Method for constructing a distributed boundary clock over a dedicated communication channel
AssigneeQulsar, Inc.
InventorKishan Shenoi
Life of this patent
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Abstract
A method for implementing a distributed boundary clock in situations where book-end devices such as microwave TX/RX pairs must collaborate in achieving PTP on-path support is described. A dedicated channel, generally low-speed compared to the main channel is used to transfer timing from the master side to the slave side using framing and super-framing applied to the digital channel. Time-stamps of events such as super-frame boundaries are communicated between the two sides to enable timing transfer.
Claims12
A method, comprising synchronizing a first clock located at a receiving side to a second clock located at a sending side including aligning the first clock to the second clock by adjusting the first clock using forward and reverse error estimates εF(i) and εR(i) where
- ɛ
- F
-
- (
- i
- )
- -
- Δ
- MS
- =
- -
- 1
- N
- ·
- ∑
- n
- =
- 0
- N
- -
- 1
-
- (
- T
- 2
-
- (
- n
- )
- -
- T
- 1
-
- (
- n
- )
- )
- ɛ
- R
-
- (
- i
- )
- +
- Δ
- SM
- =
- 1
- N
- ·
- ∑
- k
- =
- 0
- N
- -
- 1
-
- (
- T
- 4
-
- (
- k
- )
- -
- T
- 3
-
- (
- k
- )
- )
- where i is an index that represents an iteration number, each iteration representing N estimates of one-way delay from time-stamps that are averaged to reduce measurement noise,
- where ΔMS is forward delay from the second clock to the first clock,
- where ΔSM is reverse delay from the first clock to the second clock,
- where subscripts F and R represent forward and reverse directions, respectively,
- where T1 is a first time of departure measured according to the second clock,
- where T2 is a first time of arrival measured according to the first clock,
- where T3 is a second time of departure measured according to the first clock and
- where T4 is a second time of arrival measured according to the second clock.
A method, comprising synchronizing a first clock located at a receiving side to a second clock located at a sending side including aligning the first clock to the second clock by adjusting a frequency of the first clock using an estimate of a frequency error of the first clock δfm(i) based on change in time error from iteration to iteration where
- δ
-
-
- f
- m
-
- (
- i
- )
- =
- (
- 1
- mT
- )
- ·
- (
- ɛ
-
- (
- i
- )
- -
- ɛ
-
- (
- i
- -
- m
- )
- )
- where the frequency error estimate in the current iteration i is developed as the difference between the time error estimate, ε(i), in iteration i and the time error estimate, ε(i−m), m iterations in the past, scaled by the effective time interval mT, where T is the duration of each iteration and the iterations are contiguous.
Dependencies are inferred from the claim text.