio units may pre-compensate for the instrumental terms by subtracting the calibration phase information before sending the e.g. primary or primary response phase information to the processor. A phase sum may then be determined as (from Equations 3, 4, and 5): Da = P12 + Q21- P11— P22 = - Or1- Oa - P12- Oa2- Or2- Or2- On - Oo1 - OM - ORri+ Ori + Or + Or2+ Or? =- Q12- 2042- P21- 2041. (6) N In embodiments where calibration phase information is determined, an a arrangement 100 may employ antenna units 104, 106 which have a switch <Q implemented in the antenna unit 104, 106 (and not the radio unit 108, 110). 3 25 Here, possible changes in the active transmit or receive lines and E components in the radio units 108 and 110 are essentially eliminated by the o calibration. Only the antenna cable lengths remain as instrumental terms in 3 the determined phase sum. However, these are rather constant and can be N separately calibrated simply by doing one calibration measurement with a N 30 known distance between the first antenna unit 104 and second antenna unit

106.

The above considerations may apply also to any possible auxiliary and auxiliary response signals, subsequent primary and primary response signals, and subsequent primary auxiliary and auxiliary response signals. Figure 4 exhibits other exemplary first and second antenna units 104 and 106 and radio units 108 and 110 that may be used in an arrangement 100. In this embodiment, the antenna units 104, 106 are comprised in the radio units 108, 110, or advantageously connected only with a single antenna cable. Figure 5 shows, on a graph of determined phase sum as a function of transmitted signal frequency, possible determined primary phase sums, auxiliary phase sums, and integer ambiguity lines corresponding to a set of determined distance values in one use case scenario according to one embodiment of the invention. The e.g. numbers, lines, and calculated values of Fig. 5 are merely exemplary and are intended as visual aids in describing the invention. The exact depicted values might be possible e.g. in a case where a distance D between antenna units is only about 25 mm. However, the principle remains the same for much larger distances. Depicted points 302 and 304 may correspond to a first primary phase sum and second primary phase sum, respectively. In this example, first and second primary signals (having frequencies of f1 and f2) and first and second primary response signals (with frequencies fi and f2) have therefore been transmitted. The primary (response) signals are in a first frequency range fa. The exemplary first frequency range fa spans a frequency range of about 40 MHz. E.g. the number of transmitted signals and the frequencies that the first frequency range fa spans, along with the width of first band (range of spanned = 25 frequencies) may of course differ between use cases.

O a The primary (response) signals may be sent in one transmission where a > plurality of e.g. sine waves may be transmitted simultaneously. The difference S in frequency between consecutive signals may be e.g. between 1 and 40 E MHz, between 5 and 20 MHz, such as about 10 MHz. 2 30 Points 308 and 310 may correspond to a first auxiliary phase sum and second = auxiliary phase sum respectively. In this example, first and second auxiliary S signals (with freguencies of f3 and f4) and first and second auxiliary response signals have therefore been transmitted. The auxiliary (response) signals are in a second frequency range f» The exemplary second frequency range fy spans a frequency range of about 40 MHz. Again, the number of transmitted signals and the frequencies that the second frequency range f, spans (which could be e.g. only one frequency), and with the width of second band may also differ.

First and second frequency ranges fa, fo may be equivalent in bandwidth or they may differ from each other. Yet, the first and second frequency ranges are advantageously both narrow enough to enable the use of narrow band receivers (cf. WiFi receivers) or even Internet-of-Things receivers operating on a coin battery.

The difference Af between the first frequency range fa and second frequency range fi is about 550 MHz in the example of Fig. 5. The frequencies of the primary signals can be larger than the frequencies of the auxiliary signals or the frequencies of the primary signals can be smaller than the frequencies of the auxiliary signals, yet there is advantageously a difference Af between the frequencies/frequency ranges that is sufficiently large that a likely distance — value can be determined.

In some embodiments of the invention, signals may be transmitted also in third and possibly fourth and subsequent narrow bands in addition to the first band or first frequency range fa and second band or second frequency range fo.

A number of frequency ranges that should preferably be utilized in order to be able to determine or select a likely distance value from the set of determined possible distance values may vary depending on the environment, use case or embodiment.

N When at least two signals, e.g. a first primary signal and second primary a 25 — signal having carrier frequencies fi and f2 are utilized (it may be assumed <Q herein that in the case of transmitting a primary or auxiliary signal, a response 3 signal having corresponding frequency is also transmitted), a difference E between respective phase sums (difference between a first (primary) phase o sum and second (primary) phase sum) may be expressed in terms of the 3 30 distance between the first and second antenna units as: O Aas = Dan - Paz = 21 * (f1- fo) * (2D) / €, (7) where c is the speed of light.

From equation (7), a first approximate of distance D between the antenna units may be considered as a distance variable D4 that is indicative of an approximate distance D and may be determined as Di =(A®q1 * c)/ [4 Tr (f1- f2)] (8).

The inaccuracy of the distance D determined through equation (8) may however, be relatively high due to measurement error or estimated possible error Öö in measurements of phase sums Tan and Pam. Of course, an error ö could theoretically also be zero, in which case the distance D could be determined precisely, and integer ambiguity could be resolved.

The measurement error öin e.g. Paris typically caused by signal components reflected from nearby objects that sum up with the direct signal component. If the reflected components are summed and their total signal voltage is marked in the receiver as € and the direct signal component is marked as (, the maximum phase error dmax in Pun May be given approximately as Smax = 2 arctan (| < |) (9), where the factor of 2 arises from the fact that dmax is the sum of two phase measurements.

A reflection level may be known or estimated for the environment.

Through the estimated maximum error value Omax, limits for any errors in values determined using the determined phase information may be determined. An estimate for a maximum error Omax May be sufficient for the procedure described herein to be feasible. In what follows, dmax should be understood as the maximum value that the phase measurement error can N 25 take.

& = The maximum measurement error Omax May be determined for a specific use 0 case or arrangement 100. The maximum measurement error may be known 7 a priori or may be received by an arrangement 100. For instance, the = maximum measurement error Omax May be determined based on a known o 30 phase measurement/determination accuracy of the arrangement 100.

O = In some embodiments, the maximum measurement error dmax, which could S be considered an error variable, may be determined based on e.g. the environment. A maximum measurement error Omax May be e.g. 5-20 degrees, such as around 10 degrees. Omax May be a value that is selected such that it is known that a true error in phase measurements will likely always be below this value. The maximum measurement error Omax May be utilized to determine a maximum error in the distance variable D4. Because the phase sum measurements may be used to determine distances, it may be understood that a maximum error in a phase measurement may be used to define a maximum error in any distance or distance value derived from said phase measurement. It should be noted that using a value Omax that is too large does not in any way make the following procedure invalid. Too small a value, however, can lead to unaccounted for phase rotations between the freguency ranges and can lead to incorrect distance determination. Therefore, dmax should preferably be selected conservatively. For instance, if f1 and fa differ from each other by 40 MHz and considering a measurement error Omax Of 10 degrees, the maximum error in the determined distance variable D, may be about 10 cm. This may be seen from equations (7) and (8) by varying the measured phase values Dar and Pan by Omax. A determined approximate distance between the first antenna unit and second antenna unit may in some embodiments alternatively (instead of through phase measurements such as described above) be obtained e.g. through previous knowledge or a measured approximate distance (measured e.g. using a radio, optical, or sound-based method). This approximate distance may be used as the distance variable. A maximum error for an e.g. otherwise measured approximate distance (variable) may then also be determined or obtained. A maximum error for the approximate distance = (variable) may for instance be determined in some cases as a maximum N dimension of a contained space where the method, such as positioning, 5 occurs. 3 In addition to ambiguity arising from the measurement error dmax, there may E 30 also be an ambiguity of 21 in the determined Ad 44 but this would already o mean an ambiguity of about 3.75 m considering the above example scenario. 5 In this case if there is preliminary information regarding the distance D that is = more accurate than the 3.75 m, the 211 inaccuracy could be eliminated.

O N This problem of 2m uncertainty may also be reduced by transmitting consecutive primary signals that differ in frequency by less than a threshold value. The consecutive primary signals (such as fi and f2) may e.g. be separated by under 20 MHz, under 15 MHz, or e.g. by 10 MHz or 5 MHz or under. In the case of 5 MHz signal frequency difference (difference between e.g. fi and f2), a 211 uncertainty / measurement error in the distance D determined through eguation (8) would be about 30 m. Upon having a priori knowledge about the distance that has accuracy better than 30m, the 2m uncertainty can be eliminated in this particular case. Yet, it is advantageous to have the transmitted primary signals cover a freguency range that in total spans e.g. at least 40 MHz in order to limit the inaccuracy of the approximate distance determination. Upon considering that the distance D must be the sum of N + IA half wavelengths and a fractional component Drac (always smaller than quarter of a wavelength in magnitude), eguations (7) and (8) may be utilized to determine the integer ambiguity through: D = (N + IA) * (1 / 2) + Drrac = (APa,1 * c) / [4 Tr (f1-f2)], (10) where M is the wavelength of the first primary signal and AP... is given in radians. The possible values of N + IA correspond to those which satisfy equation (10), taking into account the maximum error in the measurement of A®q 1 which is max (the factor of 2 following from the fact that Ada, is the difference of two 20 phase sums). Omax therefore defines a range which integer ambiguity values IA or N + |A may take, giving a set of possible integer ambiguity values. The set of possible integer ambiguity values corresponds to or defines a set of possible distances D, or set of possible distance values if Drac can be determined. _ 25 N, which is the best estimate of the number of half wavelengths between the O antennas, can be derived as the closest match to eguation (10) by setting a IA=0.

O © The possible range of IA (-AIA < IA < AIA) is limited by this maximum phase r estimation error Omax as follows (as can be derived from the previous & 30 equation):

D 3 AIA = 5 (11). N 51 N By setting f2 (and correspondingly also Par) in equation (7) to zero and noting that Oa must correspond to the fractional component of Drac, it follows that the phase sum fulfills the following equation:

Pan = 2T *fi * (2*D)/c + (N + IA) * 217 (12). This is assuming that the phase error (the instrumental component that cannot be canceled out with the basic measurement, for example - 2042 - 2041 in equation (6)) of the arrangement is zero (or is known and may be eliminated from the phase sum determination). From this, the distance D may be determined as c[Pgar - (N + 1A) *2m] D=" - CD , (13) from which D may be determined with higher accuracy than with equation (8), because fi is much larger in magnitude than fi - fo.

Theproblem with eguation (13) is then the integer ambiguity (not knowing the value of N+IA, or, if N is determined from equation 10, the value of IA). For example, with a signal frequency fi of 6 GHz, the ambiguity in D is IA*25 mm.

Eguation (13) may however be used to determine all possible distance values, from which the set of possible distance values and the likely distance value may be determined, based on the obtained phase information, approximate distance D, and estimated maximum errors therein.

Yet, as given before, through determining the phase sum difference Ada = Pan - Pam, the distance D may be known (through the distance variable D1) roughly to an accuracy of +100 mm if fi and f2 are separated by 40 MHz and if the maximum measurement error Omax in the phase sums is 10 degrees.

In this case, the integer ambiguity is limited to about 13 different possible values (a set of determined possible integer ambiguity values). The set of possible integer ambiguity values may be graphically understood — to correspond to integer ambiguity lines, when considering phase sum as a O 25 function of transmission frequency, where the integer ambiguity lines have MN slopes determined by the distance given by eguation (13) (with a scaling 2 factor of 417/c). This is illustrated in Fig. 5. The set of possible IA values or set © of possible distance values are shown as integer ambiguity lines that cross E the first primary phase sum 302. The line corresponding to slope determined o 30 from (13) with IA=0 (the best preliminary match), which also determines the 3 value for N, is shown as 316. The neighboring possibilities are IA=+1 (318) N and 1A=-1 (314), corresponding to distance differences of D of half a a wavelength larger or smaller, respectively.

All of these fit the error margins 20max of the primary phase sum measurements shown as error bars in the phase sum measurement and are therefore part of the set of possible IA values or possible distance values. In embodiments where subseguent primary or auxiliary phase sums are determined, the integer ambiguity line IA=0 may be determined as the line thatcrosses two of the determined primary phase sums or a line that has the best least-sguares fit to the primary phase sum points. Upon transmission of at least one auxiliary signal and at least one auxiliary response signal, preferably where the auxiliary signal frequency fz differs from f1 or f2 by at least e.g. 400 MHz, at least a first auxiliary phase sum ®q4 may then be determined. With a determined second phase sum difference Adg,2 = Pan - Pass and f1- fz and utilizing equation (8), a second, better approximation of distance D may be determined, in which the inaccuracy may be e.g. £10 mm instead of the £100 mm for the first approximation obtained from equation (8) using Add 1 and f1- fo. It should be noted that the values are here estimated for the considered frequencies and may vary between use cases. Numerical values are given here to illustrate differences in error magnitudes of determined approximate distances D. Through equation (8), but utilizing the first primary phase sum and the first auxiliary phase sum to obtain a second phase sum difference A®q 2, a second distance variable D> being indicative of a second approximate distance D may be determined as: D2 = (AOa2 * c) / [4 Tr (f1- f3)] (14). Using the estimated maximum error dmax in the first primary phase sum and/or an estimated maximum error in the first auxiliary phase sum, which may also _ 25 be e.g. Ömax an estimated maximum error for A®4 > may be obtained (possibly O amounting to 20max). This may give also a maximum error for the second a distance variable.

O © The second distance variable D> may be used to determine possible distance Ir values for the distance D which correspond to distance variations of integer E 30 numbers of half wavelengths at the first primary freguency. The maximum > error of the second distance variable may give error limits in which the likely D distance value should fit.

N a Through the above, there may only be one possible distance value or, in other words, only one possible value of IA left, giving the likely IA value or likely distance value which may be obtained from the likely IA value, and the integer ambiguity may thereby be resolved.

Through the determined likely integer ambiguity value IA, the distance D may be calculated/determined using eguation (13), and the distance D between the first antenna unit 104 and the second antenna unit 106 may be determined to an accuracy of e.g. under 1 mm.

In embodiments of the invention, the possible distance values may be determined directly as distances or the distance values may e.g. be determined as IA values or other parameters (such as slopes of integer ambiguity lines) that are indicative of the possible distance between the first and second antenna unit.

If it is observed that the likely distance values are not limited to one possible distance value, a third frequency range may be selected that differs from the second frequency range by a selected frequency difference and auxiliary — signals may be transmitted in the third frequency range to further limit the set of possible distance values.

In Fig. 5, it is seen that the likely integer ambiguity value is one which corresponds to an integer ambiguity line that fits the measurement error 20max, Which in this example would be IA=0, corresponding to line 316. In cases where a plurality of primary and/or auxiliary phase sums are determined, e.g. least squares fitting or some other fitting technique may be used to determine integer ambiguity lines or possible distance values, through slopes of integer ambiguity lines, that are fit taking into account preferably all of the measured phase sums. O 25 In one embodiment, an arrangement 100 may be configured to perform the 5 above discussed integer ambiguity determination protocol at least once and © thereafter operate in a tracking mode, where the arrangement 100 may be - configured to track the distance between the first and second antenna unit & 104 and 106 by repeatedly sending subseguent primary signals and primary 2 30 response signals (in an e.g. first frequency range, spanning a narrow range D of frequencies fa), determining subsequent primary phases and primary S response phases, and determining primary phase sums to repeatedly determine distance information being indicative of a change in distance between the first and second antenna unit. By summing up such distance changes the true distance D can be continuously tracked in this mode.

After the integer ambiguity has been determined at least once, it may be assumed (e.g. based on a known or approximated velocity or a change in distance between the first antenna unit 104 and the second antenna unit 106) that the integer ambiguity does not change between subsequent measurements in the tracking mode. An integer ambiguity could also be determined e.g. between predetermined time intervals to ensure that the integer ambiguity value determined previously is still valid, i.e. no phase slips have occurred.

The tracking mode is advantageously used in position tracking as only one narrow frequency band (e.g. a first frequency range fa comprising primary signals) may be required for transmission of signals during regular operation. Transmissions in a different (narrow) frequency range (e.g. second frequency range fn) may only be needed once before transitioning into the tracking mode or at predetermined time intervals which may still be only rare compared to the signals transmitted in the tracking mode. For example, the phase tracking (through transmission of (primary) signals and (primary) response signals in a first narrow band) could be repeated between time intervals ranging between for instance 0.1 and 50 ms or 1 and 20 ms, e.g. every 10 ms. A new IA determination (through additional transmission of at least one (auxiliary) signal and (auxiliary) response signal in a second narrow band) could be only done between time intervals ranging between for instance 0.1 s and 10s s or

0.5s and 5 s, e.g. once per second.

Figure 6 shows one possible embodiment of a radio unit 108, 110 that may = 25 beusedinanarrangement 100, where an antenna unit 104, 106 is comprised N in the radio unit 108, 110. The radio unit 108, 110 of Fig. 6 comprises two 5 receivers and transmitters, the frequency of which can be set separately. 00 7 Utilizing a radio unit 108, 110 with a plurality of receivers, simultaneous = measurement of multiple bands, such as a first band comprising primary O 30 frequencies and at least a second band comprising auxiliary frequencies may D be possible. At least a portion of primary signals that are to be transmitted N and at least a portion of auxiliary signals that are to be transmitted can be N transmitted at least partially simultaneously.

In some embodiments, a radio unit 108, 110 may comprise more than two receivers, and more than two primary or auxiliary signals may be transmitted (and received) simultaneously. In addition to a first band comprising primary frequencies a second band comprising auxiliary frequencies, e.g. a third band comprising further frequencies could be transmitted and received at least partially simultaneously.

In still another embodiment, the primary and auxiliary signals and response signals in a plurality of frequency ranges can be sent in a succession (only one signal at a time). Such a system could operate with extremely narrow bandwidth (e.g. 100 Hz-100 kHz) and use extremely low-cost hardware and small batteries.

Figures 7A and 7B illustrate how time slots may be allocated in measurement cycles for transmission and receiving of signals and possibly also communication of data in an arrangement 100. A measurement cycle may refer to a set of transmitted signals or a time duration within which signals are sent one after another such that the time between subsequent transmissions is below a threshold value. For instance, a first measurement cycle could comprise the transmission (and receiving) of primary signals, primary response signals, auxiliary signals, and auxiliary response signals. In some embodiments, a second measurement cycle may be carried out. The second measurement cycle could e.g. be equivalent to the first measurement cycle or a second measurement cycle could e.g. comprise only transmission (and receiving) of primary signals and primary response signals in embodiments where a tracking mode is utilized.

One measurement cycle may comprise at least one measurement frame (with = 25 N measurement slots). During the measurement frame, the at least first N antenna unit 104 and second antenna unit 106 may transmit their respective 5 signals separately, each in their own time slot which is allocated to them. One © measurement frame may comprise the transmission of signals having one I frequency. For example, primary signals could be transmitted in a first - 30 measurement frame, while auxiliary signals are transmitted in a second 2 measurement frame. The measurement cycle of Fig. 7A is applicable to an = arrangement 100 comprising N antenna units, where the distance between I each antenna unit may be evaluated. Each antenna unit may transmit their respective signals in their own time slot.

Transmissions may be carried out so that transmissions occur in subseguent time slots so that no empty time slots are left between the transmissions. The transmissions and time slots may also be proportioned such that there a time interval between the end of a transmission and the start of a subsequent time slot where a subsequent antenna unit will start its transmission is below a selected maximum time interval. A time interval between the end of a transmission and the start of a subsequent transmission may be less than less than 50 ps, preferably less than 20 us, such as less than16 ps. The subsequent provision of a compact transmission signal may be advantageously used in combination with e.g. WiFi networks. With the present invention, a wireless channel for the transmissions only needs to be reserved once per measurement cycle. This feature may enable compatibility of the present invention with networks such as WiFi. Without transmissions occurring in subsequent time slots a, a measurement cycle could take longer and an unknown time duration to complete. This is because one measurement cycle could not be carried out effectually as a single transmission in a wireless channel that only needs to compete for the channel once as defined e.g. in ETSI EN 301 893 (the standard specification regulating 5GHz WiFi transmissions). The channel would have to be competed for by each transmitting antenna unit separately during transmission, which could cause arbitrarily long measurement sequences if the channel gets occupied by other users between the transmissions. Figure 7B shows how time slots may be allocated in measurement cycles where at least one communication frame (with one or more communication slots) is also employed. During a communication frame, signals, = 25 measured/determined data, or any other data may be transmitted to a N processor 102. At least one data communication may be transmitted and 5 multiplexed with the measurement signals transmitted by the antenna units in © time or frequency domain. The at least one data communication may I comprise at least the determined phase information. A data communication - 30 may additionally or alternatively comprise any other information. An 2 arrangement 100 may thus serve as a measurement arrangement and a = communication network simultaneously.

O N The reguired time synchronization accuracy should preferably be better than one tenth of the duration of a possible guard time between subseguent signals) in order to prevent overlapping transmissions.

Figure 8 illustrates a flow chart of a method according to one embodiment of the invention. At least one primary signal with a frequency in a first frequency range fa is sent 802 via a first antenna unit 104, which is received 804 at a second antenna unit 106, through which primary phase information is determined. At least one primary response signal is sent 806 by the second AU 106, which is received 808 at the first AU, through which primary response phase information is determined. Based on the determined phase information, at least one primary phase sum is determined 810. An approximate distance between the first and second antenna unit and a maximum error in the approximate distance may be obtained at 812, while a set of possible distance values being indicative of the distance between the AUs is determined 814, preferably being based at least on the approximate distance and its error and the first primary phase sum. At least one auxiliary signal with a frequency in a second frequency range fp is then sent 816 via the first antenna unit 104, which is received 818 at a second antenna unit 106, through which auxiliary phase information is determined. At least one auxiliary response signal is sent 820 by the second AU 106, which is received 822 at the first AU, through which auxiliary response phase information is determined. Based on the determined auxiliary phase information, at least a first auxiliary phase sum and its maximum error is determined 824.

N N At 826, the likely distance value is selected from the set of possible distance 5 25 values preferably based at least on the first primary phase sum, first auxiliary 2 phase sum, and the maximum error in the first primary and/or auxiliary phase I sums. = O Figure 9 shows a flow chart of a method of selecting freguency ranges to be D utilized in embodiments of the invention. A first freguency range fa is selected S 30 902, with a first bandwidth. At least a first primary frequency is then set, while N possible second and subseguent primary freguencies may also be set. A maximum error in the phase information that is determined may be estimated or obtained at 904.

At 906 a maximum error in a determined or obtained approximate distance between the first and second antenna unit is determined. The maximum error in the approximate distance may be based on maximum errors in phase sums (if at least two primary frequencies are used), being based on the determined maximum error in phase information at step 904. Alternatively, any other means to determine the maximum error in the approximate distance may be used, e.g. a maximum error in another measurement method that may be used to determine the approximate distance.

A maximum frequency difference Afmax between the first frequency range fa and the second frequency range f, may be determined 908, such that unaccounted phase rotations are avoided. It may be advantageous to set the frequency difference Af as large as possible, i.e. to the maximum value Afmax to reduce the set of possible distance values most efficiently, preferably to be able to unambiguously select the likely distance value from the set of possible distance values.

The first frequency range fa may comprise frequencies that are larger than those comprised in the second frequency range fo or vice versa. In determining the maximum frequency difference Afmax, to ensure that unaccounted phase rotations, i.e. phase slips of 2m do not occur, minimum and maximum possible values of at least the first distance variable (or approximated distance) could in one embodiment be used to determine a possible range for at least the first distance variable. If an obtained range for — the first distance variable D1 is between [D1min, D1max] (range between the O 25 — minimum and maximum values for D1) and a determined primary phase sum = at a first primary frequency fi is ®1 then it is known that a first auxiliary 0 frequency f3 should be in a range limited by expected minimum and maximum 7 values of the first auxiliary phases sums and determined by [Pzmin,P3max] = = P1 + (f1-f3) * phase slope range = O; + (f1-f3) * 411 * [D1min, D1max] / C, Where O 30 C%bsisthe first auxiliary phase sum and the phase slope range refers to a range D of possible slopes for integer ambiguity lines, which could also be expressed N in terms of an error in distance values. If the difference between the expected N minimum and maximum values of the at least first auxiliary phase sum, |P3max — Osmin|, is larger than 211, then the first primary frequency fz is too far from the first primary frequency fi in other words, the frequency difference exceeds a maximum frequency difference Afmax Which is the largest value that still realizes this condition. The difference between the expected minimum and maximum values of the at least first auxiliary phase sum ®s could be selected to be under a threshold value, such as 211. This may give a possible range for the at least one first auxiliary frequency fs, giving a possible second frequency range fn, which differs from the first frequency range fa by Afmax at most. A second frequency range f, may then be determined and at least a first auxiliary frequency may be set 910. After determining at least a first auxiliary phase sum and its error, the size of the set of possible distance values may be determined 912. Advantageously, the set has only one possible distance value left, which can be determined as the likely distance value. Yet, if at 914 it is determined that there is ambiguity in the distance value, i.e. the size of the set of possible distance values is larger than 1, the process may be continued at 908, and a maximum frequency difference Afmax2 between the second frequency range f, or the first frequency range fa and new, third frequency range may be determined. Signals in the third frequency range may be set and subsequent phase information may be determined to determine a new, third set of possible distance values. Selection of a new auxiliary frequency range may be carried out any number of times, if it is determined that there is ambiguity in the distance value, i.e. the likely distance value cannot be selected uniquely. The process is ended 916 when there is only one possible distance value left, this being the likely distance value from which the distance between the first and second antenna unit may be determined with an accuracy that is higher than the approximate distance.

QA N The invention has been explained above with reference to the 5 aforementioned embodiments, and several advantages of the invention have © been demonstrated. It is clear that the invention is not only restricted to these I embodiments, but comprises all possible embodiments within the spirit and - 30 scope of inventive thought and the following patent claims. o D The features recited in dependent claims are mutually freely combinable 3 unless otherwise explicitly stated.

Claims

1. A method for evaluating at least one distance between a first antenna unit and a second antenna unit, the method comprising at least resolving an integer ambiguity by: sending one or more primary signals comprising frequencies in a first frequency range, and determining a set of one or more possible distance values being indicative of possible distances between the first antenna unit and second antenna unit through: - sending at least a first primary signal having a first primary frequency via a first antenna unit - receiving the first primary signal at a second antenna unit, - determining at least first primary phase information related to the first primary signal, said first primary phase information being indicative of a phase of the received first primary signal with respect to a local oscillator of a radio unit with which the second antenna unit is associated with, - sending at least a first primary response signal having a primary response frequency via the second antenna unit, wherein the primary response frequency essentially corresponds to the first primary frequency, - receiving the first primary response signal at the first antenna unit, - - determining at least first primary response phase information O 25 related to the first primary response signal, said primary = response phase information being indicative of a phase of the 0 received primary response signal with respect to a local oscillator 7 of the radio unit with which the at least one first antenna unit is & associated, O 30 - determining at least a first primary phase sum being indicative of D a sum of the first primary phase information and the first primary N response phase information, N - determining the set of one or more possible distance values, based at least on the first primary phase sum, a determined first distance variable, said distance variable being indicative of a first approximated distance between the first antenna unit and second antenna unit, and an estimated maximum error in the determined first distance variable, and sending one or more auxiliary signals comprising frequencies in at least one second frequency range, and determining the distance between the between the first antenna unit and second antenna unit by:

- receiving the first auxiliary signal at the second antenna unit,

- sending at least one first auxiliary response signal having an auxiliary response frequency via the second antenna unit, wherein the auxiliary response frequency essentially corresponds to the first auxiliary frequency,

- receiving the first auxiliary response signal at the first antenna unit,

- determining at least first auxiliary response phase information related to the first auxiliary response signal, said auxiliary response phase information being indicative of a phase of the received auxiliary response signal with respect to a local N oscillator of the radio unit with which the at least one first antenna Y unit is associated, > - determining at least a first auxiliary phase sum being indicative 3 of a sum of the first auxiliary phase information and the first E 30 auxiliary response phase information, and o - determining the distance between the first antenna unit and 3 second antenna unit based on a selected likely distance value N from the set of possible distance values, the selecting of the likely S distance value being based at least on the first primary phase sum, the first auxiliary phase sum, and estimated maximum error in the first primary phase sum and/or estimated maximum error in the auxiliary phase sum.

2. The method of claim 1, wherein the method comprises sending a plurality of primary signals and primary response signals, preferably wherein the method additionally comprises sending a plurality of auxiliary signals and auxiliary response signals, further wherein preferably the frequency of at least consecutive primary signals and/or frequency of consecutive auxiliary signals are separated from each other by under 20 MHz, more preferably under 10 MHz.

3. The method of any previous claim, wherein a difference between the first frequency range and the second frequency range is at least 150 MHz, preferably at least 200 MHz, most preferably at least 500 MHz.

4. The method of any previous claim, wherein the first frequency range and/or the second frequency range encompasses a maximum bandwidth of 100 Hz-100 kHz, preferably 10-100 kHz in the case of only one signal sent in said range or 5-100 MHz, preferably 10-50 MHz in the case of a plurality of signals being sent in said range.

5. The method of any previous claim, wherein at least a second primary signal and second primary response signal are sent to determine respective phase information and a second primary phase sum, and the distance variable is determined by comparing at least the first primary phase sum and the second primary phase sum, optionally based on a difference between the first primary phase sum and second primary - phase sum divided by the frequency difference of the first primary and O 25 second primary signal. O

6. The method of claim 5, wherein the maximum error in the distance 3 variable is determined based on at least the estimated maximum error E in the determined phase information. 2

7. The method of any previous claim, wherein the set of possible distance = 30 values is determined based at least on the first primary phase sum and I variation of the integer ambiguity corresponding to distance variations of integer numbers of half wavelengths at the first primary freguency, said set of possible distance values being limited by the estimated maximum error in the distance variable.

8. The method of any previous claim, wherein the likely distance value is selected by determining a second distance variable corresponding to a second approximate distance between the first and second antenna unit, the determining of the second distance variable being based on comparing at least the first primary phase sum and the first auxiliary phase sum, optionally based on a difference between the first primary phase sum and first auxiliary phase sum divided by the frequency difference of the first primary and first auxiliary signal, and selecting as the likely distance value the distance value from the set of possible distance values fitting an error margin in the second distance variable, said error margin being determined by the estimated maximum error in the first primary phase sum and/ the estimated maximum error in the first auxiliary phase sum.

9. The method of any previous claim, wherein the method comprises determining, based at least on the determined first or subsequent, previously determined auxiliary phase sum, that the likely distance value cannot be unambiguously selected from the set of possible distance values, and sending one or more second or subsequent auxiliary signals and auxiliary response signals comprising frequencies in a third or subsequent frequency range.

10. The method of any previous claim, wherein the method additionally comprises tracking the distance between the first and second antenna unit by resolving the integer ambiguity at least once in an integer SN ambiguity determination mode and subsequently repeatedly sending N subseguent primary signals and primary response signals, determining 5 subsequent primary phases and primary response phases, and © determining primary phase sums to repeatedly determine distance I 30 information being indicative of a change in distance between the first = and second antenna unit in a tracking mode. o 3

11. The method of claim 10, wherein the method comprises resolving the N integer ambiguity at least once in an integer ambiguity determination N mode at predetermined time intervals while otherwise operating in the tracking mode.

12. The method of any previous claim, wherein the method comprises selecting the second frequency range based on the estimated maximum error in the determined first distance variable so that the difference between the first and second frequency range ensures that unaccounted phase rotations are avoided, optionally by determining a possible range for the distance variable based on its maximum error and selecting the second frequency range such that expected minimum and maximum values of the at least first auxiliary phase sum corresponding to the minimum and maximum values of the first distance variable do not differ more than a threshold value, such as 21.

13. The method of any previous claim, wherein the method comprises sending at least the first primary signal and at least a second primary signal and/or the first primary signal and the first auxiliary signal in succession.

14. The method of any previous claim, wherein the method comprises sending at least the first primary signal and at least a second primary signal and/or the first primary signal and first auxiliary signal at least partially simultaneously.

15. The method of any previous claim, wherein the method additionally comprises determining of amplitude information being indicative of an amplitude of a received primary, primary response, auxiliary, or auxiliary response signal.

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16. A computer program product comprising program code means adapted a 25 to execute the method items of any previous claim when run on a > computer.

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17. An arrangement for evaluating at least one distance, the arrangement - comprising at least a first antenna unit and a second antenna unit, the 2 arrangement being configured to

LO N 30 send one or more primary signals comprising freguencies in a first N freguency range, and determine a set of one or more possible distance values being indicative of possible distances between the first antenna unit and second antenna unit, wherein said arrangement is configured to: - send a first primary signal having a first primary frequency via the first antenna unit - receive the first primary signal at the second antenna unit and determine at least first primary phase information related to the first primary signal, said first primary phase information being indicative of a phase of the received first primary signal with respect to a local oscillator of a radio unit with which the second antenna unit is associated with, - send a first primary response signal having a primary response frequency via the second antenna unit, wherein the primary response frequency essentially corresponds to the first primary frequency, - receive the first primary response signal at the first antenna unit and determine at least first primary response phase information related to the first primary response signal, said primary response phase information being indicative of a phase of the received primary response signal with respect to a local oscillator of the radio unit with which the at least one first antenna unit is associated, - determine at least a first primary phase sum being indicative of a sum of the first primary phase information and the first primary response phase information, - determine the set of possible distance values, said possible - distance values being indicative of possible distances between O the first antenna unit and second antenna unit, based at least on = the first primary phase sum, a determined distance variable, said 0 distance variable being indicative of a first approximated 7 30 distance between the first antenna unit and second antenna unit, = and an estimated maximum error in the determined distance O variable, and

D N send one or more auxiliary signals comprising freguencies in at least N 35 one second freguency range, and determining the distance between the between the first antenna unit and second antenna unit, wherein the arrangement is configured to:

- send at least one first auxiliary signal having a first auxiliary frequency via the first antenna unit, - receive the first auxiliary signal at the second antenna unit and determine at least a first auxiliary phase related to the first auxiliary signal, said first auxiliary phase being indicative of a phase of the received first auxiliary signal with respect to a local oscillator of a radio unit with which the second antenna unit is associated with, - send a first auxiliary response signal having an auxiliary response frequency via the second antenna unit, wherein the auxiliary response frequency essentially corresponds to the first auxiliary frequency, - receive the first auxiliary response signal at the first antenna unit and determine at least first auxiliary response phase information related to the first auxiliary response signal, said auxiliary response phase information being indicative of a phase of the received auxiliary response signal with respect to a local oscillator of the radio unit with which the at least one first antenna unit is associated, - determine at least a first auxiliary phase sum being indicative of a sum of the first auxiliary phase information and the first auxiliary response phase information, and - determine the distance between the first antenna unit and second antenna unit based on a selected likely distance value from the set of possible distance values, the selecting of the likely = distance value being based at least on the first primary phase N sum, the first auxiliary phase sum, and estimated maximum error 5 in the first primary phase sum and/or estimated maximum error © 30 in the auxiliary phase sum.

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