In this letter, we present the analytical investigation of the non-orthogonal multiple access (NOMA) assisted underwater visible light communication (UWVLC) system. The proposed system can cater to the needs such as low latency, high reliability and high data rate underwater multicasting to the sensor nodes. The UWVLC link is characterized by Exponential-Generalized Gamma (EGG) distribution. In particular, we derive the exact closed-form expressions of average bit error rate (BER) and ergodic capacity for underwater NOMA users. Further to understand the impact of the underwater scenario over the system performance, the analysis is carried out for parameters such as air bubble levels, gradient temperature and salinity level of the water. The obtained results validate the feasibility of the proposed system model.

Energy efficiency is a major concern in the emerging mobile cellular wireless networks since massive connectivity is to be expected with high energy requirements from the network operators. Non-orthogonal multiple access (NOMA) being the frontier multiple access scheme for 5G, there exists numerous research attempts on enhancing the energy efficiency of NOMA enabled wireless networks while maintaining its outstanding performance metrics such as high throughput, data rates and capacity maximized optimally.The concept of green NOMA is introduced in a generalized manner to identify the energy efficient NOMA schemes. These schemes will result in an optimal scenario in which the energy generated for communication is managed sustainably. Hence, the effect on the environment, economy, living beings, etc is minimized. The recent research developments are classified for a better understanding of areas which are lacking attention and needs further improvement. Also, the performance comparison of energy efficient, NOMA schemes against conventional NOMA is presented. Finally, challenges and emerging research trends, for energy efficient NOMA are discussed.

In this paper, we consider the use of non-orthogonal multiple access (NOMA) assisted mobile ad-hoc networking (MANET) for sustainable future radio access. We analyze the performance of the considered NOMA based system over Nakagami-m fading channels for the downlink scenario. In particular, we derive the closed-form expression of bit-error rate (BER) at the end-users supported by the ad-hoc networks cooperated through the near NOMA user as well as through the far NOMA user. Further, we also derive the closed-form expression for the ergodic capacity and packet error rate for the considered system. Based on the obtained results, the impact of the power allocation coefficient over the performance of the considered system is analyzed to determine the optimal power allocation coefficient. The analytical results are corroborated with the simulations for various parameters to validate the analysis. It is observed that the NOMA assisted MANET system outperforms the conventional orthogonal multiple access based system in terms of ergodic capacity.

In this article, we investigate a selective decode-and-forward (DF)-aided cooperative nonorthogonal multiple access (NOMA) system performance in the presence of practical impairments using imperfect successive interference cancellation (SIC) and channel estimation error (CEE). The base station communicates directly and via a relay with the two NOMA users in two-time phases. In particular, the selective DF with synchronized direct and relay transmission relaying protocol is proposed for the considered downlink NOMA system to offer enhanced quality of service and improved data reliability compared with the conventional NOMA and DF NOMA systems. The closed-form of exact and asymptotic expressions of the average bit error rate (ABER) at both NOMA users are derived considering the impact of imperfect SIC and CEE. Furthermore, the outage probability is also obtained. Finally, the improvement in the system performance acquired by the proposed scheme over the existing methods is corroborated by Monte Carlo simulations.

The next-generation networks are supposed to handle the large number of connections required for fifth-generation (5G) and beyond applications. Cooperative multi-relay communication with the downlink non-orthogonal multiple access (DL-NOMA) technique has the capability to provide increased energy and spectral efficiency (SE) by enabling such large connections. It promotes green communication by efficiently serving multiple users through a common resource and improving the system’s diversity without compromising the existing infrastructure. This paper investigates the performance of a multi-relay cooperative NOMA system to support 5G and beyond scenarios with practical impairments. The base station communicates with the NOMA end users using cooperative selective decode-and-forward (DF) based ${K}$ multiple relays and direct links. The asymptotic closed-form expression of the symbol error rate (SER) is derived for the NOMA users with imperfect channel state information (CSI) and successive interference cancellation (SIC) errors. The analysis is carried out for the generalized modulation pair, i.e., BPSK-BPSK, QPSK-BPSK and QPSK-QPSK, for NOMA end users. The efficacy of channel estimation error (CEE), power allocation coefficient and diversity order for the aforesaid system is also demonstrated. Finally, the theoretical analysis is endorsed by the Monte Carlo simulations.