  In this paper, we propose a novel modulation concept which we call
\emph{index and composition modulation (ICM)}. In the proposed concept, we use
indices of active/deactive codeword elements and compositions of an integer to
encode information. In this regard, we first determine the activated codeword
elements, then we exploit energy levels of these elements to identify the
compositions. We depict a practical scheme for using ICM with orthogonal
frequency division multiplexing (OFDM) and show that OFDM with ICM (OFDM-ICM)
can enhance the spectral efficiency (SE) and error performance of OFDM-IM. We
design an efficient low-complexity detector for the proposed technique.
Moreover, we analyze the error and SE performance of the OFDM-ICM technique and
show that it is capable of outperforming existing OFDM benchmarks in terms of
error and SE performance.
