A New Constellation Rearrangement without Signaling for IR-HARQ in the IMT-Advanced System
Jun Xu, Jin Xu · 2009
This paper has presented a new constellation rearrangement (CoRe) theme for a good performance/complexity tradeoff if circular buffer rate matching (CBRM) is applied for incremental Hybrid ARQ (IR-HARQ) with turbo coding or LDPC coding. The presented technique is applied to high order modulation, such as 16QAM and 64QAM, with 2 versions. For all transmissions of one HARQ process, the previous half uses the first version depicted by the constellation, and the last half uses the second version which swaps the high reliability bits and low reliability bits within each QAM symbol. The constellation rearrangement version distribution is the same among all transmissions for the same HARQ Process. This scheme doesn't need any signaling bit to indicate the CoRe version of the current transmission, and easily average out the unequal bit reliabilities of the overlapping section. For example, when the overlapping happens in IR-HARQ with CBRM, the beginning/tail part of the second transmission shall overlap with the tail/beginning part of the first transmission, which provides an averaging effect among the reliability of the overlapped bits. Simulation results have proved that the proposed scheme outperforms the traditional CoRe scheme with 2 versions, and has close performance to traditional CoRe scheme with 4 versions.