A data transmission apparatus and a method of modifying a symbol constellation for use in the data transmission apparatus, wherein a processor receives a starting symbol constellation suitable for use in a frequency domain parallel modulation system and defined in a complex space. The starting symbol constellation does not necessarily comprise a symbol at a zero point in the complex space. The processor is configured to locate or move one of the symbols of the starting symbol constellation at the zero point of the complex space. The newly created symbol constellation may be stored in a storage medium, such as volatile or non-volatile storage, or immediately used for data transmission by mapping bits of data to the symbol constellation and by transmitting the mapped data to a receiver of a frequency domain parallel modulation system.