  A relatively simple low complexity multiuser communication system based on
simultaneous code and frequency index modulation (CFIM) is proposed in this
paper. The proposed architecture reduces the emitted energy at the transmitter
as well as the peak-to-average-power ratio (PAPR) of orthogonal
frequency-division multiplexing (OFDM)- based schemes functions without
relegating data rate. In the scheme we introduce here, we implement a joint
code- frequency- index modulation (CFIM) in order to enhance spectral and
energy efficiencies. After introducing and analysing the structure with respect
to latter metrics, we derive closed-form expressions of the bit error rate
(BER) performance over Rayleigh fading channels and we validate the outcome by
simulation results. Simulation are used verify the analyses and show that, in
terms of BER, the proposed CFIM outperforms the existing index modulation (IM)
based systems such as spatial modulation (SM), OFDM-IM and OFDM schemes
significantly. To better exhibit the particularities of the proposed scheme,
PAPR, complexity, spectral efficiency (SE) and energy efficiency (EE) are
thoroughly examined. Results indicate a high SE while ensuring an elevated
reliability compared to the aforementioned systems. In addition, the concept is
extended to synchronous multiuser communication networks, where full
functionality is obtained. With the characteristics demonstrated in this work,
the proposed system would constitute an exceptional nominee for Internet of
Things (IoT) applications where low-complexity, low-power consumption and high
data rate are paramount.
