The increasing densification of small-cell networks substantially expands cable-based backhaul infrastructure, creating heightened vulnerability to cable link failures. This paper proposes a reconfigurable intelligent surface (RIS)-assisted backup framework that exploits a key insight: during backhaul cable failures, base station (BS) radio components remain functional, enabling wireless backhaul traffic redistribution. Our framework maintains network connectivity by redistributing disconnected BS backhaul traffic to neighboring BSs through RIS-assisted wireless links. To maximize survivability across varying traffic conditions, we formulate a joint optimization problem that maximizes total resolvable backhaul traffic by jointly deciding BS selection, RIS phase shifts, and precoding vectors. The inherent non-convexity arising from coupling and quadratic fractional term is addressed through an alternating optimization algorithm that iteratively solves tractable convex subproblems via quadratic transformation. Comprehensive numerical evaluations demonstrate that the proposed RIS-enhanced framework significantly improves survivability from 58% to 72% under challenging high-intensity hotspot traffic conditions. Moreover, RIS provides the greatest gains for antenna-constrained systems by extending coverage to access more spare capacity of the distant BSs as well as enhancing the signal strength. Consequently, high survivability is achieved even with only two antennas per BS under moderate traffic intensity.

翻译：小小区网络密度的增加显著扩展了基于电缆的回程基础设施，导致电缆链路故障的脆弱性加剧。本文提出一种可重构智能表面（RIS）辅助的备份框架，该框架利用一个关键洞察：在回程电缆故障期间，基站（BS）的无线组件仍保持功能，从而允许无线回程流量重新分配。我们的框架通过RIS辅助的无线链路将断连BS的回程流量重新分配到邻近BS，从而维持网络连通性。为在不同流量条件下最大化生存性，我们构建了一个联合优化问题，通过联合决定BS选择、RIS相位偏移和预编码向量最大化总可解析回程流量。由于耦合项和二次分式项导致的固有非凸性，我们采用了一种交替优化算法，通过二次变换迭代求解易处理的凸子问题。全面的数值评估表明，所提出的RIS增强框架在具有挑战性的高强度热点流量条件下，将生存性从58%显著提升至72%。此外，对于天线受限系统，RIS通过扩展覆盖范围以利用远端BS的更多备用容量并增强信号强度，带来了最大增益。因此，在中等流量强度下，即使每个BS仅配备两根天线，也能实现高生存性。