RIS-Aided LDM System: A New Prototype in Broadcasting System

Layer-division multiplexing (LDM) system has developed with significant improvement in spectrum efficiency and service diversity. LDM technology, that superposes multiple signals with different transmit powers, has been adopted by ATSC 3.0 to deliver robust high-definition services. However, due to the high mobility of devices, the wide signal coverage, and the uneven geographical channel condition, there exists under-utilized energy and significant potential of enhancing communication capacity in the LDM system. In this paper, we employ reconfigurable intelligent surface (RIS) to improve the reception quality in the LDM system, especially the SINR performance of the terminals in the edge area. We formulate a problem of maximizing the minimum SINR among all the terminals by jointly optimizing the power control and pairing mechanism, which is a Mixed-integer Nonlinear Programming (MINLP) problem. To solve it, we use the convex-concave procedure (CCCP). We further explore the high-mobility scenario with the limited channel state information (CSI) and the missing knowledge of detailed prediction of terminals’ mobility. We use Brownian Motion to model the possible variation of the terminals’ positions in the high mobility scenario to guarantee the successful reception probability. The analysis shows the RIS can bring obvious SINR gain to the LDM system, and the mobility modification could greatly help improve the successful reception probability.