A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> D. SM Based Simultaneous Wireless Information and Power Transfer (SWIPT) <s> In echoing Varshney's seminal concept of jointly transmitting information and energy, we propose the concept of an energy pattern aided Simultaneous Wireless Information and Power Transfer (SWIPT) system, where in addition to power transfer, information is conveyed both by the specific Receive Antenna (RA) indices to which the power is delivered as well as by the particular intensity of the power assigned to that particular RA pattern. By embedding information into energy patterns rather than imposing it by modulating classic radio waveforms, our proposed solution is capable of operating both in an integrated receiver mode and in a power-split mode, while relying on a low-complexity two-stage non-coherent detection algorithm. Both our analysis and simulations show that our energy pattern aided SWIPT system exhibits a beneficial immunity to any potential performance degradation imposed by power-conversion. Moreover, the achievable rate versus power conversion trade-off bounds are characterized, demonstrating that our proposed energy pattern aided SWIPT system leads to a beneficial wireless information and power transfer convergence. <s> BIB001 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> D. SM Based Simultaneous Wireless Information and Power Transfer (SWIPT) <s> This paper proposes a spatial modulated simultaneous wireless information and power transfer (SM SWIPT) scheme to save multiple radio frequency (RF) chains at the transmitter. As SM is adopted, only one RF chain is equipped at the transmit side. To harvest energy and in the same time to transfer information, the received signal is split into two parts according to the defined power splitting factors. The power splitting factors are determined by maximizing the throughput of the information decoding (ID) receiver under the given energy harvesting (EH) constraint. An iterative power splitting algorithm (ISPA) is developed to solve the maximization problem. Its performance is investigated through simulations. In addition, the computational complexity of the proposed algorithm is analyzed. Results show the superiority of the proposed SM SWIPT in throughput through comparison with single-input multiple-output (SIMO) SWIPT and beamformed MIMO SWIPT. What is more, unlike the conventional beamformed MIMO SWIPT that requires perfect channel state information at the transmitter (CSIT), the proposed scheme is open loop and requires no any CSIT, thus can further enhance the superiority in energy efficiency. <s> BIB002 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> D. SM Based Simultaneous Wireless Information and Power Transfer (SWIPT) <s> In this paper, we study the performance of receive spatial modulation (RSM) with simultaneous wireless information and power transfer (SWIPT) capabilities. RSM is a multi-antenna modulation scheme, where the information bits are encoded into complex constellation symbols and the indices of the receive antennas. We show how RSM can be combined with SWIPT, by allowing the receivers to increase their data rate and, at the same time, to recharge their batteries. An optimization problem is formulated in order to optimize the fraction of transmit power to be used for information decoding and energy harvesting, as well as the covariance matrix of the energy waveform. Efficient numerical algorithms to tackle the associated optimization problems are proposed. Our analysis shows that RSM-SWIPT is a flexible transmission scheme that is capable of achieving different rate-energy demands. RSM-SWIPT, in particular, can be configured to leverage only the energy waveform for transmitting information data and power simultaneously. Compared with conventional SWIPT-enabled multiple-antenna systems, the proposed RSM-SWIPT scheme increases the amount of harvested energy for low values of the rate and avoids the need of using energy cancellation algorithms if information and power are transmitted only through the energy waveform. <s> BIB003 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> D. SM Based Simultaneous Wireless Information and Power Transfer (SWIPT) <s> In this letter, we propose to utilize spatial modulation (SM) at the wireless device (WD) in a wireless-powered communication (WPC) system for information transmission (IT) by mapping information to the active antenna indices, so that the remaining antennas can be dedicated to energy harvesting (EH) simultaneously. Consequently, the proposed scheme enjoys the advantages of improved system achievable rate (AR), simultaneous EH and IT, and self-energy recycling (SE-R) while requiring no backhaul links between the WD and the information receiver. Numerical results verify the AR enhancement of the proposed scheme with a Gaussian input over the existing time switching-based WPC protocol, the antenna selection-based WPC protocol, and SE-R without SM. <s> BIB004 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> D. SM Based Simultaneous Wireless Information and Power Transfer (SWIPT) <s> This letter proposes a dual-hop two-way full-duplex cooperative system, where spatial modulation is used at the sources and energy harvesting is employed at the wireless powered relay. We combine the physical-layer network coding and the fixed-gain amplify-and-forward relaying techniques for two-way transmission. For the simultaneous information and wireless power transfer, the power-splitting protocol is employed at the relay, which has no external power supply. A new unified tight upper-bound bit error rate (BER) expression is derived in a closed-form for both full-duplex and half-duplex transmission schemes. The accuracy of our analyses is verified by various Monte Carlo type computer simulations. The numerical results reveal that the full-duplex scheme can provide considerably better BER performance compared to the conventional half-duplex scheme as the quality of loop-interference cancellation improves and/or the spectral efficiency requirement increases. <s> BIB005 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> D. SM Based Simultaneous Wireless Information and Power Transfer (SWIPT) <s> In this paper, we investigate the application of spatial-modulation (SM) in multi-antenna full-duplex (FD) decode-and-forward (DF) relay networks with simultaneous wireless information and power transfer (SWIPT). Both the time switching (TS) and power splitting (PS) protocols are employed. In the proposed scheme, a subset of relay antennas are selected to forward the received information signal with the harvested energy and the remaining inactive antennas receive the energy signal/information signal from the source node. The application of SM at the relay node leads to the throughput improvement of the relay-to-destination link because of the additional information mapped to the active antenna indices, which consequently leads to the overall system throughput improvement. According to the proposed tight SM mutual information (MI) upper bound, we provide a theoretical solution for the system throughput optimization. Monte-Carlo simulations verify the significant throughput gain facilitated by SM as well as the validity of the throughput optimization. <s> BIB006
In all works mentioned above, the inactive antennas of an SM node are either kept idle or turned on for signal reception when operating in full-duplex mode. With the development of SWIPT technology, researchers begin to realize a new energy harvesting function of the inactive antennas in SM systems. SM based SWIPT has been therefore receiving considerable attention recently. Since the research topic is relatively new, there are only a few works in the literature. In summary, they can be still classified into three categories. In the first category, the SM signal is exploited for SWIPT by power splitting BIB002 - BIB001 , BIB003 . Specifically, in BIB002 a power splitting-based SWIPT is considered for an SM system with a multiple-antenna receiver. The authors assume different power splitting factors for different receive antennas and develop an iterative algorithm to find the optimal values in maximizing the achievable rate under certain energy harvesting constraints. Reference BIB005 develops a dual-hop relaying network using SM at both sources and physical-layer network coding, where the relay obtains required energy from the RF SM signals via the power splitting protocol. Both full-duplex and half-duplex modes are considered for the network, and the full-duplex mode is shown to outperform its half-duplex counterpart as the quality of self-interference cancellation and/or the spectral efficiency increases. While BIB002 and BIB005 consider transmit SM, BIB001 and BIB003 shed light on the application of receive SM to SWIPT. In BIB001 , an energy pattern aided SWIPT system is proposed, where the information is conveyed not only by the indices of the activated receive antennas but also by the specific intensity of the delivered power. Results on BER demonstrate the beneficial immunity of the proposed system to power conversion. Unlike BIB001 that focuses on joint design, BIB003 proposes to transmit a separated energy and receive SM signals, such that the predefined energy signal can be removed at the information receiver to facilitate signal detection. In the second category, the SM node participates in both information decoding and energy harvesting BIB004 , BIB006 . This idea was first coined in BIB004 , where a GSM node communicates to an information receiver through the active antennas while harvesting energy transmitted from an energy transmitter and recycling part of its self-energy through the inactive antennas. Enhancement in terms of achievable rate over the existing time switching-based and antenna selection-based wireless powered communication protocols is verified therein. Later, the idea was extended to a dual-hop relaying network in BIB006 , where a GSM-based full-duplex relay without an external power supply is assumed, and three different realizations were proposed. While both the first and second methods are based on time switching, the third method is based on power splitting. The first method performs energy harvesting first, suffering from self-interference in the following information decoding step, while by reversing the order the second method turns the adverse self-interference into an advantage to energy harvesting as BIB004 . The third method carries out information decoding and energy harvesting simultaneously all the time, improving the transmission efficiency. In the third category, the SWIPT capability is developed for distributed SM  . Assuming multiple geometrically separated single-antenna relays to form distributed SM, the authors of  propose two different protocols to enable SWIPT. The first protocol allows each relay node to harvest energy transmitted from the source, which is used by the activated relay to forward the source's and its own data simultaneously. The second protocol exploits the inactive relays to recycle part of the transmitted energy in the network in addition to harvesting the transmitted energy from the source. Both protocols retain the original properties of DSM, but the second protocol enjoys a lower hardware complexity and better error performance than the first protocol in certain scenarios.