Non-Orthogonal Multiple Access in Coordinated Direct and Relay Transmission

In this paper, we propose a highly efficient protocol for non-orthogonal multiple access (NOMA) based coordinated direct and relay transmission (CDRT) to improve the spectral efficiency (SE) over Nakagami-m fading channel. In this scheme, the base station (BS) connects with a cell-center user (CCU) directly while communicating with a cell-edge user (CEU) via a relay and the CCU. Then, the relay and the CCU use network coding to process and retransmit the signals sent by the BS first and the CEU later. Finally, the BS and the relay simultaneously broadcast downlink signals. We derive the closed- form expressions for the ergodic sum capacity (ESC) using both perfect and imperfect successive interference cancellation (SIC). Simulations verify the correctness of our theoretical analysis and the superiority of the proposed scheme in ESC.

In this paper, the performance of a non-orthogonal multiple access (NOMA) based coordinated direct and relay transmission (CDRT) system without reliable energy supply is analysed in Rayleigh fading channels. In the analysis, there is no direct link between the base station (BS) and the remote NOMA user so that an energy harvesting relay using simultaneous wireless information and power transfer is incorporated to assist the BS to provide service for the remote NOMA user. Exact expressions at closer user and approximate expressions at remote user are derived for outage probability and ergodic capacity, respectively. The asymptotic analysis for outage probability in high signal-to-noise ratio regime is also provided to examine the achievable diversity order. Simulation results are good agreement with the theoretical analysis, and show the superiority of proposed system over orthogonal multiple access.

This letter investigates a device-to-device (D2D) communication aided coordinated direct and relay transmission (CDRT) using non-orthogonal multiple access (NOMA) framework, where a cell-center user (CU) is served by a base station (BS) directly while a cell-edge user (EU) needs the help of a relaying user (RU) to communicate with BS. Specifically, with the use of the NOMA principle, we propose to exploit a D2D communication link from RU to CU for transmitting a new signal during the information forwarding of RU in the second phase, so as to enhance the network spectrum efficiency. Analytical closed-form expressions of the system ergodic sum capacity are derived and verified by computer simulations. Both analytical and simulation results demonstrate that the D2D aided NOMA scheme achieves higher sum rates than the conventional CDRT scheme and orthogonal multiple access (OMA) scheme.

In hybrid device-to-device (D2D) and cellular networks, the cross interference between different communication systems severely limits the system performance. Fortunately, non-orthogonal multiple access (NOMA)-based coordinated direct and relay transmission (CDRT) can fully exploit the inherent property of NOMA to minimize such interference, which provides a potential strategy for hybrid networks to enhance the spectral efficiency (SE) and extend the cell coverage. Based on this idea and the superior SE requirements in future wireless networks, a D2D communication assisted uplink CDRT using NOMA is proposed, in which a base station (BS) directly communicates with a cell-center user (CCU) while communicating with a cell-edge user (CEU) with the aid of a relay. Particularly, uplink transmission of CCU and D2D communication from CCU to CEU are jointly designed according to NOMA principle in the cooperative phase. To verify the system performance of the proposed scheme, closed-form expressions of the system ergodic sum rate (SR), outage performance and outage throughput are derived, respectively. Numerical results illustrate that the proposed scheme achieves superior system ergodic SR as well as outage throughput with slight outage performance loss of uplink transmission, compared with conventional NOMA-based uplink CDRT.

This article proposes a simultaneous wireless information and power transfer (SWIPT)-enabled Internet of Things (IoT)-based cognitive nonorthogonal multiple access (NOMA) with coordinated direct and relay transmission (CDRT) system. It incorporates overlay cognitive radio (CR) and time switching (TS)-based SWIPT technology to enhance spectrum utilization and energy efficiency (EE). The proposed system comprises a primary network having a primary transmitter and its intended NOMA receivers (UE1 and UE2), accompanied by an energy-constrained secondary transmitter (ST) and its designated receiver (IoT-U). The primary transmitter communicates directly with its strong user UE1 and exploits the ST as an IoT relay to communicate with a weak user UE2. The IoT-relay node employs a TS-based receiver architecture and a decode-and-forward (DF) protocol to convey the weak user’s information along with its own information by following the NOMA principle. We evaluate the performance of the proposed system by considering both the perfect and imperfect successive interference cancellation (SIC) at the legitimate users over Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${m}$ </tex-math></inline-formula> fading in terms of outage probability (OP), system throughput, and EE. Moreover, we propose an iterative algorithm to minimize the OP by optimizing the TS factor. Furthermore, the impact of key parameters is also highlighted, which lays the guidelines for the practical design of energy-efficient and spectrum-efficient futuristic wireless communication networks.

In this paper, a novel cooperative non-orthogonal multiple access (NOMA) system is proposed, where one near user is employed as decode-and-forward relaying switching between full-duplex (FD) and half-duplex (HD) mode to help a far user. Two representative cooperative relaying scenarios are investigated insightfully. The first scenario is that no direct link exists between the base station (BS) and far user. The second scenario is that the direct link exists between the BS and far user. To characterize the performance of potential gains brought by the FD NOMA in two considered scenarios, three performance metrics outage probability, ergodic rate, and energy efficiency are discussed. More particularly, we derive new closed-form expressions for both exact and asymptotic outage probabilities as well as delay-limited throughput for two NOMA users. Based on the derived results, the diversity orders achieved by users are obtained. We confirm that the use of direct link overcomes zero diversity order of far NOMA user inherent to FD relaying. In addition, we derive new closed-form expressions for asymptotic ergodic rates. Based on these, the high signal-to-noise ratio (SNR) slopes of two users for FD NOMA are obtained. Simulation results demonstrate that: 1) the FD NOMA is superior to the HD NOMA in terms of outage probability and ergodic sum rate in the low SNR region; and 2) in delay-limited transmission mode, the FD NOMA has higher energy efficiency than the HD NOMA in the low SNR region; However, in delay-tolerant transmission mode, the system energy efficiency of the HD NOMA exceeds the FD NOMA in the high SNR region.

Performance analysis of CDRT based cognitive NOMA vehicular networks with ambient backscatter relays

This letter investigates an energy harvesting (EH)-assisted coordinated direct and relay transmission in an overlay cognitive non-orthogonal multiple access (NOMA) system assuming perfect and imperfect successive interference cancellation. Specifically, we derive analytical expressions of the outage probability (OP) which include an infinite series, system throughput, and energy efficiency. Moreover, an asymptotic analysis of the OP in the high signal-to-noise ratio is carried out. Closed-form expressions of the exact OP and the ergodic sum capacity (ESC) are intractable owing to the complexity of the proposed scheme. To tackle this problem, we propose a deep learning (DL) framework to predict both the OP and ESC performances. The predicted results through the DL framework are shown to be consistent with the numerical results.

Wireless power transmission in the next-generation wireless networks is the subject that attracts a lot of attention from academia and industry. In this work, we study and analyze the performance of relay selection on uplink non-orthogonal multiple access (NOMA) networks with wireless power transmission. Specifically, the considered system consists of one base station, multiple power-constrained relays and a pair of NOMA users. The best relay (with highest energy harvested from the base station) is chosen to cooperate with two users which use NOMA scheme to send messages to the base station. To analyze the performance, based on the statistical characteristics of signal-to-noise ratio (SNR) and signal-to-interference-plus-noise ratio (SINR), using the Gaussian-Chebyshev quadrature method, the closed-form expressions of outage probability and throughput for two users are derived. In order to understand more details about the behavior of this considered system, the numerical results on outage probability and throughput of a given system are provided following the system key parameters, such as the transmit power, the number of relays, time switching ratio and energy conversion efficiency. In the end, the theoretical result is also verified by using the Monte-Carlo simulation. The simulation results demonstrate that the performance of the system is improved by increasing the number of relays.

In this paper, a coordinated direct and relay transmission (CDRT) based cognitive underlay downlink nonorthogonal multiple access network is considered, in which the source serves the near user (NU) directly while a dedicated relay assists the communication to the far user (FU). To ensure good performance in a power-constrained underlay scenario, NU combines (along with successive interference cancellation) the signals from the source and the relay in this unique CDRT framework. The secondary transmitter transmits with controlled power to ensure that the interference is below the interference temperature limit of the primary user. NU and FU performance is analyzed in terms of their outage probability and throughput in closed-form. Furthermore, we investigate how the choice of target rates and power allocation parameters is crucial to attaining the best performance. Extensive computer simulations are provided to validate the accuracy of the derived results.

In this letter, a cooperative non-orthogonal multiple access (NOMA) method is utilized in millimeter wave (mmWave) communications to active non-line-of-sight (NLOS) users, where NOMA users are modeled with the aid of Poisson point process (PPP) and all users are severed by a central base station (BS). Closed-form expressions for outage probabilities of paired NOMA users are derived to characterize the performance of the proposed networks. Our numerical results show that the proposed system outperforms the traditional mmWave networks using non-cooperative NOMA.

In this paper, we investigate the performance of full duplex relay (FDR) assisted cognitive radio (CR) network employing Non-orthogonal multiple access (NOMA) scheme. In this system, the secondary and primary users are paired according to the NOMA protocol and also the users share the common relay for cooperative transmission. The exact closed-form expressions for outage probability and average throughput of secondary user(SU) is provided. According to results, the proposed system enhance the system performance significantly. To get more insights, we also make a fair comparison of our system over the existing half-duplex scenario.

Due to the successive interference cancellation (SIC) technique, Non orthogonal multiple Access (NOMA) users have the capability of decoding the other paired users sharing the same resource bloc. As a result, NOMA technique is not only exposed to external eavesdropping, but also to internal eavesdropping which raises security risks regarding NOMA users' privacy. Therefore, this research aims to analyse a Multi-antenna cooperative NOMA system where both Decode and Forward (DF) and Amplify and Forward (AF) strategies are studied. In this context, we investigate the secrecy performance of our system with both internal and external eavesdropping scenarios. Closed-form expressions of the secrecy outage probability (SOP) and the strictly positive secrecy capacity (SPSC) metrics are derived. Numerical results are given to illustrate the validity of the obtained theoretical results.

In this paper, we study the relay transmission of uplink non-orthogonal multiple access (NOMA) network in terms of performance analysis. Specifically, two users applying NOMA scheme intent to transmit the message to base station (BS) by the help of amplify-and-forward (AF) relay. The expressions of outage probability and throughput for two users are derived based on the statistical characteristics of signal-to-noise ratio (SNR) and signal-to-interference-plus-noise ratio (SINR) of transmission links by using Gaussian-Chebyshev quadrature method. In order to look into the behaviour of this considered system, the numerical results are provided using system key parameters, e.g., transmit power, distances. The Monte-Carlo simulation results are also provided to verify the correctness of our analysis.

In view of the scarce spectrum resources and inconvenient deployment in wireless communications, this work focuses on an unmanned aerial vehicle (UAV) enabled non-orthogonal multiple access (NOMA) system where a UAV deployed as a base station serves two users by NOMA. A joint power allocation and aerial jamming (PAAJ) scheme is proposed to achieve reliable and secure communications for the system in the presence of a malicious eavesdropper. To be specific, dynamic power allocation is adopted to ensure the reliability of the system and another friendly UAV jammer is introduced to improve the security of the system. The closed-form expressions of connection outage probability (COP), secrecy outage probability (SOP), and effective secrecy throughput (EST) are derived to evaluate the performance of the security-required user in the practical condition of probabilistic line-of-sight (LoS) and non-line-of-sight (NLoS) air-to-ground (A2G) channels. Moreover, the asymptotic EST is analyzed to obtain further insights. Numerical results show the validity of theoretical derivations and the superiority of the proposed PAAJ scheme over benchmark schemes. The EST of the UAV-enabled NOMA communication system outperforms the conventional terrestrial NOMA system at the low transmitting power from the UAV base station. There exists an optimal height of the UAV base station to maximize the EST, which provides a useful framework for designing UAV-enabled communication systems with heterogeneous service requirements.