On the comparison between code-index modulation and spatial modulation techniques

Recently, two promising modulation techniques have been developed aiming to increase data rate and save energy while being simple to implement. These modulation schemes belong to two different communication methods, however, they share the common structure of using an index as an additional parameter to convey information. The first scheme known as spatial modulation (SM), is a scheme that uses multiple antennas at the transmitter side where just one antenna is activated at a time and its index is used as means to convey information. The second is known as code-index modulation (CIM), a system that uses multiple spreading codes, where a certain code is selected and its index is used as a mechanism to ferry data. In this paper, we present these two modulation techniques and we discuss the associated set of challenges for each scheme. Moreover, in order to evaluate the advantages and disadvantages of each technique, we compare the energy efficiency, the system complexity, and the bit error rate performance of the SM and CIM schemes.