基于LDPC编码辅助的OFDM-IM子载波索引保护方案

The receiver of OFDM with Index Modulation (OFDM-IM) usually adopts a Log Likelihood Ratio (LLR) detection algorithm based on the activation state of subcarriers. However, the LLR detection algorithm will cause detection errors in subcarrier activation pattern (SAP) or get illegal SAP. Consequently, further errors occur in demodulation, increasing the bit error rate (BER). To solve this problem, we propose the protection scheme of subcarrier index aided by LDPC coding, which reduces the SAP detection errors by encoding the index information bits. On the receiver, the LDPC Coding Aided (LA) detection algorithm is designed, and the formula of LLR of index information bits is derived in detail. Monte Carlo simulation is carried out over multi-path fading channel by MATLAB software. The results show that under the condition that the spectrum efficiency is not lower than the classical OFDM-IM scheme, the proposed protection scheme can obtain a gain of about 5~9 dB when the BER is 10^-4, effectively improving the BER performance of OFDM-IM scheme.