Near User Research Articles

Wireless Powered Mobile Edge Computing With NOMA and User Cooperation

Integrating mobile edge computing (MEC) and wireless power transfer (WPT) is a promising technology that provide sustainable energy supply and cloud-like computing services at network edge. In this article, we propose a non-orthogonal multiple access (NOMA)-aided user cooperative scheme in a three-node WPT-MEC system, which is composed of a far user (FU), a near user (NU) and an access point (AP). What is innovative is that the FU employs NOMA so that it can simultaneously offload data to NU and AP which can overcome the doubly near-far effect of FU. We design an energy consumption minimization problem by jointly optimizing offloading time, task allocation and computation frequency. The optimal solution for the non-convex problem is obtained by some ingenious mathematical methods. Simulations are conducted to demonstrate that the proposed joint design has obvious improvement over other benchmark schemes.

Robust Secure Design for RIS-Aided NOMA Network Against Internal Near-End Eavesdropping

The reconfigurable intelligent surface (RIS) aided non-orthogonal multiple access (NOMA) network is applied to improve spectral efficiency and energy efficiency of wireless systems. Due to the incorporation of NOMA, RIS-aided NOMA system suffers from physical layer security (PLS) problem when an internal near user (NU) is the eavesdropper. In this case, it is difficult to always guarantee positive secrecy rate. Therefore, a scheme of artificial noise (AN) cooperative jamming and beamforming design is proposed against internal eavesdropper for RIS-aided NOMA in this paper. It is proved theoretically that the positive secrecy rate can be guaranteed if providing sufficient power. In addition, the power allocation of base station is further studied to minimize the total power consumption under the constraints of data rate and secrecy rate, and the closed-form solutions are achieved. Simulation results show that the performance of the proposed scheme is superior to the existing solutions.

Device-to-Device Aided Cooperative Relaying Scheme Exploiting Spatial Modulation: An Interference Free Strategy.

In this paper, a novel interference free dual-hop device-to-device (D2D) aided cooperative relaying strategy (CRS) based on spatial modulation (SM) (termed D2D-CRS-SM) is proposed. In D2D-CRS-SM, two cellular users (e.g., a near user (NU) and a relay-aided far user (FU)) and a pair of D2D transmitter (D)-receivers (D) are served in two time-slots. Two different scenarios are investigated considering information reception criteria at the NU. Irrespective of the scenarios, the base station (BS) exploits SM to map information bits into two sets: modulation bits and antenna index, in phase-1. In the first scenario, the BS maps FU information as the modulation bits and NU information as antenna index, whereas modulation bits correspond to NU information and the antenna index carries FU’s information in scenario-2. The iterative-maximum ratio combining (i-MRC) technique is then used by NU and D to de-map their desired information bits. During phase-2, D also exploits SM to forward FU’s information received from BS and its own information bits to the D2D receiver D. Then, FU and D retrieve their desired information by using i-MRC. Due to exploiting SM in both phases, interference free information reception is possible at each receiving node without allocating any fixed transmit power. The performance of D2D-CRS-SM is studied in terms of bit-error rate and spectral efficiency considering M-ary phase shift keying and quadrature amplitude modulation. Finally, the efficiency of D2D-CRS-SM is demonstrated via the Monte Carlo simulation.

Cooperative Wireless-Powered NOMA Relaying for B5G IoT Networks With Hardware Impairments and Channel Estimation Errors

Massive connectivity and limited energy are main challenges for the beyond 5G (B5G)-enabled massive Internet of Things (IoT) to maintain diversified Qualify of Service (QoS) of the huge number of IoT device users. Motivated by these challenges, this article studies the performance of cooperative simultaneous wireless information and power transfer (SWIPT) nonorthogonal multiple access (NOMA) for massive IoT systems. Under the practical assumption, residual hardware impairments (RHIs) and channel estimation errors (CEEs) are taken into account. The communication between the base station (BS) and two NOMA IoT device users is realized through a direct link and the assistance of multiple relays with finite energy storage capability that can harvest energy from the BS. Aiming at improving the system performance, an optimal relay is selected among K relays by using the partial relay selection (PRS) protocol to forward the received signal to the two NOMA IoT device users, namely, the far user (FU) and near user (NU). To evaluate the system performance, exact analytical expressions for the outage probability (OP) are derived in closed form. In order to get a better understanding of the overall system performance, we further undertake diversity order analyses by deriving asymptotic expressions for the OP in the high signal-to-noise ratio (SNR) regime. In addition, we also investigate the energy efficiency (EE) of the considered system, which is a crucial performance metric in massive IoT systems so that the impact of key system parameters on the performance can be quantified. Finally, the optimal power allocation scheme to maximize the sum rate of the considered system in the high SNR regime is also designed. Numerical results have shown that: 1) hardware impairment parameter has a deleterious effect on system performance while the channel estimation parameter is always beneficial to the OP; 2) the expected performance improvements obtained by the user of PRS protocol are enhanced by increasing the number of relays; and 3) the proposed power allocation scheme can optimize the sum-rate performance of the considered system.

Non-Orthogonal Multiple Access With Coordinated Direct and User-Assisted Transmission

In this letter, we investigate the coordinated direct and user-assisted transmission in a non-orthogonal multiple access (NOMA) system. By integrating the coordinated direct transmission into user-cooperative NOMA, one far user (FU) is served along with two near users (NUs) that are opportunistically selected from a pool of K NUs. For the considered system, an NU scheduling strategy is proposed to minimize the outage probabilities of the NUs whilst ensuring the performance requirement of the FU. Exact and asymptotic outage probability of each served user is derived. Results demonstrate that the FU and one of the scheduled NUs can both achieve the full diversity order K, and the other scheduled NU achieves a diversity order equal to ${K}-1$ or K, depending on the transmit rate of the base station.

NOMA With Battery-Assisted Energy Harvesting Full-Duplex Relay

This paper investigates the performance of a non-orthogonal multiple access (NOMA) network with simultaneous wireless information, and power transfer (SWIPT) based battery-assisted energy harvesting (EH) full-duplex relay (FDR). In each signalling interval, the base-station communicates directly to a near user (NU), and through an EH FDR to a far user (FU). Considering the power-splitting (PS) protocol with a non-linear EH model, we derive closed-form expressions for the NU, and FU outage probabilities. We also demonstrate how the battery energy, and PS parameter can be chosen to maximize the FU throughput while ensuring a desired NU throughput when there is imperfect interference cancellation at the NU. Computer simulation results validate the accuracy of the derived expressions, and demonstrate that augmenting the harvested energy with a small quantum of the relay's battery energy can considerably improve the FU performance.

Enhancing Secrecy for NOMA Untrusted Relay Networks With User Scheduling and Jamming

This letter investigates secure transmission for a cooperative non-orthogonal multiple access (NOMA) network consisting of multiple near users (NUs), a far user (FU) and an untrusted relay. In each slot, the base station serves an opportunistically scheduled NU along with the FU by using NOMA. We design a cooperative jamming based secure transmission strategy to prevent the information leakage of the NU and the FU against the untrusted relay. A novel NU selection scheme is proposed to enhance the secrecy performance, while guaranteeing the scheduling fairness among all NUs. Considering that all channels of NUs experience independent but non-identically distributed Rayleigh fading, the closed-form average secrecy rate and its scaling law are theoretically derived for the FU and the scheduled NU. Finally, simulations are provided to validate the secrecy enhancement and the scheduling fairness of the proposed scheme.

Opportunistic Adaptive Non-Orthogonal Multiple Access in Multiuser Wireless Systems: Probabilistic User Scheduling and Performance Analysis

This paper designs a novel opportunistic adaptive non-orthogonal multiple access (OA-NOMA) strategy, where a base station (BS) employs NOMA to serve a near user (NU)-far user (FU) pair opportunistically scheduled from $M$ NUs and $K$ FUs. In particular, the NOMA transmission to the scheduled NU-FU pair adaptively operates in one of two modes: Direct NOMA mode , in which the BS directly serves the scheduled NU-FU pair with using NOMA; Cooperative NOMA mode , in which the scheduled NU receives the messages intended by both scheduled users from the BS, and then forwards the message intended by the scheduled FU. For the OA-NOMA strategy, a scheduling candidate acquisition method and a probabilistic user pair scheduling scheme are proposed to guarantee the transmission reliability and improve the scheduling fairness, respectively. To evaluate the scheduling fairness, we develop a max-min fairness criterion and show that the OA-NOMA strategy approximately achieves max-min fairness. The reliability of the OA-NOMA strategy is also evaluated in terms of outage probability and diversity order. For the outage probability, we derive an approximate expression and numerically verify its tightness. For the diversity order, we show that the proposed OA-NOMA strategy achieves a diversity order of $M$ .

A Hybrid Multiple Access Scheme via Deep Learning-Based Detection

In this article, we propose an uplink hybrid multiple access scheme (HMAS) in order to support a highly overloaded multiuser system. In HMAS, for a fixed $K$ -orthogonal resources, there are $K$ -near users (NUs) adopting orthogonal frequency division multiple access and $J>K$ far users (FUs) adopting sparse code multiple access for uplink transmission. To improve the performance of HMAS, we propose two deep learning-based detectors via deep neural network (DNN) models, one for NUs symbol detection, and the other for FUs symbol detection. Both DNN models are trained offline via simulated data and-then-applied for online symbol detection. Simulation results demonstrate the effectiveness of HMAS in terms of symbol error rate performance over Rayleigh fading channels. In particular, it shows that the HMAS with DNN-based detections outperforms significantly the one using conventional message passing algorithm and successive interference cancellation-based detection.

ARQ Assisted Short-Packet Communications for NOMA Networks Over Nakagami-m Fading Channels

Non-orthogonal multiple access (NOMA) is expected as a promising technology for satisfying massive connectivity requirements in Internet of Things (IoT). Besides, short-packet communications are a notable characteristic in IoT for low delay transmissions or massive machine-type communications (MTC). The co-channel interference from NOMA and packet error caused by finite packet will reduce system performance. In view of this, this article adopts automatic repeat request (ARQ) to assist short-packet communications for NOMA networks where a near user (NU) and a far user (FU) are paired to share the same non-orthogonal communication resources. The closed-form expressions for average packet error rate (APER) and effective throughput (ET) of both NU and FU are derived over Nakagami-$m$ channels. For gaining an insight into system performance, the performance of the scheme without ARQ is also studied. Results show that ARQ improves APER for both NU and FU, and an optimal power allocation factor or packet length exists for achieving higher ET.

Joint Power Allocation and User Scheduling for Device-to-Device-Enabled Heterogeneous Networks With Non-Orthogonal Multiple Access

Device-to-device (D2D) communications-enabled dense heterogeneous networks (HetNets) with non-orthogonal multiple access (NOMA) are promising solutions to meet the high-throughput requirement and support massive connectivity. In this paper, we propose a novel framework on the D2D-enabled HetNets with NOMA, where small cells underlay the uplink spectrum of macrocells to make full use of spectrum resources, NOMA technique is invoked to serve more downlink users simultaneously, and D2D-enabled multi-hop transmission is established to enhance signal reception of the far users (FUs) on cell edge. We investigate joint power allocation and user scheduling to maximize the ergodic sum rate of the near users (NUs) in the small cells while guaranteeing the quality-of-service requirements of the FUs and the macro-cell users. The optimal solution to this problem is complexity-prohibitive especially with large numbers of users and small base stations (SBSs) because it requires an exhaustive search over all possible combinations of SBSs, NUs, and FUs. To simplify the solution, we develop a two-step approach by decomposing the original problem into a power allocation problem and a user scheduling problem. We derive the closed-form solution of the power allocation problem via analyzing the objective function and constraints. The user scheduling problem is a joint user pairing and access point assignment problem. To solve it, we propose an SBS-NU-FU matching algorithm to obtain a near-optimal one-to-one three-sided matching of SBSs, NUs, and FUs. The simulation results show that the two-step method gets around 95% of the system throughput of the optimal one and can significantly improve the spectral efficiency of the D2D-enabled HetNets.