A method of transmitting a data signal is provided that includes integrating a trellis encoder/decoder into a transmitter for 16 quadrative amplitude modulation (QAM) to provide a first and second mode of modulation, wherein each mode has a same baud rate. Data is transmitted from the transmitter at the first mode of modulation with a plurality of first subcarriers with DP16QAM modulation to provide a substantially 400G data transmission rate, or data is transmitted from the transmitter at the second mode of modulation with a plurality of second subcarriers with trellis coded modulation to provide a substantially 1T data transmission rate.