A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> In this paper, the spatial modulation (SM) is considered as a novel physical layer technique to improve the physical layer security of wireless networks. Exploiting the index of antenna as an additional dimension to convey part of source information bits, SM helps to achieve multiplexing gain and realize higher data rates. Moreover, by properly designing the transmission signal, SM can also improve physical layer security. The secrecy mutual information of SM with finite alphabet input is derived in this work, and a preceding scheme is proposed to improve the physical layer security performance of SM. Analysis and numerical results verify the validity and effectiveness of the proposed scheme, and it also shows that the maximum achievable secrecy mutual information is the logarithm of the number of transmit antennas. <s> BIB001 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> Spatial modulation (SM) and space shift keying (SSK) use only one out of several transmit antennas at a time to transmit data via an antenna index. In such a system, the information is encoded by exploiting channel randomness i.e. the fact that channels between different transmit and receive antennas are random. This difference is used to distinguish among the transmit antennas. While SSK uses only antenna index to transmit data, SM also uses ordinary signal modulation. In wireless secrecy systems, one of the key performance measures is secrecy capacity. It specifies the rate at which the transmitter can communicates on the main link to the desired receiver while this information cannot be decoded by the eavesdropper. We investigate SM and SSK in the context of wireless secrecy capacity when the underlying modulation and the difference between the legitimate and eavesdropper signal to noise ratios (SNRs) are varied. <s> BIB002 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> Spatial modulation (SM) and space shift keying (SSK) represent transmission methods for low-complexity implementation of multiple-input multiple-output (MIMO) wireless systems in which antenna indices are employed for data transmission. In this paper, we focus our attention on the secrecy behavior of SSK and SM. Using an information-theoretic framework, we derive expressions for the mutual information and consequently compute achievable secrecy rates for SSK and SM via numerical evaluations. We also characterize the secrecy behavior of SSK by showing the effects of increasing the number of antennas at the transmitter as well as the number of antennas at the legitimate receiver and the eavesdropper. We further evaluate the secrecy rates achieved by SM with different sizes of the underlying signal constellation and compare the secrecy performance of this scheme with those of general MIMO and SIMO systems. The proposed framework unveils that SM is capable of achieving higher secrecy rates than the conventional single-antenna transmission schemes. However, it underperfoms compared to a general MIMO system in terms of the achievable secrecy rates. <s> BIB003 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> In this letter, the precoding-aided spatial modulation (PSM) is generalized to a secret PSM (SPSM) scheme, which has the capability to resist malicious eavesdropping from an eavesdropper that is unknown to the transmitter. We design a time-varying precoder for the SPSM so that it can retain all the PSM's advantages at the desired receiver while producing time-varying interference to the eavesdropper. The secrecy capacity of our proposed SPSM is studied, and the optimal power allocation between signal and interference transmission is investigated. Our studies and performance results demonstrate that our SPSM can significantly improve the secrecy performance of the PSM, particularly in a high-signal-to-noise-ratio region. Furthermore, the SPSM is capable of achieving a nonzero secrecy rate even when the eavesdropper has more antennas than the desired receiver. <s> BIB004 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> In multiple-input–multiple-output (MIMO) wireless communications, spatial modulation (SM) has recently emerged as a new transmission method. This letter explores the physical-layer security in typical SM systems. We present a secrecy rate analysis for multiple antenna destination and eavesdroppers receivers. Targeting against passive eavesdroppers in unknown locations, we study the efficacy of active security measure through joint signal and jamming transmission without the typical requirement of eavesdropper channel information. We demonstrate the secrecy rate and transmission power tradeoff in active source jamming by providing numerical results on achieved secrecy rate and the bit error rate (BER) at different receivers. <s> BIB005 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> Precoding-aided spatial modulation (PSM), which conveys information partially by the indices of receive antennas, has some advantages over conventional spatial modulation (SM) using the indices of transmit antennas. In PSM, the precoder may be optimized for different purposes. In this paper, the authors study the transmitter design in the PSM systems, which motivates to provide secrecy communications. Specifically, the authors consider a pair of communication terminals overheard by an eavesdropper. The precoder is optimized by jointly minimizing the power received by the eavesdropper and maximizing the power received by the desired terminal. Both the error performance and the ergodic secrecy rate achievable are studied when assuming communications over independent Rayleigh fading channels. The authors studies show that positive secrecy rate and low-complexity detection can be attainable simultaneously for the desired receiver even when the eavesdropper employs more receive antennas than the desired receiver. <s> BIB006 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> This letter generalizes the precoding-aided spatial modulation (PSM) to a multiuser (MU) downlink scenario. With precoding vectors elaborately designed, a proposed MU-PSM scheme has the capability to resist a multiple antenna eavesdropper. Specifically, signal precoding matrices (SPMs) are designed to cancel the MU interference and modulate partial information bits on the indices of receive antennas. To improve physical layer security, scrambling on SPMs is conceived to construct a fast-varying precoding matrix, which contributes to the degradation at Eve’s blind estimation and detection. Moreover, issues of detection algorithms and a lower bound of secrecy rate are addressed to verify security enhancement in the proposed scheme. <s> BIB007 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> In this paper, the spatial modulation (SM) technique is explored to improve physical layer security in time-division duplex (TDD) wireless communication network. In the designed transmission scheme, the transmitter first exploits the knowledge of legitimate channel state information (CSI) to redefine the transmit antennas' indices which are used to map into spatial bits, then selects one activated antenna based on the renaming rule to transmit the modulation symbol. The communications security can be improved because the eavesdropper cannot detect the spatial bits information without the perfect legal CSI. Our studies derive the secrecy mutual information of the presented method. The numerical results on secrecy mutual information and bit error rate (BER) demonstrate the effectiveness and robustness of the proposed secrecy communications scheme. <s> BIB008 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> Existing secure strategies based on precoding-aided spatial modulation (PSM) ensure the secrecy communication by introducing time-varying interference with extra power towards the eavesdropper, which, however, reduces the energy efficiency. In this paper, we propose two novel schemes to enhance the secrecy performance based on PSM. The first scheme utilizes the random antenna selection (RAS) technique, namely RAS- PSM, to generate zero-forcing (ZF) precoding matrices with randomly activated transmit antennas. It ensures efficient transmission to the legitimate user, while confusing the eavesdropper via the turbulence of RAS without extra power consumption. The second scheme, called hybrid secret PSM (HS-PSM), is an enhanced version of RAS-PSM by introducing the time-varying artificial noise into RAS-PSM. The resulting secrecy rates by the two proposed schemes are theoretically analyzed and evaluated via Monte Carlo simulations as well, whose results demonstrate that RAS-PSM achieves a higher secrecy rate than the existing schemes and HS- PSM is capable of further improving the secrecy performance especially at high signal-to-noise ratio (SNR). <s> BIB009 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> We propose and investigate a full-duplex receiver assisted secure spatial modulation (FDR-SSM) scheme, whose security is enhanced by the jamming sent from a full-duplexing legal receiver. In our FDR-SSM system, jamming signals are designed to allow the legal receiver free from self-interference, while imposing time-varying interference on the passive eavesdropper. Therefore, the FDR-SSM scheme can maintain all the advantages of spatial modulation. In this letter, the secrecy performance of the FDR-SSM system is analyzed via analyzing its ergodic secrecy rate (ESR). Furthermore, the asymptotic ESR is analyzed, when assuming that the number of transmit antennas at the legal receiver approaches infinite. Finally, performance results are provided to demonstrate the efficiency of the FDR-SSM scheme, and to verify the analytical expressions. <s> BIB010 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> To resist the passive eavesdropping while reserving the same hardware cost and receiver structure of the legitimate receiver, a secure quadrature spatial modulation (QSM) scheme is proposed in this letter. Instead of the information symbol, a mixture of the information symbol and artificial noise is transmitted through the activated transmit antennas. The mixed signals are designed, so that the artificial noise is cancelled at the legitimate receiver but cause random interference to the eavesdropper. The secrecy rate is analyzed and the optimal power allocation between the artificial noise and the information signal is investigated. The influence of the number of the eavesdropper’s antennas is discussed. Simulation results show that, for multiple-input-single-output systems, the proposed secure QSM scheme achieves the best secrecy performance among the existing similar schemes by using less radio frequency chains. For multiple-input-multiple-output systems, the secure QSM scheme performs better than the existing secure SM scheme does under the same power constraint and transmission rate. <s> BIB011 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> We propose in this paper a physical layer security (PLS) scheme for dual-hop cooperative networks in an effort to enhance the communications secrecy. The underlying model comprises a transmitting node (Alice), a legitimate node (Bob) and an eavesdropper (Eve). It is assumed that there is no direct link between Alice and Bob, and the communication between them is done through trusted relays over two phases. In the first phase, precoded spatial modulation (PSM) is employed, owing to its low interception probability, while simultaneously transmitting a jamming signal from Bob. In the second phase, the selected relay detects and transmits the intended signal, whereas the remaining relays transmit just the jamming signal received from Bob. We analyze the performance of the proposed scheme in terms of the ergodic secrecy capacity (ESC) and secrecy outage probability (SOP) where we obtain closed form expressions for those metrics. We also optimize the performance with respect to the power allocation among the participating relays in the second phase. We provide examples with numerical and simulations results through which we demonstrate the effectiveness of the proposed scheme. We also provide a comparison of the bit error rate (BER) at Bob and Eve by simulation. <s> BIB012 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> Mobile crowdsensing enables convenient sensory data collection from a large number of mobile devices and has found various applications. In the real practice, however, the sensory data collected from various mobile devices are usually unreliable. To extract truthful information from the unreliable sensory data in mobile crowdsensing, the topic of truth discovery has received wide attention recently, which essentially operates by estimating user reliability degrees and performing reliability-aware truthful aggregation. Despite the effectiveness, applying truth discovery in mobile crowdsensing faces several privacy and security challenges. First, the sensory data and reliability degrees of users may reveal privacy-sensitive information and, thus, demand strong protection. Second, the requester that initiates a crowdsensing application usually needs to have monetary investment, so the inferred truths can be the requester's proprietary information and should be protected as well. In this paper, we propose a new system architecture enabling encrypted truth discovery in mobile crowdsensing. We focus on general and realistic mobile crowdsensing scenarios with varying levels of user participation, and our security design is built on the confidence-aware truth discovery (CATD) approach for its state-of-the-art accuracy in such scenarios. In our system architecture, users send encrypted sensory data to the cloud, where CATD is then conducted in the encrypted domain. The final encrypted inferred truths are sent to the requester for decryption. Along the whole workflow, the sensory data and reliability degrees of users, as well as the inferred truths of the requester, are kept private. Extensive experiments over real-world mobile crowdsensing dataset show that our design achieves practical performance on mobile devices. <s> BIB013 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> The precoding-aided spatial modulation (PSM) is first characterized with respect to its secrecy performance, which shows that the PSM is a secrecy embedded communication scheme when operated in the time-division duplex mode, but experiences security risk under frequency-division duplex mode. Therefore, we extend the PSM to a secret PSM (SPSM) that is suitable for operation in any communications scenarios experiencing passive eavesdropping. In the proposed SPSM, the secrecy performance is enhanced by using a part of transmit power to interfere the eavesdropper’s reception. In this paper, the secrecy performance of SPSM with discrete inputs is comprehensively investigated in terms of both bit error rate and secrecy rate and by both analysis and simulations. Relying on the asymptotic analysis, we also derive the upper and lower bounds for the error performance and secrecy rate of SPSM. Furthermore, we study the power allocation between information and interference transmission in order to maximize SPSM’s secrecy performance. Our studies result in a range of expressions, which are validated by Monte Carlo simulations. Furthermore, our studies demonstrate that the analytical formulas are beneficial to the optimization of SPSM systems for maximizing its security performance. <s> BIB014 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> In this paper, a secure spatial modulation (SM) system with artificial noise (AN)-aided is investigated. To achieve higher secrecy rate (SR) in such a system, two high-performance schemes of transmit antenna selection (TAS), leakage-based and maximum secrecy rate (Max-SR), are proposed and a generalized Euclidean distance-optimized antenna selection (EDAS) method is designed. From simulation results and analysis, the four TAS schemes have an decreasing order: Max-SR, leakage-based, generalized EDAS, and random (conventional), in terms of SR performance. However, the proposed Max-SR method requires the exhaustive search to achieve the optimal SR performance, thus its complexity is extremely high as the number of antennas tends to medium and large scale. The proposed leakage-based method approaches the Max-SR method with much lower complexity. Thus, it achieves a good balance between complexity and SR performance. In terms of bit error rate (BER), their performances are in an increasing order: random, leakage-based, Max-SR, and generalized EDAS. <s> BIB015 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> Advances in physical layer security techniques have increasingly demonstrated their potential to replace security functionalities that are traditionally included in the upper layers of the Open Systems Interconnection model. This has made it possible for devices with limited layer structures or/and restricted hardware components to offer security measures. In this paper, we consider spatial modulation (SM) systems and propose a unique physical layer technique that uses a random constellation mapping criterion for secret key exchange. The principle idea here is to exploit the inherent symbol-antenna mapping feature of the SM technique to encode the secret key. Specifically, a random phase shift is imposed on each of the modulated symbols using a channel driven approach to uniquely authenticate the transmitted key bits or/and the encrypted confidential data. The results demonstrate that the proposed technique is superior to benchmark techniques in terms of computational complexity and key bit error rate. It will also be shown that the proposed technique offers greater flexibility in terms of the authentication process preference, which is normally unattainable in most of the key exchange proposed techniques. <s> BIB016 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> In this letter, we propose a new secrecy enhancement scheme for spatial modulation systems by exploiting the knowledge of the legitimate channel state information to rotate the indices of the transmit antennas and the constellation symbols, which are mapped into spatial and constellation bits. A secrecy rate analysis shows that the eavesdropper cannot recover any information carried by spatial and constellation bits. The numerical results on the secrecy rate and the bit error rate verify the effectiveness and robustness of the proposed scheme. <s> BIB017 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> In this paper, a novel transmission strategy, referred to as mapping-varied spatial modulation, is proposed for physical layer security, where the transmitter varies mapping patterns for the radiated information and the antenna information of spatial modulation, based on the instantaneous pattern of legitimate channel quality information that is unknown to eavesdroppers. Therefore, eavesdroppers cannot successfully decode the confidential information and the transmission over the legitimate link is secured from the wire-tap of eavesdroppers, without relying on higher-layer encryption. An important virtue of the proposed transmission strategy is that the transmitter does not need to know eavesdroppers’ channels states at all. To further demonstrate the advantage of this scheme, its secrecy rate was formulated for the purpose of facilitating the performance evaluation. Moreover, illustrative numerical results pertaining to the metrics of ergodic secrecy rate and secrecy outage probability not only substantiate the validity of the proposed transmission strategy, but also provide useful references for the system design with the mapping-varied spatial modulation, from the view of physical layer security. <s> BIB018 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Security Provisioning in SM <s> The security issue is considered for a cooperative communication system with multiple nondedicated relays, which have their own information to transmit. Distributed spatial modulation (DSM) is a promising technique for nondedicated relay networks. However, any receiver in the relays’ coverage can decode the source information by examining the status of the relays in conventional DSM systems. To prevent the eavesdropper from intercepting the source information and, at the same time, guarantee the transmissions of the relays, a secure distributed spatial modulation (SDSM) scheme is proposed in this paper. In the broadcasting phase, the relays that can successfully decode the source signal form a decoding set. In the relaying phase, only a certain number of the relays in the decoding set carry the source information via their indices, while all the relays in the decoding set transmit their own information simultaneously. By designing a precoder for these relays’ signals, the destination can extract the source information in the spatial domain, but the eavesdropper is confused by the concurrent transmissions of the relays. The secrecy rate analysis shows that the mutual information from the source to the eavesdropper is zero. Simulation results validate the superiority of the proposed SDSM scheme when compared with the competing candidates. <s> BIB019
Due to the broadcast characteristics of the wireless interface, like other wireless transmission technologies, SM transmissions also face the security and information leakage challenges. Specifically, the confidential messages delivered to legitimate users may be intercepted by malicious eavesdroppers. As a result, ensuring secure transmission of SM becomes a critical topic in the application of wireless networks. By complementing cryptographic techniques at the upper networking layers BIB013 , PLS is an efficient alternative to improve the secrecy performance by exploiting the features of the wireless interface (e.g., randomness, variability, discrimination, reciprocity, etc.) BIB001 . It is worth pointing out that from the physical layer perspective, both PLS and SM highly rely on the randomness and discrimination properties of the wireless interface. Thus, an interesting problem arises when exploiting the channel properties to achieve confidential information exchange among legitimate nodes using SM techniques such that eavesdroppers fail to recover the information. Therefore, advanced signal processing techniques may be applied to amplify the discrimination between the legitimate channel and wiretap channel, which benefits the legitimate node and impairs the eavesdropper at the same time. Moreover, SM activates one antenna randomly for each channel use via a fast antenna-switching mechanism, which presents a fast time-varying environment to the received signal of the eavesdropper. This information-driven antenna-switching mechanism makes it more difficult for the eavesdropper to intercept the modulation information carried on the randomly activated antenna, especially when the mapping rule is unknown to the eavesdropper. Therefore, SM enjoys a great potential not only in the increased spectral efficiency and energy efficiency, but also in enhancing secure transmission. In BIB002 and BIB003 , some preliminary results on the secrecy capacity for both SSK and SM are presented, and the effects of the constellation size, received signal-to-noise ratio (SNR), and number of antennas at the transceiver on the secrecy behavior are examined. Assuming that the CSI of the eavesdropper is available in the multiple-input-singleoutput (MISO) system, BIB001 studies the secrecy mutual information of SM under the finite input alphabet constraint and develops a precoding based SM method to enhance the security performance. Under the assumption of an available global CSI at the transmitter, the optimization problem of the precoding-aided SM system is investigated in BIB006 to improve the secure performance, which maximizes the ratio of the received signal power at the legitimate user to that at the eavesdropper. However, acquiring the eavesdropper's CSI may not be possible at the transmitter for passive eavesdroppers. Without knowing the eavesdropper's CSI, artificial interference is introduced to the SM system for ensuring secure transmission in BIB007 , BIB004 , BIB005 , BIB014 , where BIB007 extends the precoding-aided SM technique to a multiuser downlink case against the multiple antenna eavesdropper. In BIB009 , two random antenna selection methods are developed for precoding based SM to improve the secrecy rate, which severely degrades the reception quality of the passive eavesdroppers without degrading the received signal at destination. In BIB015 , two transmit antenna selection methods based on the maximization of signal-to-leakage-and-noise ratio and secrecy rate are developed for artificial interference-aided SM systems to enhance the transmission security. A full-duplex legitimate receiver is introduced to the secure SM system in BIB010 , which not only receives the secret information from the source, but also emits jamming signals to cause time-varying interference at the passive eavesdropper. Under the framework of QSM, an anti-eavesdropping scheme is proposed by transmitting mixed signals of the information symbol and the carefully designed artificial noise via randomly activated antennas BIB011 . In BIB016 , by exploiting the randomness of the constellation mapping principle to encrypt the secret information, a novel scheme is presented for the secret key exchange and authentication in the SM system. In BIB008 , based on the channel reciprocity of time-division duplexing communications and knowledge of legitimate CSI, the transmitter dynamically redefines the mapping rule of the spatial information to the active antenna indices for security purpose, and then chooses the active antenna according to the redefined mapping rule. Since a redefined mapping rule is unknown by the eavesdropper due to lack of the legitimate CSI, the security of the spatial information can be guaranteed whereas the constellation information is not secure. Attentive to the security issue of the constellation information, BIB017 dynamically rotates the active antenna indices and the constellation symbols at the transmitter according to the instantaneous legitimate CSI, which is totally unknown to the eavesdropper. As a result, both the spatial information and constellation information are secure from the eavesdropper. Moreover, by leveraging the random state of the legitimate channel, the mapping-varied SM scheme is proposed in BIB018 , which dynamically rearranges the mapping patterns of the antenna index bits and constellation bits according to the instantaneous legitimate channel quality. Without knowing the legitimate channel state, the eavesdroppers are confused with variable information mapping patterns and the PLS can be further enhanced. The design of the SM technique for secure cooperative communication systems is also investigated in BIB019 and BIB012 . In BIB019 , a securely distributed SM scheme is deployed in multiple non-dedicated relays to defend against eavesdropping attacks and coordinate the transmission of source-destination information via the indices of the selected relays. In particular, the selected relays are equipped with specifically designed precoder to facilitate the decoding of spatial information at the legitimate receiver while confusing the eavesdropper. In BIB012 , a precoded SM-based cooperative network using relay selection and jamming is investigated with secrecy considerations, where Alice applies precoded SM and Bob emits a jamming signal simultaneously for security protection in the first phase while multiple relays coordinate the information transmission and jam the eavesdroppers in the second phase. Moreover, the power allocation optimization problem among the cooperative relays and the performance in terms of secrecy capacity and outage probability are studied.