Transmission Design for DMA- and RIS-Assisted Satellite Symbiotic Radio Systems with Low-Resolution DACs

Dynamic metasurface antennas (DMAs) are emerging as a promising technology for future satellite communications, offering reductions in power consumption and hardware costs. However, the proliferation of Internet of Things (IoT) applications has exacerbated spectrum scarcity in DMA-assisted satellite communication systems. To tackle this limitation, we propose a novel integrated reconfigurable intelligent surface (RIS) and DMA empowered satellite symbiotic radio (SR). Specifically, the satellite equipped with a DMA transmits signals to primary users with the assistance of the RIS. Meanwhile, following the RIS-assisted SR principle, the RIS transmits its own signal to the secondary user. Considering low-resolution digital-to-analog converters (DACs) at the transmitter, we investigate the maximization of the weighted sum rate (WSR) through the joint optimization of the transmit beamforming vectors, the weight matrix associated with the DMA, and the phase shifts of the RIS. The strong coupling of optimization variables and the structural limitations inherent to the DMA make the problem highly challenging. To overcome these difficulties, we develop an efficient alternating optimization method based on the Lagrangian dual transform and quadratic transform algorithms to reformulate the original problem as a computationally tractable form. Then, we apply the penalty convex-concave procedure principle and the complex circle manifold algorithm to design the RIS phase shifts and the DMA weight matrix, respectively. In addition, an energy efficiency (EE) maximization formulation is developed to further evaluate the power-consumption benefit of the DMA-assisted transmitter. Numerical results demonstrate the effectiveness of the developed algorithm and highlight the favorable rate-power tradeoff of the DMA-assisted architecture, which achieves competitive WSR with improved EE compared with the conventional full-digital scheme.