HARQ Combining Scheme based on Channel Impulse Response and Confidence Level

In order to improve the reliability of data transmission, this paper proposes a HARQ combining scheme based on channel impulse response and confidence level in OFDM wireless system. The confidence level of subchannel is obtained according to the position of comb pilot sequence. In the proposed scheme, the same data is retransmitted immediately as soon as NACK is received at the transmitting terminal. The position of comb pilot sequence is changed before IFFT. The each subchannel impulse response is estimated according to received comb pilot sequence at the receiving terminal. The received data in two transmissions is weighted and combined according to channel impulse response and confidence level. Under Rayleigh fading channel environment, simulation experiment shows that this scheme improves combining precision. The BER (Bit Error Rate) is reduced effectively.