Enabling fast OFDM-based wireless networks with combined transmit diversity and multi-level modulation

In this paper, we present some simple techniques for enhancing the diversity provided by retransmissions in OFDM modulations. The primary techniques of interest is constellation rearrangement (CoRe) for retransmission. CoRe consists in swapping the positions and/or negation of the least significant bits (LSB) and aims at ldquoequalizingrdquo the protection degree experienced by the bits transmitted in multilevel modulation schemes such as M-QAM. The main idea in this paper is to consider a combined orthogonal transmit diversity and multi-level modulation scheme and view the signal constellations of the modulation scheme in an augmented signal space formed by the modulation signal dimension and the number of branches of the transmitter diversity scheme as one entity. Simulation results validate the efficiency of this method in reducing the BER and increasing throughput.