In this work, we evaluate the bit error rate (BER) and block error rate (BLER) performances of a downlink two-user non-orthogonal multiple access system considering the received energy per bit per noise spectral density (Eb/N0). A one-to-one mapping between the Eb/N0and transmit signal to noise ratio (SNR) is derived for the uncoded and coded systems. Furthermore, the channel coding gain is quantified for turbo product codes with various code rates and block lengths. In addition, the performance is evaluated for Mn-ary quadrature amplitude modulation of selected orders. It is shown that the BER and BLER performances reach the waterfall region with smaller Eb/N0values compared to transmit SNR, which reduces the simulation run time to capture the desired performance.

This work presents a novel nonorthogonal multiple access (NOMA) cognitive radio (CR) system where the base station (BS) opportunistically multiplexes the secondary user (SU) with the primary user (PU) using power-domain NOMA. As the PU has the priority to transmit and SU is satisfied on best-effort basis, four different transmission-modes (TMs) are produced at the BS, which are PU orthogonal multiple access (PU-OMA), SU-OMA, PU/SU-NOMA, and silent mode. Consequently, the considered protocol can be classified as a hybrid underlay-interweave CR-NOMA. The TM adaptation should be seamless for the PU where its detector configuration remains unchanged regardless of the active TM. In contrast, the SU has to identify the active TM blindly, i.e. without side information, to select the appropriate detector. The identification process is performed using a classifier that is designed based on the maximum likelihood criterion. The performance of the proposed system is analyzed in terms of throughput, packet error rate (PER), and classification error. The Binomial and Multinomial theorems are utilized to simplify and allow a tractable analysis. The derived closed-form expressions, corroborated by Monte-Carlo simulation results, show that the hybrid CR-NOMA can provide substantial throughput improvement over conventional NOMA, which is about a 100%.

In this work, we derive new closed-form expressions for the throughput of non-orthogonal multiple access (NOMA) system with adaptive modulation orders. The system design considers a packet-based transmission where the base station adapts the modulation orders to satisfy the block error rate (BLER) requirement for each user and maximize the throughput by minimizing the maximum signal to noise ratio (SNR) requirements of the users. The optimization problem is formulated as a minmax problem to jointly optimize the modulation orders and SNR thresholds, where the original mixed-integer programming is simplified to integer programming by introducing an auxiliary variable. Compared to the grid search approach, the analytical and simulation results show that the min-max approach can improve the throughput with a significant reduction in the number of transmission modes, the throughput can be improved by up to 2.5 dB at moderate SNRs and by 1 bit/symbol at extremely high SNRs.

Nonorthogonal multiplexing (NOM) is a novel superposition coding scheme that has been recently proposed to improve the throughput of wireless systems. However, restricting the number of multiplexed packets to two limits the throughput improvement of nonorthogonal multiplexing (NOM) to 100% in best-case scenarios. Therefore, this work presents a generalized NOM (GNOM) design with an unlimited number of multiplexed packets. In the multiplexing process, new and retransmitted packets due to arq are combined while considering the impact of channel conditions on the power assigned per packet. The proposed GNOM employs an efficient heuristic algorithm to perform the power assignment and multiplexing decisions. Moreover, the complexity can be controlled by enforcing a limit on the maximum number of multiplexed packets per transmission, making it suitable for iot nodes with diverse computational capabilities and quality of service requirements. The obtained results demonstrate the effectiveness of the proposed scheme, which offers up to 200% throughput 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.

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, which requires accurate knowledge of the channel state information at the transmitter (CSIT). However, providing accurate CSIT can be challenging. Therefore, this paper proposes a data-aware adaptive power assignment NOMA scheme called PANOMA which adaptively changes the signal power based on the transmitted data to maximize the constructive interference. To quantify its potential, closed-form bit error rate (BER) expressions are derived for two users over the broadcast Rayleigh fading channel. Based on these expressions, the power assignment that minimizes the system’s average BER is found. The results demonstrate that PANOMA provides a tangible BER performance gain over conventional power-domain NOMA when both schemes use optimal power and sub-optimal power assignments. Also, PANOMA provides robustness to imperfect power assignment which results from imperfect CSIT. The integrity of the analytical results is verified by Monte Carlo simulation.

Nonorthogonal 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 article 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 suboptimal 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 reduction 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 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.