Joint Optimization on Mode Switching and Power Adaptation in Semantic-Assisted Hybrid NOMA

• Published in: IEEE open journal of the Communications Society Vol. 5; pp. 4797 - 4807
• Main Authors: Tang, Wenqian, Liu, Ronghua, Li, Qiang, Meng, Zian, Pandharipande, Ashish, Ge, Xiaohu
• Format: Journal Article
• Language: English
• Published: New York IEEE 2024; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Adaptation; Algorithms; Bit rate; Channel estimation; ergodic semantic rate; Fading; Fading channels; Frequencies; Lagrangian duality method; NOMA; non-orthogonal multiple access; Nonorthogonal multiple access; Optimization; power adaptation; Semantic communication; Semantics; Switches; Switching
• ISSN: 2644-125X; 2644-125X
• DOI: 10.1109/OJCOMS.2024.3437357

In this paper, a semantic-assisted hybrid non-orthogonal multiple access (NOMA) is investigated, in which a secondary far user (F-user) wishes to transmit to a common access point simultaneously with a primary near user (N-user) in the same frequency band. In order to take advantages of both semantic communication (SemCom) and traditional bit communication (BitCom), a SemCom/BitCom mode switching is proposed at the F-user, by adapting to the varying fading states of the channel. On this basis, in order to optimize the performance of F-user while providing adequate protection to the primary N-user, an optimization problem of maximizing the ergodic semantic rate of F-user is formulated, subject to an instantaneous bit rate constraint of N-user. This problem is non-convex and requires a joint design on the SemCom/BitCom mode switching and power adaptation over different fading states. To provide insights, it is first proved that the formulated problem satisfies the time-sharing condition, indicating that there exists a dual problem with zero duality gap to the original problem. A Lagrangian Sub-Gradient Algorithm is then proposed to solve the dual problem. Simulation results demonstrate that in the proposed semantic-assisted hybrid NOMA, significant performance improvement can be achieved for the F-user while meeting the instantaneous bit rate requirement of N-user. Furthermore, by adapting to the varying fading states, the proposed joint SemCom/BitCom mode switching and power adaptation scheme outperforms both BitCom and SemCom.