Space Shift Keying System Research Articles

Novel space shift keying MIMO technique based on a Steiner triple system

A novel space shift keying (SSK) multiple–input multiple–output (MIMO) technique based on Steiner triple system is proposed and analyzed in this article. SSK attracted considerable research interest in the past few years driven by the several promised inherent advantages including low error probability, low computational complexity and a very simple hardware implementation with very low cost and power consumption. Yet, the spectral efficiency of SSK increases with a base two logarithm of the number of transmit antennas and high data rates are only viable with a massive and impractical number of transmit antennas. Alternatively, generalized SSK (GSSK) scheme is considered, where a combination of antennas is activated at each time instant. GSSK promises the use of arbitrary number of transmit antennas not necessarily a power of two integer. Also, GSSK can attain high data rate with low number of transmit antennas at the cost of substantial degradation in the error performance. In this study, a Steiner triple system is utilized to propose a tailored SSK scheme with substantial reduction in the required number of transmit antennas, without compromising the error probability. It is shown that the proposed Steiner–SSK (S–SSK) MIMO system achieves almost identical error performance to a conventional SSK system but with nearly 90% reduction in the number of transmit antennas. As well, the average bit error rate (ABER) of S–SSK is shown to outperform GSSK by at least 3dB. It is also reported that a S–SSK system accomplishes significant reduction in hardware cost, power consumption, and computational complexity as compared to conventional SSK scheme. Yet, GSSK is shown to marginally outperforms S–SSK in these metrics as it requires smaller number of transmit antennas per a target spectral efficiency.

Effect of Channel Estimation Errors on the Asymptotic Secrecy Outage Performance for Space Shift Keying

This paper presents the derivation of exact and asymptotic closed-form formulas of the secrecy outage probability (SOP) for space shift keying (SSK) systems over Rayleigh fading channels, especially in the presence of imperfect channel state information (CSI) at a legitimate receiver. Comprehensive analyses of the achievable secrecy performance limit for the SSK systems were performed by judiciously exploiting the derived SOP expressions, which enable us to obtain explicit and useful insights into the effect of channel estimation errors on the secrecy performance for the considered systems. The exactness of our theoretical analyses was validated numerically.

Secrecy enhancing for SSK‐based communications in the presence of imperfect CSI estimation

In this letter, a new security enhancement scheme for space shift keying (SSK) systems under imperfect channel state information (CSI) is proposed. In this scheme, the legitimate receiver is always accompanied by an eavesdropper, and the secrecy enhancing of the SSK system is realized by adding the designed artificial noise (AN). Since the AN is designed by the CSI of the legitimate channel, it can be canceled at the legitimate receiver and remained at the eavesdropper. In addition, the impacts of the CSI estimation error on the secrecy rate (SR) and bit error ratio (BER) of the SSK system have also been taken into account. The simulation results show that compared with the traditional SSK under imperfect CSI environment, the proposed scheme improves the SR and BER. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Secrecy Enhancing of SSK Systems for IoT Applications in Smart Cities

The secure exchange of messages between different communication devices is a major issue of Internet-of-Things (IoT) applications in future smart cities. Current security mechanisms focus on multiple antennas technology, such as spatial modulation (SM), but in space shift keying (SSK), there is still a space to explore. In this article, we propose a secrecy-enhancing SSK scheme for IoT applications by applying security technologies in the physical layer wherein the number of transmit antennas is arbitrary rather than the value of power of two. In this scheme, the security performance of the communication system is improved by using two technologies, namely, artificial noise (AN) and antenna selection. We assume that the application scenario of the SSK system is under the classic eavesdropping model. First, we design ANs according to the channel state information (CSI) to interrupt the eavesdropper and benefit the legitimate receiver via the appropriate cancellation technology. Second, the antenna selection method is designed based on the signal to leakage noise ratio (SLNR) to further boost the secrecy performance by expanding the mutual information difference between the main channel and the eavesdropping channel. Results from our simulations indicate that by the use of the proposed scheme, significant secrecy enhancing can be achieved in terms of bit error ratio (BER) and secrecy rate (SR) when compared with existing schemes. This achieved secrecy enhancing can benefit the suitable IoT communication applications in the smart city environment to avoid the leakage of data transmission.

Space Shift Keying With Reconfigurable Intelligent Surfaces: Phase Configuration Designs and Performance Analysis

Reconfigurable intelligent surface (RIS)-assisted transmission and space shift keying (SSK) appear as promising candidates for future energy-efficient wireless systems. In this article, two RIS-based SSK schemes are proposed to efficiently improve the error and throughput performance of conventional SSK systems, respectively. The first one, termed RIS-SSK with passive beamforming (RIS-SSK-PB), employs an RIS for beamforming and targets the maximization of the minimum squared Euclidean distance between any two decision points. The second one, termed RIS-SSK with Alamouti space-time block coding (RIS-SSK-ASTBC), employs an RIS for ASTBC and enables the RIS to transmit its own Alamouti-coded information while reflecting the incident SSK signals to the destination. A low-complexity beamformer and an efficient maximum-likelihood (ML) detector are designed for RIS-SSK-PB and RIS-SSK-ASTBC, respectively. Approximate expressions for the average bit error probabilities of the source and/or the RIS are derived in closed-form assuming ML detection. Extensive computer simulations are conducted to verify the performance analysis. Results show that RIS-SSK-PB significantly outperforms the existing RIS-free and RIS-based SSK schemes, and RIS-SSK-ASTBC enables highly reliable transmission with throughput improvement.

Secrecy enhancing for space shift keying‐based communication systems

In this letter, a novel space shift keying (SSK)‐based communication scheme for secrecy enhancing is proposed. In the proposed scheme, one legitimate user and one eavesdropper exist as the receivers. The secrecy rate (SR) performance is achieved by applying the designed artificial noise (AN) to the traditional SSK system. In this way, we can effectively interfere the eavesdropper while maintaining the communication for the legitimate user. Results from the simulations demonstrate that the proposed scheme outperforms the traditional scheme in terms of the SR. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Reconfigurable Intelligent Surface-Assisted Space Shift Keying

The concept of reconfigurable intelligent surface (RIS)-assisted transmission, where phases of reflected signals are adjusted in an effective arrangement, has been recently put forward as a promising solution for 6G and beyond networks. Considering this and the undeniable potential of index modulation (IM) techniques, an RIS-based space shift keying (SSK) scheme is proposed in this letter to maintain all inherent advantages of both RISs and SSK. Specifically, a mathematical framework is presented by using a maximum likelihood (ML) detector for the calculation of the average bit error rate (ABER). Extensive computer simulation results are provided to assess the potential of the proposed RIS-based SSK system and to verify the theoretical derivations. The obtained results indicate that the proposed scheme enables highly reliable transmission with unconventionally high energy efficiency, however with the added cost of increased receiver complexity.

First Hardware Implementation of an SSK MIMO System With no RF-Chain at the Transmitter

This article presents the hardware implementation of a space shift keying (SSK) multiple-input multiple-output (MIMO) system with no radio frequency (RF)-chain at the transmitter. The transmitter design was solely based on RF-switches. SSK relays information strictly through spatial symbols and does not require the generation of any modulated symbol. It has been always anticipated in literature that SSK can be implemented with a single or no RF chain, but the physical realizations were never accomplished. This work demonstrates a 4 × 2 and 2 × 2 MIMO implementation of an SSK system using commercial-off-the-shelf (COTS) RF-switches. As a result, the achieved implementation paves the way towards commercial deployments of space modulation techniques. A detailed discussion of the hardware implementation is presented and results reveal an accurate match with theoretical SSK results over a Rician fading channel with variant Rician K- factors.

Error Analysis of SSK With Euclidean Distance Based Selection Combining

In this paper, we analyze the performance of space shift keying (SSK) modulation scheme with Euclidean distance based selection combining (ED-SC) at the receiver. This scheme utilizes a single radio frequency (RF) chain receiver that selects one out of $N_{r}$ receiver antennas based on the Euclidean distance between the SSK constellation points. In addition to this, the performance of generalized ED based SC (GED-SC) is also analyzed by utilizing two or more RF chains at the receiver. The closed form expressions for the average bit error probability (ABEP) of ED-SC and GED-SC schemes are derived for two transmit and $N_{r}$ receive antennas. Further, the theoretical ABEP analysis of ED-SC is derived for $N_{t} > 2$ . In addition to this, we also derive the diversity order analysis of ED-SC SSK system for $N_{t} = 2$ . From the diversity order analysis, it can be inferred that the diversity order obtained by the ED-SC SSK system is $N_{r}$ . It is observed from the simulation results that the performance of $2\times 4$ GED-SC SSK system with two and three RF chains is only slightly worse than the optimal detection with $N_{r}=4$ . Since only a single RF chain is utilized for signal reception in ED-SC, the receiver complexity of employing $N_{{RF}}$ RF chains in GED-SC and $N_{r}$ RF chains in optimal detection is greatly reduced. Moreover, the simulation results of the ABEP performance of ED-SC SSK system in imperfect channel state information at the receiver is shown.

Orthogonal Array Testing for Transmit Precoding based Codebooks in Space Shift Keying Systems

In Space Shift Keying (SSK) systems, transmit precoding based codebook approaches have been proposed to improve the performance in limited feedback channels. The receiver performs an exhaustive search in a predefined Full-Combination (FC) codebook to select the optimal codeword that maximizes the Minimum Euclidean Distance (MED) between the received constellations. This research aims to reduce the codebook size with the purpose of minimizing the selection time and the number of feedback bits. Therefore, we propose to construct the codebooks based on Orthogonal Array Testing (OAT) methods due to their powerful inherent properties. These methods allow to acquire a short codebook where the codewords are sufficient to cover almost all the possible effects included in the FC codebook. Numerical results show the effectiveness of the proposed OAT codebooks in terms of the system performance and complexity.

Space shift keying for multi-hop multi-branch networks

In this paper, we propose two different multi-hop multiple-input multiple-output (MIMO) space shift keying (SSK) schemes and investigate their error performance. In the first scheme, we consider a multi-hop multi-branch SSK system, in which the source and destination are equipped with multiple transmit and receive antennas, respectively. In this scheme, SSK is applied by using the source transmit antennas. Moreover, in each branch, single-antenna relays are used to amplify the transmitted signal from the source and forward it to the next relay until it reaches to the destination. In the second scheme, we consider a multi-hop MIMO-SSK system with path selection. In this scheme, the best path is selected among multiple branches and a multiple-antenna source communicates with a multiple-antenna destination via the relays of the selected path. Each relay is equipped with multiple transmit and receive antennas. Moreover, the source and all relays employ SSK modulation to transmit information bits and each relay in each path follows the decode-and-forward protocol. Approximate theoretical error probability expressions are derived for both schemes. Furthermore, an asymptotic symbol error probability performance analysis is also performed for the multi-hop MIMO-SSK system with path selection. It is shown that the proposed multi-hop SSK systems outperform conventional multi-hop M-PSK systems in terms of the error performance for especially high data rates and sufficient number of receive antennas at the receiving nodes.

Performance analysis of space shift keying for AF relaying with relay selection

In this paper, we propose an amplify-and-forward multiple-input multiple-output (MIMO) relaying scheme, which combines space shift keying (SSK) with the best and partial relay selection. In this scheme, SSK transmission is considered by using the source (S) transmit antennas. Besides the direct link transmission, a relay, which is selected according to the best or partial relay selection techniques, amplifies the data received from S and forwards it to the destination (D). Theoretical error probability expressions of the proposed cooperative SSK systems are derived and an asymptotic diversity analysis is also performed to demonstrate the achievable diversity orders of the systems. It is shown that the proposed SSK systems outperform the conventional cooperative single-input multiple-output (SIMO) systems. It is also revealed that there is an interesting trade-off between SSK with the best and the partial relay selection in terms of error performance and complexity as in conventional cooperative SIMO systems. However, it is shown that the partial relay selection provides an almost identical error performance compared to the best relay selection with a considerably lower complexity when the number of relays is less than or equal to the number of receive antennas at D in the cooperative SSK system.

Source Transmit Antenna Selection for Space Shift Keying With Cooperative Relays

In this letter, we propose a cooperative multiple-input multiple-output (MIMO) scheme combining transmit antenna selection (TAS) and space shift keying (SSK). In this scheme, source transmit antennas are selected and SSK is applied by using the selected antennas. Besides the direct link transmission, the relays, that decode the source signal correctly, take part in the transmission. Exact expressions and a considerably accurate approximate expression for the symbol error rate of the proposed SSK system are derived. It is shown that the proposed scheme outperforms the SSK system without TAS and also the conventional cooperative MIMO system, which employs source TAS, at practical signal-to-noise ratio values for especially high data rates and sufficient number of receive antennas at the destination.

Achievable Error Rate Performance Analysis of Space Shift Keying Systems with Imperfect CSI

Achievable Error Rate Performance Analysis of Space Shift Keying Systems with Imperfect CSI

Layered Space Shift Keying Modulation over MIMO Channels

Space shift keying (SSK) modulation is an emerging transmission technique for multiple-input multiple-output (MIMO) wireless channels, which exploits the spatial domain to convey information. In this paper, we present a layered space shift keying (LSSK) modulation scheme to fully exploit the spatial domain to transmit information bits, where a layered architecture is developed to achieve spatial multiplexing transmission in an SSK system. Specifically, LSSK leverages the rotated signals predetermined at the transceiver to identify different layers and improve the bit-error-rate (BER) performance. The layered signals are directly generated by the proposed LSSK modulation method with a low computational overhead. Furthermore, we propose a layered-and-joint (LJ) near-optimal detection algorithm based on the layered architecture of LSSK to reduce the detection complexity. In LJ detection, layered detection is performed to find a set of detection candidates for each layer, and then, joint detection is performed with these candidates. We show that the performance of LJ detection is quite close to that of optimal maximum-likelihood detection with significantly reduced detection complexity for high-spectrum-efficiency scenarios. Results demonstrate that the proposed LSSK scheme substantially improves the spectrum efficiency of an SSK system and outperforms other existing MIMO schemes.

Pre-Scaling Optimization for Space Shift Keying Based on Semidefinite Relaxation

The performance of space shift keying (SSK) is known to be dominated by the minimum Euclidean distance (MED) in the received SSK constellation. In this paper, we propose a method of enhancing the MED in the received SSK constellation and improving both the attainable performance and the power efficiency by means of symbol scaling at the transmitter. To this aim, we formulate a pair of optimization problems, one for maximizing the MED subject to a specific transmit power constraint and one for minimizing the transmit power subject to a MED threshold. As these problems are NP-hard, we re-formulate their optimization using semidefinite relaxations, which results in convex problem formulations that can be efficiently solved using standard approaches. Moreover, we design pre-scaling techniques for imperfect channel state information at the transmitter, where the existing approaches are inapplicable. Our results show that the proposed schemes substantially improve the power efficiency of SSK systems with respect to state-of-the-art techniques by offering an improved performance for specific transmit power requirements or, equivalently, a transmit power reduction for a given MED threshold.

Ergodic capacity analysis of spatially modulated systems

Spatial Modulation (SM) is a newly introduced wireless transmission scheme, and Space Shift Keying (SSK) is its simplified version. Their capacity performance has not been well examined to date. Starting from basic definitions of information theory, through theoretical analyses and numerical calculations, this paper evaluates the capacity of SM systems in various channels. Our conclusion is that under Rayleigh fading channels, the capacity of the SSK system is limited by the Signal-to-Noise Ratio (SNR) or the number of transmit antennas, whichever one is smaller. From the capacity point of view, the SM system is better than the Single-Input and Single-Output (SISO) system, but worse than the Multiple-Input and Single-Output (MISO) system. The correlation between transmit antennas will degrade the performance of the SSK system. Line-of-Sight (LOS) may cause performance degradation for SSK, but capacity increases for SM.

A General Framework for Performance Analysis of Space Shift Keying (SSK) Modulation in the Presence of Gaussian Imperfect Estimations

In this letter, accurate performance analysis of wireless communication system adopting Space Shift Keying (SSK) modulation scheme is introduced. More specifically, the performance of SSK system consisting of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> transmit and N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> receive antennas with Maximum-Likelihood (ML) detection and imperfect Channel State Information (CSI) at the receiver is studied. The exact Average Bit Error Probability (ABEP) over Rayleigh fading channels is obtained in closed-form for N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> =2 and arbitrary N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> ; while union upper bound is used to compute the ABEP when N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> >;2 and arbitrary N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> . Furthermore, simple and general asymptotic expression for the ABEP is derived and analyzed. Numerical results are also provided, sustained by simulations which corroborate the exactness of the theoretical analysis.