Sacrificing CSI for a Greater Good: RIS-enabled Opportunistic Rate Splitting

TL;DR

This paper introduces a RIS-enabled rate splitting scheme that sacrifices some channel information to reduce estimation overhead, effectively improving net data rates despite practical channel estimation challenges.

Contribution

It proposes a novel opportunistic rate splitting method that balances CSI acquisition costs and interference mitigation in RIS-assisted systems.

Findings

Achieves up to 160% net rate gain over NOMA.

Effectively mitigates interference through rate splitting.

Reduces channel estimation overhead in RIS systems.

Abstract

In reconfigurable intelligent surface (RIS)-assisted systems, the optimization of the phase shifts requires separate acquisition of the channel state information (CSI) for the direct and RIS-assisted channels, posing significant design challenges. In this paper, a novel scheme is proposed, which considers practical limitations like pilot overhead and channel estimation (CE) errors to increase the net performance. More specifically, at the cost of unpredictable interference, a portion of the CSI for the RIS-assisted channels is sacrificed in order to reduce the CE time. By alternating the CSI between coherence blocks and employing rate splitting, it becomes possible to mitigate the interference, thereby compensating the adverse effect of the sacrificed CSI. Numerical simulations validate that the proposed scheme exhibits better performance in terms of achievable net rate, resulting in gains of up to 160% compared non-orthogonal multiple access (NOMA), when CE time and CE errors are considered.