Fixed Power Allocation Scheme Research Articles

Dynamic Power Allocation for Downlink NOMA

Dynamic Power Allocation for Downlink Non-Orthogonal Multiple Access (NOMA) is a critical research area in wireless communication systems. This study focuses on implementing and evaluating dynamic power allocation strategies in the context of downlink NOMA. We compare the performance of dynamic power allocation with fixed power allocation schemes to assess their impact on system throughput, interference management, and overall efficiency. Through extensive simulations and analysis in this paper using MATLAB, we demonstrate a comparison between dynamic power allocation and fixed power allocation, and the advantages of dynamic power allocation in adapting to changing channel conditions and user requirements, leading to improved system performance. Our results show the data rate and outage probability which provides valuable insights into the benefits of dynamic power allocation in downlink NOMA systems and highlight the importance of adaptive power management techniques in enhancing wireless communication networks.

A novel power allocation strategy for cooperative PDMA systems

Cooperative communication technology is of great importance for increasing the user reachable rate, further improving throughput and reducing the outage probability of non-orthogonal multiple access (NOMA) systems. This paper mainly studies the power allocation optimization method based on amplify-and-forward (AF) pattern division multiple access (PDMA) to obtain the maximum achievable throughput. We formulate an optimization problem of user power allocation in a downlink PDMA system with cooperative relaying, the exact expressions of system throughput and user outage probability of the AF-PDMA system are derived, and a novel power allocation optimization method based on uniform distribution and restricted constraints is proposed. The effectiveness of the restricted constraints and optimization method is verified by theoretical analysis and simulation. The studies we have performed showed that the proposed scheme with uniform distribution and restricted constraints can be significantly improved in terms of the system throughput in comparison to the case with a genetic algorithm (GA) and fixed power allocation scheme. Concerning the proposed method, the search space is reduced to 1/3 of the original feasible region, and the runtime of the algorithm accounts for only 20% of the GA runtime.

Splitting Energy of Transmit Power Serving Grouping Users in Full-Duplex Networks under Imperfect Hardware

In this paper, we consider a wireless system providing power allocation fairness for grouping users by conducting a non-orthogonal multiple access (NOMA). In particular, a rigorous analysis is performed to evaluate performance of destination in a downlink of wireless system. With advances of NOMA, the user grouping scheme allows users to be shared the same frequency/power domain, and hence, fairness is guaranteed. In this regard, we focus on evaluation of the performance of a cell-center user and a cell-edge user in dedicated group. To enable forwarding function at cell-center user, we require the assistance of a full-duplex– (FD–) based relay to serve the cell-edge user. These users are assigned a fixed power allocation scheme. To characterize system performance, the closed-form expressions of the outage probability are computed for two users. To generalize channels in such system, Nakagami-m fading channels could be adopted to achieve complete theoretical analysis. Furthermore, we provide some comparisons of such FD NOMA under the impact of hardware impairment. We find that a significant improvement of outage probability can be achieved when the signal-to-noise ratio (SNR) at the source is high. Numerical results illustrate that both the analytical outage probability of the central user and the cell-edge user match the simulation results.

Ergodic capacity of internet of things’ devices in presence of channel state information imperfection

Non-orthogonal multiple access (NOMA) is deployed to improve spectral efficiency for applications in fifth generation networks. NOMA system splits power domain to many parts to further serve massive users by relaxing the orthogonal use of radioresources. In this paper, a relay is required to help the source communicate with destinations with a fixed power allocation scheme. We derive expressions to highlight ergodic performance of two users the deployment of NOMA is suitable to different rate requirements from destinations (e.g., a cellular users have different requirements compared with internet of things devices). By conducting Monte-Carlo simulations, we find main system parameters which have crucial impacts on ergodic capacity. This paper is different other recent studies since we emphasize on imperfect channel state information (CSI) and Rician fading model for our analytical results.

Secure Multiantenna Transmission With an Unknown Eavesdropper: Power Allocation and Secrecy Outage Analysis

This paper investigates the power allocation problem for secure multiple-input single-output transmission with the injection of artificial noise (AN), in the presence of an unknown eavesdropper (Eve). Two power allocation schemes, the optimal adaptive power allocation (OAPA) and suboptimal fixed power allocation (SFPA) schemes, are proposed to enhance the physical layer security of the considered system. Since the noise power at Eve is unknown, both power allocation schemes are designed for the worst-case scenario in which the noise power at Eve is assumed to be zero, aiming to minimize the secrecy outage probability (SOP). To characterize the performance of the proposed power allocation schemes, approximate closed-form expressions for average SOP under a preset noise power level are derived by applying Gauss-Chebyshev quadrature. We also address the worst-case secrecy outage performance for the proposed OAPA and SFPA schemes. Our analytical and numerical results show that, compared with the exhaustive search method that requires Eve’s prior information, the proposed OAPA scheme exhibits comparable secrecy outage performance without Eve’s prior information. Additionally, the SFPA scheme, also without Eve’s prior information, is capable of achieving almost the same worst-case SOP as the OAPA scheme, with a much lower implementation complexity.

Coefficient-Scaling-Based Fair Power Allocation for Multi-User Power-Domain Nonorthogonal Multiple Access Network

Fair power allocation to the users in a power domain nonorthogonal multiple access (PD-NOMA) networks is an essential aspect. In this paper, we have proposed a coefficient-scaling-based fair power allocation scheme, for a single cell multi-user PD-NOMA network. First, we have developed a model for two users with a fixed power allocation scheme, and proposed a modified strong user fair-power allocation scheme. Furthermore, this two-user scheme is extended for an ad-hoc multi-user PD-NOMA network and a coefficient-scaling-based approach for fair power allocation is proposed to address the outage issue. The performance of the proposed schemes is evaluated through bit-error-rate, sum-rate, outage, and fairness index. The simulation results reveal a remarkable increase in fairness performance of the proposed scheme, in comparison with a state-of-the-art method.

Performance Analysis for Cooperative Communication System in Optical IoUT Network With HDAF Strategy

In this work, a cooperative optical Internet of Underwater Things (IoUT) system with hybrid decode-amplify-forward (HDAF) strategy is first proposed and investigated over the aggregated underwater wireless optical communication (UWOC) channel. The impacts of absorption, scattering and the misalignment caused by spatial spreading in the sea, which are modeled by the beam spread function (BSF), as well as the oceanic turbulence on the underwater optical links are all included to describe the practical channel characteristics. With the help of Gauss-Hermite and Gauss-Legendre quadrature numerical methods, the closed-form expressions of the average bit error ratio (ABER) and outage probability for this cooperative optical HDAF-IoUT system are derived and verified by the Monte Carlo (MC) simulations. Furthermore, numerical analyses are offered to explore the effects of water type, turbulence strength, relay location and power allocation scheme on this HDAF-IoUT system. The performance of this optical system over the mixture Exponential Generalized Gamma (EGG) channel is also given for comparison. The obtained results indicate that the optical HDAF-IoUT system is superior to the IoUT system with fixed amplify-and-forward (FAF) strategy, and has a better performance when the relay is close to the middle position for a fixed power allocation scheme. This work is beneficial for the cooperative system design in IoUT network.

Employing non-orthogonal multiple access scheme in UAV-based wireless networks

This paper studies the two-hop transmission relying unmanned aerial vehicle (UAV) relays which is suitable to implement in the internet of things (IoT) systems. To enhance system performance in order to overcome the large scale fading between the base station (BS) and destination as well as achieve the higher spectrum efficiency, where non-orthogonal multiple access (NOMA) strategies were typically applied for UAV relays to implement massive connections transmission. In particular, outage probability is evaluated via signal to noise ratio (SNR) criterion so that the terminal node can obtain reasonable performance. The derivations and analysis results showed that the considered fixed power allocation scheme provides performance gap among two signals at destination.The numerical simulation confirmed the exactness of derived expressions in the UAV assisted system.

Enabling User Grouping and Fixed Power Allocation Scheme for Reconfigurable Intelligent Surfaces-Aided Wireless Systems

This paper considers a two-user downlink transmission in reconfigurable intelligent surface (RIS)-aided network over fading channels. Particularly, by employing user grouping and fixed power allocation scheme to enable non-orthogonal multiple access (NOMA) approach, RIS-aided network can significant benefit from NOMA. To highlight the advantages of RIS, we compare the system performance of NOMA-RIS and traditional orthogonal multiple access (OMA) based RIS. Main practical circumstances are carefully analyzed, such as, RIS with direct link, system without RIS, and imperfect phase shifts. More specifically, we consider a RIS-aided downlink network, where the base station communicates with a group of two users under assistance of RIS, which acts equivalently as relay. As key expectation, the RIS is efficiently designed to improve the performance of users. To evaluate the system performance, two main system performance metrics including outage probability and average capacity are studied by deriving new closed-form expressions. The goal is to find out which system parameters need to be adjusted to achieve the expected performance. The numerical results reveal that: i) <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">the outage probability and average capacity of considered NOMA-RIS aided wireless system outperforms the conventional NOMA network over fading channels</i> ; ii) <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">with different power allocation factors assigned to users, the performance gap among two users can be adjusted to guarantee the fairness characteristic</i> ; iii) <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">the number of reflecting elements in RIS has significant impact on the system performance of the considered NOMA-RIS</i> system, which shows advantage of both RIS and NOMA compared with conventional OMA system.

Improving Performance of User Pair Using Reconfigurable Intelligent Surfaces

With the given scope for new use cases and the demanding needs of future 6th generation (6G) wireless networks, the development of wireless communications looks exciting. The propagation medium has been viewed as a randomly behaving entity between the transmitter and the receiver since traditional wireless technology, degrading the quality of the received signal due to the unpredictable interactions of the broadcast radio waves with the surrounding objects. On the other hand, network operators could now manipulate electromagnetic radiation to remove the negative impacts of natural wireless propagation due to the recent arrival of reconfigurable intelligent surfaces (RIS) in wireless communications. According to recent findings, the RIS mechanism benefits nonorthogonal multiple access (NOMA), which can effectively deliver effective transmissions. For simple design, of RIS‐NOMA system, fixed power allocation scheme for NOMA is required. The main system performance metric, i.e., outage probability, needs to be considered to look at the efficiency and capability of transmission mode relying on RIS and NOMA schemes, motivated by the potential of these developing technologies. As major performance metrics, we derive analytical representations of outage probability, and throughput and an accurate approximation is obtained for the outage probability. Numerical results are conducted to validate the exactness of the theoretical analysis. It is found that increasing the higher number of reflecting elements in the RIS can significantly boost the outage probability performance, and the scenario with only the RIS link is also beneficial. In addition, it is desirable to deploy the RIS‐NOMA since it is indicated that better performance compared with the traditional multiple access technique.

Power Allocation and Outage Analysis for Secure MISO Cognitive Radio Networks With an Unknown Eavesdropper

This paper investigates the power allocation problem for secure secondary transmission in a multiple-input single-output cognitive wiretap system with artificial noise (AN). The secondary transmitter exchanges confidential information with the secondary destination in the presence of an unknown eavesdropper. Since the eavesdropper's channel state information (CSI) is unavailable, we propose an optimal adaptive power allocation scheme, and derive a closed-form expression of the optimal power allocation factor that minimizes the secrecy outage probability (SOP). A suboptimal fixed power allocation scheme is also proposed to reduce the system complexity. Moreover, exact closed-form expressions of SOP under both schemes are derived. Numerical results are provided to corroborate the accuracy of our analytical results and the superiority of the proposed schemes to the benchmarks.

NOMA Versus OMA in Finite Blocklength Regime: Link-Layer Rate Performance

In this article, we investigate the latency performance of non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) technologies in finite blocklength regime. In the comparative study, we derive the achievable effective capacity of two-user NOMA and its OMA counterpart under delay quality-of-service constraints. We then obtain closed-form expressions for the achievable effective capacity of the weak and strong users in both scenarios considering transmissions over Rayleigh fading channels. Numerical results are provided. In particular, it is shown that at low signal-to-noise ratios (SNRs), the OMA user with better channel condition outperforms both NOMA users. We also evaluate the impact of fixed power allocation scheme on the achievable effective capacity of two-user NOMA. The comparative analysis of the total link-layer rate shows that at high SNRs, the total link-layer rate of NOMA with finite blocklength outperforms the one of OMA when the delay exponent is loose.

Joint users selection and beamforming in downlink millimetre‐wave NOMA based on users positioning

In this study, joint users selection and beamforming based on users positioning are proposed for enabling non-orthogonal multiple access (NOMA) in the millimetre-wave (mmWave) transmissions. In the proposed scheme, the mmWave users are arranged in descending order based on their estimated distances from the mmWave base station (BS), which guarantees the users ordering based on their line-of-sight availability, as well. Out of the ordered users, the two users having the minimum pairing angle and expected to lie within the specified mmWave beamwidth are selected as the two NOMA users. In this study, the users' pairing angle is defined as the maximum expected difference angle between two users considering their location-uncertainty areas. Consequently, the BS antenna beam is formed towards the two selected NOMA users by adjusting its boresight angle to lie in between their estimated location angles. Then, the fixed power allocation scheme is used to adjust the power allocation coefficients of the selected NOMA users. Mathematical analysis is performed to bound the performance of the proposed mmWave NOMA scheme. Also, numerical simulations are conducted to prove the mathematical findings and to show the superior performance of the proposed scheme over the well-known technique of using random beamforming.

Joint evaluation of imperfect SIC and fixed power allocation scheme for wireless powered D2D-NOMA networks with multiple antennas at base station

In this study, device-to-device (D2D) communication is exploited to adopt the proximity transmission among two nearby devices. The base station in this scenario transmits both information and energy to both D2D users to deploy wireless power transfer feature in green communications. In addition, to enhance the overall spectrum utilization of considered system, downlink non-orthogonal multiple access (NOMA) network is considered to evaluate performance in such network. In particular, a downlink from the base station (BS) equipping multiple antennas is designed to robust performance. We further determine the worse case of considered NOMA at the receiver in cellular network as considering impact of imperfect successive interference cancellation (SIC). A two-user downlink NOMA scenario is considered, where a far user directly communicates with the BS without SIC, whereas a near user is assigned to serve D2D link with imperfects on SIC. The ergodic capacity of D2D NOMA is further analyzed under both perfect and imperfect SIC. The performance gap among two considered users in D2D NOMA network is demonstrated through simulation and analysis.

A Unified QoS and Security Provisioning Framework for Wiretap Cognitive Radio Networks: A Statistical Queueing Analysis Approach

Due to the spectrum-sharing feature of cognitive radio networks (CRNs) and the broadcasting nature of wireless channels, providing quality-of-service (QoS) provisioning for primary users (PUs) and protecting information security for secondary users (SUs) are two crucial and fundamental issues for CRNs. Consequently, in this paper, we establish a unified QoS and security provisioning framework for wiretap CRNs. Specifically, different from the widely used deterministic QoS provisioning method and information-theoretical security protection approach, our established framework, which is built on the theory of statistical queueing analysis, can quantitatively characterize the PU’s QoS and the SU’s security requirements. By adopting the theories of effective capacity and effective bandwidth , we further convert the QoS and security requirements to the equivalent PU’s effective capacity and SU’s effective bandwidth constraints. Following our developed framework, we formulate the nonconvex optimization problem, which aims at maximizing the average throughput of SU subject to PU’s QoS requirement, SU’s security constraint, as well as SU’s average and peak transmit power limitations. Then, we adopt the techniques of convex hull and probabilistic transmission to convert the original nonconvex problem to the equivalent convex problem and obtain the optimal power allocation scheme through the Lagrangian method. Moreover, we also develop a fixed power allocation scheme which is suboptimal but has low complexity. The simulation results are also provided, which demonstrate the impact of the PU’s QoS and the SU’s security requirements on SU’s throughput as well as the advantage of our proposed optimal power allocation scheme over the fixed power allocation scheme and the conventional security-based water-filling policy.

Channel and Bit Adaptive Power Control Strategy for Uplink NOMA VLC Systems

Non-orthogonal multiple access (NOMA) can be an effective solution to the limited bandwidth of light emitting diodes for visible light communication (VLC) systems to support multiuser communication. The current available works for NOMA VLC systems mainly concentrate on downlinks and the existing power allocation algorithms mainly focus on the channel state information and ignore the influence of transmitted signals. In this paper, we propose a channel and bit adaptive power control strategy for uplink NOMA VLC systems by jointly considering the channel state information and the transmission bit rate. Under this adaptive power control strategy, it is proved that the received signal at the photodiode (PD) receiver constitutes a sizeable pulse amplitude modulation constellation and low-complexity maximum likelihood detection is admitted. The simulation results indicate that our proposed adaptive power control strategy outperforms the gain ratio power allocation scheme, fixed power allocation scheme, and time division multiple access scheme.

Outage Performance of NOMA in Cooperative Cognitive Radio Networks With SWIPT

This paper considers the application of non-orthogonal multiple access (NOMA) into cooperative cognitive radio (CR) networks with simultaneous wireless information and power transfer (SWIPT). For NOMA in cooperative CR networks with SWIPT, the cognitive relay harvests the transmission power from the secondary transmitter with power splitting scheme, while the fixed power allocation scheme is used for the NOMA protocol. The closed-form analytical expression of the overall outage probability for the proposed networks is derived, as well as its diversity order at high signal-to-noise ratio (SNR) region is investigated. Furthermore, compared to OMA in cooperative CR networks with SWIPT, the proposed scheme can always achieve the same diversity order, but lower overall outage performance. Compared with NOMA in cooperative CR networks using its own battery for transmission, the SWIPT NOMA in cooperative CR networks will lead to losing a little of the overall outage performance, but without losing the diversity order.

Exact Outage Performance Analysis of Amplify-and-forward-aware Cooperative NOMA

In this paper, new radio access scheme that combines Amplify-and-Forward (AF) relaying protocol and non-orthogonal multiple access (NOMA) system is introduced. In particular, different scenarios for fixed power allocation scheme is investigated. In addition, the outage probability of both weak and strong user is derived and provided in closed-form expressions. Such outage is investigated in high SNR scenario and comparison performance between these NOMA scenarios is introduced. Numerical simulations are offered to clarify the outage performance of the considered scheme if varying several parameters in the existing schemes to verify the derived formulas.

Bound-based power optimization for multi-hop heterogeneous wireless industrial networks under statistical delay constraints

The noticeably increased deployment of wireless networks for battery-limited industrial applications in recent years highlights the need for tractable performance analysis methodologies as well as efficient QoS-aware transmit power management schemes. In this work, we seek to combine several important aspects of such networks, i.e., multi-hop connectivity, channel heterogeneity and the queuing effect, in order to address these needs. We design delay-bound-based algorithms for transmit power minimization and network lifetime maximization of multi-hop heterogeneous wireless networks using our previously developed stochastic network calculus approach for performance analysis of a cascade of buffered wireless fading channels. Our analysis shows an overall transmit power saving of up to 95% compared to a fixed power allocation scheme in case when the service is modeled via a Shannon capacity. For a more realistic set-up, we evaluate the performance of the suggested algorithm in a WirelessHART network, which is a widely used communication standard for industrial process automation applications. We find that link heterogeneity can significantly reduce network lifetime when no efficient power management is applied. Using extensive simulation study we further show that the proposed bound-based power allocation performs reasonably well compared to the real optimum, especially in the case of WirelessHART networks.

Optimal Power Allocation for Underlay-Based Cognitive Radio Networks With Primary User's Statistical Delay QoS Provisioning

Due to the highly-stochastic nature of wireless channels, how to provide efficient delay quality-of-service (QoS) provisioning for primary users (PU) while optimizing the performance of secondary users (SU) is a critically important task for cognitive radio networks (CRN). To address the above issue, we investigate the optimal power allocation strategy for underlay-based CRN with PU's statistical delay QoS protection. Instead of utilizing the widely-used interference power constraint to protect PU's transmission, we aim at satisfying PU's statistical delay QoS requirement characterized by the queue-length bound violation probability. By applying the theory of effective capacity, we further convert PU's queue-length bound violation probability constraint to the equivalent maximum sustainable traffic load requirement. Then, we formulate the optimization problem to maximize SU's average throughput while meeting PU's statistical delay QoS requirement as well as SU's average and peak transmit power constraints, which can be proved as a nonconvex problem. By employing the theories of convex hull and probabilistic transmission, we convert the original nonconvex problem to the equivalent strictly convex problem and then obtain the optimal power allocation strategy, which adapts to both PU's delay QoS requirements and channel conditions. Moreover, we also develop for comparison a fixed power allocation scheme that only adjusts with PU's delay QoS requirements. Simulation results are provided which demonstrate that both the optimal and fixed schemes can flexibly allocate the upperbounded transmit power budget according to PU's delay QoS requirements, but the proposed optimal power allocation strategy can also efficiently exploit the time-varying nature of wireless channels and thus significantly outperforms the fixed power allocation scheme.