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In this paper, a cyber-physical system (CPS) is considered, whose state estimation is done by a central controller (CC) using the measurements received from a wireless powered sensor network (WPSN) over fading channels. An adversary injects false data in this system by compromising some of the idle sensor nodes (SNs) of the WPSN. Using the WPSN for transmitting supervision and control data, in the aforementioned setting, makes the CPS vulnerable to both error and false data injection (FDI). The existing techniques of launching stealthy FDI attack are not applicable to the aforementioned network due to the random nature of wireless channels, which is used for both transmitting control and false data. The objectives of the adversary and the CC to launch stealthy FDI attack and to detect the same, respectively, are found to be depending on the powers they use for transmitting data over wireless channels. The transmit powers of the CC, and the adversary that fulfill their respective objectives are derived by modeling their interaction as a Bayesian Stackelberg game. Based on their objectives, novel utility functions are defined for the CC and the adversary. Subsequently, the equilibrium of the proposed game is obtained by solving a non-convex bi-level quadratic-quadratic program. Finally, the analytical results are verified and compared with other state-of-art techniques by applying them in a realistic smart grid simulations.

In this article, a two-dimensional channel characterization of a molecular motor signal in a diffusive fluid environment is provided by deriving the first hitting time probability density function of the motor signal to an absorbing lattice point. A temporal modulation scheme to establish communication between two nodes using the motor signal is also proposed. Detection of the motor signal is achieved by using the maximum likelihood detector with erasures for a negligible or no-interference scenario. On the other hand, for motor signal reception with inter-symbol interference, the reception process is modeled as a hidden Markov model, and a Viterbi sequence detection algorithm is devised for decoding the sequence of input Markov states. Efficient criteria to determine the memory length of a diffusive molecular communication (MC) system are defined, which address the problem of choosing a detector for a given MC system. It is demonstrated using numerical results that the hitting probability and, consequently, the error performance of the motor signal worsens with an increase in the unbound probability ( $\epsilon /2$ ). Furthermore, it is also quantitatively established, as to, why in nature directed signals are preferred for communication over purely random diffusive signals at larger distances.

In this article, we propose a limited feedback-based space-shift keying (SSK) modulation scheme where transmitter (Tx) obtains partial channel state information (CSI) via a feedback link from receiver (Rx). More specifically, the Tx does not receive perfect information of channel gain, but is aware only of channel gain ordering. Based on the received partial CSI, the Tx adapts the spatial constellation and allocates different transmit weights to each transmit antenna representing spatial constellation points. Furthermore, the power adapted spatial constellation points are encoded by using gray coding scheme, which results in unit hamming distance between adjacent spatial constellation points. Next, a multiple-input single-output (MISO) system with maximum–likelihood detection is investigated. Accurate expressions for the average bit error rate (ABER) for ${2}\times {1}$ and ${4}\times {1}$ MISO systems over Rayleigh fading channel are derived. Further, an approximate expression for the ABER of a generalized MISO system is also obtained. It is shown analytically that the ABER performance of the proposed SSK scheme can be improved by applying a non-uniform power allocation to make transmit links more distinguishable at the Rx. Moreover, we demonstrate analytically that the proposed scheme attains a diversity order which is twice of the conventional SSK scheme. Numerical results, corroborated by Monte Carlo simulations, verify the proposed analysis and clearly highlight that, the proposed scheme significantly outperforms existing closed-loop spatial constellation-based schemes relying on full CSI in Tx and conventional open-loop SSK scheme.

Evolution and accessibility of smart-phones have led to a huge demand in network bandwidth. The ubiquitous use of smart-phones in high-speed trains poses a unique challenge in delivering high-speed internet service on board. This challenge can be overcome by employing free-space optics, an alternative to radio-frequency technology. Previous coverage models for ground-train communications employed single laser systems with a larger divergence angle to cover a larger distance. Larger divergence angles lead to larger geometric losses, which may result in a non-reliable communication link. This study proposes a sectorised multi-beam coverage model with a smaller divergence angle to reduce the impact of geometric losses in the system. This study also proposes two receiver (Rx) architectures for Rxs deployed on the train. Along with geometric losses, the atmospheric attenuation is taken into consideration for the FSO link. The performance of the ground-train communications system in terms of bit-error-rate is evaluated under weak turbulence conditions via numerical simulation.

In this article, we summarize the research conducted for YFRFs of Visvesvaraya PhD Programme. The research work is mainly focused on the design and analysis of wireless communication networks. We also explore the spectral and energy efficiency aspects of future generation networks like smart grid communications. This research is useful for improving the performance of current and future generation of communication systems.

In this paper, we study the impact of correlation on the bit error rate (BER) and the channel capacity of a free-space optical (FSO) multiple-input-multiple-output (MIMO) system employing optical space shift keying (OSSK) over a fading channel. In order to study a practical correlated channel, we consider the effect of channel correlation due to both small-and large-scale eddies and show that the use of OSSK over correlated FSO channel can lead to an improved system performance with increasing correlation level of upto 0.9. In this work, we first develop an analytical framework for different performance metrics of the OSSK multiple-input single-output system with correlation and then extend our investigation by proposing an asymptotically accurate mathematical framework for MIMO. We also validate all the analytical results using MATLAB simulations. Finally, we develop an experimental setup of FSO with two correlated links to study the throughput and latency of the links at different turbulence levels.

In this paper, the effect of jamming in free space optical (FSO) link, is evaluated by deriving closed-form expressions of the bit error rate (BER) and outage probability (OP) for single-input single-output (SISO) and multiple-input single-output (MISO) FSO systems. The effects of partial-band jamming and broadband jamming over the error performance of the considered FSO systems are also analyzed. The jammer behaves as a random noise source, following the negative exponential distribution–due to the atmospheric turbulence. Therefore, in the presence of jammer, the error performance of FSO systems is governed by the additive negative exponential noise. It is shown by a rigorous analysis that a MISO FSO system can significantly mitigate the effect of jamming. Specifically, we consider a $2\times 1$ FSO system for analysis, and demonstrate the improvement in BER and OP performance an FSO system can gain by using an additional spatial dimension, in the presence of a random jammer. The mitigation of jamming, due to implementation of arbitrary transmit apertures, is also verified through simulation results; which lies in complete agreement with the analytical results. Also, the error performance under the jamming effect is studied numerically over the Gamma-Gamma fading channel incorporated with pointing error effect.

The motion of molecules in a constrained fluid environment is defined by specified boundary conditions. Deriving analytical channel characterization of a bounded fluid environment is challenging as the solution must satisfy the given boundaries. In this letter, we derive the probability distribution function (PDF) of molecular motion inside a rectangular container with reflective and absorbing boundaries. Using the molecular motion’s PDF, we deduce an analytical expression for the PDF of the first arrival time (FAT) of the molecules to an absorbing wall. Furthermore, we also evaluate the capacity for a temporally modulated molecular communication (MC) system in the bounded environment.

The diversity-multiplexing tradeoff (DMT) in a multiple-input multiple-output (MIMO) free-space optical (FSO) communication with limited channel state information at the transmitter (CSIT) is investigated. Using the limited CSIT based power and rate control strategy, we optimally allocate the power among the good and bad channels in such a fashion that the DMT performance of the system enhances significantly unlike the no-CSIT based MIMO-FSO DMT. In this way, a new limited CSIT based technique/model with optimal power and rate control strategy is proposed to enhance the DMT performance. The optimal DMT is studied for two different transmission scenarios: single-rate and adaptive-rate transmission. It is shown that how the optimal DMT is influenced when the concept of minimum guaranteed multiplexing gain in the forward link is taken into account. It is illustrated that power control based on the feedback plays a vital role in attaining the optimal DMT, and rate adaptation is significant in obtaining a high diversity gain, especially at high rates. Moreover, the analysis of upper and lower bounds on the optimal DMT is done by giving useful insights. Furthermore, a novel study based on the optimal tradeoff between the degrees of freedom and the number of transmit apertures in a coherent MIMO-FSO channel is also done. To validate the results of the proposed model, we compare the derived results with the no-CSIT based MIMO-FSO DMT. It is observed that the proposed technique/model outperforms the no-CSIT based MIMO-FSO DMT.

Introduction: In this paper, we consider a fundamental problem of testing faced by the health staff on testing COVID 19 patients. In general, the number of testing kits or testing capabilities is limited, and the number of COVID 19 patients is much larger than that. This paper tries to answer this fundamental question that how to perform COVID 19 testing to reduce the death rate. Materials and Methods: We consider that the survival rate of patients is dependent over two parameters: their age and severity of symptoms at a time. Based on these observations, we propose a survival rate function. Using the survival rates, the death rate for an individual is obtained. MATLAB was used for plotting the graphs. Results: It is shown by numerical results that by using the proposed mechanism, the average death rate can be significantly reduced. Conclusion: It is proposed to conduct the testing for those patients who lie in the high death rate regimen.

In this paper, a novel signal-space diversity (SSD) technique based multipoint-to-multipoint cooperative scheme for a multiuser free-space optical communication system is proposed. In SSD technique, constellation points of the transmitted signal are rotated by a certain angle and in-phase and quadrature components of two different symbols are interleaved to obtain diversity from the signal space. In the proposed scheme, the diversity of each cooperative user gets improved through joint encoding/decoding of the rotated symbols using subcarrier intensity modulation (SIM). The joint encoding/decoding can be done by connecting all the users' transceivers by wires that ensure the availability of the information of a user to all other users. The average symbol error rate for the proposed scheme under log-normal and gamma-gamma channel models is evaluated analytically and corroborated through Monte Carlo simulations. It is reported through intensive analyses and comparisons that the proposed cooperative scheme not only achieves full diversity order but also outperforms non-cooperative and repetition coding schemes.

In this paper, the groundwork on jamming effect and its alleviation mechanisms in free space optical (FSO) communication are studied over Gamma-Gamma (GG) fading channels along with the pointing error (PE) effects. A closed-form expression of the bit error rate (BER) is evaluated analytically for a single-input single-output (SISO) FSO system in the presence of jammer. The worst case jamming condition for maximization of error is calculated numerically. The jammer channel is considered to be GG distributed. Being the most dominating noise, the jamming signal is acted as the only noise source in the considered FSO set-up. Therefore, this study is performed over additive GG noise channel. The error performances are investigated for different atmospheric turbulence (AT) regimes (weak to strong) and for different PE parameters of jamming noise. Moreover, to combat the jamming effect, a multiple-input single-output (MISO) FSO system is considered. A closed-form expression of the BER of the multiple transmit channels over the GG noise is analytically calculated. The analytical results for both SISO and MISO FSO systems are verified with the help of the simulation results obtained by MATLAB software. It is established that MISO FSO performs better than SISO FSO system in terms of BER performance under the influence of jamming noise. Furthermore, many important observations are made upon the BER performances for different AT and PE parameters for SISO and MISO FSO systems.

In this work, the authors consider the communication network of a power substation, where multiple intelligent electronic devices (IEDs) transmit their delay sensitive control and monitoring messages to a common receiver over a wireless network; in the presence of a broadband jammer, which is capable of jamming multiple channels simultaneously. The objective of the IEDs is to successfully transmit their messages within a specified time, whereas the jammer wants to obstruct IED's transmission. A novel utility function is designed for the players, that addresses the time-critical nature of communication. Due to the conflicting interest of the IEDs and the jammer, they model the interaction between them as a repeated Bayesian zero-sum game, which also addresses the repeated interaction among the IEDs and the jammer, and the unavailability of exact information about the jammer. The equilibrium strategies for both the scenarios of perfect and imperfect monitoring are derived and verified through simulation results. Further, the performance of the proposed game model in various scenarios is thoroughly compared in the result section. Finally, the efficacy of the proposed defence strategies is tested in a practical communication network of a power substation under jamming, which is simulated in Optimised Network Engineering Tool (OPNET).

In this paper, a partially informed transmitter-based optical space shift keying (PIT-OSSK) scheme is proposed, wherein the transmitter only possesses the knowledge of channel gain ordering. This partial information is used to adapt the OSSK constellation and power allocation (PA). The adaptation of OSSK constellation reduces the number of bits in error between two consecutive constellation points, which in turn lowers the overall bit error rate (BER) of the proposed scheme. On the other hand, it is demonstrated by a mathematical analysis that the PA achieves improved diversity order as compared to the conventional OSSK scheme. These modifications make the PIT-OSSK scheme significantly better than the conventional OSSK scheme in terms of the BER under both indoor and outdoor conditions. For a single receiver aperture, accurate closed-form expressions of average BER (ABER) for two and four transmitter aperture-based PIT-OSSK schemes are derived under negative-exponential channel model. Moreover, a very tight approximate closed-form expression of the ABER for an arbitrary number of transmitter apertures is also developed. All the derived expressions are verified via Monte-Carlo simulations. Furthermore, the proposed strategy is extended and examined for an arbitrary number of receiver apertures by the simulation-based results under different channel models.

In this study, the authors propose a novel virtual full-duplex relaying scheme, which is referred to as centre-partition max-link relaying by using buffer-aided half-duplex relays for multi-hop decode-and-forward cooperative networks. In the proposed scheme, they aim to select two independent available links for data packet transmission in the same time slot, which, in turn, improves the overall performance of the system. By modelling the evolution of buffer state transition as a Markov chain, the performance of the system is analysed in terms of outage probability and end-to-end average packet delay. The state transition matrix of the Markov chain is constructed and its steady-state distribution is obtained to derive the outage probability. Numerical results demonstrate that the proposed scheme has a potential to provide significant outage performance with reduced average packet delay as compared to that of buffer-aided multi-hop decode-and-forward relaying networks using the conventional max-link scheme.