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In this article, the problem of joint relay assignment and energy-efficiency maximization (J-RA-EE-MAX) in energy-harvesting downlink (DL) and uplink (UL) clustered nonorthogonal multiple-access (NOMA) networks is considered. Specifically, the aim is to perform relay assignment to user clusters in the DL and UL directions, while simultaneously maximizing energy efficiency (EE) over each relay via multiobjective optimization, and satisfying users' quality-of-service (QoS) constraints. However, problem J-RA-EE-MAX happens to be nonconvex in each link direction, and thus is computationally prohibitive. Alternatively, a low-complexity solution procedure is devised to solve problem J-RA-EE-MAX in each link direction by: (i) optimally solving the energy-efficiency maximizing power allocation (EE-MAX-PA) for each (user cluster, relay) combination to construct the relays' preference profile, and (ii) performing relay assignment via Gale's top trading cycles (TTC) matching mechanism. In particular, the optimal solution of the EE-MAX-PA problem is obtained by transforming it into a concave maximization problem, while the TTC mechanism is executed in linear time-complexity so as to obtain a stable relay assignment. Simulation results are presented to validate the proposed solution procedure, which is shown to yield comparable user cluster sum-rate and relay EE to the J-RA-EE-MAX scheme, and superior to other schemes in both link directions, however, at lower computational complexity, while satisfying users' QoS constraints. Finally, this work sheds light on the importance of decoupling relay assignment in the DL/UL directions, which significantly improves user cluster sum-rate and relay EE in comparison to coupled relay assignment schemes, and thus serves the requirements of 5G networks and beyond. K E Y W O R D Senergy-efficiency, matching, nonorthogonal multiple-access, power allocation, relay assignment Trans Emerging Tel Tech. 2020;31:e3962.wileyonlinelibrary.com/journal/ett
The antenna selection (AS) in non-orthogonal multiple access (NOMA) networks is still a challenging problem since finding optimal AS solution may not be available for all channel realizations and has quite computational complexity when it exists. For this reason, in this paper, we develop a new suboptimal solution, majority based transmit antenna selection (TAS-maj), with significant reduction in computational complexity. The TAS-maj basically selects the transmit antenna with the majority. It is more efficient when compared to previously proposed suboptimal AS algorithms, namely maxmax-max (A 𝟑 ) and max-min-max (AIA) because these schemes are merely interested in optimizing the performance of the strongest and weakest users, respectively at the price of worse performance for the remaining users. On the other hand, the TAS-maj scheme yields better performance for more than half of mobile users in the NOMA networks. In this paper, we consider a multiple-input multiple-output communication system, where all the nodes are equipped with multi-antenna. Besides the TAS-maj is employed at the base station, a maximal ratio combining (MRC) is also employed at each mobile user in order to achieve superior performance. The impact of the channel estimation errors (CEEs) and feedback delay (FD) on the performance of the TAS-maj/MRC scheme is studied in the NOMA network over Nakagami-m fading channels. The outage behavior of the network is investigated by deriving the exact outage probability (OP) expression in closed-form. In addition, the corresponding upper bound of the OP is obtained in the presence of the CEEs and FD. The OP expression in high signalto-noise ratio region is also provided to illustrate an error floor value in the presence of the CEEs and FD as well as diversity and array gains in the absence of the CEEs and FD. The analytical results in the presence and absence of the CEEs and FD are verified by the Monte Carlo simulations. The numerical results imply that the system performance is more sensitive to the CEE than FD and shows the superiority of the proposed TAS-maj/MRC scheme over both A 𝟑 /MRC and AIA/MRC schemes.
This study investigates power‐domain non‐orthogonal multiple access based wireless information exchange process. The investigation considers a dual‐hop non‐regenerative full‐duplex wireless one‐way relaying networks in the system model, where the source terminal transmits two different types of information and subtracts the interference signal at the destination by using successive interference cancellation technique. The outage probability, error probability, achievable rate, and ergodic rate of the considered system is analytically derived. In addition, optimum power allocation coefficients and relay terminal position are determined using the optimization techniques. Monte‐Carlo simulation results validate the analytical and asymptotic derivations. The derived analytical expressions are found closely in agreement with the system level numerical results.
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