Radio transmitter, radio receiver, and multilevel modulation communication system

A transmission method comprising:

• modulating data into a 16QAM symbol;
• transmitting, in a first transmission, said data modulated into said 16QAM symbol as a string of 4 bits;
• and
• retransmitting, in a retransmission, data modulated into a 16QAM symbol that contains all of said 4 bits as a rearranged string of said 4 bits, wherein said rearranged string is provided by exchanging the positions of the upper 2 bits and the lower 2 bits of said string in the first transmission.

A transmission system comprising:

• a transmitting apparatus that:
• modulates data into a 16QAM symbol;
• transmits, in a first transmission, said data modulated into said 16QAM symbol as a string of 4 bits;
• and
• retransmits, in a retransmission, data modulated into a 16QAM symbol that contains all of said 4 bits as a rearranged string of said 4 bits, wherein said rearranged string is provided by exchanging the positions of the upper 2 bits and the lower 2 bits of said string in the first transmission;
• and
• a receiving apparatus that:
• receives said data transmitted in said first transmission and retransmitted in said retransmission.