Signal Design for Frequency-Domain Enhanced Spatial Modulation

Abstract

Spatial Modulation (SM) was first introduced to reduce the number of radio frequency (RF) chains in a multiple-input multiple-output (MIMO) transmitter and thereby reduce cost and power consumption. Although it is very appealing in theory, this concept actually has two main problems, which are not sufficiently highlighted in the existing literature: The first is that the antenna switching involved destroys the spectral shaping of the transmitted signal, and the second is the limited spectral efficiency due to the presence of silent antennas. In order to remedy the second problem, Enhanced Spatial Modulation (ESM) was introduced. As for the problem of antenna switching, it actually disappears when SM is implemented in the frequency-domain, because the switching operation in Frequency-Domain SM (FD-SM) occurs at baseband. But the number of RF chains needed becomes equal to the number of transmit antennas. In this paper, we investigate Frequency-Domain ESM (FD-ESM), which avoids both the spectral efficiency limitations and the antenna switching of the original SM. Exploiting the property that switching occurs at baseband and no savings in terms of the number of RF chains can be achieved in frequency-domain implementation, we design FD-ESM schemes which provide spectacular gains with respect to conventional Multi-Stream SM (MSM) and also significant gains compared to spatial multiplexing.