The convergence of blockchain and the Internet of Things (IoT) enables secure, decentralised, and verifiable data exchange across distributed smart environments. However, traditional blockchain frameworks suffer from inherent scalability constraints, limited throughput, and high latency, which conflict with the stringent real-time requirements of IoT applications such as industrial automation, intelligent healthcare, and smart transportation. These systems demand ultra-low latency, high transaction throughput, lightweight computation, and efficient resource utilisation. This review provides a comprehensive, structured analysis of state-of-the-art scalability solutions specifically adapted to blockchain-enabled IoT. The discussion encompasses Layer 1 enhancements, Layer 2 off-chain processing, sharding-based parallelisation, integration of edge and fog computing, and hybrid consensus mechanisms. For each approach, the review highlights operational principles, performance benefits, trade-offs in decentralisation and security, and suitability for latency-sensitive deployments. Furthermore, real-time quality-of-service considerations are examined to understand how scalability strategies impact system responsiveness, energy efficiency, and data integrity. Key open challenges, including the scalability-security trade-off, privacy preservation, interoperability, and sustainable resource management, have been identified as persistent barriers to large-scale adoption. Finally, the review outlines future research directions, emphasising adaptive and AI-driven consensus algorithms, quantum-safe cryptographic models, the convergence of blockchain with 5G/6G networks, and edge intelligence. By consolidating diverse technical insights and emerging trends, this work serves as a timely reference for developing scalable, secure, and sustainable blockchain architectures for real-time IoT applications.

翻译：区块链与物联网的融合使得分布式智能环境能够实现安全、去中心化且可验证的数据交换。然而，传统区块链框架存在固有的可扩展性限制、吞吐量有限以及高延迟等问题，这与工业自动化、智能医疗和智慧交通等物联网应用的严格实时需求相冲突。这些系统要求超低延迟、高事务吞吐量、轻量级计算以及高效的资源利用。本文对专门适用于区块链驱动物联网的现有可扩展性解决方案进行了全面且结构化的分析。讨论涵盖第一层增强、第二层链下处理、基于分片的并行化、边缘计算与雾计算的集成，以及混合共识机制。针对每种方法，本文重点阐述了其运行原理、性能优势、在去中心化与安全性方面的权衡，以及对延迟敏感型部署的适用性。此外，本文还审视了实时服务质量考量，以理解可扩展性策略如何影响系统响应性、能效和数据完整性。关键性开放挑战（包括可扩展性-安全性权衡、隐私保护、互操作性以及可持续资源管理）已被识别为大规模采用的主要障碍。最后，本文概述了未来研究方向，着重强调了自适应与人工智能驱动的共识算法、抗量子密码模型、区块链与5G/6G网络的融合，以及边缘智能。通过整合多样化的技术见解与新兴趋势，本文为开发面向实时物联网应用的可扩展、安全且可持续的区块链架构提供了及时的参考。