  In this paper, we present throughput analysis and optimization of bandwidth
efficient selective retransmission method at modulation layer for conventional
Chase Combining (CC) method under orthogonal frequency division multiplexing
(OFDM) signaling. Most of the times, there are fewer errors in a failed packet
and receiver can recover from errors receiving partial copy of original frame.
The proposed selective retransmission method at modulation layer for OFDM
modulation requests retransmission of information corresponding to the poor
quality subcarriers. In this work, we propose cross-layer multiple selective
Chase combining (MSCC) method and Chase combining with selective retransmission
(CCWS) at modulation level. We also present bit-error rate (BER) and throughput
analysis of the proposed MSCC and CCWS methods. In order to maximize throughput
of the proposed methods under OFDM signaling, we formulate optimization problem
with respect to amount of information to be retransmitted in selective
retransmission in the event of packet failure. We present tight BER upper
bounds and tight throughput lower bounds for the proposed selective Chase
combining methods. The simulation results demonstrate significant throughput
gain of the optimized selective retransmission methods over conventional
retransmission methods. The throughput gain of the proposed selective
retransmission atmodulation layer are also holds for conventional for hybrid
automatic repeat request (HARQ) methods.
