Frequency error estimating apparatus and method, frequency error compensating apparatus, and optical receiver

1. A frequency error estimating apparatus used for a coherent optical receiver, comprising:

a data phase canceller including:

an amplitude determiner configured to receive a baseband digital electrical signal converted from a received light signal modulated with a phase and amplitude shift keying and determine an amplitude for each of a plurality of groups of symbols in the baseband digital electrical signal, the plurality of groups of symbols being based on a radius; and

an amplitude directed phase determiner configured to determine a modulated phase component of the determined amplitude of at least one of the plurality of groups, the data phase canceller being configured to cancel the modulated phase component from the baseband digital electrical signal to obtain a resultant signal; and

a frequency error calculator configured to calculate a frequency error based on the resultant signal.

2. A frequency error compensating apparatus, comprising:

the frequency error estimating apparatus according to claim 1 ; and

a frequency error compensator configured to generate a signal used to compensate a frequency error obtained by the frequency error estimating apparatus.

3. An optical receiver, comprising:

a front-end processor configured to convert a received light signal modulated with a phase and amplitude shift keying into a baseband digital electrical signal; and

the frequency error compensating apparatus according to claim 2 configured to perform frequency error compensation on the baseband digital electrical signal obtained by the front-end processor.

4. The frequency error estimating apparatus according to claim 1 , further comprising:

a parallelization processor configured to parallelize the baseband digital electrical signal into M signals (M is an integer of 2 or more); and

M parallel branches to which the M signals parallelized from the baseband digital electrical signal are inputted, respectively,

wherein each of the parallel branches comprises the amplitude determiner, the amplitude directed phase determiner, and the frequency error calculator,

the parallel branches are configured such that two parallel branches form a branch pair, and

the inter-symbol phase difference is obtained for the baseband digital electrical signals of different symbol times between the parallel branches forming a branch pair.

5. A frequency error compensating apparatus, comprising:

the frequency error estimating apparatus according to claim 4 ; and

a frequency error compensator that generates a signal used to compensate the frequency error obtained by the frequency error estimating apparatus.

6. An optical receiver, comprising:

a front-end processor configured to convert a received light signal modulated with a phase and amplitude shift keying into a baseband digital electrical signal; and

the frequency error compensating apparatus according to claim 5 configured to perform frequency error compensation on the baseband digital electrical signal obtained by the front-end processor.

7. A frequency error estimating method in a coherent optical receiver, comprising:

receiving a baseband digital electrical signal converted from a received light signal modulated with a phase and amplitude shift keying;

determining an amplitude for each of a plurality of groups of symbols in the baseband digital electrical signal, the plurality of groups of symbols being based on a radius;

determining a modulated phase component of the determined amplitude of at least one of the plurality of groups;

cancelling the modulated phase component from the baseband digital electrical signal to obtain a resultant signal; and

calculating a frequency error based on the resultant signal.