Downlink Cooperative Non-orthogonal Multiple Access Research Articles

Outage probability analysis of a cooperative NOMA UWOC system with multiuser scheduling under weak oceanic turbulence.

A downlink cooperative non-orthogonal multiple access (NOMA) multiuser underwater wireless optical communication (UWOC) system with a greedy scheduling scheme has been proposed for the Internet of Underwater Things. In particular, the near user plays as a relay to assist the far user, and both decode-and-forward and amplify-and-forward relaying protocols are considered. Relying on the Gauss-Laguerre quadrature formula, the analytical expressions for the outage probability of users are derived considering the degrading effects of the underwater channel, namely, absorption, scattering, and turbulence-induced fading. The outage performance is further analyzed systematically under different water types, targeted data rates, the number of users, the receiver aperture size, and the power allocation coefficient. Numerical results demonstrate that the performance of the far user can be improved by the proposed cooperative NOMA technology. Moreover, the proposed cooperative NOMA system performs better compared with both conventional OMA and non-cooperative NOMA systems. Monte Carlo simulation results are presented to confirm the accuracy of derived expressions, which have a tight agreement with analytical results.

Enhancement of outage probability for down link cooperative non-orthogonal multiple access in fifth-generation network

<span lang="EN-US">Future wireless networks are expected to face several issues, but cooperative non-orthogonal multiple access (C-NOMA) is a promising technology that could help solve them by providing unprecedented levels of connection and system capacity. In this regard, the influence of the power location coefficient (PLC) for remote users adopting multiple-input-multiple-output (MIMO) and massive MIMO has been explored to provide effective performance. The goal of this study is to design fifth-generation (5G) downlink (DL) NOMA power domain (PD) networks with a variety of distances and PLCs for remote users and then to compare their outage probability (OP) performance versus signal to noise ratio (SNR). As a novel approach to improving OP performance rate and mitigating the influence of the PLC for remote users, DL C-NOMA is combined with 16×16, 32×23, and 64×64 MIMO and 128×128, 256×256, and 512×512 massive MIMO. The results were obtained that the 64×64 MIMO improves the OP for the remote user by 65.0E-03, while the 512×512 massive MIMO achieved an improvement that reaches 1.0E-06 for the PLC of 0.8 at SNR of 14 dB. The Rayleigh fading channels and MATLAB simulation tools were utilized to carry out the study work.</span>

On Performance of NOMA-Based Wireless Powered Communication Networks Assisted With Power Beacons and PPP Distributed IN

This work studies the performance of power beacon (PB) assisted downlink cooperative non-orthogonal multiple access (NOMA) in a wireless powered communication network (WPCN) with realistic non-linear energy harvesting (EH) model. The paper proposes an analytical methodology for improving performance at blocked user at the edge of network via an intermediate node (IN). IN deployed in the coverage area of the base station (BS), acts as decode-and-forward relay to perform cooperative transmission. IN assists the BS in communicating with the blocked Internet of Things (IoT) device after harvesting energy from PB mounted on the BS. IN employs NOMA to serve IoT devices with heterogeneous quality of service requirements in order to achieve higher spectral and energy efficiency. A practical non-linear EH model is employed at IN to power the cooperative transmission to the IoT devices. The performance of the proposed scheme is compared with the system employing orthogonal multiple access and it is shown that the proposed scheme attains improved performance in terms of outage probability, system throughput, and energy efficiency.

Performance Analysis of Full-Duplex Cooperative NOMA Short-Packet Communications

This paper presents the performance analysis for the two-user downlink cooperative non-orthogonal multiple access (C-NOMA) short-packet communication (SPC) over Rayleigh channels. The near user acts as a relay, which operates in full-duplex (FD) mode and employs decode-and-forward protocol, to forward the information to the far user. Two kinds of residual self-interference (RSI) models, which are modeled as being free of fading and following Rayleigh fading, are considered. We first derive the approximate closed-form expressions of average block error rate (BLER) at both users under these two RSI models. Then, simulations are provided to verify the validity of our theoretical analysis. Finally, we evaluate the BLER performance difference between long-packet and short-packet transmissions for FD C-NOMA and that between FD relaying and half-duplex (HD) relaying. The analysis and simulation results show that, for ultra-reliable and low-latency communication, we can use RSI link modeled as being free of fading to simplify the system analysis. Furthermore, compared to long-packet communication, for FD C-NOMA SPC have a narrow range of power allocation to achieve high-reliable transmission, and because BLER outperformance of FD relaying over HD relaying degrades when the RSI signal becomes strong, the optimal duplex mode for FD C-NOMA SPC is determined by the RSI signal and the target BLERs at both users.

Security Optimization of Cooperative NOMA Networks With Friendly Jamming

We investigate physical layer security of a downlink cooperative non-orthogonal multiple access system with an untrusted relay. A friendly jammer (FJ) is employed in order to improve the secrecy sum rate. Aiming at maximizing the secrecy sum rate by optimizing the power allocation at both the source and the FJ, an optimization problem is formulated and solved iteratively by using alternating optimization method. Specifically, the problem is decoupled into two sub-problems, each of which is optimally solved. Moreover, the secrecy sum rate of the proposed system with imperfect channel state information is studied. Finally, simulation results validate the effectiveness of the proposed FJ based schemes.

On the Secrecy Outage Performance of Cooperative NOMA-Assisted Hybrid Satellite-Terrestrial Networks

This paper investigates the secrecy outage performance of a downlink cooperative nonorthogonal multiple access- (NOMA-) assisted hybrid satellite-terrestrial network, where a satellite source communicates with two terrestrial users based on NOMA, in the presence of a terrestrial eavesdropper. We assume that there is no direct link between the satellite source and the far terrestrial user, and the near terrestrial user acts as a relay to forward the information to the far terrestrial user. The near user is assumed to support both half-duplex mode and the full-duplex mode for information relaying. We derive the closed-form exact expressions for the secrecy outage probability (SOP) of the near user, as well as the closed-form approximate expressions for the SOP of the far user based on the Gaussian-Chebyshev quadrature. Theoretical results are validated by conducting simulations. The impacts of various system parameters on the performance comparison between the half-duplex mode and full-duplex mode are investigated. Particularly, the full-duplex mode is shown to outperform the half-duplex mode when the received signal-to-noise ratio (SNR) at the near user is low or the residual self-interference is low.

On Performance of Energy Harvested Cooperative NOMA Under Imperfect CSI and Imperfect SIC

With the advent of 5G and the need for energy-efficient massively connected wireless networks, in this work, we consider an energy harvesting (EH) based multi-relay downlink cooperative non-orthogonal multiple access (NOMA) system with practical constraints. The base station serves NOMA users with the help of decode-and-forward based multiple EH relays, where relays harvest the energy from the base station's radio frequency. A relay is selected from the multiple K-relay by using a partial relay selection protocol. The system is considered to operate in half-duplex mode over a generalized independent and identical Nakagami$-m$ fading channel. The closed-form expression of outage probability and ergodic rate are derived for users, under the assumption of imperfect channel state information (CSI) and imperfect successive interference cancellation (SIC) at the receiver node. Expression of outage probability and ergodic rate for both users under the assumption of perfect CSI and perfect SIC are also presented. Further, the asymptotic expression for the outage probability is also shown. The derived analytical expressions are verified through Monte-Carlo simulations.

Sum Rate Maximization for Cooperative NOMA with Hardware Impairments

This paper investigates the sum rate (SR) maximization problem for downlink cooperative non-orthogonal multiple access (C-NOMA) systems with hardware impairments (HIs). The source node communicates with users via a half-duplex amplified-and-forward (HD-AF) relay with HIs. First, we derive the SR expression of the systems under HIs. Then, SR maximization problem is formulated under maximum power of the source, relay, and the minimum rate constraint of each user. As the original SR maximization problem is a non-convex problem, it is difficult to find the optimal resource allocation directly by tractional convex optimization method. We use variable substitution method to convert the non-convex SR maximization problem to an equivalent convex optimization problem. Finally, a joint power and rate allocation based on interior point method is proposed to maximize the SR of the systems. Simulation results show that the algorithm can improve the SR of the C-NOMA compared with the cooperative orthogonal multiple access (C-OMA) scheme.

Joint User Pairing, Subchannel Assignment and Power Allocation in Cooperative Non-Orthogonal Multiple Access Networks

This paper addresses the problem of user pairing, subchannel assignment and power allocation in a downlink cooperative non-orthogonal multiple access (NOMA) network. A joint user pairing and subchannel assignment algorithm is proposed that pairs a user having strong channel conditions with a user having weak channel conditions and assigns them a subchannel simultaneously. Each strong user acts as a relay for the weak user. A Stackelberg game (SG) is employed and a closed-form solution is given to allocate power among the users by the base station (BS) considering the mutual benefits of each user and the BS. Simulation results prove the effectiveness of the proposed scheme in terms of average sum rate of users as compared to that of the cooperative orthogonal multiple access (OMA) scheme and existing NOMA schemes.

Full-duplex cooperative NOMA system under impacts of residual SI and MAI

ABSTRACT In this paper, we investigate the performance of a downlink cooperative non-orthogonal multiple access (C-NOMA) system with full-duplex decode-and-forward relaying, where a NOMA user with better channel operates as a full-duplex (FD) relay to assist other NOMA-user to forward its messages to the base station (BS). Specifically, we derive the exact expressions of the system performances in terms of outage probability and ergodic capacity for two users over the Nakagami- fading channels for the case with the direct link from the BS to users. We then analyse the impacts of residual self-interference (SI) due to imperfect self-interference cancellation in the FD mode and multiple access interference (MAI) due to imperfect co-channel interference cancellation (CCIC) on the system performance. Simulation results are provided to verify the theoretical analysis and demonstrate the advantages of the FD-C-NOMA system over the FD non-cooperative NOMA (FD-NC-NOMA) system and the half-duplex C-NOMA (HD-C-NOMA) one.

Three-User Cooperative NOMA Transmission

This letter presents a new downlink cooperative non-orthogonal multiple access (NOMA) transmission scheme to serve three users within only two time slots. The scheme involves a base station (BS), two direct-link users and one indirect-link user. The BS sends superposed signals to the two direct-link users which decode and forward the signals to the indirect-link user in an alternating fashion. Closed-form expression is derived for the sum-rate of the proposed scheme and a simple expression of sum-rate is also derived in the high signal-to-noise ratio (SNR) region. In the presence of strong inter-user interference (IUI), the proposed scheme can be applied by having each direct-link user to detect the IUI first and then cancel the IUI to decode the signals destined for the indirect-link user and itself. Simulation results show that the scheme with configurable decoding orders at the users is able to achieve a higher sum-rate than existing orthogonal multiple access (OMA) based alternatives.

Performance Analysis of Cooperative NOMA Networks with Imperfect CSI over Nakagami-m Fading Channels.

In this paper, we investigate a downlink cooperative non-orthogonal multiple access (NOMA) network with decode-and-forward relaying, where two scenarios of user relaying with direct link and user relaying without direct link are discussed in detail. More particularly, the performance of cooperative NOMA system under the assumption of imperfect channel state information (ipCSI) is studied over Nakagami-m fading channels. To evaluate the outage performance of the above discussed two scenarios, the closed-form expressions of outage probability for a pair of users are derived carefully. The diversity orders of users are achieved in the high signal-to-noise region. An error floor appears in the outage probability owing to the existence of channel estimation errors under ipCSI conditions. Simulation results verify the validity of our analysis and show that: (1) NOMA is superior to conventional orthogonal multiple access; (2) The best user relaying location for cooperative NOMA networks should be near to the base station; and (3) The outage performance of distant user with direct link significantly outperforms distant user without direct link by comparing the two scenarios.

Exploiting hybrid decode-and-forward – amplify-and-forward in NOMA: an application to device-to-device networks

A novel model regarding downlink cooperative non-orthogonal multiple access (NOMA) in device-to-device network will be investigated in this paper, especially combining amplify-and-forward (AF) and decode-and-forward (DF) to achieve a hybrid scheme. We consider a remarkable trade-off between outage performances and power allocation factors. Especially, we study a hybrid AF and DF scheme, namely HDAF scheme for NOMA as follows: 1) The proposed scheme applies the AF scheme when the signal-to-interference-plus-noise ratio (SINR) at the relay is below a predefined threshold such that the relay cannot successfully decode the signal; 2) On the other hand, when the SINR at the relay is greater than the predefined threshold, the system will be applied the DF scheme to decode the signal and then forwards it to the destination, i.e., avoids noise and interference amplification at the relay. An analytical expression of the outage probability of the hybrid HDAF NOMA is derived based on the outage probability function in AF and DF mode. Numerical results are provided to illustrate the influence of network parameters such as transmit power, power constraint, and link distances on the outage probability.

Cooperative Relay Transmission under Physical Layer Security for Non-Orthogonal Networks

In this paper, the secrecy performance for a downlink cooperative non-orthogonal multiple access (NOMA) communication system is studied under two cases. In the first case, the presence of an untrusted user is studied. While, the presence of an eavesdropper node is considered in the second case. The base station transmits superimposed information signals to the half-duplex two-way relay node. The relay amplifies-and-forwards the received signal towards the users. This paper studies the effectiveness of two factors on the secrecy performance in terms of secrecy capacity. these factors are the power allocated for each user, and the distance between the untrusted user and the cooperative relay node with respect to the strong user. Moreover, this paper proposes the shared jamming signal strategy in order to enhance the physical layer security of the cooperative NOMA in the presence of an eavesdropper node. Furthermore, simulations of the secrecy capacity are presented and compared with a conventional scheme based on null-steering jamming scheme. Based on the result the proposed technique outperforms the conventional technique in terms the of secrecy capacity.

Exploiting Hybrid Decode-and-Forward - Amplify-and-Forward in NOMA: An application to Device-To-Device Networks

A novel model regarding downlink cooperative non-orthogonal multiple access (NOMA) in device-to-device network will be investigated in this paper, especially combining amplify-and-forward (AF) and decode-and-forward (DF) to achieve a hybrid scheme. We consider a remarkable trade-off between outage performances and power allocation factors. Especially, we study a hybrid AF and DF scheme, namely HDAF scheme for NOMA as follows: 1) The proposed scheme applies the AF scheme when the signal-to-interference-plus-noise ratio (SINR) at the relay is below a predefined threshold such that the relay cannot successfully decode the signal; 2) On the other hand, when the SINR at the relay is greater than the predefined threshold, the system will be applied the DF scheme to decode the signal and then forwards it to the destination, i.e., avoids noise and interference amplification at the relay. An analytical expression of the outage probability of the hybrid HDAF NOMA is derived based on the outage probability function in AF and DF mode. Numerical results are provided to illustrate the influence of network parameters such as transmit power, power constraint, and link distances on the outage probability.

Cooperative NOMA Short-Packet Communications in Flat Rayleigh Fading Channels

A two-user downlink cooperative non-orthogonal multiple access (NOMA) short-packet communication network is investigated in flat Rayleigh fading channels, where a central user cooperatively relays the signals intended to a cell-edge user. To derive the average block error rate (BLER) of the central user, unlike the work in the literature where the product term is neglected, a new method that works well for the whole range of power allocation factor is proposed. Furthermore, the average BLER of the cell-edge user is theoretically derived. Numerical results demonstrate that while remaining almost the same average BLER for the central user, the cell-edge user in our proposed cooperative NOMA network achieves lower average BLER than those in the conventional NOMA network and the cooperative orthogonal multiple access network.

Energy Efficient Resource Allocation for Downlink Cooperative Non-Orthogonal Multiple Access Systems

Energy Efficient Resource Allocation for Downlink Cooperative Non-Orthogonal Multiple Access Systems

Performance Analysis of a Downlink Cooperative NOMA Network Over Nakagami-m Fading Channels

This paper assesses the performances of a downlink cooperative non-orthogonal multiple access (C-NOMA) network over Nakagami-m fading channels. The analytical outage probability expression for each user is derived and verified by Monte Carlo simulations. Based upon the outage probability, the maximal throughputs are obtained and analyzed under different channel conditions. Furthermore, the effects of channel fading on the probability and throughput are investigated. The results indicate that the performance of the C-NOMA system is excellent over the source-relay link with less fading. This analysis can be used for designing the C-NOMA systems in the future fifth-generation wireless communication.

Joint Subcarrier Pairing and Power Allocation for Cooperative Nonorthogonal Multiple Access

In this correspondence, a downlink cooperative nonorthogonal multiple access transmission scheme is considered in the multicarrier scenario, where the user equipment (UE) with strong channel conditions acts as a relay to help the UE with weak channel conditions. A joint optimization of subcarrier pairing and power allocation is formulated as a mixed-integer nonconvex problem, with the objective to minimize the transmit power of the base station and the relay (strong UE) under the quality of service requirements of both UEs. We first explore the inherent property of power allocation for a single subcarrier pair. Then, in light of the property, we employ the Lagrange dual method and the Hungarian algorithm, in an asymptotically optimal manner, to solve the joint subcarrier pairing and power allocation problem. Numerical results show that our proposed algorithm outperforms other schemes with or without cooperation.