Hybrid NOMA Assisted OFDMA Uplink Transmission

TL;DR

The paper addresses energy-efficient uplink resource allocation in a hybrid NOMA-OFDMA system with dynamic CSI. It formulates a multi-domain optimization problem, analyzes optimality conditions for pure OMA and pure NOMA, and proposes a low-complexity SRA algorithm to exploit frequency diversity. It introduces power outage probability and power diversity gain as statistical metrics to quantify performance gains, showing that H-NOMA-OFDMA can significantly reduce energy consumption and adapt to diverse energy profiles, with gains growing with the number of users. The findings highlight the potential of H-NOMA-OFDMA to enhance spectrum and energy efficiency in 6G, particularly for ultra-massive MTC and energy-constrained devices.

Abstract

Hybrid non-orthogonal multiple access (NOMA) has recently received significant research interest due to its ability to efficiently use resources from different domains and also its compatibility with various orthogonal multiple access (OMA) based legacy networks. Unlike existing studies on hybrid NOMA that focus on combining NOMA with time-division multiple access (TDMA), this work considers hybrid NOMA assisted orthogonal frequency-division multiple access (OFDMA). In particular, the impact of a unique feature of hybrid NOMA assisted OFDMA, i.e., the availability of users' dynamic channel state information, on the system performance is analyzed from the following two perspectives. From the optimization perspective, analytical results are developed which show that with hybrid NOMA assisted OFDMA, the pure OMA mode is rarely adopted by the users, and the pure NOMA mode could be optimal for minimizing the users' energy consumption, which differs from the hybrid TDMA case. From the statistical perspective, two new performance metrics, namely the power outage probability and the power diversity gain, are developed to quantitatively measure the performance gain of hybrid NOMA over OMA. The developed analytical results also demonstrate the ability of hybrid NOMA to meet the users' diverse energy profiles.

Figures (7)

• Figure 1: An illustration of the hybrid NOMA assisted OFDMA network. Compared to the TDMA case studied in 9679390hnomadown, the patten of resource allocation in the OFDMA case is more complex. For example, in TDMA, a user chooses to use either all the time slots (i.e., the hybrid NOMA mode) or just its own TDMA time slot (i.e., pure OMA), where ${\rm T}_m$ denotes the $m$-th time slot. But in OFDMA, a user, e.g., ${\rm U}_2$, may adopt the pure NOMA mode, and the time slots a user chooses to use are necessarily continuous.
• Figure 2: The total power consumption achieved by hybrid NOMA assisted OFDMA, where the users' channel gains are assumed to be complex Gaussian distributed with zero mean and unit variance. NPCU denotes nats per channel use, and $\epsilon=10^{-5}$.
• Figure 3: The users' individual power consumption achieved by hybrid NOMA assisted OFDMA, where $\epsilon=10^{-4}$ and $M=5$.
• Figure 4: The performance of hybrid NOMA assisted OFDMA in the two-user special case, where the analytical results are based on Lemma \ref{['lemma4']}.
• Figure 5: Comparison between the solutions obtained from Lemma \ref{['lemma4']} and an exhaustive search, where $\epsilon=10^{-5}$, $M=2$ and $R=1$ NPCU.

Theorems & Definitions (6)

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