1. A coding method, wherein the method comprises:obtaining, by a sending device, positions of information bits, positions of fixed bits, and positions of assistant bits;
allocating, by the sending device, the information bits, the fixed bits, and the assistant bits in a to-be-coded sequence based on the positions of the information bits, the positions of the fixed bits, and the positions of the assistant bits;
obtaining, by the sending device, a scrambling sequence;
scrambling, by the sending device, a bit in a to-be-scrambled bit set based on the scrambling sequence to obtain a scrambled sequence, wherein the to-be-scrambled bit set is determined based on at least one of the fixed bits or the assistant bits;
performing, by the sending device, polar coding on the scrambled sequence to obtain a coded sequence; and
sending, by the sending device, the coded sequence.