Upgrading SIM–OFDM Using a Threshold for Correct Operation with Analytical Proofs

A new upgrade to the SIM–OFDM is suggested to solve a critical problem that crashes the system even over noiseless channel. This problem is the interference of the zeros at the IFFT output with the BOOK\u27s zeros that confuses the receiver during demodulation which leads to BER accumulation. The suggested solution is to use a threshold to differentiate the data carried by the BOOK from the IFFT\u27s symbols. The new system is called Threshold SIM–OFDM (TSIM–OFDM). The mathematical analysis of TSIM–OFDM proves it operates normally and meets the theoretical bounds. The TSIM–OFDM preserves the probability of 1 equal to 1/2. This preservation comes from the direct connection of the ON/OFF switching bits to the subcarrier which overrides the majority condition. This new switching technique simplifies the system operation resulting in higher transmission speed and increased spectral and power efficiency. A simple approach to derive the BER for the SIM–OFDM is presented which proves that the SIM–OFDM will never reach zero BER level unlike the TSIM–OFDM. The simulation results show that the TSIM–OFDM BER reaches zero level and the output power is almost half of the OFDM. Adding the threshold will increase the transmitted power slightly and tends to decrease with the increase of IFFT length

A New Analytical Model for SIM–OFDM Contradicts the Previously Claimed Features

The Subcarrier Index Modulation OFDM (SIM–OFDM) appeared in 2009 promising a –3 dB transmitted power reduction without affecting the system performance. Therefore, it became an attractive choice to upgrade the communication systems with researchers’ increasing interest. Despite the research efforts in SIM–OFDM field, there was no in-depth investigation for such transmitted power reduction or the system’s performance. The claimed power reduction relies on probabilistic assumptions that were not validated considering system operation concepts. This paper provides a new analytical model that characterizes the actual SIM–OFDM behavior. The contribution of this model is the inclusion of the majority condition in the derivation of 1’s pmf which modifies the 1’s pmf into a complex nonlinear function that is always higher than 1/2. The new pmf effect upon the power reduction, synchronization, and the overall Bit Error Rate (BER) is investigated. The new analytical model shows that the –3 dB power reduction cannot be achieved. Also, no successful synchronization can be established unless extra subcarrier is added that will create a frame like communication system. Such scheme increases BER if the carrier is falsely detected creating a Frame Error Rate (FER) which might lead to serious problem