Airframe timestamping technique for point-to-point radio links
An example system comprising a first transceiver configured to receive a request airframe from a second transceiver over a wireless link, the request airframe including a first time indication indicating a first time TS 1 , a second time indication indicating a second time TS 2 that the request airframe was received, generate a respond airframe and including a third time indication indicating a third time TS 3 that the respond airframe is transmitted to the second transceiver, transmit the respond airframe to the second transceiver, provide a timestamp information request to second transceiver, receive a timestamp information response, the timestamp information response including a fourth time indication indicating a fourth time TS 4 , calculate a counter offset using the first time, second time, third time and fourth time as follows: counter offset = ( TS 1 + TS 4 - TS 3 - TS 2 ) 2 , calculate a phase offset based on the counter offset, and correct a phase of the first transceiver.
1 . A method comprising:
receiving, at a first transceiver, a first airframe from a second transceiver over a wireless link of a network, the first airframe including a first time indication indicating a first time TS 1 that the first airframe was transmitted to the first transceiver, the first transceiver and the second transceiver including a first and second counters, respectively;
timestamping a second time indication indicating a second time TS 2 that the first airframe was received;
generating a respond airframe and including within the respond airframe a third time indication indicating a third time TS 3 that the respond airframe is to be transmitted to the second transceiver;
transmitting the respond airframe to the second transceiver;
receiving, from the second transceiver, a fourth time indication indicating a fourth time TS 4 ;
calculating, by the first transceiver, a counter offset using the first time, second time, third time, and fourth time as follows:
counter
offset
=
(
T
S
1
+
T
S
4
-
T
S
3
-
T
S
2
)
2
;
calculating, by the first transceiver, a phase offset based on the counter offset, the calculating including:
determining asymmetry (ASY) in the wireless link, the asymmetry (ASY) in the wireless link comprising round trip radio link path asymmetry corresponding to different modulations for radio ingress and egress based on adaptive coding modulation (ACM) associated with one or more of the first airframe or the response airframe, and
applying the following:
phase
offset
=
(
T
S
1
+
T
S
4
-
T
S
3
-
T
S
2
)
2
±
A
s
y
2
;
and
correcting, by the first transceiver, a phase of the first transceiver based on the calculated phase offset, wherein the calculated phase offset is a result at a physical layer and is caused to be made available to higher layers.
2 . The method of claim 1 , where the first and second counters are synchronized with each other before the counter offset is calculated.
3 . The method of claim 2 , wherein the first counter is a precision time protocol counter.
4 . The method of claim 1 , where the first transceiver and the second transceiver have synchronized frequencies.
5 . The method of claim 1 , wherein the first transceiver generates and transmits the respond airframe after receiving the first airframe.
6 . The method of claim 1 , wherein the first transceiver transmits a timestamp information request to the second transceiver after the respond airframe is received.
7 . The method of claim 1 , further comprising:
receiving from the first transceiver, at least the second time indication;
calculating, by the second transceiver, a counter offset using the first time, second time, third time, and fourth time as follows:
counter
offset
=
(
TS
1
+
TS
4
-
TS
3
-
TS
2
)
2
;
calculating, by the second transceiver, a phase offset based on the counter offset; and
correcting, by the second transceiver, a phase of the second transceiver.
8 . The method of claim 7 , where calculating the phase offset by the first transceiver is not synchronized with calculating the phase offset by the second transceiver.
9 . The method of claim 1 , wherein the wireless link is a microwave link.
10 . The method of claim 1 , wherein the first transceiver and the second transceiver each include a phase lock loop configured to assist in recovery of clock signals using data received over the wireless link of the network.
11 . A method comprising:
generating, by a first transceiver, a first airframe to be sent to a second transceiver over a wireless link of a network, the first airframe including a first time indication indicating a first time TS 1 that the first airframe is to be transmitted by the first transceiver, the first transceiver and the second transceiver including a first and second counters, respectively;
transmitting the first airframe to the second transceiver;
receiving a respond airframe from the second transceiver, the respond airframe including within the respond airframe a third time indication indicating a third time TS 3 that the respond airframe is to be transmitted to the first transceiver;
determining a fourth time indication indicating a fourth time TS 4 that the respond airframe was received;
receiving, from the second transceiver, a second time indication indicating a second time TS 2 that the first airframe was received by the second transceiver;
calculating, by the first transceiver, a counter offset using the first time, second time, third time, and fourth time as follows:
counter
offset
=
(
TS
1
+
TS
4
-
TS
3
-
TS
2
)
2
;
calculating, by the first transceiver, a phase offset based on the counter offset, the calculating including:
determining asymmetry (ASY) in the wireless link, the asymmetry (ASY) in the wireless link comprising asymmetry on a round trip radio link path asymmetry corresponding to different modulations for radio ingress and egress based on adaptive coding modulation (ACM) associated with one or more of the first airframe or the response airframe, and
applying the following:
phase
offset
=
(
TS
1
+
TS
4
-
TS
3
-
TS
2
)
2
±
Asy
2
;
and
correcting, by the first transceiver, a phase of the first transceiver based on the calculated phase offset, wherein the calculated phase offset is a result at a physical layer and is caused to be made available to higher layers.
12 . The method of claim 11 , where the first and second counters are synchronized with each other before the counter offset is calculated.
13 . The method of claim 12 , wherein the first counter is a precision time protocol counter.
14 . The method of claim 11 , where the first transceiver and the second transceiver have synchronized frequencies.
15 . The method of claim 11 , wherein the first transceiver transmits a timestamp information request to the second transceiver after the respond airframe is received.
16 . The method of claim 11 , further comprising:
providing to the second transceiver, at least the fourth time indication;
calculating, by the second transceiver, a counter offset using the first time, second time, third time, and fourth time as follows:
counter
offset
=
(
TS
1
+
TS
4
-
TS
3
-
TS
2
)
2
;
calculating, by the second transceiver, a phase offset based on the counter offset; and
correcting, by the second transceiver, a phase of the second transceiver.
17 . The method of claim 16 , where calculating the phase offset by the first transceiver is not synchronized with calculating the phase offset by the second transceiver.
18 . The method of claim 11 , wherein the first transceiver and the second transceiver each include a phase lock loop configured to assist in recovery of clock signals using data received over the wireless link of the network.
19 . A system comprising:
a first transceiver including memory and a processor, the first transceiver configured to:
receive a first airframe from a second transceiver over a wireless link of a network, the first airframe including a first time indication indicating a first time TS 1 that the first airframe was transmitted to the first transceiver, the first transceiver and the second transceiver including a first and second counters, respectively;
timestamp a second time indication indicating a second time TS 2 that the first airframe was received;
generate a respond airframe and including within the respond airframe a third time indication indicating a third time TS 3 that the respond airframe is to be transmitted to the second transceiver;
transmit the respond airframe to the second transceiver;
receive, from the second transceiver, a fourth time indication indicating a fourth time TS 4 ;
calculate a counter offset using the first time, second time, third time, and fourth time as follows:
counter
offset
=
(
TS
1
+
TS
4
-
TS
3
-
TS
2
)
2
;
calculate a phase offset based on the counter offset, the calculating including:
determining asymmetry (ASY) in the wireless link, the asymmetry (ASY) in the wireless link comprising asymmetry on a round trip radio link path asymmetry corresponding to different modulations for radio ingress and egress based on adaptive coding modulation (ACM) associated with one or more of the first airframe or the response airframe, and
applying the following:
phase
offset
=
(
TS
1
+
TS
4
-
TS
3
-
TS
2
)
2
±
Asy
2
;
and
correct a phase of the first transceiver based on the calculated phase offset, wherein the calculated phase offset is a result at a physical layer and is caused to be made available to higher layers.
20 . A system comprising:
a first transceiver including memory and a processor, the first transceiver configured to:
generate a first airframe to be sent to a second transceiver over a wireless link of a network, the first airframe including a first time indication indicating a first time TS 1 that the first airframe is to be transmitted by the first transceiver, the first transceiver and the second transceiver including a first and second counters, respectively;
transmit the first airframe to the second transceiver;
receive a respond airframe from the second transceiver, the respond airframe including within the respond airframe a third time indication indicating a third time TS 3 that the respond airframe is to be transmitted to the first transceiver;
determine a fourth time indication indicating a fourth time TS 4 that the respond airframe was received;
receive, from the second transceiver, a second time indication indicating a second time TS 2 that the first airframe was received by the second transceiver;
calculate a counter offset using the first time, second time, third time, and fourth time as follows:
counter
offset
=
(
TS
1
+
TS
4
-
TS
3
-
TS
2
)
2
;
calculate a phase offset based on the counter offset, the calculating including:
determining asymmetry (ASY) in the wireless link, the asymmetry (ASY) in the wireless link comprising asymmetry on a round trip radio link path asymmetry corresponding to different modulations for radio ingress and egress based on adaptive coding modulation (ACM) associated with one or more of the first airframe or the response airframe, and
applying the following:
phase
offset
=
(
T
S
1
+
T
S
4
-
T
S
3
-
T
S
2
)
2
±
A
s
y
2
;
and
correct a phase of the first transceiver based on the calculated phase offset, wherein the calculated phase offset is a result at a physical layer and is caused to be made available to higher layers.