METHOD AND APPARATUS FOR DETERMINING PROPAGATION DELAY
Embodiments of the present invention provide a method of determining a propagation delay of wireless communications between wireless network devices, comprising exchanging first and second messages with a wireless network device; determining first time information based upon the exchange of the first and second messages; receiving second time information from the wireless network device, the second time information based upon the exchange of the first and second messages; and determining a propagation delay based upon the first and second time information.
1 . A method of determining a propagation delay of wireless communications between wireless network devices, comprising:
exchanging first and second messages with a wireless network device;
determining first time information based upon the exchange of the first and second messages;
receiving second time information from the wireless network device, the second time information based upon the exchange of the first and second messages; and
determining a propagation delay based upon the first and second time information.
2 . The method of claim 1 , wherein the first time information indicates a time between sending the first message and receiving the second message and the second time information indicates a time between receiving the first message and sending the second message.
3 . The method of claim 2 , wherein the first and second time information includes a portion of a clock period between the respective events.
4 . The method of claim 2 , wherein the propagation delay is determined by:
t
pd
=
(
t
tA
-
t
rB
)
2
wherein the first time information is tA, the second time information is tB, and the propagation delay is t pd .
5 . The method of claim 1 , comprising:
exchanging two further messages with the wireless network device;
determining third time information based upon the exchange of the two further messages;
receiving fourth time information from the wireless network device, the fourth time information based upon the exchange of the two further messages; and
determining a mean propagation delay of the propagation delay of the first and second messages, and a propagation delay of the two further messages based upon the third and fourth time information.
6 . The method of claim 5 , wherein the third time information indicates a time between receiving a first of the two further messages and transmitting a second of the two further messages and the fourth time information indicates a time between sending the first of the two further message and receiving the second of the two further messages.
7 . The method of claim 6 , wherein the propagation delay of the two further messages is determined according to the equation:
t
pd
=
(
t
tB
-
t
rA
)
2
wherein the third time information is t rA , the fourth time information is t tB , and the propagation delay of the two further messages is t pd .
8 . A wireless network device, comprising:
means for wirelessly exchanging first and second messages with another wireless network device; and
means for determining a first time period based upon the exchange of first and second messages; and
means for determining a propagation delay based upon the first time period and information indicative of a second time period received from the other wireless network device.
9 . The wireless network device of claim 8 , wherein the means for determining the first time period is arranged to determine the first time period between sending the first message and receiving the second message.
10 . The wireless network device of claim 9 , wherein the means for determining the first time period is arranged to determine the first time period including a fraction of a clock period.
11 . The wireless network device of claim 8 , wherein the means for determining the propagation delay is arranged to determine the propagation delay according to:
t
pd
=
(
t
tA
-
t
rB
)
2
wherein the first time information is t tA , the second time information is t rB , and the propagation delay is t pd .
12 . The wireless network device of claim 8 , comprising:
means for wirelessly exchanging two further messages with the other wireless network device;
means for determining a third time period based upon the exchange of the two further messages; and
means for determining the propagation delay based upon the first time period, the information indicative of the second time period, the third time period and information indicative of a fourth time period received from the other wireless network device.
13 . A wireless network, comprising:
a first node arranged to wirelessly exchange first and second communications with a second node;
wherein the first node is arranged to determine first time information based upon the exchange of the first and second communications;
the second node is arranged to determine second time information based upon the first and second communications and to transmit a third communication to the first node containing the second time information; and
the first node is arranged to determine a propagation delay between the first and second nodes according to the first and second time information.
14 . The wireless network of claim 13 , wherein the first time information indicates a duration between the first node transmitting the first communication and receiving the second communication from the second node and the second time information indicates a duration between the second node receiving the first communication and transmitting the second communication.
15 . The wireless network of claim 14 , wherein the first node is arranged to determine the first time information including a fraction of a clock cycle between transmitting the first communication and receiving the second communication from the second node.
16 . The wireless network of claim 14 , wherein the first node is arranged to determine the propagation delay according to the equation:
t
pd
=
(
t
tA
-
t
rB
)
2
wherein the first time information is t tA , the second time information is t rB , and the propagation delay is t pd .
17 . The wireless network of claim 13 , wherein:
the first and second nodes are arranged to exchange fourth and fifth communications;
the first node is arranged to determine third time information based upon the exchange of the fourth and fifth communications;
the second node is arranged to determine fourth time information based upon the exchange of the fourth and fifth communications and to transmit a sixth communication to the first node containing the fourth time information;
the first node is arranged to determine a mean propagation delay based upon the first, second, third and fourth time information.
18 . The wireless network of claim 17 , wherein the third time information indicates a time between the first node receiving the fourth communication and transmitting the fifth communication and the fourth time information indicates a time between the second node transmitting the fourth communication and receiving the fifth communication.
19 . The wireless network of claim 18 , wherein the first node is arranged to determine a propagation delay of the fourth and fifth communications according to the equation:
t
pd
=
(
t
tB
-
t
rA
)
2
wherein the third time information is t rA , the fourth time information is t tB , and the propagation delay is t pd .
20 . The wireless network of claim 13 , wherein the second node is a mobile node and the first node is arranged to determine a distance to the mobile node according to the propagation delay.