Blockchain-based Internet of Things (BIoT) is an emerging paradigm of Internet of Things (IoT) which utilizes the blockchain technology to provide security services to the IoT applications. In essence, the blockchain built-in security mechanism can provide services such as availability, authentication, authorization, confidentiality, and integrity to the IoT applications. While most of the IoT devices are inherently resource-constrained in terms of computational power and storage capacity, the downside for blockchain is a requirement of massive amount of energy and computational resources for its operation, which poses challenges to the realization of BIoT. This paper strives to explore the challenges associated with the integration of blockchain and IoT and review their solutions. First, a brief introduction of blockchain technology is presented, followed by characterization of blockchain-based IoT applications as per their heterogeneous traffic demand and Quality of Service (QoS) requirements. Next, challenges that limit the design, development, and deployment of BIoT applications are explained in detail such as energy efficiency, privacy, throughput, latency, fork problem, security, legal issues, smart contracts, storage, and network broadcast mechanism and their proposed solutions are discussed. Finally, future research directions of blockchain and IoT integration are indicated. This investigation will benefit the researchers and developers to identify and solve blockchain and IoT integration challenges in order to realize efficient BIoT applications.

基于区块链的物联网 (BIoT) 是一种新兴的物联网 (IoT) 范式，它利用区块链技术为物联网应用提供安全服务。本质上，区块链内置的安全机制可以为物联网应用提供可用性、认证、授权、机密性和完整性等服务。虽然大多数物联网设备在计算能力和存储容量方面都存在固有的资源限制，但区块链的缺点是其运行需要大量的能源和计算资源，这对 BIoT 的实现提出了挑战。本文致力于探索与区块链和物联网集成相关的挑战并回顾其解决方案。首先简要介绍一下区块链技术，其次是根据其异构流量需求和服务质量 (QoS) 要求对基于区块链的 IoT 应用程序进行表征。接下来，详细解释了限制 BIoT 应用程序设计、开发和部署的挑战，例如能源效率、隐私、吞吐量、延迟、分叉问题、安全、法律问题、智能合约、存储和网络广播机制及其建议讨论了解决方案。最后，指出了区块链和物联网集成的未来研究方向。这项调查将有利于研究人员和开发人员识别和解决区块链和物联网集成挑战，以实现高效的 BIoT 应用。