Joint semi-blind channel identification in punctured ARQ retransmissions

We study the channel estimation of a bandwidth efficient automatic repeat request (ARQ) system in which re-transmissions are symbol or bit-wise punctured. Unlike simple ARQ in which an erroneous packet is retransmitted, many hybrid ARQ systems aim to conserve bandwidth by only retransmitting a punctured or recoded data packet. We formulate a joint semi-blind channel estimation algorithm for the punctured retransmission in a hybrid ARQ network. We show that the joint semi-blind estimation is quite simple and naturally combines training in the first transmission with retransmitted data statistics. We show that bandwidth savings resulting from puncturing the retransmission only lead to a marginal degradation to the accuracy of channel estimation.