Design and Performance Evaluation of Dual Mode OFDM-DIM and OFDM-CDIM Systems.

In this paper, we like to propose 2 kinds of orthogonal frequency division multiplexing with direct index modulation (OFDM-DIM) and OFDM with coded DIM (OFDM-CDIM) systems which improve the efficiency of conventional OFDM system. The proposed systems transmit information data using two quadrature phase shift keying (QPSK) constellation modes. Here, the data is mapped into an index of a subcarrier and QPSK symbol and is transmitted. This process is very similar to the existing orthogonal frequency division multiplexing with direct index modulation (OFDM-IM) and DM-OFDM-IM, but the proposed systems do not use complex combinatorial operations that are used in the existing systems. Since this operation has to be repeatedly calculated for each subcarrier, it increases very high complexity and the long processing time. Moreover, since 5th generation (5G) and beyond 5G systems consider more than 4k subcarriers in near future, the problem will become more serious if the systems use this operation. Simulation results show that the proposed system has similar performance and efficiency to the conventional OFDM system in the additive white Gaussian noise channel. However, the Rayleigh fading channel, which is similar to the real environment, OFDM-CDIM using dual modes can improve transmission efficiency of 25%.