Continuous Aperture Array (CAPA)-Based Multi-Group Multicast Communications

Mengyu Qian

doi:10.1109/TCOMM.2026.3655762

Continuous Aperture Array (CAPA)-Based Multi-Group Multicast Communications

2026-01-19

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DOI：10.1109/TCOMM.2026.3655762

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As a novel antenna array architecture, continuous aperture arrays (CAPAs) have garnered wide attention in recent years. While existing CAPA-based research has predominantly addressed unicast scenarios, the critical area of multicast beamforming remains unexplored. In this paper, a CAPA-based multi-group multicast communication system is investigated. An integral-based CAPA multi-group multicast beamforming design is formulated for the maximization of the system energy efficiency (EE), subject to a minimum multicast SE constraint of each user group and a total transmit power constraint. To address this non-convex fractional programming problem, we employ Dinkelbach’s method, such that the non-convex group-wise multicast spectral efficiency (SE) constraint is first equivalently transformed into a tractable form using auxiliary variables. Then, an efficient block coordinate descent (BCD)-based algorithm is developed to solve the reformulated problem. The CAPA beamforming design subproblem can be optimally solved via the Lagrangian dual method and the calculus of variations (CoV) theory. It reveals that the optimized CAPA beamformer should be a combination of all the groups’ user channels. To further reduce the computational complexity, a low-complexity zero-forcing (ZF)-based approach is proposed. The closed-form ZF CAPA beamformer is derived using each group’s most representative user channel to mitigate the inter-group interference while ensuring the intra-group multicast performance. Then, the beamforming design subproblem in the BCD-based algorithm becomes a convex power allocation subproblem, which can be efficiently solved. Numerical results demonstrate that: 1) the CAPA can significantly improve the EE compared to conventional spatially discrete arrays (SPDAs); 2) due to the enhanced spatial resolutions, increasing the aperture size of CAPA is not always beneficial for EE enhancement in multicast scenarios; and 3) wider user distributions of each group cause a significant EE degradation of CAPA compared to SPDA.

Keyword:

Continuous-aperture array (CAPA)

continuous source current patterns

multi-group multicast

energy efficiency

Continuous Aperture Array (CAPA)-Based Multi-Group Multicast Communications

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