Method for estimating relative clock frequency offsets to improve radio ranging errors
View Patent ↗A method and system improves two-way radio ranging accuracy by estimating a relative clock frequency offset between a first clock X of a first transceiver and a second clock Y a second transceiver. The first transceiver transmits a first packet at time t 0 received by the second transceiver at a time t 1 . The second transceiver transmits a second packet at a time t 2 received by first transceiver at a time t 3 . The second transceiver transmits a third packet at a time t 4 received at a time t 5 . The relative clock frequency offset is then Δ f XY ′ ≅ 2 f ( N 24 Y - N 35 X ) N 24 Y + N 35 X , where f is a nominal clock frequency of the first and second clocks, N Y 24 is a measured first delay between times t 2 and t 4 of the second clock, N X 35 is a measured second delay between times t 3 and t 5 of the first clock X.
1. A method for improving two-way radio ranging accuracy by estimating a relative clock frequency offset between a first clock X of a first transceiver and a second clock Y a second transceiver, comprising:
transmitting, by the first transceiver, a first packet at time t 0 of the first clock X;
receiving, by the second transceiver, the first packet at a time t 1 of the second clock Y;
transmitting, by the second transceiver, a second packet at a time t 2 of the second clock;
receiving, by the first transceiver, the second packet at a time t 3 of the first clock X;
transmitting, by the second transceiver, a third packet at a time t 4 of the second clock Y;
receiving, by the first transceiver, the third packet at a time t 5 of the first clock X, and calculating the relative clock frequency offset by the first transceiver in which the relative clock frequency offset is
Δ
f
XY
′
≅
2
f
(
N
24
Y
-
N
35
X
)
N
24
Y
+
N
35
X
,
where f is a nominal clock frequency of the first and second clocks, N Y 24 is a measured first delay between times t 2 and t 4 of the second clock, N X 35 is a measured second delay between times t 3 and t 5 of the first clock X; and
canceling an effect of channel impulse response, RF circuit and baseband circuit imperfection while determining the relative clock frequency offset.
2. The method of claim 1 , further comprising:
measuring a distance between the first transceiver and the second transceiver based on the relative clock frequency offset.
3. The method of claim 1 , in which the first delay is predetermined by a network in which the first and second transceivers operate.
4. The method of claim 1 , in which the first delay is predetermined by the second transceiver and transmitted in the second packet.
5. The method of claim 1 , in which the first delay is transmitted in the second packet.
6. The method of claim 1 , in which the first delay is transmitted by the second transceiver to the first transceiver in the third packet.
7. The method of claim 1 , in which a structure of the first and second packets complies with a communications standard.
8. The method of claim 1 , further comprising:
increasing the first delay to reduce quantization errors.
9. The method of claim 1 , in which an estimated flight-time of the signals between the first and second transceivers is
t
p
C
=
1
2
(
t
03
X
-
t
12
Y
·
(
1
-
Δ
f
XY
′
f
)
)
,
in which t X 03 =t 3 −t o measured by the first clock X, and t Y 12 =t 2 −t 1 measured by clock Y.
10. A system for improving two-way radio ranging accuracy by estimating a relative clock frequency offset between a first clock X of a first transceiver and a second clock Y a second transceiver, comprising:
a first transceiver transmits a first packet at time t 0 of a first clock X;
a second transceiver receives the first packet at a time t 1 of a second clock Y, and in which the second transceiver transmits a second packet at a time t 2 of the second clock, which is received by the first transceiver at a time t 3 of the first clock X, and in which the second transceiver transmit a third packet at a time t 4 of the second clock Y, which is received by the first transceiver at a time t 5 of the first clock X, and the first transceiver calculates the relative clock frequency offset in which the relative clock frequency offset is
Δ
f
XY
′
≅
2
f
(
N
24
Y
-
N
35
X
)
N
24
Y
+
N
35
X
,
where f is a nominal clock frequency of the first and second clocks, N Y 24 is a measured first delay between times t 2 and t 4 of the second clock, N X 35 is a measured second delay between times t 3 and t 5 of the first clock X, wherein an effect of channel impulse response, RF circuit and baseband circuit imperfection is canceled while determining the relative clock frequency offset.