WO2001084175A1

WO2001084175A1 - Method and system for determining geographical co-ordinates in mobile communications networks

Info

Publication number: WO2001084175A1
Application number: PCT/IT2001/000205
Authority: WO
Inventors: Giorgio Grego
Original assignee: Telecom Italia Lab S.P.A.
Priority date: 2000-05-04
Filing date: 2001-04-26
Publication date: 2001-11-08
Also published as: ITTO20000417A1; ITTO20000417A0; IT1320072B1; AU5873601A

Abstract

First (1) and a second (2) sources of radiation located in two points of a given space are used. The sources (1, 2) create angular scanning of the space with first and second radiations respectively. The first and the second radiation have a respective characteristic which varies on the basis of the position reached in the scanning movement. Therefore in correspondence with every point in the space (S) the first and the second radiation have a respective pair of values for said characteristic which univocally identifies the position of said point in the context of said space (S). The position of the point in the context of said space (S) is therefore identified by said pair of values.

Description

METHOD AND SYSTEM FOR DETERMINING GEOGRAPHICAL CO-ORDINATES IN MOBIL≤ COMMUNICATIONS NETWORKS Technical Field

This invention faces the problem of determining geographical co-ordinates in the context of mobile communications networks .

The determination of the geographical co-ordinates (absolute and/or relative) of a mobile terminal in the framework of a communications network can be advantageous as it can be used in a broad range of services such as, for example, location billing, calls for help, indication of distances and/or paths between the current position of a mobile terminal and places or destinations, etc. Background Art At the moment, location techniques are known, based on the triangulation of several Base Ter ianal Stations (BTS) received by the mobile terminal and/or GPS systems.

There are problems associated with these known solutions associated, for example, with the insufficient precision of the locating action (for example, triangulation systems usually have levels of precision which do not fall below 100 metres) or with the fact that they cannot work inside building .

As well as this, the increasing attention given to protecting confidentiality makes it desirable for there to be techniques available in which the real locating action requires a positive display of assent from the person using the mobile receiver. As a consequence it would be impossible for the network operator to attempt location on its own without this assent.

Disclosure of the Invention

Object of this invention is to provide a solution which, in the embodiment preferred at the moment, is capable of overcoming the problems outlined above and meeting the above- mentioned confidentiality needs.

According to this invention, this object is achieved thanks to a location system with the characteristics recalled in a specific manner in the claims which follows .

The invention also regards the mobile terminal equipped to operate as a consequence^ Brief Description of Drawings

The invention will now be described, in an exemplificative and not limiting manner, with reference to the attached drawings, in which:

- figure 1 schematically illustrates the theoretical principles at the basis of the invention,

- figure 2 schematically illustrates the architecture of a system in accordance with the invention,

- figure 3 illustrates the criteria for carrying out a geographical location operation including a mobile receiver operating according to the invention, in the form of a flow diagram, and - figures 4 and 5 are two diagrams explaining the manner in which some of the steps in the flow diagram in figure 3 are actuated. Best mode for Carrying Out the Invention

Figure 1 schematically illustrates the terms of the problem currently indicated in geometry as "resolution of a triangle" .

Specifically, given two points A and B a known distance d apart, all the geometrical parameters of the triangle identified by these points A and B as well as a third point C (constituting the third vertex of the triangle) are univocally determined as soon as the values are known for the angles α and β formed, with respect to the segment joining points A and B, respectively by the segment AC and by the segment BC . The above-mentioned geometry is reproduced in a system according to the invention, represented in figure 2, and comprising two transmitters or sources 1, 2 which illuminate

- by means of the radiation generated by them - a space S in which there is a mobile receiver 3.

The transmitters 1 and 2, as well as the receiver 3, can typically be included in X mobile telephone system of the cellular type, or of the type destined for ensuring microcell or picocell coverage, in accordance with the DECT standard, for example .

In any case, the specific system integration criteria according to the invention in the context of a mobile communications system are not important as such for understanding and/or actuating the invention. In this regard it is sufficient to note that transmitters 1 and 2 are also easy to place inside buildings so as to ensure coverage of spaces S selected in any manner.

An important characteristic of the solution according to the invention is given in that the angular coding of the radiation emitted is such that space S is scanned cyclically. All of this occurs concomitantly with a corresponding variation of at least one characteristic of the radiation emitted on the basis of the angle instantaneously formed by the main irradiation direction with respect to a reference direction.

For simplicity of illustration, it can be supposed here that the above-mentioned reference direction is made up of the straight line identified by the positions occupied by the transmitters 1 and 2 situated at the distance d. These positions can in fact be identified for references purposes as points A and B in figure 1.

The above-mentioned scanning of the space S can be actuated both with mechanical means, for example using respective antennas with high directionality characteristics to which a traverse movement is given, or - in accordance with the solution preferred at the moment - using antennas Tl and T2 operating in accordance with the techniques of_, the type currently known as "phased array" . In this way, the radiation emitted by the antenna during the cyclical scanning movement is concentrated at every moment in a principle irradiation lobe with, for example, an opening value at -3 dB of around 5-10° for example.

The radiation emitted by each of the transmitters 1 and 2 is subjected to a modulation or encoding such as to vary at least one characteristic of the radiation on the basis of the position instantaneously reached by the above-mentioned scanning movement .

In a first example of actuation, the above-mentioned result can be obtained by subjecting the frequency emitted by the transmitters 1 and 2 to a modulation law of the type

for transmitter 1 , and of the type

f₂ = f₂₀ + βΔf₂ (II) for transmitter 2.

What this is therefore a frequency modulation with respect to a fixed reference value fι_0/ f₂o with the respective value of coordinates α, β identified starting from the deviation of the frequency f_{l t} f₂ with respect to the reference value f₁₀, f₂o .

Values and β are representative of the corresponding magnitudes shown in figure 1, that is, by the angle instantaneously formed by the direction of alignment from sources 1 and 2 and from the segments which connect the mobile receiver respectively to transmitter 1 and 2.

For simplicity of illustration, it can be supposed that both the angle α and the angle β are between the value 0 and the value π/2 (90°) , where the value 0 corresponds to ^^ alignment direction of the two transmitters 1 and 2. In general, the amplitude ^'of the scanning or transverse movement can be greater however, being equal to 180° for example.

By appropriately selecting the values of fio and f₂o (as well as the value of the maximum deviations Δfi and Δf₂) , for example in such a way as to prevent superimposition of the values to the frequency emitted by transmitters 1 and 2, it is possible to establish a bijective correspondence between the geographical co-ordinates of each point in space S and the two frequency values of the radiation received in this point starting, respectively, from transmitter 1 and transmitter 2.

In this way a matrix of frequencies univocally associated with each individual point or position in space S is created in space S itself. The degree of precision obtainable when establishing the above-mentioned bijective correspondence is a function of the frequency deviation Δf used (hereinafter it will be supposed for simplicity that Δfi = Δf₂ = Δf) and of the extension of the territory with which the same is associated.

For example, assuming a value of Δf of 90 KHz, with 90° scanning and resolving a frequency value at 1Hz, an angular resolution of 1/1000° is obtained and this is the equivalent of 1.7 cm at a distance of 1 Km. Functionally equivalent solutions can be obtained by varying other characteristics of the radiation emitted as a function of the angle instantaneously reached by the scanning movement .

For example, for transmitters 1 and- 2 • it ^■ is possible to use an emission at a fixed carrier frequency subjected to modulation of the numerical type, for example by means, of words comprising a predetermined number of bits.

For example, by using 17 bits it is 'possible to obtain 2¹⁷ different coding combinations, each associable wit¹- - respective angular value of the scanning movement in space S by transmitters 1 and 2 .

This variant lends itself in a particularly advantageous manner to use in combination with the 1MB (Ultra Wide Band) transmission technique, instead of the CDMA technique commonly used in traditional location systems.

As is known, the UWB technique has the advantage that it uses extremely low powers and has high immunity to echoes .

The flow diagram in figure 3 illustrates a possible configuration modality for receiver 3 for the purposes of exploiting the variation in the characteristics of the radiation emitted by the transmitters 1 and 2 to permit determination of the geographical co-ordinates of the place in which the mobile terminal 3 is found within space S . Starting from an initial step 100, in the steps indicated by 101 and 102 (here represented as carried out sequentially from one another, but susceptible to being advantageously carried out in parallel to achieve a greater information processing speed) the receiver 3 "reads" the signals received respectively by transmitter 1 and by transmitter 2.

Referring for simplicity to the situation in which the radiation emitted by transmitters 1 and 2 are subjected to frequency modulation as a function of the scanning movement (which can be both cyclical or come and go) , the receiver is generally able to distinguish between the two emissions as a function of the two different frequency ranges used.

In reality, each of the values fi and f₂ is preferably obtained as mean (or central) value of a possible range of variation in accordance with the criteria best illustrated (with reference to transmitter 1) in figures 4 and 5.

However directional antennas Tl and T2 may be, the irradiation diagrams for transmitters 1 and 2 have still got a certain angular opening (see the value of 5-10° mentioned previously) . Therefore the mobile receiver 3 - supposed for simplicity to be in 'a fixed position - is in any case illuminated by each transmitter 1 or 2 not simply for an instant (t_x in figure 5) but for a certain time interval (t'_x; t"_x) .

As an effect of the progress of this scanning movement, the frequency emitted by the transmitter (and received by the receiver 3) varies, for example between a value f_x and a value f"_x. This typically occurs with a ramp pattern of the type illustrated in figure 5.

The value of fi or f₂ effectively used is therefore identified as the mean or central value of the aforesaid ramp (for example, selecting the value f_x = (f'_x + f"_x)/2). This corresponds to selecting a frequency value fi or f₂ corresponding to the bisecting line (or central axis) of the envelope of all the lobes which illuminates the mobile receiver .

The same considerations naturally apply in the case in which the characteristic exploited for location purposes is made up of a different characteristic with respect to the frequency of the radiation which illuminates the mobile receiver .

For example, in the case in which this characteristic is a codification applied to the signal emitted by transmitters 1 or 2 , the corresponding value used for location purposes can be made up, for example, of the mean or central value assumed by the code during the time interval in which the mobile receiver 3 is illuminated by the transmitter 1 or 2.

The set of operations described corresponds in practice to taking the values fi and f₂ of formulae (I) and (II) seen above and corresponding to the point in which the mobile receiver 3 finds itself at that moment.

Knowing the values fio, f₂o, Δfi and Δf₂ (as they have been memorised previously and/or received by the transmitters 1 and 2) the receiver is able to implement formulae (I) and (II) in the subsequent ^'steps 103 and 104, so as to deduce the angle values a and β which identify the geographical _< coordinates of receiver 3. At this point receiver 3 has the information available regarding its location within the limits of space S, that is, the data which (knowing the^' distance d from the transmitters 1 and 2) permit the "resolution" of the triangle identified by transmitters 1 and 2 as well as by receiver 3 itself. It is significant in this regard to note the fact that this information resides in receiver 3 and can therefore be made available to the system which transmitters 1 and 2 are part of only as an effect of transmission of the information from transmitter 3 to the system. This can occur in accordance with current modalities in the context of mobile communications systems, for example as an effect of transmitting the data from receiver 3 towards the base station or base stations to which it is connected at the time (not necessarily corresponding to transmitters 1 and '2)-, for example by means of messages in SMS (Short Message Signalling) format.

In particular, in a subsequent selection step 105 receiver 3 may decide (e.g. on the basis of an order K given at the moment or memorised previously by the user of the mobile receiver) regarding the possibility of proceeding with location within the limits of space S.

If the outcome of step 105 is negative (the user of the mobile receiver 3 has decided not to be located) control of the receiver simply evolves upstream from step 101, so as to repeat the operations described previously.

In the opposite case (the holder of mobile receiver 3 decides to let himself be located) , in a subsequent step 106 receiver 3 transmits the values of angles and β to the radio communications system it is part of, or rather the values of the corresponding geographical co-ordinates obtained - in accordance with known criteria - as an effect of the transformation of the above-mentioned angular _^ coordinates into a system of co-ordinates of a different kind, of the Cartesian type, for example.

Starting from this point it is possible, in one step or set of steps indicated schematically by 107, to carry out one or more operations (transactions) associated with the completion of location (supposed here to have been carried out by the system in a step indicated by L) .

As has already been said in the introductory part of this description, these operations can be made up, for example, by orders for billing based on position (location billing) , calls for help, indications of distances and/or paths between the current position of the mobile receiver and various places or destinations, etc.

Having carried out the above operations, the operation of the receiver 3 evolves towards a final step indicated as 108, as far as the carrying out of operations for determining geographical co-ordinates are concerned.

This datum is then associated with a database, managed in the framework of the system, which identifies the corresponding absolute position values (latitude and longitude) of the mobile receiver 3. Naturally, in an alternative configuration (not explicitly illustrated in the diagram in figure 3), location can be carried out directly by receiver 3, while still having information available regarding the distance d, as it has been received by the system for example. The configuration of receiver 3 for the purposes of actuating the operating mode shown schematically by the flow diagram in figure 3 can take place both by providing specific hardware components, in mobile terminal 3, or by appropriate programming of programmable elements already available in receiver 3 itself. Such a set-up at software level can be achieved advantageously, for example, by means of programming codes (program code means) entered at the level of what is known as the SIM CARD or, possibly, by means of codes loaded remotely into the mobile terminal and coming from the mobile communications system it is part of.

Naturally, without prejudice to the principle of the invention, the realisation details and the forms of implementation can be widely varied with respect to what has been described and illustrated, without leaving the framework of this invention as a result.

Claims

1. Method for determining the position of a mobile receiver (3) within the limits of a given space NS ) , characterised in that it comprises the steps of: - providing a first (1) and a second (2) source of radiation, located at a known distance (d) in two points of said space (S) ; said first (1) and second (2) source realising angular scanning of said space by a first and second radiation, respectively, said first and second radiation each presenting at least one respective characteristic which varies on the basis of the position ( ex, β) reached in said angular scanning, whereby each point in said space (S) is illuminated by said first and second radiation having, in correspondence with said each point, a respective pair of values (fi, f₂) of said at least one characteristic univocally identifying the position of said point within the limits of said space (S) ,

- receiving said first and second radiation in at least one point of said space (S) and measuring (101, 102) the respective pair of values (fi, f ) of said at least one characteristic corresponding to said at least one point, and

- identifying (103, 104) the position of said at least one point within the limits of said space (S) starting from said respective pair of values (fi, f₂) and from said known distance (d) .

2. Method in accordance with claim 1, characterised in that the values (fi, f₂) of said respective pair are identified as mean or central value (f_x) of said at least one respective characteristic within the limits of the time interval (t'_x, t"_x) in which said each point is illuminated by the respective radiation.

3. Method in accordance with claim 1 or claim 2, characterised in that said at least one characteristic is made up of a frequency (fi, *f₂) of said radiation.

4. Method in accordance with claim 1 or claim 2, characterised in that ' said at least one characteristic is made up of a code transmitted by said radiation.

5. Method in accordance with any of claims 1 to 4, characterised in that said angular scanning has an amplitude of 180°.

6. Method in accordance with claim 1, characterised in that at least one of said first and second radiation is subjected to frequency modulation or deviation ( Δf_1; βΔf₂) with respect to a fixed reference value ( f ₁₀ , f₂o) and in that the respective value of said at least one of said first and second radiation is identified by the deviation of said frequency with respect to said fixed reference value.

7. Method in accordance with any of claims 1 to 6, characterised in that it further comprises the step of selectively transmitting said respective pair of values or the position identified by using said respective pair of values from said at least one point on the basis of an enabling datum (K) available at said at least one point.

8. System for determining the position of a mobile receiver (3) within the limits of a given space (S), characterised in that it comprises:

- a first (1) and a second (2) source of radiation, located at a known distance (d) in two points of said space (S) ; said first (1) and second (2) source realising an angular scanning of said space with a first and second radiation, respectively, said first and second radiation each presenting at least one respective characteristic which varies as a function of the position (a, b) reached in said angular scanning, whereby each point in said space (S) is illuminated by said first and second radiation having, in correspondence with said each point, a respective pair of values (fi, f₂) of said at least one characteristic univocally identifying the position of said point within the limits of said space (S) , and receiving means (3) for receiving said first_, and second radiation in at least one point of said space (S), measuring (101, 102) the respective pair of values (fi, f₂) of said at least one characteristic at said at least one point, and identifying (103, 104) the position of said at least one point within the limits of said space (S) starting from said respective pair of values (fi, f₂) and from said known distance (d) .

9. System in accordance with claim 8, characterised in that said receiving means (3) measures the values (fi, f₂) of said respective pair as mean or central value (f_x) of said at least one respective characteristics within the limits of the time interval (t'_x, t"_x) in which said each point is illuminated by the respective radiation.

10. System in accordance with claim 8 or claim 9, characterised in that said at least one characteristic is made up of a frequency (fi, f₂) of said radiation.

11. System in accordance with claim 8 or claim 9, characterised in that said at least one characteristic is made up of a code carried by said radiation.

12. System in accordance with any of claims 8 to 11, characterised in that the amplitude of said angular scanning is 180°.

13. System in accordance with claim 8, characterised in that at least one of said first and second radiation is subjected to frequency modulation or deviation (αΔfi, βΔf₂) with respect to a fixed reference value ( fιo , f₂o) and in that the respective value of said at least ^"one of said first and second radiation is identified from the deviation of said frequency with respect to said fixed reference value.

14. System in accordance with any of the claims 8 to 13 , characterised in that said receiving means (3) are configured to selectively transmit said respective pair of values or the position identified by' using said respective pair of values from said mobile receiver on the basis of an enabling datum (K) available at said receiving means(3).

15. Receiver for a communications system, said receiver (3) being mobile within the limits of a given space (S), characterised in that the receiver is configured for: receiving a first and a second radiation, respectively, starting from a first (1) and a second (2) source of radiation, located at a known distance (d) in two points in said space; said first and second radiation each having at least one respective characteristic which varies as a function of the position occupied by the receiver (3) within the limits of said space, whereby each point in said space (S) susceptible to being occupied by said receiver (3) is illuminated by said first and second radiation having, in correspondence with said each point, a respective pair of values (fi, . f₂) of said at least one characteristic univocally identifying the position of said point within the limits of said space (S) , and

- measuring (101, 102) the respective pair of values (fi, f₂) of said at least one characteristic corresponding to the point in said space (S) in which the receiver (3) is positioned.

16. Receiver in accordance with claim 15, characterised in that the receiver is configured to measure the values (fi, f₂) of said respective pair as mean or central value (f_x) of said at least one respective characteristic within the limits of the time interval (t'_x, t"_x) in which said each point is illuminated by the respective radiation.

17. Receiver in accordance with claim 15 or claim 16, characterised in that said at least one characteristic is made up of a frequency (fi, f₂) of said radiation.

18. Receiver in accordance with claim 15 or claim 16, characterised in that ' said at least one characteristic is made up of a code carried by said radiation.

19. Receiver in accordance with claim 15, characterised in that said receiver is configured for measuring, in at least one of said first and said second radiation, a frequency modulation or deviation (αΔfi, βΔf₂) with respect to a fixed reference value (fio, f₂o) and identifying the respective value of said at least one of said first and said second radiation on the basis of the deviation of said frequency with respect to said fixed reference value.

20. Receiver in accordance with claim 15, characterised in that the receiver is configured for identifying (103, 104) the position occupied by the receiver (3) itself within the limits of said space (S) starting from said respective pair of values.

21. Receiver in accordance with any of claims 15 to 20, characterised in that the receiver (3) is configured for selectively transmitting said pair of values or the position identified by using said pair of values from the receiver (3) itself on the basis of an enabling datum (K) available at the receiver (3 ) .

22. Receiver in accordance with any of claims 15 to 21, characterised in that it comprises means for reading means of program code and in that the receiver (3) itself can be configured, at least in part, on the basis of means of program code read by said mobile receiver (3) .

23. Receiver in accordance with claim 22, characterised in that it can be configured for reading said means of program code coming from a card preferably consisting of a card known as the receiver's SIM CARD.

24. Receiver in accordance with claim 22, characterised in that it is a receiver configured to selectively load said means of program code coming from the communications system the receiver (3) itself is inserted into.