Using reliability of checkout formula outputted decoding through low-density parity check (LDPC), the invention discloses method for selectable requests of automatic retransmission. The method defines serial number of checkout formula of LDPC code consistent between sending and receiving ends. When the receiving end carries out LDPC decoding for data from forwarding transmission channel, it indicates that there is error code if checkout formula of hard decision is not all zeros. Then, sorting reliabilities (value of likelihood ratio) of checkout formula, the method defines several checkout formulas with smallest values as not reliable checkout formulas. Then, through backward feedback channel, not reliable serial numbers are informed to the sending end. When receiving the serial numbers, the sending end finds out information bits associated with not reliable checkout formulas; and then through forward transmission channel, the sending end retransmits the information bits. |