Accurate short range positioning with wireless signals
Positioning determination of a communication device in a wireless communication network is supported by a positioning device receiving [ 230 ] tight synchronization signals from a master positioning cell; determining [ 232 ] therefrom a plurality of time differences between their actual and theoretical times of arrival; synchronizing [ 234 ] a positioning cell clock based on the received tight synchronization signals adjusted by the time differences; and emitting [ 236 ] to the communication device a positioning signal at a time determined by the synchronization. The positioning signal includes an identifier of the positioning cell, and it is transmitted so as not to interfere with positioning pilot signals transmitted by the wireless communication network. The positioning device may alternatively receive synchronization signals from another positioning cell instead of a master positioning cell.
1. A method implemented by a positioning cell for supporting positioning determination of a communication device in a wireless communication network, the method comprising:
receiving by the positioning cell from a master positioning cell a tight synchronization signal, wherein the positioning cell is in direct line-of-sight to the master positioning cell;
determining by the positioning cell a time difference between time of arrival of the tight synchronization signal and theoretical time of arrival of the tight synchronization signal, where the theoretical time of arrival is corrected by theoretical time of flight along a direct line-of-sight path from the master positioning cell to the positioning cell;
synchronizing the positioning cell based on the received tight synchronization signal adjusted by the time difference, wherein the synchronizing comprises synchronizing a clock in the positioning cell;
emitting by the positioning cell to the communication device in the wireless communication network a positioning signal at a time determined by the synchronized clock; wherein the positioning signal comprises data indicative of an identifier of the positioning cell.
2. The method of claim 1 further comprising:
receiving by the positioning cell positioning signals transmitted from two adjacent positioning cells in direct line-of-sight with the positioning cell;
measuring by the positioning cell a drift error between the positioning signals of the two adjacent positioning cells, wherein the drift error is determined from a difference between estimated times of arrival of the positioning signals and theoretical times of flight of the positioning signals; and
transmitting by the positioning cell the drift error to the adjacent positioning cells, whereby the adjacent positioning cells can use the drift error for calibration.
3. The method of claim 1 wherein the tight synchronization signal received from the master positioning cell is not synchronized to an external system.
4. The method of claim 1 wherein the tight synchronization signal received from the master positioning cell is synchronized by the master positioning cell to synchronization signals from another master positioning cell, or to an external system.
5. The method of claim 1 wherein emitting the positioning signal comprises emitting the positioning signal after a time shift following reception of the received synchronization signal, wherein the time shift is a multiple of a predetermined unit of time longer than a longest expected time of flight between the positioning cell and the communication device.
6. The method of claim 1 wherein emitting the positioning signal comprises emitting the positioning signal using an orthogonal time domain cover code.
7. The method of claim 1 wherein emitting the positioning signal comprises emitting the positioning signal using a cyclic shift per symbol in time domain.
8. The method of claim 1 wherein emitting the positioning signal comprises emitting the positioning signal using a recycled PCI of a macro cell.
9. The method of claim 1 wherein emitting the positioning signal comprises emitting the positioning signal within 1 second of receiving the tight synchronization signal.
10. The method of claim 1 wherein emitting the positioning signal comprises emitting the positioning signal periodically at a predetermined repetition period.
11. The method of claim 5 further comprising emitting dummy data prior to emitting the positioning signal, so as to reserve an LBT type medium.