WO2010022785A1

WO2010022785A1 - Positioning of a user terminal

Info

Publication number: WO2010022785A1
Application number: PCT/EP2008/061344
Authority: WO
Inventors: Henrik Asplund; Bo Hagerman; Arne Simonsson
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2008-08-28
Filing date: 2008-08-28
Publication date: 2010-03-04

Abstract

The present invention relates to a system for determining a position of an object (1) within a volume (10), the object (1) comprising a first antenna function (9). The system comprises at least one node (3) for wireless communication, the node (3) comprising a second antenna function (4), in which system a transmitted polarisation is detected. The polarization of at least one of said antenna functions (4, 9) is variable within the volume (10), and where the system is arranged for at least partly determining the position of the object (1) by means of the detected polarization. The present invention also relates to units comprised in the system, and to a corresponding method.

Description

TITLE

Positioning of a user terminal

TECHNICAL FIELD

The present invention relates to a system for determining a position of an object within a volume, the object comprising a first antenna function. The system comprises at least one node for wireless communication, the node comprising a second antenna function. In the system, a transmitted polarisation is detected.

The present invention also relates to a first unit which is arranged for transmitting signals via a corresponding antenna function, and a corresponding second unit.

The present invention also relates to a third unit which is arranged for receiving signals.

The present invention also relates to a corresponding method

BACKGROUND ART

Today, it is of interest to obtain an enhanced positioning of a user terminal, for example in order o track persons who phone an emergency number. There are a number of passive radio positioning solutions.

DECCA enables passive positioning based on frequency phase difference. Each pair of radio beacons creates a hyperbola, and with three beacons the intersection defines the two dimensional position. Global Positioning System (GPS) enables positioning by triangulation based on time delay from synchronized satellite radio transmissions of a timing signal. Accuracy is around ±15 meters.

VOR, short for VHF (Very High Frequency) Omni-directional Radio Range, uses the phase relationship between a reference-phase and a rotating-phase signal to encode direction. The reference 30 Hz signal is frequency modulated (FM) on a 9960 Hz sub-carrier. A second 30 Hz signal is derived from the electronic rotation of a directional antenna array 30 times a second. The predictable accuracy of the VOR system is ±1.4°. There is also a similar military system Tactical Air Navigation, called TACAN. It also provides the user with a distance by the Distance Measuring Equipment (DME) system.

One cellular network-based positioning method is CGI + TA (Cell Global Identity + Timing Advance). This system is based on the fact that the system can identify the cell or cell sector surrounding a base station in which the user is located and can use TA to determine the distance between the user and the radio mast. The precision depends on the cell size and is typically

200 or 300 meters in urban environments and several kilometers in rural areas.

Another cellular positioning method is the terminal-based E-OTD (Enhanced Observed Time Difference). It calculates a user's position using signals from three base stations. The phone compares the time it takes for a signal to be received from each of the three base stations and uses measurement equipment called a Location Management Unit (LMU) consisting of the GSM radio, a GPS (Global Positioning System) receiver and the mobile phone and a reference time transmitted by a GPS satellite to calculate the position. The system, which is commercially available in the US, has an accuracy of 50 to 250 meters.

However, there exist drawbacks with the existing system. - GPS and DECCA require reception from 3 transmitters for two dimensional positioning, and GPS from 4 transmitters for three dimensional positioning.

- GPS requires accurate synchronized clocks in transmitters.

- GPS does not work indoor.

- VOR is only two dimensional.

- VOR requires two receivers.

- CGI+TA is not so accurate.

- E-OTD is based on GPS and has the same drawbacks.

There thus exists a need for an enhanced positioning of user terminals.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an enhanced positioning of user terminals.

Said object is achieved by means of a system for determining a position of an object within a volume, the object comprising a first antenna function. The system comprises at least one node for wireless communication, the node comprising a second antenna function. In the system, a transmitted polarisation is detected, where the polarization of at least one of said antenna functions is variable within the volume. The system is arranged for at least partly determining the position of the object by means of the detected polarization.

According to an embodiment example, the variable polarisation is a function of a polarization angle which starts at a first reference line and runs around the node, thus constituting a range of angular values, where the first reference line extends radially out from the node at a certain fixed point.

According to another embodiment example, the position is in the form of an angular position which is defined between the first reference line, and a second reference line, extending radially out from the node and passing trough the object, the angular position being one of said angular values. The second antenna function is arranged for presenting a varying polarization.

According to another embodiment example, the variable polarisation is a function of a polarization angle which starts at a first reference line and runs around the object, thus constituting a range of angular values. The first reference line extends radially out from the object at a certain fixed point.

According to another embodiment example, the position is in the form of an angular position which is defined between the first reference line, and a second reference line, extending radially out from the object and passing trough the node, the angular position being one of said angular values. The first antenna function is arranged for presenting a varying polarization.

According to another embodiment example, at least one of the antenna functions comprises a number of sector antennas, each sector antenna covering a corresponding sector.

According to another embodiment example, the antenna function that presents a varying polarization uses two different frequencies, where the polarization variation is different for each one of the two frequencies, or where the antenna has a polarization variation that varies with time.

Said object is also achieved by means of a first unit which is arranged for transmitting signals via a corresponding antenna function. The signals have a polarization that is variable within a volume, where a second unit receives the signals and detects the received polarization, which enables the position of the first and/or the second unit to, at least partly, be determined by means of the detected polarization.

According to an embodiment example,, the antenna function has a first polarization and a second polarization and is continuously variable, from the first polarization to the second polarization.

According to another embodiment example, each antenna function with a continuously variable polarization comprises a first element with a first polarization vector and a second element with a second polarization vector, the polarization vectors presenting an angle between them, where the elements radiate essentially equal radiation patterns, the elements being separated by a distance. Alternatively, the elements radiate unequal radiation patterns.

Said object is also achieved by means of a corresponding second unit.

Said object is also achieved by means of a third unit which is arranged for receiving signals and for handling information from the first and second units according to the following: rreceiving information regarding the manner in which the polarizations of one or more first units are varying, and/or receiving information originating from one or more second units on the detected polarizations of transmissions from one or more first units, or a combination thereof, and evaluating this information in order to determine the desired positions of the first or the second units. Said object is also achieved by means of a method for determining a position of an object within a volume, the object comprising a first antenna function, where at least one node for wireless communication comprises a second antenna function. The method comprises the step of detecting a transmitted polarisation. The method further comprises the steps: using one antenna function for transmitting signals where the polarization is variable within the volume (10); and at least partly determining the position of the object (1 ) using the detected polarization.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described more in detail with reference to the appended drawing, where:

Figure 1 shows a simplified view of a base station and a user terminal;

Figure 2a shows a simplified top view of a first type of antenna arrangement which is arranged to present an angularly varying polarization;

Figure 2b shows a simplified front view of a first type of antenna arrangement which is arranged to present an angularly varying polarization;

Figure 3a shows a simplified top view of a second type of antenna arrangement which is arranged to present an angularly varying polarization; and

Figure 3b shows a simplified front view of a second type of antenna arrangement which is arranged to present an angularly varying polarization. DETAILED DESCRIPTION

With reference to Figure 1 , a user terminal 1 is present in an area 2. In the area 2 there is also a base station 3. A certain antenna 4 at the base station covers the user terminal.

According to the present invention, the user terminal 1 is equipped with means 5 for determining its position within the area 2 by measuring and evaluating the polarization of the signals received from the base station 3.

Said position is in the form of an angular position α which is defined between a first reference line 6 extending radially out from the base station at a certain fixed point, and a second reference line 7, extending radially out from the base station 3 and passing trough the user terminal 1.

This is made possible by means of a varying polarization of the base station antenna within the area. Although only one antenna 4 is shown, the base station 3 may comprise several antennas in order to cover the area 2.

The angular position α is preferable used in combination with other information from other existing methods to improve the granularity and accuracy of the positioning. Different combinations are exemplified in the following embodiment examples.

In a first embodiment example for positioning, the polarization p(* ) is measured by the user terminal 1. Hence, the polarisation p is a function of a polarization angle • which starts at the first reference line 6 and runs around the base station 3, thus constituting a range of angular values. Thus the angular position α is one of those angular values. The angular position α can either be compared to a gravity reference or a reference signal. A reference signal can for example be broadcast by a pilot antenna with a fixed polarization. The polarization information gives the transmission direction, the angular position α, which can be used together with the CGI+TA method refining the position information within a cell.

Also the polarization of neighbour cells can be measured further improving the accuracy or replacing the reference by measuring the difference in polarization.

The polarization information can be reported from the user terminal 1 to the network for network based positioning services such as emergency call positioning. It can also be used in the user terminal 1 for terminal services.

A second embodiment example for positioning is related to GPS. When only two satellites are detected, the geographical position can not be defined with existing GPS. This can for example be the case indoor where two satellites are found through a window. The position is then detected to be anywhere on a line. If the GPS signals are polarized as a function of angle, the position on this line can be defined by measuring their polarization difference.

The altitude can be based on only three satellites.

A third embodiment example for positioning is related to terrestrial radio beacons. One radio beacon and polarization gives the bearing, either by comparing to a reference signal polarization or to a gravity reference.

Similarly to the GPS embodiment, two radio beacons give the position. By varying the polarization as a function of elevation angle the altitude can be estimated. This can be done from a single radio beacon if combined with VOR and DME which then supports with azimuth and distance.

A fourth embodiment example for positioning is related to a simplified antenna embodiment. The method can also improve the positioning accuracy with a simpler antenna solution. The simplest is transmitting only two polarisations with 90 degrees differentiated polarizations on each half of the antenna diagram. This reduces the uncertainty of the positioning method to the half.

In a cellular three sector site, comprising a base station with three antenna functions, this is 60° transmitted with each polarisation. Combined with the CGI method, the position can be measured down to half the cell and combined with the CGI+TA even more accurate.

Such simplified antenna solutions are also applicable to the terrestrial radio beacon positioning both on direction and elevation angle.

The whole range of refinement from this simple two polarizations to the continuous p(* ) variation described above can be used.

In the following, a description of how antennas that have varying polarizations over the azimuth directionsmay be devised is provided.

With reference to Figure 2a and Figure 2b, in a first version of the antenna 4 as used in the present invention, it is composed of a first element 4a and a second element 4b with a corresponding first radiation pattern 8a and second radiation pattern 8b, the radiation patterns 8a, 8b being essentially similar. The first element 4a radiates with a first polarization having a first polarization vector vi and the second element 4b radiates with a second polarization, having a second polarization vector V₂, with an angle • presented between their extensions. The first polarization vector vi and the second polarization vector V₂ are orthogonal in this example, i.e. the angle • = 90°, but this is not absolutely necessary, some degree of parallelity can be accepted. The two antenna elements 13, 14 are separated by a small distance d.

An incoming time-varying signal x(t) is divided into two signals xi(t), x₂(t) to the two elements 4a, 4b, where weights w1 , w2 are added to the corresponding signals xi(t), x₂(t).

The net polarization vector for transmissions in a direction φ will be:

p(φ) = V^g₁ (φ) V₁ + w₂g₂ (φ)v₂ • expf ^-sinφ

For simplicity, in this example w1 =w2=1 and g1 (φ) = g2(φ) = 1. Thus, the net polarization vector is an angular-dependent linear combination of the two element polarizations: p( /φ x) = v₁ + v₂ - exp ( I —2π\ά s .inφ

With reference to Figure 3a and Figure 3b, in a second version of an antenna 4' as used in the present invention, it is composed of a first element 4a' and a second element 4b' with a corresponding first radiation pattern 8a' and second radiation pattern 8b', the radiation patterns 8a', 8b' being dissimilar. The first element 4a' radiates with a first polarization having a first polarization vector vi' and the second element 4b' radiates with a second polarization, having a second polarization vector V₂', with an angle • presented between their extensions. The elements 4a', 4b' preferably have a common phase centre, although this is not required. The net polarization in any given direction will be a result of a weighted sum of the first polarization vector vi' and the second polarization vector V₂',

An incoming time-varying signal x(t) is divided into two signals xi(t), x₂(t) to the two elements, where weights w1 , w2 are added to the corresponding signals xi(t), x₂(t). The weights w1 , w2 are the antenna gains for the elements in that particular direction. By shaping the radiation patterns of the two elements, it is possible to control how the net polarization will behave.

According to the above, the net polarization vector for transmissions in a direction φ is:

p(φ) = w₁g₁ (φ)v^" + w₂g₂ (φ)v₂ - expf -^-sinφ l

and, without loss of generality, setting d=0, w1 =1 , w2=1 gives

According to another embodiment example which is more general, a number of radio beacons, each being equipped with antennas with varying polarization according to the above, are present in a certain area. In the area a number of units, not necessarily user terminals such as cell phones etc, may be positioned by means of the method according to the invention. The present invention is not limited to the embodiments described above, but may vary freely within the scope of the appended claims.

According to one aspect of the invention, the polarization variation over angle p(^» ) is made time- and/or frequency-dependent. The antenna described with reference to Figure 2 is suitable for this aspect of the invention. For different frequencies, this antenna will provide different polarization variations as a function of the angle • . The weights w1 , w2 may also be given variations in time and/or frequency, resulting in a polarization variation over the corresponding dimension. This aspect is particularly suited to the use of three or more antenna elements, whereby any ambiguities in direction can be resolved. The added granularity in the polarization variations can also be used to improve the accuracy of the positioning.

According to one alternative aspect of the present invention, the user terminal 1 may be equipped with an antenna 9 with varying polarization, and the base station antenna 4 detects the polarization of the user terminal 1. The base station 3 is arranged for determining the position of the user terminal 1 in dependence of the detected the polarization of the user terminal 1.

Base stations and/or user terminals may communicate with each other, transmitting information regarding which polarizations they estimate and use. In this way it may be communicated how the polarization varies, allowing a receiver to determine the direction from a transmitter, or which polarization that is estimated, allowing the transmitter to determine the direction to the receiver. There may also be special combining units, which combine information from transmitters and receivers and evaluate this information in order to determine the desired position. Such a combining unit may receive information either by means of wire-bound or wireless communication. All antennas 4, 9 described may be of any suitable type, for example wire antennas, patch antennas or dipole antennas, generally constituting antenna functions, where an antenna function in itself may comprise more than one antenna.

The present invention is not limited to an area, but may also relate to vertical positions, hence the present invention generally relates to a volume 10 as indicated in Figure 1. When the term "volume" is used, the corresponding area is also aimed at where applicable.

The present invention thus relates to the determining of a position of an object 1 within a volume, the object 1 comprising a first antenna function 9, the system comprising at least one node 3 for wireless communication, the node 3 comprising a second antenna function 4.

The term "wireless communication" relates to any kind of transmission and/or reception. A node for wireless communication may be any type of suitable node, for example a radio beacon, a satellite or a base station.

An object in this case for example refers to a vehicle, a vessel, an aeroplane or a user terminal such as a laptop or a cell phone.

The present invention is not limited to geographical positioning, but also applies to relative positioning between two moving objects, such as two aeroplanes.

Generally, the present invention may be regarded to relate to first unit which is arranged for transmitting signals via a corresponding antenna function 4, 9. The signals have a polarization that is variable within the volume 10, where a second unit receives the signals and detects the received polarization, which enables the position of the first unit and/or the second unit to, at least partly, be determined by means of the detected polarization. The second unit is arranged for receiving signals via a corresponding antenna function, where the signals have a polarization that is variable within the volume 10. The second unit is arranged to detect the received polarization, enabling that the position of the first unit and/or the second unit at least partly is determined by means of the detected polarization.

Furthermore, a third unit may be arranged for handling information from said first and second units according to the following: receiving information regarding the manner in which the polarizations of one or more first units are varying, and/or receiving information originating from one or more second units on the detected polarizations of transmissions from one or more first units, or a combination thereof, and evaluating this information in order to determine the desired positions of the first or the second units.

The first unit may be arranged to communicate, via wire or wireless, information regarding the manner in which the polarization of the first unit is varying, to either the second unit or to the third unit.

The second unit may be arranged to communicate, via wire or wireless, information regarding the detected polarization of signals received from the first unit to either the first unit or to the third unit.

The first unit may be a base station, and the second unit may be a user terminal, or vice versa.

Claims

1. A system for determining a position of an object (1 ) within a volume (10), the object (1 ) comprising a first antenna function (9), the system comprising at least one node (3) for wireless communication, the node (3) comprising a second antenna function (4), in which system a transmitted polarisation is detected, characterized in that that the polarization of at least one of said antenna functions (4, 9) is variable within the volume (10), and where the system is arranged for at least partly determining the position of the object (1 ) by means of the detected polarization.

2. A system according to claim 1 , characterized in that the variable polarisation (p) is a function of a polarization angle (• ) which starts at a first reference line (6) and runs around the node (3), thus constituting a range of angular values, where the first reference line (6) extends radially out from the node (3) at a certain fixed point.

3. A system according to claim 2, characterized in that the position is in the form of an angular position (α) which is defined between the first reference line (6), and a second reference line (7), extending radially out from the node (3) and passing trough the object (1 ), the angular position (α) being one of said angular values, the second antenna function (4) being arranged for presenting a varying polarization.

4. A system according to claim 1 , characterized in that the variable polarisation (p) is a function of a polarization angle (• ) which starts at a first reference line (6) and runs around the object (1 ), thus constituting a range of angular values, where the first reference line (6) extends radially out from the object (1) at a certain fixed point.

5. A system according to claim 4, characterized in that the position is in the form of an angular position (α) which is defined between the first reference line (6), and a second reference line (7), extending radially out from the object (1 ) and passing trough the node (1 ), the angular position (α) being one of said angular values, the first antenna function (9) being arranged for presenting a varying polarization.

6. A system according to any one of the previous claims, characterized in that at least one of the antenna functions is an omni- directional antenna function.

7. A system according to any one of the previous claims, characterized in that at least one of the antenna functions comprises a number of sector antennas, each sector antenna covering a corresponding sector.

8. A system according to any one of the previous claims, characterized in that the antenna function that presents a varying polarization uses two different frequencies, where the polarization variation is different for each one of the two frequencies.

9. A system according to any one of the previous claims, characterized in that the antenna function that presents a varying polarization has a polarization variation that varies with time such that for two different moments in time, the polarisation variation has different properties.

10. A system according to any one of the previous claims, characterized in that the object (1 ) is a user terminal and that the node (3) is a base station in a wireless communication system.

11. A system according to any one of the previous claims 1 -9, characterized in that the object (1 ) either is a vehicle, vessel or aeroplane.

12. A system according to any one of the previous claims 1 -10, characterized in that the node (3) either is a radio beacon or a satellite.

13. A first unit which is arranged for transmitting signals via a corresponding antenna function (4, 9), characterized in that the signals have a polarization that is variable within a volume (10), where a second unit receives the signals and detects the received polarization, which enables the position of the first and/or the second unit to, at least partly, be determined by means of the detected polarization.

14. A first unit according to claim 13, characterized in that said antenna function (4) has a first polarization (p1 ) and a second polarization

(p2) and is continuously variable, from the first polarization (p1 ) to the second polarization (p2).

15. A first unit according to claim 14, characterized in that each antenna function (4) with a continuously variable polarization comprises a first element (4a) with a first polarization vector (V₁) and a second element (4b) with a second polarization vector (v₂), the polarization vectors (vi, V₂) presenting an angle (• ) between them, where the elements (4a, 4b) radiate essentially equal radiation patterns (8a, 8b), the elements (4a, 4b) being separated by a distance (d).

16. A first unit according to claim 14, characterized in that each antenna function (4) with a continuously variable polarization comprises a first element (4a¹) with a first polarization vector (v!,) and a second element (4b¹) with a second polarization vector (v₂), the polarization vectors (v!,, V₂) presenting an angle (• ) between them, where the elements (4a¹, 4b') radiate unequal radiation patterns (8a¹, 8b').

17. A first unit according to claim 16, characterized in that the elements (4a¹, 4b') have an essentially common phase centre.

18. A first unit according to any one of the previous claims 14-17, characterized in that each one of the elements (4a, 4b; 4a', 4b') is fed with the same signal (x(t)), the signal being weighted by a certain weight (w1 , w2) for each one of the elements (4a, 4b; 4a', 4b').

19. A first unit according to any one of the claims 13-18, characterized in that it either is a user terminal, vehicle, vessel, aeroplane, base station, radio beacon or satellite.

20. A first unit according to any one of the claims 13-19, characterized in that it is arranged to communicate information regarding the manner in which the polarization of the first unit is varying, to either the second unit or to a third unit which is arranged for handling information from the first and second units according to the following: receiving information regarding the manner in which the polarizations of one or more first units are varying, and/or receiving information originating from one or more second units on the detected polarizations of transmissions from one or more first units, or a combination thereof, and evaluating this information in order to determine the desired positions of the first or the second units.

21. A second unit which is arranged for receiving signals via a corresponding antenna function, characterized in that the signals have a polarization that is variable within a volume (2), where the second unit is arranged to detect the received polarization, enabling that the position of the first unit and/or the second unit at least partly is determined by means of the detected polarization.

22. A second unit according to claim 21 , characterized in that it either is a user terminal, vehicle, vessel, aeroplane, base station, radio beacon or satellite.

23. A second unit according to claim 22, characterized in that the second unit is arranged to communicate information regarding the detected polarization of signals received from the first unit according to claim 13 to either the first unit or to or to a third unit which is arranged for handling information from the first and second units according to the following: receiving information regarding the manner in which the polarizations of one or more first units are varying, and/or receiving information originating from one or more second units on the detected polarizations of transmissions from one or more first units, or a combination thereof, and evaluating this information in order to determine the desired positions of the first or the second units.

24. A third unit which is arranged for receiving signals, characterized in that it is arranged for handling information from the first and second units according to claims 13-23 according to the following: receiving information regarding the manner in which the polarizations of one or more first units are varying, and/or receiving information originating from one or more second units on the detected polarizations of transmissions from one or more first units, or a combination thereof, and evaluating this information in order to determine the desired positions of the first or the second units.

25. A method for determining a position of an object (1 ) within an volume (10), the object (1 ) comprising a first antenna function (9), where at least one node (3) for wireless communication comprises a second antenna function (4), where the method comprises the step: detecting a transmitted polarisation characterized in that the method further comprises the steps: using one antenna function for transmitting signals where the polarization is variable within the volume (10); and at least partly determining the position of the object (1 ) using the detected polarization.