Integrating unmanned aerial vehicles (UAV) with reconfigurable intelligent surfaces (RIS) can provide ubiquitous deployment services in areas with limited communication infrastructure, especially for the Internet of Things and wireless sensor network applications. However, the onboard energy capacity of the UAVs and the sensor module in IoT/WSN networks poses a significant limitation on the system performance. This paper introduces a comprehensive theoretical model to evaluate the performance of a combined RIS-UAV system, equipped with energy harvesting capabilities for a ground-to-UAV uplink communication system. The proposed system consists of a wireless device (WD), a single antenna power station (PS), and a RIS-fitted UAV that functions as a data collector for the WD. For the underlying system, we assume that both UAV and the WD, are energy-limited, hence both devices first harvest energy from the radio-frequency signal supplied by PS, before data transfer/data collection operations. A unified mathematical expression is developed concerning outage probability , effective throughput, and average bit error rate performance over a generalized κ -μ shadowed fading channels. In addition, we also present an asymptotic analysis under a high signal-to-noise ratio assumption to gain a better understanding of the system behavior. The analytical simulation results reveal that RIS-enabled UAV wireless communication significantly enhances the overall system performance compared to conventional UAV-only data collection networks.

In the recent times, the demand for better spectral efficiency and lower power consumption has increased significantly. As a result, effective methods for reducing the peak-to-average power ratio (PAPR) are crucial. Orthogonal frequency division multiplexing (OFDM) is a fundamental technology in 5G and Beyond 5G (B5G) systems. To enhance its performance, implementing an efficient PAPR reduction technique is necessary. Based upon these grounds, this paper introduces a novel PAPR reduction method that integrates Schur decomposition with Walsh-Hadamard Transform (WHT) and Constant Amplitude Zero Auto-Correlation (CAZAC) transform in a precoded OFDM system. The mathematical expression of the time-domain signal for the proposed Schur-based WHT+CAZAC-OFDM system is derived. The simulation results of this work unveil that the proposed SCHUR+WHT+CAZAC-based OFDM system significantly minimizes PAPR by exhibiting a remarkable PAPR reduction of 8.736 dB and 9.86 dB compared to conventional OFDM over AWGN and Rayleigh Fading channels. In addition, the proposed system enhances spectral containment, and reduces spectral regrowth with substantial improvement in power spectral density (PSD) performance. A comparative analysis with singular value decomposition (SVD) and QR decomposition-based approaches is also performed. The results indicate that all three techniques effectively reduce PAPR. However, the SCHUR+WHT+CAZAC method achieves a better balance between computational complexity and overall performance. These advancements make it highly suitable for various B5G applications, including ultra-reliable low-latency communications (URLLC), massive machine-type communications (mMTC), and enhanced mobile broadband (eMBB), where high data rates, low latency, and reliable connectivity are crucial.

A single-intelligent reflecting surface (IRS) assisted communication system is one of the potential solutions to address blockage issues by creating a virtual line-of-sight (LOS) link between the transmitter and the receiver. In this work, to address the limited coverage angle posed by single-IRS, a multi-antenna multi-IRS supported system model is considered under a generalized alpha - mu wireless fading channel. Deriving the statistical information of the equivalent signal-to-noise ratio (SNR), the theoretical expressions of bit error rate (BER), Ergodic capacity (EC), and outage probability were derived, which cover Rayleigh, Nakagami-m, and exponential distributions as corner cases. Extensive Monte Carlo (MC) simulations demonstrate the validity of all the analytical expressions. The investigation focused on examining the impact of individual parameters such as fading parameters, the number of IRSs, the number of reflecting elements, the number of antennas at the transmitter, and the position of the IRSs. A thorough comparative analysis reveals the fact that the multiple antenna multiple IRS system outperforms in all the performance metrics under consideration, with respect to the single IRS single-input single-output (SISO) system. Furthermore, we present an energy efficiency (EE) and energy consumption gain assessment for the multi-IRS system.

Future wireless communication technologies must be upgraded to serve the upcoming seamless data-intensive applications and support a minimum information rate. To this end, an intelligent reflecting surface (IRS) technology was recently proposed as a viable solution to cover the uncovered regions with enhanced performance by means of a controlled wireless environment using multiple reflecting elements. In this paper, to elevate the end-user experience, we intend to improve the outage probability (OP) perforntance utilizing multiple IRS for multiple-input-multiple-output (MIMO) communication systems under a generalized -u fading channel, which is suitable for non-line-of-sight (NLS) scenarios. We derived a closed form expression for OR and validated the same using a rigorous Monte-Carlo (MC) simulation setup under the considered system model. A comprehensive analysis of each system parameter impacting the likelihood that the communication channel supports the information rate has been detailed based on the number of IRSs, the number of reflecting elements, antenna count & aring;t transmitter and receiver, fading parameters, and the placement of IRSs. Results suggest that employing multiple IRSs redutes the outage scenarios in blockage zones, and further improvement can be observed with multiple antennas positioning the IRSs closer to either the transmitter or the receiver. Furthermore, we present an energy efficiency (EE) assessment for the multi-IRS system

Visible Light Communication (VLC) has emerged as a promising alternative for indoor and vehicular wireless communication, offering several advantages over traditional radio frequency (RF) technology. With the adoption of optical-orthogonal frequency division multiplexing (O-OFDM) schemes, visible light communication (VLC) has become more robust and adaptable in indoor, outdoor, vehicular, and underwear communications. Recently, an orthogonal time frequency space (OTFS) modulation technique has evolved with better performance than OFDM. The recent finding in the context of VLC shows that the OTFS technique shows remarkable advantages over conventional OFDM techniques except for the modem design complexity. This work introduces a low-complexity direct current-biased optical OTFS (DCO-OTFS) modulation based on OFDM. This paper evaluates the proposed system’s performance through simulations, providing evidence of its bit-error-rate (BER), peak-to-average power ratio (PAPR), and complexity behavior. Comparative assessments against the DCO-OFDM system are presented to understand the advantages of the low-complex DCO-OTFS system. The findings reveal that the proposed system not only provides low computational complexity in modem design but also maintains superior error performance, with a notable 10 dB signal-to-noise ratio (SNR) gain over DCO-OFDM along with a superior PAPR, making it a commendable choice for VLC applications.

The generalized frequency division multiplexing (GFDM) system has attracted the interest of the research community due to its unique characteristics such as high spectrum efficiency, low latency, and high transmission rate. However, like every multicarrier technique superimposition of a number of subsymbols in the time domain results in a high peak-to-average power ratio (PAPR). In general, the PAPR reduction system in the literature increases the average power while decreasing the PAPR which is not a plausible solution for practical 5G applications. In order to address this issue, we propose an efficient PAPR reduction strategy that maintains the PAPR without increasing the average power. In this method, an optimal orthogonal precoding matrix based on singular value decomposition (SVD) is designed to reduce the system’s average power. Because this optimal precoding matrix cannot successfully reduce the PAPR, we introduce a second technique called peak samples affixing to minimize both the peak and average power. For the proposed method’s assessment, using LabVIEW software and the universal software radio peripheral 2953R (USRP) as hardware, we developed an experimental setup to enable real-time transmission. The received spectral response from USRP authenticated the proposed method by showing a good agreement with simulations.

Objective: The revolution of the solid-state lighting technology and the looming radio frequency (RF) spectrum crisis enabled the rapid evolution of visible light communication (VLC) in the recent times. To furnish contemporaneous illumination and communication, VLC relies on white light emitting diodes (WLEDs). However, the limited modulation bandwidth of WLEDs poses a threat to VLC as the achievable data rates are drastically minimized. Eventually, to enhance the achievable throughput, the pre-eminent way is to apply orthogonal frequency division multiplexing (OFDM) to a VLC system. Furthermore, a VLC system can also exploit non-orthogonal multiple access (NOMA) scheme to bestow with seamless services to the multiple users. However, much similar to the RF-based OFDM system, the OFDM-VLC system also inherits one of the serious disadvantages like the high peak to average power ratio (PAPR). In addition, the rapid fluctuations of the continuous time-domain signal amplitude in DC-biased optical OFDM (DCO-OFDM) results in much complicated design of the LED driver circuitry for driving the LED. Thus, to overcome such drawbacks, we incorporate delta-sigma modulators (DSM) to the NOMA-VLC system which is making use of DCO-OFDM, and we analyze its performance over VLC channel environment. The stunning advantage imparted by the proposed DSM-based DCO-OFDM-NOMA-VLC system is that the continuous amplitude of the time-domain transmitted signal is converted into two levels for driving the LED. Additionally, with the major goal to maximize the sum throughput of the proposed multiuser VLC system by taking into consideration both the user fairness as well as the intensity constraints, we derived the optimal values for the power allocation coefficients corresponding to the fair power allocation algorithm. Furthermore, the dynamically varying fair power allocation algorithm is compared with the fixed/static power allocation algorithm. Achieved Results: The major contribution of this work is of two-fold: firstly, the proposed DCO-OFDM-NOMAVLC system which is making use of DSM exhibits a remarkable reduction in PAPR when compared with the conventional system without the application of DSM, where the proposed system demonstrates a significant gain of 4.78 dB in terms of PAPR reduction. Secondly, from the simulated results it can affirmed that the proposed system not only achieves enhanced sum rates and better outage performance but also imparts a better bit error ratio (BER) performance corresponding to the far user.

Asymmetrically clipped direct current (DC) biased optical orthogonal frequency division multiplexing (ADO-OFDM) is a recently emerged waveform in the visible light communication (VLC) to obtain the optimal solution for the spectral and power efficiency problems. However, in ADO-OFDM, high DC-bias is used to attain unipolar signals, which decreases the power efficiency. In this work, we conceive a novel modulation technique called variably biased asymmetrically clipped optical orthogonal frequency division multiplexing (VAO-OFDM) for VLC systems. In which the bias varies with respect to the amplitude of the specific samples, which results in power efficiency. Further, the performance of the VAO-OFDM system is evaluated using LabView software-based simulations and validated on the experimental setup by the VLC testbed using USRP hardware.

Intelligent Reflecting Surface (IRS) has gained a lot of attention for 6G communication systems due to low-cost reconfigurable meta-materials which can smartly control the wireless propagation channel like never before. In this work, we considered a non-line of sight (NLOS) between the base station and the user. We used the moment generating function (MGF) approach to derive the precise closed-form expression of the probability of bit error rate (BER), and an IRS is used to help create a virtual line of sight (LOS). The wireless channel between the base station-IRS and IRS user is considered to be the log-normal fading channel. The Monte-Carlo (MC) simulated results match the derived theoretical expression. We have investigated the system model under various parameters, namely, the number of reflecting elements, and the log-normal fading parameter. Our analysis suggests that the impact of log-normal fading can be minimized by increasing the number of reflecting elements. In addition, BER is also sensitive to the fading parameter.

Orthogonal Time Frequency Space modulation (OTFS) has evolved as an astounding modulation technique for high-speed communication in a doubly dispersive channel. In any wireless communication system, channel estimation and equalization are essential at the receiver to recover the transmitted data. To accomplish this for the emerging OTFS based systems, a modified embedded pilot-based channel estimation technique and low complexity feedback equalization algorithm for integer Doppler shifts in the delay-Doppler domain are proposed in this paper. Our channel estimation scheme exploits embedded-pilot arrangement, and the symbol equalization relies on the Interference calculation and its mitigation iteratively. To achieve this we contemplate a prudent arrangement of symbols in the OTFS frame in such a way that the Guard symbols prevent the interference between data symbols and the pilot symbol at the receiver. Two distinct lumps of received data of the same OTFS frame will be engaged in channel estimation and data detection. An analytical expression of the theoretical Cramer Rao Lower Bound (CRLB) is derived and plotted for the proposed channel estimation scheme. The attained simulation results for Bit-Error-Rate (BER) under the proposed scheme show a significant error rate improvement over the Minimum Mean Squared Error (MMSE) equalization algorithm. Further, a lower computational complexity is also achieved in comparison with modified MMSE detection and MP detection algorithms.

Orthogonal Time Frequency Space modulation (OTFS) is a promising modulation technique expected to counter the severe Doppler effects encountered in a doubly dispersive channel. OTFS scheme is developed on the basis of Orthogonal Frequency Division Multiplexing (OFDM) systems to support communication between high-speed vehicles, whose superiority lies in the domain of the equivalent channel. OTFS converts the Time-Frequency (TF) domain channel in the OFDM system to Delay-Doppler (DD) domain channel that becomes a handy tool to overcome the difficulties faced in a frequency selective channel. This letter presents an OTFS system design that is developed on the Discrete Fractional Fourier Transform (DFrFT) based OFDM system, which is designed to perform better compared to the conventional OTFS system with the same design complexity. The simulation results evidentially show 1 dB gain in power at a Bit-Error-Rate (BER) of 10−5 and a significant 3 dB decrement in the PAPR when a high power pilot with a 25 dB is inserted in the OTFS data frame.

Visible Light Communication (VLC) exploits the renowned modulation scheme like orthogonal frequency division multiplexing (OFDM) to accomplish high data rate transmission. However, the optical OFDM system like DC biased optical OFDM (DCO-OFDM) is vulnerable to high peak to average power ratio (PAPR) which results in detrimental clipping distortion which in turn degrades the overall system performance. The limited dynamic range of the LEDs further agitates this issue. On these grounds, PAPR reduction techniques like precoding matrix schemes have been proposed for reducing the high amount of PAPR in DCO-OFDM system. In this paper, discrete Hartley Matrix transform (DHMT) precoded discrete Hartley transform (DHT)-based DCO-OFDM system is proposed for reducing PAPR. In addition, we comparatively investigate the PAPR performance of a new precoding technique like T-transform which is a hybrid combination of Walsh Hadamard transform (WHT) and Zadoff chu transform (ZCT) with other precoding matrix techniques like discrete cosine matrix transform (DCMT), discrete Fourier matrix transform (DFMT), Walsh Hadamard Matrix transform (WHMT) and DHMT. Furthermore, this paper derives the mathematical analysis corresponding to the time-domain signal formats for the precoded DCO-OFDM system which is exploiting complex Fourier signal processing and real trigonometric transform like DHT. From the simulated results, it can be surmised that when compared with other precoding techniques, DHMT precoded DHT-based DCO-OFDM system not only achieves a significant reduction in PAPR but also achieves a better bit error rate (BER) and spectral efficiency performance. Furthermore, less computational complexity is required to implement it.

Generalized frequency division multiplexing (GFDM) is a flexible radio waveform which offers high degree of freedom in varying the number of time slots, number of subcarriers, and pulse shaping filters. In addition to this, it also covers orthogonal frequency division multiplexing (OFDM) and single carrier frequency domain equalization (SC-FDE) as corner cases. A well-known fact is that the performance of a wireless communication system is predominately effected by the characteristics of the fading environment. In this paper, symbol error rate (SER) closed-form expression of GFDM system under the generalized η−μ fading channel is derived. The proposed derivation includes Rayleigh, Nakagami-m, and Nakagami-q fading channels as special cases. A Mote-Carlo simulation test-bed is carried out using MATLAB to compare with analytical results and to validate the derived expressions based on the probability density function (PDF) approach. Further, this paper investigates the performance of the GFDM system by varying various parameters such as fading values, pulse shaping filters, roll-off factor, and modulation order. The detailed analysis suggests that the probability of SER is highly dependent on the above parameters. The results obtained are more useful in evaluating the performance of GFDM based communication system in a generalized manner.

To recent trends, Reconfigurable Intelligent Surfaces (RIS) has gained much attention, which is anticipated to serve the next generation wireless communication system due to enhanced reliability using intelligent low cost surfaces. It is desired to assess this technology under various channel models. In this work we assume a non-line-of-sight (NLOS) path between the base station and the user. We derived the probability of symbol error rate (SER) analysis of RIS-assisted wireless communication system over the Nakagami-m fading channel considering M−ary phase shift keying (MPSK) signalling using a simple moment generating function (MGF)-based approach. To validate the simulated results carried out in MATLAB, theoretical expressions are also derived. In addition, the impact of different parameters, namely, fading parameter value, number of reflecting elements and M−ary signaling on the performance of the RIS-assisted Nakagami-m faded communication system is also investigated. A detailed analysis suggests that the probability of SER highly depends on the above parameters.

The extensive enhancement of wireless communication industry over the last decade revolutionized the change of our daily life. In this scenario, it becomes utmost difficult for the network providers to cater the needs of the end users. Consequently, this mandates the necessity to rely on alternative communication-based technologies. Therefore, one such communication is visible light communication (VLC) which is regarded as a promising complement to radio frequency (RF) based wireless communication. The renowned nature of VLC is that it renders simultaneous illumination and communication by utilizing light emitting diodes (LEDs). However, VLC by itself cannot be employed directly as an information source. Therefore, this necessitates for VLC to be connected to a backhaul network to furnish communication. Based upon these grounds, power line communication (PLC) turns out to be the most feasible communication technology which reinforces as an excellent communication backbone for VLC systems. Predominantly, the inherent benefit offered by the integrated PLC–VLC systems is that the existing power line infrastructure can be leveraged to supply power to the LED, while the energy-efficient LED-based illumination systems render wireless support. Accordingly, this paper presents a comprehensive review of the integrated PLC–VLC systems, physical layer aspects which includes detailed study on PLC–VLC channel modeling and modulation techniques. In addition, this survey focuses in detail on the multiple access techniques and clearly discusses several technical aspects that are associated with the cascaded PLC–VLC systems as well as highlights the current state-of-the-art research aspects in the directions of hybrid PLC-VLC-RF systems. Additionally, this survey outlines the societal applications of PLC–VLC systems which includes the applications of PLC–VLC in hospitals, aircrafts, military, Internet of Things (IoT) devices, etc., as well as summarizes the challenges that are of paramount important while designing high speed integrated PLC–VLC systems.

With the proliferation of automated services in recent years, the demand for reliable communication among the devices and machine-human interactions has increased like never before. In general, the amount of information that is exchanged for mission-critical applications is tiny for service categories such as ultra reliable and low latency communication (URLLC) and massive machine-type communications (mMTC). To handle short packet transmission, sparse vector coding (SVC) was recently proposed where the packet information is embedded into the positions of the sparse vector. In this paper, to further improve the performance of SVC in terms of reliability, maximal ratio transmission (MRT) is employed. The distinctive feature of the proposed scheme to that of conventional SVC is that the composite of weighted MRT coefficients with sparse vector is transmitted over the channel. Simulated results under realistic international telecommunication union (ITU) channel models suggest that by exploiting spatial diversity at the transmitter side, the block error rate (BLER) can be reduced with the increased number of antennas. In brief, MRT-aided SVC transmission can be a key enabler for reliable communication and a practical choice for beyond 5G (B5G) communication systems.

In this paper, to quench the fifth-generation (5G) communication system’s standards, we propose a new modulation technique called a nonlinear modelled low-complex asymmetrically clipped DC-biased optical-orthogonal frequency-division multiplexing (LADO-OFDM) for visible light communication (VLC) systems. The main idea of this scheme is to make use of the pre-distortion technique to mitigate the mutual interference between the even subcarriers correspond to DC biased optical-OFDM (DCO-OFDM) and asymmetrically clipped optical-OFDM (ACO-OFDM) at the transmitter section. Thus, the demodulation process can be done parallelly at the receiver, which results in decreased computing-complexity and latency when compared to asymmetrically clipped DC-biased optical-OFDM (ADO-OFDM). The performance of the proposed LADO-OFDM is studied under two generalized light-emitting diode (LED) models. The effect of nonlinear clipping distortion has been examined concerning the dynamic range and bias point of the LED. To improve the system performance, the LED dynamic range can be linearized by pre-distorting the transmitted signal and increasing the knee factor in the piecewise polynomial model and Rapps models respectively. The simulation results obtained by means of a Monte Carlo bit-error ratio (BER) simulations show that the BER performance of the proposed scheme is improved in comparison with the ADO-OFDM. Thus, the proposed scheme outperforms the ADO-OFDM in terms of BER, computing complexity, and latency.

Recently, orthogonal frequency division multiplexing (OFDM) based visible light communication (VLC) technology gaining more attention due to its advantages, namely, high data rates, unlimited bandwidth and radio frequency interference-free. However, a high peak to average power ratio (PAPR) resulting in clipping distortion at the front end light-emitting diode (LED), and it is the major issue in the DC-biased optical-OFDM (DCOOFDM). In this work, we proposed a PAPR reduction technique called peak sample detection and appending (PSDA) algorithm for DCO-OFDM systems for VLC. In the PSDA algorithm, a maximum peak sample can be found and utilized to increase the average power, which results in PAPR reduction. The simulation results show that the proposed PSDA outperforms the selective mapping (SLM) and top samples detection and appending (TSDA) schemes in terms of PAPR performance. Further, the computational complexity of the proposed PSDA and TSDA are the same, whereas substantially decreased when compared to SLM. Moreover, the side-information is not required in PSDA and TSDA, unlike SLM.

With an aim to render high data rates and to overcome spectrum crisis, Visible Light Communication (VLC) is explored in which the transmitted signal is constrained to be unipolar. Timing synchronization is one of the critical issue that deteriorates the performance of VLC systems in real time. In this work, traditional synchronization methods are modified according to a realistic VLC channel for Optical Orthogonal Frequency Division Multiplexing (OOFDM) based systems. Further, a new training symbol is designed and a novel frame synchronization method is proposed to improve the estimation accuracy of timing offset. The new training symbol is designed by employing symmetry on a repetitive symbol pattern in frequency domain. Simulation results proves that the proposed frame detection is giving accurate estimate of the symbol timing compared to conventional methods, in the channel having both Line of Sight (LoS) and Non-Line of Sight (NLoS) components under DC bias with clipping distortion.