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US 7,751,503 B2Granted
Method for acquiring timing and carrier synchronization of offset-QPSK modulated signals
AssigneeJennic Limited
InventorsIvan Lawrow, Stephen Bate
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Abstract
Embodiments of the invention consist in a method of carrier synchronization, comprising determining a frequency offset estimate from a rate of change of a phase difference between a local oscillator signal and a carrier signal of a received signal; and adjusting a frequency of the local oscillator signal by the frequency offset estimate.
Claims17
A method of carrier synchronisation, comprising:
- determining a phase difference between a local oscillator signal and a carrier signal of a received signal by performing a phase detection function P(t) such that the value of P(t) at periodic instants indicates the phase difference θ between the carrier signal of the received signal R(t) and at least one of first and second local oscillator signals, wherein
- P
-
- (
- t
- )
- =
- {
- tan
- -
- 1
-
- (
- X
-
- (
- t
- )
- Y
-
- (
- t
- )
- )
- -
- sgn
-
- (
- X
-
- (
- t
- )
- ·
- Y
-
- (
- t
- )
- )
- ·
- π
- 4
- for
-
-
- Y
-
- (
- t
- )
- ≠
- 0
- π
- 4
- ·
- sgn
-
- (
- X
-
- (
- t
- )
- )
- for
-
-
- Y
-
- (
- t
- )
- =
- 0
- where X(t) is derived from the received signal R(t) mixed with a first local oscillator signal, and Y(t) is derived from the received signal R(t) mixed with a second local oscillator signal;
- determining a frequency offset estimate from a rate of change of the phase difference between the local oscillator signal and the carrier signal of the received signal;
- and
- adjusting a frequency of the local oscillator signal by the frequency offset estimate.
76 more elements
A demodulator comprising:
- an input for receiving a received signal R(t);
- a controllable oscillator for generating a first local oscillator signal and a second local oscillator signal;
- a first mixer for mixing the received signal R(t) with the first local oscillator signal;
- a first filter for filtering an output of the first mixer to produce a first signal X(t);
- a second mixer for mixing the received signal R(t) with the second local oscillator signal;
- a second filter for filtering an output of the second mixer to produce a second signal Y(t);
- a data processor arranged to perform a phase detection function on P(t) on X(t) and Y(t) and determine a frequency offset estimate from a rate of change of the phase detection function, such that the value of P(t) at periodic instants indicates a phase difference θ between a carrier signal of the received signal R(t) and at least one of first and second local oscillator signals, wherein:
- P
-
- (
- t
- )
- =
- {
-
- tan
- -
- 1
-
- (
- X
-
- (
- t
- )
- Y
-
- (
- t
- )
- )
- -
- sgn
-
- (
- X
-
- (
- t
- )
- ·
- Y
-
- (
- t
- )
- )
- ·
- π
- 4
- for
-
-
-
- Y
-
- (
- t
- )
- ≠
- 0
- π
- 4
- ·
- sgn
-
- (
- X
-
- (
- t
- )
- )
- for
-
-
-
- Y
-
- (
- t
- )
- =
- 0
- a loop filter for filtering the frequency offset estimate to produce a control value and providing the control value to the controllable oscillator.
82 more elements
Dependencies are inferred from the claim text.