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Summary In this paper, we propose two downlink multiple access architectures for networks where human‐type communication users (HTCUs) and machine‐type communication devices (MTCDs) coexist. The proposed schemes combine non‐orthogonal multiple access (NOMA), orthogonal frequency division multiplexing (OFDM), and index modulation (OFDM‐IM) concepts. In the first scheme, the base station (BS) transmits bits of HTCUs using modulated symbols and bits of MTCDs by the subcarrier activation pattern (SAP). This approach called IM‐NOMA with null subcarriers (IM‐NOMA‐NS) ensures that inactive subcarriers are always null, which improves the system bit error rate (BER) performance. To improve the spectral efficiency (SE), we propose a second approach, termed IM‐NOMA with dual‐mode modulation (IM‐NOMA‐DM), in which the HTCUs' bits are transmitted using two‐dimensional modulation and the MTCDs' bits are transmitted using one‐dimensional modulation and the SAP. For each proposed system, a near‐optimal low‐complexity detector, based on the energy‐detection (ED) and the log‐likelihood ratio (LLR) criterion, is provided to mitigate the detection burden of the optimal maximum‐likelihood (ML) detector. The BER performances and SE of the proposed schemes are investigated. The average BERs of IM‐NOMA‐NS and IM‐NOMA‐DM are derived in closed‐form expressions corroborated by the simulation results. We have proved numerically that the proposed schemes achieve a good trade‐off between BER performance, SE, and the number of supported users, making them more suitable for Internet of Things (IoT) applications. [ABSTRACT FROM AUTHOR]

In this paper, a non‐orthogonal multiple access (NOMA) scheme is considered for downlink millimeter‐wave (mmWave) transmissions over beamspace massive multiple‐input multiple‐output (MIMO) channels. To improve the NOMA detection and reduce its complexity, it is assumed that users are grouped in clusters. The major benefit of the NOMA depends on the power allocation (PA) among users. In this context, to ensure the quality of service (QoS) of users, a threshold rate for each user is defined. The aim of this work is to propose a new PA strategy that takes into account the pre‐defined threshold rates and maximizes the achievable sum rate. Thereafter, considering the Karush‐Kuhn‐Tucker (KKT) conditions, a closed‐form solution for the PA issue under perfect and imperfect channel state information (CSI) assumptions is derived. Through simulation results, it is shown that the proposed scheme outperforms the conventional orthogonal multiple access techniques in terms of spectral efficiency (SE) and energy efficiency (EE). In addition, the proposed robust PA scheme for the imperfect CSI case reduces the performance loss due to the channel uncertainty. [ABSTRACT FROM AUTHOR]