# Receiver-driven Video Multicast over NOMA Systems in Heterogeneous Environments

## TL;DR

This paper introduces Supcast, a receiver-driven multicast scheme integrating Softcast with NOMA to improve video transmission efficiency and quality in heterogeneous environments.

## Contribution

It proposes a novel joint power allocation and chunk scheduling method for NOMA-based Softcast, enhancing multicast performance for heterogeneous receivers.

## Key findings

- Supcast outperforms Softcast and other schemes in simulations.
- The proposed algorithm achieves near-optimal performance with low complexity.
- Supcast effectively manages bandwidth and quality in diverse channel conditions.

## Abstract

Non-orthogonal multiple access (NOMA) has shown potential for scalable multicast of video data. However, one key drawback for NOMA-based video multicast is the limited number of layers allowed by the embedded successive interference cancellation algorithm, failing to meet satisfaction of heterogeneous receivers. We propose a novel receiver-driven superposed video multicast (Supcast) scheme by integrating Softcast, an analog-like transmission scheme, into the NOMA-based system to achieve high bandwidth efficiency as well as gradual decoding quality proportional to channel conditions at receivers. Although Softcast allows gradual performance by directly transmitting power-scaled transformation coefficients of frames, it suffers performance degradation due to discarding coefficients under insufficient bandwidth and its power allocation strategy cannot be directly applied in NOMA due to interference. In Supcast, coefficients are grouped into chunks, which are basic units for power allocation and superposition scheduling. By bisecting chunks into base-layer chunks and enhanced-layer chunks, the joint power allocation and chunk scheduling is formulated as a distortion minimization problem. A two-stage power allocation strategy and a near-optimal low-complexity algorithm for chunk scheduling based on the matching theory are proposed. Simulation results have shown the advantage of Supcast against Softcast as well as the reference scheme in NOMA under various practical scenarios.