An Overview of Physical Layer Security With Finite-Alphabet Signaling <s> G. Secure Spatial Modulation <s> Spatial modulation (SM) is a recently developed transmission technique that uses multiple antennas. The basic idea is to map a block of information bits to two information carrying units: 1) a symbol that was chosen from a constellation diagram and 2) a unique transmit antenna number that was chosen from a set of transmit antennas. The use of the transmit antenna number as an information-bearing unit increases the overall spectral efficiency by the base-two logarithm of the number of transmit antennas. At the receiver, a maximum receive ratio combining algorithm is used to retrieve the transmitted block of information bits. Here, we apply SM to orthogonal frequency division multiplexing (OFDM) transmission. We develop an analytical approach for symbol error ratio (SER) analysis of the SM algorithm in independent identically distributed (i.i.d.) Rayleigh channels. The analytical and simulation results closely match. The performance and the receiver complexity of the SM-OFDM technique are compared to those of the vertical Bell Labs layered space-time (V-BLAST-OFDM) and Alamouti-OFDM algorithms. V-BLAST uses minimum mean square error (MMSE) detection with ordered successive interference cancellation. The combined effect of spatial correlation, mutual antenna coupling, and Rician fading on both coded and uncoded systems are presented. It is shown that, for the same spectral efficiency, SM results in a reduction of around 90% in receiver complexity as compared to V-BLAST and nearly the same receiver complexity as Alamouti. In addition, we show that SM achieves better performance in all studied channel conditions, as compared with other techniques. It is also shown to efficiently work for any configuration of transmit and receive antennas, even for the case of fewer receive antennas than transmit antennas. <s> BIB001 </s> An Overview of Physical Layer Security With Finite-Alphabet Signaling <s> G. Secure Spatial Modulation <s> In this paper, we present space shift keying (SSK) as a new modulation scheme, which is based on spatial modulation (SM) concepts. Fading is exploited for multiple-input multiple-output(MIMO) channels to provide better performance over conventional amplitude/phase modulation (APM) techniques. In SSK, it is the antenna index used during transmission that relays information, rather than the transmitted symbols themselves. This absence of symbol information eliminates the transceiver elements necessary for APM transmission and detection (such as coherent detectors). As well, the simplicity involved in modulation reduces the detection complexity compared to that of SM, while achieving almost identical performance gains. Throughout the paper, we illustrate SSK's strength by studying its interaction with the fading channel. We obtain tight upper bounds on bit error probability, and discuss SSK's performance under some non-ideal channel conditions (estimation error and spatial correlation). Analytical and simulation results show performance gains over APM systems (3 dB at a bit error rate of 10-5), making SSK an interesting candidate for future wireless applications. We then extend SSK concepts to incorporate channel coding, where in particular, we consider a bit interleaved coded modulation (BICM) system using iterative decoding for both convolutional and turbo codes. Capacity results are derived, and improvements over APM are illustrated (up to 1 bits/s/Hz), with performance gains of up to 5 dB. <s> BIB002 </s> An Overview of Physical Layer Security With Finite-Alphabet Signaling <s> G. Secure Spatial Modulation <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> BIB003 </s> An Overview of Physical Layer Security With Finite-Alphabet Signaling <s> G. Secure Spatial Modulation <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> BIB004 </s> An Overview of Physical Layer Security With Finite-Alphabet Signaling <s> G. Secure Spatial Modulation <s> Security capacity improvement is always the implementation goal of physical layer security, which can be achieved by deliberate randomization based on differentia and uniqueness of wireless channels through signal processing method. An information-guided randomization secure transmission scheme is proposed combined with a spatial modulation system in which information can be carried by receiving antennas index but actually by channel differentia. Randomization is generated along with channel modulation procedure realized by corresponding preprocessing to transmitting signals. We provide three approaches for designing preprocessing weights under different constraint conditions. The former two can only be used when the number of receiving antennas is less than transmitting and have a tradeoff with varying degrees between receiving performance and security. The third one then relaxes the limits via generalized spatial modulation and can be used for arbitrary antennas configuration but with a receiving performance compromise. Lastly, results of performance analysis and numerical evaluation show that the proposed secure scheme is effective to prohibit the eavesdropper from intercepting information. <s> BIB005 </s> An Overview of Physical Layer Security With Finite-Alphabet Signaling <s> G. Secure Spatial Modulation <s> A key challenge of future mobile communication research is to strike an attractive compromise between wire- less network's area spectral efficiency and energy efficiency. This necessitates a clean-slate approach to wireless system design, embracing the rich body of existing knowledge, espe- cially on multiple-input-multiple-ouput (MIMO) technologies. This motivates the proposal of an emerging wireless commu- nications concept conceived for single-radio-frequency (RF) large-scale MIMO communications, which is termed as SM. The concept of SM has established itself as a beneficial transmission paradigm, subsuming numerous members of the MIMO system family. The research of SM has reached sufficient maturity to motivate its comparison to state-of-the-art MIMO communica- tions, as well as to inspire its application to other emerging wireless systems such as relay-aided, cooperative, small-cell, optical wireless, and power-efficient communications. Further- more, it has received sufficient research attention to be im- plemented in testbeds, and it holds the promise of stimulating further vigorous interdisciplinary research in the years to come. This tutorial paper is intended to offer a comprehensive state-of-the-art survey on SM-MIMO research, to provide a critical appraisal of its potential advantages, and to promote the discussion of its beneficial application areas and their research challenges leading to the analysis of the technological issues associated with the implementation of SM-MIMO. The paper is concluded with the description of the world's first experimental activities in this vibrant research field. <s> BIB006 </s> An Overview of Physical Layer Security With Finite-Alphabet Signaling <s> G. Secure Spatial Modulation <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> BIB007 </s> An Overview of Physical Layer Security With Finite-Alphabet Signaling <s> G. Secure Spatial Modulation <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> BIB008 </s> An Overview of Physical Layer Security With Finite-Alphabet Signaling <s> G. Secure Spatial Modulation <s> We investigate the effect of transmitter side channel state information on the achievable secrecy rates of space shift keying. Through derivation of the gradient of the secrecy rate, we formulate an iterative algorithm to maximize the achievable secrecy rates. We also introduce two lower complexity signal design algorithms for different scenarios based on the number of antennas at the eavesdropper. Our results illustrate the effectiveness of the proposed precoding techniques in attaining positive secrecy rates over a wide range of signal to noise ratios. <s> BIB009 </s> An Overview of Physical Layer Security With Finite-Alphabet Signaling <s> G. Secure Spatial Modulation <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> BIB010 </s> An Overview of Physical Layer Security With Finite-Alphabet Signaling <s> G. Secure Spatial Modulation <s> We propose a secure transmission scheme based on space shift keying (SSK) in which the indices associated with the transmit antennas are assigned dynamically according to the channel towards the legitimate receiver. We first derive an asymptotic secrecy rate under the perfect channel reciprocity assumption. Then, we study the impacts of imperfect reciprocity and presence of a nearby eavesdropper on the reliability and eavesdropping resilience of the proposed scheme. Finally, we introduce an enhanced antenna index assignment algorithm which is more robust to imperfect reciprocity, and is capable of preventing a nearby eavesdropper from acquiring the transmitted bits. <s> BIB011
Spatial modulation and space shift keying (SSK) are relatively new MIMO transmission schemes, which rely on transmitting information via active antenna indices. Similar to the amplitude or phase modulation schemes, in spatial modulation and SSK, the channel inputs are drawn from discrete and finite sets. More specifically, in spatial modulation BIB001 , the data bits are mapped onto two information carrying blocks: 1) an antenna index selected from the set of transmit antennas, and 2) a symbol drawn from a standard constellation. Space shift keying is a special case of spatial modulation where no amplitude of phase modulation is employed, i.e., the transmit antenna index serves as the only information carrying unit BIB002 . Different studies explore the advantages offered by spatial modulation over state-of-the-art MIMO schemes (see BIB006 for a comprehensive overview). Along with different application areas of spatial modulation and SSK, studying these transmission schemes in the context of physical layer security has been of recent interest. Secrecy capacity of spatial modulation for the scenarios with two transmit antennas is studied in BIB003 , and the results are extended to MISOSE and MIMOME scenarios in BIB004 and BIB007 , respectively. Different secure spatial modulation based transmission schemes are also proposed with the aid of MCSI and ECSI at the transmitter, and for systems with channel reciprocity. A precoder optimization algorithm for maximizing secrecy rates with SSK transmission using full CSI is proposed in BIB009 . Wu et al.  provide a precoder design and artificial noise injection approach for securing spatial modulation for the scenarios with passive eavesdroppers (with no ECSI at the transmitter). The secrecy rates of spatial modulation with artificial noise injection are characterized in BIB008 . While the conventional artificial noise injection (similar to what is considered in BIB008 ) requires multiple antennas to be activated, a novel secure artificial noise aided transmission is introduced in BIB010 , which requires only two antennas to be activated OFDM wiretap channel modeled as set of independent parallel channels. K: number of subcarriers (i.e., the number of parallel channels). at each time instance. Existing secure transmit signal design approaches for spatial modulation and SSK are summarized in Table VI . For the scenarios where channel reciprocity holds, a transmit preprocessing technique is proposed in BIB005 under the assumption that the training sequences are transmitted from Bob to Alice, and no CSI is available at the receiver nodes. Aghdam and Duman BIB011 propose a dynamic antenna index assignment based on the main channel when training is carried out at both directions, which prevents an eavesdropper from obtaining the antenna index assignment pattern.