Near User Research Articles

Performance analysis of non-linear constellation precoded NOMA over Rayleigh fading channel

Non-orthogonal multiple access (NOMA), an advanced technology for 5G and beyond, has emerged as a promising solution to address the escalating wireless data traffic and enhance the efficiency of wireless systems. Nonlinear constellation precoding (NCP) improves the diversity gain using the maximum distance separable codes property. In this paper, we propose a novel (NCP-NOMA) scheme to enhance the diversity performance of the NOMA system. NCP pre-codes the far user (FU) and near user (NU) data separately and the binary codeword is obtained. The codeword is then subjected to QAM modulation, followed by superimposing the FU and NU codewords for NOMA transmission. This paper investigates the performance of the proposed system in terms of bit error rate (BER) for FU and NU using Monte Carlo simulation and compares the results with the conventional NOMA scheme. The simulation results demonstrate that integrating the NCP encoder achieves a 6dB diversity gain, resulting in a BER of 10−3.

An adaptive relay selection strategy for user cooperation networks based on social-aware

As independent individuals with social attributes, the users for collaborative transmission may have private behaviors such as refusing to relay. By leveraging both near user (NU) and alternative dedicated relay node, an adaptive relay selection strategy based on social-aware is proposed for downlink non-orthogonal multiple access (NOMA) networks. In this framework, a social relationship model is established based on the interest similarity and contact duration between NU and far user (FU). On this basis, the closed form and asymptotic expressions for the outage probability are derived. And the K+1 order diversity gain of the proposed strategy is proved. Simulation results show that the proposed strategy can improve the reliability of communication links and transmission performance.

Secrecy Enhancement of relay cooperative NOMA network based on user behavior

From the perspective of information security, relays exhibit varying levels of trustworthiness when forwarding information. For screening and eliminating the malicious users of cooperative NOMA relay networks, a reputation-based algorithm is proposed, in which the user relays (URs) are categorized into three types based on their behaviors—malicious users, speculative users, and honest users. Meanwhile, in order to minimize information leakage at the relay, cooperative interference signals are transmitted by far user (FU) and near user (NU) via the uplink while the base station (BS) is also transmitting signals to the relay. This approach increases inter-user interference (IUI) to confuse the eavesdropping capability of the relay. To verify the superiority of the proposed scheme, an asymptotic lower bound expression for the ergodic secrecy rate (ESR) of the downlink is derived to characterize the secrecy performance of the proposed scheme. Furthermore, in the case of limited system power, a joint power allocation algorithm based on the golden section method is also proposed to further enhance the security performances of the system. The simulation results validate the accuracy of the derived analysis results and demonstrate that the proposed scheme has a significant improvement in the ESR compared with the traditional scheme.

Blue-LED based electrical and optical PD-NOMA systems: Characterization in underwater environment

This paper presents the characterization of blue LED-based two different power domain non-orthogonal multiple access(PD-NOMA)-assisted underwater optical wireless communication (UOWC) systems, which use on-off keying (OOK) signal, in an emulated seawater channel. We first characterize the electrical PD-NOMA (EPD-NOMA) system having different power allocation ratios (PAR). In the next study, we characterize two configurations of optical PD-NOMA (OPD-NOMA) systems. The first configuration of OPD-NOMA uses LEDs positioned over a 2-D plane at the transmitter. Conventional OPD-NOMAis found to maintain the desired PAR only at a particular location at the receiver. We next propose, design, and characterize a new architecture of OPD-NOMA transmitter, in which LED lights are combined to produce a collinear OPD-NOMA beam. For collinear beam OPD-NOMA transmitter, the PAR value is maintained within 0.1 of its targeted value over viewing angle of ±4 degrees. Both EPD-NOMA and Collinear-beam OPD-NOMA systems with 10Mbps data rate are characterized using two different users at distances of 2.5 m (far user (FU)) and 1 m (near user (NU)) in tap water and in an emulated seawater channel. The received optical power of approximately −30.2 dBm(−30 dBm)is found to produce a pre-FEC BER of 10−3 in EPD-NOMA (collinear beam OPD-NOMA)for both the users and in tap water channels at a data rate of 10 Mbps with a PAR value of 0.5. For the saline water channel, corresponding values are −29.85 dBm (−29.7 dBm) for the EPD-NOMA (collinear beam OPD-NOMA) system at a 10 Mbps data rate with PAR =0.5.

Energy-efficient resource allocation and user grouping for multi-IRS aided MU-MIMO system

In this paper, we consider a multiple-intelligent reflecting surface (IRS)-aided multi-user multiple-input-multiple-output (MU-MIMO) down-link communication system, wherein a base station (BS), equipped with multiple antennas, serves massive single-antenna users. In order to mitigate high inter-user interference, we divide all the users into a single near-user (NU) group and multiple cell-edge user (CEU) groups based on their connection with BS. In particular, we assign a single IRS for each CEU group such that the BS communicates and serves the set of CEUs using their corresponding IRS. Subsequently, we formulate a problem of energy-efficient resource allocation design subject to optimal beamforming design at BS and multiple IRS under given power constraints. Due to the non-convexity of the formulated resource allocation problem, we proposed two different alternating optimization frameworks which solve the joint optimization problem based on 1) minimum mean square error (MMSE) and Riemannian conjugate gradient (RCG) and 2) fractional programming and successive convex approximation techniques for active beamforming vectors at the BS and passive beamforming vectors for IRSs, respectively. Simulation results confirm that the MMSE-RCG-based resource allocation design attains fast convergence when compared to sequential fractional programming (SFP) based solution. Moreover, the MMSE-RCG attains better energy efficiency whereas the SFP renders better spectral performance. Nevertheless, both the proposed solution achieve 70%–80% better performance than random phase-shift settings.

Performance of Novel Adaptive Schemes for Cognitive Full-Duplex Relaying-Based Downlink Cooperative NOMA

In this paper, we demonstrate that due to large variations in link signal-to-noise-ratios, the key to good performance in underlay cooperative non-orthogonal multiple access (CNOMA) is intelligent adaptation. First adaptation involves switching between the cooperative mode (CM) and the non-cooperative mode (NCM). While a full-duplex near user (NU) assists the multiple-antenna base-station in communication to a far user (FU) in CM, allowing the NU to switch to NCM ensures that its performance is same as in a network without the FU. The second adaptation relates to transmit antenna selection. In the first scheme, the NOMA power allocation parameter (NPAP), and the interference temperature limit (ITL) apportioning parameter (ITLAP) depend on channel statistics. The third adaptation (presented for the first time in literature) used in two other proposed schemes involves selection of inter-dependent NPAP and ITLAP based on channel state information (CSI). The fourth adaptation used in the third proposed scheme relates to use of CSI-dependent ITL, which is shown to dramatically improve performance. Optimum choices of NPAP and ITLAP are expressed in closed-form for all three schemes, and performance with these is analyzed (and validated by computer simulations) assuming imperfect successive interference cancellation and residual self-interference cancellation at the NU.

Effective capacity analysis of NOMA with transceiver hardware and SIC imperfections

In this paper, we study the performance of the non-orthogonal multiple access (NOMA) networks. By considering two practical factors of residual hardware impairments (RHIs) and imperfect serial interference cancellation (ipSIC), we adopt effective capacity as a metric to characterize the effects of latency on the performance of NOMA networks and derive the analytical expressions of the effective capacity for the near user (NU) and the far user (FU). For further insights, we provide asymptotic analysis by invoking high signal-to-noise ratio (SNR) slope and high SNR power offset. Numerous analytical and simulated results have shown that: (1) The effective capacities of NU and FU are positively proportional to the SNR at low SNR, while at high SNR, the effective capacities approach to the constants; (2) Comparing the two users of the considered NOMA network, the effective capacity of NU shows pronounced advantages under the requirements of low quality of service. (3) RHIs are detrimental to the effective capacities of both NU and FU, especially for the high SNR regime. (4) The effective capacity of NU is limited by ipSIC.

Reconfigurable Intelligent Surfaces Assisted Hybrid NOMA System

In a device-to-device communication scenario, the number of far users (FUs) is higher than the near users (NUs) in each cluster. In such a scenario, the paired NUs and FUs communicate through non-orthogonal multiple access (NOMA), and the remaining FUs communicate through orthogonal multiple accesses (OMA) schemes. This system is called as hybrid-NOMA (HNOMA). This letter proposes a reconfigurable intelligent surface (RIS)-assisted HNOMA system to enhance the energy and spectral efficiencies of the conventional HNOMA. In this proposed RIS-assisted HNOMA (PR-HNOMA) system, the NU is paired with multiple FUs with allocations of different bandwidths. The PR-HNOMA system’s sum rate is maximized by considering joint beamforming at BS and RIS via semidefinite relaxation (SDR) and alternatively optimization (AO) techniques. Further, the sum rate of the PR-HNOMA under imperfect successive interference cancellation (ISIC) is analyzed and compared with different NOMA and OMA schemes. Simulation results show that the PR-HNOMA achieves better sum-rate performance than the conventional RIS assisted HNOMA (R-HNOMA), and RIS assisted NOMA (R-CNOMA), and OMA (R-OMA).

A Three-Phase CDRT Strategy Based on Successive Relay for Smart Grid

In the vision of the future smart grid, the communication is often featured by wide range, massive connect, and low latency, which poses new requirements on the reachable distance and spectral efficiency of wireless communication. In this regard, this paper studies ergodic capacity enhancement by applying successive relay (SR) technology to a non-orthogonal multiple access (NOMA) based Coordinated Direct and Relay transmission (CDRT) system, where a base station (BS) communicates with a near user (NU) directly while communicating with a far user (FU) with the help of a group of relays. We design a novel three-phase CDRT strategy based on SR technology to overcome the half-duplex (HD) constrain without introducing additional noise. The proposed strategy can improve the spectral efficiency while expanding the communication coverage, which to some extent improves the communication quality of the edge users of the smart grid and reduces the communication delay. To analyze the performance of the proposed three-phase CDRT strategy, an exact and closed-form expression for ergodic capacity of the NU, the FU, and the whole system is derived. Finally, the numerical and simulation results validate the analysis results and show that the proposed strategy can improve the ergodic capacity of FU without reducing the capacity scaling of NU.

UAV-Enabled Non-Orthogonal Multiple Access Networks for Ground-Air-Ground Communications

Both unmanned aerial vehicle (UAV) and non-orthogonal multiple access (NOMA) have gradually become promising technologies for the fifth generation (5G) driven green Internet-of-Things (IoT) networks on account of their unique advantages of massive connections, higher spectral efficiency and flexibility. Motivated by this, we propose a 3-hop NOMA UAV-aided green communication network framework, where UAVs serve as aerial relays to support two groups of ground users. A stochastic geometry approach is invoked to model the spatial positions of the two group users. Under the realistic assumption, imperfect successive interference cancelation (ipSIC) is considered. To evaluate the performance of the proposed framework, theoretical expressions are derived to facilitate the outage performance evaluation of the far user (FU) and the near user (NU). Moreover, the asymptotic behaviors for the outage probability (OP) of both the FU and the NU in the high signal-to-noise ratio (SNR) regime are explored by obtaining diversity orders. Finally, the system throughputs under the delay-limited transmission mode are investigated. Numerical results confirm that: 1) For uplink transmission, there exist outage floors for the OP of both ipSIC and perfect SIC (pSIC) due to interference from the NU; 2) For downlink transmission, an outage floor exists for the OP of the NU under the condition of ipSIC; 3) For uplink NOMA/orthogonal multiple access (OMA) transmission, the outage performances of both the FU and the NU with NOMA outperform OMA in the low SNRs, while OMA has better performance in the high SNR regime; 4) For downlink NOMA/OMA, the outage performances of both the FU and the NU under pSIC outperform OMA.

Adaptive Multiuser Cooperative NOMA Scheme With Energy Buffer-Aided Near-Users for High Spectral and Energy Efficiency

In this article, a multiuser cooperative nonorthogonal multiple access (NOMA) network is considered. In order to improve their battery lifetime, the near-user (NU) Internet of Things (IoT) nodes relay information to the far-user (FU) IoT nodes using only the energy harvested from the ambience. The harvested energy at all the NU IoT nodes is stored in energy buffers. To improve the throughput performance, the best NU and best FU (BNBF) user selection scheme is employed. Moreover, unlike conventional orthogonal multiple access (OMA) networks, an adaptive NOMA network is considered in this article that switches between direct NOMA, NOMA with relaying, and OMA modes to maximize throughput. To improve accuracy and reduce the computational complexity, the energy buffer states at the NU IoT nodes are modeled using a continuous state-space Markov chain (CSMC) instead of discrete state-space Markov chain (DSMC). We derive the limiting distributions of the stored energy in energy buffers with either the best effort policy (BEP) or the on–off policy (OOP) applied for buffer energy management. Expressions for throughput are derived for both harvest-store-use (HSU) and harvest-use (HU) architectures. The Monte Carlo simulations are used to validate the derived analytical expressions.

Capacity enhancement for cooperative NOMA systems by successive user relaying

This paper proposes a novel multi-phase coordinated direct and user-assisted transmission (MP-CDUAT) strategy for a non-orthogonal multiple access system consisting of a base station (BS), K near users (NUs) and a far user (FU). In the first phase, the BS directly serves an opportunistically scheduled NU. For the rest phases, an NU scheduling scheme is developed to jointly select two NUs in each phase, where one receives desired message from the BS and the other one serves as a relay to help FU's receiving. To evaluate the performance of the proposed MP-CDUAT strategy, the analytical expression of the ergodic capacity (EC) for both NU and FU is derived. With the derived results, the EC scaling of NU and FU are, respectively, derived in the high ρ regime, where the EC scaling of FU increases with the transmission phase, while the EC scaling of NU remains the same. Finally, the numerical and simulation results show that (a) our proposed strategy can improve the performance of FU without affecting the capacity scaling of served NUs; (b) the performance gain achieved by the proposed strategy is more prominent with the increasing number of the transmission phases.

A Coordinated Direct AF/DF Relay-Aided NOMA Framework for Low Outage

This paper investigates the performance of a new framework for low-outage downlink non-orthogonal multiple access (NOMA) using a coordinated direct and relay transmission (CDRT) scheme with direct links to both the near-user (NU) and the far-user (FU). Both amplify-and-forward and decode-and-forward relays are considered. In this framework, the NU combines the signals from base-station and relay at each stage of the successive interference cancellation (SIC) to attain good outage performance. For both NU and FU, the expressions for outage probability and throughput are derived in closed form. We also derive the high-SNR expressions for the outage probability to demonstrate that with the proposed framework, both users harness a diversity of two without feedback bits (this is the only framework to achieve this). We demonstrate that the choice of power allocation coefficient and target symbol rates is crucial to maximizing the NU throughput while ensuring a desired target FU throughput. We demonstrate that CDRT with the proposed framework outperforms known schemes in terms of outage probability, sum throughput, and energy efficiency. Moreover, we also show that optimal rate selection is important to maximize the energy efficiency. Monte Carlo simulations validate the accuracy of the derived analytical expressions.

Device-to-Device Aided Cooperative NOMA Transmission Exploiting Overheard Signal

A novel device-to-device (D2D) aided cooperative non-orthogonal multiple access (NOMA) scheme (termed as D2D-SG-NOMA) is proposed, where two similar gain (SG) near users (NUs) with the capability of D2D communication and one far user (FU) are served within two time slots. The NOMA pair is formed with a NU and the FU. The paired NU is employed as a decode-and-forward relay to assist FU. Contrarily, the unpaired NU can receive signals simultaneously from the base station (BS) and the other NU during the second time slot. Two different scenarios (i.e., S₁ and S₂) are investigated insightfully. In S₁, the direct link between the BS and FU does not exist, whereas the direct link between the BS and FU exists in S₂. The delay-tolerant capacity (DTC), outage probability, diversity order, and delay-limited capacity are investigated along with analytical formulation. The D2D-SG-NOMA achieves an increase of around 66% and 85% in DTC at 0 dB signal-to-noise (SNR) under S₁ and S₂, respectively than the existing NOMA scheme with successive relaying (termed as SR-NOMA). Contrarily, a reduced DTC improvement (i.e., around 3% and 10% in S₁ and S₂, respectively) is obtained at 40 dB SNR due to increased inter-symbol interference.

Cooperative Mode Switching-Based Cognitive NOMA With Transmit Antenna and User Selection

The paper presents performance analysis of a multiuser Cooperative Non-Orthogonal Multiple Access (CNOMA) network that is underlay to a primary network. A selected secondary Full-Duplex (FD) Near User (NU) cooperates with a selected secondary Far User (FU) by apportioning the Interference Temperature Limit (ITL) with an ITL Apportioning Parameter (ITLAP). This Cooperative Mode (CM) is exercised only when NU meets its own performance criteria, else the network switches to a Non-Cooperative Mode (NCM). The network is therefore made adaptive in such a way that performance of the NU is same as in a network without the FU. Performance of the network is further improved using Maximum Transmit Power-based Transmit Antenna Selection (MTP-TAS), Best NU-Best FU (BNBF) selection, and optimal power allocation, thereby also motivating NOMA even in power-constrained underlay environments where transmit powers are not always high. The selection mechanisms are designed in a way that additional overheads for Channel State Information (CSI) estimation and feedback are not imposed. Analytical expressions for outage probability are presented for both end users, assuming only statistical knowledge of channel gains under the assumption of imperfect Successive Interference Cancellation (SIC) at the NU. Outage minimizing optimal values of the NOMA Power Allocation Parameter (NPAP) and ITLAP are derived that minimize FU outage. Simulations validate the derived expressions, and demonstrate superiority of the proposed scheme over FD NU-based conventional NOMA as well as conventional OMA signalling.

On the Comparison of Optimal NOMA and OMA in a Paradigm Shift of Emerging Technologies

Non-orthogonal multiple access (NOMA) is a better multiple access technique than orthogonal multiple access (OMA), precisely orthogonal frequency division multiple access (OFDMA) scheme, at the conceptual level for fifth-generation (5G) networks and beyond 5G (B5G) networks. We investigate the potentials of the schemes by comparing the proposed NOMA scheme with the traditional cooperative communication NOMA (CCNOMA) scheme, rather than the comparison between NOMA and OMA only. To probe the effectiveness of NOMA as a multiple access technique, we propose a novel NOMA scheme considering two adjacent BSs with a special design of the transceiver architecture. The proposed scheme provides a reasonable data rate to both near user (NU) and far user (FU) without compromising the quality of service (QoS) to anyone of them. The conclusive analyses on the optimization framework of multi-user sum rate, capacity, transmit power, spectral efficiency (SE), and energy efficiency (EE) trade-off for NOMA and OFDMA schemes have been established to a succession of derivations. Under the analytical optimization framework, we also prove quite a few properties for them. Simulation results confirm the theoretical findings and show that the two schemes can efficiently approach the optimal power allocation, minimization of power consumption, and optimal SE-EE trade-off, and the proposed NOMA scheme provides comparatively better data sum rates than the baseline OMA scheme.

Intelligent reflecting surface‐assisted downlink nonorthogonal multiple access systems

SummaryRecently, intelligent reflecting surface (IRS)‐based communication systems are analyzed for 6G and beyond wireless networks. In this paper, we propose an IRS‐assisted downlink nonorthogonal multiple access (NOMA) system by considering separate IRS for near users (NUs) and far users (FUs). The optimal power allocation strategy among NUs and FUs is formulated for the proposed downlink IRS‐NOMA system. The symbol error probability and the sum‐rate performance of the IRS‐NOMA system are analyzed. Further, the impact of the modulation order, the number of reflecting surfaces, the number of phase shifts of reflected signals on symbol error, and power allocation between NU and FU is studied.

A Comparative Study of Perfect and Imperfect SIC in Downlink PD-NOMA based on Sharing Bandwidth

In this paper, a scheme for sharing bandwidth-non-orthogonal multiple access (SB-NOMA) based on coordinated multi-point (CoMP) is proposed to improve total sum capacity and user capacity. The proposed algorithm is implemented in a cellular network platform, and the performance is analysed via two cases. First, the network performance is evaluated considerning both channel conditions and interference effects, which is addressed as the worst-case condition. The total network capacity is evaluated assuming Channel Estimation Error (CEE) and Imperfect Successive Interference cancelation (SIC). Second, the network is tested assuming ideal case condition materialized by canceling the effect of inter-channel interference (ICC) of the Base Station (BS) on Near User (NUE). The simulation results show that the capacity increases for SB-NOMA with installed by increasing the number of Cooperative BS (CBSs), where (2bits/Hz/s) is the gain in total capacity that is achieved by increasing the CBSs by one. Moreover, power allocation to the proposed scheme shown (0.15 - 0.85) represents the best value for maintaining capacity achievement.

Performance analysis of power-splitting relaying protocol in SWIPT based cooperative NOMA systems

This paper investigates a relay assisted simultaneous wireless information and power transfer (SWIPT) for downlink in cellular systems. Cooperative non-orthogonal multiple access (C-NOMA) is employed along with power splitting protocol to enable both energy harvesting (EH) and information processing (IP). A downlink model consists of a base station (BS) and two users is considered, in which the near user (NU) is selected as a relay to forward the received signal from the BS to the far user (FU). Maximum ratio combining is then employed at the FU to combine both the signals received from the BS and NU. Closed form expressions of outage propability, throughput, ergodic rate and energy efficiency (EE) are firstly derived for the SWIPT based C-NOMA considering both scenarios of with and without direct link between the BS and FU. The impacts of EH time, EH efficiency, power-splitting ratio, source data rate and distance between different nodes on the performance are then investigated. The simulation results show that the C-NOMA with direct link achieves an outperformed performance over C-NOMA without direct link. Moreover, the performance of C-NOMA with direct link is also higher than that for OMA. Specifically, (1) the outage probability for C-NOMA in both direct and relaying link cases is always lower than that for OMA. (2) the outage probability, throughput and ergodic rate vary according to beta, (3) the EE of both users can obtain in SNR range of from -10 to 5 dB and it decreases linearly as SNR increases. Numerical results are provided to verify the findings.

Simultaneous Cellular and D2D Communications Exploiting Cooperative Uplink NOMA

A novel device-to-device (D2D) aided uplink transmission scheme exploiting non-orthogonal multiple access (termed as D2D-UNOMA) is proposed and investigated. In D2D-UNOMA, two similar gain near users (NUs) and a far user (FU) can transmit their information to the base station (BS) in two time slots. The NUs can directly communicate with the BS, whereas the FU requires assistance of one of the NUs to facilitate the communication. In addition, as part of D2D communications, one of the NUs can transmit to the other NU in the first phase, whereas the FU can transmit to a NU in the second phase. The performance of D2D-UNOMA is studied in terms of ergodic rate along with analytical formulation. Through numerical results, it is demonstrated that the proposed D2D-UNOMA can ameliorate the ergodic sum rate significantly compared to the conventional orthogonal multiple access.