When utilizing all subcarrier activation patterns in the combinatorial index modulation (IM) scheme, existing techniques either fail to realize the maximum possible throughput enhancement or fail to address the bit-level synchronization issue (or error propagation) due to the variable-length nature of the index-domain codebook. To address these drawbacks, we propose using Huffman coding for IM together with two constellation mappings for the bandpass modulation. The proposed scheme induces no signal overhead and is applicable when the index-domain codebook has the maximum encoding rate. Simulations demonstrate the effectiveness of the proposed scheme in mitigating bit-level synchronization errors.
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- Huffman coding