  Spatial modulation (SM) is an innovative and promising digital modulation
technology that strikes an appealing trade-off between spectral efficiency and
energy efficiency with a simple design philosophy. SM enjoys plenty of benefits
and shows great potential to fulfill the requirements of future wireless
communications. The key idea behind SM is to convey additional information
typically through the ON/OFF states of transmit antennas and simultaneously
save the implementation cost by reducing the number of radio frequency chains.
As a result, the SM concept can have widespread effects on diverse applications
and can be applied in other signal domains such as frequency/time/code/angle
domain or even across multiple domains. This survey provides a comprehensive
overview of the latest results and progresses in SM research. Specifically, the
fundamental principles, variants of system design, and enhancements of SM are
described in detail. Furthermore, the integration of the SM family with other
promising techniques, applications to emerging communication systems, and
extensions to new signal domains are also extensively studied.
