Multi-antenna relay assisted NOMA network with multiple imperfect factors

This paper has investigated a downlink non-orthogonal multiple access (NOMA) cooperative scheme with user-assisted relaying, where near users are viewed as decode-and-forward (DF) relays operating full/half-duplex mode to assist multiple far users. Especially, the impact for the randomness of users location on the system performance has also been studied. Further, to overcome the zero diversity gain inherent to full-duplex (FD) operation, the direct link between a base station (BS) and each far user is exploited. The comprehensive performance analysis is conducted through the closed-form expressions in terms of outage probability, the diversity gain, system throughput, and ergodic sum rate. With respect to outage behavior, throughput, and ergodic sum rate, FD-based NOMA outperforms half-duplex (HD) NOMA in the lower signal-to-noise ratio (SNR) region. However, with the negative influence brought by residual loop-interference (LI), the advantage of FD NOMA scheme is not pronounced enough in the high SNR regime. Therefore, according to different SNR levels, we further propose a hybrid relaying scheme that switches opportunistically between the FD and HD modes. Afterward, the mode switching threshold is characterized such that the outage probability of each user is minimized. The simulation results confirm the correctness of our analysis and offer a significant guideline for system design in practice.

We study the fundamental capacity trade-off between full-duplex and half-duplex transmission modes in a two- hop communication system with a fixed infrastructure-based amplify-and-forward relay. First, we derive closed-form expressions for the average end-to-end capacity in the relay link. We show that it may be better to tolerate some loop interference with the full-duplex mode than to consume channel resources by allocating two orthogonal channels with the half-duplex mode. Furthermore, we evaluate the maximum loop interference power levels that still allow the full-duplex mode to achieve the same capacity as the half-duplex mode. Our results indicate that with practical signal-to-noise ratio values, the full-duplex mode is preferable in terms of capacity.

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.

Hybrid duplex wireless networks, use half duplex (HD) as well as full duplex (FD) modes to utilize the advantages of both technologies. This paper tries to determine the proportion of the network nodes that should be in HD or FD modes in such networks, to maximize the overall throughput of all FD and HD nodes. Here, by assuming imperfect self-interference cancellation (SIC) and using ALOHA protocol, the local optimum densities of FD, HD and idle nodes are obtained in a given time slot, using Karush–Kuhn–Tucker (KKT) conditions as well as stochastic geometry tool. We also obtain the sub-optimal value of the signal-to-interference ratio (SIR) threshold constrained by fixed node densities, using the steepest descent method in order to maximize the network throughput. The results show that in such networks, the proposed hybrid duplex mode selection scheme improves the level of throughput. The results also indicate the effect of imperfect SIC on reducing the throughput. Moreover, it is demonstrated that by choosing an optimal SIR threshold for mode selection process, the achievable throughput in such networks can increase by around 5%.

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: 1) the FD-based RS schemes obtain a zero diversity order, which is due to the influence of loop interference at the relay; and 2) 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 ratio (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 and orthogonal multiple access based RS schemes.

NOMA-based cognitive radio network with hybrid FD/HD relay in industry 5.0

Reconfigurable intelligent surface (RIS) has recently been envisioned to provide an adaptable channel for futuristic wireless communication networks. This work characterized the impact of hardware impairments in the downlink RIS-aided non-orthogonal multiple access (NOMA) wireless networks. We considered the hardware impairments in the transceivers of the base station (BS) and users, phase error at the RIS and the imperfect successive interference cancellation (SIC) for the NOMA users. Specifically, the performance is evaluated by deriving the closed-form expressions for the outage probability (OP), spectral efficiency (SE) and energy efficiency (EE). Additionally, the performance of the orthogonal multiple access (OMA) system is also evaluated and compared with its NOMA counterpart. The RIS-aided NOMA outperforms OMA for the ideal hardware scenario. However, the hardware impairments significantly deteriorate RIS-aided NOMA's performance compared to RIS-aided OMA. Further, we have also compared the proposed RIS-aided NOMA with the baseline full-duplex relaying (FDR) based NOMA. The results show that the gains are more significant for a RIS-aided system than FDR.

With the increasing shortage of satellite spectrum resources, non-orthogonal multiple access (NOMA) scheme is applied to satellite communication (SatCom) networks, which is regarded as one of the key technologies to improve spectrum efficiency. In this paper, we investigate the joint impact of non-ideal limitations, i.e., channel estimation errors, co-channel interference and imperfect successive interference cancellation on the performance of NOMA-based SatCom networks. To evaluate the performance improvement under practical scenarios, we obtain a closed-form expression for the outage probability (OP) in the presence of non-ideal limitations. To investigate the effect of non-ideal factors at high signal-to-noise ratios, an asymptotic analysis for the OP is also presented. Besides, an optimal power allocation scheme based on the non-ideal limitations is proposed to minimize the OP of the system. Finally, Monte Carlo simulations corroborate the correctness of the presented theoretical results.

This article studies the energy efficiency (EE) of a three-node decode-and-forward (DF) relay channel, where the relay operates in full-duplex (FD) or half-duplex (HD) mode. In particular, for the FD mode, both the residual self-interference (RSI) and the extra circuit power consumption introduced by the self-interference cancellation (SIC) at the relay node are considered and modeled as linear functions over the relay transmission power. Under this setup, the EE maximization problems for the considered FD and HD modes subject to the total transmission power and spectral efficiency (SE) constraints are formulated as max–min problems, whose optimal power allocation is computed by fractional programming. Next, the EEs for the FD, HD, and direct transmission (DT) modes are compared under different channel conditions, and a hybrid mode selection scheme, i.e., selecting the one with the maximum EE among the above three modes, is proposed. Besides, we also prove that both the EE and the SE monotonically increase with the total transmission power under a given condition. Finally, numerical results show that the maximum EE of the FD relaying exceeds those of the HD and DT ones when the required SE is relatively high. Furthermore, the proposed hybrid mode selection scheme can provide up to 192.4% higher EE compared with the DT mode.

This article studies a new non‐orthogonal multiple access (NOMA) assisted decode‐and‐forward cooperative relay (NOMA‐DFCR) system, where the downlink NOMA principle is employed to communicate between a source‐destination pair through a dedicated relay. Performance of the proposed system is analyzed in terms of the outage probability (OP), system throughput (ST), and ergodic sum rate with channel estimation errors (CEEs) and imperfect successive interference cancellation (SIC). An approximate expression of the OP and the diversity order of the presented scheme are derived. To gain further insights, asymptotic analysis of the OP is carried out at high signal‐to‐noise ratio (SNR) regime. Further, we also investigate the impact of power allocation coefficients and CEEs on the system performance. Moreover, the OP of orthogonal multiple access (OMA) assisted cooperative relay system is evaluated and compared with the proposed scheme. To validate the correctness of the derived analytical results, Monte Carlo simulations are performed. Numerical and simulation results have shown that the proposed system outperforms its OMA counterpart and the schemes in References 14 and 15, in terms of both the ST and OP.

SummaryCooperative communication is a significant technology for fifth generation (5G) and beyond wireless communication to improve the quality of service (QoS) in massive networks. In addition, it serves as a promising candidate along with non‐orthogonal multiple access (NOMA) scheme to increase the spectral efficiency. Conventionally, cooperative‐NOMA (C‐NOMA) systems are analysed by assuming perfect successive interference cancellation (SIC) and imperfect SIC (I‐SIC) over Rayleigh, Rican, Hoyt fading channels, and so on. In this paper, near–far relay (NFR) C‐NOMA system is analysed aiding perfect SIC, perfect channel state information (CSI), imperfect (I‐CSI) and (I‐SIC) over Rayleigh fading channel. Initially, we derive analytical expressions of outage probability (OP) by considering I‐SIC and I‐CSI for NFR‐C‐NOMA system. The accuracy of analytical results is verified through Monte Carlo (MC) simulations. Interpretation of the results conveys that I‐CSI and I‐SIC have a substantial impact on OP in NFR‐C‐NOMA scheme and existing schemes. Later, we examined impact on OP in NFR‐C‐NOMA by varying relay position, target rate of users and jointly considering the I‐SIC, I‐CSI. Further, it is also observed that the NFR‐C‐NOMA scheme shows better outage performance than state‐of‐the‐art schemes.

Integrating reconfigurable intelligent surface (RIS) and non-orthogonal multiple access (NOMA) provides a promising solution to support large-scale secure communications. However, reducing the impact of transceiver hardware impairments (HWI) on the performance of RIS-aided NOMA secure networks remains a challenge. In this paper, we propose a robust transmission scheme for RIS-aided NOMA secure networks with transceiver HWI under two proposed eavesdropping scenarios and two artificial noise methods. A closed-form expression for the distortion noise power caused by transceiver HWI in NOMA networks is derived to quantify transceiver HWI. The sum secrecy rate of NOMA users with imperfect successive interference cancellation (SIC) is maximized under distortion noise for more robust security. Further, to tackle the resulting non-convex problem, we decompose it into two sub-problems. Both of them are converted into convex problems using the multi-dimensional quadratic transform (MDQT) method, semi-definite relaxation (SDR) technique, and the successive convex approximation (SCA) algorithm, and then employing the alternate optimization (AO) algorithm solve them. Numerical results demonstrate that the proposed scheme has superior security performance over orthogonal multiple access (OMA) networks, time division multiple access (TDMA) networks, and traditional NOMA networks, achieving more robust performance than the conventional scheme that ignores HWI and imperfect SIC.

We investigate the outage performance of a non-orthogonal multiple access (NOMA) network assisted by multiple active simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-ARISs), under hardware impairments (HIS) and imperfect successive interference cancellation (ipSIC). To accurately evaluate system reliability, we employ the moment matching technique to approximate the composite channel gain distribution as a Gamma random variable within a Nakagami-m fading environment. Building on this approximation, closed-form expressions characterizing the outage performance are deduced. To corroborate the theoretical framework, simulation experiments are conducted, demonstrating three major outcomes: i) The outage performance improves as the number of STAR-ARIS or their constituent reflective elements increases; ii) Under the constraint of a constant total number of elements, a single large-scale STAR-ARIS configuration can outperform a distributed setup of multiple smaller surfaces; and iii) The STAR-ARISs-assisted NOMA network achieves a lower outage probability than its orthogonal multiple access (OMA) counterpart.

The severe interference in full-duplex (FD) cellular network largely degrade the system performance, especially for cell edge users. In this paper, hybrid full/half duplex cellular network which is composed of a mixture of FD and half duplex (HD) base-stations (BSs) is focused. In order to relieve the received inter-cell interference, frequency reuse (FR) is applied. The adopted FR schemes include traditional full FR and two kinds of fractional FR (FFR) named Strict FFR (StFFR) and Soft FFR (SoFFR). Stochastic geometry is adopted to evaluate the system performance. Tractable results of the ergodic rate and coverage probability for different FR schemes are obtained. Through the numerical results, we can observe that full FR and StFFR schemes can improve the user coverage probability at the expense of system spectrum efficiency (SE). SoFFR can improve both the coverage probability and the system SE. The numerical results also show that if the residual Self-interference is not very strong, operating all the BSs in FD mode can achieve the best performance, otherwise, it is better to operate all the BSs in HD mode.

In this paper, a three‐user non‐orthogonal multiple access (NOMA) system based on device‐to‐device (D2D) communication and full‐duplex (FD) transmission is proposed, in which the D2D user acts as a decode‐and‐forward (DF) relay to forward the signal from the base station (BS) to the far user, forming a system termed the FD D2D transmitter aided NOMA (FD‐D2D‐NOMA). In practical NOMA systems, due to the limitation of decoding ability, the near user cannot always perform successive interference cancellation (SIC) successfully. By considering perfect SIC (pSIC) and imperfect SIC (ipSIC), the close‐form expressions for the ergodic sum capacity and outage probability of the proposed FD‐D2D‐NOMA scheme are derived, which match well with the simulation ones. The ergotic sum capacity and outage probability under different levels of residual self‐interference at the FD user and residual interference at the far/near user due to ipSIC are investigated, and the results show that, such interferences have significant impact on the performance of the proposed scheme. Moreover, the analytical and simulation results illustrate the performance gain of the proposed scheme compared with other ones under both pSIC and ipSIC scenarios. The impacts on performance exerted by channel conditions and design parameters are also discussed in this paper.