Allocation Coefficients Research Articles

Max-Min Fair Precoder Design and Power Allocation for MU-MIMO NOMA

In this correspondence, transmit precoders and their power allocation coefficients are designed jointly for a downlink non-orthogonal multiple access (NOMA) wireless communication system. The objective is to provide max-min fairness (MMF) among the strongest users in each group, while maintaining minimum target rates for all the other users. The proposed solutions are respectively based on semi-definite relaxation (SDR) and successive convex approximation (SCA) and on the minimum mean square error (MMSE) approaches. For the latter approach, a simplification is also suggested to lower complexity. It is shown that while rate-splitting (RS) has the best MMF rates, the low-complexity MMSE approach has the least complexity. Moreover, the SDR/SCA approach offers an excellent tradeoff between the two.

Power‐domain non‐orthogonal multiple access based full‐duplex one‐way wireless relaying network

AbstractThis study investigates power‐domain non‐orthogonal multiple access based wireless information exchange process. The investigation considers a dual‐hop non‐regenerative full‐duplex wireless one‐way relaying networks in the system model, where the source terminal transmits two different types of information and subtracts the interference signal at the destination by using successive interference cancellation technique. The outage probability, error probability, achievable rate, and ergodic rate of the considered system is analytically derived. In addition, optimum power allocation coefficients and relay terminal position are determined using the optimization techniques. Monte‐Carlo simulation results validate the analytical and asymptotic derivations. The derived analytical expressions are found closely in agreement with the system level numerical results.

Cooperative SM-Based NOMA Scheme With SWIPT

In this paper, a cooperative spatial modulation (SM) based non-orthogonal multiple access (NOMA) scheme with simultaneous wireless information and power transfer is proposed. In particular, NOMA is applied at the base station (BS) and the near user (U1) acts as an energy harvesting full-duplex relay to assist the far user (U2). The data bits of U1 and U2 are mapped into SM symbols and amplitude/phase modulation symbols, respectively. Furthermore, the rate of U1 is maximized while satisfying the target rate of U2 by jointly designing the power allocation coefficient, power-splitting ratio, and transmit power of U1. To solve the non-convex problem, a successive convex approximation-based iterative algorithm is developed. Finally, numerical results reveal that the proposed scheme can achieve the superior performance compared to existing schemes.

Full-duplex cooperative relaying with NOMA for the performance enhancement of underwater acoustic sensor networks

Cooperative relaying scheme is identified as an efficient method for improving the reliability and energy efficiency of underwater acoustic sensor networks (UASNs) by exploiting the spatial diversity. Unlike the existing research works, we propose a full-duplex cooperative relaying with NOMA (FD-CR-NOMA) for UASNs. We derive accurate mathematical equations for the calculation of ergodic rate, outage probability, and energy efficiency in UASNs by considering the underwater specific characteristics, namely distance-dependent usable bandwidth, acoustic spreading, propagation losses, and fading effects. Analytical and simulation results show that the FD-CR-NOMA can significantly improve the performance of energy-constrained and bandwidth-limited UASNs in terms of ergodic rate, outage probability, and energy efficiency compared to the other existing cooperative relaying schemes. We analyse the impacts of residual self-interference and imperfect successive interference cancellation on the performance of FD-CR-NOMA. Later, we examine the impact of change in relay position on the FD-CR-NOMA and also the effects of wind speed and shipping activities on the proposed FD-CR-NOMA. It is also observed from results that the high-speed winds and high shipping activities considerably degrade the ergodic sum rate and energy efficiency of the FD-CR-NOMA. In addition, we jointly optimise the signal frequency and power allocation coefficient for the FD-CR-NOMA with respect to the transmission distance using particle swarm optimisation, to further enhance the ergodic rate.

GSVD-Based MIMO-NOMA Security Transmission

Recently, the physical layer security over multiple-input multiple-output (MIMO) non-orthogonal multiple-access (NOMA) systems has been taken more and more seriously. In this letter, a generalized singular value decomposition (GSVD) based MIMO-NOMA security transmission scheme is proposed. The distribution characteristics of the GSVD are applied as tools for the outage performance analysis for the scheme. To minimize the outage probability, the optimal power allocation coefficients are obtained. The theoretical contrast with the Orthogonal Multiple Access (OMA) scheme is also presented, which proves the more superior performance, especially at high signal-noise ratio (SNR) condition. Simulation results are developed to verify the analytical results.

Achievable Rate of NOMA-Based DF Relaying System With Imperfect SIC Over Imperfect Estimation of κ-μ Shadowed Fading Channels

A cooperative relaying system based on non-orthogonal multiple access (NOMA) is considered a promising technique in next-generation wireless communications. In this letter, we investigate the performance of a dual-hop decode-and-forward based on the NOMA relaying system in terms of achievable rate and power allocation coefficient over imperfect estimation of $\kappa $ - $\mu $ shadowed fading channels. Moreover, we consider imperfect successive interference cancellation at the relay in the first phase of transmission. Specifically, we derive the closed expressions for the average achievable rate and power allocation coefficient in terms of hypergeometric function. Finally, the numerical results confirm that our derived analytical results fit well the Monte Carlo simulations.

Outage Analysis of Multi-Source Energy Harvesting in a NOMA assisted Network.

ABSTRACT Most Wireless Sensor Networks (WSN) and Internet of Things (IoT) often involve remotely located nodes which are power constrained and can operate with low power and low rate. Such a node can harvest energy from dedicated Radio Frequency (RF) signals to gather the energy required for information transmission. In this paper, we consider the performance analysis of a wireless-powered communication network (WPCN), where a source node harvests energy from two RF sources, which are also the destination or user nodes. Information transmission is accomplished using the power domain Non-Orthogonal Multiple Access (NOMA) technique. The outage analysis of WPCN is carried out under energy harvesting (EH) constraints. We have also developed a closed-form expression for the outage probability and validated the analytical results with simulation results. The effect of various network parameters, such as NOMA power allocation coefficients, EH efficiency and fractional time constant on the outage probability of the network has also been studied.

Rate Maximization of Wireless-Powered Cognitive Massive MIMO Systems

In order to combat the challenges of scarce spectrum bandwidth and energy supply in the Internet-of-Things networks, this article investigates a wireless-powered massive multiple-input-multiple-output (MIMO) underlay cognitive radio (CR) system, where the secondary user (SU) harvests the energy from the primary network through a time-switching (TS) strategy. Moreover, the detection technique of maximum-ratio combining (MRC) is applied at base stations (BSs) due to its low complexity. Thereon, the achievable rate of the secondary network is thoroughly analyzed by accounting for spatial correlations at both users and BSs, which significantly differentiates the analysis from the prior literature. With the analytical results, the impacts of the number of antennas and the spatial correlations are quantified. In particular, the negative impact of the spatial correlation on the achievable rate is theoretically proved based on the majorization theory. Furthermore, the TS factor and/or power allocation coefficients are optimally designed based on the statistical channel state information (CSI) only to maximize the achievable rate while ensuring the maximum endurable interference constraint. It is found that the optimal power allocation matrix is a variant of water-filling solution with two water levels associated with sum power constraint and sum weighted power constraint, respectively. The weighting matrix is aligned with the transmit spatial correlation in the SU. The joint design of TS factor and power allocation coefficients is also shown to reach a superior performance over the algorithms-based solely on TS factor or power allocation coefficients optimizations. Finally, the analytical results are validated by conducting simulations.

On the Performance of Downlink NOMA in Underlay Spectrum Sharing

Non-orthogonal multiple access (NOMA) and spectrum sharing are two potential technologies for providing massive connectivity in beyond fifth-generation (B5G) networks. In this paper, we present the performance analysis of a multi-antenna-assisted two-user downlink NOMA system in an underlay spectrum sharing system. We derive closed-form expressions for the average achievable sum-rate and outage probability of the secondary network under a peak interference constraint and/or peak power constraint, depending on the availability of channel state information (CSI) of the interference link between secondary transmitter (ST) and primary receiver (PR). For the case where the ST has a fixed power budget, we show that performance can be divided into two specific regimes, where either the interference constraint or the power constraint primarily dictates the performance. Our results confirm that the NOMA-based underlay spectrum sharing system significantly outperforms its orthogonal multiple access (OMA) based counterpart, by achieving higher average sum-rate and lower outage probability. We also show the effect of information loss at the ST in terms of CSI of the link between the ST and PR on the system performance. Moreover, we also present closed-form expressions for the optimal power allocation coefficient that minimizes the outage probability of the NOMA system for the special case where the secondary users are each equipped with a single antenna. A close agreement between the simulation and analytical results confirms the correctness of the presented analysis.

Effects of Accelerated Carbonation Testing and by-Product Allocation on the CO2-Sequestration-to-Emission Ratios of Fly Ash-Based Binder Systems

Carbonation of cementitious binders implies gradual capture of CO2 and significant compensation for the abundant cement-related CO2 emissions. Therefore, one should always look at the CO2-sequestration-to-emission ratio (CO2SP/EM). Here, this was done for High-Volume Fly Ash (HVFA) mortar (versus two commercial cement mortars). Regarding their CO2 sequestration potential, effects of accelerated testing (at 1–10% CO2) on as such estimated natural carbonation degrees and rates were studied. Production related CO2 emissions were evaluated using life cycle assessment with no/economic allocation for fly ash. Natural carbonation rates estimated from accelerated tests significantly underestimate actual natural carbonation rates (with 29–59% for HVFA mortar) while corresponding carbonation degrees are significantly overestimated (67–74% as opposed to the actual 58% for HVFA mortar). It is advised to stick with the more time-consuming natural tests. Even then, CO2SP/EM values can vary considerably depending on whether economic allocation coefficients (Ce) were considered. This approach imposes significant portions of the CO2 emissions of coal-fired electricity production onto fly ash originating from Germany, China, UK, US and Canada. Ce values of ≥0.50% lower the potential CO2SP/EM values up to a point that it seems no longer environmentally worthwhile to aim at high-volume replacement of Portland cement/clinker by fly ash.

Security Enhancement With a Hybrid Cooperative NOMA Scheme for MEC System

This article investigates how to exploit the cooperative mechanism between non-orthogonal multiple access (NOMA) user pairs to enhance the security of the mobile-edge computing (MEC) system. Considering the different delay requirements of Internet of Things (IoT) users, we propose a two-slot hybrid cooperative NOMA security (THCNS) scheme that utilizes the cooperative interference between NOMA user pairs to enhance the security of offloading. In the first time slot, the interference to the eavesdropper comes from the task signals (TSs) transmitted by the two users, while in the second time slot comes from jamming signal (JS) transmitted by the user who has completed the offloading tasks. The weighted sum secrecy outage probability (wSOP) and secrecy computation probability (SCP) are utilized to measure the security performance of users in the proposed scheme. To confirm the feasibility and applicability of the proposed scheme, we analyze the impact of some key parameters on users’ security, including the users’ local computation time and offloading time, transmit power, task allocation coefficients of two time slots. The analysis results indicate that the proposed scheme is more suitable for the case where the wiretap channel outperforms the main channel, and it can enhance the system security when selecting the optimal parameters. Finally, the numerical simulation results reveal how the analysis parameters affect the security performance of users and validate the theoretical analysis, it provides good insights about how to design parameters of IoT users to enhance their security performance in MEC system.

Full-Duplex Non-Orthogonal Multiple Access Cooperative Overlay Spectrum-Sharing Networks With SWIPT

This article proposes a novel non-orthogonal multiple access (NOMA) assisted cooperative spectrum-sharing network, in which one of the full-duplex (FD) secondary transmitters (STs) is chosen among many for forwarding the primary transmitter's and its own information to primary receiver and secondary receivers, respectively, using NOMA technique. To stimulate the ST to conduct cooperative transmission and sustain its operations, the simultaneous wireless information and power transfer (SWIPT) technique is utilized by the ST to harvest the primary signal's energy. In order to evaluate the proposed system's performance, the outage probability and system throughput for the primary and secondary networks are derived in tight closed-form approximations. Further, the sum rate optimization problem is formulated for the proposed cooperative network and a rapid convergent iterative algorithm is proposed to obtain the optimized power allocation coefficients. Numerical results show that FD, SWIPT, and NOMA techniques greatly boost the performance of cooperative spectrum-sharing network in terms of outage probability, system throughput, and sum rate compared to that of half-duplex NOMA and the conventional orthogonal multiple access-time division multiple access networks.

Cooperative Spectrum Sharing in Spectrum Domain with Discrete Time Energy Harvesting for Primary User

In this paper, we propose a spectrum sharing protocol for cognitive radio networks with an energy-constraint primary transmitter (PT), which performs energy harvesting from the received radio frequency (RF) signals broadcasting by two secondary users (SUs). After the amount of harvested energy at the PT is sufficient for data transmission, a SU will cooperatively forward PT's signal using amplify-and-forward (AF) scheme along with transmitting its own signal to increase the spectrum efficiency of the system. To be specific, the data transmission block can be divided into two phases. During the first phase, the PT will optimally select a relay from nodes S1 and S2 in order to further improve the overall throughput, then the PT transmits primary signal to the selected SU and primary receiver (PR), respectively, while the non-selected SU transmits signal to secondary receiver (SR). In the second phase, the selected SU transmits signals of both the primary and secondary systems simultaneously. A discrete Markov chain is used to simulate the charging and discharging processes of the PT's battery. In order to avoid mutual interference between the primary and secondary systems, a fraction of spectrum is used to transmit primary data and the residual spectrum is served for data transmission of the secondary system. An appropriate bandpass filter (BF) is deployed at the receive front-end of each receiver to extract the desired signals from assigned bandwidth. Based on this, the exact expressions of the outage probabilities for both the primary and secondary systems are derived. Moreover, the optimal bandwidth allocation coefficient is determined by utilizing convex optimization to maximize the achievable rate of the secondary system while guaranteeing the achievable rate of the secondary system in information transmission mode. Numerical results show that the proposed spectrum sharing protocol outperforms to other scheme and non-cooperative scenario in terms of average spectrum efficiency.

Performance Analysis of Short-Packet Non-Orthogonal Multiple Access With Alamouti Space-Time Block Coding

This paper presents the analytical performance analysis for short-packet non-orthogonal multiple access (NOMA) systems with the Alamouti space-time block coding (STBC) scheme over Nakagami- $m$ fading channels. In the considered system, the base station (BS) with two antennas transmits short packets to two users with single antenna simultaneously by using Alamouti STBC, assuming that statistical and instantaneous channel state information (CSI) is known at the BS and the two users, respectively. The exact closed-from expressions are derived for the average block error rate (BLER) at each user. Then the simple expressions are derived for the asymptotic average BLER at high signal-to-noise ratios (SNRs). We further derive the optimal power allocation coefficients and the minimum blocklength to satisfy the average BLERs at two users. Finally, Monte Carlo simulations are used to verify the theoretical results and numerical results demonstrate the performance advantage of the STBC-NOMA scheme over the counterpart STBC-OMA one in terms of achieving low-latency transmission.

Crop Biomass Mapping Based on Ecosystem Modeling at Regional Scale Using High Resolution Sentinel-2 Data

We evaluate the potential of using a process-based ecosystem model (BEPS) for crop biomass mapping at 20 m resolution over the research site in Manitoba, western Canada driven by spatially explicit leaf area index (LAI) retrieved from Sentinel-2 spectral reflectance throughout the entire growing season. We find that overall, the BEPS-simulated crop gross primary production (GPP), net primary production (NPP), and LAI time-series can explain 82%, 83%, and 85%, respectively, of the variation in the above-ground biomass (AGB) for six selected annual crops, while an application of individual crop LAI explains only 50% of the variation in AGB. The linear relationships between the AGB and these three indicators (GPP, NPP and LAI time-series) are rather high for the six crops, while the slopes of the regression models vary for individual crop type, indicating the need for calibration of key photosynthetic parameters and carbon allocation coefficients. This study demonstrates that accumulated GPP and NPP derived from an ecosystem model, driven by Sentinel-2 LAI data and abiotic data, can be effectively used for crop AGB mapping; the temporal information from LAI is also effective in AGB mapping for some crop types.

Power allocation for D2D aided cooperative NOMA system with imperfect CSI

Non-orthogonal multiple access (NOMA) has become one of the promising technologies for 5G, which can improve the spectrum resource utilization and system throughput along with the support of effective resource allocation algorithms. Most previous works on NOMA-enhanced cooperative relay systems assume perfect channel state information (CSI), which degrades the performance of their schemes severely when used in imperfect CSI environment. In this article, a power allocation algorithm in D2D aided cooperative NOMA communications with imperfect CSI is proposed. In the proposed algorithm, the probabilistic non-convex optimization problem is transformed into a non-probabilistic convex optimization problem by evaluating the channel gains and using the successive convex programming (SCP) which approximately gives the lower bound of the maximum transmission rate. In the SCP enhanced power allocation algorithm (SCPPAA), we iteratively obtain the sub-optimal power allocation coefficients for the optimization problem by Lagrangian dual multiplier method and Karush–Kuhn–Tucker conditions. This program is divided into two layers for updating the power allocation coefficients and the multipliers respectively. Numerical results demonstrate that our algorithm has a fast convergence performance and the algorithm in D2D-based cooperative NOMA scheme has significant sum-data-rate advantages compared with it in traditional ways.

Resource allocation method based on massive MIMO NOMA MEC on distribution communication network

The current smart distribution network has problems of slow fault detection and low efficiency. This paper reasonably derives the expression of delay from two aspects of transmission time and calculation time based on technologies such as massive multiple input multiple output, non-orthogonal multiple access, and mobile edge computing (MIMO-NOMA-MEC). In addition, a multi-objective iterative algorithm is designed to minimize the delay by jointly optimizing the transmission power, task allocation coefficient, and the computing resources of the MEC server. Finally, the simulation results show that the processing delay of the system gradually decreases as the number of antennas increases. In addition, the processing delay of the system can still be below 10ms under the extremely bad situation that there are many devices currently requesting services.

Spectrum sharing protocol in two-way cognitive radio networks with energy accumulation in relay node

In this paper, we consider a two-way cognitive radio network where an energy-constrained secondary transmitter (ST) first performs energy accumulation and then assists bidirectional communication for a pair of primary users (PUs) based on the principle of two-way relaying (TWR) strategy. To be specific, the ST can harvest energy from the received radio frequency (RF) signals broadcasting by both the primary users. After the residual energy at the ST is sufficient for data transmission, the ST will forward PUs’ signals by using decode-and-forward (DF) manner. In return, the ST is allowed to access the primary spectrum for its own data transmission. Moreover, according to whether the ST can correctly decode PUs’ signals or not, the ST will opportunistically switch between the silent mode and data transmission mode. A discrete Markov chain is used to simulate the charging and discharging processes of the ST’s battery. Based on this, closed-form expressions of outage probabilities for both the primary and secondary systems are derived. In addition, the optimal sub-slot switching coefficient and power allocation coefficient are determined by maximizing the spectrum efficiency of the secondary system while the spectrum efficiency of the primary system exceeding a given threshold. Numerical results not only validate the accuracy of the analytical results but also show that the proposed spectrum sharing protocol can provide a better performance in terms of energy efficiency over other similar TWR schemes.

Performance Analysis of NOMA-Based AF Cooperative Overlay System With Imperfect CSI and SIC

This paper studies a new amplify-and-forward cooperative overlay cognitive radio (CR) non-orthogonal multiple access (AFCO-NOMA) system, where a primary network shares its license spectrum with a secondary network by using NOMA principles. An approximate closed-form expression for the outage probability of the proposed system is analyzed. Asymptotic expressions for the outage probability in high signal-to-noise ratio (SNR) regime of both secondary and primary destinations are derived assuming channel estimation error (CEE) and imperfect successive interference cancellation (SIC). Further, the optimal power allocation coefficients to maximize the system throughput for different target rates are determined to ensure priority to the primary user. The diversity order at the primary and secondary destinations are also derived. Moreover, the AFCO-NOMA system is compared with the OMA-based cooperative overlay system in terms of outage probability. The paper also studies the impact of various parameters such as power allocation coefficients, CEE, and detection threshold, on the outage performance of the proposed system. Monte Carlo simulations are used to confirm the correctness of the derived analytical results.

PSO‐Based UAV Deployment and Dynamic Power Allocation for UAV‐Enabled Uplink NOMA Network

Recently, unmanned aerial vehicles (UAVs) have been used as flying base stations (BSs) to take advantage of line‐of‐sight (LOS) connectivity and efficiently enable fifth‐generation (5G) and cellular network coverage and data rates. On the other hand, nonorthogonal multiple access (NOMA) is a promising technique to help achieve unprecedented requirements by simultaneously allowing multiple users to send data over the same resource block. In this paper, we study a UAV‐enabled uplink NOMA network, where the UAV collects data from ground users while flying at a certain altitude. Unlike all existing work on this topic, this study consists of two stages. In the first stage, we use the well‐known Particle Swarm Optimization (PSO) algorithm, which is a metaheuristic algorithm, to deploy the UAV in 3D space, so that the users’ sum pathlosses are minimized. In the second stage, we investigate the user pairing problem and propose a dynamic power allocation technique for determining the user’s power allocation coefficients, as well as a closed‐form equation for the ergodic sum‐rate. Results show our PSO‐based algorithm prevailing over the Genetic Algorithm (GA) and random deployment methods. The proposed dynamic power allocation strategy maximizes the network’s ergodic sum‐rate and outperforms the fixed power allocation strategy. Additionally, the results reveal that the best pairing scheme is the one that keeps uniform channel gain difference in the same pair.