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）被提出作为一种替代方案，以解决链上交易所面临的可扩展性、吞吐量和成本开销问题。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、更低的交易费用以及更强的隐私保护。尽管存在这些优势，当前PCNs的研究仍面临诸多需要进一步探索的挑战。本文从多个方面综述了PCNs的最新研究成果，例如路径查找与路由、虚拟通道、状态通道、支付通道枢纽和再平衡。本综述旨在为读者提供对PCN研究当前最新进展的详细理解，并重点介绍若干重要进展。此外，我们强调了PCN研究领域中尚未解决的各种问题。具体而言，本文试图回答以下关键问题：PCN研究中存在哪些有趣且非平凡、亟需学术界和研究界立即关注的挑战？通过探讨这一问题，我们旨在确定最紧迫的问题和未来的研究方向，以便感兴趣的读者能够立即着手研究。通过这一分析，我们希望激励研究人员和实践者应对这些挑战，使PCNs更加安全和多功能。