Hybrid non-orthogonal multiple access (H-NOMA), which combines the advantages of pure NOMA and conventional OMA, has emerged as a highly promising multiple access technology for future wireless networks. While recent studies have proposed various H-NOMA systems using different successive interference cancellation (SIC) methods, their analyses typically assume a fixed channel gain order between paired users. However, in practice, user pairing is often configured typically based on long-term network deployment requirements or statistical channel characteristics (e.g., geographic layout or average channel gain) rather than instantaneous channel states. This practical pairing strategy leads to random channel gain ordering, where the relative channel gains between paired users are inherently stochastic and time-varying. This aspect is critical and fundamentally affects system performance, yet remains understudied. To address this issue, this paper analyzes the performance of three H-NOMA schemes under such random channel gain ordering: (a) fixed-order SIC (FSIC) aided H-NOMA; (b) hybrid SIC with non-power adaptation (HSIC-NPA) aided H-NOMA; and (c) hybrid SIC with power adaptation (HSIC-PA) aided H-NOMA. For the opportunistic users seeking to maximize data rate, the closed-form expressions for the probability that each H-NOMA scheme underperforms conventional OMA are derived rigorously. Asymptotic analyses in the high SNR regime are also developed. Simulation results validate the theoretical derivations and demonstrate the performance of the H-NOMA schemes across different SNR scenarios, thereby offering foundational insights for deploying robust H-NOMA in next-generation wireless systems.

This paper systematically analyzes and optimizes the outage performance for a multi-cell vehicle-to-infrastructure (V2I) network, wherein each cell is assisted by a roadside-mounted reconfigurable intelligent surface (RIS) for signal enhancement. We first derive the closed-form outage probability (OP) expression for Nakagami-m-fading V2I links by modeling signal and interference distributions via the moment-matching technique. The OP expression reveals that enlarging the element quantity of RISs can significantly reduce OP, as the inter-cell interference grows much slower than the signal power due to incoherent combination of interference paths. To further optimize the network-wide outage performance, we propose two power control mechanisms: a distributed game-based approach achieving Nash equilibrium through properly-designed utility functions, and a centralized deep reinforcement learning (DRL)-based approach that minimizes the maximum OP of all the V2I links by leveraging the advanced soft actor-critic (SAC) algorithm. Finally, simulations verify our theoretical derivations, and demonstrate that RIS deployment combined with optimized power control substantially improves the reliability of V2I networks.

Hybrid non-orthogonal multiple access (H-NOMA) technology, which combines the benefits of non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) through flexible resource allocation in a single transmission, has shown great potential for enhancing the performance of wireless communication systems. To further exploit the potential of H-NOMA, this paper proposes a novel design of H-NOMA which jointly incorporates hybrid successive interference cancellation (HSIC) and power adaptation (PA) in the NOMA transmission phase, by introducing a power adaptation factor . For a given power reducing coefficient β, which ensures that the energy consumption of the proposed scheme is lower than that of conventional OMA, the probability that the achievable rate of the proposed HSIC-PA aided H-NOMA scheme fails to outperform its OMA counterpart is derived in closed form. Besides, the impact of user pairing is considered. Furthermore, the asymptotic analysis shows that the aforementioned probability of the proposed H-NOMA scheme can approach zero in the high signal-to-noise ratio (SNR) regime without constraints on either users’ target rates or transmit power. By dynamically adjusting the transmission power of the opportunistic user and the decoding order of HSIC, signal interference between the legacy user and the opportunistic user can be effectively controlled, thereby improving the achievable rate and energy efficiency of the opportunistic user. This represents a significant improvement over conventional H-NOMA schemes, which require specific restrictive conditions to make the probability that their achievable rate underperforms OMA approach zero at high SNR, as shown in existing work. The above observation indicates that, with lower energy consumption, the proposed HSIC-PA aided H-NOMA can achieve a higher data rate than pure OMA with probability 1 at high SNR, leading to improved energy efficiency. Finally, numerical results are provided to verify the accuracy of the analysis and also to demonstrate the superior performance of the proposed H-NOMA scheme.

This paper aims to reveal the potential of hybrid non-orthogonal multiple access (NOMA) in improving energy efficiency, which combines the advantages of NOMA and conventional orthogonal multiple access (OMA). In particular, a novel hybrid NOMA scheme is proposed, which can be implemented as an simple add-on to the legacy OMA network. Specifically, in the proposed hybrid NOMA scheme, a user can transmit signals by using not only its own allocated channel resource block as in OMA, but also sharing the channel of other users via NOMA. To release the potential of hybrid NOMA, a flexible successive interference cancellation (SIC) method is adopted. Rigorous analysis is provided, which indicates that even with less energy consumption, the proposed hybrid NOMA scheme offers a higher data rate than the conventional OMA scheme. The numerical results support the analysis and highlight the superior performance of HSIC in comparison to FSIC.

This paper aims to study the impact of non-orthogonal multiple access (NOMA) assisted grant-free transmissions on reducing age of information (AoI) in status updating systems. Particularly, an uplink communication scenario is considered, where multiple users upload their status updates to a destination competitively. To mitigate collisions among users,$K$reception signal-to-noise ratio (SNR) levels are pre-configured, which can be chosen randomly by the users. By applying NOMA, successive interference cancellation (SIC) is carried out at the receiver to decode the signals from different users sequentially. Different from most existing works which adopt generate-at-will (GAW) model for modeling the generating process of status updates' arrivals, this paper considers a more general model to characterize the randomness of the status updates' arrivals. Closed-form expressions for AoI achieved by the proposed NOMA assisted grant-free scheme is obtained. Numerical results are provided to validate the accuracy of the analytical results and also demonstrate the superior performance of the proposed scheme in reducing AoI compared to conventional OMA based methods.

Cognitive vehicle-to-vehicle (V2V) communication, operating as an underlay to vehicle-to-infrastructure (V2I) communication systems, serves as a critical enabler for platoon driving applications. In practice, ensuring reliable V2I links while maintaining high-throughput intra-platoon links is essential for road safety. This paper investigates the joint optimization of relay selection and resource allocation in a long platoon network, where a single relay vehicle facilitates intra-platoon connectivity. The objective is to maximize the long-term V2V sum-rate while satisfying V2I signal-to-interference-plus-noise ratio (SINR) constraints and relay service duration limitations. To solve this temporally coupled optimization problem with hybrid decision variables—involving discrete relay and channel selection as well as continuous power control—we adopt a Hybrid Proximal Policy Optimization (H-PPO) framework. The proposed solution employs dual actor networks to simultaneously learn optimal discrete and continuous policies. Extensive simulations validate that the H-PPO algorithm achieves substantial improvements in V2V throughput while guaranteeing V2I reliability and energy-efficient relay operation in high-mobility long-platoon scenarios.

ABSTRACT To tackle the challenge of recognizing highly similar interleaved signals, this paper proposes a novel recognition method leveraging a spatial dimensional upgrading transformation squeeze and excitation (SD‐SE) block. Unlike traditional attention mechanisms reliant on internal back‐propagation, SD‐SE block offers enhanced controllability and effectiveness. It introduces SD‐SE, a pre‐weighted training network, using a lightweight, manually controllable approach. The block addresses issues of initial weight randomness and incomplete signal characteristic utilization in attention mechanisms. Furthermore, SD‐SE mitigates CNN's tendency to lose key information during feature extraction. Experiments show SD‐SE achieves superior accuracy in recognizing highly similar interleaved signals, resolving challenges in complex signal recognition. Notably, this lightweight module is compatible with various attention networks, broadening its applicability.

This paper studies the application of cognitive radio inspired non-orthogonal multiple access (CR-NOMA) to reduce age of information (AoI) for uplink transmission. In particular, a time division multiple access (TDMA) based legacy network is considered, where each user is allocated with a dedicated time slot to transmit its status update information. The CR-NOMA is implemented as an add-on to the TDMA legacy network, which enables each user to have more opportunities to transmit by sharing other user’s time slots. A rigorous analytical framework is developed to obtain the expressions for AoIs achieved by CR-NOMA with and without re-transmission, by taking the randomness of the status update generating process into consideration. Numerical results are presented to verify the accuracy of the developed analysis. It is shown that the AoI can be significantly reduced by applying CR-NOMA compared to TDMA.Moreover, the use of re-transmission is helpful to reduce AoI, especially when the status arrival rate is low.

In advanced vehicular networks, Roadside Unit (RSU)-based amplify-and-forward (AF) relay and passive Reconfigurable Intelligent Surface (RIS) are two potential helpers to enhance the vehicle-to-vehicle (V2V) communications when the direct link experiences poor quality. This paper presents a comprehensive comparison of the two enhancement modes from the outage performance perspective. In the presence of both direct link and enhanced link, the analytical expressions of the outage probability (OP) for the V2V communication under the two enhancement modes are derived respectively. Moreover, considering the co-channel interference caused by relay/RIS, the OP of the neighbouring vehicle-to-infrastructure (V2I) communication is also derived. Additional analysis compares the diversity order and the strength of interference created by the V2V communication under the two enhancement modes. Further discussions are presented on the effect of the channel estimation error and phase quantization error under the RIS mode. Finally, the pros and cons of the two enhancement modes are demonstrated by both the analytical and numerical results.

Hybrid non-orthogonal multiple access (NOMA), which organically combines pure NOMA and conventional OMA, has recently received significant attention to be a promising multiple access framework for future wireless communication networks. However, most of the literatures on hybrid NOMA only consider fixed order of successive interference cancellation (SIC), namely FSIC, for the NOMA transmission phase of hybrid NOMA, resulting in limited performance. Differently, this paper aims to reveal the potential of applying hybrid SIC (HSIC) to improve the energy efficiency of hybrid NOMA. Specifically, a HSIC aided hybrid NOMA scheme is proposed, which can be treated as a simple add-on to the legacy orthogonal multiple access (OMA) based network. The proposed scheme offers some users (termed “opportunistic users”) to have more chances to transmit by transparently sharing legacy users’ time slots. For a fair comparison, a power reducing coefficient$\beta $is introduced to ensure that the energy consumption of the proposed scheme is less than conventional OMA. Given$\beta $, the probability for the event that the achievable rate of the proposed HSIC aided hybrid NOMA scheme cannot outperform its OMA counterpart is obtained in closed-form, by considering impact of user pairing. Furthermore, asymptotic analysis shows that the aforementioned probability can approach zero in the high SNR regime under some given conditions, which are compositely determined by the users’ transmit powers, primary user’s target data rate and$\beta $, indicating that the energy efficiency of the proposed scheme is almost surely higher than that of OMA for these given conditions. Numerical results are presented to verify the analysis and also demonstrate the benefit of applying HSIC compared to FSIC.

Vehicle-to-infrastructure (V2I) network is a new paradigm of wireless system with special topology where roadside units (RSUs) are linearly deployed along the roadside and vehicles linearly move on the road. For such system, some classical problems would have new formulations and solutions. We in this paper investigate the joint power control and user scheduling problem for a multi-cell downlink V2I network, the objective of which is to maximize the sum-rate of the network under the signal-to-interference-plus-noise ratio (SINR) constraint of each V2I link. Considering the high mobility of vehicles, the objective function is set as the mean of the sum-rate over a sequence of time slots. For ease of handling, we first decouple the problem into multiple separate subproblems based on the linear distribution of RSUs. Then we employ the quadratic transform technique for fractional programming (FP) to transform the mixed integer nonlinear programming (MINLP) subproblems into convex problems, and obtain the solutions with Branch and Bound method. Finally the validity of our proposed algorithm is verified by numerical simulations.

This paper aims to study the role of cognitive radio inspired non-orthogonal multiple access (CR-NOMA) in improving information freshness of status updating systems with random arrivals. Particularly, a time slotted multiuser scenario is considered, where each user transmits its status update to a receiver. Each user is allocated with a time slot. In CR-NOMA, each user can transmit signal as a primary user by using its own time slot, besides, it can also transmit signal as a secondary user by sharing the time slot of another user. Hence, more transmission opportunities are provided by CR-NOMA compared to conventional time division multiple access (TDMA) based schemes. In this paper, age of information (AoI) is utilized as the performance metric. For comparison purpose, exact expressions for the average AoIs achieved by CR-NOMA and benchmark TDMA are obtained. Numerical results are provided to validate the accuracy of the analytical results and also demonstrate the superior performance of CR-NOMA on reducing AoI. It is shown that the AoI can be significantly reduced by CR-NOMA compared to TDMA.

Reconfigurable holographic surfaces (RHSs) constitute a promising technique of supporting energy-efficient communications. In this paper, we formulate the energy efficiency maximization problem of the switch-controlled RHS-aided beamforming architecture by alternately optimizing the holographic beamformer at the RHS, the digital beamformer, the total transmit power and the power sharing ratio of each user. Specifically, to deal with this challenging non-convex optimization problem, we decouple it into three sub-problems. Firstly, the coefficients of RHS elements responsible for the holographic beamformer are optimized to maximize the sum of the eigen-channel gains of all users by our proposed low-complexity eigen-decomposition (ED) method. Then, the digital beamformer is designed by the singular value decomposition (SVD) method to support multi-user information transfer. Finally, the total transmit power and the power sharing ratio are alternately optimized, while considering the effect of transceiver hardware impairments (HWI). We theoretically derive the spectral efficiency and energy efficiency performance upper bound for the RHS-based beamforming architectures in the presence of HWIs. Our simulation results show that the switch-controlled RHS-aided beamforming architecture achieves higher energy efficiency than the conventional fully digital beamformer and the hybrid beamformer based on phase shift arrays (PSA). Moreover, considering the effect of HWI in the beamforming design can bring about further energy efficiency enhancements.

The aim of this paper is to reveal the importance of hybrid successive interference cancellation (SIC) and power adaptation (PA) for improving transmission robustness of uplink non-orthogonal multiple access (NOMA). Particularly, a cognitive radio inspired uplink NOMA communication scenario is considered, where one primary user is allocated one dedicated resource block, while$M$secondary users compete with each other to be opportunistically served by using the same resource block of the primary user. Two novel schemes are proposed for the considered scenario, namely hybrid SIC with PA (HSIC-PA) scheme and fixed SIC with PA (FSIC-PA) scheme. Both schemes can ensure that the secondary users are served without degrading the transmission reliability of the primary user compared to conventional orthogonal multiple access (OMA) based schemes. The novelty of the proposed schemes compared to those existing schemes is the introduction of power adaptation. This paper presents rigorous analytical results to show that both schemes can avoid outage probability error floors without any constraints on users’ target rates in the high SNR regime, which cannot be achieved by the existing schemes. Furthermore, it is shown that the diversity gain achieved by the HSIC-PA scheme is$M$, while that of the FISC-PA scheme is only 1. Numerical results are provided to verify the developed analytical results and also demonstrate the superior performance achieved by the proposed schemes by comparing with the existing HSIC without PA (HSIC-NPA) scheme. The presented simulation results also show that HSIC-PA scheme performs the best among the three schemes, which indicates the importance of the combination of HSIC and PA for improving transmission robustness.

We propose a hybrid beamforming architecture for near-field reconfigurable holographic surfaces (RHS) harnessed in cell-free networks. Specifically, the holographic beamformer of each base station (BS) is designed for maximizing the channel gain based on the local channel state information (CSI). By contrast, the digital beamformer at the central processing unit is designed based on the minimum mean squared error criterion. Furthermore, the near-field spectral efficiency of the RHS in cell-free networks is derived theoretically by harnessing the popular stochastic geometry approach. We consider both the phase shift error (PSE) at the RHS elements and the hardware impairment (HWI) at the radio frequency (RF) chains of the transceivers. Furthermore, we theoretically derive the asymptotic capacity bound, when considering an infinite physical size for the RHS in the near-field channel model. The theoretical analysis and simulation results show that the PSE at the RHS elements and the HWI at the RF chains of transceivers limit the spectral efficiency in the high signal-to-noise ratio region. Moreover, we show that the PSE at the RHS elements and the HWI at the RF chains of BSs can be compensated by increasing the number of BSs. Finally, we also demonstrate that the ergodic spectral efficiency based on the near-field channel model is higher than that based on the far-field channel model assumption.

The application of network non-orthogonal multiple access (N-NOMA) technique to coordinated multi-point (CoMP) systems has attracted significant attention due to its superior capability to improve connectivity and maintain reliable transmission for CoMP users simultaneously. Based on the concept of quasi-degraded channel for N-NOMA, this paper studies the precoding design for downlink N-NOMA scenarios with two base stations (BSs) equipped with multiple antennas. In specific, under quasi-degraded channels, simple linear precoding based N-NOMA can achieve the same minimal total transmission power as theoretically optimal but complicated dirty paper coding (DPC) scheme, when the users’ target rates and minimal transmission power of each BS are given. In this paper, the channel quasi-degradation (QD) condition is first rigorously derived for the scenario with single CoMP user and two NOMA users. The closed-form optimal precoders for N-NOMA under quasi-degraded channels are also provided. Then, based on QD condition, a novel hybrid N-NOMA (H-N-NOMA) scheme is proposed, which is a mixture of N-NOMA and conventional zero-forcing beamforming (ZFBF) scheme. Further, for the scenarios with more users, a low-complexity QD based user pairing (QDUP) algorithm is proposed, which is then combined with H-N-NOMA to make a novel scheme termed H-N-NOMA/QDUP into being. Numerical results are presented to reveal the impact factors on QD channels, and also demonstrate the superior performance of the proposed H-N-NOMA/QDUP scheme. It is shown that the proposed H-N-NOMA/QDUP scheme can effectively exploit the benefit of multi user diversity.

Reconfigurable intelligent surfaces (RIS) are capable of beneficially ameliorating the propagation environment by appropriately controlling the passive reflecting elements. To extend the coverage area, the concept of simultaneous transmitting and reflecting reconfigurable intelligent surfaces (STAR-RIS) has been proposed, yielding supporting 360° coverage user equipment (UE) located on both sides of the RIS. In this paper, we theoretically formulate the ergodic sum-rate of the STAR-RIS assisted non-orthogonal multiple access (NOMA) uplink in the face of channel estimation errors and hardware impairments (HWI). Specifically, the STAR-RIS phase shift is configured based on the statistical channel state information (CSI), followed by linear minimum mean square error (LMMSE) channel estimation of the equivalent channel spanning from the UEs to the access point (AP). Afterwards, successive interference cancellation (SIC) is employed at the AP using the estimated instantaneous CSI, and we derive the theoretical ergodic sum-rate upper bound for both perfect and imperfect SIC decoding algorithm. The theoretical analysis and the simulation results show that both the channel estimation and the ergodic sum-rate have performance floor at high transmit power region caused by transceiver hardware impairments.

The aim of this paper is to present a groundwork on the delay-minimized routing problem in a vehicular ad-hoc network (VANET) where some of the vehicles are equipped with full-duplex (FD) radios. We first give the generalized delay calculation model for a multi-hop path, and prove that the Dijkstra algorithm is unable to get the delay-minimized routing path from source to destination. Then we propose two routing methods: graph-based method and deep reinforcement learning (DRL)-based method. In the graph-based method, the network topology is reformulated as an equivalent graph and then an evolved-Dijkstra algorithm is proposed. In the DRL-based method, the deep Q network (DQN) is employed to learn the shortest end-to-end path, wherein the delay is modeled as the rewards for routing actions. The graph-based method can achieve the exact minimum end-to-end delay, while the DRL-based method is more feasible due to its acceptable complexity. Finally, extensive simulations demonstrate that the DRL-based approach with proper hyper-parameters can achieve near minimum end-to-end delay, and the achieved delay has a notably decline as the number of FD nodes increases.

Full-duplex (FD) radio, which enables co-time co-channel receiving and forwarding at one device, is expected to be leveraged to improve the relay efficiency of multi-hop inter-vehicle communications. This paper considers a vehicular ad-hoc network (VANET) with some of the vehicles being FD enabled. We first present the new calculation model of the end-to-end delay, and then prove that the Dijkstra algorithm is unable to get the shortest (i.e. delay-minimized) path from source to destination. To handle this, we reformulate the network topology as an equivalent graph through decoupling all the FD-related links, and then propose an evolved-Dijkstra algorithm to find the shortest routing path of the reformulated graph with low complexity. Extensive simulations demonstrate that our approach can achieve the minimum end-to-end delay of inter-vehicle communications, and the achieved delay has a notably decline as the number of FD nodes increases.

Abstract Unmanned aerial vehicles (UAVs) have gained considerable interests in numerous civil applications. To push forward its potentials, cellular-connected UAVs have been introduced. Nevertheless, cellular networks face several bottlenecks such as spectrum scarcity and limited concurrent connectivity. To address these issues, non-orthogonal multiple access (NOMA) can be adopted. NOMA provides several opportunities for cellular-connected UAVs such as larger rate region, balanced performance between system throughput and fairness, and reduced delay. In this paper, we review important findings of the related studies, and outline new opportunities and challenges in NOMA for cellular-connected UAVs. Monte-Carlo simulations are then performed to analyze the new aerial user’s (AU)’s signal characteristics and evaluate the NOMA performance for co-existence of AU and terrestrial user (TU). Our preliminary results show that NOMA is a promising strategy for cellular-connected UAVs.

Efficiency of cellular-connected UAVs is challenged by spectrum inefficiency, limited number of concurrent connectivity, and strong interference. To overcome these issues, in this paper, we study the performance of downlink non-orthogonal multiple access for cellular-connected UAVs. We develop a novel framework based on stochastic geometry for the co-existence of aerial users (AUs) and terrestrial users (TUs), where the spatial distribution of the base stations (BSs) follows a Poisson Point Process. In our analysis, two user association policies and two types of receive antennas are considered while an inter-cell interference coordination (ICIC) technique is also in place. As the main performance measures, we then analytically derive the coverage probability and average rate of AUs and TUs. These derivations are then used to provide quantitative insights on the impact of different system parameters and settings including AU's altitude, TU's distance from the BS, power allocation, successive interference cancellation (SIC) constraints, user association policy, antenna beamwidth, and the number of coordinated BSs. Based on our analysis we then propose an interference-aware scheme based on maximum-SINR user association, directional antenna, and ICIC. A benchmark scheme based on minimum-distance user association, omni-directional antenna, and without ICIC is considered. Compared to the benchmark scheme, our proposed scheme improves the AU's coverage probability by threefold and TU's average rate by six-fold. Compared to the orthogonal multiple access, our proposed scheme trades off a slight reduction in the AU's coverage probability (~1%) with a significant increase in the achieved rate of the TUs (603Kbps/resource block).

Connecting aerial users (AU)s to cellular networks expands the potential of many applications. Nevertheless, existing cellular networks are not designed to efficiently serve AUs and terrestrial users (TU)s. Limited spectrum and high interference make the task even more challenging. Thus, in this paper, we examine the feasibility of fixed-power non-orthogonal multiple access (NOMA) scheme in meeting the demands of AUs and TUs by leveraging stochastic geometry. To this end, we propose a tractable framework for evaluating the coverage of AU and TU in cellular networks, where BSs are distributed using Poisson Point Process (PPP). We then derive the coverage probability of AU and TU. Using these analytical expressions, we further analyze the impact of different network parameters such as AU's altitude, TU's distance, and power allocation, and obtain key insights for designing an efficient NOMA scheme. Our results show that i) increasing AU's altitude does not always degrade the signal-to-interference ratio (SIR), ii) fixed-power NOMA scheme cannot be employed solely to serve AU's control and command (C& C) link, iii) pairing a near TU with a typical AU may prevent significant performance degradation, and iv) mitigating the interference of TU could improve the performance of AU.

This paper studies the application of the unmanned aerial vehicles (UAVs) to a malfunction area. Note that the ground base stations (GBSs) inside the malfunction area are broken, whereas the GBSs outside work well and are distributed according to a homogeneous Poisson point process (HPPP). A user-centric cooperative scheme is proposed to serve the user equipments(UEs) in the malfunction area. Specifically, based on the UEs' connections to the UAV and nearest GBS, the users in the malfunction area can be served by the UAV only, both the UAV and the nearest GBS or the nearest GBS only. The proposed scheme can be tuned by a parameter δ. Analytical framework is developed to obtain the expression for the coverage probability achieved by a UE in the malfunction area, which is verified by computer simulations.

A promising application of unmanned aerial vehicles (UAVs) to the future communication networks is to address emergency communications. This paper considers such a scenario where a UAV is employed to a malfunction area (modeled as a circular disc) in which all ground base stations (BSs) break down. The ground BSs outside the malfunction area are modelled as a homogeneous Poisson point process (HPPP). Particularly, a user-centric cooperative scheme is proposed to serve the UEs in the malfunction area. According to the user equipment's (UE's) connections to the UAV and the nearest ground BS, the malfunction area is divided into three regions, namely the UAV region, the cooperation region and the nearest ground BS region, in which the UEs are served by the UAV only, both the UAV and the nearest ground BS, and the nearest ground BS, respectively. The region size of each type can be adjusted by a cooperation parameter $\delta$. Through rigorous derivations, an expression for the coverage probability achieved by the UE in the malfunction area is obtained. In order to provide a fair comparison, the normalized spectral efficiency (NSE) which is defined by taking both system throughput and the number of serving BSs into consideration, is used as a criterion for the performance evaluation. Numerical results are presented to verify the accuracy of the analytical results and also to demonstrate the superior performance of the proposed scheme.

To improve the system throughput, this paper proposes a network non-orthogonal multiple access (N-NOMA) technique for the uplink coordinated multi-point transmission (CoMP). In the considered scenario, multiple base stations collaborate with each other to serve a single user, referred to as the CoMP user, which is the same as for conventional CoMP. However, unlike conventional CoMP, each base station in N-NOMA opportunistically serves an extra user, referred to as the NOMA user, while serving the CoMP user at the same bandwidth. The CoMP user is typically located far from the base stations, whereas users close to the base stations are scheduled as NOMA users. Hence, the channel conditions of the two kinds of users are very distinctive, which facilitates the implementation of NOMA. Compared to the conventional orthogonal multiple access-based CoMP scheme, where multiple base stations serve a single CoMP user only, the proposed N-NOMA scheme can support larger connectivity by serving the extra NOMA users, and improve the spectral efficiency by avoiding the CoMP user solely occupying the spectrum. A stochastic geometry approach is applied to model the considered N-NOMA scenario as a Poisson cluster process, based on which insightful closed-form or quasi closed-form analytical expressions for outage probabilities and ergodic rates are obtained. Numerical results are presented to show the accuracy of the analytical results and also demonstrate the superior performance of the proposed N-NOMA scheme.

To study the feasibility of network non-orthogonal multiple access (N-NOMA) techniques, this paper proposes a N-NOMA scheme for a downlink coordinated multipoint (CoMP) communication scenario, with randomly deployed users. In the considered N-NOMA scheme, superposition coding (SC) is employed to serve cell-edge users as well as users close to base stations (BSs) simultaneously, and distributed analog beamforming by the BSs to meet the cell-edge user's quality of service requirements. The combination of SC and distributed analog beamforming significantly complicates the expressions for the signal-to-interference-plus-noise ratio at the receiver, which makes the performance analysis particularly challenging. However, by using rational approximations, insightful analytical results are obtained in order to characterize the outage performance of the considered N-NOMA scheme. Computer simulation results are provided to show the superior performance of the proposed scheme as well as to demonstrate the accuracy of the analytical results.