MIMO spread spectrum GFDM communication systems with index modulation

In the fourth-generation communication system (4G), orthogonal frequency division multiplexing (OFDM) is widely used. However, due to the cyclic prefix (CP) being added, the low spectrum efficiency and high out-of-band radiation (OOB) cause OFDM not to be suitable for the beyond fifth-generation (B5G) communication system. Therefore, to meet the rigorous demands in B5G for the Internet of Things (IoT) and massive machine-type communications (MMTC), generalized frequency division multiplexing (GFDM) technology has received significant attention. On the other hand, index modulation (IM) can provide flexible settings of different parameters to achieve the ideal system goals. Therefore, this paper considers the combination of spread spectrum (SS) and IM under the framework of GFDM, called SS-IM-GFDM. In this scheme, the information bits are jointly conveyed by the indices of spreading codes and the conventional M-ary modulated symbols, which increase the spectrum efficiency and improve the bit error rate performance. Furthermore, a low-complexity maximum likelihood (ML) detector is proposed to recover the transmitted signal effectively at the receiver. Finally, the space-time block code (STBC) is employed to construct the multi-input multi-output SS-GFDM-IM (MIMO SS-GFDM-IM) system to improve the system's reliability. The simulation results show that the proposed scheme is superior to the existing systems.