Monitoring apparatus for an optical signal to noise ratio, signal transmission apparatus and receiver

A monitoring apparatus for an optical signal to noise ratio, comprising:

• a memory that stores a plurality of instructions;
• and
• a processor coupled to the memory and configured to execute the instructions to:
• select a range of at least one of a time domain and frequency domain for calculating noise power of received signals according to a location of a pilot signal in the received signals in the at least one of the time domain and the frequency domain;
• and
• calculate the noise power of the received signals according to the received signals in the selected range of the at least one of the time domain and frequency domain, and calculate an optical signal to noise ratio of the received signals according to the noise power, and
• wherein one of:
• the processor is configured to execute the instructions to select a time domain range having a distance from a center of the pilot signal less than or equal to a first threshold value in the time domain, and calculate the noise power of the received signals according to the selected time domain range, and
• the processor is configured to execute the instructions to select a frequency domain range having a distance from a frequency of the pilot signal greater than or equal to a second threshold value in the frequency domain, and calculate the noise power of the received signals according to the selected frequency domain range.