FR2897424A1 - 888 Mobile station e.g. cellular telephone, direction, speed and position determining method for terrestrial positioning system, involves calculating projection of acceleration of station on plane perpendicular to gravitation - Google Patents

888 Mobile station e.g. cellular telephone, direction, speed and position determining method for terrestrial positioning system, involves calculating projection of acceleration of station on plane perpendicular to gravitation Download PDF

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FR2897424A1
FR2897424A1 FR0601224A FR0601224A FR2897424A1 FR 2897424 A1 FR2897424 A1 FR 2897424A1 FR 0601224 A FR0601224 A FR 0601224A FR 0601224 A FR0601224 A FR 0601224A FR 2897424 A1 FR2897424 A1 FR 2897424A1
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mobile station
characterized
reference
method according
rotation
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Jean Leveque
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Jean Leveque
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01CMEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C21/00Navigation; Navigational instruments not provided for in preceding groups G01C1/00-G01C19/00
    • G01C21/10Navigation; Navigational instruments not provided for in preceding groups G01C1/00-G01C19/00 by using measurements of speed or acceleration
    • G01C21/12Navigation; Navigational instruments not provided for in preceding groups G01C1/00-G01C19/00 by using measurements of speed or acceleration executed aboard the object being navigated; Dead reckoning
    • G01C21/16Navigation; Navigational instruments not provided for in preceding groups G01C1/00-G01C19/00 by using measurements of speed or acceleration executed aboard the object being navigated; Dead reckoning by integrating acceleration or speed, i.e. inertial navigation
    • G01C21/165Navigation; Navigational instruments not provided for in preceding groups G01C1/00-G01C19/00 by using measurements of speed or acceleration executed aboard the object being navigated; Dead reckoning by integrating acceleration or speed, i.e. inertial navigation combined with non-inertial navigation instruments

Abstract

The present invention details the operation of an inertial navigation system for a mobile station (cell phones, electronic organizers, etc.) whose operation is based solely on accelerometers. This invention is intended to supplement in real time the information given by a primary positioning system (GPS) and thus form a hybrid navigation system for mobile station.

Description

Technical Field of the Invention The present invention relates to the

  field of land positioning systems. More specifically, this system is an inertial captive preservative composed solely of three three-dimensional accelerometers, electronic components known by the abbreviation of M.E.M.S (Micro Electro Mechanical Systems). This invention is intended to be used in conjunction with a G.P.S receiver, or any assimilated system capable of giving an absolute position, thereby forming a hybrid navigation system. Small in size, this inertial positioning system can be integrated into personal electronic assistants, pocket computers or cell phones. These three types of products will be referred to as the mobile station. 2 State of the art Several types of positioning systems exist: 1. Inertial platforms composed of a mechanical or optical gyroscope and accelerometers, giving the distance traveled by double integration and a fixed direction over time . 2. GPS (Global Positioning System) whose operating principle is based on the use of satellite networks to locate the user in longitude, latitude and altitude on the Earth's surface with a theoretical accuracy of about 20 meters . 3. Hybrid positioning system based on these last two inventions, and intended to precisely determine (accuracy less than 5 meters) the trajectory of moving vehicles. 4. Positioning system by triangulation. This method is based on the use of cell phone transmitter networks to determine the user's position within the network. The accuracy of such a system is of the order of 100 meters.

  The processes giving the best precisions are the hybrid positioning systems, whose use today is essentially military. There are a few civilian applications most likely to be used in the automotive industry. Nevertheless, the large size of these products does not allow them to be used for mobile stations. More precisely in the field of application of the invention, the patents whose publication numbers are WO 2004/001337 and US 2002/0021245 explain the operation of an inertial positioning system for a mobile station composed of accelerometers, magnetometers and inclinometers.

  The present invention has the following objective: To propose an inertial positioning system using only accelerometers. In contrast to the inventions in both patents cited this invention has the advantage of not being sensitive to the magnetic field of the mobile station. SUMMARY OF THE INVENTION The object of the present invention is to develop a method, by means of an inertial navigation device, which can determine the instantaneous speed, the distance traveled, as well as the direction relative to a direction. reference of a mobile station. The mobile station is thus composed of an inertial navigation device and a primary navigation system (Figure 0). The underlying method comprises the following steps: 1. Performing an attitude calculation to determine the coordinates of the acceleration of the mobile station in a fixed repository over time. 2. Algorithm for determining a first direction, subsequently used by the inertial navigation system. is 3. Projection of acceleration in a fixed reference over time, perpendicular to gravitation. This is followed by a double integration to determine the instantaneous speed and the distance traveled. In the case where the primary navigation system is available, information from both types of navigation systems can be processed by a Kalman filter. This provides better accuracy of the position, speed and direction of the mobile station. Subsequently, only the operation of the inertial unit will be considered as well as the detail of its operation within the mobile station. DESCRIPTION OF THE FIGURES The full description of the invention and thereafter the claims refer to the drawings, figures and numbers which annotate them, included in this document.

  Figure 0 is a simplified schematic representation of the role of the invention in the mobile station.

  Figure 1 represents the modeling of a map of an urban environment by a network of nodes composed of 5 branches.

  Figure 2A and Figure 2B show the algorithm of operation of the invention. Figure 3 shows the algorithm for performing the attitude calculation of the mobile station.

  Figure 4 shows the algorithm for acquiring the acceleration of the mobile station in the fixed frame of reference.

  Figure 5 is a diagram showing the physical organization of the various electronic components that make up the invention.

  Figure 6 is a diagram showing the organization and role of all the electronic components that constitute the invention.

  DETAILED DESCRIPTION OF THE EMBODIMENT OF THE INVENTION The proposed invention is an inertial navigation device consisting solely of three-dimensional accelerometers for a mobile station 888 (FIG. 0). This invention can thus determine the instantaneous speed, the distance traveled, as well as the direction relative to a reference direction between two distinct points in a route. s The route is calculated from the modeling of a map in the form of a network (Figure 1.) consisting of a set of branches. A branch includes the following information: 1. Coordinates of the origin and endpoints. 2. Distance between the origin point and the end point. 3. Angles that exist between a given branch and branches that are contiguous to it. Io 4. Name of the street to which the branch corresponds. Depending on the initial (or final) position of the user of the mobile station, the network can be easily modified by inserting new points. These data on the algorithm that serves as an interface between the invention and the user are sufficient to subsequently understand the operation of the invention, therefore we will not go into more detail of the program. The detailed operation of the invention is illustrated with FIGS. 2A and 2B. Initially (Figure 2A) Earth's gravity is measured while the mobile station is at rest (201). It can be considered that this measure is acquired by the system at the instant tao. At this same moment, the attitude calculation of the mobile station is started (202). Then the user must give the information on the route he wants to follow (203) with for example the data on the starting point and the point of arrival. Next, the mobile station determines whether the primary navigation system is available (204). If this is the case, an updating of the data of the departure is carried out (205). In the opposite case, the starting position is evaluated (206) from the information given by the user. At this stage, the network of nodes that models the urban environment can be modified according to the information received. The system then proceeds (207) to a first route calculation. After that, the system determines the distance D which separates the user from the nearest next node belonging to the route (208). The system then requests the user to move normally along the axis of the street in which he is (belonging to the route) to the next node (209). The user can indistinctly go down or up the street. After a confirmation step with the user (210), the algorithm for determining the reference direction is started (211). At the same time, the speed and the distance traveled are calculated.

  It is then determined whether new data received by the primary navigation system is available and whether the data of the starting point is accurate (212). If one of the two conditions is not verified, after the acquisition of the distance traveled (215) we compare it to the distance D. If the distance traveled is not worth D we return to the previous step 212. s If the distance traveled is D, the user is asked if a new node is reached (217). If this is not the case (Figure 2B), a new route calculation (218) is performed. A variant of step 217 is possible by asking the user whether the distance separating him from the next node is greater than a reference distance. If step 212 is checked, the next node to which the user is pointing is determined (213). In the case where the next node does not belong to the route (214), another route is computed that includes it (218). Steps 201 to 217 thus make it possible to initialize the attitude calculation of the mobile station, to determine a reference direction and to adjust the user's route according to the initial direction he has chosen. After this adjustment, the distance and speed are calculated to be made available to the user continuously. If a new node is reached (220) and if it is not the endpoint (221) the user is notified of the next direction to take (223). After acquisition of the new direction taken, it is compared (225) with the known theoretical direction from the data of the network. If the direction is correct, it returns to step 219 otherwise the calculation of a new route is made (226) before proceeding to step 219. Steps 219 to 226 are performed until step 221 be true. During the steps 218 25 to 226 the user is guided by the inertial navigation system without any intervention on his part being necessary. Let's look in more detail at the attitude calculation of the mobile station described in Figures 3 and 4. The sensors of the navigation system are directly located on the main PCB IC (Figure 5) of the mobile station 888. The assembly comprises three three-dimensional accelerometers. We have an accelerometer ao which reliably occupies the center of symmetry of the mobile station 888 in C on the printed circuit C1 (Figure 5). In addition two other accelerometers ai and a2 were arranged. The accelerometers used are readily available on the market for a sensitivity close to the mg (102 m.s-2). All the signals emitted by these sensors 610 (FIG. 6) are conditioned by filters and then converted (620) from analog to digital. The data is then processed continuously by a processor and stored (630) temporarily. It should also be emphasized that the accuracy of the results of the attitude calculation depends on the alignment of the axes of the accelerometer ao with the accelerometers ai and a2.

  Starting hypothesis for the computation: One is as previously in the case where the system functions since the moment tdo. We will detail the process between the instants tdA and td, in addition, we suppose known the matrix of passage which makes it possible to determine the coordinates of the acceleration in ao in R ~ (x, y, z) (Figure 5) at the moment tdo from the reference Rc (x, y-, z-) at time td5. This matrix will be named later Rk_, (A8, 01d, _,). Let C and Rc (x, y, z) respectively be the center of symmetry of the mobile station and the center reference C, of axes x, y, z (Figure 5) linked to the mobile station between instants td, and td,. The relative movement of the mobile station around the center of symmetry between these two moments will be explained and justified thereafter. io Let Ro (x, p, z) be a terrestrial reference of center O of arbitrary orientation and in Galilean first approximation. The detail of the calculation is as follows: The accelerometer ao is arranged in C, with each of its axes following xx 'yy' and zz '. The accelerometer has, is arranged on the axis xx '(Figure 5.), a2 on the axis yy'. For reasons of convenience, the two peripheral accelerometers have the same orientation as ao. Subsequently, we will treat the computation of the acceleration in a, and we will deduce that of a2 for a moment t = t; between tdk and tdA. According to the law of composition of the velocities at a, we have: dOC + R ~ dt + C2R, Ro, Ro where V is the velocity at a, in the reference Ro (X, y, Z). V, - 1 is the speed at a, in the reference frame Rc (x, y, z). This component is zero. R, is the speed of the center of symmetry of the mobile station in the reference frame Ro (X, @, Z) Ro S2 Rc / Ro is the rotation vector of the mobile station with respect to the terrestrial reference and d, is the distance between C and a ,. Deriving the previous expression with respect to time in Ro (X, Y, Z) we obtain: V Ra = d V ~ + dnnd'x + ORc / R0 nd (of x) d1 dt R0 dt dt Or always in using the law on the composition of the velocities we have: = d (d, x) + SLR, / R0 nd, x dt Ro R, dOC dt Rp d (d, x) dt d 1 _ d -1 + dç nd x + nR / RA (d (of x) dt Ro dt Ro dt `dt From where + êRe / Ro Ad, x) Re _ d (d, x) Or in Rc (x, y, z) dt is zero. So finally: Rc -d Ro dt c = d-nd, x + ûRe / R0 A (QRc_ / R0 Ad, x) Ro dt d dd d ù dt v RO is the acceleration vector in ai, in the terrestrial frame. d ùVc is the acceleration vector of the center of symmetry C of the mobile station Mans Preferential terrestrial. The vectors of accelerations of VRo 'and Vc Ro, which are quantities directly measured with the three-dimensional accelerometers respectively ao, ai and a2, cesd Ro and also dt Va2

  vectors will be noted respectively ao, al, a2 to lighten the writing. Subsequently, the rotation vector n Rc / Ro will be denoted by: / R = and_ 0.4 With cos; = y, x + y2 y + y3 z and E y, = I defines in Rc (x, y, z) for t = t ;. and is the instantaneous angular velocity around COI; , in t = t ;. Developing the expression of the difference of the acceleration vectors we find: a, ùao = ùd, Bt 2 (y2 + s) x + d, (Y, Y2et; 2 + Y3et; + d, (YiY3et2 ùY2Bt;) z Similarly for a2 where we have: ls a2 ùa0 = d2 (y, y2BI, 2 + y30, i) xu2 2 0ii + Ys). + d2 (Y2y30,; 2 + r1Br,) z The difference a, where ao is contained in a plane perpendicular to vector û. Moreover, it is obvious that the unit vector carrying S2 is the axis of rotation of the mobile station and exists uniquely between two instants tdk and tdk for which a, ùao and a2 ùa0 are zero. The proof of this proposition is as follows: Suppose that the mobile station is subject to two successive rotations of distinct axes. Consider the moment when the first rotation ends and the second begins. According to the expression of al ù ao that it is contained in a plane orthogonal to the axis of rotation.

  So whatever the point j belongs to C.I, ai - ao is perpendicular to the axis of rotation. This property must also be true for the second rotation. But the intersection of two distinct planes is a straight line, necessarily for the property to remain true ai - ao is zero at the instant when the first rotation ends and the second begins. Therefore, as long as t> tdk- and a, -ao and a2 -ao different from the null vector, the coordinates of the col, and B for each moment will be calculated using only one of the following methods, and whatever may be that td S t; <_ td ~ 1. If for t = t; (a, - ao) .x = 0 necessarily y2 = y3 = 0 y, = 1 and tr = x 2. If for t = t; (a2 - ao) .y = 0 necessarily y, = y3 = 0 and col, Y io 3. For a, - ao ≠ 0 and a2 - ao ≠ 0 but (a, - ao) A (a2 - ao) = 0 the axis of rotation is in the plane (x, y) Oh, is such that: - (a, - ao) nza, ù a 4. Otherwise in all other cases we have - (a, ùa,) A (a2 -ao) = (a, -ao) ^ (a2 -a,) Once the axis of the determined rotation can be calculated the value of e ,, for each moment t; between tdk and tdk We have: (a, ù a,) .x di (Yz + Ya) Similarly, for the acceleration at a2, projecting the following result y:

  (a, ùao) • Y B = d 2 (Y? + Y3)

  According to the definition of Tax W ,, at least one of the two expressions of Bt is valid. These data will allow us to determine the components of the acceleration in ao in R (x, y, z) at the instant t ,, from the 15 B, 1 20 measurements for any instant 4 To fulfill this task, consider the instant t1, the first instant for which an expression of the rotation vector i1 can be calculated, in Rc (x, y, z). We consider here the case where at most one of the components of wt,, is zero. For this instant, a new base (u ,,,, cor,) is defined in which the vectors ut, and vt, are defined by: The transition matrix between Rc (x, y, z) and (ut,, vt, , col,) for the moment ti is denoted P, with: a, Ar Yi P = a2 / Q2 Y2 \ a3 / 33 Y3 / The columns are the coordinates of the vectors of the base (ut,, wt,) expressed in the base Rc (x, y, z). In the base (u ,,, vt,, wt,) the rotation of an angle Aet. between instants i and t i, around COI, s writes: (cos AB, sin 3, B, 0 "R ', coi,) = sin cos A0 ,, 0 0 0 1) Aer, is calculated in integrating by the trapezoid formula we have: e 3, B = E '+ Bt (tk -tk_,) k = 2 2

  Similarly, in the base ut, v,, cor,) the rotation of an angle ù A and between times t1 and tdk, around oh, is written: cosM ,, sin A9 ,, ù sin 3.0, , cos A8 ,, 0 0 0 1/15 R '(ùO Br, co ,,) = with B, A8, = 2 (t,) Now these rotation matrices are also base change matrices. Indeed, the columns of the matrix R '(48,,, w ,,) are the coordinates of the base (u t,) for t = t; expressed in the base

  (ut,,) for t = t1. Similarly, the columns of the matrix R '(- O8,, wt) are the coordinates of the base (ut ,, k, v, k, w, Jk i) for t = tdt expressed in the base (ut,, vt,, wt,) for t = t ,.

  s From where PR '(A8,,) .P-' is the transition matrix of Rc, (x, y, z) for t = t, to Rc (x, y, z) for t = t; and PR '(-48,, ah,) .P-' is the transition matrix of Rc (x, y, z) for t = t, to t = tdk. From all that precedes the components of acceleration in ao verify: ao. ao. ## EQU1 ## where

  ao = P.R '(L8 ,,, wt,). R' (L, B,, w ,,) .P- 'ao. Moreover, knowing from the starting hypothesis Rk_,), we have: (a ao = Rk_, (z 9, wtdk_,) PR '(08,) .P-' ao,. \ Ao = / Rc'do \ ao: / R pa, = P.R '(È8t;, wa) • P-' ao ao: / Reu ;, (*) aor are the components of the acceleration measured in Rc (x, y, z). where 15 and ao, ao,. R rueo are the components of the acceleration computed in Rc (x, y, z) at time tdo.

  In the case where ah, at two of its zero components, the matrix calculation is simpler. The basic change is written:

\ 's ao a0s

  o = Rk_, (~ B, wl ~ k I) .R '(A91i) .R' (O B ,;). ao

  a 'cl, ~> ao with MI, equal to x, y or z.

  It remains for us at this stage to determine the sign of the variation of angle AB for a rotation of the mobile station between tdk and tdk. Two cases arise: 1. The components of 011 are all non-zero we can consider the expression (*) applied to the coordinates of 01, 'To determine the sign of the rotation, the coordinates of calculated thanks to the change of base will have to be identical to those deduced from the measurements for t = tl.

  2. At least one of the components of W1 'is zero, the axis of the rotation is included in one of the (x, y), (x, z) or (y,) planes of the base Rc (x, y , z). We can assume that â (t) is a function of class Cl for t E [tdk, tdk]. We have B (t = td,) = 8 (t = tdk) = 0 necessarily according to the finite increments theorem there exists tM E [tdk, tdk] such that B (t = tM) = 0. So in the neighborhood of tM, B changes sign. The sign of the variation of the angle of rotation

  is deduced from the computation of w. ((ai ù ao), =,; A (agi ù ao) 1 =,;,) with j E {1,2} and tI tM <tj. . Consider the case where y, = 0 to illustrate this property. We then have the remaining components of COI that are invariable over time:

  Whatever is t E [tdk I, tdk] coi = co = yz y + y3 z 20 If we use the expression of a, where ao we find: w ((a, ùao) 1 = 1; A (ai ùa ) 1 = 1;)) = d12y, y, (y2 + yi) (Bl2el, ùâ 81 ;.)

  If the previous expression is negative, necessarily BI; <0 and BIr,> 0 so B (t) is a relative minimum in the vicinity of t = tM. So A9 is negative between t = tdk 1 and t = tdk. Conversely, if the expression

  previous was positive the variation of the angle of rotation between these two instants would be positive. In the case where w, = w = y2y ona: w. ((Ai ù (20), = 1; A (a, ù ao) 1-1 ;,) = di y3 yi (el2 e, 81281 ,,) a For ah = = y3 z we have: w. ((a, ù ao), A (a, ù ao) = d i2Ys (1212, e, ù 6, ZB). For each of these particular cases of rotation, the relation between the sign of the expression and that of 6 is the same as in the case where ah = CO = y2 y + 73. The calculations for the three other possible cases, namely (y, ≠ 0, y2 = 0, y3 = 0) (y, ≠ 0, y2 ≠ 0, y3 = 0) (yi = 0.72 ≠ 0, n ≠ 0), for the writing of Co. and the mixed product associate do not present any particular difficulties, therefore it will not be discussed here.

  The attitude calculation algorithm in Figure 3 is based on the previous calculations. Once the measurement of the gravitation in ao is made at time t = tdo (mobile station initially at rest), the acceleration in al and a2 (300) is measured at the same time. Then a series of tests is performed on al ù ao and a2 ù ao (301 to 303). Step 301 serves to delimit the rotations. This step delimits at the same time the end of a rotation and possibly the beginning of a new one. If for a moment ti and ti.11 al ù ao and a2 ù ao are zero (327) then the returned transition matrix will be the one between the time tdo and ti_1 multiplied by the identity matrix (331). If the test 327 is false then it is the last step of a given rotation. Knowing in this case the sign of the rotation, it remains only to determine the variation of the angle of the last step of this rotation (328) and also calculate the matrix of passage between tdo and ti (329). This matrix is maintained from one iteration to another and transmitted to the algorithm that determines the heading of the mobile station (330). In the case where at least one of the two aj ù ao is non-zero following step 300, then the instantaneous axis of rotation (302 and 303) is determined according to the calculations carried out previously. In the case where these two steps are not satisfied, then the axis of rotation may be z in the y, z (x, z) (304) plane or be a non-zero linear combination of the basic vectors. (X Y Z). The next step 305 is to calculate the absolute value of 9.

  Then it is a question of determining the sign of the rotation. The method employed depends solely on the number of non-zero components of the axis of rotation, namely two (or even one) or three. The coordinates on the axis of rotation and the values of 0 (t) are stored until a relative maximum is reached (314 and 316). Once a relative maximum is known, it is possible to determine the sign of the rotation by calculating the combined product of two measurements of the accelerations ai ù ao, for different instants and in the vicinity of the relative maximum, with the axis of the rotation. (319). Steps 320 to 324 make it possible to restore, by calculation, the transition matrices of Rc (x, y, z) at time t, to Rc (x, y, z) at time t0. The test 302 makes it possible to determine whether the axis is along the vector x or y (311) and to calculate the associated value of 0 (312). If the test 303 is checked then the axis of rotation, included in the plane, is determined in the same manner as that illustrated above. Subsequently the result of steps 326 or 305 are used in the same series of steps (306 to 310 or 313 to 324) as those (x, y described above for calculating the passing matrix of the reference frame Rc (x , y, z) at time t, at tda In all cases, once the steps 309, 329 are completed or after the step 324 is verified, the time step is incremented by one. This attitude allows us to determine the horizontal component of the acceleration at a0 minus gravity, because we recall that the vector a0 is written: 15 ao = g + ac Where g is the terrestrial gravity ac is the acceleration due to movement of the center of symmetry of the mobile station in the terrestrial frame The vector a0 is calculated for t = te and g is measured for t = td, when the system is at rest, Thus, after steps 401, 402 and 403 (Figure 4) possible thanks to the calculation of attitude of the mobile station, if t = tdo one defines a reference in a plane orthogonal to the gravity measured in td0 This base (v, w) must check in t = t4: v.g = 0 where g is the gravity measured for t = tao

  This basis is therefore defined when t = tao. Then projecting on this basis (405) the result of step 403 we obtain the course that follows the mobile station in the repository v, w) for t = tdo. Finally one can perform a double integration (407) of the value of the projection of the acceleration to know the instantaneous speed and the distance traveled by the user. In general, the time step (408) is then incremented to determine the heading, the speed and the distance traveled for t = ti. The present invention thus makes it possible to improve the location of the mobile station initially including a primary positioning system. The addition of an inertial navigation system based solely on accelerometers, on the one hand to give the position of the user when the primary navigation system is unavailable and secondly, this invention can be easily integrated into any mobile station that generates a magnetic field. This allows for example the simultaneous operation of the invention and the use of the network of a cell phone. (

Claims (9)

    claims
  1.   A position determination method using an inertial navigation system for a mobile station, characterized in that it consists of: - determining a reference direction by means of a route initialization algorithm. s - To calculate the attitude of the mobile station. - To calculate the projection of the acceleration of the mobile station on a plane perpendicular to the gravitation along a reference direction.
  2.   2. Method according to claim 1 characterized in that the attitude calculation is performed from the determination of the rotation matrix of the inertial reference of the mobile station. io
  3.   3. Method according to claim 2 characterized in that the determination of the matrix is obtained by calculating the axis of rotation expressed in the reference system of the mobile station and the variation of the associated angle between two consecutive instants where the angular velocity is zero.
  4.   4. Method according to claim 3 characterized in that the variation of the angle of rotation and the coordinates of the axis of the rotation are determined by the computations of the expressions of accelerations with respect to the terrestrial reference expressed in the reference system. inertial.
  5.   5. Method according to claim 4 characterized in that the numerical values of the accelerations are obtained thanks to the data provided by three three-dimensional accelerometers.
  6.   6. Method according to claim 1 characterized in that the projection of the acceleration of the mobile station is performed by a calculation of attitude of the mobile station and on the definition of a reference 20 perpendicular to the gravity.
  7.   7. Method according to claim 6 characterized in that the reference is defined at the beginning of the use of the inertial unit during the measurement of the gravitation effected by the accelerometers.
  8.   8. Method according to claim 1, characterized in that the initialization algorithm is based on the evaluation of the starting data and on an algorithm that allows the acquisition of a reference direction.
  9.   9. Method according to any one of claims 1 or 8 characterized in that the acquisition of the reference direction is based on the taking into account of information given by the user to the mobile station.
FR0601224A 2006-02-13 2006-02-13 888 Mobile station e.g. cellular telephone, direction, speed and position determining method for terrestrial positioning system, involves calculating projection of acceleration of station on plane perpendicular to gravitation Pending FR2897424A1 (en)

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