  Massive MIMO, a candidate for 5G technology, promises significant gains in
wireless data rates and link reliability by using large numbers of antennas
(more than 64) at the base transceiver station (BTS). Extra antennas help by
focusing the transmission and reception of signal energy into ever-smaller
regions of space. This brings huge improvements in throughput. However, it
requires a large number of Radio Frequency (RF) chains (usually equal to number
of transmit antennas), which is a major drawback. One approach to overcome
these issues is to use Spatial Modulation (SM). In SM, an index of transmit
antenna is used as an additional source of information to improve the overall
spectral efficiency. In particular, a group of any number of information bits
is mapped into two constellations: a signal constellation based on modulation
scheme and a spatial constellation to encode the index of the transmit antenna.
However, a low spectral efficiency is main drawback of SM. Therefore, a
combination of SM with Spatial Multiplexing is an effective way to increase
spectral efficiency with limited number of RF chains.
