Vehicle clustering improves communication efficiency, safety, and comfort in connected vehicular networks. Cluster heads (CHs) manage critical tasks such as handoff (HO), coordination, and resource allocation. However, in overlapping regions, CH-based group HO handling is hindered by high traffic and limited channel access, causing delays, signaling overhead, and reduced bandwidth efficiency. These issues increase HO latency and risk congestion and HO failures. To address HO loading, latency in overlapping regions, and poor convergence in dynamic environments, this paper proposes an evolutionary game-theoretic framework that selects multiple HO agents (HOAs) in overlapping areas. These agents form HO clusters to distribute load and mitigate channel contention, achieving up to 72.21% lower delay compared to conventional CH-based HO. The buffering of HO data at HOAs, necessitated by the distinct variability of vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) links, is addressed through a queueing-theoretic model. This is followed by optimal resource block (RB) allocation, minimizing total waiting time to 2.063 ms at optimal RB values for two HO-clusters and enhancing network stability. At an average vehicle speed of 140 km/h, the proposed HOA-based HO achieves a total average HO delay of 0.91 ms, corresponding to an 83.8% reduction compared with direct V2I HO. Analytical proof of equilibrium and Lyapunov-based stability validation ensure robustness in dynamic environments. It is observed that, under high incentive, a 12.5% increase in vehicle velocity slows the convergence rate by approximately 60%, primarily due to increased channel variability at higher speeds.

Cluster Head (CH)-based group handoff (HO) management in VANETs faces challenges in overlapping regions, where high traffic and limited channel access exacerbate HO delays. These delays, along with loading problems, signaling overhead, and reduced bandwidth (BW) efficiency, lead to congestion and potential failures, further complicating HO management. CHs in VANETs are responsible for various essential functions beyond HO management, including coordination and communication, resource management, and data aggregation. To address the challenges of loading and delay during HO in the overlapping area and the problem of low convergence in dynamic environments, we propose an evolutionary game-theoretic (EGT) framework. This framework selects multiple handoff agents (HOAs) in overlapping regions, effectively distributing the load and reducing HO delays. Given VANETs’ dynamic topology, frequent cluster reformation can disrupt stability; however, the proposed EGT model ensures an evolutionarily stable strategy (ESS), maintaining efficient HO performance despite sudden network changes. The equilibrium point is analytically proven, and stability is further validated using the Lyapunov function, ensuring robustness against disruptions. This work offers valuable insights into achieving stable and efficient HO clustering in VANETs, especially in highly dynamic environments where traditional CH-based HO management approaches struggle. Simulation results confirm that the system quickly stabilizes, preventing failures caused by selfish user behavior.

This work presents a novel mathematical framework of a machine learning algorithm for linear regression under non-Gaussian estimation noise. The Laplacian noise is selected as a contender for the non-Gaussian noise, as it is found in many real-world scenarios, like the differential privacy of users and as impulsive noise in wireless communication channels. In particular, we show the use-case of our analytical work in the regression-based application of wireless communication systems, specifically channel estimation. We exhibit the fundamental technique of linear regression to evaluate the wireless channel coefficients over additive Laplacian noise. In order to establish the need for the proposed framework, we illustrate a comparison between the behaviour of Gaussian and non-Gaussian noises. Furthermore, we investigate the maximum-likelihood estimator using gradient descent, the maximum a posteriori estimator, and the mean square error performances for the considered system scenario; to observe that the estimators derived under the actual non-Gaussian noise assumption yield better results as compared to those found under mathematically tractable simplified Gaussian assumption.

This work aims to present a modeling approach for an intelligent reflecting surface (IRS)-assisted unmanned aerial vehicle (UAV) based free-space optical (FSO) communication system emphasizing hovering of UAV. The hovering of UAV is accounted for at both the IRS and receiver (Rx) nodes. Because of the highly line-of-sight (LOS) nature of the FSO communication, the hovering of UAV significantly impacts the system performance. Therefore, a hovering UAV-enabled-IRS (UIRS) based FSO model is proposed. For the first time, we statistically model the impact of UAV hovering at both the IRS and the Rx nodes by proposing distribution functions accounting angle-of-arrival (AoA) fluctuations. Moreover, to account for realistic findings, we incorporate independent fading statistics between the transmitter (laser source)-UIRS link and UIRS-Rx (photodetector) link. Further, we analyze the performance of the proposed UIRS-FSO model considering bit error rate as the metric. Our findings reveal that the UIRS-FSO system is highly impacted when accounting for the AoA fluctuations at both the IRS and Rx nodes.

We propose differential modulation-based non-orthogonal multiple access (NOMA) scheme for a multiple access wireless set-up containing a near user and a far user, in this paper. The proposed scheme avoids the need for channel state information for decoding and interference cancellation. We derive the error rate for both users and based on the derived analytical result we also propose optimized power allocation to improve the error performance of the considered system. It is observed through simulations that it is advantageous to allocate more power to the far user, which results in reduced interference for the far user and improved interference cancellation performance for the near user. Further, it is observed via rigorous numerical results that the proposed differential NOMA scheme performs only 2 dB poorer than the existing coherent NOMA scheme, in terms of the average bit error rate of both users.

This work is concerned with the physical layer security of the free space optical (FSO) communication network comprising of a transmitter, a receiver, an eavesdropper (Eve), and a friendly reactive jammer that aims to thwart the activity of the Eve. As the key feature of this work, we calculate the discrete-input-continuous-output for memory-less channel (DCMC) capacity of the authentic and eavesdropping channel in the presence of the atmospheric turbulence characterised by$\alpha -\mu $probability density function (PDF), zero and non-zero boresight pointing error, and partial band or broadband jamming noise. For this purpose, novel PDFs for all-encompassing conditions of FSO channel and the received signals at different nodes of the considered system are formulated. Thereafter, we devise schemes to wane the effect of a vicious Eve by formulating novel closed-form expressions of average secrecy capacity for both strategies. Our derived analytical expressions can be used as tools to examine the DCMC capacity and secrecy capacity for different turbulence regimes of FSO link, severity of boresight errors, and activity of a friendly jammer. The mathematical results are affirmed by Monte-Carlo simulation. We exhibit that deploying a friendly jammer to assist enhancing the security of an FSO system is very conducive as it makes the Eve to hike its signal-to-jamming-noise ratio by almost 10 dB when the jammer’s activity increases from 10% to 100% of the time frame of data transmission.

In this study, we jointly investigate the connectivity probability and the number of required resource blocks (RBs) for load reduction during handoff (HO) decision for hybrid vehicle-to-everything (V2X) communication. Frequent HOs is a major issue in vehicular communication, causing various concerns such as loading problems in the overlapping area, signalling overhead, and decreasing the bandwidth efficiency of the network. To combat the loading problem due to HO in the overlapping area and the low convergence issues, we propose a game-theoretic approach to resolve the imbalance of resource allocation amongst the clusters at the edge of the coverage area. The proposed game-based Flexible Resource Allocation (FRA) approach optimally redistributes the resources to all clusters within a g-NodeB (g-NB). We obtain a closed-form expression of the transmit power for a cellular-vehicle-to-everything (C-V2X) standard of 5G network, besides analyzing the effects of connectivity probability and required resources for vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) during HO. We explore the implications of non-uniform speeds among the clusters and perform an analysis of time complexity. Additionally, we compare two types of cost functions. A linear cost function links a player’s cost to their action proportionally, while a nonlinear cost function shows a non-proportional relationship between a player’s cost and their action. The simulation results indicate that, with an increasing number of clusters, the linear cost case outperforms the non-linear case in both connectivity probability (which increases by 30.18%) and the number of required resources (which is reduced by 39%) in the HO region. The analytical derivation has been verified through simulation results.

In this study, we jointly investigate the connectivity probability and the number of required resource blocks (RBs) for load reduction during handoff (HO) decision for hybrid vehicle-to-everything (V2X) communication. Frequent handoffs (HOs) is a major issue in vehicular communication, causing various concerns such as loading problems in the overlapping area, signalling overhead, and decreasing the bandwidth efficiency of the network. To combat the loading problem due to HO in the overlapping area and the low convergence issues, we propose a game-theoretic approach to resolve the imbalance of resource allocation amongst the edge clusters. The proposed game-based Flexible Resource Allocation (FRA) approach optimally redistributes the resources to all clusters within a base station (BS). We obtain an approximate closed-form expression of the transmit power for a 5G network, besides analyzing the effects of connectivity probability and required resources for vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) during HO. The analytical derivation has been verified through simulation results.

Satellite systems are widely used in applications such as broadcasting, navigation, emergency services, etc., because of some unique advantages such as providing service over wide coverage area, especially in regions where terrestrial communication fails. In this paper, channel capacity of satellite system subjected to three adaptive transmission policies namely, optimal rate adaptation with constant transmit power (ORA), optimal simultaneous power and rate adaptation (OPRA) and channel inversion with fixed rate (TIFR) is studied. Exact closed-form expressions of the Shannon capacity under these schemes are derived. The channel fading of the system is modelled using Shadowed Rician (SR) distribution. The derived expressions are applicable to integer as well as non integer valued severity/Nakagami-m parameter of the SR distribution. In addition to this, the effect of shadowing severity parameter on the capacity of adaptive schemes is also investigated. Numerical results reveal that OPRA scheme results in more capacity gain than the other two. On the other hand, TIFR scheme suffer a large outage probability which causes large capacity penalty as compared to ORA and OPRA schemes. Furthermore, increase in shadowing severity degrades the capacity of the satellite channel.

This work studies the impact of jamming on an unmanned aerial vehicle (UAV) transmitting to a ground station through free-space optical communication. The UAV transmission link gets deteriorated from Gaussian noise and jamming signal simultaneously. The optical channel is modeled as Gamma-Gamma for atmospheric turbulence with pointing error. The error performance of the system is evaluated and closed-form expression of the bit error rate (BER) is derived considering different degrees of jamming activity. The derived analytical results are confirmed by simulations. It is observed that as the probability of the jammer's activity raises from 0.1, the error performance of the system gets saturated. Furthermore, it is noted that the jammer has more adverse impact on system's BER than the Gaussian noise, irrespective of the turbulence regime. Additionally, the jammer aggravates the effect of turbulence on the system.

In this work, a vehicle-to-vehicle (V2V) visible light communications (VLC) model for twopractical scenarios, is proposed. Inscenario 1, the random lateral shift of vehicles and the deterministic longitudinal separation between two communicating vehicles are considered, whereas inscenario 2, longitudinal separation between two vehicles is considered to be random, and lateral shift of vehicles is considered to be deterministic. To this end, we emphasizecomprehensive modelingof thepractical characteristicsof the considered V2V-VLC system, such asrandom path lossdue to therandom mobilityof the vehicle,random lateral shiftandrandom longitudinal separationof the vehicle. Moreover, we analyze the performance of the proposed V2V-VLC model in terms of different metrics under the consideration of anovel channel model. Considering ourfindings, it is observed that the random lateral shift of the vehicle and the random longitudinal separation between two vehicles have a significant impact on the V2V-VLC system performance. Further, at a distance of 40 m, for example, the path losspenaltiesfor moderate and dense fog weather scenarios are 2 and 3 dB, respectively, compared with the clear weather. Furthermore, thecombined impactof path loss and atmospheric turbulence affects the V2V-VLC performance significantly.

In this paper, we study the pulse jamming effect thoroughly in aperture-averaged free space optical (FSO) systems. The FSO fading channels are considered to be Exponentiated Weibull (EW) distributed due to its excellent fit for all aperture sizes over the ranges of atmospheric turbulence conditions. It is inferred from the theoretical analysis that random jamming behaviour is impulsive and it reveals a destructive property over aperture-averaged FSO receivers. Analytical expressions of the average bit error rate (ABER) and outage probability (OP) are formulated for the considered FSO system in the presence of random jammer. The effects of pulse jamming on ABER and OP performances are shown. Additionally, the asymptotic ABER analysis is performed in order to investigate the response of the considered FSO system in high transmit power region and to analyze the diversity order under the pulse jamming effect. Pointing error impairments, being another important performance degrading parameter of the FSO communication system, are studied along with the pulse jamming effect. Also, asynchronous jamming effect over the ABER performances is described by both analytically and graphically.

Free space optical (FSO) channel provides a significantly large transmission capacity. However, in the presence of random jamming attacks, the efficacy of FSO communication channel can be affected critically. In this paper, the discrete-input continuous-output memoryless channel (DCMC) capacity of a single-input single-output FSO communication system is investigated under the random jamming effects. The ergodic channel capacity analysis is performed over additive non-Gaussian noise channel (jamming noise channel). The derived closed-form expression of DCMC capacity for the considered FSO system and also, the effects of partial-band jamming and broadband jamming over the FSO channel capacity are verified through simulation results. It is observed that the FSO channel capacity is very sensitive to the degree of jamming and the ergodic channel capacity alters crucially even for small change in jamming probability. The derived results are utilized to study the considered network in the presence of a rational jammer whose ability to jam is limited by its battery capacity. The presence of a rational jammer is addressed by modelling the interaction between the FSO transmitter and the jammer as a non-cooperative game. The closed-form expressions of the equilibrium of the proposed game are derived and verified through simulation. The game-theoretic solution provides a performance improvement of 74% in comparison to uniform power allocation.

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 paper, we investigate the physical layer security based on space shift keying (SSK) in which bit-to-spatial mapping of antenna indices dynamically adapts according to the partial channel state information (CSI) of the legitimate channel at the transmitter (Tx). Further, the Tx also adapts transmit power allocation to each transmit antenna according to partial CSI. Since an eavesdropper (Eve) is not (usually) aware of the legitimate CSI, it cannot successfully decode the antenna index; thus, transmission over the legitimate channel is secured from the wiretapping of Eve. An important virtue of the proposed scheme is that the Tx does not require full CSI of the legitimate and eavesdropper channels to secure the confidential information. The proposed work focuses on the secrecy rate (SR) and bit error rate (BER) of the considered multiple-input single-output system over Rayleigh fading channels. Approximate expressions of Bob's data rate for 2-ary and 4-ary SSK modulations are derived in closed-form. Furthermore, an upper-bound of Bob's data rate for Na-ary SSK modulation is also derived. In order to obtain the secrecy rate for the proposed scheme, we also evaluate Eve's data rate. Analytical results of SR and BER demonstrate the robustness of the proposed scheme. All numerical results are thoroughly verified by using extensive Monte Carlo simulations.

In the last decade Internet of Things (IoT) grew up in an exponential behavior with applications requiring long range and low power wireless transmissions. Factory of the Future (FoF), also called Industry 4.0, aims to use IoT technologies to enhance productivity, therefore adding high reliability constraints. Several IoT standards were proposed and LoRa has emerged as a high potential candidate for a variety of applications. LoRa modulation is based on a chirp spread-spectrum technique and offers efficient transmission up to 50 kbps over several kilometers. The performance of LoRa in terms of symbol or bit error probability has been theoretically analyzed in few recent papers for a Gaussian channel. However, the industrial environment is often corrupted with impulsive non Gaussian noise generated by high-power equipment. In this paper, the impact of impulsive noise, modeled by the Middleton Class-A noise, is introduced and the robustness of a LoRa communication is studied. Compared to the Gaussian case, simulations show that impulsive noise may severely degrade system performance. This Signal-to-Noise Ratio loss can reach up to 10 dB, but increasing the spreading factor can reduce the noise impact.

In this paper, we propose an adaptive antenna index (AI) mapping scheme with the aid of partial channel state information (CSI) (i.e., channel gain order information) of legitimate channel. Based on the received partial CSI that is unknown to an eavesdropper (Eve), transmitter (Tx) adapts AI mapping patterns. In addition, Tx also adapts transmit power allocation to each transmit antenna according to the partial CSI. Since Eve is unaware of the partial CSI of the legitimate channel, it cannot successfully decode the AI patterns; and transmission over the legitimate channel is secured from wiretapping of Eve. Further, we offer an accurate analytical framework for ergodic secrecy rate (ESR) and bit error rate (BER) of 2-ary space shift keying modulated multiple-input single-output system in the presence of a passive eavesdropper. Moreover, the analytical results of ESR and BER demonstrate the robustness of the proposed scheme. All numerical results are thoroughly verified by using the Monte Carlo simulations.

Power line communications (PLC) system performance is severely affected by the presence of impulsive noise and channel gain. Many communication systems employ a combination of forward error correction and automatic repeat request (ARQ) to detect transmission errors known as hybrid ARQ (HARQ). Thus, HARQ can be used to improve the reliability of a PLC system. In this paper, we evaluate the performance of a PLC system under the influence of impulsive noise over Rayleigh and Log-Normal channel gains using HARQ with chase combining scheme. Closed-form expressions of the analytical outage probability are derived for these two channel gain scenarios. Using the expression for outage probability, we also compute the average throughput for the PLC system under the given channel gain scenarios. It is observed by the analysis that the outage performance of the considered PLC system is significantly improved with the use of HARQ.

In this paper, we employ a differential modulation technique for a butter-aided cooperative network. A differential decode-and-forward relaying protocol is proposed for transmission with priority-based link selection. The proposed technique does not require channel state information at any node of the buffer-aided cooperative network. A Markov chain-based approach is used to analyze the state transition matrix which models the evolution of butter status. An analytical expression for the steady state probability is derived, and with the help of that, analytical expressions of outage probability and average bit error rate (ABER) are obtained. The performance gap between the considered system and coherent butter-aided system is observed through the derived analytical results. The considered differential system suffers a signal-to-noise ratio penalty of 1 dB at the ABER level of 10-4with a two-bit butter, which is a significant improvement over non-butter-aided networks; which offer a performance gap of 3 dB between coherent and differential relaying.

In the past few years, visible light communication (VLC) has been a surge of interest in the research community. Different studies on VLC based communication systems were part of the research in the recent few years. However, there is no study on the development of the diversity-multiplexing tradeoff (DMT) metric to compare and design new multiple-input multiple-output (MIMO) VLC schemes. This paper introduces the concept of DMT for indoor VLC-based communication systems that utilize intensity modulation and direct detection technique for which channel coefficients are real and positive. DMT is characterized as a vital performance metric for comparing different MIMO techniques. For simplifying the presentation, we start with a single-input single-output VLC system and broaden this analysis to MIMO-VLC systems to have better useful insights.

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.

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 × 1 and 4 × 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.

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, various link characteristics and bit error rate (BER) performance of a free-space optical (FSO) multiple-input-single-output (MISO) system with repetition coding (RC) is investigated both experimentally and theoretically. The study is performed in the presence of atmospheric turbulence (AT) over a correlated channel with an erbium- doped fiber amplifier employed at the receiver (Rx). It is shown experimentally that the measured AT levels of two parallel links are different and the links experience non-identical fading influence. The analytical BER expression for an optically pre-amplified correlated FSOMISO system with non-identical AT channel is derived. The BER results of the considered system with pre- amplifier is compared with the BER results of an FSO system without pre-amplifier, and it is shown analytically that a 2 X 1 FSO system with pre-amplifier offers better BER performance in terms of coding gain of /spl approx/ 6 dB over the system without pre-amplifier. Moreover, it is also shown that the FSO system with RC gives better performance with identical links as compared to non- identical links. Further, it is also revealed that the diversity order of the considered system is independent of correlation and use of pre- amplifier. All the analytical results are validated by comparing them with Matlab simulations.

In this paper, we propose a space shift keying (SSK) modulation scheme where a transmitter (Tx) has partial information of the channel states through feedback from the receiver. More specifically, the Tx does not receive perfect information of the channel coefficients, but only has information about channel gains ordering. This information is exploited by Tx to adapt the spatial constellation and transmit power weights. Thus, gray encoding based adapted spatial constellation decreases the number of bits in error between two consecutive constellation points and also reduces the average bit error rate (ABER). For mathematical analysis, we focus on a 2 × 1 multiple-input single-output (MISO) system over Rayleigh fading channels. An accurate expression of the ABER for the considered MISO system is derived. The proposed scheme outperforms the conventional SSK scheme for a given transmission rate, as demonstrated by both analysis and simulation. It is shown analytically that the ABER performance of the proposed SSK scheme can be improved by applying asymmetric power allocation (PA) to make links more distinguishable. Moreover, the proposed SSK scheme achieves a higher diversity order, as compared to the conventional SSK scheme; due to asymmetric PA. For a 4 × 1 MISO system, we present simulation based results of ABER performance for the proposed SSK scheme. Further, all analytical results are verified via simulation.

We analyze the outage performance of a buffer- aided dual-hop decode-and-forward cooperative relaying network with co-channel interference (CCI) and additive white Gaussian noise (AWGN) at the relay and the destination nodes. We propose a max-signal-to-interference plus noise ratio (max- SINR) relaying protocol in which the data transmission takes place in the link having the maximum SINR among the available source-relay and relay-destination links. It is assumed that the envelopes of the desired signal and the interfering signal follow asymmetric channel configuration with Rayleigh distributed fading. We consider a finite size data buffer equipped at the relay nodes. A discrete Markov chain approach is adopted to model the evolution of the relay buffers' status and to derive a closed-form expression for the outage probability. Numerical results demonstrate that in the cooperative networks with CCI and AWGN, employing a data buffer at the relays and adopting the max- SINR relaying protocol lead to an improvement in the performance of outage in comparison to the max-min relaying protocol without a buffer. The buffer-aided relaying protocol can improve the reliability of a cooperative network with CCI and AWGN as compared to the non buffer-aided relaying protocol.

In free space optical (FSO) communication, jamming can cause inaccuracy in the received information. In this paper, we investigate the impact of jamming over atmospheric turbulence (AT) fading channels. To describe the AT, negative exponential (NE) and Gamma-Gamma (ΓΓ) fading channel models are considered. The effect of jamming is studied over a single-input single-output (SISO) FSO link. We introduce a theoretical framework to acquire a closed-form expression of the average bit error rate (ABER) under jamming-leading to an additive non-Gaussian noise channel. It is observed by thorough analysis that a 2 x 1 FSO system performs better than SISO FSO system in presence of jamming signal. It is realized that under jamming the performance of FSO link is dependent on different AT conditions. Furthermore, increasing number of transmit apertures allows FSO system to significantly overcome the effect of jamming, in order to obtain an improved ABER.

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 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.

In this paper, we investigate the physical layer security (PLS) of cooperative wireless-powered networks where a source transmits confidential information to a destination with the aid of wireless-powered intermediate nodes equipped with multiple antennas in the presence of a passive eavesdropper. We consider two generalized joint relay and jammer selection (GJRJS) frameworks based on the power splitting (PS) and time switching (TS) techniques, respectively. Specifically, the intermediate nodes which cannot decode the source signal successfully are selected to act as friendly jammers to transmit artificial noise, and the remaining nodes are exploited as relays to simultaneously forward the source signal through cooperative beamforming. We further propose two cooperative secure beamforming (CSB) schemes for the PS-based GJRJS (PS-GJRJS) and TS-based GJRJS (TS-GJRJS) frameworks, respectively. To be specific, we investigate the optimization of the beamforming vector of our selected relays for maximizing the secrecy rate of the source–destination transmission. A closed-form solution is derived under the assumption of available instantaneous channel state information (CSI) of the main link and statistical CSI of the wiretap link. In addition, we also illustrate that the pure relay selection (PRS) scheme is a special case of our GJRJS framework at high signal-to-noise ratios (SNRs). The numerical results show that the proposed CSB scheme achieves a higher secrecy rate than the traditional maximal ratio transmission (MRT) method for both the PS-GJRJS and TS-GJRJS frameworks. Additionally, the GJRJS framework outperforms the PRS as well as the joint best relay and jammer selection (JBRJS) methods in terms of secrecy rate.

In this paper, imperfect feedback-based linear precoding schemes are proposed for multiple-input-multipleoutput (MIMO) wireless communication systems, where input symbol streams are encoded by using generalized-orthogonal space-time block codes. The imperfect feedback information drastically degrades the system performance. Therefore, to overcome the effect of erroneous feedback information, error-tolerant weighting (ETW) schemes are implemented by employing diagonal precoder. The communication links are assumed to be Nakagami-m distributed for accurately characterizing practical wireless channels under different fading scenarios. Exact and asymptotic symbol-error-rate (SER) expressions of the considered MIMO system are derived under imperfect feedback with the help of order statistics. The most appropriate values of the transmit weights of the precoder matrix are obtained by minimizing the derived average SER over fixed and adaptive signal-to-noise ratio. Further, we study the trade-off between the proposed optimal and suboptimal feedback-based precoding schemes. Moreover, the ergodic-rate of the ETW schemes is also derived with imperfect feedback for arbitrary MIMO system by using the moment generating function approach. The simulated and analytical results show that a significant performance gain is achieved by the ETW schemes as compared to the uniform power allocation and existing precoding techniques under erroneous feedback information.

This paper investigates the problem of energy efficiency maximization (EEM) for the small cells that coexist with a macro cell in an underlay heterogeneous cellular network, where a macro base station and a number of small base stations transmit signals to a macro user and small users through their shared spectrum. We propose a joint power and bandwidth allocation (JPBA) scheme for the sake of maximizing the energy efficiency (EE) of small cells under the constraint of a guaranteed quality-of-service requirement for the macro cell. Considering that our formulated EEM-based JPBA (EEM-JPBA) problem is non-convex, we convert the original fractional problem into an equivalent subtractive form by adopting the Dinkelbach's method, which is addressed through the augmented Lagrange multiplier approach. Moreover, a new two-tier iterative algorithm is presented to obtain the optimal solution of our EEM-JPBA scheme. Simulation results demonstrate that the proposed two-tier iterative algorithm can quickly converge to the optimal EE solution. In addition, it is shown that the proposed EEM-JPBA scheme significantly outperforms the conventional power and bandwidth allocation methods in terms of their EE performance.

Due to the rapid growth of free-space optical (FSO) communication over the last few years, there is an exigency to develop diversity-multiplexing tradeoff (DMT) metric in order to compare and design new multiple-input multiple-output (MIMO) FSO schemes. This paper introduces the DMT for MIMO-FSO systems that utilize the intensity modulation and direct detection technique for which the channel gains are real and positive, contrary to MIMO radio-frequency (MIMO-RF) systems where the channel gains are complex. Log-normal, gamma-gamma, and negative exponential channel models are used in this paper to cover weak to saturated turbulence environments. It is shown that at zero multiplexing gain (r), the log-normal channel offers maximum but finite diversity order that depends on the block length within which the channel matrix is constant. On the other hand, negative exponential channel offers minimum diversity order. However, for r ≥ 1, DMT curves under all channel models are of the same nature; and for a given r, the diversity is half as that observed in the MIMO-RF channels. To gain additional insights into the DMT of an MIMO-FSO system, we also develop upper and lower bound expressions of DMT and determine the minimum block length at which these bounds are identical.

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 paper, we propose, for decode-and-forward cooperative networks, a relaying scheme which is based on giving a priority to the status of relay buffers along with the highest channel gain of wireless links. Specifically, we divide the set of relay buffer status into three priority classes: i) the first priority is given to relay buffers which are full, ii) the second priority to relay buffers which are empty, and iii) the third priority to relay buffers which are neither full nor empty. Within a priority class, a relay node is selected corresponding to the link having the highest channel gain. We adopt a Markov chain approach to analyze the state transition matrix that models the evolution of the relay buffer status. Analytical expressions for the outage probability and the diversity order are derived. The proposed scheme is illustrated with an example and analytical expressions for the steady-state probability vector are obtained. It is also shown that the states having the same probabilities can be grouped. Furthermore, we explain the construction of the reduced state transition matrix. Our analytical and simulation results demonstrate that the proposed scheme has the potential to provide better outage performance over the conventional maxlink scheme.

Multi‐hop relaying is used to extend the reach of wireless communication systems whereas cooperative relaying is used to improve the performance gain by exploiting the spatial diversity. In this study, the authors combine these two techniques to improve the range as well as the performance gain of cognitive radio networks (CRNs). Selective decode‐and‐forward relays are considered and two relay selection schemes are used to study the performance of multi‐hop CRNs over Rayleigh fading channels. The exact outage probability and throughput of the considered system are derived for both the schemes by considering the effect of both peak‐power and peak‐interference constraints. By using the derived outage probability, the diversity gains for both considered schemes are determined. Numerical results show that the outage probability monotonically improves, whereas the throughput has concave behaviour with respect to increasing number of relaying hops.

In this paper, we propose an imperfect quantized feedback-based diagonal precoding scheme for generalized orthogonal space-time block codes in an N × 1 multiple-input single-output (MISO) wireless communication system employing M-QAM constellation. It is well known that a feedback-based precoding scheme aids channel adaptive signaling in wireless communication system and capitulates large improvements in almost all performance metrics. However, a practical feedback link is susceptible to error due to wireless channel fading and leads to wrong precoder selection. Therefore, a signal-to-noise ratio (SNR) adaptive error-tolerant weighting scheme is introduced which provides significant gain in comparison with another proposed arbitrarily fixed SNR error-tolerant weighting scheme. At first, a tight approximate closed-form expression of average symbol-error-rate (SER) and an exact analytical expression of outage probability are derived under imperfect feedback information with the help of order statistics. By minimizing the derived average SER, optimized transmit weights for the diagonal precoding matrix (based on feedback bits) are obtained. Later, a closed-form expression of the ergodic capacity with erroneous feedback bits for arbitrary MISO system is also provided by using the moment generating function approach. Further, numerical results show that the considered error-tolerant schemes outperform the uniform power allocation scheme in term of all the investigated performance metrics.

In this paper, the bit error rate (BER) and the channel capacity of a multiple-input multiple-output (MIMO) system employing optical space shift keying (OSSK) scheme (termed as MIMO-OSSK) are investigated under combined effect of atmospheric turbulence (AT) and pointing errors (PEs). The analysis reveals that the diversity order of MIMO-OSSK remains intact over all AT regimes and under PE severity. This behavior is contrary to traditional pulse-based modulation schemes, where diversity order depends upon AT conditions and PE severity. In addition, the analysis also demonstrates that the MIMO-OSSK utilizes receiver diversity efficiently as compared to existing pulse-based modulations. In order to examine the effect of all ranges of AT along with PE severity on MIMO-OSSK, three different channel models are considered, i.e., log normal, gamma-gamma, and negative exponential. The probability density functions of the sum of squares of difference between two channel coefficients under these channel models are evaluated, to develop analytical expressions of average BER and ergodic channel capacity for the considered setup. On comparing MIMO-OSSK with the same rate MIMO-pulse amplitude modulation (MIMO-PAM) scheme employing repetition coding, it is observed that the MIMO-OSSK scheme outperforms the MIMO-PAM for a spectral efficiency of more than 2 b/s/Hz, provided that the number of receivers is sufficiently large.

In a communication system employing coherent reception, pilot symbols are used for estimating the channel state information (CSI) at the receiver. The amount of training, which is quantified by the fractional pilot duration for a fixed-length pilot-plus-data frame, should be kept as low as possible for saving bandwidth and increasing data rate. However, reducing training leads to degraded error performance due to poor CSI estimate although it increases data rate, while increasing training improves error performance but reduces data rate. Expressing the tradeoff between symbol error probability (SEP) and data rate by the normalized error-free data rate, we present an analytical framework for its maximization with respect to pilot symbol duration fraction in a pilot-aided single-input multiple-output wireless communication system with reception over independent and identically distributed flat Rayleigh fading diversity branches, employing M -ary phase-shift keying, and using maximal-ratio combining. Closed-form expressions for the approximate optimal pilot symbol duration fraction are derived for the high signal-to-noise ratio (SNR) case. Numerical results are presented to highlight the system behavior with changes in parameters like SNR, pilot symbol quality, and number of receive diversity branches. It is found that the optimization maximizes normalized error-free data rate with close to minimum SEP.

In this paper, we propose a new relaying scheme, referred to as priority-based max-link relay selection, for buffer-aided decode-and-forward cooperative networks. We give the first priority to the relay buffers having status full, the second priority to the relay buffers having status empty, and the third priority to the relay buffers having status neither full nor empty. The best relay node is selected corresponding to the link having the highest channel gain among the links within a priority class. By adopting a Markov chain approach to analyze the state transition matrix that models the evolution of the buffers status, we derive analytical expressions for the outage probability and the average bit error rate. Analytical expressions for the steady-state probability vector are also obtained, and through these expressions, it is shown that states with the same probabilities can be grouped, thus reducing the size of the state transition matrix. We propose a general state-grouping-based method to obtain the reduced state transition matrix, which in turn reduces the computational complexity in obtaining the steady-state distribution. Our analytical and simulation results demonstrate that the proposed relaying scheme has better performance gain over the conventional max-link scheme.

In this paper, the ergodic capacity of optical space shift keying (OSSK) based multiple-input multiple-output (MIMO) system under atmospheric turbulence (AT) is investigated. Negative exponential (NE) and Gamma-Gamma (G-G) channel models are used to characterize the AT. At first, a novel expression of the distribution of a sum of square of the difference between two NE/G-G random variables is evaluated. Later, a closed-form expression of the ergodic capacity for OSSK-MIMO system under different AT conditions is obtained with the help of derived distributions. It is shown by the analysis that the value of signal-to-noise ratio (γ̅th) to reach 90% of the maximum achievable capacity (Cmax) is same under moderate, strong, and saturation AT regimes for a particular OSSK-MIMO system. The required value of γ̅thremains constant irrespective of number of transmitter (Txs); however, Cmaxis enhanced with increasing number of Txs. On the other hand, a reduction in requirement of 7th is observed when the number of receivers (Rxs) is increased, while Cmaxremains constant irrespective of number of Rxs. Additionally, a new series based average bit error rate (ABER) expression, which has better accuracy and less mathematical complexity than a previously known ABER expression for OSSK-MIMO system, is obtained using the proposed distributions.

This paper evaluates the exact performance of the triple-hop decode-and-forward (DF) based mixed radio fre-quency/free space optical/radio frequency (RF/FSO/RF) cooperative communication system. The mixed RF/FSO/RF system finds application where the FSO link can be used to provide high speed optical connectivity between two RF networks. The RF links are characterized by independent but not identically distributed (i.n.i.d.) Nakagami-m fading links and the FSO link is characterized by path loss, Double Generalized Gamma (DGG) distributed turbulence, and pointing errors. For this mixed triplehop communication system, novel analytical expressions are derived for the key performance metric, i.e., the average bit error rate for various modulation techniques. Numerical results show the effect of fading parameters and pointing errors on the performance of the considered cooperative system.

In this paper, we perform a unified performance analysis of a triple-hop amplify-and-forward (AF) based mixed radio frequency/free space optical/radio frequency (RF/FSO/RF) cooperative communication system, for both types of detection, i.e., heterodyne and intensity modulation/ direct detection (IM/DD). In the considered system, two variable gain AF relays connect the source and the destination using RF links, which are modeled by independent but not identically distributed (i.n.i.d.) Rayleigh fading and the FSO link, which is modeled by path loss, Malaga distributed turbulence, and pointing errors. This triple-hop RF/FSO/RF system can be employed in scenarios where the high-speed FSO link can be used to provide connectivity between two new/existing RF networks, for example, campus connectivity. For the considered system, new mathematical expressions are derived for the end-to-end signal-to-noise ratio (SNR), yielding novel analytical expressions of various performance metrics, i.e., outage probability and average bit error rate for different modulation techniques. Monte Carlo simulation results validates the proposed analysis, which depicts the effect of fading, turbulence, and pointing errors on the performance of the considered cooperative system.

The performance of a free space optical (FSO) communication system is significantly affected by atmospheric turbulence and pointing errors (PEs) apart from the additive noise which is assumed to be Gaussian. The Málaga or M-distribution encompasses various proposed statistical models for atmospheric turbulence in FSO systems. An optical pre-amplifier is an essential component of FSO systems for improving the receiver (Rx) sensitivity. However, optical pre-amplification results in amplified spontaneous emissions (ASE), which dominate the Rx thermal and shot noises. The square law photodetection process at the Rx in a FSO system necessitates the consideration of Chi-square statistics for the decision variable contrary to the Gaussian approximation that is widely used in the literature. In this paper, we evaluate the bit error rate (BER) performance of a FSO system assuming non-return-to-zero on-off keying modulation in the presence of ASE noise under M-turbulence and PEs. We also derive asymptotic BER expressions for the considered FSO system for large values of signal-to-noise ratio in terms of simple elementary functions. A further insight into the system is provided by performing the diversity analysis.

The performance of a free-space optical (FSO) communication system is significantly affected by atmospheric turbulence (AT) and pointing errors (PEs) apart from the additive noise which follows the Gaussian distribution. Optical pre-amplifier is an essential component of FSO systems for improving the receiver sensitivity. However, optical pre-amplification results into amplified spontaneous emissions (ASEs) which dominate the receiver thermal and shot noises. The square law photodetection process at the receiver in a FSO system necessitates the consideration of Chi- square statistics for the decision variable; contrary to the Gaussian approximation that is widely used in literature. In this paper, we evaluate the bit error rate (BER) performance of a FSO system assuming non-return-to-zero on-off keying modulation in the presence of ASE noise under Gamma-Gamma ($\Gamma\Gamma$) AT and PEs. We also derive an expression of asymptotic BER for the considered FSO system for large values of signal-to-noise ratio in terms of simple elementary functions. A further insight into the system is provided by performing the diversity analysis.

In this paper, an underlay based cognitive radio network (CRN) consisting of a secondary base station (SBS), a secondary receiver (SR), an energy harvesting node (EHN), and a primary transmitter-receiver (PT-PR) pair, is considered. The EHN is assumed to have a power splitter (PS) at the receiver to decode information and harvest energy simultaneously from the SBS transmission, thus reducing the secrecy capacity of SBS. Since both the SBS and the malicious EHN are selfish with conflicting interests, we model the interaction between them as a non-cooperative Stackelberg game. The objective of the SBS is to maximize the secrecy rate and minimize its interference at the PR, whereas the EHN aims at maximizing both the energy it can harvest and the information it can decode from the received SBS signal. The existence of a unique equilibrium point is proved through mathematical analysis. Further, a distributed algorithm is proposed, following which the players will attain the equilibrium of the game as predicted by analytical results. Analytical and simulation results demonstrate that both SBS and EHN can achieve their optimal utilities by adopting the equilibrium strategy.

In this paper, the information theoretic analysis of the decode-and-forward based dual hop free space optical (FSO) communication system is performed. The FSO links are modeled by the Gamma-Gamma distributed turbulence, pointing error, and path loss. For the considered cooperative system, using the statistical characteristics of the end-to-end SNR, new closed-form analytical expressions are obtained for the average channel capacity under simultaneous optimal power and rate adaptation (OPRA) and truncated channel inversion with fixed rate (TCIFR) adaptive transmission policies in terms of Extended Bivariate Generalized Meijer-G function. The effect of atmospheric conditions and pointing errors is analyzed by using the average channel capacity expressions. It is observed that the OPRA capacity outperforms the comparatively simpler TCIFR based capacity.

In this paper, we study the performance of cluster based multi-hop underlay cognitive radio networks using an ad-hoc path selection mechanism. Both peak power and peak interference constraints are taken into account. The exact end-to-end outage probability of the considered system employing decode-and-forward relays is derived for Rayleigh fading channels. Also, an approximate expression of the outage probability at high signal-to-noise ratio is derived. For fixed-rate and fixed distance between the source and destination, an expression is derived for the number of hops that minimizes the outage probability. Simulation results are presented to validate the derived analytical expressions.

In this paper, we study the problem of one bit imperfect feedback based diagonal precoding for Alamouti space-time block code in a 2 × 1 multiple-input single-output (MISO) communication system. The communication links are assumed to be Nakagami-m distributed. An accurate bit error rate (BER) expression of the considered MISO system is derived with erroneous feedback by using the order statistics. The average BER of the precoding scheme is minimized to find the optimized transmit weights. Further, we also derive the Shannon capacity of the scheme by using the moment generating function approach. Simulated and analytical results show that a significant capacity gain is achieved by the considered scheme as compared to the uniform power allocation over the Nakagami-m fading channels.

Multi-hop relaying is an important strategy for improved link performance and increasing the range of communication, while the buffers at the relays improve the diversity advantage of the system. In this paper, we investigate the performance of multiple clusters of relays with buffers using max-link relay selection scheme for decode-and-forward cooperative networks. A generalized Markov chain is proposed to model the evolution of buffer status for more than one cluster. Construction of the state diagram for two clusters of relays is discussed as an example. Analytical expressions for the outage probability and the average packet delay are derived. It is shown through numerical results that at moderate to high signal-to-noise ratios, the outage improves with increasing number of clusters. Furthermore, closed-form analytical expressions are obtained for the steady-state probability vector by considering different numbers of clusters and relays. Through examples, we observe that states with the same steady-state probabilities can be grouped. The size of the state transition matrix grows with increasing number of clusters and relays in each cluster. Thus, by exploiting the property of grouping the same state probabilities, we provide an approach to reduce the size of the state transition matrix.

Power line communication (PLC) has recently grabbed the attention of the researchers owing to its huge potential to provide high speed access to video and data. Since power lines were not initially designed for communication purposes, they offer a difficult communication environment in the form of impulsive noise and multiplicative noise, in addition to the background noise. This elucidates the need for evaluating the performance of PLC systems by taking into account all these factors. In this paper, we study the performance of a PLC system in the presence of Rayleigh channel gain under the combined effects of Nakagami-m distributed background noise with non- uniformly distributed phase and Middleton class A distributed impulsive noise. We evaluate closed- form expressions of the analytical average bit error rate for different cases depending on the presence or absence of impulsive noise and channel gain. We provide a further insight into the system by obtaining the diversity of the PLC system. Our analysis is validated by a close matching with the simulation results.

In this study, the authors have analysed the performance of selection relaying at each hop in a decode‐and‐forward (DF)‐based multi‐hop cognitive radio (CR) system deploying cooperative spectrum sensing. The decisions on spectrum availability are taken by a number of sensing CRs (SCRs) at the first level and are sent to a fusion centre (FC) over pre‐existing clusters of relaying CRs (RCRs). The RCRs are being used in a secondary role for relaying the spectrum decision besides sensing their own area primary user. The decision of each SCR is relayed to FC one‐by‐one via number of RCR clusters by selecting a maximum signal‐to‐noise ratio link at each cluster independently. The selected RCR forwards the decision to the next level using DF protocol. The closed‐form expressions for probability of missed detection and false alarm are derived at the FC. An optimal combining rule is devised at the FC. A comparative graphical analysis of power saving in case of multi‐hop transmission to that of single‐hop transmission is also presented. The number of hops for the considered system is optimised based on a trade‐off relation between error rate and transmission delay.

We propose a quantized feedback-based differential signaling scheme for 2 × 1 free space optical (FSO) multiple-input single-output communication systems. The analytical bit error rate (BER) for the proposed differential signaling scheme is derived and compared with the existing differential signaling scheme for FSO systems. The asymptotic BER of the proposed scheme is also determined and it is shown by using the asymptotic BER expression that the proposed scheme achieves full spatial diversity of two. Moreover, the effect of the feedback error on the performance of the proposed scheme is studied and it is demonstrated by simulation-based and analytical results that the proposed scheme significantly outperforms a previously proposed differential signaling scheme in terms of turbulence fades reduction for tolerable feedback errors.

This paper analyzes the performance of a buffer-aided multi-hop relaying system using the max-link relay selection scheme for decode-and-forward cooperative networks. A Markov chain approach is adopted to analyze the state transition matrix that models the evolution of the status of relay buffers. Analytical expressions for the steady-state probability vector are obtained for a three-hop buffer-aided system, and through these expressions, we observe that states with the same probabilities can be clustered, thus reducing the size of the state transition matrix. We propose a state-clustering-based method to obtain the reduced state transition matrix, which is further used to derive an analytical expression for the outage probability with reduced computational complexity. The method is general in the sense that it does not require any prior knowledge about the steady-state probability vector and the state transition matrix. Furthermore, we illustrate, in detail, the construction of the reduced state transition matrix and the related steady-state distribution by an example. An analytical expression for the average packet delay is also derived. Both analytical and simulation results are provided to investigate the performance of buffer-aided multi-hop relaying networks.

In this paper, we analyze a free space optical (FSO) cooperative communication system utilizing the Gamma-Gamma fading optical links and a single decode-and-forward (DF) erroneous relay. We adopt the subcarrier intensity modulation (SIM) technique for transmitting the M-ary phase shift keying (M-PSK) modulated optical data over an FSO link. For the considered DF-FSO cooperative system, we derive an optimum maximum-likelihood (ML) decoder and a sub-optimal piecewise linear (PL) decoder in the destination of the system. The proposed PL decoder performs very close to the ML decoder and provides significantly reduced decoding complexity as compared to the optimal decoder. Both the ML and PL decoders incorporate the possibility of erroneous transmission by the DF relay and require the average statistics of the source-relay link for decoding the data of the source in the destination. We also derive the approximate average symbol error rate (SER) of the proposed PL decoder for M-PSK constellation.

In this paper, we study the equal gain combining (EGC) scheme in free space optical (FSO) multiple-input multiple-output (MIMO) communication systems over the Gamma-Gamma fading channel with pointing errors. The probability density function (PDF) of the Gamma-Gamma fading with pointing errors contains the Meijer-G function, which makes the error analysis of the considered system very difficult (almost undoable). We propose a new power series based representation for the PDF of the Gamma-Gamma fading with pointing errors. The average bit error rate (BER) for the EGC scheme is derived by using the proposed series based expression of the PDF. We also derive the asymptotic BER for the EGC scheme. The effect of pointing errors over the performance of the scheme is analyzed under different scenarios and it is observed that the pointing errors significantly degrade the diversity of the FSO MIMO system; but under strong atmospheric turbulence pointing errors can be neglected.

The information theoretic study of decode-and-forward based mixed radio frequency-free space optical (RF-FSO) cooperative communication system is performed in this paper. The RF link is assumed to be Nakagami-m distributed and the FSO link is modeled by the Gamma-Gamma distributed turbulence, pointing error, and path loss. Novel closed-form analytical expressions of the average channel capacity are derived for the considered asymmetric system under various adaptive transmission policies, i.e., optimal rate adaptation (ORA), simultaneous optimal power and rate adaptation (OPRA), and truncated channel inversion with fixed rate (TCIFR) in terms of Meijer G-function and Extended Bivariate Generalized Meijer-G function. Simulation results validate the proposed analysis. The effect of atmospheric conditions and pointing errors is analyzed by using the average channel capacity expressions. It is observed that the capacity under OPRA scheme outperforms capacity under other schemes.

In this paper, information theoretic analysis of the amplify-and-forward based mixed radio frequency-free space optical (RF-FSO) cooperative communication system is performed. The RF link is assumed to be Nakagami-m distributed and the FSO link is modeled by the Gamma-Gamma distributed turbulence, pointing error, and path loss. Novel finite power series analytical expressions of the average channel capacity are derived for the considered asymmetric system under simultaneous optimal power and rate adaptation (OPRA) and truncated channel inversion with fixed rate (TCIFR) adaptive transmission policies in terms of Extended Bivariate Generalized Meijer-G function. Simulation results validate the proposed analysis. The effect of atmospheric conditions and pointing errors is analyzed by using the average channel capacity expressions. It is observed that the OPRA capacity outperforms TCIFR capacity.

Power line communication (PLC) utilizes power lines for the purpose of electronic data transmission. The performance of a PLC system is significantly affected by the additive and multiplicative power line noises; the additive noises are of two types, namely background noise and impulsive noise. Whereas, the multiplicative PLC noise leads to fading in the received signal strength. In this paper, we evaluate the performance of a PLC system over log-normal fading channel under Nakagami-m distributed additive background noise assuming binary phase shift keying modulation scheme. The analysis involving log-normal fading is very complicated. Hence we use a novel gamma approximation to log-normal distribution for our analysis. We evaluate the probability density function of the decision variable. A closed-form expression of the analytical average bit error rate of the considered system is derived. We also compute the diversity order of the considered PLC system. The validity of the derived analytical expressions is closely verified by the simulation results.

Power line communication (PLC) deals with the transmission of data through the use of power lines. It is an emerging field of communication for the home area network of smart grid. The presence of the additive and multiplicative power line noises significantly affects the performance of PLC systems. There are two types of additive noises in PLC systems, namely background noise and impulsive noise. The multiplicative PLC noise results in fading in the received signal strength. The Rician fading model has been experimentally found to be applicable to the PLC systems and has been widely used in conventional and current literature on PLC. In this paper, we provide the performance analysis of a PLC system over Rician fading channel under Nakagami-m distributed additive background noise assuming binary phase shift keying modulation scheme. We derive the probability density function of the decision variable and the instantaneous signal-to- noise ratio (SNR). A closed-form expression of the outage probability of the considered system is obtained. The validity of the derived analytical expressions is closely verified by the simulated results.

In this paper, we study a beamforming scheme for multiple-input single-output (MISO) free space optical (FSO) system over Gamma-Gamma fading channels. The considered beamforming scheme requires feedback of only one information bit from the receiver about the channel state information. If the feedback bit is always received error free, then the beamforming technique reduces to best transmit aperture selection scheme. It is inferred by bit error rate (BER) analysis in a 2 × 1 FSO system over Gamma-Gamma fading links, that repetition coding is the best of all arbitrary beamforming schemes with non-zero transmit weights. Further, it is also analytically shown that the simple transmit aperture selection scheme (or one bit feedback based beamforming with error free feedback) has a coding gain advantage over repetition coding in 2 × 1 FSO system over Gamma-Gamma fading links. However, it is shown by analysis that the simple transmit aperture selection based beamforming scheme is very sensitive to errors in the feedback bit and loses diversity gain even for very small error in the feedback. Then we establish conditions under which a 2 × 1 FSO system, employing one bit based beamforming with erroneous feedback, achieves full diversity. A simplified asymptotic upperbound of BER of the proposed scheme is obtained by using the order statistics and an optimized beamforming vector is found by minimizing this upperbound. We also analyze the BER performance of a general FSO MISO system that employs equal partitioning of transmit apertures for beamforming, based on one bit feedback. It is shown by simulations that the proposed beamforming scheme

In this paper, we study two-way satellite relaying between two earth stations (ESs) willing to exchange their signals via a satellite. The satellite communication has big problems of propagation delay and fast channel gain fluctuations, due to which it is difficult to generate perfect channel information in ESs for self interference cancellation and decoding of transmitted symbols. Therefore, the usual two-way relaying developed for the terrestrial links is not applicable for the satellite links. In order to avoid the problem of channel estimation, we propose to use differential modulation in both ESs. Then we develop a differential detector of the symbols transmitted by the ESs. The satellite is assumed to be of transparent type. The proposed differential decoder allows for self interference cancellation and detection of the transmitted symbols without any channel information. However, the proposed differential detector requires a relative rotation between the constellations of both ESs for performing satisfactorily. The proposed two-way relaying is useful for the satellite communication systems as it allows the ESs to exchange their data via satellite without any training. The pairwise error probability (PEP) of the proposed scheme is also derived. Based on the PEP, we analytically find the diversity of the considered system.

We consider the two-way relaying of orthogonal space time block codes (OSTBCs) with imperfect channel information. We derive a maximum likelihood (ML) decoder of OSTBC, by assuming perfect channel knowledge at both user nodes. The decoding of OSTBC data at a user terminal is performed by replacing the exact channel state information (CSI) by the estimated CSI, in the ML metric. An approximate closed-form expression for the moment generating function (m.g.f.) of the received signal-to-noise ratio at a user is derived. By using the m.g.f. expression, the analytical average error performance of the scheme is obtained for M-ary phase shift keying constellation. The diversity order of the considered scheme is analytically calculated, for certain system configurations. It is deduced by the simulations and analysis that the channel estimation does not affect the diversity order of the two-way amplify-and-forward multiple-input multiple-output relay system.

In this paper, the performance analysis of the fixed gain amplify-and-forward (AF) based dual-hop asymmetric radio frequency (RF)/free space optical (FSO) communication system is performed. The RF link is assumed to follow the Nakagami-m distribution and the FSO link follows the Gamma-Gamma distribution. For this mixed RF/FSO communication system, new and finite power series based mathematical expressions of cumulative distribution function, probability density function, and moment generating function of the end-to-end signal-to-noise ratio are derived. Using them, novel finite power series based expressions for the outage probability and the average bit error rate are obtained for various modulation techniques. Similar analysis is performed for the scenario when the FSO link undergoes significant pointing errors. Simulation results validate the proposed mathematical analysis.

In this paper, the analytical channel capacity of the decode-and-forward (DF) based dual-hop free space optical (FSO) system is studied. The FSO links are assumed to be asymmetric in nature and the turbulence is considered to follow the Gamma-Gamma distribution. For the considered DF FSO cooperative system, power series based mathematical expressions of the average channel capacity are derived, under the influence of atmospheric turbulence with negligible and significant pointing errors in the FSO links. Simulation results validate the proposed capacity analysis. The effect of channel conditions and pointing errors, on the capacity of DF FSO communication system, is analyzed by using the derived expressions. It is observed that the average capacity of the system, with significant pointing errors, is severely degraded as compared to the average capacity with only atmospheric turbulence; because the pointing errors contribute with the turbulence, in a multiplicative manner.

Power lines render very harsh and hostile environment for electronic data communication. The key characteristics of the power line channel are time varying nature, frequency selective attenuation and presence of impulsive noise because of random switching of power appliances. The impulsive nature of the additive noise has been ignored so far in the literature for resource allocation in power line communication system because this assumption results in intractable solutions. In this study, an approach of efficient resource allocation is introduced in order to maximise the throughput and achieve tolerable bit error rate of the power line system, by adapting power transmitted in each cycle, under additive Middleton class A impulsive noise (MCAIN). The proposed resource allocation technique utilises sub‐channel ordering to obtain a higher throughput; and provides improvement as compared to the existing zero forcing based resource allocation technique under additive MCAIN.

In this paper, we consider relay selection based decode-and-forward (DF) cooperative communication over free space optical (FSO) links. A relay selection scheme is considered in which source selects a relay on the basis of highest instantaneous signal-to-noise ratio (SNR) of the source-relay links. We derive the cumulative distribution function (CDF) and probability density function (PDF) of the highest instantaneous SNR of Gamma-Gamma distributed source-relay links. The average error performance of the DF protocol with relay selection over the Gamma-Gamma fading channels is derived in terms of power series. Coding gain and diversity order of the relay selection based DF scheme are analytically obtained. It is inferred by the analysis and simulation that the performance of the DF FSO system can be significantly improved by using the simple relay selection scheme considered in this paper.

In the existing literature, a single sample based improved energy detector has been analyzed for multiple antennas based cooperative spectrum sensing. In this paper, we derive the expressions of the probability of false alarm and missed detection of multiple antenna based dual-hop cooperative spectrum sensing scheme which uses multiple samples of the primary user's signal in the improved energy detector. By minimizing the total error rate (weighted sum of the probability of missed detection and probability of false alarm), we derive a closed-form solution of optimal number of CRs required for dual-hop cooperation. It is shown by simulations that this generalized scheme significantly outperforms the conventional energy detector based spectrum sensing, while keeping quality-of-service in desired limits. A multi-hop cognitive radio network containing multiple antenna based CRs and using an improved energy detector with multiple samples is also analyzed in this paper. It is inferred by analysis and simulation that the error performance of the multi-hop cognitive relaying can be significantly improved by using multiple antennas and improved energy detector.

In a demodulate-and-forward (DF) based cooperative communication system, erroneous relaying of the data leads to degradation in the performance of the destination receiver. However, a maximum likelihood (ML) decoder in the destination can improve the receiver performance. For achieving a diversity gain, the Alamouti space-time block code (STBC) can be used in the DF based cooperative system in a distributed manner. In this paper, we derive an ML decoder of the distributed Alamouti STBC for the DF based cooperative system with two imperfect relaying nodes. We also consider a DF cooperative communication system in which one out of two relays is in outage. A piece-wise linear (PL) decoder for the DF cooperative system with the distributed Alamouti code and one relay in outage is proposed. The PL decoder provides approximately the same performance as that of the ML decoder with reduced decoding complexity. We derive the pairwise error probability (PEP) of the proposed ML decoder with binary phase-shift keying constellation. An optimized transmit power allocation for the relays is performed by minimizing an upper bound of the PEP. It is shown by simulations that the proposed ML decoder enables the DF protocol based cooperative system to outperform the same rate amplify-and-forward protocol based cooperative system when both systems utilize the distributed Alamouti STBC.

We derive a maximum likelihood (ML) decoder in the differential decode-and-forward (DF) based cooperative communication system utilizing complex-valued unitary constellations like M-PSK. We also derive a low complexity piecewise linear (PL) decoder of the differential data transmitted in the DF based cooperative system. The proposed ML and PL decoders are applicable to the complex-valued unitary constellations suitable for differential modulation, whereas, the existing ML and PL decoders of the differentially modulated data in the DF based cooperative communication system are only applicable to binary modulated signals like binary phase shift keying (BPSK) and binary frequency shift keying (BFSK). An approximate average symbol error rate (SER) of the proposed PL decoder is also obtained by ignoring the higher order noise terms. Based on this approximate SER, it is analytically shown that the proposed PL decoder provides full diversity of second order in the DF based differential cooperative system with one source-destination pair and a single relay.

In this paper, we derive a maximum-likelihood (ML) decoder for the demodulate-and-forward (DF) based cooperative communication system using Alamouti space-time block code (STBC) in a distributed manner. We also propose a sub-optimal low complexity piece-wise linear (PL) decoder of the distributed Alamouti code in a DF cooperative system in which one relay out of two relays is in outage. The proposed PL decoder does not lead to any significant performance degradation and performs very close to the proposed ML decoder. Moreover, the proposed ML decoder of the DF cooperative system significantly outperforms an amplify-and-forward (AF) based cooperative system when both systems use the same data rate and distributed Alamouti STBC.

In this paper, we explain how to implement differential modulation in multiple access channel (MAC) based uplink two-user multiple-input multiple-output (MIMO) communication system. It is assumed that the users cannot exchange their information and transmit data over uplink MAC channels simultaneously in the same frequency band and without any orthogonal signatures (no CDMA). We derive two types of differential decoders for two-user MIMO MAC system namely 1) Partial differential decoder, 2) Heuristic based differential decoders. The partial differential decoder is able to avoid the knowledge of the channel gains of one user at the receiver for joint decoding of the data of both users. Whereas, the heuristic differential decoders are obtained heuristically and work without any channel knowledge of both users. For the heuristic differential decoder to work properly, the data of one user must be rotated before transmission. An upper bound of the pairwise error probability (PEP) is derived for the proposed scheme. The upper bound of the PEP is minimized for obtaining an optimized value of the rotation angle.

In this paper, we derive a maximum-likelihood (ML) decoder of the decode-and-forward (DF) protocol utilizing an arbitrary complex-valued M-point constellation. Existing decoders of the DF based cooperative systems are applicable only to real-valued constellations like BPSK and M-PAM, hence, also to square M2-QAM. We have considered a DF based cooperative system with a single source-destination pair and one relay. The ML decoder is obtained by maximizing the probability density function (p.d.f.) of the received signal at the destination. The proposed ML decoder provides lower decoding complexity than an existing decoder. We also propose an approximate piecewise linear (PL) decoder for M-PSK constellation which performs similar to the proposed ML decoder. The proposed PL decoder provides significant lower decoding complexity than the proposed ML decoder. We analytically derive the approximate symbol error rate of the proposed PL decoder. The DF based cooperative system with the proposed ML and PL decoders outperforms the same rate amplify-and-forward based cooperative communication system from moderate to high signal-to-noise ratio values.

Optimization of cooperative spectrum sensing with an improved energy detector in each cognitive radio (CR)over imperfect reporting channels is discussed in this paper. The improved energy detector compares an arbitrary positive power p of the amplitude of the received samples of the signals of a primary user (PU)with a threshold to make a decision. The binary decision of each CR is forwarded over an imperfect reporting channel to a fusion center which makes a final decision on the presence of the PU. We obtain an expression of the total error rate of detection of a spectrum hole for this cooperative set-up. The optimized values of the normalized threshold and p in each CR and optimal number of CRs required for the decision are obtained by minimizing the total error rate. It is shown by simulations that the proposed scheme significantly outperforms an existing scheme using the conventional energy detector.

Decode-and-forward (DF) protocol based cooperative communication is vulnerable to the erroneous relaying by the relay. In this paper, we derive a maximum-likelihood (ML) decoder for the DF protocol utilizing arbitrary complex-valued constellations including M-PSK, M-PAM, and M-QAM. A set-up of a single pair of source and destination with one relay is studied. The source and the relay utilize orthogonal uncoded transmissions. The relay performs ML decoding and forwards the decoded symbol to the destination, and it might commit errors in decoding the data. The ML decoder at the destination is obtained by maximizing the probability density function (p.d.f.) of the data received during two orthogonal transmissions at the destination under the assumption that the average probability of error of the source-relay link is known at the destination. The proposed ML decoder is a generalized decoder which is applicable to arbitrary constellations, whereas, one existing DF cooperative decoder is applicable to the real valued constellations like BPSK and M-PAM. One existing decoder is also applicable to M2-QAM constellations. We also derive a low-complexity piecewise linear (PL) decoder for arbitrary complex-valued M-point constellations which performs similar to the ML decoder for all signal-to-noise ratio values. An approximate expression of the symbol error rate (SER) of the PL decoder for M-PSK constellation is derived. By using the approximate SER expressions, it is proved that the proposed ML and PL decoders achieve full diversity of two in the cooperative system studied.

In this paper, we propose a maximum likelihood (ML) decoder for differentially encoded orthogonal spacetime block codes (OSTBCs) based on multiple received data blocks. The proposed ML decoder differs from the existing ML decoders of differential OSTBC as follows: 1) Most existing ML decoders are derived on the basis of two consecutively received data matrices, whereas the proposed decoder takes multiple consecutively received data matrices into account. 2) One existing ML decoder considers multiple consecutively received specific differential OSTBC using two transmit antennas and is applicable to M-PSK constellation only, whereas the proposed ML decoder works with arbitrary differential OSTBCs using arbitrary number of transmit and receive antennas and arbitrary constellations which do not include zero. We have also derived an upper bound of the pairwise error probability (PEP) of the proposed ML decoder for differentially encoded orthogonal STBC (OSTBC) with M-QAM constellation over Rayleigh fading channels.

We derive a decoder for differential data of two multiple access channel (MAC) based uplink users. Both users utilize differential modulation for transmitting their data. It is assumed that the users cannot exchange their information. In addition, it is assumed that the users transmit data over multiple access uplink channels simultaneously in the same frequency band and without any orthogonal signatures (no CDMA). Their transmissions are assumed to be perfectly synchronized in time, phase, and frequency. The decoder is obtained by maximizing the joint probability distribution function (p.d.f.) of consecutively received data samples. We first obtain a partially differential decoder which avoids the knowledge of channel of one user at the base-station. Then we derive a heuristic differential decoder which completely avoids the knowledge of the channels of both users. For the heuristic differential decoder to work properly, both users must use rotated constellations. Optimized values of rotation angles for different M-PSK constellations are numerically obtained. It is further shown by simulations that the proposed differential decoders perform better than a same rate existing TDMA based two-user transmission scheme.

A linear precoder is designed to minimize an upper bound of the pairwise error probability (PEP) when using arbitrary space-time block codes (STBC) over correlated Ricean fading channels. The proposed precoder design differs from the previously proposed precoders as follows: 1) Existing precoders are applicable when there exists only transmit correlation and no receive correlations, however, the proposed precoder is applicable to correlated Ricean MIMO channels with an invertible correlation matrix. 2) We minimize the upper bound of the PEP of non-orthogonal STBC for obtaining a precoder over correlated Ricean channels, whereas, one existing precoder minimizes an upper bound of PEP for orthogonal STBC (OSTBC). The proposed precoder outperforms two existing precoders for non-orthogonal STBC especially for highly correlated channels.

In this paper, we propose a TDMA based simple transmission scheme, which overcomes the effect of the delays caused by the poor synchronization of the relaying nodes over Ricean channels. The proposed scheme is able to provide an optimized coding gain in unsynchronized cooperative networks as compared to the existing delay tolerant distributed space-time block codes.

The presence of carrier offsets in the multiple-input multiple-output (MIMO) channels is an important practical and theoretical problem. Double-differential coding is a technique which allows the receiver to decode the data without any channel or carrier offset knowledge. We propose a double-differential (DD) coding scheme which is applicable to square orthogonal space-time block codes (OSTBC) using M-PSK constellation. The main advantages of our proposed DD coding scheme are: 1) The previously proposed DD codes are applicable only to the specific class of space-time block codes which follow the diagonal unitary group property, whereas our DD coding is applicable to any square OSTBC. 2) We propose a suboptimal decoder which preserves the linear decoding property of the OSTBC. 3) A theoretical analysis is performed to find a pairwise error probability (PEP) upper bound of the proposed double-differential orthogonal space-time block codes (DDOSTBC). 4) In order to improve the performance of DDOSTBC over the arbitrarily correlated Rayleigh channels we propose a precoder which minimizes an upper bound of the PEP. The proposed DDOSTBC are able to achieve higher coding gain than the similar rate existing DD coding scheme. In addition, the proposed precoded DDOSTBC achieves performance gain for correlated channels as compared to the unprecoded DDOSTBC.

In this paper, we study how to improve the performance of a decode-and-forward protocol based cooperative system over the delay constrained channels. We propose a simple transmission scheme, which makes the cooperative system tolerant of the delays caused by the poor synchronization of the relaying nodes. The proposed scheme is able to provide an improved coding gain in unsynchronized cooperative network as compared to the existing delay tolerant distributed space-time block codes.

We consider the performance of orthogonal and non-orthogonal space-time block codes (STBCs) over arbitrarily correlated Rayleigh fading multiple-input multiple-output (MIMO) channels. A pairwise error probability (PEP) bound of arbitrary STBC is derived. Based on this PEP bound, we design a precoder to improve the performance of the orthogonal and non-orthogonal STBC over arbitrarily correlated channels.

This paper considers multihop wireless networks that are used for multicast traffic i.e., networks in which subsets of users are interested in identical information such as a video clipping. We calculate an upper bound on the achievable throughput per multicast flow as a function of the number of sources, number of destinations per source, number of interfaces per node, and the number of channels available. Then we propose a methodology that achieves the upper bound in an order sense under certain circumstances. We study the impact of the ratio of the number of channels to number of interfaces per node on the multicast capacity region of wireless networks.

Joint transmitter and receiver design problem for frequency-selective, time-invariant fading channels are studied. The authors first propose a simple approximate maximum likelihood serial decision-feedback equaliser (A-ML-SDFE) through DFE, a Gaussian approximation, a pre-whitening filter and a matched filter. Secondly, assuming full channel knowledge available at the transmitter side, the authors perform pre-equalisation in a downlink scenario by moving the decision-feedback part of the A-ML-SDFE to the transmitter. The proposed A-ML-SDFE achieves much better performance than linear minimum mean square error (MMSE) and MMSE-DFE with a lower complexity. The pre-equaliser further improves the system performance at low signal-to-noise ratio with a reduced receiver complexity.

In this paper, we propose a maximum likelihood (ML) decoder for differentially encoded full-rank square nonorthogonal space-time block codes (STBCs) using unitary or non-unitary signal constellations, which is also applicable to full-ranked orthogonal STBC (OSTBC). As the receiver is jointly optimized with respect to the channel and the unknown data, it does not require any knowledge of channel power, signal power, or noise power to decode the signal, and the decision is purely based on two consecutively received data blocks. We analyze the effect of channel correlation on the performance of the proposed system in Rayleigh fading channels. Assuming a general correlation model, an upper bound of the pair-wise error probability (PEP) of the differential OSTBCs is derived. An approximate bound of the PEP for the differential nonorthogonal STBCs is also derived. We propose a precoder designing criterion for differential STBC over arbitrarily correlated Rayleigh channels. Precoding improves the system performance over the correlated Rayleigh MIMO channels. Our precoded differential codes differ from the previously proposed precoder designs for differential OSTBC in the following ways: 1) We propose a precoder design for arbitrarily correlated Rayleigh channels, whereas the previous work considers only for transmit correlation. 2) The previous work is only applicable to the OSTBCs with PSK constellations, whereas our precoder is applicable to any type of full-rank square STBCs with unitary and non-unitary signal constellations.

In this paper, distributed double-differential coding is proposed to avoid the problem of carrier offsets in amplify and forward protocol based cooperative network with two relays. A double-differential orthogonal-space-time block code is transmitted by the relays in a distributed manner without channel knowledge. We derive a low complexity linear decoder which does not require the channel and carrier offset knowledge. A pairwise error probability (PEP) analysis is also conducted and we found an upper bound of the PEP for the proposed system. In addition, an optimized power allocation is proposed to improve the SER performance of the system.

Communications over multiple-input multiple-output (MIMO) channels with carrier offsets is an important practical and theoretical problem. Double-differential coding is a technique, which allows the receiver to decode the data without any channel or carrier offset knowledge. We propose a double-differential (DD) coding scheme which is applicable to any square orthogonal space-time block codes (OSTBC) using M-PSK constellation. The main advantages of the proposed DD coding scheme are: 1) The previously proposed DD codes are applicable only to the specific class of space-time block codes which follow the diagonal unitary group property, whereas our DD coding is applicable to any square OSTBC. 2) We propose a suboptimal decoder which preserves the linear decoding property of the OSTBC. We derive an upper bound of the pairwise error probability (PEP) of the proposed double-differential orthogonal space-time block codes (DDOSTBCs). The proposed DDOSTBC is able to achieve better performance than the similar rate existing DD coding scheme. In addition, the proposed DDOSTBC outperforms the conventional training based system.

In this paper, we consider the joint transmitter and receiver design problem based on a novel approximate maximum likelihood decision feedback equalizer (A-ML-DFE) over frequency-selective, time- invariant fading channels. By applying decision feedback equalization, Gaussian approximation, a pre-whitening filter, and a matched filter, the proposed A-ML-DFE can realize single symbol detection. The proposed scheme achieves near-optimal performance with a complexity lower than the linear MMSE and the MMSE-DFE. By assuming full channel knowledge, we perform pre-equalization and precoding in a downlink scenario at the transmitter side. The pre-equalizer can achieve perfect decision feedback and thus, provide better performance at low signal- to-noise ratio (SNR) with a reduced receiver complexity. The precoder designed to minimize the analytical symbol error rate (SER) of this system can further improve the performance.

In this paper, we consider the effect of carrier offsets in arbitrarily correlated flat-fading multiple-input multiple-output (MIMO) Rayleigh channels. We propose a double-differential coding for square orthogonal space-time block code (OSTBC) with non-unitary constellations over flat-fading MIMO channels with carrier offsets. In order to improve the performance of the proposed double-differential orthogonal space-time block code (DDOSTBC) over arbitrarily correlated Rayleigh channel we introduce a full memoryless precoder matrix in the transmitter. For the proposed precoded DDOSTBC, a pair-wise error performance (PEP) analysis is conducted. Then we propose a precoder design based on the PEP upper bound. The proposed DDOSTBC differs from the previously proposed DDOSTBC by: 1) The previously proposed DDOSTBC is aplicable to only a specific class of OSTBC which follows diagonal group property, whereas, the proposed DDOSTBC is applicable to any square OSTBC. 2) The previously proposed DDOSTBC can work withM-PSK constelation only, whereas, the proposed DDOSTBC is applicable toM-QAM,M-PAM, orM-PSK constellations. The proposed DDOSTBC provides higher performance gain as compared to the same rate previously proposed DDOSTBC. In addition, the proposed precoded DDOSTBC is able to perform better than the unprecoded DDOSTBC over arbitrarily correlated Rayleigh channels.

In this paper, we propose a novel and simple approximate maximum likelihood detector (A-ML-D) for single input and single output (SISO) systems over frequency-selective fading channels based on Tomlinson-Harashima pre-equalizer. By assuming full channel state information (CSI) at the transmitter side, the pre-equalizer can remove some inter-symbol interference (ISI) at the transmitter. At the receiver, we implement a Gaussian approximation, a pre-whitening filter and a matched filter to realize a set of parallel SISO schemes, and thus, facilitate single symbol detection. The proposed scheme can obtain full multi-path diversity and achieve near-optimal performance with a complexity lower than linear MMSE and MMSE-DFE. Analytical symbol error rate (SER) is derived to further justify the proposed detector.

In this paper, we propose double-differential (DD) modulation for an amplify-and-forward protocol based on cooperative communication over Nakagami-m fading channels. The proposed scheme is able to achieve performance gain in the presence of random carrier offsets and without channel knowledge at relay or destination. The proposed scheme reflects its utility for the Nakagami-m type flat fading channels with carrier offsets, where the conventional single differential scheme breaks down. In addition, the proposed scheme outperforms the conventional direct transmission double-differential system.

We present symbol error rate (SER) expressions for the double differential (DD) modulation with MPSK constellations (DDMPSK) over AWGN, Rayleigh, and Ricean fading channels with carrier offsets in a single-input single-output (SISO) system. A closed-form expression is derived for SER in double differential binary phase shift keying (DDBPSK) over AWGN channels with carrier offset. Next, we derive a closed-form solution for the SER of DDBPSK and lower and upper bounds over the SER for DDMPSK signals over Rayleigh fading channels with carrier offset. A closed-form SER formulation for DDBPSK over Ricean fading channel with carrier offset is also presented.