Abstract: On the basis of two constellation shaping forms on the multicarrier modulation channel, the relation between shaping gain and the bit and power allocation of the system has been analyzed. It has been proved theoretically that if continuous approximation exists, the performance of separate shaping on the subchannel and united shaping across the subchannel are the same; and then the conclusion that if continuous approximation doesn't hold, the gain of the latter can be slightly higher than the former's has been obtained by simulations results.

Key words: channel coding, shaping, multicarrier modulation