Dual-Mode OFDM with Coded Direct Index Modulation for the Spectrum Efficiency Improvement

In this paper, we propose an orthogonal frequency division multiplexing with coded direct index modulation (OFDM-CDIM) system to improve transmission efficiency and performance and evaluate the performance of this system. OFDM with index modulation (OFDM-IM) transmits additional information using combination information for determining the position of the used subcarriers, and provides a trade-off control function between performance and transmission efficiency. However, as OFDM-IM uses combinatorial operations, the amount of computation to be processed in transmission and reception increases as the number of subcarriers increases. In this paper, we propose a method to directly map data to indexes of subcarriers to solve this problem. In order to improve performance and transmission efficiency, we only encode data mapped to indexes of subcarriers. Simulation results show that the proposed system using dual-mode (DM) can improve bit error rate (BER) performance and transmission efficiency compared to conventional OFDM system in multipath fading channel environment.