Coordinated Direct And Relay Transmission Research Articles

A power-domain NOMA based overlay spectrum sharing scheme

Non-orthogonal multiple access (NOMA) and cooperative spectrum sharing (CSS) are integrated into this work to enhance both spectrum efficiency and utilization. A clustering-based overlay spectrum sharing is proposed by exploiting NOMA in coordinated direct and relay transmission (CDRT) (termed as CSS-NOMA-CDRT). In CSS-NOMA-CDRT, a primary strong NOMA user is directly served by the primary transmitter, whereas a primary NOMA weak user needs the assistance of a relay to communicate with the primary transmitter within a cluster. Instead of using a dedicated relay, a secondary transmitter acts as a relay to forward the primary symbol to NOMA weak user and the secondary transmitter transmits own symbol to its receiver at the same time. The performance of the proposed CSS-NOMA-CDRT is evaluated with closed-form solutions, in terms of ergodic sum capacity and outage probability. Through the analytical and Monte Carlo simulation results, it is demonstrated that CSS-NOMA-CDRT can obtain remarkable capacity gain as compared to the conventional NOMA-based CDRT.

Design and Performance Analysis of Cooperative NOMA With Coordinated Direct and Relay Transmission

This paper studies the coordinated direct and relay transmission (CDRT) in the non-orthogonal multiple access network, which consists of a base station (BS), a cell-center user (CCU), a cell edge user (CEU), and a group of half-duplex relays. During each transmission, the BS sends information to the CCU directly and to the CEU with the help of one of the relays. To improve the transmission reliability, a novel dynamic detection CDRT (DD-CDRT) strategy is designed, which fully exploits the available side information to eliminate the inter-user interference. Based on the DD-CDRT strategy, we further propose a relay selection scheme which maximizes the CCU’s successful decoding probability with guaranteeing the reliable reception of the CEU. To evaluate our designs, exact and asymptotic outage probabilities are derived for each user. The results show that the achievable diversity order for the CEU is equal to the number of relays. Meanwhile, the CCU achieves a diversity order as one. Specifically, when the system sum rate is relatively small or the relay number is large enough, the outage performance of the CCU can approach the performance of the interference-free situation. Finally, the numerical results are presented to verify the theoretical analysis and to demonstrate the advantages of the DD-CDRT strategy using the proposed relay selection scheme.

Performance of D2D Aided Uplink Coordinated Direct and Relay Transmission Using NOMA

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.

Full/Half Duplex Cooperative NOMA Under Imperfect Successive Interference Cancellation and Channel State Estimation Errors

This paper investigates the application of non-orthogonal multiple access (NOMA) in a coordinated direct and relay transmission (CDRT) system, where the base station (BS) directly communicates with the near (i.e., cell-centric) user, while it requires the help of a dedicated full duplex (FD) relay to communicate with the far (i.e., cell-edge) user. For the considered NOMA-FD-CDRT system, we derive closed-form expressions for the outage probabilities and ergodic rates experienced by the downlink users, under the realistic assumptions of imperfect channel state information (I-CSI) and imperfect successive interference cancellation (I-SIC). Expressions for system outage probability and ergodic sum rate are also presented. The links are assumed to experience independent, non-identically distributed Nakagami-m fading. The analysis of outage probabilities are carried out for both integer and non-integer values of the fading severity index. Extensive simulation results are described to validate the accuracy of analytical results, and to illustrate the performance gain of the considered system, as compared to NOMA-HD-CDRT system and the orthogonal multiple access (OMA) based CDRT system. Our results show that, both channel estimation error variance and I-SIC factor have significant impact on the performance of the considered NOMA-FD/HD-CDRT system. Further, to ensure fairness in terms of outage, we numerically determine the power allocation coefficient at the BS that provides equal outage performance for both the near and the far users in the presence of I-CSI and I-SIC. Furthermore, we derive closed-form expression for the optimal power allocation (OPA) coefficient at the BS that minimizes the system outage probability of the NOMA-FD/HD-CDRT network under I-CSI. With the help of numerical and simulation investigations, we establish that the proposed OPA significantly reduces the system outage probability, as compared to random (i.e., non-optimal) power allocation at the BS.

Performance of NOMA‐based coordinated direct and relay transmission using dynamic scheme

In this study, non-orthogonal multiple access (NOMA)-based coordinated direct and relay transmission (CDRT) is considered, where a base station (BS) directly communicates with two cell-centre users (CCUs) while communicating with a cell-edge user (CEU) via a relay. A novel dynamic scheme is proposed, in which the CCU close to the BS will act as a relay to assist the CEU in the second phase if it can obtain the prior information of the CEU in advance, otherwise it will switch to the receiving mode. To evaluate the system performance of the proposed scheme, the closed-form expressions of the outage probability, diversity order and ergodic sum rate (SR) are, respectively, derived. Simulation results demonstrate that the proposed scheme attains greater diversity order for the CEU as well as superior outage performance without performance loss of the ergodic SR, compared with conventional one in NOMA-based CDRT. In addition, a suboptimal power allocation (SPA) for this dynamic scheme is put forward, for which the closed-form expression is also obtained. It is also indicated that the presented SPA for dynamic scheme achieves near-optimal ergodic SR performance at high SNR region.

Non-Orthogonal Multiple Access in Coordinated Direct and Relay Transmission

In this work, non-orthogonal multiple access (NOMA) in coordinated direct and relay transmission (CDRT) is introduced, where a base station (BS) directly communicates with user equipment 1 (UE1) while communicating with user equipment 2 (UE2) only through a relay. The main challenge of non-orthogonal CDRT can be solved by using the inherent property of NOMA that allows a receiver to obtain side information such as other UE's data for interference cancellation. Analytical expressions for outage probability and ergodic sum capacity are provided. It is shown that the proposed NOMA in CDRT provides remarkable performance gain compared with NOMA in non-coordinated direct and relay transmission (nCDRT); the sum capacity scaling of the proposed scheme is $\log \rho_b$ as signal-to-noise-ratio (SNR) $\rho_b$ increases, but $\frac{1}{2_{}}\log \rho_b$ for NOMA in nCDRT. Exact and closed-form expressions for outage probability of each stream for UE1 and UE2 are respectively derived, and it is shown that the achievable diversity orders for each stream are same as one.