A converter unit for an M-order digital modulation to map L input binary sequences of N bits onto M complex values being transmitted through a communication channel, where M=2N and L and N are positive integers. The converter unit comprises an input to receive a respective input binary sequence. The converter unit is arranged to individually convert each N bits of the input binary sequence into a real number to obtain a sequence with N real numbers. The converter unit is arranged to execute complex arithmetic operations on the sequence of real numbers and to compute a respective complex value. The respective complex value corresponds to said respective input binary sequence.