Arrival-delta position determination
View Patent ↗Embodiments provide an indoor position system that can be used by an mobile device (legacy or non-legacy) without changes at the mobile device. In an embodiment, to use the indoor position system, a user of the mobile device downloads an application to the mobile device, which interfaces with the mobile device's existing wireless radio technology circuitry or module (e.g., WLAN chip) to obtain the position of the mobile device. In one embodiment, the indoor position system includes a plurality of wireless anchors with known positions that are each configured to receive a packet transmitted by the mobile device, time-stamp the packet per the arrival time of the packet, and forward the time-stamped packet to a pre-defined site. At the pre-defined site, the position of the mobile device is computed and sent to the application running on the mobile device.
1. A positioning system, comprising:
radio frequency (RF) circuitry configured to transmit and receive signals; and
processor circuitry, coupled to the RF circuitry, configured to:
receive a time-stamped packet from a first wireless anchor of a plurality of wireless anchors, the time-stamped packet including a first arrival time at the first wireless anchor of a packet transmitted by a mobile device, wherein the first arrival time of the packet is determined based on a clock at the first wireless anchor;
determine a first difference between the first arrival time of the packet and a second arrival time of the packet at a second wireless anchor of the plurality of wireless anchors, wherein the second arrival time of the packet is determined based on a clock at the second wireless anchor; and
compute a position of the mobile device, without time synchronizing the clock at the first wireless anchor with the clock at the second wireless anchor, based at least in part on the first difference and a common time reference that associates time values of the first wireless anchor and the second wireless anchor.
2. The positioning system of claim 1 , wherein the processor circuitry is further configured to:
determine a second difference between the first arrival time of the packet and a third arrival time of the packet at a third wireless anchor of the plurality of wireless anchors; and
determine a third difference between the first arrival time of the packet and a fourth arrival time of the packet at a fourth wireless anchor of the plurality of wireless anchors.
3. The positioning system of claim 2 , wherein the processor circuitry is further configured to compute the position of the mobile device based at least in part on the first, second, and third differences.
4. The positioning system of claim 3 , wherein the processor circuitry is further configured to:
determine first, second, third, and fourth positions of the first, second, third, and fourth wireless anchors respectively; and
perform a multi-lateration calculation using the first, second, third, and fourth positions and the first, second, and third differences to compute the position of the mobile device.
5. The positioning system of claim 1 , wherein the processor circuitry is further configured to:
establish the common time reference; and
determine the first difference between the first arrival time of the packet and the second arrival time of the packet using the common time reference.
6. The positioning system of claim 1 , wherein the processor circuitry is further configured to:
receive a second time-stamped packet from the first wireless anchor, the second time-stamped packet including a third arrival time at the first wireless anchor of a second packet transmitted from a known location; and
receive a third time-stamped packet from the second wireless anchor, the third time-stamped packet including a fourth arrival time at the second wireless anchor of the second packet.
7. The positioning system of claim 6 , wherein the processor circuitry is further configured to:
determine, based on the third arrival time, a first time value associated with the first wireless anchor corresponding to a transmission time of the second packet;
determine, based on the fourth arrival time, a second time value associated with the second wireless anchor corresponding to the transmission time of the second packet; and
associate the first time value with the second time value to establish the common time reference.
8. The positioning system of claim 7 , wherein the processor circuitry is further configured to:
calculate a propagation time of the second packet from the known location to the first wireless anchor; and
subtract the propagation time from the third arrival time of the second packet to determine the first time value associated with the first wireless anchor.
9. The positioning system of claim 6 , wherein the second packet is transmitted from a third wireless anchor of the plurality of wireless anchors.
10. The positioning system of claim 5 , wherein the processor circuitry is further configured to:
establish a second common time reference between the first wireless anchor and the second wireless anchor, the second common time reference being later in time with respect to the common time reference;
determine a difference between the common time reference and the second common time reference; and
calculate a polynomial approximation based on the difference between the common time reference and the second common time reference to determine a common time reference drift value.
11. A method, comprising:
receiving a time-stamped packet from a first wireless anchor of a plurality of wireless anchors, the time-stamped packet including a first arrival time at the first wireless anchor of a packet transmitted by a mobile device, wherein the first arrival time of the packet is determined based on a clock at the first wireless anchor;
determining a first difference between the first arrival time of the packet and a second arrival time of the packet at a second wireless anchor of the plurality of wireless anchors wherein the second arrival time of the packet is determined based on a clock at the second wireless anchor; and
computing a position of the mobile device, without time synchronizing the clock at the first wireless anchor with the clock at the second wireless anchor, based at least in part on the first difference and a common time reference that associates a time value of the first wireless anchor with a time value of the second wireless anchor.
12. The method of claim 11 , further comprising:
determining a second difference between the first arrival time of the packet and a third arrival time of the packet at a third wireless anchor of the plurality of wireless anchors; and
determining a third difference between the first arrival time of the packet and a fourth arrival time of the packet at a fourth wireless anchor of the plurality of wireless anchors.
13. The method of claim 12 , further comprising:
determining first, second, third, and fourth positions of the first, second, third, and fourth wireless anchors respectively; and
performing a multi-lateration calculation using the first, second, third, and fourth positions and the first, second, and third differences to compute the position of the mobile device.
14. The method of claim 11 , further comprising:
establishing the common time reference; and
determining the first difference between the first arrival time of the packet and the second arrival time of the packet using the common time reference.
15. The method of claim 11 , further comprising:
receiving a second time-stamped packet from the first wireless anchor, the second time-stamped packet including a third arrival time at the first wireless anchor of a second packet transmitted from a known location; and
receiving a third time-stamped packet from the second wireless anchor, the third time-stamped packet including a fourth arrival time at the second wireless anchor of the second packet.
16. The method of claim 15 , further comprising:
determining, based on the third arrival time, a first time value associated with the first wireless anchor corresponding to a transmission time of the second packet;
determining, based on the fourth arrival time, a second time value associated with the second wireless anchor corresponding to the transmission time of the second packet; and
associating the first time value with the second time value to establish the common time reference.
17. The method of claim 16 , further comprising:
calculating a propagation time of the second packet from the known location to the first wireless anchor; and
subtracting the propagation time from the third arrival time of the second packet to determine the first time value associated with the first wireless anchor.
18. A positioning system, comprising:
a plurality of wireless anchors, wherein a first wireless anchor of the plurality of wireless anchors is configured to:
receive a packet from a mobile device; and
time-stamp the packet per a first arrival time of the packet, wherein the first arrival time of the packet is determined based on a clock at the first wireless anchor; and
processor circuitry configured to:
receive the time-stamped packet;
determine a first difference between the first arrival time of the packet and a second arrival time of the packet at a second wireless anchor of the plurality of wireless anchors, wherein the second arrival time of the packet is determined based on a clock at the second wireless anchor; and
compute a position of the mobile device, without time synchronizing the clock at the first wireless anchor with the clock at the second wireless anchor, based at least in part on the first difference and a common time reference that associates time values of the first wireless anchor and the second wireless anchor.
19. The positioning system of claim 18 , wherein the processor circuitry is located in the mobile device, a third wireless anchor of the plurality of wireless anchors, or a server.
20. The positioning system of claim 18 , wherein the processor circuitry is further configured to:
determine a second difference between the first arrival time of the packet and a third arrival time of the packet at a third wireless anchor of the plurality of wireless anchors;
determine a third difference between the first arrival time of the packet and a fourth arrival time of the packet at a fourth wireless anchor of the plurality of wireless anchors;
determine first, second, third, and fourth positions of the first, second, third, and fourth wireless anchors respectively; and
perform a multi-lateration calculation using the first, second, third, and fourth positions and the first, second, and third differences to compute the position of the mobile device.