Intelligent Reconfigurable Surface Assisted Constellation Index Selection Spatial Modulation Over Nakagami-m Fading Channels

Intelligent Reconfigurable Surface has become a promising technique in recent years due to its inherent ability to overcome the severe wireless fading channel characteristics such as reflection, refraction, scattering, and diffraction, etc. On the other hand, spatial modulation (SM) is a special type of index modulation technique that is utilized to enhance the spectral efficiency of wireless communication systems. In this paper, we combine these two techniques and propose the two IRS-assisted bi-constellation index spatial modulation (BCI-SM) and multi-constellation index spatial modulation (MCI-SM) schemes operating under Nakagami-m fading channels. The main idea is to select the receive antenna and constellation set indices according to the incoming information bits, thus yielding enhanced spectral efficiency and bit error rate (BER) performance. We also propose the low complex log-likelihood ratio detector for both schemes. In addition, we derive the analytical results for the union bound on the average BER with the ML detector. These results can be generalized for both IRS-assisted BCI-SM and IRS-assisted MCI-SM schemes and are valid for any arbitrary value of m in Nakagami-m fading channels. Simulation results show the superiority of IRS-assisted BCI-SM and IRS-assisted MCI-SM schemes over the existing IRS-aided SM in terms of BER performance. In particular, BCI-SM shows an SNR gain of around 3-5 dB while MCI-SM exhibits an SNR gain of nearly 7-12 dB when compared with the existing IRS-aided SM scheme.