In recent years, reconfigurable intelligent surfaces (RIS) have emerged as a promising technology for enhancing link reliability in wireless communication systems. This paper introduces a novel RIS-assisted terahertz (THz) communication system utilizing the spatial modulation (SM) technique. We derive the closed-form expressions for the probability density function (PDF) and moment generating function (MGF) of the SM-based RIS-assisted THz system over α-μ fading. Leveraging these derived channel statistics, we obtain an upper bound on the average bit error rate (BER) and a lower bound on the ergodic capacity to evaluate the performance of the proposed system. The asymptotic BER is analyzed to determine the system’s diversity gain. The numerical results validate the theoretical findings and provide valuable insights into the system’s performance. The analysis shows that the SM-based RIS-assisted THz system outperforms the existing traditional systems. Lastly, a trade-off between average BER performance and spectral efficiency is observed.

This paper investigates the effectiveness of employing multiple reconfigurable intelligent surfaces (RIS) for simultaneous wireless information and power transfer (SWIPT) in a vehicle-to-infrastructure (V2I) system. The optimal RIS is selected for transmission based on instantaneous signal-to-noise ratio (SNR) values, with the objective of optimizing the SWIPT system employing the power-splitting (PS) protocol and nonlinear energy harvesting (NL-EH). A unified objective is proposed to maximize information rate and harvested energy via joint optimization of transmit power and power splitting factor. Nonconvexity is addressed via an iterative algorithm, supported by closed-form expressions obtained through Karush-Kuhn-Tucker (KKT) conditions. Monte-Carlo simulations are performed to validate the accuracy of the analytical expressions. Additionally, a deep neural network (DNN) framework is introduced for realtime optimization prediction, achieving superior SWIPT performance over single RIS configurations with reduced complexity and faster execution.

Channel encoders are essential for mitigating errors in digital communication; however, their blind identification remains a significant challenge in non-cooperative systems. Further, the blind recognition of channel encoders plays a significant role in the design of blind receivers for future-generation communication systems. This paper proposes a capsule network (CapsNet)-based model for the blind recognition of low-density parity-check (LDPC) codes, designed to distinguish between wireless fidelity (Wi-Fi) and fifth generation (5G) new radio (NR) signals. The model successfully classifies Wi-Fi-based and 5G-NR-based LDPC encoders, under both additive white Gaussian noise (AWGN) and Rayleigh fading channels. The proposed approach achieves over 95% classification accuracy at a signal-to-noise ratio (SNR) value of 5 dB under AWGN channel condition and exceeds 85% accuracy beyond 5 dB SNR under Rayleigh fading conditions. Furthermore 100% accuracy is achieved in both the scenarios at the SNR levels of 10 dB (AWGN) and 20 dB (Rayleigh). Real-time validation using GNU Radio platform and universal software radio peripheral (USRP) B210 devices confirms the alignment of experimental results with simulations, demonstrating the practical feasibility of the proposed model. Comparative analysis shows that the proposed model outperforms the existing methods, particularly under Rayleigh fading, making it a promising solution for next-generation wireless communication systems.

This paper presents a comprehensive performance analysis of a multi-hop free-space optics (FSO) communication system enhanced by optical reflecting surfaces (ORS) and employing the decode and forward (DF) relaying technique. The proposed system model accounts for key impairments such as atmospheric turbulence, pointing errors, and fog, which pose significant challenges to FSO communication. Atmospheric turbulence is modeled using the recently introduced double inverted Gamma-Gamma (IGGG) turbulence channel model. This study examines its potential to improve channel quality and system performance by leveraging ORS technology for intelligent beam redirection. Further, closed-form expressions for outage probability, average symbol error rate (ASER), ergodic capacity, and outage capacity are derived, considering crucial parameters such as the number of hops and relay positions, while incorporating the combined effects of turbulence, pointing errors, and fog. Numerical results demonstrate a substantial enhancement in performance is achieved with ORS, particularly under severe turbulence conditions, with further improvements observed as the number of hops increases. These findings highlight the potential of ORS to significantly improve the reliability and efficiency of FSO communication, enabling high-capacity optical wireless networks in challenging atmospheric environments. The accuracy of the analytical results is validated through Monte-Carlo simulations, ensuring their practical applicability for the design and optimization of next-generation wireless communication systems.

Free-space optics (FSO) and radio frequency (RF)-based non-orthogonal multiple access (NOMA) are key enablers for 5G and beyond communication. This paper proposes a novel mixed FSO/RF communication system with the NOMA framework leveraging high-altitude platform stations (HAPS) and unmanned aerial vehicles (UAVs) as relays to enhance reliability and spectral efficiency. The proposed system employs decode-and-forward (DF) relaying, with FSO links modeled using a doubly inverted Gamma-Gamma (IGGG) distribution incorporating atmospheric turbulence, pointing errors, and angle-of-arrival (AoA) fluctuations, while RF links follow a Nakagami-m fading model. A relay selection scheme based on channel conditions is implemented to optimize UAV selection. Further, closed-form expressions for outage probability (OP), ergodic capacity (EC), and throughput are derived and validated through Monte-Carlo simulations. Numerical results show that system performance is dominated by the link reliability of FSO communication at shorter user-to-UAV distances and transitions to RF link dominance at longer distances. For the two-user scenario, the analysis reveals that user 1 experiences interference-limited saturation at a high signal-to-noise ratio (SNR), while user 2 achieves linear capacity growth due to successive interference cancellation (SIC). The proposed system model effectively mitigates channel impairments, offering valuable insights for the next-generation wireless networks.

The conventional reflection-only Reconfigurable Intelligent Surface (RIS) extends its 180-degrees coverage to 360-degrees with Simultaneously Transmitting and Reflecting-RIS(STAR-RIS). When integrated with the Simultaneous Wireless Information and Power Transfer (SWIPT) system, it enhances performance by directing energy and information signals to energy receiver (ER) and information receiver (IR), with Energy Splitting (ES) and Mode Switching (MS) operational protocol. Considering a practical system with discrete phase shift (DPS) model and non-linear energy harvesting (EH) model, we aim to maximize the weighted rate-energy (WRE) function, with certain QoS constraints by optimizing power parameters. An alternating optimizing (AO) algorithm solves the complicated WRE maximization problem. Numerical results highlight the impact of energy split ratio and element division on the performance, with the critical selection of DPS level (quantization bits) balancing device bulkiness (phase control bits) and system efficiency.

This work analyzes the performance of a hovering unmanned aerial vehicle (UAV)-based intelligent reflecting surface (IRS)-assisted free-space optics (FSO) communication system. The impact of UAV hovering on both the IRS and receiver ($\mathbf{R x}$) nodes is modeled, accounting for angle-of-arrival (AoA) fluctuations, path loss, atmospheric turbulence, and pointing errors. Atmospheric turbulence is characterized using the doubly inverted Gamma-Gamma (IGGG) distribution, and independent fading statistics are incorporated for the Tx-to-IRS and IRS-toRx links. Closed-form expressions for outage probability, average symbol error rate (ASER), and ergodic capacity are derived. The analysis demonstrates that the UAV based IRS-FSO system is highly sensitive to AoA fluctuations at both the IRS and Rx nodes, emphasizing the critical importance of accounting for these factors in practical implementations. Furthermore, it is observed that increasing the number of IRS elements significantly enhances the system performance, outperforming both decode-and-forward (DF) and amplify-and-forward (AF) relaying techniques. All the derived analytical expressions are validated through Monte-Carlo simulations.

This study explores a hybrid framework that merges terahertz (THz) and free space optics (FSO) technologies in a backhaul network. The combined FSO and THz systems leverage reconfigurable intelligent surfaces (RIS) and employ maximal ratio combining (MRC) at the receiver. Specifically, the closedform expressions for cumulative distribution function (CDF) of channel and signal-to-noise ratio (SNR) for RIS-assisted FSO and THz channels are derived by assuming the impediments such as atmospheric turbulence, fading, pointing errors, and pathloss. Using these statistics, outage probability, average symbol error rate (SER), and outage capacity are computed for the proposed RIS-assisted hybrid FSO/THz system. Numerical results compare the proposed hybrid FSO/THz system against various wireless systems, including RIS-assisted FSO, RIS-assisted THz, and hybrid FSO/THz systems without RIS.

Distributed Reconfigurable Intelligent Surfaces (D-RIS) in a Simultaneous Wireless Information and Power Transfer (SWIPT) framework is investigated in this paper to enhance spectral efficiency (SE) and energy harvesting (EH) for an Internet-of-Things (IoT) node utilizing a power-splitting (PS) protocol with non-linear EH model. Two types of RIS selection strategies, namely Exhaustive RIS Approach (ERA) and Optimal RIS Approach (ORA) are analyzed and compared. Algorithmic solutions based on divide-and-conquer strategy are developed to optimize the PS ratio and transmission power, ensuring improvements in distinct objective of SE and EH. The analysis is performed through a comprehensive case study of five different scenarios, focusing on various factors such as RIS surface placement, node-to-RIS distance, RIS size, and their combined impact on system performance. Numerical simulations provide insights into the system's behavior under different configurations, revealing that the ERA strategy consistently outperforms the ORA in achieving better SE and EH outcomes. These results are viable in designing IoT systems using distributed RISs in data and energy domains.

Intelligent reflecting surfaces (IRSs) possess the capability to enrich connectivity within dynamic sixth-generation (6G) vehicular communication networks by redirecting signals in desired directions. This study explores a vehicle-to-vehicle (V2V) communication setup bolstered by multiple IRSs, evaluating its efficacy and pinpointing the optimal IRS considering end-to-end channel conditions tailored for applications within the Internet of Vehicles (IoV). The investigation extends to crafting an optimization framework aimed at maximizing data rates while minimizing transmit power. We derive approximate closed-form equations for key performance metrics, such as outage probability (OP), average symbol error rate (ASER), and ergodic capacity (EC), over an independent and nonidentically distributed (i.n.i.d.) double generalized Gamma (dGG) fading channel. To corroborate our theoretical findings, Monte-Carlo simulations are conducted. Moreover, we formulate closed-form expressions for optimization quandaries leveraging the Karush-Kuhn–Tucker (KKT) conditions. Additionally, we introduce a deep neural network (DNN) framework to extract various performance metrics based on Monte-Carlo simulations and to predict optimizations in real-time scenarios. Our findings underscore that the integration of multiple IRSs, along with augmenting the number of elements within each IRS, significantly amplifies system performance in contrast to existing V2V systems detailed in the literature. Furthermore, the DNN framework mitigates computational complexity and streamlines execution times compared to conventional simulation methods.

Channel encoders and interleavers are crucial for correcting random and burst errors introduced by noisy channels in digital communication systems. Typically, information about the types of channel encoders and interleavers, along with their parameters used at the transmitting end, is available at the receiver. However, in military communication systems, the encoder/interleaver type and parameters are often partially known or unknown. In reconfigurable receivers and adaptive modulation and coding (AMC)-based systems, blind identification of channel encoders and interleavers enhances spectral efficiency. This paper explores the use of a deep learning approach to identify three different types of interleavers namely block, convolutional, and helical, under Rayleigh fading conditions. We propose a hybrid convolutional neural network (CNN)- support vector machine (SVM) model for classification, with input data consisting of block-encoded and convolutional-encoded data. Our hybrid CNN-SVM model achieves over $\mathbf{9 5 \%}$ classification accuracy across varying signal-to-noise ratio (SNR) values. The findings also show that accuracy improves with longer input sample lengths, albeit at the cost of increased training and testing time. Finally, our proposed model demonstrates superior classification accuracy compared to the CNN model.

Utilizing unmanned-aerial-vehicle (UAV)-based FSO communication can enhance the capability of current network infrastructure by adding wide range of capabilities. Most impor-tantly, use of UAVs as relays can overcome the stringent line-of-sight (LoS) requirement of FSO links. In this paper, we propose a multiple UAV-based FSO communication system with decode and forward (DF) relaying. The FSO links are modeled using a unified fading model that encompasses Malaga distribution reflecting atmospheric turbulence, atmospheric attenuation, pointing errors, and angle-of-arrival (AoA) fluctuations. Opportunistic relay selection (ORS) is employed to choose the suitable UAV for forwarding the signal to the destination. We derive the closed-form expressions for outage probability, average bit error rate (BER), and ergodic capacity. Thereafter, we perform asymptotic analysis to understand the proposed system's behaviour at high signal-to-noise ratio (SNR). We confirm the validity of the derived expressions using Monte Carlo simulations. Finally, numerical results are provided showing the impact of various link parameters on the performance of multi-UAV-based FSO system.

In this paper, we explore the utilization of multiple reconfigurable intelligent surfaces (RIS) for simultaneous wireless information and power transfer (SWIPT) in a Vehicle-to-Infrastructure (V2I) system. The selection of RIS from several options is determined by the end-to-end instantaneous signal-to-noise ratio (SNR). Specifically, our work focuses on the time-switching (TS) SWIPT protocol, integrating non-linear energy harvesting (EH). The primary goal is to maximize information rate and harvested energy at the receivers by jointly optimizing transmit power and time-switching factors. To address the non-convex nature of the problem, the formulation is relaxed and solved iteratively in an alternating manner. In addition, closed-form expressions for optimization problems are derived using the Karush-Kuhn-Tucker (KKT) conditions, and the accuracy of the analysis is validated through comprehensive Monte Carlo simulations. Results demonstrate the significant superiority of our proposed multi-RIS aided schemes over single RIS configurations in terms of both information rate and maximum energy harvesting requirements. The integration of multi-RIS assisted communication setups exhibits substantial potential for enhancing SWIPT performance in V2I systems.

Recently, reconfigurable intelligent surfaces (RISs) have emerged as a highly promising technology within the realm of wireless communication systems, as they offer the potential to minimize obstructions, enhance reliability, and establish alternative paths for signal propagation. This article presents the performance of a free space optics (FSOs) system empowered by multiple optical reflecting surfaces (ORSs) over a Gamma-Gamma turbulence-induced fading channel with pointing errors by considering imperfections in channel state information (CSI). The expressions for probability density function (PDF) of the end-to-end FSO channel considering both perfect and imperfect CSI cases are derived. Further, the unified PDF and cumulative distribution function (CDF) of instantaneous signal-to-noise ratio (SNR) are determined under two detection schemes, i.e., intensity modulation/ direct detection and heterodyne detection for both perfect and imperfect CSI cases. Utilizing the derived CDFs, the closed-form expressions for outage probability and average symbol error rate (ASER) of the proposed multiple ORSs system are obtained along with performing asymptotic analysis. Finally, the numerical results indicate that the performance of ORS-assisted FSO systems is significantly degraded by severe turbulence, pointing errors, and imperfect CSI. However, the inclusion of ORSs and increasing their number improves the performance of ORS-assisted FSO systems in the presence of turbulence, pointing errors, and imperfect CSI, compared to FSO systems without ORSs.

This paper investigates a hybrid framework that combines free space optics (FSO) and terahertz (THz) technologies for a backhaul network. In this hybrid configuration, the FSO and THz systems are empowered by reconfigurable intelligent surface (RIS) and are combined at the receiver using either maximal ratio combining (MRC) or selection combining (SC). The performance of the RIS-assisted hybrid FSO/THz system is evaluated under multiple impairments for FSO and THz links. The exact closed-form expressions for probability density function (PDF), cumulative distribution function (CDF), and moment-generating function (MGF) of the output signal-to-noise ratio (SNR) of both RIS-assisted FSO and THz links are derived. Leveraging these SNR statistics, we compute the outage probability and the average symbol error rate (SER) of the proposed hybrid FSO/THz system with MRC and SC schemes. Additionally, this paper conducts an asymptotic analysis at high SNR levels, yielding asymptotic expressions for outage and average SER, which not only reduce computational complexity but also provide insights into the system’s diversity gain. In the numerical results, the performance of the proposed hybrid FSO/THz system is compared against other state-of-the-art wireless systems, including direct link FSO without RIS, RIS-aided FSO, and the hybrid FSO/THz systems without RIS using diversity combining techniques.

Gaussian filtering is a commonly used nonlinear filtering method. This letter proposes an advanced Gaussian filtering method for handling cyber-attacked measurement data. It considers three general forms of measurement data irregularities due to the attack, including false data injection (FDI), time asynchronous measurements (TAM), and denial-of-service (DoS). The proposed method introduces a modified measurement model to incorporate the possibility of these irregularities occurring simultaneously. Subsequently, it re-derives the traditional Gaussian filtering for the modified measurement model, resulting in the proposed filtering method. The improved accuracy of the proposed method is validated for two simulation problems.

Free space optics (FSO) communication offers various advantages like higher bandwidth, higher data rates, etc., when compared with its counterpart, i.e. radio frequency (RF) communication. Despite that the FSO link is adversely affected due to atmospheric turbulence, obstructions between transmitter and receiver, and pointing errors. In this work, we propose a mixed FSO/RF system based on decode-and-forward (DF) relaying technique consisting of a FSO-based transmitter node (i.e. source), a relay node, which is capable of receiving FSO signal and transmitting RF signal, and an RF-based receiver node (i.e. destination). Furthermore, both FSO and RF links are aided with intelligent reflecting surfaces (IRS). The main goal of the proposed system model is to increase the coverage and overall system reliability of the existing mixed FSO/RF system. Specifically, we investigate the performance of the proposed system by deriving the closed-form expressions for outage probability and average bit error rate (BER) in terms of multivariate Fox’s H-function without using central limit theorem. Moreover, the numerical results are shown along with some insightful discussions. From numerical results, it is deduced that IRS-assisted mixed FSO/RF system performs better than the existing mixed FSO/RF systems without IRS. Finally, analytical results are verified by performing Monte-Carlo simulations.

The deployment of intelligent reflecting surfaces (IRSs) in wireless communication systems have recently garnered much attention due to its potential to reduce blockages by providing an alternate propagation path and improving reliability. This paper reports the performance analysis of multiple optical reflecting surfaces (ORSs)-assisted free space optics (FSO) communication. Specifically, the performance is investigated by utilizing the selection of the best ORS from the multiple available ORSs. Firstly, we have derived the exact probability density function (PDF) of the end-to-end maximum instantaneous signal-to-noise ratio (SNR) among multiple ORSs-aided FSO links. Further, using the above PDF statistics, the outage and average symbol error rate (SER) expressions of the considered multiple ORSs system are derived in closed-form. Additionally, the asymptotic expressions, which are mathematically more tractable, for both outage and average SER are presented with the diversity gain analysis. Finally, numerical results along with Monte-Carlo simulation results are provided to corroborate the derived analytical results.

Recently, the use of reconfigurable intelligent surfaces (RIS) has gained popularity and is emerging as a promising technique to provide improved link reliability and enhanced coverage area. In this paper, we propose an optical reflecting surface (ORS)-assisted free space optics (FSO) communication system, which is based on optical space shift keying (OSSK) technique. Specifically, the closed-form expression for probability density function (PDF) of the ORS-assisted FSO channel is derived over Malaga turbulence model. Further, we have obtained the moment generating function (MGF) of the instantaneous signal-to-noise ratio (SNR) of the overall OSSK-based multiple-input multiple-output (MIMO)-FSO system. Using the derived channel statistics, an upper bound expression for the average bit error rate (BER) and a lower bound for the ergodic capacity are derived. Further, the asymptotic BER is utilized to calculate the diversity gain of the system. Numerical results are provided to corroborate the theoretical analysis of the system, along with insightful discussions. It is observed from the numerical results that the atmospheric turbulence and pointing errors have a negligible effect on the performance of the proposed system. Finally, a trade-off is noticed with respect to the average BER performance versus the spectral efficiency of the proposed system.

The present paper investigates the performance of a space shift keying (SSK)-based multiple-input single-output (MISO) hybrid free space optical (FSO)/radio frequency (RF) system. The proposed hybrid system considers an optical space shift keying (OSSK)-based FSO sub-system as a default transmission option with Nx1 apertures. The millimeter wave (MMW) RF link with M-ary pulse amplitude modulation (MPAM) signaling is utilized when FSO sub-system is in outage. A unified performance analysis is addressed and novel expressions for average bit error rate (BER) are obtained. Significant performance improvement is observed for the proposed system compared to the individual OSSK-based FSO sub-system. The theoretical analysis is verified by Monte-Carlo simulations.

In this paper, a decode-and-forward (DF)-relaying-based hybrid free space optical (FSO)/radio frequency (RF) system is proposed. The hybrid system incorporates DF-relayingbased FSO and RF sub-systems, where FSO sub-system transmits with higher priority and RF sub-system is used in case of FSO link failure. The exact and asymptotic expressions for outage probability and average symbol error rate (SER) are derived and diversity order is determined. To minimize the effect of pointing errors, the optimum transmit beam width and radius of receiver aperture are calculated. The obtained theoretical results are verified with the Monte-carlo simulations. The results show that the proposed system improves the performance compared to that of individual FSO and RF systems.

Free space optics (FSO) communication has garnered significant importance to provide gigabit capacity links owing to its unique features. However, its performance is limited by the adverse effects of transmission medium such as atmospheric turbulence induced fading, wind, etc. Therefore, it is wise to backup with reliable radio frequency (RF) links to improve the performance of FSO communication. The fusion of FSO and RF technologies is a suitable candidate for future satellite communication (SATCOM) systems. In this context, the present paper proposes a novel system model for High-Altitude Pseudo-Satellite (HAPS)-based relaying for downlink scenario utilizing both FSO and RF links. The performance of the proposed hybrid FSO/RF SATCOM system is investigated through average and asymptotic symbol error probability (SEP) analyses. Further, the obtained closed-form expressions for average SEP are validated using Monte-Carlo simulation results.

This study deals with the performance analysis of adaptive combining‐based hybrid free‐space optics (FSO)/radio‐frequency (RF) system in a terrestrial communication scenario with and without pointing errors. Here, outage probability and average symbol error rate (SER) are used as the performance metrics. Adaptive combining is a switching scheme in which the FSO link is active throughout, whereas the RF link is activated based on the transmission reliability of the FSO link and maximal‐ratio‐combining (MRC) of RF and FSO links is performed at the destination. The small‐scale fading in RF and atmospheric turbulence induced fading in FSO links have been characterised by Nakagami‐ m and Gamma–Gamma distributions, respectively. In addition, the radial displacement between the beam centre and detector centre, which induces pointing errors, is modelled using Rayleigh distribution. The exact closed form expressions for the outage and average SER have been derived along with their corresponding asymptotic expressions. Diversity gain of the system has also been determined using the asymptotic expressions. Further, the variation in the performance of the system has been analysed with respect to various parameters including link distance, fading severity parameter, average signal‐to‐noise of the RF link, and the pointing errors parameter.

In this paper, we propose a switching scheme for a decode-and-forward (DF)-relaying-based hybrid free-space op-tics/radio frequency (FSO/RF) system. We consider two scenarios, a dual-hop (DH) scenario without direct link and a DH scenario with direct link using selection combining (SC) at the destination. The system switches between FSO and RF sub-systems based on the received SNR at the destination, where the FSO sub-system is given higher priority. The probability density function (PDF) of the FSO channel is in the form of Meijer G function and the derivation of the analytical expressions for a DH scenario involve multiple such Meijer G functions which are too complex to comprehend. Therefore, simpler asymptotic outage probability and the average symbol error rate (SER) expressions are derived for the FSO sub-system. The exact closed form expressions have been derived for the RF sub-system. The diversity order is determined using the asymptotic expressions.

Blind reconstruction of channel coding parameters plays a significant role in non‐cooperative military and spectrum surveillance applications. Further, it also gives additional advantages in applications such as cognitive radio, adaptive modulation and coding, and so on. In this study, blind estimation algorithms are proposed to identify code dimension and codeword length parameters of low‐density parity‐check (LDPC) codes at the receiver over noisy or erroneous channel conditions assuming a non‐cooperative scenario. The proposed algorithms are validated using different test cases. Moreover, the accuracy of estimation of code dimension and codeword length parameters of LDPC codes using the proposed algorithms is also given for different M ‐ary phase‐shift keying schemes. From the simulation results, it is observed that the accuracy of estimation improves with decrease in code rate, codeword length, and modulation order.

In this paper, we propose a switching scheme for a multiple-input-single-output (MISO) hybrid free-space op-tics/radio frequency (FSO/RF) system to switch the transmission between MISO FSO and RF sub-systems. We consider transmit aperture/antenna selection (TAS) scheme for selecting the best antenna/aperture among multiple transmit antennas/apertures. The proposed FSO sub-system transmits through its selected best link as long as the instantaneous signal-to-noise ratio (SNR) at the FSO receiver is greater than the threshold SNR. The system switches to the best link of the RF sub-system when the SNR falls below the threshold value. The outage probability and average symbol error rate (SER) of the proposed hybrid system is extensively analyzed and the results are validated using Monte-Carlo simulations. Asymptotic expressions are derived to obtain the diversity order of the proposed system. Finally, the performance of the MISO hybrid FSO/RF system is compared with the performance of a MISO FSO system to calculate the performance gain obtained using the proposed switching scheme.

Blind estimation of code and interleaver parameters plays a vital role in various applications such as non-cooperative systems, adaptive modulation and coding, signal intelligence, etc. The present paper proposes novel algorithms to jointly estimate code and interleaver parameters from Reed-Solomon (RS) coded and convolutionally interleaved data stream based on the rank ratio and non-zero-mean-ratio values for noiseless and noisy environments, respectively. Simulation results validating the proposed algorithms are given for various test cases and the accuracy of estimation of convolutional interleaver and RS code parameters is investigated for different values of interleaver width and modulation schemes. It is inferred that the accuracy of parameter estimation improves with decrease in modulation order and interleaver width of convolutional interleaver.

In this paper, we propose a novel switching scheme for hybrid free-space optical (FSO)/radio frequency (RF) system. The outage probability and average bit error rate (BER) expressions are derived for the proposed hybrid system considering decode-and-forward (DF) relaying dual-hop (DH) scenario with and without a direct link. For the scenario with direct link, selection combining (SC) scheme is assumed at the destination. Specifically, the system transmits over FSO channel as long as the instantaneous signal-to-noise ratio (SNR) at the FSO receiver is greater than the threshold SNR. If it falls below the threshold, then the system switches its transmission over millimeter wave (mmW) RF channel. Moreover, Gamma-Gamma and Nakagami-m distributions are used to characterize FSO and mmW RF links, respectively. The exact theoretical expressions are derived in closed-form and validated by Monte-carlo simulations for the proposed system. Finally, to confirm the efficiency of the proposed switching scheme, the performance of the hybrid FSO/RF system is compared with the performance of the FSO system.

Blind reconstruction of code parameters plays a vital role in non-cooperative applications. It also provides additional advantages in applications such as adaptive modulation and coding, reconfigurable receivers, etc. In this paper, blind estimation algorithm is proposed to identify Reed-Solomon (RS) code parameters at the receiver over noisy channels. Simulation results validating the proposed algorithm are given for various test cases. Further, the accuracy of estimation of RS code parameters using the proposed algorithm is also evaluated for various M-ary quadrature amplitude modulation schemes. From the simulation results, it is observed that the accuracy of estimation improves with a decrease in code dimension and modulation order and the proposed algorithm outperforms other algorithms in the prior works.

To improve the error performance of digital storage and communication systems, forward error correcting (FEC) codes and interleaver play a significant role by counteracting random and burst errors, respectively. In most of the applications, accurate information about the type of FEC codes, coding and interleaving parameters are known at the receiver in order to successfully decode and de-interleave the message bits, respectively. However, in certain applications such as spectrum surveillance, adaptive modulation and coding (AMC)-based communication systems, cognitive radio, etc., all the coding and interleaving parameters need not be known at the receiver and blind/semiblind recognition of the same is mandatory. Therefore, in this paper, innovative algorithms for automatic recognition of type of FEC codes along with the parameter estimation of helical scan interleaver are proposed considering both erroneous and non-erroneous scenarios without any prior knowledge about the encoding scheme used in the transmitter. Note that the proposed algorithms will classify among block coded, convolutional coded, and uncoded data streams.

Distributed switched diversity combining has drawn significant attention in the recent past due to its low‐complexity nature in terms of channel state information requirement at the receiving end to achieve full diversity order. In this study, the authors propose a hybrid selection and switch‐and‐examine combining (HSSEC) scheme, which is a combination of selection combining and SEC schemes, for a multi‐relay decode‐and‐forward system to improve the performance of distributed switched diversity combining schemes proposed in the literature. Furthermore, the performance of HSSEC scheme is investigated over non‐identical Nakagami‐ m fading channels. Average end‐to‐end symbol error probability (SEP) expression is derived for M‐ ary phase‐shift keying signalling, and in addition asymptotic SEP expression is also derived to analyse diversity order. From the derived asymptotic expression, it is inferred that the HSSEC scheme attains full diversity order over Nakagami‐ m fading channels, except for the case when threshold signal‐to‐noise ratio (SNR) is very much lesser than the average SNR. Furthermore, exact outage probability expression is derived for the HSSEC scheme. Finally, in the numerical results, the outage and SEP performances are compared with other schemes proposed in the literature.

In this paper, we analyse the performance of a single-relay cooperative diversity system, which is an effective technique to combat the effects of small scale fading, in a more realistic scenario by assuming a correlation among source-to-relay (SR), relay-to-destination (RD), and source-to-destination (SD) links. A generalised closed form end-to-end symbol error probability (SEP) expression for M-ary phase-shift keying (MPSK) scheme using paired error approach has been derived over correlated Nakagami-m fading channels with decode and forward (DF) protocol being used at the relay node. Moreover, we use similar error approach to analyse the performance of a double correlated cooperative diversity system by assuming the correlation between SR and RD channels. Finally, Monte Carlo simulation has been performed to validate the theoretical results.

A $\{ 0,1\} $-matrix M has the consecutive-retrieval property if there exists a tree M such that the vertices of T are indexed on the rows of M and the columns of M are the incidence vectors of the vertex sets of paths of . If such a T exists, then T is a realization for M. In this paper, an $O(r^2 c)$ algorithm is presented to determine whether a given standard, $r \times c$ matrix has the consecutive-retrieval property and, if so, to construct a realization.

A simple decomposition of a r/spl times/c/spl lcub/0,1/spl rcub/-matrix is defined in terms of a collection of disjoint submatrices obtained by deleting a "minimal" set of columns. In general, the number of such simple decompositions is /spl Theta/(2/sup r/). A class of matrices, namely, vertex-tree graphic, is defined, and it is shown that the number of simple decompositions of a vertex-tree graphic matrix is at most r/spl minus/1. Finally, the relevance of simple decomposition to the well-known problem of cluster formation on /spl lcub/0,1/spl rcub/-matrices is uncovered, and an O(r/sup 2/c) time algorithm is given to solve this problem for vertex-tree graphic matrices.>

The problem of decomposing a general polygonal chain, open or closed, into a minimum number of monotone subchains is studied in this paper. We show that this geometric optimization problem can be solved in linear time (in the number of edges) by a strategy related to the selection of a minimum cardinality cover of a circle by a subset of its arcs. We also introduce a special class of polygonal chains, called stable configurations. These stable configurations are certificates of when a greedy procedure is guaranteed to be optimal for the monotone chain decomposition problem. The greedy procedure translates to a very simple linear-time algorithm. Further, the presence of the stable-configuration-certificate in any given polygonal chain can also be recognized in linear time. INFORMS Journal on Computing, ISSN 1091-9856, was published as ORSA Journal on Computing from 1989 to 1995 under ISSN 0899-1499.