A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Non-Orthogonal Multiple Access (NOMA) Aided SM <s> In this study, we seek to characterise the behaviour of Spatial modulation (SM) in the multiple access scenario. By only activating a single transmit antenna for any transmission, SM entirely avoids inter-channel interference, requires no synchronisation between the transmit antennas and a single radio frequency chain at the transmitter. Most contributions thus far have only addressed aspects of SM for a point-to-point communication system. We propose a maximum-likelihood (ML) detector which can successfully decode incoming data from multiple simultaneous transmissions and does not suffer from the near-far problem. We analyse the performance of the interference-unaware and interference-aware detectors. We look at the behaviour of SM as the signal-to-interference-plus-noise ratio goes to infinity and compare it to the complexity and cost equivalent single-input-multiple-output (SIMO) system. Two systems are considered to be equivalent in terms of complexity if their respective detection algorithms are of the same order in O(·) notation. Simulation results show that the interference-aware SM detector performs better than the complexity equivalent multi-user ML-SIMO detector by at least 3 dB at an average bit-error-ratio of 10 −3 . <s> BIB001 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Non-Orthogonal Multiple Access (NOMA) Aided SM <s> Non-orthogonal multiple access (NOMA) is a promising candidate for future radio networks, as it effectively utilizes frequency and time resources and has higher spectral efficiency. In this problem we address a problem in NOMA based communication systems when both the users has the same channel gain, in which case NOMA performance degrades considerably. To solve this issue a switching mechanism between NOMA and spatial modulation (SM) is introduced. Simulation results shows that better spectral efficiency can be achieved using the proposed switching scheme. <s> BIB002 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Non-Orthogonal Multiple Access (NOMA) Aided SM <s> The non-orthogonal multiple access (NOMA) technology has been proposed and regarded as one of the potential promising technologies for the future 5G network. The extension of generalized spatial modulation multiple-input multiple-output (MIMO) to NOMA system improves both the spectral and energy efficiencies of the system, while maintaining the massive connectivity and low latency advantages, but it puts forward challenges for the multi-user and signal detection as well. In this paper, we propose a joint user activity and signal detection scheme based on the block-sparse compressive sensing (BS-CS) method in the uplink NOMA system, in which the generalized spatial modulation MIMO technology is used. By exploiting the structure and sparsity of the multi-user generalized spatial modulation signals, we formulate the detection problem into a block-sparse recovery problem. Then a BS-CS based detection algorithm, enhanced structured block-sparse compressive sampling matching pursuit (ESB-CoSaMP), is proposed to detect the active users and transmitted data efficiently. Moreover, the information of active antennas at each user is exploited in ESB-CoSaMP to further improve the accuracy. Simulations show that the proposed detection scheme outperforms the conventional CS and BS-CS based schemes. <s> BIB003 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Non-Orthogonal Multiple Access (NOMA) Aided SM <s> Spatial modulation (SM) has emerged as a low-complexity and energy-efficient multiple-input multiple-output transmission technique, where the information bits are not only transmitted by amplitude phase modulation but also conveyed by the index of activated transmit antenna (TA). By deploying SM in downlink multi-user (DL-MU) scenarios, conventional orthogonal multiple access-based SM (OMA-SM) allocates exclusive time-frequency resources to users, but suffers from low spectral efficiency. TA grouping-based SM (TAG-SM) divides TAs into sub-groups to serve different users independently, but suffers from severe inter-user interference. By introducing non-OMA (NOMA) into SM for DL-MU transmission, NOMA-based SM (NOMA-SM) is proposed to mitigate inter-user interference, while maintaining high spectral efficiency. Specifically, by applying successive interference cancellation at user side, the inter-user interference could be effectively eliminated with the sacrifice of increased computational complexity. Afterward, based on a symbol error rate analysis, a low-complexity power allocation scheme is provided to achieve high spectral efficiency through power domain multiplexing. When considering near-far effect from user distribution, user pairing issue is also discussed. Numerical simulation compares NOMA-SM with OMA-SM and TAG-SM, and verifies the effectiveness of the proposed low-complexity power allocation and user pairing methodologies. <s> BIB004 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Non-Orthogonal Multiple Access (NOMA) Aided SM <s> As the conventional spatial modulation (SM) system lacks an efficient downlink multiple access scheme, this paper proposes a novel downlink nonorthogonal multiple access aided multiple-input multiple-output SM system with finite alphabet inputs. Mutual information (MI) is used to characterize the system's achievable spectral efficiency (SE). Because the MI lacks a closed-form formulation, in this paper we propose a computational-efficient lower bound to provide an approximation to the simulated MI. Besides, preprocessing is also designed at the receiver to mitigate the detrimental effect of channel correlation, which leads to striking a higher SE performance. Simulation results not only confirm the accuracy of our SE analysis, but also substantiate the superior SE performance achieved by the proposed preprocessing. <s> BIB005 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Non-Orthogonal Multiple Access (NOMA) Aided SM <s> In this paper, a novel spatial modulation aided non-orthogonal multiple access (SM-NOMA) system is proposed. We use mutual information (MI) to characterize the achievable spectral efficiency (SE) of the proposed SM-NOMA system. Due to the finite-alphabet space-domain inputs employed by SM, the expression of the corresponding MI lacks a closed-form formulation. Hence, a lower bound is proposed to quantify the MI of the SM-NOMA system. Furthermore, its asymptotic property is also theoretically investigated in both low and high signal-to-noise ratio (SNR) regions. The SE performance and its analysis of our proposed SM-NOMA system are confirmed by simulation results. <s> BIB006 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Non-Orthogonal Multiple Access (NOMA) Aided SM <s> Among the key technologies that have been developed for efficient transmission for 5G, are spatial modulation (SM) and non-orthogonal multiple access (NOMA). In SM, multiple transmission antenna is modulated as information in order to increase capacity. On the other hand, NOMA allows to share the same frequency resources at the same time. Obviously, combination of these two techniques offers a new accomplishment for wireless transmission. In this paper, we develop a new technique to combine SM and NOMA for uplink transmission. A hybrid detection scheme is introduced in order to estimate information in receiver side. In transmitter, we set maximum transmission power for near-end user (NEU) and lower transmission power for far-end user (FEU). The main idea of our proposed detection scheme is to perform maximum receive ratio combining (MRRC) to obtain antenna index and then estimate the corresponding symbol for NEU. Afterwards, we apply successive interference cancellation (SIC) to the total received signal in order to eliminate NEU's signal. Finally, maximum likelihood estimation (MLE) is applied to the remaining signal to estimate FEU's antenna index and transmitted symbol. As the result, we also present the bit error rate (BER) comparison and achievable user and system transmission bits. <s> BIB007 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Non-Orthogonal Multiple Access (NOMA) Aided SM <s> At the time of writing, vehicle-to-vehicle (V2V) communication is enjoying substantial research attention as a benefit of its compelling applications. However, the ever-increasing tele-traffic is expected to result in overcrowding of the available band. As a first resort, multiple input multiple output (MIMO) can be utilized to enhance the attainable bandwidth efficiency or link reliability. However, in hostile V2V wireless propagation environments, the achievable multiple-antenna gain is eroded by the channel correlation. As a promising MIMO technique, spatial modulation (SM) only activates a single transmit antenna (TA) in any symbol interval and, hence, completely avoids the inter-antenna interference, hence showing robustness against channel correlation. As a further powerful solution, non-orthogonal multiple access (NOMA) has been proposed for improving the bandwidth efficiency. Inspired by the robustness of SM against channel correlation and the benefits of NOMA, we intrinsically amalgamate them into NOMA-SM in order to deal with the deleterious effects of wireless V2V environments as well as to support improved bandwidth efficiency. Moreover, the bandwidth efficiency of NOMA-SM is further boosted with the aid of a massive TA configuration. Specifically, a spatio-temporally correlated Rician channel is considered for a V2V scenario. We investigate the bit error ratio performance of NOMA-SM via Monte Carlo simulations, where the impact of the Rician $K$ -factor, spatial correlation of the antenna array, time-varying effect of the V2V channel, and the power allocation factor is discussed. Furthermore, we also analyze the capacity of NOMA-SM. By analyzing the capacity and deriving closed-form upper bounds on the capacity, a pair of power allocation optimization schemes are formulated. The optimal solutions are demonstrated to be achievable with the aid of our proposed algorithm. Again, instead of simply invoking a pair of popular techniques, we intrinsically amalgamate SM and NOMA to conceive a new system component exhibiting distinct benefits in the V2V scenarios considered. <s> BIB008 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Non-Orthogonal Multiple Access (NOMA) Aided SM <s> Inspired by the robustness of spatial modulation (SM) against channel correlation and the benefits of non-orthogonal multiple access (NOMA), in this paper, we intrinsically amalgamate them into NOMA-SM in order to deal with the deleterious effects of wireless vehicle-to-vehicle (V2V) environments as well as to support improved bandwidth efficiency. Specifically, a spatio-temporally correlated Rician channel is considered for a V2V scenario. We derive the capacity of NOMA-SM and a pair of analytical capacity upper bounds in closed form. A power allocation optimization scheme is formulated accordingly and the optimal solution is demonstrated to be achievable with the aid of our proposed algorithm. By investigating the bit error ratio (BER) performance of NOMA with different multiple-antenna techniques and the bandwidth efficiency of SM combined with distinct multiple access methods, NOMA and SM are shown to cooperatively improve V2V transmissions. <s> BIB009 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Non-Orthogonal Multiple Access (NOMA) Aided SM <s> The terrestrial return channel provides interactive services in digital television terrestrial broadcasting systems to meet various consumers’ demands around the world. The extension of non-orthogonal multiple access and generalized spatial modulation multiple-input multiple-output to the terrestrial return channel improves both the spectral and energy efficiencies of the system, but it puts forward detection challenges. In this paper, a joint user activity and signal detection scheme based on the block-sparse compressive sensing (BS-CS) method in the terrestrial return channel is proposed, in which the generalized spatial modulation technology is used. By exploiting the structure and sparsity of the multi-user generalized spatial modulation signal, we formulate the detection problem into a block-sparse recovery problem. Then a BS-CS-based detection algorithm, enhanced structured block-sparse compressive sampling matching pursuit (ESB-CoSaMP), is proposed to detect the active users and transmitted data efficiently. Moreover, the information of active antennas at each user is exploited in ESB-CoSaMP to further improve the accuracy. Simulations show that the proposed detection scheme outperforms the conventional CS and BS-CS-based schemes. <s> BIB010 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Non-Orthogonal Multiple Access (NOMA) Aided SM <s> Multi-antenna non-orthogonal multiple access (NOMA) is a promising technique to significantly improve the spectral efficiency and support massive access, which has received considerable interests from academic and industry. This article first briefly introduces the basic idea of conventional multi-antenna NOMA technique, and then discusses the key limitations, namely, the high complexity of successive interference cancellation(SIC) and the lack of fairness between the user with a strong channel gain and the user with a weak channel gain. To address these problems, this article proposes a novel spatial modulation (SM) assisted multi-antenna NOMA technique, which avoids the use of SIC and is able to completely cancel intra-cluster interference. Furthermore, simulation results are provided to validate the effectiveness of the proposed novel technique compared to the conventional multi-antenna NOMA. Finally, this article points out the key challenges and sheds light on the future research directions of the SM assisted multi-antenna NOMA technique. <s> BIB011 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Non-Orthogonal Multiple Access (NOMA) Aided SM <s> In order to support high-user-load multiple-access (MA), we propose a non-orthogonal MA scheme based on a beneficial amalgam of spatial modulation (SM) and sparse code-division multiple-access (SCDMA), which is termed the SM-SCDMA. Hence, SM-SCDMA inherits both the merits of SM with single radio-frequency MIMO transceiver implementation and the advantages of SCDMA relying on low-complexity signal detection. In this paper, we evaluate the potential of SM-SCDMA as well as its low-complexity near-optimum signal detection. Given these objectives, we consider both the maximum likelihood detection and the message passing algorithm aided detection (MPAD) that is derived based on the maximum a posteriori principles. In order to evaluate the performance of large SM-SCDMA without relying on time-consuming simulations, we propose new approaches for analyzing the performance of SM-SCDMA systems. A range of formulas that are valid in the signal-to-noise ratio region of practical interest are derived. Finally, the performance of SM-SCDMA systems is investigated by addressing diverse design concerns. Our studies and performance results show that SM-SCDMA constitutes a promising MA scheme for the future ultra dense systems. Assisted by the MPAD, it is capable of supporting high-user-load MA transmission associated with a normalized user-load factor of two. <s> BIB012 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Non-Orthogonal Multiple Access (NOMA) Aided SM <s> In this paper, a novel multi-user multiple-input multiple-output (MIMO) transmission scheme, called non-orthogonal multiple access (NOMA) aided precoded spatial modulation (PSM) (NOMA-PSM) is proposed for overloaded downlink transmissions. NOMA-PSM beneficially amalgamates the concept of index modulation (IM) and NOMA techniques, and therefore it inherits both the merits of IM with low-complexity transceiver and the advantages of NOMA with high bandwidth efficiency. For the proposed scheme, we develop a pair of low-complexity yet effective detection algorithms by combining the spatial index demodulation and successive interference cancellation. The spectral efficiency (SE), implementation cost, and multi-user interference of NOMA-PSM are evaluated and compared with conventional designs. Furthermore, we derive the mutual information (MI) of the proposed NOMA-PSM to characterize its achievable SE and also obtain a lower bound for simplifying the measurement of MI. Our simulation results show that the proposed NOMA-PSM scheme is capable of achieving considerable performance gains over conventional orthogonal multiple access aid PSM and antenna-grouping-based PSM in wireless MIMO fading channels. <s> BIB013 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. Non-Orthogonal Multiple Access (NOMA) Aided SM <s> The combination of non-orthogonal multiple access (NOMA) and multiple-input multiple-output (MIMO) signaling is capable of providing significantly improved spectral efficiency and effective multiple access. However, conventional MIMO-NOMA entails significantly increased power consumption and implementation complexity. Inspired by the essence of spatial modulation (SM), in this paper, a novel three-node cooperative relaying system (CRS) using SM-aided NOMA, termed CRS-SM-NOMA, is proposed, in which the messages for two users are conveyed by two different information-bearing units of SM. As the reference scheme, conventional CRS-NOMA is further re-investigated with multiple receive antennas. Besides the achievable rate, which is adopted by most of the existing NOMA works as the performance metric, the bit error rate (BER) of CRS-SM-NOMA and CRS-NOMA is analyzed assuming maximum-likelihood detection. Approximate bit error probability expressions are derived in closed form for both users. Simulation results verify the analysis and show that the proposed CRS-SM-NOMA outperforms conventional CRS-NOMA and SM-OMA in terms of the BER as well as ergodic sum rate. <s> BIB014
NOMA, which exhibits great potential in supporting both massive connectivity and low transmission latency, has been envisioned as one of the most promising technologies to accommodate more active users in the future network  . In NOMA networks, multiple users share the same channel resource and are multiplexed in the power domain via superposition coding at the transmitter  . To mitigate inter-user interference, multi-user detection (MUD) techniques such as successive interference cancellation (SIC) are typically employed at the receiver. On the other hand, most research works of SM focus on the point-to-point transceiver design and current multi-user SM systems usually suffer from inter-user interference BIB001 . Recalling that NOMA can effectively mitigate inter-user interference, NOMA aided SM emerges as a competitive technology in multi-user communications to achieve high spectral efficiency and energy efficiency yet maintain low deployment cost and reduced inter-user interference. In particular, NOMA-SM strikes an appealing trade-off between spectral efficiency, energy efficiency, and interference mitigation. Towards this direction, researchers are motivated to promote the deployment of NOMA aided SM and aim to explore both the potential benefits of SM with low-complexity design and NOMA with high bandwidth efficiency. In BIB010 and BIB003 , (G)SM is introduced to the NOMA system to improve both spectral efficiency and energy efficiency in the terrestrial return channel and uplink channel, respectively, in which the joint detection problem of user activity and (G)SM signals is explored by exploiting the block-sparse model. NOMA-based SM is proposed in BIB004 for downlink multi-user communications, which mitigates inter-user interference effectively via SIC and achieves high spectral efficiency at the cost of some performance degradation. In BIB013 , NOMA-aided precoded SM is proposed for downlink multi-user communications under overloaded transmissions, in which the demodulation of precoded SM is integrated into SIC to obtain effective detection algorithms and analytical results in terms of spectral efficiency, implementation cost, multi-user interference, and mutual information are also derived to evaluate the system performance. In BIB005 and BIB006 , NOMA-aided SM schemes with finite alphabet inputs are proposed for uplink and downlink communications, respectively, in which the lower bound on mutual information is derived to characterize the system's achievable rate. It is noted that NOMA generally exploits inter-user channel strength disparities to achieve an effective spectral utilization. Nevertheless, NOMA performance may degrade considerably when different users have a similar channel gain. Noticing this issue, BIB002 proposes a switching mechanism between NOMA and SM, which maintains better spectral efficiency under minor inter-user channel strength disparities. Against the switching mechanism, the combination scheme of NOMA and SM is developed for uplink transmissions in BIB007 , in which a hybrid detection scheme is proposed to estimate the antenna index and then the constellation symbols. In BIB008 and BIB009 , the combination scheme of NOMA and SM is proposed for vehicle-to-vehicle communications, in which the index of one active antenna embeds one specific user's information and the superposition coded symbol carried by the active antenna conveys the information for other users. It is worth pointing out that in the works mentioned above, the implementation of superposition coding and SIC may incur a high computational cost as the number of users grows large. Moreover, interference cancellation can be imperfect in practice, which causes error propagation and further degrades the system performance. To circumvent this issue, the study of BIB011 develops a primitive SM assisted NOMA technique with antenna partitioning to support multi-user access, which avoids the utilization of SIC at the receiver and refrains from multi-user interference. Furthermore, the SM-aided NOMA scheme is investigated under a three-node cooperative network in BIB014 , in which the information carried by the index of one active antenna and the constellation symbol is separately delivered to two users to avoid the utilization of SIC as well as improve the system performance. To support massive connectivity, SM aided code-division multiple-access is proposed as a NOMA-SM scheme for uplink communications in BIB012 , whose performance and low-complexity signal detection problem are also investigated.