As energy concerns grow with the rise of energy-constrained devices, it becomes imperative to design an energy-efficient and adaptive multiple access (MA) scheme, supported with accurate energy efficiency (EE) evaluation. Non-orthogonal multiple access (NOMA) enhances EE, yet downlink NOMA faces challenges in terms of computational complexity and power demands of successive interference cancellation (SIC), problematic particularly for energy-limited devices. Existing studies overlook the additional SIC power consumption at NOMA receivers, thus overestimating EE, and giving misleading insights for real system design. Besides the need for more accurate EE evaluation, an adaptive MA approach based on this additional power consumption is required. This paper proposes a SIC-power-aware adaptive SDMA/cooperative NOMA system. An optimization problem is formulated by optimizing MA mode decision, BS beamforming, power allocation factors, and strong user relaying power, to maximize the system EE. We decouple the problem into SDMA/NOMA selection and power allocation sub-problems, solved via a modified semi-orthogonal user selection (SUS) algorithm, successive convex approximation (SCA), difference-of-convex (DC) programming, and semidefinite programming (SDP) approaches. Numerical evaluation confirms the efficiency of the proposed scheme, compared to the baseline schemes.

Beyond diagonal reconfigurable intelligent surface (BD-RIS) has emerged as an innovative and generalized RIS framework that provides greater flexibility in wave manipulation and enhanced coverage. In comparison to conventional RIS, optimization of BD-RIS is more challenging due to the large number of optimization variables associated with it. Typically, optimization of large-scale optimization problems utilizing traditional optimization methods results in high complexity. To tackle this issue, we propose a gradient-based meta learning algorithm which works without pre-training and is able to solve largescale optimization problems. With the objective to maximize the sum rate of the system, to the best of our knowledge, this is the first work considering joint optimization of receiving beamforming vectors at the base station (BS), scattering matrix of BD-RIS and transmission power of users equipment (UEs) in uplink rate-splitting multiple access (RSMA) communication. Numerical results demonstrate that our proposed scheme can outperform the conventional RIS RSMA framework by 22.5 %.

This paper analyzes a downlink C-NOMA scenario where a base station (BS) is deployed to serve a pair of users equipped with movable antenna (MA) technology. The user with better channel conditions with the BS will be able to transmit the signal to the other user providing an extra transmission resource and enhancing performance. Both users are equipped with a receiving MA each and a transmitting MA for the relaying user. In this regard, we formulate an optimization problem with the objective of maximizing the achievable sum rate by jointly determining the beamforming vector at the BS, the transmit power at the device and the positions of the MAs while meeting the quality of service (QoS) constraints. Due to the non-convex structure of the formulated problem and the randomness in the channels we adopt a deep deterministic policy gradient (DDPG) approach, a reinforcement learning (RL) algorithm capable of dealing with continuous state and action spaces. Numerical results demonstrate the superiority of the presented model compared to the other benchmark schemes showing gains reaching 45% compared to the NOMA enabled MA scheme and 60% compared to C-NOMA model with fixed antennas. The solution approach showed 93% accuracy compared to the optimal solution.

We explore in this paper a scenario involving UAV-assisted NOMA, where the UAV serves a dual purpose by providing communication and sensing capabilities, thus supporting ISAC technology. To this end, we formulate an optimization problem aimed at minimizing the Cramér-Rao Bound (CRB) for target localization, with the goal of jointly determining the beamforming vectors at both the base station (BS) and the UAV, as well as the UAV’s position, while maintaining the communication quality of service (QoS) for the users. Given the complex interdependencies between variables and the stochastic nature of the environment due to channel variations, we adopt a deep deterministic policy gradient (DDPG) algorithm, a reinforcement learning (RL) approach suited for continuous state and action spaces. Our numerical results demonstrate the system’s advantages over the conventional NOMA approach and underscore the algorithm’s accuracy in achieving near-optimal solutions.

This paper examines the downlink scenario where a transmitting base station (BS) provides communication services to a set of users by utilizing the rate-splitting multiple access (RSMA), while concurrently providing sensing functionalities. Owing to the available transmit power of the cellular users and their capabilities of decoding the RSMA common stream, we propose to leverage the users in the network to assist the sensing process by collectively forming a probing beam towards the target(s). Using this proposed system and to evaluate its potential gains, we formulate an optimization problem to jointly determine the beamforming design at the transmitting BS, the common stream split, and the distributed beamforming design at the users as well as at the receiving BS aiming to maximize the minimum rate of the users. Due to the non-convexity posed by the formulated problem, we perform rigorous mathematical operations and leverage the semi-definite relaxation (SDR) method to solve it using a successive convex approximation (SCA) algorithm. Our numerical results demonstrate the advantage of exploiting users' resources to assist in the sensing process which is reflected in an enhancement in the achieved rate by the users. Moreover, we present the advantage of our model in comparison to Spatial Division Multiple Access (SDMA) scheme.

This paper examines the integrated sensing and communication technology (ISAC) in the downlink scenario where a base station exploits cooperative non-orthogonal multiple access (CNOMA) to jointly offer communication functions to users and sensing functions to targets. CNOMA allows the user with good channel conditions to assist another user with a weak channel using the decode and forward strategy in full duplex mode while forming a beam-pattern that is capable of sensing the targets. The main objective in this work is to maximize the sum rate of the users by jointly optimizing the communication beamformers and the power allocation of the near user subject to the quality of service requirements for sensing and communication functions. The formulated problem is non-convex and hard to solve using traditional solvers. For that reason, a penalty-based approach is adopted to provide an efficient solution. Numerical results demonstrated the advantage of C-NOMA in ISAC, showing gains reaching up to 38% compared to the traditional NOMA, and 65% compared to the spatial division multiple access (SDMA).

This paper studies the downlink scenario of an unmanned aerial vehicle (UAV)-assisted rate-splitting multiple access (RSMA). The UAV serves as a full duplex (FD) amplify-and-forward relay to assist the base station (BS) in its communication with a set of user equipments (UEs). In this framework, we formulate an optimization problem with the goal of maximizing the minimum achievable rate by jointly optimizing the BS precoding vectors, the common-stream split, UAV transmit power, and the UAV location subject to the power budget constraints of the BS and UAV. Due to the non-convex nature of the problem, we propose an alternating optimization algorithm that decomposes the main problem into a power allocation subproblem and a UAV location subproblem, which are solved in an alternative way. Both subproblems are solved using a successive convex approximation approach. Our numerical results show that the proposed model outperforms traditional RSMA, non-orthogonal multiple access (NOMA), and UAV-assisted NOMA, demonstrating the efficacy of our approach in achieving higher minimum achievable rates.