On the Performance of Trellis Coded Spatial Modulation

Trellis coded modulation (TCM) is a well known scheme that applies mapping by set partitioning. The key idea is to group the constellation symbols into sets with each set having the maximum free distance between its symbols. In this paper, a similar approach is applied to antenna constellation points of spatial modulation (SM) in order to enhance its performance in correlated channel conditions. In SM, multiple antennas exist at the transmitter side, but only one of them is active at any particular time instant. The incoming data bits determine the active transmit antenna and the signal constellation point transmitted from it. At the receiver side, the active antenna index and the transmitted symbol are estimated and used together to decode the transmitted information bits. The locations of the transmit antennas are considered as spatial constellation points, and TCM is applied to enhance the bit error ratio (BER) performance of bits encoded into the physical location of an antenna within an antenna array. TCM partitions the entire set of transmit antennas into sub-sets such that the spacing between antennas within a particular sub-set is maximized. The performance of TCSM is analyzed in this paper and compared to the performance of SM and coded V-BLAST (vertical Bell Labs layered spacetime) applying optimum sphere decoder algorithm. It is shown that under the same spectral efficiency, TCSM performs nearly the same as SM and V-BLAST in idealistic channel conditions. However, a significant enhancement is reported in the presence of realistic channels performance such as Rician fading and spatial correlation (SC).