RIS Empowered Index Modulation-Based Receive Diversity Wireless System With Nakagami-$m$ Fading Channels

Reconfigurable intelligent surfaces (RIS) and index modulation (IM) have been proven as potential technologies for improving the performance of next-generation wireless communication systems. In this paper, we consider the study of a receive diversity RIS-assisted wireless communication system employing two IM schemes, namely, space-shift keying (SSK) and spatial modulation (SM) for data transmission over Nakagami-
$m$
fading channels. Considering the RIS to lie in close proximity to the transmitter, a receiver structure based on a greedy detection rule is proposed to select one of the receive diversity branches with the highest received energy for demodulation. Based on this system model, novel closed-form expressions for the probability of erroneous index detection (PED) of the considered target receive diversity branch, and the corresponding asymptotic expressions at a high signal-to-noise ratio (SNR) are obtained using a characteristic function approach. Furthermore, closed-form and asymptotic expressions at high SNR for the bit error rate (BER) for the SSK-based system and the SM-based system employing
$M$
-ary phase-shift keying and
$M$
-ary quadrature amplitude modulation schemes are also derived. The dependencies of the performance of the considered system are also corroborated via numerical results. The asymptotic expressions and results of PED and BER at high and low SNR values lead to the observation of a performance saturation and the presence of an SNR value as a point of inflection attributed to the greedy detector's structure.