Payment Channel Networks (PCNs) have been proposed as an alternative solution to the scalability, throughput, and cost overhead associated with on-chain transactions. By facilitating offchain execution of transactions, PCNs significantly reduce the burden on the blockchain, leading to faster transaction processing, reduced transaction fees, and enhanced privacy. Despite these advantages, the current research in PCNs presents a variety of research challenges that require further exploration. In this paper, we survey the recent work in several aspects of PCNs, such as pathfinding and routing, virtual channels, state channels, payment channel hubs and rebalancing. This survey aims to provide the reader with a detailed understanding of the current state-of-the-art in PCN research, highlighting a few important advancements. Additionally, we highlight the various unresolved issues in the area of PCN research. Specifically, this paper seeks to answer the following crucial question: What are the various interesting and non-trivial challenges in PCN research that require immediate attention from the academic and research community? By addressing this question, we aim to identify the most pressing problems and future research directions that interested readers can immediately work on. Through this analysis, we hope to inspire researchers and practitioners to tackle these challenges to make PCNs more secure and versatile

翻译：支付通道网络（PCNs）被提出作为解决链上交易可扩展性、吞吐量和成本开销的替代方案。通过促进交易的链下执行，PCNs显著减轻了区块链的负担，从而实现更快的交易处理、更低的交易费用和更强的隐私保护。尽管存在这些优势，当前PCNs研究仍面临诸多需要进一步探索的挑战。本文从路径发现与路由、虚拟通道、状态通道、支付通道枢纽和再平衡等多个维度系统梳理了PCNs的最新研究成果。本综述旨在帮助读者深入理解PCN研究的前沿进展，重点阐述若干重要突破。同时，我们着重指出了PCN研究领域中尚未解决的关键问题。具体而言，本文试图回答以下核心问题：PCN研究中存在哪些值得关注且非平凡的研究挑战，亟需学术界和研究界立即关注？通过探讨这一问题，我们期望明确最紧迫的研究难题和未来方向，为相关领域研究者提供可立即开展工作的切入点。通过此项分析，我们希望激励研究者和实践者共同应对这些挑战，推动PCNs向更安全、更通用的方向发展。