Cooperative Orthogonal Multiple Access Research Articles

High Reliable Uplink Transmission Methods in GEO–LEO Heterogeneous Satellite Network

As a significant component of non-terrestrial networks, satellite communication has gradually evolved into a heterogeneous topology where the network nodes are classified as low Earth orbit (LEO) and geostationary Earth orbit (GEO) nodes. Considering the advantage of low transmission delay of LEO satellites in a heterogeneous network, ground users are arranged to access LEO satellites in the first priority. By fully understanding the equivalent channel gain difference in the beam-edge and beam-center users, we develop non-orthogonal multiple access (NOMA) in an LEO network where different users are allocated in the same resource block. As a complementary strategy, the beam-edge user has the ability to connect the GEO satellite if the LEO links are not available. That is, the two users are served cooperatively by LEO and GEO satellites in an orthogonal manner. In this paper, we provide deep insights for the uplink transmission performance of NOMA and cooperative orthogonal multiple access methods. As a general metric, the analytical expressions of outage probability are derived and the diversity orders are also provided. The simulation results show that NOMA is capable of providing remarkable performance in low signal-to-noise ratio regions and is more promising when the channels are assumed to be ordered.

Outage analysis for user selection based downlink cooperative NOMA network over generalized fading channels

Recently, non-orthogonal multiple access (NOMA) scheme is integrated with cooperative communication (C-NOMA) to increase the connectivity and coverage area. In this paper, we analyzed the outage performance of downlink C-NOMA system with the imperfect successive interference cancellation (I-SIC) and imperfect channel state information (I-CSI) aiding multiple users over κ−μ and η−μ independent and identically distributed fading environments. Further, a user selection scheme is adopted for downlink C-NOMA scheme for enhancing the performance of the system. To be precise, the system model considers multiple users at the destination, out of which two users are selected to serve with NOMA standards. The analytical expressions of outage probability (OP) are derived, analyzed, and compared with cooperative-orthogonal multiple access (C-OMA) scheme over generalized fading environments. Moreover, the accuracy of analytical results is validated through Monte Carlo simulation. In addition, the analytical expression of OP for the paired user is also derived, analyzed, and correlated with the C-OMA scheme. Furthermore, through κ−μ and η−μ fading distribution, the outage performance of Rayleigh, Nakagami-m, Rice, Hoyt, and one-sided Gaussian fading environment is also investigated. From the obtained results, it is evident that when compared to C-OMA scheme, the C-NOMA scheme achieves 4.4 and 6.6 percentage gain in terms of SNR for a near user and a far user, respectively at κ=1.0,μ=1.0 to attain outage of 10−1. On the other hand, for the same outage, C-NOMA achieves 4.6 and 6.7 percentage gain in terms of SNR for a near user and a far user, respectively at η=1.0,μ=1.5.

Outage probability and throughput of cooperative non‐orthogonal multiple access with moving relay in heterogeneous network

AbstractThe demand of high data rate, high quality of service (QoS), and seamless connectivity are growing continuously for vehicular communication over the last few years. Moving relay (MR) is one of the promising techniques to achieve these demands. In the past, heterogeneous network (HetNet) models with one MR on the top of the train have been proposed for high‐speed railway (HSR) using the orthogonal multiple access (OMA) technique. Cooperative non‐orthogonal multiple access (NOMA) is a promising multiple access technique for next‐generation wireless networks. This paper proposes one MR‐based HetNet model using the NOMA over Rayleigh fading channels for downlink communication. Here, half‐duplex (HD) type amplify and forward (AF) relay is used as MR for investigation. We derive the outage probability of a train‐user using the successive interference cancellation (SIC) technique and the outage probability of a cell‐edge‐user by using both direct and indirect signals via MR. The system throughput of the proposed NOMA system is also simulated by considering the effects of perfect and imperfect SIC. The simulation results show that cooperative NOMA provides lower outage performance in comparison with cooperative OMA and outage of vehicular user decreases with lower value of residual interference (RI). Also, the system throughput of the NOMA system decreases with higher values of residual interference. We use Monte Carlo simulation to verify the derived analytical results.

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.

On the performance of cooperative NOMA Using MRC at road intersections in the presence of interference

As the traffic safety has become of utmost importance, much attention is given to intelligent transportation systems (ITSs), and more particularly to vehicular communications (VCs). Moreover, 50 % of all crashes happen at road intersections, which makes theme critical areas. In this paper, we investigate the improvement when implementing maximum ratio combining (MRC) in cooperative VCs transmission schemes using non-orthogonal multiple access scheme (NOMA) at road intersections. We consider that a source transmits a message to two destinations with an aid of a relay. The transmission undergoes interference generated from a set of vehicles on the roads. We obtained closed form outage probability expressions, and we extended the derivations for a scenario involving K destination nodes and several road lanes. The performance of MRC cooperative NOMA are compared with the standard cooperative NOMA, and we show that implementing MRC with NOMA offers a significant improvement over the standard cooperative NOMA. Also, we compare the performance of MRC using NOMA with MRC cooperative orthogonal multiple access (OMA), and demonstrate that NOMA significantly outperforms OMA. We conclude that, it is always beneficial for vehicles to use MRC and NOMA even at the cost of implementation complexity. Finally, we demonstrate that the outage probability increases drastically when vehicles are closer to the road intersection, and that using MRC with NOMA improves significantly the performance in this context. To verify the correctness of our analysis, extensive Monte-Carlo simulations are carried out.

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.

Joint C-OMA and C-NOMA Wireless Backhaul Scheduling in Heterogeneous Ultra Dense Networks

Heterogeneous ultra dense network (UDN) emerges as one of the potential techniques to tackle the $1000\times $ data challenge in 5G network. However, by cell densification, backhaul becomes one of the key issues in 5G heterogeneous UDN. In this paper, the cooperative wireless backhaul scheduling is concerned. First, a novel two-layers hierarchical model is proposed for the cooperative wireless backhaul, based on which energy efficiencies (EEs) of the cooperative orthogonal multiple access (C-OMA) and the cooperative non-orthogonal multiple access (C-NOMA) schemes are derived and analyzed. Moreover, based on the proposed model, a cooperative wireless backhaul optimization which maximizes EE is formulated. To solve this mixed integer non-linear optimization problem, the greedy algorithm-based C-OMA, C-NOMA and joint C-OMA and C-NOMA (JCC) schemes for cooperative wireless backhaul are proposed. Due to the benefits of both the C-OMA and C-NOMA, the proposed JCC scheme shows its superiority over C-OMA, C-NOMA and the traditional OMA schemes, which is validated by the simulation results.

Ergodic Capacity and Outage Performance Analysis of Uplink Full-Duplex Cooperative NOMA System

We propose an uplink full-duplex (FD) cooperative non-orthogonal multiple access (NOMA) system, where a dedicated Full-duplex (FD) relay is used to help two uplink users transmitting information to the base station. A novel FD relay transmission mode is proposed, in which the FD relay utilizes successive interference cancellation (SIC) and self-interference cancellation to decode two users symbols at the relay receiving antenna, and the relay transmitting antenna transmits superimposed signal to the base station using superposition coding. In this paper, we also consider a more realistic scenario where self-interference cancellation is imperfect. Hence, the residual-self interference exists. Moreover, the ergodic sum rate and the outage probability of the proposed system are investigated and the accurate analytical expressions are derived. Simulation results validate that, compared with the uplink half-duplex (HD) cooperative NOMA system and the uplink HD cooperative orthogonal multiple access (OMA) system, our proposed system obtains better performance of the ergodic sum rate and outage probability in the main signal to noise ratio (SNR) regime.

User fairness for RSS‐based positioning in uplink cooperative NOMA

Geolocation of mobile nodes with non-orthogonal multiple access (NOMA) is a crucial process for enabling advanced location-based services (LBSs) in 5G networks. In this study, the authors investigate the theoretical limits of received-signal-strength (RSS)-based positioning for uplink cooperative NOMA under different network conditions with special emphasis on the user fairness feature. In addition, they compare the performance of the RSS-based positioning of cooperative NOMA with that of orthogonal multiple access (OMA). The Cramer-Rao lower bounds are derived in order to show the fundamental limits of position estimation error by taking amplify-and-forward and decode-and-forward relaying into account. The numerical results for both schemes are presented and compared considering the effects of number of relays and user equipments, different relaying on the performance of RSS positioning. The effects of power allocation on the user fairness of cooperative NOMA are also investigated. The results show that the cooperative NOMA outperforms cooperative OMA in terms of positioning. It provides high precision position accuracy and user fairness under different network conditions. Hence, the results suggest that the RSS-based positioning for uplink cooperative NOMA is a promising technique for achieving user fairness and supporting diversified low-cost LBSs in 5G networks.

Performance analysis of cooperative NOMA at intersections for vehicular communications in the presence of interference

Road traffic safety is a crucial issue, and more specifically at road intersections. At the same time, vehicular communications (VCs) are attracting a great attention thanks to their useful safety applications. In this paper, we study the performance of cooperative VCs at intersections, in the presence of interference when the communication system implements a non-orthogonal multiple access (NOMA) scheme. First, we derive the outage probability and the average achievable rate for a scenario involving a source, a relay, and two destinations, when the destinations can be either on the roads or outside the roads. The derivations are extended for K destinations. Closed form outage probability expressions and quasi-closed form average achievable rate expressions are obtained. Both perfect and imperfect successive interference cancellation (SIC) are incorporated into the analysis. We show that the outage probability increases and the average achievable rate decreases when vehicles move toward the intersection. We also compare the performance of VCs at intersections and at highways, and show that the performance of VCs at intersections is worse than at highways. We compare cooperative NOMA with cooperative orthogonal multiple access (OMA) in VCs, and show that average achievable rate NOMA outperforms average achievable rate OMA in terms of outage probability and average achievable rate. We also demonstrate that the benefits of cooperative NOMA over cooperative OMA becomes greater for high data rates. We also investigate the best relay position for the two destinations. Finally, we show that the performance of cooperative NOMA decreases drastically when the system parameters are not chosen carefully. All the analytical results are validated by Monte-Carlo simulations.

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.

Successive User Relaying in Cooperative NOMA System

User relaying in cooperative non-orthogonal multiple access (C-NOMA) system is able to enhance reliability. However, for user operates in half-duplex (HD) mode, additional bandwidth is needed for relaying operation. This reduces spectral efficiency of C-NOMA system. This letter proposes a successive user relaying (SR) to improve the spectral efficiency of C-NOMA system. In the proposed SR scheme, a pair of HD users decode the received signal and relay the decoded signal successively to improve the spectral efficiency. A novel algorithm is proposed to optimize power split factor in order to improve fairness of outage performance between users. The performance of the proposed SR scheme is superior to existing HD relaying scheme in C-NOMA system and existing SR in cooperative orthogonal multiple access system in terms of outage probability and ergodic sum rate. The closed-form expressions of outage probability and asymptotic ergodic sum rate of proposed SR are also derived.

Exploiting Full-Duplex Two-Way Relay Cooperative Non-Orthogonal Multiple Access

In this paper, a novel full-duplex cooperative non-orthogonal multiple access (FD CNOMA) system is proposed, where users intend to exchange messages with the assistance of a decode-and-forward relay. To characterize the potential performance gain brought by the proposed FD CNOMA scheme, the outage probability and ergodic rate are analyzed. Specifically, the closed-form expressions for the outage probabilities, diversity orders, ergodic rates, and system throughputs in delay-limited and delay-tolerant transmission modes are derived under the realistic assumption of imperfect self-interference cancellation. Furthermore, to present the comprehensive performance evaluation, both perfect and imperfect successive interference cancellations (SICs) are taken into consideration. Simulations are performed to validate the accuracy of the derivation results and to illustrate the outstanding performance of the proposed scheme in low signal-to-noise ratio region compared with half-duplex CNOMA system and cooperative orthogonal multiple access system. Our results show that under the conditions of both perfect and imperfect SICs, outage probability floors and ergodic rate ceilings exist for the proposed FD CNOMA scheme due to the inter-user interference among superimposed NOMA signals and the residual self-interference caused by the imperfect self-interference cancellation.

Outage Performance of Cooperative Underlay CR-NOMA With Imperfect CSI

In this letter, a decode-and-forward cooperative underlay cognitive radio (CR) non-orthogonal multiple access (NOMA) network is studied. Exact closed-form expressions for the outage probability (OP) of two NOMA secondary destination users ( $U_{1}$ and $U_{2}$ ) are derived in the case of imperfect channel state information. Then, we find optimal power allocation factors for different distances of $U_{1}$ to satisfy the OP fairness for both users. Moreover, the proposed system model shows the superiority of the CR-NOMA compared with cooperative orthogonal multiple access. The derived analytical expressions are corroborated through Monte Carlo simulations.

The impact of channel estimation errors on the performance of cooperative nonorthogonal multiple access 5G systems under Nakagami‐m fading

AbstractNonorthogonal multiple access (NOMA), which can provide high data rates and spectral efficiency in wireless communication, is a promising multiple access technique for the fifth‐generation systems. In this paper, a cooperative NOMA downlink network is investigated over Nakagami‐m fading channels with channel estimation errors taken into consideration. We assume that the direct links between the base station and the users are available and selection combining is conducted at the receiver of the users. First, the closed‐form expressions for the exact and lower bounds of the outage probability are obtained, respectively. Furthermore, due to the presence of the imperfect channel state information, an error floor exists by approximating the outage probability at the high‐signal‐to‐noise‐ratio regime. Next, the ergodic sum rate for the proposed network is analyzed, and the closed‐form expressions for the upper bound of the ergodic sum rate are attained. Finally, extensive numerical results are presented to confirm the correctness of our analysis and to show the superiority of NOMA over conventional cooperative orthogonal multiple access.

Outage Performance for Cooperative NOMA Transmission with an AF Relay

This letter studies the outage performance of cooperative non-orthogonal multiple access (NOMA) network with the help of an amplify-and-forward relay. An accurate closed-form approximation for the exact outage probability is derived. Based on this, the asymptotic outage probability is investigated, which shows that cooperative NOMA achieves the same diversity order and the superior coding gain compared to cooperative orthogonal multiple access. It is also revealed that when the transmit power of relay is smaller than that of the base station, the outage performance improves as the distance between the relay and indirect link user decreases.

Performance Analysis of Cooperative Pattern Division Multiple Access (Co-PDMA) in Uplink Network

As a promising candidate non-orthogonal multiple access scheme for the fifth generation (5G) wireless communication system, pattern division multiple access (PDMA) has received considerable attention recently. Using pattern matrix (G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PDMA</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[2,3]</sup> , as an example, is used in this paper), PDMA directly maps the information bits of different users to radio resources, such as code, power, time and frequency, and space resource. PDMA can meet the requirements of massive connectivity and higher spectral efficiency for the 5G mobile network. In order to further improve transmission reliability and enhance the coverage, an uplink cooperative PDMA (Co-PDMA) scheme with half-duplex decode and forward relay is proposed. The analytical expressions of outage probability (OP) and sum data rate are derived to characterize the performance of the proposed scheme. The results show that the proposed Co-PDMA scheme achieves superior outage performance, with gains of 8 and 12 dB over the nonCo-PDMA and cooperative orthogonal multiple access (Co-OMA), respectively, @ OP = 0.1. Besides, the scheme is found to outperform two other schemes in terms of higher sum data rate and achieve an almost maximum 50% gain over Co-OMA when every user has the same target data rate.