Master station device, slave station device, and wireless communication system

A slave station device comprising:

• a receiver which, in operation, receives an optical signal via a fronthaul;
• and
• a processor which, in operation, identifies a subcarrier modulation signal based on an in-phase (I) component and a quadrature-phase (Q) component of the subcarrier modulation signal mapped to the optical signal, wherein:
• the subcarrier modulation signal is coded in a first quadrature amplitude modulation scheme having a plurality of signal points,
• the optical signal is coded in a second quadrature amplitude modulation scheme having a plurality of candidate signal points, the second quadrature amplitude modulation scheme having a higher modulation multilevel number than the first quadrature amplitude modulation scheme, and
• the processor sets each of the plurality of candidate signal points of the optical signal to a corresponding signal point of the plurality of signal points of the subcarrier modulation signal, a distance from the each of the candidate signal points of the optical signal to the corresponding signal point being a shortest distance in an IQ plane of the subcarrier modulation signal.

A wireless communication system comprising:

• a master station device including
• a processor which, in operation, outputs a subcarrier modulation signal, and
• a transmitter which, in operation, maps an in-phase (I) component and a quadrature-phase (Q) component of the subcarrier modulation signal to an optical signal to be transmitted to a fronthaul, wherein:
• the subcarrier modulation signal is coded in a first quadrature amplitude modulation scheme having a plurality of signal points,
• the optical signal is coded in a second quadrature amplitude modulation scheme having a plurality of candidate signal points, the second quadrature amplitude modulation scheme having a higher modulation multilevel number than the first quadrature amplitude modulation scheme, and
• the transmitter sets each of the plurality of signal points of the subcarrier modulation signal to a corresponding candidate signal point of the plurality of candidate signal points of the optical signal, a distance from the each of the signal points of the subcarrier modulation signal to the corresponding candidate signal point being a shortest distance in an IQ plane of the optical signal;
• and
• a slave station device including
• a receiver which, in operation, receives the optical signal via the fronthaul, and
• a processor which, in operation, identifies the subcarrier modulation signal based on the I component and the Q component of the subcarrier modulation signal mapped to the optical signal.