Method and apparatus for performing harq in wireless communication system

A method of performing hybrid automatic repeat request (HARQ) in a wireless communication system, the method comprising:

• storing an encoded information bit into a circular buffer;
• selecting a first transport block from the circular buffer;
• mapping a bit set comprising n bits of the first transport block to a data symbol on a constellation for 2n-QAM modulation according to a first mapping order;
• transmitting the data symbol of the first transport block;
• receiving a retransmission request for the information bit;
• selecting a second transport block for retransmission of the information bit from the circular buffer;
• mapping a bit set comprising n bits of the second transport block to a data symbol on a constellation for 2n-QAM modulation;
• and
• transmitting the data symbol of the second transport block,
• wherein a bit set of the first transport block or the second transport block is mapped according to a second mapping order when bits of the first transport block or the second transport block are subject to wrap-around at the end of the circular buffer.

A transmitter in a wireless communication system, the transmitter comprising:

• a circular buffer configured to store an encoded information bit;
• a mapper configure to select a transport block from the circular buffer and map a bit set comprising n bits of the transport block to a data symbol on a constellation for 2n-QAM modulation according to a first mapping order;
• and
• a radio frequency (RF) unit coupled to the mapper,
• wherein the mapper maps the bit set according to a second mapping order when the bits of the transport block are subject to wrap-around at the end of the circular buffer.