Method and system for decoding a modulated signal
In a method and system for decoding a differential M-ary phase or quadrature amplitude modulated signal, the incoming signal is decoded according to a plurality of different decoding rules, wherein said plurality of decoding rules correspond to different values of a resulting frequency difference or mismatch between a signal frequency and a local oscillator reference frequency. The invention allows to increase a tolerance window for the maximal allowable frequency offset, and thus helps to speed up an initial locking process or to allow for equipment which has a lower tuning granularity.
1. A method for decoding a modulated signal, said method comprising:
receiving an encoded signal, said encoded signal comprising a pair of an in-phase component and a quadrature component being extracted from a mixing signal, said mixing signal being obtained from mixing a received modulated signal at a first frequency with a local oscillator signal at a second frequency; and
decoding said encoded signal according to a plurality of different decoding rules, said plurality of decoding rules corresponding to different values of a resulting frequency difference or mismatch between said first frequency and said second frequency.
2. The method according to claim 1 , wherein said decoding step comprises a step of identifying a pre-determined reference outcome in said decoded signal.
3. The method according to claim 2 , further comprising a step of determining said frequency difference or mismatch based on said identified reference outcome.
4. The method according to claim 2 , further comprising a step of adjusting said frequency difference or mismatch in accordance with said identified reference outcome, wherein said adjusting step preferably comprises a step of tuning a local oscillator that supplies said local oscillator signal.
5. The method according to claim 1 , further comprising a step of selecting a decoding rule among said plurality of different decoding rules, and employing said selected decoding rule to decode subsequent encoded signals.
6. The method according to claim 1 , wherein said decoding step comprises a step of assigning different information symbols to said encoded signal in accordance with different assignment rules.
7. The method according to claim 6 , further comprising a step of comparing a plurality of sequences of said information symbols to a predetermined reference outcome, said plurality of sequences corresponding to said different assignment rules.
8. The method according to claim 1 , wherein said decoding step comprises a step of assigning information symbols to said encoded signal in accordance with an assignment rule, and comparing said information symbols against a plurality of reference outcomes.
9. The method according to claim 1 , wherein said modulated signal is an optical M-ary modulated signal, M being a positive integer, in particular an optical M-ary phase modulated signal or an optical M-ary quadrature amplitude modulated signal.
10. The method according to claim 1 , wherein said in-phase component ( 32 ) and said quadrature component are extracted from said mixing signal by means of heterodyne detection.
11. A computer program product comprising computer-readable instructions stored on a computer-readable medium that when the instructions are executed by a computer coupled to a system cause the computer to implement on said system a method according to claim 1 .
12. A system for decoding a modulated signal, said system comprising:
a receiving unit adapted to receive an encoded signal, said encoded signal comprising a pair of an in-phase component and a quadrature component being extracted from a mixing signal, said mixing signal being obtained from mixing a received modulated signal at a first frequency with a local oscillator signal at a second frequency; and
a decoding unit adapted to decode said encoded signal according to a plurality of different decoding rules, said plurality of decoding rules corresponding to different values of a resulting frequency difference or mismatch between said first frequency and said second frequency.
13. The system according to claim 12 , wherein said system comprises a local oscillator unit providing said local oscillator signal at said second frequency, and further comprises a mixing unit adapted to receive said modulated signal at said first frequency, to mix said modulated signal with said local oscillator signal and to extract said pair of said in-phase component and said quadrature component from said mixing signal, wherein said mixing unit is further adapted to provide said extracted pair to said decoding unit.
14. The system according to claim 12 , wherein said decoding unit comprises a frame hunter unit adapted to compare said decoded signal to a pre-determined reference outcome.