Recently, data traffic is explosively increasing due to various contents and the spread of smart devices. As a result, spectrum resources are gradually becoming saturated. For this reason, there are many studies to improve the spectral efficiency. SSB modulation method in analog communication was an effective way to double the spectral efficiency. DFT-s-SSB OFDM using DFT spreading was studied to apply analog SSB modulation technique to OFDM which is a multi-subcarrier technique.
There is also OFDM-IM technique that improves spectral efficiency through additional bit transmission using a combination in OFDM system. OFDM-IM determines a sub-carrier to be used by using a combination and can additionally transmit a bit according to a combination of sub-carriers to be used as well as bit-by-symbol transmission. OFDM-IM system has the effect of improving the spectral efficiency depending on the combination. However, there are problems in both DFT-s-SSB OFDM aND OFDM-IM. DFT-s-SSB OFDM can not utilize both LSB spectrum and USB spectrum. Also in the case of OFDM-IM, the spectral efficiency decreases depending on the combination. In this study, we propose SSB OFDM-IM using (M-2)-Point DFT-s-SSB OFDM and OFDM-IM to improve spectral efficiency. The proposed system improves LSB and USB simultaneously in DFT-s-SSB OFDM system. We also analyze the spectrum efficiency according to the combinations and modulation levels used in OFDM-IM system to find the optimal combination. Finally, we apply the proposed system in multi-user environment to identify various ways of using spectrum and evaluate spectrum efficiency and performance. It is confirmed that BER performance deterioration or spectral efficiency improvement is different depending on used combinations, and that it is more efficient in lower order modulation than higher order modulation. Also, in the multi-user environment, the spectrum can be utilized variously and the spectral efficiency can be improved through the proposed system.