A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Precoding/TCM Aided SM <s> Trellis coded modulation (TCM) is a well known scheme that reduces power requirements without any bandwidth expansion. In TCM, only certain sequences of successive constellation points are allowed (mapping by set partitioning). The novel idea in this paper is to apply the TCM concept to the antenna constellation points of spatial modulation (SM). The aim is to enhance SM performance in correlated channel conditions. SM considers the multiple transmit antennas as additional constellation points and maps a first part of a block of information bits to the transmit antenna indices. Therefore, spatial multiplexing gains are retained and spectral efficiency is boosted. The second part of the block of information bits is mapped to a complex symbol using conventional digital modulation schemes. At any particular time instant, only one antenna is active. The receiver estimates the transmitted symbol and the active antenna index and uses the two estimates to retrieve the original block of data bits. In this paper, 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 scheme is called trellis coded spatial modulation (TCSM). Tight analytical performance bounds over correlated fading channels are proposed in this paper. In addition, the performance and complexity of TCSM is compared to the performance of SM, coded V-BLAST (vertical Bell Labs layered space-time) applying near optimum sphere decoder algorithm, and Alamouti scheme combined with TCM. Also, the performance of all schemes with turbo coded modulation is presented. It is shown that under the same spectral efficiency, TCSM exhibits significant performance enhancements in the presence of realistic channel conditions such as Rician fading and spatial correlation (SC). In addition, the complexity of the proposed scheme is shown to be 80% less than the V-BLAST complexity. <s> BIB001 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Precoding/TCM Aided SM <s> Spatial modulation (SM), in which multiple antennas are used to convey information besides the conventional M-ary signal constellations, is a new multiple-input multiple-output (MIMO) transmission technique, which has recently been proposed as an alternative to V-BLAST (vertical Bell Labs layered space-time). In this paper, a novel MIMO transmission scheme, called spatial modulation with trellis coding (SM-TC), is proposed. Similar to the conventional trellis coded modulation (TCM), in this scheme, a trellis encoder and an SM mapper are jointly designed to take advantage of the benefits of both. A soft decision Viterbi decoder, which is fed with the soft information supplied by the optimal SM decoder, is used at the receiver. A pairwise error probability (PEP) upper bound is derived for the SM-TC scheme in uncorrelated quasi-static Rayleigh fading channels. From the PEP upper bound, code design criteria are given and then used to obtain new 4-, 8- and 16-state SM-TC schemes using quadrature phase-shift keying (QPSK) and 8-ary phase-shift keying (8-PSK) modulations for 2,3 and 4 bits/s/Hz spectral efficiencies. It is shown via computer simulations and also supported by a theoretical error performance analysis that the proposed SM-TC schemes achieve significantly better error performance than the classical space-time trellis codes and coded V-BLAST systems at the same spectral efficiency, yet with reduced decoding complexity. <s> BIB002 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Precoding/TCM Aided SM <s> We present a precoding approach for spatial modulation to provide robustness against both the Rayleigh/ Rician fading effects and also spatial correlations among transmit antennas. This approach, based on phase-rotation and/or amplitude scaling of the transmitted symbols according to the active transmit antenna, can be implemented while preserving the average power budget and without any explicit knowledge of the channel coefficients at the transmitter. The optimum values of the precoding coefficients are determined so as to minimize the asymptotic average bit-error rate. Both theoretical analysis and simulation results indicate significant performance improvements even in the case of heavily correlated transmit antennas. Moreover, it is also shown that optimal precoding significantly compensates for the vulnerability of the antenna index bits against direct line-of-sight channel components and/or heavy inter-antenna correlations at the transmitter. <s> BIB003
It is worth pointing out again that the detection performance of the spatial information highly depends on the distinctness of channel impulse responses associated with different transmit antennas. As a result, the detection performance suffers from spatially-correlated fading channels as the channel impulse responses become very similar from different transmit antennas. The precoding and TCM are two effective techniques to overcome the negative impact of spatial correlation on SM. In BIB003 , a diagonal precoding matrix is applied to the SM transmit vector before transmission, which is designed to minimize the asymptotic average BER while preserving the average power budget and without any explicit knowledge of the channel coefficients at the transmitter. On the other hand, in BIB001 and BIB002 the encoding scheme based on TCM is investigated for SM systems. Specifically, the spatial information bits are convolutionally encoded and interleaved according to the TCM principle in BIB001 , which differentiates the transmit antennas into multiple subsets to maximize the spatial distance between each transmit antenna within the same subset. However, although the scheme proposed in BIB001 benefits from some performance improvements in correlated fading channels, such improvements vanish in uncorrelated fading channels, compared with the conventional SM without TCM. To break the bottleneck of BIB001 , another TCM based SM scheme is proposed in BIB002 , which reaps the advantages of trellis coding and achieves performance improvement over the conventional SM in both uncorrelated and correlated fading channels.