Method for geopositioning mobile units moving around inside a closed structure
A method of positioning a group of subordinate communications units relative to a coordinating communications unit, the method comprising the following steps: the coordinating unit transmitting a specific identification table to each subordinate unit; each unit transmitting its UWB signature; each unit analyzing the received UWB signatures and determining the distances between that unit and each of the other units; each subordinate unit transmitting to the coordinating unit the distances between that subordinate unit and each of the other units; and the coordinating unit determining the relative positions of the subordinate units.
1. A method of positioning a group of subordinate communications units relative to a coordinating communications unit, the group comprising at least first, second, third, and fourth subordinate communications units, the coordinating communications unit and the subordinate communications units being movable relative to one another, each communications unit having a UWB transceiver and digital wireless communications means for communicating with the coordinating unit, each subordinate unit including an internal clock synchronized with the clock of the coordinating unit in order to define a shared communications period the method comprising the following steps:
during a preparatory stage, the coordinating unit transmitting to each subordinate unit via the wireless digital communications means a specific identification table comprising an identifier, a UWB signature, and a transmission delay duration, and communicating, via the wireless digital communications means, identification tables for each unit to the other subordinate units; and
during an operative stage:
each unit transmitting its UWB signature, this transmission taking place after the transmission delay duration has elapsed as measured from the beginning of the communications period;
each unit analyzing the UWB signatures transmitted by the other units and determining the distances separating that unit from each of the other units;
each subordinate unit transmitting to the coordinating unit the distances between that subordinate unit and each of the other units, this transmission taking place by using the wireless digital communications means; and
the coordinating unit determining the relative positions of the subordinate units.
2. The method according to claim 1 , wherein the coordinating unit has geolocation means for determining its position in a terrestrial reference frame, and the method includes an additional step of determining the relative positions of the subordinate units relative to a terrestrial reference frame.
3. The method according to claim 1 , including a prior step of determining the relative position of a subordinate unit relative to the coordinating unit, in which step the subordinate unit is positioned at a reference point of known position relative to the coordinating unit.
4. The positioning method according to claim 1 , wherein the step of the coordinating unit determining the relative positions of the subordinate units includes a step of optimizing a cost function (C 1 , C 2 ) corresponding to one of the following expressions:
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in which:
x k , y k , and z k are the coordinates of the unit k of position that is to be determined in the coordinate system associated with the unit 50 ;
d n is the distance between the unit k and the unit n;
x n , y n , and z n are the coordinates of the unit n at the distance d n from the unit k; and
w n is a weighting coefficient associated with the measured reception power of the signal coming from the node of index n.
5. The method according to claim 1 , including a prior step of determining the position of a subordinate unit relative to the coordinating unit, during which the subordinate unit remains stationary, the coordinating unit moving in a zone containing the subordinate unit, and determining the position of the subordinate unit by triangulation on the basis of UWB transmissions.
6. The method according to claim 1 , wherein the internal clocks of the subordinate units are synchronized using the periodic transmission of a synchronizing signal by the coordinating unit.
7. The method according to claim 6 , wherein the synchronizing signal is transmitted using the wireless communications means.
8. The method according to claim 7 , wherein the coordinating unit is provided with a GPS receiver, and the internal clock of the main unit corresponds to the clock of the GPS receiver.
9. The method according to claim 6 , wherein the coordinating unit is provided with a GPS receiver, and the internal clock of the main unit corresponds to the clock of the GPS receiver.
10. The method according to claim 1 , wherein the units include means for evaluating altitude, and the method includes an additional step of determining the altitudes of the subordinate units relative to the coordinating unit.
11. A positioning device comprising data processor means and storage means, an internal clock, a UWB transceiver, and wireless digital communications means, the device being characterized in that wherein it is arranged to perform the method according to claim 1 .
12. The positioning device according to claim 11 , including a GPS receiver.