Patent Abstract:
The invention relates to a mobile electronic system. In order to expand and enhance the usability of the mobile electronic system, it is proposed that it comprises a 3D magnetometer  51  performing magnetic measurements in three dimensions and providing data indicative of the current posture of the mobile electronic system based on these measurements. Further, it is proposed that the mobile electronic system comprises processing means  52, 54  processing the data provided by the 3D magnetometer  51  for enabling a posture related presentation of information via output means  12, 42  of the mobile electronic system. The invention relates equally to components of such a system and to a corresponding method.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is for entry into the U.S. national phase under §371 for International Application No. PCT/IB02/004630 having an international filing date of Nov. 5, 2002, and from which priority is claimed under all applicable sections of Title 35 of the United States Code including, but not limited to, Sections 120, 363 and 365(c). 
     FIELD OF THE INVENTION 
     The invention relates to a mobile electronic system comprising means which realize the function of a compass and to components of such a system. The invention relates equally to a method for a mobile electronic system. 
     BACKGROUND OF THE INVENTION 
     It is known from the state of the art to provide mobile electronic systems with a two dimensional compass. Such a mobile electronic system may be included for instance in a communication device like a mobile phone. 
     In German patent application DE 198 37 568 A1, it is proposed to provide a Personal Digital Assistant (PDA) with a Global Positioning System (GPS) receiver, a mobile communication unit and a compass. The compass is used for determining the current orientation of the PDA, which is required for realizing navigation functions in the PDA. 
     In British patent application GB 2 298 539 A, it is equally proposed to provide a hand held device containing a GPS receiver with a compass. A displayed information relating to the current environment, e.g. a map, is rotated in accordance with the respective orientation of the device. 
     Further, it is proposed in international application WO 01/88687 A2 to access context information with a user equipment, e.g. a mobile phone. The context information is downloaded from a network based on a location service. Then, the orientation of the user equipment is determined using a compass in the user equipment. Once the orientation is known, a visual user interface is generated at the user equipment for displaying the downloaded context information. In order to select a virtual object displayed in the visual user interface, the user can point to the respective object by orienting the user equipment. During the movement of the user equipment, the displayed virtual objects move accordingly in front of the user. 
     A mobile electronic system may also comprise an Inertial Navigation Systems (INS), which INS can be used for determining the position of the mobile electronic system. In such a system, it is essential that provided heading information remains accurate along time, since even small errors in the computed orientation cause significant errors to the position estimate. Traditionally, IN Systems utilize gyro-compasses to ensure an accurate heading. Gyro-compasses, however, have several disadvantages. They constitute quite expensive components due to their complicated electronics. Moreover, they are physically large sensors and can thus not be implemented in small modules. The use of a conventional 3-axis gyro-compass in a small INS is not feasible at all, since it requires even more complex electronics and its power consumption is much higher. As a result, it is more expensive and it also requires more space. A 3-axis operation, however, is essential for an accurate INS. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to expand and enhance the usability of a mobile electronic system. 
     This object is reached according to the invention with a mobile electronic system, which comprises output means enabling a presentation of information to a user of the mobile electronic system. The proposed mobile electronic system further comprises a 3D (three-dimensional) magnetometer performing magnetic measurements in three dimensions and providing data indicative of the current posture of the mobile electronic system based on these measurements. The 3D magnetometer thus realizes the functions of a 3-dimensional compass. Finally, the proposed mobile electronic system comprises processing means processing the data provided by the 3D magnetometer for enabling a posture related presentation of information via the output means. 
     The mobile electronic system may be a single unit or be composed of several units. It may be comprised, for example, completely in a user equipment like a mobile communication device. Alternatively, the mobile electronic system may comprise for example a user equipment including the output means, while at least the 3D magnetometer is included in a separate, complementary unit which can be connected to the user equipment. In the latter case, the connection should be rigid so that the posture of the complementary unit with the 3D magnetometer corresponds always to the posture of the user equipment. The processing means can then be included in either of the two units or be distributed to the two units. The unit comprising the output means may be for example a mobile phone and the complementary unit comprising the 3D magnetometer a functional cover for the mobile phone. 
     The object of the invention is equally reached with a corresponding complementary unit and with a corresponding user equipment comprising either the part of the proposed mobile electronic system not comprised by a complementary unit or the entire proposed mobile electronic system. 
     The object of the invention is further reached with a corresponding method for a mobile electronic system. The method comprises in a first step performing magnetic measurements in three dimensions in the mobile electronic system. The method comprises moreover determining data indicative of the current posture of the mobile electronic system based on the performed magnetic measurements. Finally, the proposed method comprises processing this data for enabling a posture related presentation of information to a user of the mobile electronic system. 
     The invention is based on the consideration that a 3D magnetometer is able to sense not only the orientation of a device in which it is included or to which it is attached in a horizontal plane, like a 2D compass, but also its current inclination. This additional data can be employed for a variety of new or enhanced functions of a mobile electronic system. It can be used for example to enhance the presentation of information and/or to select a mode of presentation depending on the current posture of the mobile electronic device. A 3D magnetometer can further be used as main source for heading information in an inertial navigation system, since it is smaller and less expensive than a gyro-compass. 
     Preferred embodiments of the invention become apparent from the dependent claims. 
     In a preferred embodiment of the invention, the presented information comprises compass information. 
     In another preferred embodiment of the invention, different modes of presentation are selected depending on the posture of the mobile electronic system. In case the output means comprise a display and the mobile electronic system is held basically horizontally, the display and functioning can resemble e.g. to a traditional compass. When the mobile electronic system is held basically vertically, in contrast, the presentation of information may be switched to some other mode. 
     In another preferred embodiment of the invention, the output means comprise a 3D display for a presentation of compass information, e.g. a presentation of a floating compass. This enables a new user experience compared to a 2D electrical compass, which cannot even be used in free posture. 
     In another preferred embodiment of the invention, the system comprises additional sensor means, which provide further measurement data. These further measurement data can be employed by the processing means in addition for enabling the posture related presentation of information via the output means. The additional measurement data allow the processing means to adjust the functionality of the system to the environment and/or to a user profile. For example, data on the posture and the characteristics of the movements of the mobile electronic system can be used to change the functionality. The adjustment of the functionality may comprise for example an adjustment of the presentation of information via the output means and/or an adjustment of a filtering of signals provided by the 3D magnetometer. 
     The additional sensor means may comprise for example a 2D or 3D linear accelerometer measuring the acceleration of the mobile electronic system in two or three dimensions, respectively, or a 3D angular accelerometer measuring the angular acceleration of the mobile electronic system in three dimensions. 
     Since a magnetic compass is subjected to unpredictable disturbances, a 3D angular accelerometer can be used to verify whether sudden changes of direction indicated by the 3D magnetometer actually occurred or whether there was only a temporary disruption. This enables a compensation of random magnetic disturbances. From an implementation point of view, angular accelerometers have the advantage that they do not require any dedicated electronics and that they can be read with the same electronics as linear accelerometers. Angular accelerometers are also inexpensive and smaller than gyro-compasses. 
     In case a 3D angular accelerometer is used as additional sensor means, the 3D magnetometer may provide first data indicating a current heading of the mobile electronic system, while the 3D angular accelerometer provides second data indicating a current heading of the mobile electronic system. Moreover, the processing means may comprise a complementary filter combining the first and second data, in order to obtain a particularly reliable information on the current heading of the mobile electronic system. 
     A combination of a 3D magnetometer and a 3D angular accelerometer is of particular advantage for an INS realized in the mobile electronic system. 
     It is understood that data provided by the 3D magnetometer may be used for various applications in the mobile electronic system. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings, wherein: 
         FIG. 1  schematically illustrates a first posture dependent display mode employed in a first embodiment of the invention; 
         FIG. 2  schematically illustrate a second posture dependent display mode employed as first example in the first embodiment of the invention; 
         FIG. 3  schematically illustrate a second posture dependent display mode employed as second example in the first embodiment of the invention; 
         FIG. 4   a - d  schematically illustrate a simulation of a floating compass in a second embodiment of the invention; 
         FIG. 5  is a block diagram of a complementary filter employed in a third embodiment of the invention; and 
         FIG. 6  is a block diagram of a complementary filter in one compass plane that is based on two axis of a magnetometer and on an angular accelerometer. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In a first embodiment of the invention illustrated in  FIGS. 1 to 3 , a mobile phone  10  can be employed as a two-dimensional compass with two different presentation modes. The mobile phone  10  comprises buttons  11 , a display  12 , a 3D magnetometer, a 3D accelerometer and processing means. 
     The 3D magnetometer constantly performs magnetic measurements in all three dimensions. The measurement results, which constitute an information on the current posture of the mobile phone  10 , are provided to the processing means. Moreover, the 3D accelerometer constantly performs acceleration measurements in all three dimensions. Also these measurement results, which allow one to draw conclusions as to the current velocity of the mobile phone, are provided to the processing means. 
     As long as the measurement results by the 3D accelerometer indicate that the mobile phone is only moved slowly, a fast acting filtering software is activated in the processing means for filtering the measurement results provided by the 3D magnetometer. The fast acting filtering software filters the measurement results with an integration period of about 1 to 3 seconds, which removes e.g. the influence of hand vibrations, of by-passing cars and of disturbances in the magnetic fields of the earth. 
     In case the measurement results by the 3D accelerometer indicate, in contrast, that the mobile phone is moved with an increased velocity, a slow filtering software is activated in the processing means for filtering the measurement results provided by the 3D magnetometer. The slow filtering software filters the measurement results with an integration period of about 5 to 10 seconds. The slow filtering is activated for instance in case the compass function is to be used while the user is driving in an urban city environment, in order to filter temporary fluctuations in the magnetic field due to bypassing trams, buses, buildings, metal constructions, etc. 
     The filtered measurement results of the 3D magnetometer are then evaluated by the processing means for presenting compass information on the display  12  of the mobile phone  10 . 
     When the magnetic measurements indicate that the phone  10  is positioned basically horizontally, which may e.g. be the case when a user of the phone  10  is walking, a first mode of presentation is selected by the processing means. In the first mode of presentation, the display  12  and the functioning resembles a traditional compass. 
     For this first mode of presentation, the processing means determine the direction in the horizontal plane to which the top of the mobile phone  10  is oriented based on the provided measurement results. The orientation information contained in the filtered signal is then reflected by an arrow  13  in a circle  14  on the display  12  of the mobile phone  10 , as shown in  FIG. 1 . The circle  14  with the arrow  13  represent a conventional compass. Accordingly, the arrow  13  is always oriented such that it points to the North. Alternatively, any other predetermined direction could be indicated based on the filtered signals. The fast acting filtering, which is activated when the user is walking, allows the user to find North without unnecessary delays. 
     When the magnetic measurements indicate, in contrast, that the degree of an inclination of the mobile phone exceeds a predetermined value, which may e.g. be the case when a person is tilting the phone or when it is kept in a car stand, a second mode of presentation is selected. 
     For the second mode of presentation, the processing means determine the orientation of the back of the tilted mobile phone based on the filtered magnetic measurement results. The presentation of the determined compass information differs moreover from the presentation in the first mode of presentation, since a simulation of a conventional compass as in the first mode of presentation is not appropriate with a tilted phone. 
     Two possibilities for the second mode of presentation are illustrated in  FIGS. 2 and 3 . 
     In the first possibility illustrated in  FIG. 2 , the presentation on the display  12  resembles a “marine compass”. In a first row, the current orientation of the phone is indicated by the points of the compass North “N”, East “E”, South “S” and West “W”, while in a second row, the current orientation of the phone is indicated by corresponding degrees “90”, “180”, “270” and “360”. In the situation depicted in  FIG. 2 , the user of the phone faces North-West or 315°, since the center of the first row lies between an indicated “N” and an indicated “W”, and the center of the second row lies between indicated “360” and “270” degrees. 
     The second possibility for the second mode of presentation illustrated in  FIG. 3  is provided in order to enable a user of a mobile phone  10  to easily keep a preset target direction. The direction may be entered via the buttons  11  of the mobile phone  10 . The desired direction can be selected in particular using the points of the compass or a corresponding indication in degrees. 
     The direction information contained in the filtered magnetic measurement results is then reflected by a simple arrow pointing in the desired direction on the display. 
       FIG. 3  presents the view of a driver of a car who is using the mobile phone  10  with the second possibility for the second mode of presentation. The mobile phone  10  is fixed in a car stand, which is connected to the dashboard on the right hand side of the steering wheel of the car. In the presented example, the arrow  15  shown on the display  12  of the mobile phone  10  indicates that the desired direction is straight ahead. 
     With the second possibility for the second mode of presentation, thus a simplified navigation system is provided. It may be used for example when driving in an urban environment towards an airport, which is lying in a known direction. The slow filtering, which is activated when the user is driving, ensures that most magnetic disturbances are not visible in the presentation of the compass information. 
     In a second embodiment of the invention, a mobile phone can be employed for simulating a floating three-dimensional compass, e.g. a floating navy compass. Like the mobile phone of the first embodiment, the mobile phone of the second embodiment comprises buttons, a display, a 3D magnetometer, a 3D accelerometer and processing means. In the second embodiment, however, the display is a 3D display. 
     The 3D magnetometer constantly performs magnetic measurements in all three dimensions, which provide an information on the current posture of the mobile phone. The 3D accelerometer further measures the accelerations of the mobile phone in all three dimensions. 
     The measurement results of the 3D magnetometer and the 3D accelerometer are used by the processing means for presenting the floating compass on the display of the mobile phone. More specifically, the measurement results provided by the 3D accelerometer are used by the processing means for filtering the measurement results provided by the 3D magnetometer with a delay, similarly as described for the first embodiment. Then, the processing means show a 3D compass on the 3D display, of which the orientation corresponds to the posture information contained in the filtered measurement results. The compass is represented by the processing means on the 3D display such that a user can view the compass from all sides by tilting the mobile phone. Due to the filtering of the signals, the displayed compass follows changes of the posture only slowly, resulting in the particular effect of a virtual floating compass. 
       FIGS. 4   a - 4   d  schematically illustrate the presentation of the floating compass on the display  42  of the mobile phone for various postures of the phone. 
     The compass is represented as a sphere  43  on the 3D display  42  of the mobile phone. The top of the sphere  43 , and thus of the virtual compass, is indicated by circles  44 . In all four cases illustrated in  FIGS. 4   a - 4   d , the user of the mobile phone is facing South-East (SE). An arrow  45  indicating the direction which the user faces is thus labeled “SE”. The arrow  45  is always pointing to the top  44  of the sphere  43 . A circle  46  is depicted around the middle of the sphere  43 , all points of the circle being equidistant to the top  44  of the sphere  43 . 
       FIG. 4   a  shows the display  42  in a first situation, in which the mobile phone is hold vertically. The top  44  of the compass is depicted next to the top  47  of the display  42 . The arrow  45  indicating South-East is rather short in the first situation. 
       FIG. 4   b  shows the display  42  in a second situation in which, proceeding from the first situation in  FIG. 4   a , the mobile phone is tilted sideways to the right. The user has exactly the same view on the represented compass as in  FIG. 4   a . That is, the top  44  of the compass is now depicted next to the upper left corner  48  of the display  42 . The arrow  45  indicating South-East has the same length as in  FIG. 4   a.    
       FIG. 4   c  shows the display  42  in a third situation, in which, proceeding from the first situation in  FIG. 4   a , the mobile phone is tilted forward. As a result, the bottom of the mobile phone is now somewhat closer to the user than the top of the mobile phone. The represented compass appears to be rotated towards the user, since the top  44  of the compass is shifted in direction of the center of the display  42 . The arrow  45  indicating South-East is slightly longer than in  FIGS. 4   a  and  4   b.    
       FIG. 4   d  shows the display  42  in a fourth situation, in which the mobile phone is hold horizontally. The user of the mobile phone has now a top view on the represented compass. Thus, the top  44  of the compass is depicted in the center of the visible part of the sphere  43 . The arrow  45  indicating South-East extends throughout the visible part of the sphere  43 . The visible part of the sphere  43  is now limited by the circle  46  depicted around the middle of the sphere  43 . 
     The second embodiment of the invention is ideal for mobile phones having a large color display. 
     In a third embodiment of the invention, a mobile phone is employed for realizing an INS. To this end, the mobile phone comprises a display, a 3D magnetometer, a 3-axis angular accelerometer and processing means. 
     Measurement results provided by the 3D magnetometer and the angular accelerometer are used by the processing means for presenting the current heading of the user of the mobile phone on the display. The 3D magnetometer provides an excellent long term reference for the angular position of the device. However, magnetometers are sensitive to external disturbances. The angular accelerometer on the contrary presents low noise operation but poor stability. Thus, the combination of the magnetometer and the angular accelerometer provides means to perform a measurement with good stability and good tolerance to external disturbances. 
       FIG. 5  is a block diagram which illustrates the processing of the signals provided by the 3D magnetometer and the angular accelerometer. The block diagram comprises a first block  50  representing the 3-axis angular accelerometer and a second block  51  representing the 3D magnetometer. The output of the angular accelerometer  50  is connected to first filter means  52  and the output of the 3D magnetometer  51  is connected to second filter means  53 . The outputs of the filter means  52 ,  53  are connected to a summing point  54 . The filter means  52 ,  53  and the summing point  54 , which form a complementary filter, are part of the processing means of the mobile phone. 
     The angular accelerometer  50  measures angular accelerations of the mobile phone in any direction proceeding from a point of time at which the heading was known until a new point of time t. Based on the measured movements and on the last known heading, the angular accelerometer then estimates the new heading at point of time t and provides a corresponding first heading signal. This first heading signal comprises the true heading s(t) at point of time t and a noise component n 1 (t), which takes account of errors in the angular measurements. 
     At the same point of time t, the 3D magnetometer  51  performs in addition magnetic measurements, in order to determine the current posture of the mobile phone. Based on the magnetic measurements, the 3D magnetometer  51  then estimates as well the new heading of the mobile phone at point of time t and provides a corresponding second heading signal. This second heading signal comprises equally the true heading s(t) at point of time t and a noise component n 2 (t), which takes account of errors in the magnetic measurements. 
     As a result, two redundant measurements of the same signal are available. These two measurements can now be combined in a way that the measurement error is minimized. This is achieved with the complementary filter, to which the two heading signals are provided. 
     The first heading signal is subjected by the first filter means  52  to a filtering function which has a transfer function G(s). Moreover, the result of the function G(s) is subtracted from 1. The second heading signal is only subjected by the second filter means  53  to a filtering with a transfer function G(s). The output of the filter means  52 ,  53  is then summed at the summing point  54 , resulting in the sum x(t). Such a complementary filtering allows to filter the noise without distorting the signal. 
     The signal output by the summing point  54  thus reflects very closely the true heading of the mobile phone at point of time t, and a corresponding information can be presented on the display of the mobile phone. 
       FIG. 6  presents a more concrete implementation of a complementary filtering based on the use of an angular accelerometer for compensating magnetic field disturbances in the signals of a magnetometer.  FIG. 6  is more specifically a block diagram of a complementary filter for one compass plane that is based on a two axis magnetometer and an angular accelerometer. A similar implementation is required for all three directions. 
     The block diagram of  FIG. 6  comprises two blocks  61 ,  62  representing measurement values m x , m y  of a 3D magnetometer in a first direction x and a second direction y, respectively. The two blocks  61 ,  62  are connected to a block  63  representing compass functions. The output of this block  63  is connected on the one hand via a block representing a derivator  64  to a first summing point  65  and on the other hand to a second summing point  66 . The block diagram moreover comprises a block  67  representing measurement values              xy  of an angular accelerometer. This block  67  is connected to an integrator  68  and further to the first summing point  65 . The output of the first summing point  65  is connected to a block representing an adaptive filter  69 . The output of block  69  is connected as well to the second summing point  66 . A dashed line separates the sensor related blocks  61 ,  62  and  67  on the left hand side from the other, digital signal processing related blocks on the right hand side.
     The compass signal θ xy  that is calculated in block  63  from the magnetometer values m x , m y  is differentiated in the derivator  64  with respect to time in order to remove the constant field value. The resulting value indicates the angular velocity based on the magnetic field, but includes high frequency disturbances. The corresponding angular acceleration signal              xy  is integrated in the integrator  68 . The resulting value indicates the true angular velocity based on the acceleration of the mobile phone, but comprises a low frequency drift. The time constants of derivator  64  and integrator  68  are matched.
     The two signals {dot over (θ)} xy  output by the derivator  64  and the integrator  68  are compared by means of the summing point  65  in order to separate the disturbances and the low frequency drift of the true angular velocity. The summing point  65  subtracts more specifically the value obtained from the derivator  64  from the value obtained from the integrator  68 . The signal is then passed through the adaptive filter  65 . The adaptive filter applies a high-pass filtering on the received signal in order to separate the disturbances of the signal. The disturbances are further integrated in the adaptive filter  65  in order to obtain an estimate of the angular error of the device for the inertial navigation purposes. 
     The high-pass filtered estimate of the angular error is then subtracted by the second summing point  66  from the compass heading information θ xy  including disturbances, which is output by block  63 . The output of the second summing point  66  is thus a corrected compass heading θ xy,corr  for one compass plane. 
     The system of  FIG. 6  can be further improved by using adaptive filters, such as Kalman filters, for the error signal processing. 
     It is to be noted that the described embodiments constitute only selected ones of a variety of possible embodiments of the invention.

Technology Classification (CPC): 7