Selective Chase combining for OSTB coded MIMO-OFDM system

We present a new selective retransmission method for orthogonal space-time block (OSTB) coded orthogonal frequency division multiplexing (OFDM) systems at modulation layer. The proposed method is independent of the conventional hybrid automatic repeat request (HARQ) methods and improves throughput by selectively retransmitting of OSTB codes corresponding to the poor quality subcarriers. A typical failed packet has fewer corrupt bits and retransmission of partial packet can help receiver to recover from bit errors. Thus, the proposed method allows selective retransmission correspond to the poor quality subcarriers of multiple-input multiple-output (MIMO) OFDM system. The receiver performs Chase combining (joint detection) of retransmitted OSTB codes by combining observations from the first transmission (preserved before retransmission request) and ensuing selective retransmission. Due to the structure of the OSTB codes, we use ℓ2-norm of the MIMO channel matrix as a channel quality metric. We also present union bound on the bit-error rate (BER) for the proposed selective Chase combining (SCC) approach.