Spatially Random Relay Selection for Full/Half-Duplex Cooperative NOMA Networks

Abstract

This paper investigates the impact of relay selection (RS) on the performance of cooperative non-orthogonal multiple access (NOMA), where relays are capable of working in either full-duplex (FD) or half-duplex (HD) mode. A number of relays (i.e., K relays) are uniformly distributed within the disc. A pair of RS schemes are considered insightfully: 1) Single-stage RS (SRS) scheme; and 2) Two-stage RS (TRS) scheme. In order to characterize the performance of these two RS schemes, new closed-form expressions for both exact and asymptotic outage probabilities are derived. Based on analytical results, the diversity orders achieved by the pair of RS schemes for FD/HD cooperative NOMA are obtained. Our analytical results reveal that: i) The FD-based RS schemes obtain a zero diversity order, which is due to the influence of loop interference (LI) at the relay; and ii) The HD-based RS schemes are capable of achieving a diversity order of K, which is equal to the number of relays. Finally, simulation results demonstrate that: 1) The FD-based RS schemes have better outage performance than HD-based RS schemes in the low signal-to-noise radio (SNR) region; 2) As the number of relays increases, the pair of RS schemes considered are capable of achieving the lower outage probability; and 3) The outage behaviors of FD/HD-based NOMA SRS/TRS schemes are superior to that of random RS (RRS) and orthogonal multiple access (OMA) based RS schemes.

Performance Analysis of Cooperative NOMA Systems with Incremental Relaying

“…), respectively. Additionally, the target rate [25] of D 1 and D 2 are R 1 = 1:5 BPCU and R 2 = 0:5 BPCU, respectively, where BPCU is an abbreviation for bit per channel use. We assume Ω i,j = ðd i,j /d 0 Þ −α [34], in which d i,j denotes the distance between i and j, d 0 is a reference distance, and α is a path loss exponent.…”

“…While the aforementioned research on cooperative NOMA and user relay NOMA systems with IR protocol has laid a solid foundation for understanding the IR protocol [31][32][33], the incremental cooperative NOMA (ICN) system is still under exploration. It is worth pointing out that, from a practical perspective, the NOMA communication networks can be employed to support IoT scenarios, especially when two NOMA users are classified into two types by their quality of service (QoS) [25], i.e., the nearby user and distant user. The nearby user requires a high targeted rate and can be served opportunistically; e.g., it is to download video files or perform some background tasks and so on.…”

“…In addition, the performance of FD cooperative NOMA systems in the presence of in-phase and quadrature-phase imbalance and imperfect SIC is analyzed and evaluated [24]. Furthermore, the authors have researched relay selection schemes to take advantages of space diversity and enhance spectral efficiency in cooperative NOMA systems [25,26]. Very recently, the impact of residual transceiver hardware impairments on cooperative NOMA networks has been investigated in [27], which has also been researched in satellite-terrestrial cooperative NOMA networks [28] and two-way multiple relay NOMA networks [29].…”

Impact of Wireless Backhaul Unreliability and Imperfect Channel Estimation on Opportunistic NOMA

“…It should be noted that k * is the selected transmitter index which depends onĥ 2k and is independent ofĥ 1k . After applying (10) in (12), OP 1 R1 can be re-expressed as…”

“…The relay-aided NOMA scheme was developed to improve the spectral efficiency as well as fairness for users [6]- [8]. In addition, work in [9] proposed the outage probability of the optimal relay selection for NOMA networks, while others investigated the random relay selection for full-duplex NOMA networks [10]. The NOMA scheme for cooperative spectrum-sharing networks over Nakagami-m fading channels was proposed in [11], where both primary and secondary users would be served by a base station simultaneously.…”