Communication device that transmits signals via a plurality of antennas and communication system

A communication system that includes a signal processing device and a remote radio device, wherein

• the signal processing device includes:
• an oscillator configured to generate an oscillator signal of a radio frequency;
• a modulated signal generator configured to generate a plurality of modulated signals of different intermediate frequencies from a plurality of transmission signals, the intermediate frequencies being different from the radio frequency and the oscillator signal being not used to generate the plurality of modulated signals;
• an optical signal generator configured to generate an optical signal that carries the plurality of modulated signals and the oscillator signal;
• a down-convert circuit configured to down-convert a feedback signal received from the remote radio device using the oscillator signal;
• and
• a correction circuit configured to correct the plurality of transmission signals based on the feedback signal down-converted by the down-convert circuit, and wherein
• the remote radio device includes:
• a converter circuit configured to convert the optical signal into an electric signal;
• an extractor configured to extract the oscillator signal from the electric signal;
• a recovery circuit configured to recover the plurality of transmission signals from the electric signal;
• a radio frequency signal generator configured to generate a plurality of radio frequency signals that respectively carry the plurality of transmission signals recovered by the recovery circuit using the oscillator signal extracted by the extractor;
• a plurality of amplifiers respectively configured to amplify the plurality of radio frequency signals;
• a plurality of antennas respectively configured to output the plurality of radio frequency signals amplified by the plurality of amplifiers;
• and
• a feedback circuit configured to generate the feedback signal from the plurality of radio frequency signals amplified by the plurality of amplifiers.