Multiple Active Spatial Modulation: A Possibility of More Than Spatial Multiplexing

For multiple active spatial modulation (MASM) technique, this letter formulates the minimum number of transmit antennas (N
_t
) and the required number of active RF chains (N
_a
) to support the following two statements. First, it is proven that MASM can achieve similar spectral efficiency to conventional spatial multiplexing (SMx) with smaller N
_t
and N
_a
, and less receive antennas (N
_r
). Secondly, for operation with the same Nt in both techniques, MASM is shown to achieve higher spectral efficiency while using fewer N
_a
and N
_r
. Furthermore, the low spectral efficiency and diversity tradeoff in MASM is highlighted, and a proposal of an enhanced MASM (E-MASM) technique is shown to achieve a better tradeoff between spectral efficiency and diversity as compared to SMx. In comparison to SMx and some prominent space modulation techniques, E-MASM is shown to achieve higher reliability, while MASM achieves superior spectral efficiency.