Browsing by Author "Liao, Chien-Hsun"

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A Geometric Approach for Optimal Power Control and Relay Selection in NOMA Wireless Relay Networks
(2020-04-01)
Gau, Rung-Hung
;
Chiu, Hsiao-Ting
;
Liao, Chien-Hsun
;
電信工程研究所
;
Institute of Communications Engineering
In this paper, we propose a geometric approach for optimal power control and relay selection in NOMA wireless relay networks. First, for each pair of relays, to derive an optimal vector of transmission power that maximizes the network throughput, we formulate a non-convex optimization problem. To obtain a closed-form solution for the non-convex optimization problem, we adopt ellipses and hyperbolas for classification of transmission power vectors. In addition, the proposed geometric approach could be used to select an optimal pair of relays and an optimal vector of transmission power in polynomial time. Furthermore, we observe that allocating all transmission power of the BS to send data to the stronger relay is not necessarily optimal in a NOMA wireless relay network. Simulation results show that the proposed geometric approach could significantly increase the end-to-end sum rate and reduce the power consumption of wireless communications for NOMA wireless relay networks with low computational complexity.
Optimal Power Control for NOMA Wireless Networks With Relays
(2018-02-01)
Gau, Rung-Hung
;
Chiu, Hsiao-Ting
;
Liao, Chien-Hsun
;
Wu, Chi-Lun
;
電信工程研究所
In this letter, we propose a novel approach for dynamically selecting an optimal relay mode and optimal transmission power levels in non-orthogonal multiple access wireless networks with relays. To maximize the network throughput, the proposed approach alternates between the one-relay mode and the two-relay mode based on channel state information. For the two-relay mode, we derive novel closed-form results on optimal power control. Unlike in a conventional one-hop network, it is not always optimal to allocate all power to the relay with the largest channel gain in the studied two-hop network. Based on the closed-form results, one could determine the optimal power levels quickly. Simulation results show that the proposed approach could significantly increase the network throughput.