Communication apparatus, frequency offset estimation method and program

A communication device comprising:

• a processor;
• a storage medium having computer program instructions stored thereon, wherein the computer program instruction, when executed by the processor, perform processing of:
• performing a true value estimation process of estimating a true value of a frequency offset based on an electrical digital signal that is a digital signal obtained based on an optical signal that is an optical signal received in a digital coherent reception method and indicating a symbol string composed of a plurality of symbols and a local oscillation light and a digital signal transmitting the symbol string with an electrical signal,
• wherein, in the true value estimation process,
• a preceding estimation process of estimating a tentative estimated value that is a value of the frequency offset for each of the symbols included in the electrical digital signal, and
• a subsequent estimation process of estimating the true value based on a set of the tentative estimated values estimated in the preceding estimation process are executed.