<div>Non-orthogonal multiple access (NOMA) is considered a promising candidate for future mobile networks due to its ability to provide improved spectral-efficiency, massive connectivity and low latency. As such, studying the bit error rate (BER) performance of NOMA is crucial, particularly as its BER performance depends on the power assignment for each user. Therefore, this paper derives exact BER expressions under additive white Gaussian noise (AWGN) and Rayleigh fading channels for an arbitrary number of NOMA users, where each user employs quadrature amplitude modulation (QAM) with an arbitrary modulation order. Furthermore, the power coefficient bounds (PCB), which ensure fairness between users and solve the constellation points ambiguity problem, are derived for the two and three users NOMA system with arbitrary, but identical, modulation orders. However, the procedure to find these bounds for any modulation orders are exemplified. In addition, this paper finds the optimal power assignment that minimizes the system's average BER for N=2 and 3 users cases. The integrity of the analytical expressions is verified by Monte Carlo simulations, where the results give a valuable insight on the system's BER performance and power assignment granularity. It is shown that the feasible power assignment range becomes significantly small as the modulation order, or the number of users, increases, where the BER performance degrades due to the increased inter-user interference (IUI).</div><div><br></div>

Non-orthogonal multiple access (NOMA) is a promising candidate for future wireless networks due to its ability to improve the spectral-efficiency and network connectivity. Nevertheless, the error rate performance of NOMA depends significantly on the power assignment for each user, which requires accurate knowledge of the channel state information (CSI) at the transmitter, which can be challenging for several applications such as wireless sensor networks (WSNs) and Internet of Things (IoT). Therefore, this paper proposes a power-tolerant NOMA by adaptively changing the signal power of each user to reduce the system sensitivity to inaccurate power assignment. The power adaptation in the power-adaptive NOMA (PANOMA) is performed based on the transmitted data, and it does not require accurate CSI. To quantify its potential, the bit error rate (BER) and the lower bound capacity performance, over Rayleigh fading channels, are derived in exact closed-forms for two and three users scenarios. The results demonstrate that PANOMA provides a tangible BER performance improvement over conventional power-domain NOMA when both schemes use sub-optimal power assignment, which is typically experienced in practical scenarios involving channel time variation and CSI estimation errors. Specifically, it will be shown that both schemes provide similar BERs using optimal assignment, but the PANOMA offers BER reeducation by a factor of 10 for certain scenarios when suboptimal power values are assigned. The integrity of the analytical results is verified via matching extensive Monte Carlo simulation experiments.

Non-orthogonal multiple access (NOMA) is a promising candidate for future mobile networks as it enables improved spectral-efficiency, massive connectivity and low latency. This paper derives exact and asymptotic bit error rate (BER) expressions under Rayleigh fading channels for NOMA systems with arbitrary number of users and arbitrary number of receiving antennas and modulation orders, including binary phase-shift keying and rectangular/square quadrature amplitude modulation. Furthermore, the power coefficients' bounds, which ensure users' fairness, and solve the constellation ambiguity problem, are derived for N = 2 and 3 users cases with any modulation orders. In addition, this paper determines the optimal power assignment that minimizes the system's average BER. These results provide valuable insight into the system's BER performance and power assignment granularity. For instance, it is shown that the feasible power coefficients range becomes significantly small as the modulation order, or N , increases, where the BER performance degrades due to the increased interuser interference. Hence, the derived expressions can be crucial for the system scheduler in allowing it to make accurate decisions of selecting appropriate N , modulation orders, and power coefficients to satisfy the users' requirements. The presented expressions are corroborated via Monte Carlo simulations.Index Terms-Non-orthogonal multiple access (NOMA), bit error rater (BER), arbitrary number of users, arbitrary modulation orders, quadrature amplitude modulation (QAM).

<div>The synergy of nonorthogonal multiple access (NOMA) and cognitive radio (CR) can provide efficient spectrum utilization for future wireless networks and enable supporting heterogeneous quality of service (QoS) requirements. In this context, this article aims at evaluating the throughput of a downlink CR-NOMA network where the secondary user (SU) data is opportunistically multiplexed with the primary user (PU) data using power-domain NOMA. The data multiplexing process is constrained by the PU QoS requirements. The multiplexing process can be considered seamless with respect to the PU because its receiver design will generally remain unchanged. Moreover, we consider the case where the SU detects its own data by blindly identifying the adopted transmission mode (TM) at the base station, which can be PU orthogonal multiple access PU-OMA, SU-OMA, PU/SU-NOMA, and no transmission. Consequently, the network can be classified as a hybrid underlay-interweave. The detection process is considered blind because the SU does not receive side information about the adopted TM. The obtained analytical results corroborated by Monte Carlo simulation results show that the proposed CR-NOMA network can provide substantial throughput improvement over conventional NOMA networks, particularly at low signal-to-noise ratios (SNRs) because the unutilized PU spectrum can be used by the SU. Moreover, in good channel conditions the PU can tolerate some interference from the SU, which may improve the channel utilization significantly. </div><div><br></div>

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<div>Abstract—Non-orthogonal multiplexing (NOM) is a novel superposition coding inspired scheme that has been recently proposed for improving the power, spectrum efficiency and delay of wireless links with packet error rate (PER) constraints. Despite its efficiency, restricting the number of multiplexed packets to two limits the throughput improvement to 100%. Therefore, this work presents a novel NOM design with unlimited number of multiplexed packets by manipulating the repeated transmissions in automatic repeat request (ARQ) to enhance the power and spectrum efficiency by multiplexing new and repeated packets while taking into account the channel conditions and varying the power per packet in different transmissions. The proposed scheme employs an efficient heuristic algorithm to perform the power assignment and multiplexing decisions. Moreover, the complexity of the proposed NOM can be controlled by enforcing a limit on the maximum number of multiplexed packets per transmission, making it suitable for different types of Internet of Things (IoT) nodes with various computational capabilities. The obtained results demonstrate the effectiveness of proposed scheme, which offers up to 200% spectral efficiency improvement at moderate signal to noise ratios (SNRs), and up to 700% at high SNRs. Furthermore, the new scheme can reduce the transmission power consumption by up to 6 dB in the high SNR region.</div>

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<div><div>Non-orthogonal multiple access (NOMA) is a promising candidate for future mobile networks as it enables improved spectral-efficiency, massive connectivity and low latency. This paper derives exact and asymptotic bit error rate (BER) expressions under Rayleigh fading channels for NOMA systems with arbitrary number of users and arbitrary number of receiving antennas and modulation orders, including binary phase-shift keying and rectangular/square quadrature amplitude modulation. Furthermore, the power coefficients' bounds, which ensure users' fairness, and solve the constellation ambiguity problem, are derived for N=2 and 3 users cases with any modulation orders. In addition, this paper determines the optimal power assignment that minimizes the system's average BER. These results provide valuable insight into the system's BER performance and power assignment granularity. For instance, it is shown that the feasible power coefficients range becomes significantly small as the modulation order, or N, increases, where the BER performance degrades due to the increased inter-user interference. Hence, the derived expressions can be crucial for the system scheduler in allowing it to make accurate decisions of selecting appropriate N, modulation orders, and power coefficients to satisfy the users' requirements. The presented expressions are corroborated via Monte Carlo simulations.</div></div><div><br></div>