WO2013008063A1

WO2013008063A1 - Positioning of an apparatus using radio signals

Info

Publication number: WO2013008063A1
Application number: PCT/IB2011/053119
Authority: WO
Inventors: Terhi Rautiainen; Fabio Belloni; Ville Ranki; Antti Kainulainen
Original assignee: Nokia Corporation
Priority date: 2011-07-12
Filing date: 2011-07-12
Publication date: 2013-01-17

Abstract

A method comprising: receiving signals associated with multiple antenna elements of an antenna arrangement; determining orientation information for the antenna arrangement; and using the received signals and the orientation information to locate an apparatus.

Description

TITLE

Positioning of an apparatus using radio signals

FIELD OF THE INVENTION

Embodiments of the present invention relate to positioning. In particular, they relate to a method, an apparatus, a module, a chipset or a computer program for positioning using radio signals.

BACKGROUND TO THE INVENTION

There are a number of known techniques for determining the position of an apparatus using radio frequency signals. Some popular techniques relate to use of the Global Positioning System (GPS), in which multiple satellites orbiting Earth transmit radio frequency signals that enable a GPS receiver to determine its position. However, GPS is often not very effective in determining an accurate position indoors. Some non-GPS positioning techniques enable an apparatus to determine its position indoors. However, some of these techniques do not result in an accurate position being determined, and others are too complex for use simply in a portable apparatus. For example, the amount of processing power required to perform the technique may be impractical to provide in a portable apparatus, which may need to perform concurrent functions.

BRIEF DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

According to various embodiments of the invention there is provided a method comprising: receiving signals associated with multiple antenna elements of an antenna arrangement; determining orientation information for the antenna arrangement; and using the received signals and the orientation information to locate an apparatus.

According to various embodiments of the invention there is provided an apparatus comprising: at least one processor; and at least one memory including computer program code the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform: determining orientation information for an antenna arrangement comprising multiple antenna elements; and using signals associated with the multiple antenna elements of the antenna arrangement and the orientation information to locate an apparatus.

According to various embodiments of the invention there is provided an apparatus comprising: means for communicating using signals associated with multiple antenna elements of an antenna arrangement; means for determining orientation information for the antenna arrangement; and means for enabling location of an apparatus using the signals and the orientation information. According to various embodiments of the invention there is provided a computer program which when loaded into a processor enables the processor to: determine orientation information for an antenna arrangement comprising multiple antenna elements; and use signals communicated using the multiple antenna elements of the antenna arrangement and the orientation information to locate an apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of various embodiments of the present invention reference will now be made by way of example only to the accompanying drawings in which:

Fig. 1 illustrates an apparatus receiving radio signals from a transmitter; Fig. 2A illustrates a bearing in an antenna coordinate system that is aligned with a global coordinate system;

Fig. 2B illustrates a bearing in an antenna coordinate system that is not aligned with a global coordinate system;

Fig. 3 is a schematic of a receiver apparatus when diversity reception is used; Fig. 4 is a flow diagram of a method of estimating a position;

Fig. 5 is a flow diagram of a compensation method for compensating for non- alignment of an antenna coordinate system and a global coordinate system; Fig. 6 is method of determining orientation information that is used to transform between an antenna coordinate system and a global coordinate system; and

Fig 7 schematically illustrates an example of a suitable mobile apparatus 10.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

Locating an apparatus typically involves measuring a parameter that depends upon a distance (or an equivalent) between a location and a plurality of diverse locations. An equivalent to distance for electromagnetic waves, such as radio frequency signals, is time as their speed is constant.

The location may be an unknown location of the apparatus and the diverse locations may be known. Alternatively, the location may be known and the diverse locations may be at the apparatus.

Time of flight or differences in time of flight for radio signals may be measured in many different ways. For example, if a transmitter and receiver are synchronized, the actual time of flight may be measured. As another example, phase differences between received signals may be measured to estimate differences in the time of flight of radio signals.

When radio frequency signals are used, the radio signal may travel from the location for reception at the plurality of diverse locations. This is commonly referred to as diversity reception. A single radio signal may be transmitted for reception at all of the diverse locations or, alternatively, different radio signals may be transmitted for separate reception at the diverse locations. Alternatively, when radio frequency signals are used, the radio signal may travel to the location from the plurality of diverse locations. This is commonly referred to as diversity transmission. A single radio signal may be transmitted from all of the diverse locations for reception or, alternatively, different radio signals may be transmitted from the diverse locations for separate reception.

The diverse locations of transmission/reception each have at least one antenna element for performing the necessary transmission/reception.

The antenna elements have a known arrangement. The antenna elements may form a fixed arrangement in which the antenna elements of the arrangement have a fixed relationship with each other, although the arrangement itself may move (rotation and/or translation).

Movement of the arrangement of antenna elements needs to be compensated for when locating an apparatus using the arrangement of antenna elements.

For clarity of explanation, the following description describes how to compensate for movement of an arrangement of antenna elements where diversity reception at a base station is used to locate a remote transmitting apparatus and phase is used as the parameter that depends upon a distance between the remote transmitting apparatus being located and the plurality of antenna elements. A common signal transmitted from the apparatus to be located is received at the diverse antenna elements of a base station. The antenna arrangement functions as an antenna, rather than a plurality of independent antennas, and the antenna elements although diverse may be closely spaced. It should, however, be appreciated that the details of the specific embodiment described below does not limit the generality of the invention which, for example, covers at least the alternatives outlined above including diverse reception, diversity transmission, different locations of the arrangement of antenna elements (e.g. mobile or base station), and the use of other parameters that depends upon a distance (or an equivalent).

Diversity Reception Fig. 1 illustrates a person 92 (carrying a mobile radio communications apparatus 10) at a position 95 on a floor 100 of a building 94. The building 94 could be, for example, a shopping center or a conference center.

A base station receiver apparatus 30 is positioned at a location 80 of the building 94. In the illustrated example, the location 80 is on the ceiling of the building 94 (i.e. the overhead interior surface) but in other implementations the receiver may be placed elsewhere such as on a wall.

The location 80 is directly above the point denoted with the reference numeral 70 on the floor 100 of the building. The receiver apparatus 30 is for enabling the position of the remote apparatus 10 to be determined although that is not necessarily the only function provided by the receiver apparatus 30. For example, the receiver apparatus 30 may be part of a transceiver for providing wireless internet access to users of remote apparatuses 10, for example, via wireless local area network (WLAN) radio signals.

The mobile apparatus 10 may, for example, be a hand portable electronic device such as a mobile radiotelephone. The apparatus 10 may transmit radio signals 50 periodically as beacons.

The radio signals may, for example, have a transmission range of 100 meters or less. For example, the radio frequency signals may be 802.1 1 wireless local area network (WLAN) signals, Bluetooth signals, Ultra wideband (UWB) signals or Zigbee signals.

Fig. 2A illustrates a schematic for estimating a position 95 of a remote apparatus 10/user 92. In this example, an antenna coordinate system that moves with an antenna 36 of the receiver apparatus 30 is aligned with a global coordinate system.

The global coordinate system, having an origin 80, can be expressed in Cartesian coordinates as (XG, y_G, z_G) or in a spherical coordinates as (r, 0G, OG) or the illustrated adapted spherical coordinates as (h, 0G, ΦΟ), where

The antenna coordinate system, having the same origin 80, can be expressed in Cartesian coordinates as (XA, y_A, z_A) or in a spherical coordinates as (r, ΘΑ, ΦΑ) or the illustrated adapted spherical coordinates as (h, ΘΑ, ΦΑ), where h=r.cos ΘΑ -

Thus the position 95 can be defined by specifying a position along a bearing 82 which runs from the position 80 of the antenna 36 of the receiver apparatus 30 through the position 95 of the remote apparatus 10. The bearing 82 is defined by an elevation angle Θ and an azimuth angle Φ. The position along the bearing (θ ,Φ) is given in this example by h, the vertical distance between the location 80 and the position 95.

The coordinate systems are aligned

and share a common origin 80 at which the antenna array 36 comprising a plurality of antenna elements 32A, 32B, 32C in a particular configuration is located. The mobile user 92 is seen in the direction of the unit vector in Cartesian coordinates as: sin Θ. cos φ

sin Θ. sin φ

COS0

The position 95 of the mobile user 92 in Cartesian coordinates (in the global and antenna coordinate systems) is: h. tan Θ. cos φ

h. tan Θ. sin φ

h where h is a known or determined height of the antenna array origin 80 above the mobile user 92 and θ, Φ are resolved using bearing estimation, an example of which is described below.

Fig. 2B illustrates a schematic for estimating a position 95 of a remote apparatus 10/user 92. In this example, an antenna coordinate system that moves with the antenna 36 is not aligned with a global coordinate system but has a rotation relative to the global coordinate system. The antenna coordinate system may, in other embodiments, have a vector offset from the global coordinate system. In some embodiments the antenna coordinate system may be rotated and/or translated relative to the global coordinate system.

The global coordinate system, having an origin 80, can be expressed in Cartesian coordinates as (XG, y_G, z_G) or in a spherical coordinates as (r, 0G, OG) or the illustrated adapted spherical coordinates as (h, 0G, G), where

The antenna coordinate system, having the same origin 80, can be expressed in Cartesian coordinates as (XA, y_A, z_A) or in a spherical coordinates as (r, ΘΑ, ΦΑ) or the illustrated adapted spherical coordinates as (h, ΘΑ, ΦΑ), where h=r.cos ΘΑ .

The mobile user 92 is seen in the direction of the unit vector in Cartesian coordinates of the antenna coordinate system as: sm i fl Θ^_Α . cos ^

sin ^ . sin ^

cos ^ where ΘΑ ΦΑ are resolved using bearing estimation, an example of which is described below.

The mobile user 92 is actually in the direction of the unit vector in Cartesian coordinates of the global coordinate system of: sin 0_G . cos _G

r ' G° = sin 0_G .sin <j>_G

cos0_G

where

C GA r A° where CGA is a direction cosine matrix The position 95 of the mobile user 92 in Cartesian coordinates (in the global coordinate systems) is:

The direction cosine matrix may be written as

The element c represents the cosine between the i axis of the global coordinate system and the j axis of the antenna coordinate system.

The direction cosine matrix is orthogonal and is formed of unit vectors orthogonal to each other. The direction cosine matrix can also be written as:

N_A is a vector defining North in the antenna coordinate system.

E_A is a vector defining East in the antenna coordinate system, and this vector is orthogonal to N_A.

GA is a vector defining gravity (down) in the antenna coordinate system and this vector is orthogonal to N_A and E_A .

Thus a plurality of orthogonal vectors define a transform for transforming the bearing of the remote apparatus 10 from the antenna 36 in an antenna coordinate system to a bearing of the remote apparatus 10 from the antenna 36 in a global coordinate system. As the vectors are orthogonal they have the following properties N_A= E_A x GA

An inclinometer 35 (illustrated in Fig 3) in the apparatus 30 may be used to enable determination of N_A, E_A ,GA. In some embodiments, the inclinometer 35 measures not only a reference vector e.g., GA but also a bearing vector that has components of N_A, or E_A.

Fig. 3 schematically illustrates one example of the base station receiver apparatus 30. The receiver apparatus 30 comprises an antenna array 36 comprising a plurality of antenna elements 32A, 32B, 32C in a particular configuration. The antenna elements 32 receive respective radio signals 50A,

50B, 50C transmitted from the mobile apparatus 10. The antenna array 36 is connected through switch 38 to receiver circuitry 34. The switch 38 may, for example, switch each antenna element 32 to the receiver circuitry 34 according to a defined sequence. The receiver circuitry 34 processes the received signals to obtain characteristics of the received signals 50. The receiver circuitry 34 provides an output to a controller 33. The receiver circuitry 34 needs to obtain 'displacement information' from the received signals 50A, 50B, 50C that is dependent upon inter alia the relative displacements of the respective antenna elements 32A, 32B, 32C. In the example described in detail below, the displacement information includes phase information.

The receiver circuitry 34 may also be configured to demodulate the received signals.

For example, the receiver circuitry 34 may demodulate using l-Q modulation, also known as quadrature phase shift modulation. In this modulation technique, two orthogonal carrier waves (sine and cosine) are independently amplitude modulated to define a symbol. At the receiver circuitry 34, the amplitude of the two orthogonal carrier waves is detected as a complex sample and the closest matching symbol determined. It should be appreciated that an identical signal received at different antenna elements will be received with different phases and amplitudes because of the inherent phase characteristics of the antenna elements 32 when receiving from different directions and also because of the different times of flight for a signal 50 to each antenna element 32 from the transmitter apparatus 10. The inherent presence of this 'time of flight' information within the phases of the received signals 50 enables the received signals 50 to be processed, as described in more detail below, to determine the bearing 82 of the transmitter apparatus 10 from the receiver apparatus 30.

In the Figure only three different displaced antenna elements 32 are illustrated, although in actual implementations more antenna elements 32 may be used. For example 16 patch antenna elements could be distributed over the surface of a hemisphere. Three is the minimum number of radio signals required at the receiver apparatus 30 to be able to determine a bearing 82.

In one embodiment, the apparatus 30 determines a bearing 82 of the remote apparatus 10 from the antenna in the antenna coordination system, the apparatus 30 transforms the bearing of the remote apparatus 10 from the antenna in the antenna coordinate system to a bearing of the remote apparatus 10 in the global coordinate system and then estimates, using the bearing in the global coordinate system and constraint/height information, the position of the apparatus 10 in the global coordinate system.

In another embodiment, the apparatus 30 determines a bearing 82 of the remote apparatus from the antenna in the antenna coordination system, the apparatus 30 estimates, using the bearing in the antenna coordinate system and constraint/height information, the position of the apparatus 10 in the antenna coordinate system, the apparatus 30 then transforms the position of the remote apparatus 10 from the antenna in the antenna coordinate system to a position of the remote apparatus 10 in the global coordinate system.

Although the processes of estimating a bearing in the antenna coordinate system, compensating for misalignment of the antenna coordinate system and the global coordinate system and determining the position of the remote apparatus 10 in the global coordinate system are described above as all being performed in the apparatus 30, it should be appreciated that all or any one or more of these processes could be performed at an apparatus other than the apparatus 30 after receiving signals at multiple antenna elements of the antenna at the apparatus 30.

The controller 33 may be any suitable type of processing circuitry. The controller 33 may be, for example, programmable hardware with embedded firmware. The controller 33 may be a single integrated circuit or a set of integrated circuits (i.e. a chipset). The controller 33 may also be a hardwired, application-specific integrated circuit (ASIC). In the illustrated example, the controller 33 may comprise a programmable processor 12 that interprets computer program instructions 13 stored in a memory 14.

The processor 12 is connected to write to and read from the memory storage device 14. The storage device 14 may be a single memory unit or a plurality of memory units. The storage device 14 may store computer program instructions 13 that control the operation of the apparatus 30 when loaded into processor 12. The computer program instructions 13 may provide the logic and routines that enables the apparatus to perform the method illustrated in Fig 4. The computer program may arrive at the apparatus 30 via any suitable delivery mechanism 21 . The delivery mechanism 21 may be, for example, a computer-readable storage medium, a computer program product, a memory device, a record medium such as a CD-ROM or DVD, an article of

manufacture that tangibly embodies the computer program 13. The delivery mechanism may be a signal configured to reliably transfer the computer program 13.

The apparatus 30 may propagate or transmit the computer program 13 as a computer data signal.

Although the memory 14 is illustrated as a single component it may be implemented as one or more separate components some or all of which may be integrated/removable and/or may provide permanent/semi-permanent/ dynamic/cached storage.

References to 'computer-readable storage medium', 'computer program product', 'tangibly embodied computer program' etc. or a 'controller',

'computer', 'processor' etc. should be understood to encompass not only computers having different architectures such as single /multi- processor architectures and sequential (Von Neumann)/parallel architectures but also specialized circuits such as field-programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other devices. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed- function device, gate array or programmable logic device etc.

It will be appreciated by those skilled in the art that, for clarity, the controller 33 is described as being a separate entity to the receiver circuitry 34. However, it will be understood that the term controller 33 may relate not only to a main processor of an apparatus, but also processing circuitry included in a dedicated receiver chipset, and even to a combination of processing circuitry included in a main processor and a dedicated receiver chipset. A chipset for performing embodiments of the invention may be incorporated within a module. Such a module may be integrated within the apparatus 30, and/or may be separable from the apparatus 30.

The apparatus 30 may in some but not necessarily all embodiments comprise a pressure sensor for providing atmospheric pressure measurements to the controller 33. The atmospheric pressure measurements may be used with an atmospheric pressure measurement made at the apparatus 10 to generate the constraint information used to position of the transmitter apparatus 10 along the bearing 82.

The computer program 13 when loaded into the processor 12 enables the processor 12 to:

determine orientation information for an antenna comprising multiple antenna elements 32 that is used with signals received at the multiple antenna elements of the antenna to determine a position of a remote apparatus and/or

enables the processor 12 to:

use signals received at the multiple antenna elements of the antenna and the orientation information to determine the position of the remote apparatus.

The orientation information is determined using inputs from an inclinometer 35. An inclinometer 35 in the apparatus 30 may be used to assist in determining N_A, E_A ,GA. In some embodiments, the inclinometer measures a reference vector e.g., GA . It some embodiments it may comprise additional functionality for measuring a bearing vector that has components of N_A, or E_A.

Fig. 4 illustrates a method 40 for estimating the position of the apparatus 10. Various embodiments of the method of Fig. 3 will be described hereinafter. A radio signal is received at spatially diverse antenna elements. In the following it will be assumed that the respective spatially diverse received radio signals 50A, 50B, 50C are received at the receiver apparatus 30 as illustrated in Figs 1 and 3. At block 200 of the method of Fig. 4, the receiver apparatus 30 detects radio signals 50 including first, second and third radio signals 50A, 50B, 50C.

At block 210, the controller 33 of the apparatus 30 uses the detected radio signals 50 to estimate a bearing 82 of the apparatus 10 from the first location 80.

The processor 12 obtains comparable complex samples (i.e. samples that represent same time instant) for the three respective radio signals 50A, 50B, 50C.

The processor 12 then estimates a bearing 82. One method of determining the bearing 82 is now described, but other methods are possible.

Once comparable complex samples (i.e. samples that represent same time instant) from each antenna element 32 are obtained the array output vector y(n) (also called as snapshot) can be formed at by the processor 12. y(n) = [x_l , x₂,... ,x_M ]^T , (1 ) Where x, is the complex signal received from the ith RX antenna element 32, n is the index of the measurement and M is the number of RX elements 32 in the array 36.

A Direction of Arrival (DoA) in the antenna coordinate system can be estimated from the measured snapshots if the complex array transfer function &(φ_Λ ,θ_Λ) of the RX array 36 is known, which it is from calibration data. The simplest way to estimate putative DoAs is to use beamforming, i.e.

calculate received power related to all possible DoAs. The well known formula for the conventional beamformer is P_BF (φ_Λ , θ_Λ ) = Ά (φ_Α , Θ_Α )Ra(<p, , Θ_Α ) , (2)

Where,

1

R =— 2-,y( )y^* (n) is the sample estimate of the covariance matrix of the

N

received signals, a((^ ,0^ ) is the array transfer function related to the

ΌοΑ(φ_Λ ,θ_Λ ) , φ_Α is the azimuth angle and Θ_Α is the elevation angle.

Once the output power of the beamformer Ρ_ΒΡ (φ_Λ , θ_Λ ) is calculated in all possible DoAs the combination of azimuth and elevation angles with the highest output power is selected to be the bearing 82 in the antenna coordinate system.

The performance of the system depends on the properties of the antenna array 36. For example the array transfer functions Ά(φ_Λ ,θ_Λ ) related to different DoAs may have as low correlation as possible for obtaining unambiguous results.

Correlation depends on the individual radiation patterns of the antenna elements 32, inter element distances and array geometry. Also the number of array elements 32 has an effect on performance. The more elements 32 the array 36 has the more accurate the bearing estimation becomes. In minimum there should be at least 3 antenna elements 32 in planar array configurations but in practice 10 or more elements should provide good performance. The output of block 210 is a bearing 82 in a defined coordinate system that is independent of an orientation of the antenna such as the global coordinate system. Next, at block 220 the processor 12 compensates for misalignment of the antenna coordinate system and the global coordinate system. This block is described in more detail below.

Next, at block 230 the processor 12 estimates a position of the apparatus 10 using the estimated bearing and the constraint information e.g. h_m.

The processor 12 may access a value that is stored in the memory or it may determines h, for example using an atmospheric pressure measurement taken at the mobile apparatus 10.

If the receiver apparatus 30 has a known height h_ref and the measured barometric pressure at the receiver apparatus 30 is p_ref , then the height h_m of the mobile apparatus 10 can be expressed in terms of the measured barometric pressure p_m at the mobile apparatus 10 and h_ref and p_ref . h_m = h_ref - H(p_ref , Pm) For example h_m = h_ref - a^{"1 *} Log_e ( pj Pref ).

It should be appreciated that in some embodiments, the order of blocks 220 and 230 may be reversed. In the illustrated example, block 220 compensates the estimated bearing. In other embodiments it may instead compensate the determined position.

An example of the compensation block 220 is illustrated in Fig 5. In this example, the block 220 determines at block 220A orientation information that is used to compensate for the misalignment between the antenna coordinate system and the global coordinate system. Then at block 220B, the method uses the orientation information to transform the bearing (or position) of the remote apparatus 10 from the antenna in the antenna coordinate system to a bearing (or position) of the remote apparatus 10 from the antenna in the defined coordinate system.

It should be appreciated that the term location or locating is intended to encompass locating a remote apparatus 10 as being positioned along a bearing in a defined coordinate system and also encompass locating a remote apparatus 10 using coordinates in a defined coordinate system.

The orientation information defines an orientation of the antenna relative to the defined coordinate system. It may be for example a direction cosine matrix

The direction cosine matrix may be expressed as:

N„

C GA

Once the direction cosine matrix C_GA is determined, the bearing of the remote apparatus 10 from the antenna in the antenna coordinate system can be converted from polar coordinates to Cartesian coordinates and then

transformed to a bearing r° of the remote apparatus 10 from the antenna in Cartesian coordinates of the global coordinate system according to:

The position of the mobile user 92 in Cartesian coordinates (in the global coordinate systems) is:

cos0_G where sin 00_GG . cos _G

sin 0_G .sin

COS0_G

Thus a plurality of orthogonal vectors N_A E_A GA define a transform for transforming the bearing of the remote apparatus from the antenna in an antenna coordinate system to a bearing of the remote apparatus from the antenna in a global coordinate system.

As the vectors are orthogonal they have the following properties N_A= E_A x GA

An example for performing the method of block 220A is illustrated in Fig 6. The determination of the orientation information, in this example, comprises at block 220C measuring in the antenna coordinate system a first vector having a specified orientation in the defined coordinate system;

at block 220D measuring in the antenna coordinate system a second vector having at least a component along a specified orientation in the defined coordinate system; and

at block 220E using the first vector and the second vector to determine the orientation information.

For example at block 220E a vector cross product may be used to determine N_A E_A G_a e.g. N_A= E_A x G_Aor E_A= G_A x N_A.

Typically an inclinometer (one or more accelerometers with inertia) is used to measure GA. An accelerometer may, for example, comprise a capacitor where one capacitor plate moves relative to the other under gravity e.g. because it is suspended on a cantilever. An accelerometer may therefore measure acceleration (gravity) in only one direction. It is therefore useful to mount three accelerometers in mutually orthogonal orientations so that no matter what the orientation of the apparatus 30 the vector GA can still be measured.

In one embodiment, block 220C performs measuring in the antenna coordinate system a first vector GA having a specified orientation in the defined coordinate system;

block 220D performs measuring in the antenna coordinate system a second vector B_A having at least a component along a specified orientation N_A in the defined coordinate system; and

block 220E performs using the first vector GA and the second vector B_A to determine the orientation information.

The second vector B_A is a measured bearing. In one embodiment it may be the vector M_A representing magnetic north as measured by a magnetometer or compass. In another embodiment it may be a vector representing the bearing of a radio transmitter beacon.

In general, the vector M_A has a component in the direction of N_A and a smaller, typically non-zero, component in the direction of GA_. A third vector E_A , orthogonal to first vector GA, is determined using the first vector GA and the second vector B_A. The third vector E_A is determined using a vector cross-product of the first vector GA and the second vector B_A.

EA= GA X BA A fourth vector N_A is orthogonal to the first vector GA and the third vector E_A and is determined using the first vector GA and the third vector E_A . The fourth vector N_A is determined using a vector cross-product of the first vector GA and the third vector E_A. N_A = E_A x GA The direction cosine matrix used to transform the bearing of the remote apparatus from the antenna in the antenna coordinate system to a bearing of the remote apparatus from the antenna in the global coordinate system is formed from the unit vectors N_A , E_A , G_A. The direction cosine matrix can be written as:

The determination of the orientation information may alternatively involve measuring how a reference vector having a specified fixed orientation in the defined coordinate system changes in the antenna coordinate system over time. In this embodiment, blocks 220C and 220D may perform measuring in the antenna coordinate system a reference vector having a specified orientation in the defined coordinate system at different times.

The reference vector may be provided by a gyroscope or the reference vector may be defined by magnetic north or gravity.

The Direction Cosine Matrix at time t+ dt can be calculated from a known Direction Cosine Matrix at time t using:

Where

άθ_χ = co_xdt

dO_y = co_ydt

and ω_χ, ω_γ, ω_ζ are e.g. gyroscope readings about the axis XA, yA, z_A respectively.

Consequently, the Direction Cosine Matrix at a later time can be found by integration.

In one implementation, an initial orientation of the antenna array 36 could be aligned with the global coordinate axes of the global coordinate system or be in some defined relationship to them. This may be achieved by, for example, using a three axis inclinometer or some other mechanism. The user can then initiate Direction Cosine Matrix calculation by, for example, providing a user input e.g. pressing a button and then the antenna array is moved to its installation orientation. The Direction Cosine Matrix calculation could then stop automatically or in response to a user input. The calculated Direction Cosine Matrix (orientation information) can then be used in block 220B of Fig 5, for example.

The gravity vector GA of the Direction Cosine Matrix can be compared to a detected gravity vector obtained from an inclinometer. If the difference is less than a threshold then the determined Direction Cosine Matrix is used. If the difference is more than the threshold then the determined Direction Cosine Matrix is not used and the antenna array is returned to the initial orientation and the process of Direction Cosine Matrix calculation is repeated. Accuracy

As an addition to any of the foregoing embodiments, the determined orientation information may be used to estimate an accuracy for locating the remote apparatus 10.

Let us assume that the antenna array has a spatial resolution of Ο(ΘΑ, Α) in the antenna coordinate system. That is although the orientation of the antenna may change, the relative configuration of the antenna elements is fixed.

We can use the determined orientation information, the Direction Cosine Matrix, to transform the spatial resolution Ο(ΘΑ, ΦΑ) in the antenna coordinate system to a spatial resolution σ(θο, Φο) in the global coordinate system. α=σ(θ₀, OG) = C_GA σ(θ_Α> Φ_Α)

We can then determine the resolution R at (h, Q_G, Φσ) using geometry as R= h{tan (Q_G + a/2) - tan (Q_G - a/2) }. R is the uncertainty of position in the plane z=h at position (h, Q_G, Φο)-

Stability

It is possible to periodically recalculate the orientation information or to monitor the inputs used to calculate the orientation information e.g. GA or M_A to detect a change. Such a change indicates that the antenna orientation has changed.

In some circumstances, if a change occurs new orientation information may be determined and then used to transform from the antenna coordinate system to the global coordinate system. A radio message may also be transmitted as an alert.

Alternatively, or in addition, positioning performed by the base station apparatus 30 may be tagged as unreliable or even discarded.

The receiver apparatus 30 is typically a base station apparatus that is fixed. That is, the diversity is provided by the infrastructure. The apparatus 30 positions the apparatus 10 which is typically a mobile apparatus relative to the known location of the apparatus 30.

The blocks illustrated in the Figs 4, 5 and/or 6 may represent steps in a method and/or sections of code in the computer program 13. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied.

Diversity Transmission It should be appreciated that instead of using diverse reception, diverse transmission can be used. For example, in dioversity transmission, the base station apparatus 30 may use the multiple antenna elements 32 to transmit a signal to the mobile apparatus 10. In this example, the base station 30 illustrated in Fig 3 would comprise a transmitter instead of receiver 34. The base measurements used to determine the orientation information or the orientation information is then transferred to the mobile apparatus 10. The mobile apparatus 10 determines the orientation information either by receiving it from the base station 30 or calculating it from the base measurements made at the base station 30. The mobile station 10 then performs the methods illustrated in Figs 4 and 5. It may use a controller/computer program similar to that described with reference to Fig 3 to carry out the methods.

There may be alternative methods for the mobile station 10 determining the orientation information. For example, the mobile station may download the orientation information from a remote server e.g. a web-site.

Fig 7 schematically illustrates an example of a suitable mobile apparatus 10. The apparatus 10 is mobile and comprises a processor 2 which is connected to at least read from a memory 6. It may also write to the memory 6. The processor 2 determines orientation information. The processor 2 controls a radio receiver 14 to receive the diverse transmitted signals 50A, 50B, 50C for positioning the mobile apparatus 10. The memory 6 stores a computer program 8 that controls the operation of the mobile apparatus 10.

The apparatus 10 thus receives signals 50A, 50B, 50C associated with multiple antenna elements of an antenna arrangement (of the base station 30);determines orientation information for the antenna arrangement; and uses the received signals and the orientation information to locate the apparatus 10.

In comparison, in the described diversity reception scenario, the base station 30: receives signals associated with multiple antenna elements of an antenna arrangement; determines orientation information for the antenna arrangement; and uses the received signals and the orientation information to locate an apparatus 10. Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. For example, the apparatus 10 may not function as a mobile telephone. It may, for example, be a portable music player having a receiver for receiving radio signals. Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

I/we claim:

Claims

1 . A method comprising:

receiving signals associated with multiple antenna elements of an antenna arrangement;

determining orientation information for the antenna arrangement; and using the received signals and the orientation information to locate an apparatus.

2. A method as claimed in claim 1 , wherein locating an apparatus comprises determining a position of an apparatus in a defined coordinate system that is independent of an orientation of the antenna arrangement.

3. A method as claimed in any preceding claim, wherein locating an apparatus comprises determining a bearing of an apparatus in a defined coordinate system that is independent of an orientation of the antenna arrangement.

4. A method as claimed in any preceding claim, wherein the orientation information defines an orientation of the antenna arrangement relative to a defined coordinate system that is independent of an orientation of the antenna arrangement wherein locating the apparatus comprises:

using the received signals to determine a bearing of the apparatus relative to the antenna arrangement; and

using the orientation information to transform the bearing of the apparatus relative to the antenna arrangement to a bearing of the apparatus relative to the defined coordinate system.

5. A method as claimed in claim 4, wherein transforming the bearing of the apparatus relative to the antenna arrangement to a bearing of the apparatus relative to the defined coordinate system, is performed at a receiving apparatus that receives transmitted positioning signals.

6. A method as claimed in any preceding claim, comprising:

measuring in an antenna coordinate system a first vector having a specified orientation in a defined coordinate system;

measuring in the antenna coordinate system a second vector having at least a component along a specified orientation in the defined coordinate system; and using the first vector and the second vector to determine the orientation information.

7. A method as claimed in claim 6, wherein a plurality of orthogonal vectors define a transform for transforming the bearing of the apparatus from the antenna coordinate system to the defined coordinate system.

8. A method as claimed in claim 7, wherein the first vector is one of the plurality of orthogonal vectors and is defined by gravity.

9. A method as claimed in claim 8, wherein the other vectors in the plurality of vectors are defined by the second vector and/or its relationship to the first vector in the defined coordinate system.

10. A method as claimed in claim 9 wherein the second vector is a measured bearing.

1 1 . A method as claimed in any of claims 6 to 10, wherein the second vector has a component orthogonal to the first vector and a third vector, orthogonal to first vector, is determined using the first and second vectors.

12. A method as claimed in claim 1 1 , wherein the third vector is determined using a vector cross-product of the first vector and the second vector.

13. A method as claimed in claim 1 1 or 12, wherein a fourth vector is orthogonal to the first and third vectors, the fourth vector being determined using the first and third vectors.

14. A method as claimed in claim 13, wherein the fourth vector is determined using a vector cross-product of the first vector and the third vector.

15. A method as claimed in claim 14, wherein the first, third and fourth vectors define a transform for transforming the bearing of the apparatus to a bearing of the apparatus in the defined coordinate system.

16. A method as claimed in any of claims 6 to 15, wherein the second vector is defined by magnetic north or by a transmitter beacon.

17. A method as claimed in any of claims 6 to 9, wherein the first vector is a reference vector measured at a first time and the second vector is the reference vector measured at a second time after the first time;

using the first vector and the second vector to determine the orientation information comprises using the first vector and the second vector to determine a change in orientation of the antenna between the first time and the second time.

18. A method as claimed in any of claims 1 to 5, wherein a plurality of orthogonal vectors define a transform for transforming the bearing of the apparatus relative to the antenna arrangement to a bearing of the apparatus relative to a defined coordinate system and the method comprises integrating small changes in an orientation of the antenna to update the orthogonal vectors .

19. A method as claimed in any preceding claim wherein the orientation information defines a direction cosine matrix that transforms a three dimensional vector in an antenna coordinate system to a three dimensional vector in a defined coordinate system.

20. A method as claimed in any preceding claim,. wherein receiving signals associated with multiple antenna elements of an antenna arrangement comprises receiving signals at the multiple elements after transmission by the apparatus

21 . A method as claimed in any of claims 1 to 19, wherein receiving signals associated with multiple antenna elements of an antenna arrangement comprises receiving signals at the apparatus after transmission by the multiple elements of the antenna arrangement

22. A method as claimed in any preceding claim, wherein the multiple antenna elements are antenna elements of a ceiling mounted antenna array.

23. A method as claimed in any of the preceding claims, wherein the received radio signals are beacon signals.

24. A method as claimed in any preceding claim wherein the orientation information is used to estimate an accuracy value for the remote apparatus location.

25. A method as claimed in any preceding claim comprising: in response to detecting an event that is indicative of a change in orientation information performing an act that reduces the risk of incorrect locations being used.

26. A method as claimed in claim 25 wherein the acts comprise: determining new orientation information, indicating that determined locations are incorrect, or preventing use of determined locations.

27. An apparatus comprising:

at least one processor; and

at least one memory including computer program code

the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform: determining orientation information for an antenna arrangement comprising multiple antenna elements; and

using signals associated with the multiple antenna elements of the antenna arrangement and the orientation information to locate an apparatus.

28. An apparatus as claimed in claim 27 configured to locate itself.

29. An apparatus as claimed in claim 27 or 28 further comprising the antenna comprising multiple antenna elements.

30. An apparatus as claimed in claim 27 configured to locate a remote apparatus.

31 . An apparatus as claimed in any of claims 27 to 30, further comprising: circuitry for measuring in an antenna coordinate system a first vector having a specified orientation in a defined coordinate system; and

circuitry for measuring in the antenna coordinate system a second vector having at least a component along a specified orientation in the defined coordinate system; wherein

the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to use the first vector and the second vector to determine the orientation information.

32. An apparatus as claimed in claim 31 , wherein the at least one memory and the computer program code are configured to transfer the orientation information to a remote mobile apparatus.

33. An apparatus as claimed in any of claims 27 to 32wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to perform the method of any of claims 2 to 26.

34. An apparatus comprising:

means for communicating using signals associated with multiple antenna elements of an antenna arrangement;

means for determining orientation information for the antenna arrangement; and

means for enabling location of an apparatus using the signals and the orientation information.

35. An apparatus as claimed in claim 34 further comprising means for performing the method of any of claims 2 to 26.

36. A computer program which when loaded into a processor enables the processor to:

determine orientation information for an antenna arrangement comprising multiple antenna elements; and

use signals communicated using the multiple antenna elements of the antenna arrangement and the orientation information to locate an apparatus.

37. A record carrier tangibly embodying the computer program as claimed in claim 36.