Non‐orthogonal multiple access (NOMA) is a strong candidate for next generation radio access networks due to its ability of serving multiple users using the same time and frequency resources. Therefore, researchers in academia and industry have been recently investigating the error performances and capacity of NOMA schemes. The main drawback of NOMA techniques is the interference among users due to the its non‐orthogonal access nature, that is usually solved by interference cancellation techniques such as successive interference cancellation (SIC) at the receivers. On the other hand, the interference among users may not be completely eliminated in the SIC process due to the erroneous decisions in the receivers usually caused by channels. In this study, for the first time in the literature, the authors derive an exact closed‐form bit error rate (BER) expressions under SIC error for downlink NOMA over Rayleigh fading channels. Besides, they derive one‐degree integral form exact BER expressions and closed‐form approximate expressions for uplink NOMA. Then, the derived expressions are validated by simulations. The numerical results are depicted to reveal the effects of error during SIC process on the performance for various cases such as power allocation for downlink and channel quality difference for uplink.

The initial 6G networks will likely operate in the upper mid-band (7-24 GHz), which has decent propagation conditions but underwhelming new spectrum availability. In this paper, we explore whether we can anyway reach the ambitious 6G performance goals by evolving the multiple-input multipleoutput (MIMO) technology from massive in 5G to gigantic in 6G. We describe how many antennas are needed to reach the envisioned 6G peak user rates, how many can realistically be deployed in practical radio equipment, and what the practical spatial degrees-of-freedom might become. We further suggest a new deployment strategy that enables the utilization of radiative near-field effects in these bands for precise beamfocusing, localization, and sensing from a single base station site. Finally, we identify open research and standardization challenges that must be overcome to efficiently use gigantic MIMO dimensions in 6G from hardware, cost, and algorithmic perspectives.

The demands for high spectral efficiency and massive connections led the researchers to investigate new multiple access techniques for the future wireless networks. Non- Orthogonal Multiples Access (NOMA) is one of them. Hence, the integration of NOMA technique with the other physical layer techniques like MIMO, cooperative communication and cognitive radio has recently taken considerable attention. Whereas these numerous studies are mostly devoted to reveal the overall capacity and outage performances of NOMA involved systems, the error performances have not been investigated in the literature. In this letter, we analyze error performance of cooperative-NOMA and the exact end-to-end (E2E) bit error probability (BEP) is derived in the closed-form. Then, the derived expressions are validated via simulations. Lastly, the effect of the power allocation coefficient on the error performance is discussed.

Non-orthogonal multiple access (NOMA) is one of the key technologies to serve in ultra-dense networks with massive connections which is crucial for Internet of Things. Besides, NOMA provides better spectral efficiency compared to orthogonal multiple access. However, NOMA systems have been mostly investigated only in terms of ergodic capacity (EC) and outage probability (OP) whereas error performances have not been well-studied. In addition, in those analysis, mostly perfect successive interference canceler (SIC) is assumed or the considered imperfect SIC model is not reasonable. Besides, channel state information (CSI) errors are also not considered in most studies. However, this is not the case for the practical scenarios, and these imperfect SIC and CSI effects limit the performance of NOMA involved systems. Moreover, the imperfect SIC causes unfairness between users. In this paper, we introduce reversed decode-forward relaying NOMA (R-DFNOMA) to improve user fairness compared to conventional DFNOMA (C-DFNOMA). In the analysis, we define imperfect SIC effect as dependant to channel fading and with this imperfect SIC and CSI errors, we derive exact expressions of EC and OP. We also provide upper bound for EC, and asymptotic and lower bound expressions for OP. Furthermore, we evaluate bit error performance of the proposed R-DFNOMA and derive exact bit error probability (BEP) in closed-form with imperfect CSI which is the first study analyzing error performances of decode-forward relaying NOMA with imperfect CSI. Then, we define user fairness index in terms of all key performance indicators (KPIs) (i.e., EC, OP and BEP). Based on extensive simulations, all derived expressions are validated, and it is proved that the proposed R-DFNOMA provides better user fairness than C-DFNOMA in terms of all KPIs. Finally, we discuss the effect of power allocations at both source and relay on the performance metrics and user fairness.

In this letter, we propose a deep learning-aided multi-user detection (DeepMuD) in uplink non-orthogonal multiple access (NOMA) to empower the massive machine-type communication where an offline-trained Long Short-Term Memory (LSTM)-based network is used for multi-user detection. In the proposed DeepMuD, a perfect channel state information (CSI) is also not required since it is able to perform a joint channel estimation and multi-user detection with the pilot responses, where the pilot-to-frame ratio is very low. The proposed DeepMuD improves the error performance of the uplink NOMA significantly and outperforms the conventional detectors (even with perfect CSI). Moreover, this gain becomes superb with the increase in the number of Internet of Things (IoT) devices. Furthermore, the proposed DeepMuD has a flexible detection and regardless of the number of IoT devices, the multi-user detection can be performed. Thus, an arbitrary number of IoT devices can be served without a signaling overhead, which enables the grant-free communication.

Non-orthogonal multiple access (NOMA)-based cooperative relaying systems (CRS) are very promising to overcome spectral inefficiency of conventional cooperative communications. Although NOMA-CRS have great recent attention, almost all studies investigate NOMA-CRS only in terms of capacity and outage probability. Error performances of NOMA-CRS have not been regarded. In this paper, we analyze error performance of NOMA-based diamond relaying network (NOMA-DRN) with imperfect successive interference canceler (SIC) as a NOMA-CRS scheme. We derive exact bit error probability (BEP) for NOMA-DRN and provide a tight approximated BEP in the closed-form. In addition, high-SNR analysis is conducted to present that NOMA-DRN has an error floor. Moreover, it is proved that NOMA-DRN turns out to be a non-equiprobable communication and we derive priori probabilities of symbols. All derived expressions are validated via computer simulations.