Introduction

The Internet of Things (IoT) envisions and offers a promising future for traditional Internet industries and societies, and the realization of smart cities is tightly bound to the IoT outlook. By deploying low-cost sensors and various types of smart objects to collect data in public infrastructure, a smart city increases operational efficiency, shares information with the public, and improves the quality of life, cost of living, and government services as well as the environment [1] [2] [3]. Nowadays, the biggest wave of urbanization around the world and people are moving toward cities because of economy growth and social transformation. Recently, the United Nations has predicted that 86% of developed countries and 64% of the developing countries will be urbanized by 2050 [4]. Gartner’s report forecast that 30% of smart cities’ healthcare applications will have robotics and smart machines, and 10% of smart cities will use streetlamps as the backbone for a network of smart cities by 2020 [5]. Such implies that billions of devices and systems will be integrated in the future, ranging from end-user devices to smart transportation, healthcare, industry, buildings, and environments. Thus, the de facto expectation for a network of smart cities is to analyze a huge volume of data generated by IoT devices, increase security and privacy, realize optimal use of network bandwidth to avoid congestion, support real-time applications, etc. Recently, blockchain technology has attracted the attention of many stakeholders in many industries such as agriculture, cryptocurrency, supply chain, etc. IoT technology and blockchain technology are felt throughout our daily lives. The Gartner report predicts that $ 3.1 trillion in business value will be added by 2030 [6]. By taking advantage of the blockchain technique in the IoT network, we can offer new ways to automate business processes without the need for costly and complex centralized IT infrastructure. This will help us build trust between devices and users, reduce the risk of falsification and cost, eliminate middlemen, and shorten the transaction settlement time. To simplify business processes, realize significant cost savings, and improve the user experience, blockchain-based IoT solutions are ideally suited. On the other hand, Software Defined Networking (SDN) is gaining prominence among technologies for its disruptive quality. As an emerging network architecture, it decouples control of the network from traditional hardware devices. SDN based solutions can be useful in meeting requirements such as scalability and seamless, efficient, and cost-effective deployment in the IoT network architecture [7]. Based on the analysis above, designing a new network architecture is needed to address the current limitations of the smart city network architecture by leveraging the strength of emerging SDN and blockchain technologies. In this paper, we propose a novel hybrid architecture for the smart city network using SDN and blockchain techniques to address these problems. We discuss the current architectural challenges that we are facing to realize a sustainable smart city network. We introduce the Argon2 based Proof-of-work (PoW) scheme into our proposed architecture for a securely distributed smart city network. We also explain the mining process of our proposed architecture at the core network. To evaluate the feasibility and performance overhead of the proposed model, experimental analysis is performed based on different parameters. The rest of this paper is organized as follows: In Section 2, we discuss the architectural challenges in the smart city network, brief overview of Proof-of-Work and Argon2, and blockchain and IoT related works; in Section 3, we present our proposed model to address the current limitations of the smart city network; in Section 4, we evaluate the feasibility and performance of our proposed model based on different performance metrics; finally, we present the conclusions of our research in Section 5.