WO2011077026A1

WO2011077026A1 - Method, computer program and device for the relative orientation of wireless mobile terminals

Info

Publication number: WO2011077026A1
Application number: PCT/FR2010/052661
Authority: WO
Inventors: Mohamed Salah Bouassida; Marcus Mohamed Shawky
Original assignee: Universite De Technologie De Compiegne; Centre National De La Recherche Scientifique (Cnrs)
Priority date: 2009-12-24
Filing date: 2010-12-09
Publication date: 2011-06-30
Also published as: FR2954884B1; FR2954884A1

Abstract

The subject of the invention is in particular the relative orientation of a first mobile terminal with respect to a second terminal, said at least one second terminal comprising means for emitting at least one signal and said first terminal comprising means, wireless means, for receiving said at least one signal and means for obtaining a representation of the power of said at least one signal received. After having obtained (110) a representation of a level of power of said at least one signal received, a power gradient of said at least one signal received is evaluated (120) according to said representation of said level of power of said at least one signal received. A direction of displacement of said first mobile terminal is then estimated (125, 405, 805), said direction being determined according to said gradient and at least one predetermined rule.

Description

"Method, computer program and device for the relative orientation of wireless mobile terminals"

The present invention relates to the relative orientation of wireless mobile terminals, relative to each other, in an indoor or outdoor environment, and more particularly a method, a computer program and a device for the relative orientation of mobile terminals. wireless that does not require a central server or third-party systems such as positioning systems.

Many applications require the relative location of a wireless mobile terminal with respect to another mobile terminal or with respect to a fixed terminal to allow, for example, to guide it to it.

Generally, the orientation of a mobile terminal to another or to a fixed terminal is based on an absolute location method and according to a predetermined map using electromagnetic signals.

By way of illustration, a mobile terminal implementing the GPS system (acronym for Global Positioning System in English terminology) comprises a sensor receiving and analyzing signals sent by satellites in order to define its position in a three-dimensional space with a margin of error evaluated between 10 and 20 meters. Although this solution is widely used, it has drawbacks, especially in terms of costs. In addition, it can only be used in an external environment, that is to say an environment with a direct view of the satellites. In addition, the start-up and initialization time is generally important, typically of the order of a few minutes.

Other solutions are based on the use of fixed ground terminals, also called beacons in English terminology.

According to a topological localization technique, also known as range free in English terminology, a mobile terminal determines its position from position information received from fixed terminals. So, by For example, according to the algorithm known as Centroid, a mobile terminal evaluates an average of the received coordinates.

According to a topographic localization technique, also called range based in English terminology, the position of a mobile terminal is estimated from physical measurements characterizing relative distances between mobile terminals and / or fixed terminals. By way of illustration, according to the algorithm known as AOA (Angle Of Arrival in English terminology), the location of a mobile terminal is achieved by a triangulation using the angles of reception of signals from three separate fixed landmarks. Still as an example, the APS technique (abbreviation Ad-hoc Positioning System in English terminology) aims at a method according to which the position of a mobile terminal is estimated according to the AOA algorithm in an environment comprising terminals fixed locating by GPS. There are other similar methods such as the methods TOA (acronym for Time Of Arrival in English terminology) and TDOA (acronym for Time Difference Of Arrival in English terminology).

The distance between a mobile terminal and a fixed terminal, between two mobile terminals or between two fixed terminals can be estimated from a measurement of the power of a signal received from a fixed terminal or a mobile terminal. Such a measure is known by the name of RSSI (acronym for Received Signal Strength Variations in English terminology). This technique consists in measuring, in a receiver, the power of signals received from a transmitter and evaluating the distance between the transmitter and the receiver. This method can be coupled with a triangulation technique to determine the location of a mobile terminal or a fixed terminal receiving signals. The distance between a transmitter and a receiver is estimated using a model of attenuation of the power of the signals received with the distance. The signal attenuation models represent the difference, in decibels (dB), of the signal strengths between transmission and reception. A frequently used mitigation model is the Friis Free Space Path Model

where λ is the wavelength of the transmitted signal and d is the distance between the transmitter and the receiver. This equation can be generalized as follows, for all distances d, from a reference power defined here at the distance of one meter,

PL (d) [dB] = 2PLfs (d ₀ ) [dB] +

where n is the signal attenuation parameter, representing the increase in signal attenuation as the distance between transmitter and receiver increases. For a free space, that is to say without obstacle, the value of n is typically equal to two. However, it is best to calibrate this setting according to the actual environment.

Although the solutions briefly described above allow the relative location of a mobile terminal with respect to another or with respect to a fixed terminal, these solutions lack precision, can only be implemented in particular environments and / or require special resources, especially in terms of computing power, and, therefore, significant energy. These solutions are therefore not suitable for the relative location of mobile terminals such as mobile phones, used in an indoor or outdoor environment and having low computing and energy resources, for orientation purposes.

The invention solves at least one of the problems discussed above.

The invention thus relates to a computer method for orienting a first mobile terminal according to the relative position of at least one second terminal, said at least one second terminal comprising means for transmitting at least one signal and said first mobile terminal comprising wireless means for receiving said at least one signal and means for obtaining a representation of the power of said at least one received signal, which method comprises the following steps, obtaining a representation of a power level of said at least one received signal;

evaluating a power gradient of said at least one received signal according to said representation of said power level of said at least one received signal; and,

estimating a direction of displacement of said first mobile terminal, said direction being determined according to said gradient and at least one predetermined rule.

The method according to the invention thus allows a first mobile terminal to go to a second terminal without requiring additional means, based on the power gradient of a received signal. The second terminal can be fixed or mobile. In addition, the method according to the invention does not require any mapping of the places where the terminals are located or calibration phase. In addition, the method can be implemented very quickly in outdoor or indoor environments. Furthermore, the method can be implemented in a mobile terminal with few resources, including computing resources, memory and energy.

Advantageously, said at least one predetermined rule is identified from a state machine. The method according to the invention is thus particularly simple to implement in a mobile terminal with few resources.

Still advantageously, said at least one predetermined rule is at least partially based on a history of directions of said first mobile terminal to optimize the movement of the first mobile terminal.

According to a particular embodiment, the method further comprises a step of calculating an angle between a first and a second direction, said first direction corresponding to a direction followed by said first mobile terminal and said second direction corresponding to a particular direction related to the relative position of said at least one second terminal with respect to said first mobile terminal, said angle defining the direction to be followed by said first mobile terminal. The method thus makes it possible to optimize the path of the first mobile terminal, especially when the one seeks to reach the second terminal.

Said calculation step of said angle can be carried out periodically or, preferably, according to a power variation of said at least one received signal. This calculation stage, whose needs in terms of resources and energy are greater, is thus not systematically implemented.

Advantageously, said step of calculating said angle is performed when said power variation of said at least one received signal is less than a predetermined threshold. This calculation step is thus used only when it is necessary to optimize the trajectory of the first mobile terminal.

Still according to a particular embodiment, the method is implemented in an ad hoc type network, said first mobile terminal and said at least one second terminal forming nodes of said network. The method according to the invention can thus be implemented in many applications and in many configurations.

The invention also relates to a computer program comprising instructions adapted to the implementation of each of the steps of the method described above, when said program is executed on a computer, and a mobile terminal comprising means adapted to the implementation of each of the steps of the method described above.

The benefits provided by this computer program and this mobile terminal are similar to those mentioned above.

Other advantages, aims and features of the present invention will emerge from the detailed description which follows, given by way of non-limiting example, with reference to the accompanying drawings in which:

FIG. 1 schematically illustrates an exemplary algorithm for evaluating a direction of movement of a first mobile terminal (receiver) receiving a signal from a second mobile terminal (transmitter) in order to orient the first mobile terminal towards the second; FIG. 2 illustrates a first example of a state machine, based on predetermined rules, for evaluating a direction as a function of a power gradient of a received signal;

FIG. 3 represents an example of each of the steps of a trajectory of a first mobile terminal pointing towards a second mobile terminal in accordance with the algorithm described with reference to FIG. 1 and with the state machine described with reference. in Figure 2;

FIG. 4 illustrates certain steps of a first orientation determination algorithm according to which the orientation is estimated according to predetermined rules and by calculations;

FIG. 5 illustrates a method of calculating an orientation enabling a receiver to orient towards an emitter;

FIG. 6, comprising FIGS. 6a and 6b, illustrates an example of choosing a direction evaluation mode;

FIG. 7 illustrates a second example of a state machine that can be used to determine the direction to be followed by a receiver towards a transmitter;

FIG. 8 illustrates certain steps of a second orientation determination algorithm according to which the orientation is estimated according to predetermined rules and by calculations;

FIG. 9 illustrates an example of trajectory followed by a receiver, the direction followed being determined according to predetermined rules and, punctually, by calculation; and,

FIG. 10 illustrates an exemplary mobile terminal adapted to implement the invention or a part of the invention.

In general, the invention implements a relative orientation technique based on the evaluation of electromagnetic signal strengths, preferably radioelectric, received by entities of a wireless network, using a power gradient, in order to to suggest directions to take to reach a target emitting these signals. More specifically, the invention aims to determine the necessary instructions to allow a mobile node of a network to be oriented towards an entity at its range of this network, using power measurements of a signal received from this entity, for example RSSIs measurements (acronym for Received Signal Strength Indicators in English terminology). It is considered here that the signals transmitted by the same network node are sent with the same transmission power.

The orientation of a first mobile terminal, called receiver, to a second or to a fixed terminal, called transmitter, is performed in steps, each step corresponding to a displacement that can be characterized, for example, in time or distance. At each step, the receiver determines a direction indication according to the power of a signal received from the transmitter.

By way of illustration, the signals transmitted by a transmitter and received by a receiver are signals conforming to the IEEE 802.1 1 standard (ISO / IEC 8802-1 1), that is to say signals transmitting packets of data. It is observed here that the measurement of the signal power is performed natively, hardware or software, by many mobile terminals to quantify the quality of reception of a signal. The invention uses this information generally accessible via an API (acronym for Application Programming Interface in English terminology).

Mobile terminals may in particular be mobile phones, PDAs, called PDAs (Personal Digital Assistant) and laptops belonging to an ad hoc network. They are here assimilated to computers including functions of calculation and memorization

The transmitter of a signal can be identified according to the data transmitted in the signal. This may be, for example, the MAC address (acronym for Media Access Control in English terminology) of the issuer.

As an illustration, the iwspy command of the Linux operating system (Linux is a brand) allows, from a list of addresses of transmitters, to read the quality, the power and the level of noise of signals received from these transmitters. This information is updated whenever data is received, typically in the form of packets. According to a first embodiment, a direction is determined, at a given moment, according to a power gradient of the signal received from the transmitter and predetermined rules, for example arranged in the form of a state machine, so that the Received signal strength increases with the movement of the receiver.

FIG. 1 schematically illustrates an exemplary algorithm for evaluating a direction of movement of a first mobile terminal (receiver) receiving a signal from a second mobile terminal (transmitter) in order to orient the first mobile terminal towards the second mobile terminal (receiver).

A first step aims to initialize a first direction of movement and to measure the power of a signal received from the transmitter (step 100). The first direction is, for example, initialized randomly. The first mobile terminal is then moved in the given direction (step 105). As an illustration, the first mobile terminal is moved a predetermined distance, for example a meter, in the given direction. Alternatively, the first mobile terminal can be moved for a predetermined time, for example a second, in the given direction.

It should be observed here that the second mobile terminal can move independently of the first.

The power P of the signal received by the receiver, emitted by the transmitter, is then measured (step 1 10). As indicated above, this power is preferably obtained from an existing function of the mobile terminal via an API. It is noted here that only the signals transmitted by the terminal (s) to which the receiving mobile terminal is to be directed are taken into consideration.

The measured power is here compared with a predetermined threshold Θ (step 1 15). If the measured power is greater than the threshold Θ, it is considered that the first mobile terminal is close to the second and the process ends.

If, on the contrary, the measured power is less than or equal to the threshold Θ, the power gradient is estimated as a function of the power of the previously measured received signal, that is to say measured in the previous step (Step 120) and the direction to be followed by the first mobile terminal is estimated according to predetermined rules (step 125).

The preceding steps (steps 105 to 125) are then repeated until the first mobile terminal is close to the second, that is to say until the measured power is greater than the threshold Θ.

Figure 2 illustrates a first example of a state machine 200, based on predetermined rules, for evaluating a direction as a function of a power gradient of a received signal.

Each node here represents a state, that is, an estimate of a direction to follow. At the beginning of the process, the direction is arbitrary (state 205). From this direction and after a first displacement, the power gradient of a received signal is determined. If the gradient is positive, noted P ++ in the figure, the direction is considered correct. The state machine goes into state 210 where the direction is not changed (transition 215). If, on the contrary, the gradient is negative, noted P ~ in the figure, the direction is considered to be incorrect, the state machine goes into state 220 (transition 225) according to which the estimated direction is the direction opposite to that previously determined. Thus, for example, if the previously selected direction was a (with respect to any reference) the new direction is α + π (with respect to the same reference).

If, from the state 210, the power gradient is positive, the direction is maintained (transition 230). On the other hand, if, from the state 210, the power gradient is negative, a first direction is defined, for example in a random manner, such that the angle α between the previous direction and the new direction is understood. between π / 4 and 3π / 4 (transition 240). The state machine thus goes into the state 245. However, advantageously, if the history of the direction sequences comprises the sequence (good direction, direction 1, direction opposite, good direction) or the sequence (good direction, direction 2, good direction), a second direction is defined, for example in a random manner, such that the angle α between the previous direction and the new direction is between n / 4 and 7π / 4 (transition 250). The state machine thus goes into state 255. If, from the state 245, the power gradient is positive, the direction previously estimated, considered good, is retained (transition 260). The state machine thus goes to state 210. On the other hand, if, from state 245, the power gradient is negative, the direction is considered to be incorrect and the state machine goes into state 220 (transition 265) in which the estimated direction is the direction opposite to that previously determined.

If, from the state 255, the power gradient is positive, the direction previously estimated, considered good, is retained (transition 270). The state machine thus goes to state 210. On the contrary, if, from state 255, the power gradient is negative, the direction is considered as incorrect and the state machine goes into the state 220 (transition 275) in which the estimated direction is the direction opposite to that previously determined.

Finally, if, from the state 220, the power gradient is positive, the direction previously estimated, considered good, is retained (transition 280). The state machine thus goes to the state 210. On the contrary, if, from the state 220, the power gradient is negative, a first direction is defined, for example randomly, so that the angle a between the previous direction and the new direction is between π / 4 and 3π / 4 (transition 285). The state machine thus goes into state 245.

FIG. 3 represents an example of each of the steps (steps 1 to 23) of a trajectory 300 of a first mobile terminal 305 going to a second mobile terminal 310 in accordance with the algorithm described with reference to FIG. the state machine described with reference to FIG. 2. The reference 315 here represents the limit according to which the power of the received signal is greater than a predetermined threshold Θ, that is to say the limit beyond which the orientation process is here halted.

According to a second embodiment, the direction of a first mobile terminal to reach a second mobile terminal is determined alternatively by predetermined rules defined, for example, by a state machine such as that described with reference to FIG. by one estimating a displacement angle calculated as a function of power variations of a received signal. The frequency of implementation of one of these two modes can in particular be random, predetermined or determined according to the available resources of the first mobile terminal.

By way of illustration, as shown in FIG. 4, it is possible to calculate a displacement angle as a function of the power variations of a signal received every n orientation estimates. For these purposes, step 100 shown in Fig. 1 includes a step of initializing a variable / to the zero value, and step 125 shown in Fig. 1 comprises the steps illustrated in Fig. 4.

As illustrated in this figure, a first step is to compare the value of the variable / with a predetermined value n (step 400).

If the value of the variable / is less than the value n, the direction of the first mobile terminal is determined according to predetermined rules (step 405), for example according to a state machine such as that described with reference to FIG. , and the variable / is incremented by one (step 410).

If, on the contrary, the value of the variable / is greater than or equal to the value n, the angle of the direction that the first mobile terminal must take with respect to its current direction is calculated as a function of the power variation of a received signal as described below (step 415) and the variable / is reset to the zero value (step 420).

The calculation of the angle formed by the line joining the first and second mobile terminals with the trajectory followed by the first mobile terminal enables the latter to move more rapidly towards the second mobile terminal than the simple application of predetermined rules. However, such a calculation requiring significant computing resources and, therefore, significant energy, can not be used systematically.

Considering the two points 500 and 505 of the trajectory followed by the first mobile terminal, as illustrated in FIG. 5, the object here is to calculate the angle β between the direction followed and a preferred direction at the midpoint noted 510. Points 500 and 505 are distant by a distance L. The first mobile terminal calculates the distances di and c / 2 separating it from the second mobile terminal at points 500 and 505, respectively, according to the Friis model. It is admitted here that the distance d between the first and second mobile terminals at point 510 is equal to the average of the distances di and c / 2 when these distances are very large compared to the distance L between the points 500 and 505, c that is to say,

d, +

d =

The geometric analysis of FIG. 5 makes it possible to deduce the following relationships,

be d? ^■ d ₂ = 2L ^■ d ^■ sin a where β = arccos

The

Thus, when the first mobile terminal is at point 505, it can calculate the angle β and the distance d. The uncertainty related to the sign of the value β (cos (3) = cos (-β)) can be solved by displacement or with the aid of a state machine such as that described with reference to FIG.

Advantageously, a calibration step can be implemented to improve the results obtained. In particular, the attenuation parameter of the attenuation model, for example the n parameter of the previously mentioned Friis model, can be evaluated as follows, when do = 1, using a second formulation of the Friis model,

where Pr, represents the power of a signal received by the receiver at a time / and d represents the average distance between the receiver and the transmitter at times / and (i-1). According to a third embodiment, the choice of the mode of evaluation of the direction, according to predetermined rules or by calculation, is carried out according to the evolution of the variation of power of a signal received when the receiver approaches the transmitter.

FIG. 6, comprising FIGS. 6a and 6b, illustrates an example of choosing a direction evaluation mode. FIG. 6a illustrates the variation of the distance between a first mobile terminal, referenced 305, and a second, referenced 310, when the first mobile terminal follows a rectilinear trajectory 300 '. At each point noted /? to 17 of the trajectory corresponds a power referenced Pi to P ₇ of the signal received from the transmitter 310 from which can be calculated the distance noted di to άγ between the receiver 305 and the transmitter 310.

It is thus possible to graphically represent, as illustrated in FIG. 6b, a theoretical power curve 600 as a function of the position of the receiver on a trajectory. This curve can in particular be obtained by extrapolation of the measured powers of a signal received from a transmitter at different points.

It is observed here that the variation of the distance between the transmitter and the receiver for two consecutive points of the trajectory of the latter increases with the distance. The power variation of a received signal being directly related to the distance between the transmitter and the receiver, it follows that the variation of power increases with the distance.

Thus, it is possible to use the variation of the power to determine the choice of the mode of evaluation of the direction. This choice may in particular be based on the second derivative of the curve representing the power of a received signal as a function of distance, representing a change in concavity of the curve. However, advantageously and to simplify the necessary calculations, the orientation of the receiver is, by default, determined according to a state machine such as that described with reference to FIG. 2, the angle of orientation being calculated if the variation of power of a received signal is positive and less than a threshold, for example a predetermined threshold, that is to say if, at the moment / ^' ,

Ο κ Ρ, - Ρ, ^ κ θ ' FIG. 7 illustrates a state machine 200 'that can be used to determine the direction a receiver must follow to turn towards a transmitter. This comprises the states and transitions described with reference to FIG. 2 as well as the calculation of an angle when the direction is generally good and the power variation of a received signal is less than a threshold θ '.

As in Figure 2, each node here represents the estimation of a direction to follow. At the beginning of the process, the direction is arbitrary (state 205 '). From this direction and after a first displacement, the power gradient of a received signal is determined. If the gradient is positive, again noted P ++ in the figure, the direction is considered correct. The state machine goes into the state 210 'where the direction is not changed (transition 215'). If, on the contrary, the gradient is negative, always noted P- in the figure, the direction is considered as incorrect, the state machine goes into the state 220 '(transition 225') according to which the estimated direction is the direction opposite to that previously determined.

If, from the state 210 ', the power gradient is positive, the direction is maintained (transition 230'). On the contrary, if, from the state 210 ', the power gradient is negative, a first direction is defined, for example in a random manner, so that the angle between the previous direction and the new direction is understood between π / 4 and 3π / 4 (transition 240 '). The state machine thus goes into state 245 '. However, advantageously, if the history of the direction sequences includes the sequence (good direction, direction 1, direction opposite, good direction) or the sequence (good direction, direction 2, good direction), a second direction is defined, for example in a random manner, such that the angle a between the previous direction and the new direction is between n / 4 and 7π / 4 (transition 250 '). The state machine thus goes into state 255 '.

If, from the state 245 ', the power gradient is positive, the direction previously estimated, considered good, is retained (transition 260'). The state machine thus goes to state 210 '. On the contrary, if, from the state 245 ', the power gradient is negative, the direction is considered incorrect and the state machine goes into state 220 '(transition 265') according to which the estimated direction is the direction opposite to that previously determined.

If, from the state 255 ', the power gradient is positive, the direction previously estimated, considered good, is retained (transition 270'). The state machine thus goes to state 210 '. On the other hand, if, from state 255 ', the power gradient is negative, the direction is considered to be incorrect and the state machine goes into state 220' (transition 275 ') in which the estimated direction is the direction opposite to that previously determined.

If, from the state 220 ', the power gradient is positive, the direction previously estimated, considered good, is retained (transition 280'). The state machine thus goes to state 210 '. On the contrary, if, from state 220 ', the power gradient is negative, a first direction is defined, for example in a random manner, such that the angle a between the previous direction and the new direction is between π / 4 and 3π / 4 (transition 285 '). The state machine thus goes into state 245 '.

If, when the direction followed is the correct {^ - Ρ ^> 0, state 210 '), the power variation of a received signal is less than a threshold θ' (^ - P ^ <# '), the machine states goes to state 705 (transition 700) where a new direction is calculated. This calculation consists here in determining the angle formed by the direction to be taken and the current direction according to the equation described above.

If, after moving the receiver in the calculated direction, the power gradient of a received signal is positive, the direction is considered good and the state machine goes to state 210 '(transition 710). If, on the contrary, the power gradient of a received signal is negative, the opposite direction is chosen. For these purposes, the state machine goes to state 220 '(transition 715).

Again, a calibration step such as that described above can be implemented to improve the results obtained. Figure 8 schematically illustrates certain steps of step 125 shown in Figure 1 to implement such an embodiment. As illustrated, a first step is to determine the sign of the power difference of a signal received at times / and i-1 and compare it to a threshold θ '(step 800).

If the power difference of a signal received at times / and i-1 is negative or greater than the threshold θ ', the direction of the first mobile terminal is determined in accordance with predetermined rules (step 805). If, on the contrary, the power difference of a signal received at times / and i-1 is positive and less than the threshold θ ', the direction of the first mobile terminal is calculated as a function of the power variation of a received signal. as previously described (step 810).

Thus, by way of illustration, the trajectory followed by a receiver can be that shown in FIG. 9 according to which the direction followed between the starting point of the receiver and the point ₁₄ is determined according to predetermined rules, the direction followed at the point U is calculated according to the equation

previously described (β =) and the direction followed after the point

U is determined according to predetermined rules.

A device adapted to implement the invention or a part of the invention, in particular the algorithms described with reference to FIGS. 1, 4 and 8, is illustrated in FIG. 10. The device 1000, representing a mobile terminal, is here assimilated to a computer including functions of calculation and memorization. This is, for example, a mobile phone, including the smartphone type, a personal digital assistant PDA, an ultra-portable computer (also called netbook in English terminology), or a computer portable type PC.

The device 1000 here comprises a communication bus 1005 to which are connected:

a central processing unit or microprocessor 1010 (CPU, Central Processing Unit); - A read-only memory 1015 (ROM, acronym for Read Only Memory in English terminology) may include the programs "Prog", "Progl" and "Prog2";

a random access memory or cache memory 1020 (RAM, acronym for Random Access Memory in English terminology) comprising registers adapted to record variables and parameters created and modified during the execution of the aforementioned programs; and,

a wireless communication interface 1050 adapted to receive and, advantageously, to transmit data in the form of signals.

Preferably, the device 1000 furthermore has:

a screen 1025 making it possible to display data and / or to act as a graphical interface with the user who can interact with the programs according to the invention, using a keyboard and a mouse 1030 or another pointing device such as an optical pen, a touch screen or a remote control. The screen 1025 is particularly adapted to indicate a direction to follow;

a hard disk 1035 that may comprise the "Prog", "Progl" and "Prog2" programs mentioned above and data processed or to be processed according to the invention; and,

a memory card reader 1040 adapted to receive a memory card 1045 and to read or write to it data processed or to be processed according to the invention.

It is observed here that the direction indications determined according to the invention can be given to a user in various forms:

visual, for example on a screen such as the screen 1025;

touching via a surface such as a vibrating surface whose points can vibrate independently of each other and thus indicate directions; and or,

- Sound via, for example, speakers (reference 1025 'in Figure 10). The device 1000 is thus equipped with a screen, loudspeakers and / or a tactile surface according to the needs of the user.

The communication bus of the device 1000 allows communication and interoperability between the various elements included in the device 1000 or connected to it. The representation of the bus is not limiting and, in particular, the central unit is able to communicate instructions to any element of the device 1000 directly or through another element of the device 1000.

The executable code of each program enabling the programmable device to implement the processes according to the invention can be stored, for example, in the hard disk 1035 or in the read-only memory 1015.

According to one variant, the memory card 1045 may contain data as well as the executable code of the aforementioned programs which, once read by the device 1000, will be stored in the hard disk 1035.

According to another variant, the executable code of the programs may be received, at least partially, via the interface 1050, to be stored in an identical manner to that described above.

More generally, the program or programs may be loaded into one of the storage means of the device 1000 before being executed.

The central unit 1010 will control and direct the execution of the instructions or portions of software code of the program or programs according to the invention, instructions which are stored in the hard disk 1035 or in the read-only memory 1015 or else in the other elements of aforementioned storage. When powering on, the program or programs that are stored in a non-volatile memory, for example the hard disk 1035 or the read-only memory 1015, are transferred into the random access memory 1020 which then contains the executable code of the program or programs according to the invention, as well as registers for storing the variables and parameters necessary for the implementation of the invention.

The invention can be used in many applications. In particular, the invention can be implemented in applications of guidance according to which a mobile terminal broadcasts a search request of other terminals, mobile or otherwise, having a given profile corresponding to the request in order to direct it to the terminals thus identified.

Naturally, to meet specific needs, a person skilled in the field of the invention may apply modifications in the foregoing description.

Claims

1. Computer method for orienting a first mobile terminal

(305) to a second terminal (310) according to the relative position of said second terminal, said second terminal including means for transmitting at least one signal and said first mobile terminal including wireless means for receiving said at least one signal and means for obtaining a representation of the power of said at least one received signal, said method being characterized in that it comprises the following steps,

obtaining (1 10) a representation of a power level of said at least one received signal;

evaluating (120) a power gradient of said at least one received signal according to said representation of said power level of said at least one received signal; and,

estimating (125, 405, 805) a direction of movement of said first mobile terminal to said second terminal, said direction being determined according to said gradient and at least one predetermined rule.

2. Method according to the preceding claim wherein said at least one predetermined rule is identified from a state machine (200, 200 ').

The method of claim 1 or claim 2 wherein said at least one predetermined rule is at least partially based on a history of directions of said first mobile terminal.

The method of any one of claims 1 to 3, further comprising a step of calculating (415, 810) an angle between a first and a second direction, said first direction corresponding to a direction followed by said first mobile terminal. and said second direction corresponding to a particular direction related to the relative position of said second terminal with respect to said first mobile terminal, said angle defining the direction to be followed by said first mobile terminal.

5. Method according to the preceding claim wherein said calculating step (405) of said angle is performed periodically.

The method of claim 4 wherein said calculating step (810) of said angle is performed according to a power variation of said at least one received signal.

7. Method according to the preceding claim wherein said calculating step (810) of said angle is performed when said power variation of said at least one received signal is less than a predetermined threshold.

8. Method according to any one of the preceding claims, the method being implemented in an ad hoc type network, said first mobile terminal and said second terminal forming nodes of said network.

9. Computer program comprising instructions adapted to the implementation of each of the steps of the method according to any one of the preceding claims when said program is executed on a computer.

10. Mobile terminal comprising means adapted to the implementation of each of the steps of the method according to any one of claims 1 to 8.