Direct Transmission Link Research Articles

Sum Rate Maximization for Intelligent Reflecting Surface-Assisted UAV-Enabled NOMA Network

In the next-generation network, intelligent reflecting surface (IRS), non-orthogonal multiple access (NOMA), and simultaneous wireless information and power transfer (SWIPT) are promising wireless communication techniques to effectively improve system sum rates. In traditional unmanned aerial vehicles (UAV) communication systems, the sum rate and coverage are greatly affected when there is an occlusion on the direct transmission link. To solve this problem, the IRS technology is introduced to improve the poor channel conditions. However, most of the previous research on IRS-assisted UAV to optimize system sum rate only considers frameworks that utilize the partially joint-combining techniques of IRS, NOMA, and SWIPT. In this paper, in order to further improve the sum rate of the system, we simultaneously integrate IRS, NOMA, and SWIPT technologies and establish a sum rate maximization optimization problem when the direct link is blocked. Then, an alternative optimization (AO) algorithm based on the maximizing system sum rate is proposed to solve the non-convex optimization problem, in which the IRS location and phase, the reflecting amplitude coefficient, UAV forwarding altitude, and power splitting factor are considered. To let the non-convex and non-linear function be transformed into a convex one, we first use an iterative approach to optimize the position of the IRS. After that, an optimization problem is constructed to maximize the system sum rate with the constraints of the IRS phase shifts, successful successive interference cancellation (SIC), maximum transmit power of base station (BS), and UAV. Numerical results show that the proposed algorithm outperforms the traditional orthogonal multiple access (OMA) and algorithms without IRS-assisted links in terms of the system sum rate.

Joint Resource Allocation in a Two-Way Relaying Simultaneous Wireless Information and Power Transfer System

Simultaneous wireless information and power transfer (SWIPT) technology provides an efficient solution to energy-limited communication terminals in a wireless network. However, in the current application scenario of SWIPT technology, relays use all the collected energy forwarding to assist communication between source nodes, while ignoring the fact that relays can accumulate and store energy. This is of great practical significance in collaborative communication. By using a transmission scheme of a time-division broadcast for the direct transmission link, improvement of the system diversity gain through combining the technology at the receiver can be realized. Based on the above, we propose a two-way relay energy accumulation communication system, which is extended from a single relay system to a multi-relay system. The instantaneous transmission rate of the system link and the system equivalent profit are optimized by jointly optimizing the relay selection, time slot allocation factor, power splitting factor and relay transmit power. Compared with the comparison algorithm, the proposed algorithm shows a significant improvement in the performance of the system.

Delay Minimization for Massive MIMO Based Cooperative Mobile Edge Computing System With Secure Offloading

Mobile edge computing (MEC) has been envisioned as a promising technology for enhancing the computational capacities of mobile devices by enabling task offloading. In this paper, we present a novel framework for a cooperative MEC system by employing Massive Multiple-Input Multiple-Output (MIMO) and non-orthogonal multiple access (NOMA) technologies, including security aspects. Specifically, in the proposed cooperative MEC system, there is no strong direct transmission link between the cell-edge user and the MEC server; consequently, the user sends their tasks to the MEC server through the helpers at the cell-centers. In the proposed framework, we minimize the overall delay, including secure offloading under the constraints of computing capability and transmit power. The proposed algorithm minimizes the overall delay in downlink and uplink transmission while satisfying security constraints to solve the formulated problem. The simulation results show that Massive MIMO based NOMA improves the performance of the secure MEC system by employing more than one helper.

Modeling of a Planetary Relay Station in Improving Deep-Space Probe Telecommunication Performance

For a deep-space probe(DSP), such as the Voyager, over an extremely far distance to transmit data back to Earth more efficiently, a model that adds one planet-based repeater(PBR) in the transmission path is developed. Firstly, a general model of the direct transmission link of any DSP is analyzed. Secondly, a general model of the relayed link is evaluated, with special cases considered. Then the simulation is conducted based on available technologies and statistics, and the results of the performance optimize the model and validate that the relayed link is effective. The conclusion is reached that, under certain constraints, a PBR located on Mars could provide the highest performance advantage over the direct link.

Performance evaluation of cognitive relay networks for end user mobile over mixed realistic channels

Cognitive relay network is a spectrum dynamic paradigm that exploits the unused portions of the licensed spectrum. This is based on merging both cooperative relaying techniques and cognitive radio network to achieve spectrum efficiency and enhance the overall system performance. In this paper, the presence of mobile users at the destination node is considered. Here, the end users can navigate at relatively fast vehicular velocities causing dynamic multipath fading and high Doppler shift. which can be fairly modelled using Nakagami- m $m\;$ fading channel (i.e. m < 1 $\;m < 1$ ). In a spectrum scarcity environment, a secondary user must deploy an optimal power allocation policy to get higher transmission rates while the overall interference affecting the primary user (PU) is kept below a certain threshold value. In particular, the outage probability (OP) performance is studied over the mixed Rayleigh and Nakagami-m fading channels for different scenarios and a tight closed-form expressions are derived for the system OP of underlay dual-hop cognitive relay networks with a single amplifiy-and-forward (AF) relay with and without the use of the direct link transmission and selection diversity at the destination with interference power constraints for the primary network over independent and non-identical (i.n.i.d) Rayleigh and Nakagami-m fading channels when m < 1 $m < 1$ based on the statistical characteristics of signal-to-noise ratio. Numerical results are presented to evaluate the impact of the fading parameter, m, the maximum aggregated intrusion constraint, and the locations of the primary users (PUs) on different channel scenarios at high vehicular speeds. Monte Carlo simulations are presented to verify and validate analytical results.

Multi-Helper NOMA for Cooperative Mobile Edge Computing

The next-generation wireless networks are expected to support a number of computation-intensive and delay-sensitive applications such as virtual reality (VR), autonomous driving, telesurgery and unmanned aerial vehicles (UAVs). Since many devices are computation and power limited, mobile edge computing (MEC) has been deemed as a promising way to enhance computation service. In this paper, we propose a novel cooperative MEC that exploits the combination of non-orthogonal multiple access (NOMA) and multiple helpers. In the proposed system featuring a user, multiple helpers and a base station (BS), the user can simultaneously offload its computation-intensive tasks to the helpers using NOMA when there is no strong direct transmission link between the user and the BS. Then, the helpers can compute and offload these tasks through NOMA. Thus, in the proposed scheme, the computation and offloading modes at the helpers are determined with respect to the optimized task offloading decision factor. The simulation results show that the proposed NOMA-based cooperative MEC significantly increases the total offloading data under the latency constraints compared to the benchmark schemes featuring one helper with strong direct transmission link.

Finite Block Length Analysis of RIS-Assisted UAV-Based Multiuser IoT Communication System With Non-Linear EH

Reconfigurable intelligent surface (RIS) has emerged as an important transmission technology for numerous applications in Internet of Things (IoT) systems. Thus, in this paper, we investigate the application of RIS in energy harvesting (EH) based unmanned aerial vehicle (UAV) communication network with finite block length (BL) codes, where a rotary wing type flying UAV communicates with the multiple single antenna IoT users with the aid of multiple RISs mounted on several skyscraper buildings. To transmit the signal to a particular IoT user, the UAV selects an RIS on the basis of either UAV-RIS (i.e., partial) or UAV-RIS-IoT (i.e., full) channel state information (CSI) and then transmits the signal through the selected RIS along with the direct link transmission. In particular, we derive (i) the expression for probability of RIS selection, (ii) the statistical distribution of instantaneously received information signal-to-noise ratio (SNR) at the IoT user. Based on the derived statistics, we analyze the performance of the considered system under finite BL codes in terms of the average outage probability, average block error rate (ABLER) and goodput averaged over entire flying duration. Moreover, the BLER performance with finite BL codes is also compared with the infinite BL codes scenario. Additionally, we also investigate the impact of various channel and system parameters like imperfect CSI, number of RISs and the number of reflecting elements at each RIS, location of IoT users, variable altitude of the UAV, and the severity of channel fading of UAV-RIS link on the system performance. Furthermore, we have obtained the optimum UAV location in each time slot which minimizes the ABLER per time slot over all the users in the network. The analytical results are corroborated with Monte Carlo simulations.

Stochastic Geometry Analysis of IRS-Assisted Downlink Cellular Networks

Using stochastic geometry tools, we develop a comprehensive framework to analyze the downlink performance of various types of users (e.g., users served by direct base station (BS) transmissions and indirect intelligent reflecting surface (IRS)-assisted transmissions) in a cellular network with multiple BSs and IRSs. For the proposed users, we provide the approximate expressions for the performance in terms of coverage probability, ergodic capacity, and energy efficiency (EE). The proposed stochastic geometry framework can capture the impact of channel fading, locations of BSs and IRSs, arbitrary phase-shifts and interference experienced by a typical user supported by direct transmission and/or IRS-assisted transmission. For IRS-assisted transmissions, we first model approximate the desired signal power from the nearest IRS as a sum of scaled generalized gamma (GG) random variables whose parameters are functions of the IRS phase shifts. Then, we derive the Laplace Transform (LT) of the received signal power in a closed form. Also, we approximate the aggregate interference from multiple IRSs as the sum of normal random variables. Then, we derive the LT of the aggregate interference from all IRSs and BSs. The derived LT expressions are used to calculate coverage probability, ergodic capacity, and EE for users served by direct BS transmissions as well as users served by IRS-assisted transmissions. Finally, we derive the overall network coverage probability, ergodic capacity, and EE based on the fraction of direct and IRS-assisted users, which is defined as a function of the deployment density of IRSs, as well as blockage probability of direct transmission links. Numerical results validate the derived analytical expressions and extract useful insights related to the number of IRS elements, large-scale deployment of IRSs and BSs, and the impact of IRS interference on direct transmissions.

Feasibility of Joint Power Optimization of Multiple Source-Destinations in an AF Relay Network

Joint power optimization of sources and relay in cooperative networks, while multiple source-destination (SD) pairs are utilizing a relay and also have direct transmission links, is addressed in this letter. In the assumed network each SD pair requires a minimum quality of service (QoS) in terms of its received SINR. We have shown that the resulted power control equations are quadratic due to coexistence of direct and relay links. The feasibility analysis of the resulted non-convex optimization problems is complicated. The necessary condition for the optimization problem feasibility is studied and two upper bounds for the achievable SINR of the users are derived. Computer simulations are used to study the achievable SINRs and the results are compared with the obtained upper bounds.

Performance Analysis of Energy Harvesting-Assisted Overlay Cognitive NOMA Systems With Incremental Relaying

In this paper, we analyze the performance of an energy harvesting (EH)-assisted overlay cognitive non-orthogonal multiple access (NOMA) system. The underlying system consists of a primary transmitter-receiver pair accompanied by an energy-constrained secondary transmitter (ST) with its intended receiver. Accordingly, ST employs a time switching (TS) based receiver architecture to harvest energy from radio-frequency signals of the primary transmissions, and thereby uses this energy to relay the primary information and to transmit its own information simultaneously using the NOMA principle. For this, we propose two cooperative spectrum sharing (CSS) schemes based on incremental relaying (IR) protocol using amplify-and-forward (AF) and decode-and-forward (DF) strategies, viz., CSS-IAF and CSS-IDF, and compare their performance with the competitive fixed relaying based schemes. The proposed IR-based schemes adeptly avail the degrees-of-freedom to boost the system performance. Thereby, considering the realistic assumption of the NOMA-based imperfect successive interference cancellation, we derive the expressions of outage probability for the primary and secondary networks under both CSS-IAF and CSS-IDF schemes subject to the Nakagami-m fading. In addition, we quantify the throughput and energy efficiency for the considered system. The obtained theoretical findings are finally validated through numerous analytical and simulation results to reveal the advantages of the proposed CSS schemes over the baseline direct link transmission and orthogonal multiple access schemes.

Stochastic Transceiver Optimization in Multi-Tags Symbiotic Radio Systems

Symbiotic radio (SR) is emerging as a spectrum-and energy-efficient communication paradigm for future passive Internet of Things (IoT), where some single-antenna backscatter devices, referred to as Tags, are parasitic in an active primary transmission. The primary transceiver is designed to assist both direct-link (DL) and backscatter-link (BL) communication. In multi-Tags SR systems, the transceiver designs become much more complicated due to the presence of DL and inter-Tag interference, which further poses new challenges to the availability and reliability of DL and BL transmission. To overcome these challenges, we formulate the stochastic optimization of transceiver design as the general network utility maximization problem (GUMP). The resultant problem is a stochastic multiple-ratio fractional nonconvex problem, and consequently challenging to solve. By leveraging some fractional programming techniques, we tailor a surrogate function with the specific structure and subsequently develop a batch stochastic parallel decomposition (BSPD) algorithm, which is shown to converge to stationary solutions of the GNUMP. The simulation results verify the effectiveness of the proposed algorithm by numerical examples in terms of the achieved system throughput.

Coverage, Probability of SNR Gain, and DOR Analysis of RIS-Aided Communication Systems

Recent studies have shown that reconfigurable intelligent surfaces (RISs) can help in extending the wireless coverage. However, no work has quantitatively analyzed the coverage. In this letter, we present the coverage analysis for an RIS-aided communication system. For comparison, the coverage analysis for relaying systems and direct-link transmission systems are also derived. Furthermore, we provide the analysis for the probability of signal-to-noise ratio (SNR) gain of the RIS over the direct link transmission. Finally, we analyze the delay outage rate of the RIS in achieving ultra-reliable low-latency transmissions. The results show that using the RIS can expand the coverage, increase the SNR gain, and reduce latency of the links.

Reliability assessment of composite generation and transmission expansion planning incorporating renewable energy sources

Modern power system exploitation of large-scale Renewable Energy Sources (RESs) is prevalent due to the RES effect of reducing the heavy dependence on fossil fuels and the resultant power quality improvement. Therefore, this paper investigates the reliability assessment of a power system with integration of large-scale RESs with emphasis on their impacts on the expansion planning procedure. A multi-state Markov model is proposed to analyze the availability and reliability of the stochastic nature of RESs and High Voltage Direct Current transmission links. A Mixed Integer Nonlinear Programming model is developed to minimize the total investment and operation cost of the generating units and the cost associated with power outage as well as improving power system reliability. An Outer Approximation Algorithm, a powerful solver embedded in the Advanced Interactive Multidimensional Modeling System, was employed in solving the proposed model and implemented using the IEEE 6- and 24-bus Roy Billinton Test System to demonstrate its effectiveness. The results obtained from the simulation reveal that the proposed model performance achieves effective reliability and an enhanced voltage profile.

Buffer-Aided Relaying With Direct Link Transmission and Spectrum Sharing

Cognitive relay networks are designed to increase access to under-utilized spectrum. The direct link communication can be exploited to decrease the outage probability with a buffer-aided relaying network. To this end, a novel transmission policy is proposed to combine the benefits of direct communication and buffer-aided relaying. In addition, a modification to the hybrid interweave-underlay spectrum access policy is presented to restrict the amount of interference caused due to a miss-detection event. Assuming independent and not necessarily identical fading channels, the analytical outage probability and the end-to-end average packet delay for the secondary system are derived. Monte-Carlo simulations show that adopting the proposed policy, compared to the conventional link selection techniques, results in a significantly larger outage gain, a lower average packet delay, a higher empty buffer probability, and a lower full buffer probability. Also, the theoretical and Monte-Carlo results coincide in the provided simulation examples which verifies correctness of the theoretical analysis.

Cost-effective and data size-adaptive OPM at intermediated node using convolutional neural network-based image processor.

A cost-effective and data size-adaptive optical performance monitoring (OPM) scheme is proposed, which is based on asynchronous delay-tap plot (ADTP) using convolutional neural network (CNN) from the perspective of image processing. First, we design an OPM framework, based on the electrical domain-processing technique for the future optical networks. These networks include coherent detection-based end-to-end channel monitoring at destination node and direct detection-based transmission link monitoring at intermediate node. Aiming at the link monitoring, CNN is applied to recognize and analyze ADTP images that are converted from two-dimension (2D) digital vectors, so that adaptive to the stable algorithm structure. In simulation system, three high-order modulation formats, 16 quadrature amplitude modulation (QAM), 32QAM, 64QAM, are investigated for optical signal-to-noise ratio (OSNR) estimation and modulation format identification (MFI). The 100% accuracies under different chromatic dispersions (CDs) at different iteration epochs are obtained. Compared with asynchronous amplitude histograms (AAH)-based method, the better accuracy and faster convergence rate are achieved, especially in terms of strong CDs. Additionally, the experimental system is also conducted of 16QAM and 64QAM signals. Based on the partially-trained CNN model from simulation, the OSNR estimation accuracies of 16QAM and 64QAM are 97.81% and 96.56%, respectively. The maximum standard deviation is less than 0.45 dB and the MFI accuracies is 99.84%, presenting the satisfactory results and proving the feasibility of ADTP-based image processor for link monitoring at intermediate nodes.

Cooperative Secondary Encryption for Primary Privacy Preserving in Cognitive Radio Networks

Aiming at protecting primary privacy messages and supporting secondary quality-of-service (QoS), we propose a secondary encrypted secure strategy for cognitive radio networks. In this scheme, a primary system directly transmits privacy messages or employs pre-transmitted secure secondary messages to encrypt the primary privacy information, and the secondary system acquires a fraction of the interference-free licensed spectrum. Following this idea, we consider two secure communication scenarios: the non-buffer scenario and the buffer-aided scenario. For the non-buffer scenario, the primary system first evaluates the channel quality of the direct transmission link. Then, the primary transmitter adaptively chooses to directly transmit the privacy messages or employ the encryption of the secure secondary messages according to the evaluation results. For this scenario, we investigate the primary ergodic secrecy performance and the secondary average performance. For the buffer-aided scenario, the secure secondary messages can be stored in the buffers at both the primary transmitter and receivers. According to the buffer states and channel quality, the primary system adaptively chooses to directly transmit the primary privacy information, permit the secondary secure transmission, or utilize the encryption of the stored secure secondary information. For this scenario, we also investigate the performances of both the primary and secondary systems, and derive the closed-form expression of the primary information delay. Numerical results are given to prove that the proposed scheme can provide privacy preserving for the primary information and acquire high secondary average transmission rate.

A novel reliable low-latency multipath routing scheme for vehicular ad hoc networks

In this paper, the existing ad hoc on demand multipath distance vector (AOMDV) routing scheme for vehicular ad hoc networks (VANETs) is extended to a reliable low-latency multipath routing (RLLMR) scheme based on multipath link reliability, capable of determining the reliable routes preemptively. Here, the link reliability refers to the probability that a direct transmission link among any two vehicles remains constantly available for a specific period of time, which can be computed based on the position, route, and velocity of the vehicles to facilitate the reliable routing process in VANETs. In the proposed RLLMR scheme, the mathematical distribution of vehicles movements and link breakages is also considered to increase the reliability of the vehicular networks. The simulation results show that proposed RLLMR scheme performs better compared to existing schemes in terms of latency, reliability, throughput, and energy consumption at the cost of marginally increased routing overhead.

RaptorQ-Based Efficient Multimedia Transmission Over Cooperative Cellular Cognitive Radio Networks

Accommodating the fast-growing multimedia traffic demands at low cost is critical to ensure the future competitiveness of cellular networks. Cognitive radio (CR) emerges as a key technology to enhance radio spectrum utilization and provides an effective solution to meet critical spectrum demands for future mobile multimedia traffics. In this paper, we investigate reliable downlink video transmission in underlay cellular CR networks by means of cooperative diversity. We use RaptorQ code as the Application Layer Forward Error Correction scheme to combat packet loss arising from the primary user interference and other channel conditions such as channel fading. For implementing cooperative diversity, we select the best relay based on the ability of successful decoding using RaptorQ and the value of signal-to-interference-plus-noise ratio at the destination node. Moreover, for efficient primary user channel utilization, the selected relay performs merging of the encoding coefficients before forwarding to the destination. We evaluate the performance of the proposed framework under various time sharing scenarios between the direct and best indirect transmission links in terms of decoding overhead, probability of decoding failure, and peak signal-to-noise ratio of the received videos. Numerical results show that the proposed scheme outperforms the baseline transmission scheme and conventional relaying schemes using Amplify-and-Forward and Decode-and-Forward transmission techniques.

Deregulated AGC of multi-area system incorporating dish-Stirling solar thermal and geothermal power plants using fractional order cascade controller

The present study highlights the attempt of incorporating geothermal power plant (GTPP), dish-Stirling solar thermal system (DSTS) and high voltage direct current transmission (HVDC) link, with the conventional thermal system, in automatic generation control of an interconnected power system under deregulated environment. Appropriate generation rate constraints are provided in thermal systems. A new fractional order (FO) cascade controller named as FO proportional-integral-FO proportional-integral-derivative (FOPI-FOPID) is proposed as secondary controller and its performance is compared with the commonly used classical controllers. A stochastic algorithm, Sine Cosine Algorithm (SCA) is used to optimize the controller gains and other parameters. Analyses of the dynamic responses reveal the superiority of FOPI-FOPID over the others in terms of settling time, peak deviation and magnitude of oscillation. Performance index comparison is carried out and integral squared error is selected. The effect of GTPP, DSTS and HVDC link have been examined separately and the responses disclose that integration of HVDC link to the combined system having both GTPP and DSTS along with thermal leads to better dynamics. Sensitivity analysis of SCA optimized FOPI-FOPID controller parameters obtained at nominal Disco Participation Matrix (DPM) validate that they are healthy enough and need not be optimized for change in DPMs.

Cognitive Full-Duplex Decode-and-Forward Relaying Networks With Usable Direct Link and Transmit-Power Constraints

The performance of an underlay cognitive radio network that coexists with a primary destination is studied in terms of the outage probability. The investigated secondary network comprises a source-destination pair communicating under the assistance of a full-duplex decode-and-forward relay. We consider the following key aspects pertinent to the underlay cognitive-radio approach and to the full-duplex operation at the relay: the transmit power constraint of the cognitive network by the maximum interference tolerated at the primary destination, as well as by the maximum-available transmit power at the cognitive terminals; the impact of the residual self-interference inherent to the relay; and the use of a joint-decoding technique at the destination in order to combine the concurrent signals coming from the source and relay, which enables the treatment of the direct-link transmission as information signal, rather than as interference. Herein, the joint effect of the maximum interference power constraint and the residual self-interference are both examined. To this end, an arbitrary power allocation between source and relay is allowed. Then, an accurate closed-form approximation to the outage probability is proposed, from which an asymptotic expression is derived for the high SNR ratio regime. Our analytical results are validated via Monte Carlo simulations. Importantly, we show that a maximum-available transmit power not only saves energy but also reduces the outage probability at medium to high SNR ratio.