1. A communication system that performs encoding and decoding for communication, comprising: a transmitting apparatus; and a receiving apparatus, wherein the transmitting apparatus includes: a turbo encoding unit including a first encoding unit that encodes an input signal and generates a first parity bit by bit-based encoding and n (n=1, 2, 3,. .. ) second encoding units that encode the input signal and generate n second parity bits by bit-based encoding; and a symbol mapping unit that maps an output from the turbo encoding unit to a symbol by bit-based mapping operation and modulates the output, and the receiving apparatus includes: a demodulating unit that demodulates a transmission signal; and a turbo decoding unit that performs turbo decoding on the demodulated transmission signal by bit-based decoding, wherein the second encoding units each include an interleaver that interleaves the input signal by bit-based interleaving, an element encoding unit that encodes the interleaved signal, and a deinterleaver that deinterleaves an output from the element encoding unit and generates the second parity bits by bit-based deinterleaving, the turbo encoding unit outputs, with respect to the input signal, one systematic bit which is a bit output of the input signal, the first parity bit, and the n second parity bits, and the symbol mapping unit maps a mixture of the systematic bit and a parity bit corresponding to the systematic bit to each of I and Q components of one symbol in accordance with a given rule as the bit-based mapping operation.