# Machine Learning for Blockchain and IoT Systems in Smart Cities: A Survey
###### Abstract  
The integration of machine learning (ML), blockchain, and the Internet of Things (IoT) in smart cities represents a pivotal advancement in urban innovation. This convergence addresses the complexities of modern urban environments by leveraging ML's data analytics and predictive capabilities to enhance the intelligence of IoT systems, while blockchain provides a secure, decentralized framework that ensures data integrity and trust. The synergy of these technologies not only optimizes urban management but also fortifies security and privacy in increasingly connected cities. This survey explores the transformative potential of ML-driven blockchain-IoT ecosystems in enabling autonomous, resilient, and sustainable smart city infrastructure. It also discusses the challenges such as scalability, privacy, and ethical considerations, and outlines possible applications and future research directions that are critical for advancing smart city initiatives. Understanding these dynamics is essential for realizing the full potential of smart cities, where technology enhances not only efficiency but also urban sustainability and resilience.  
smart cities; machine learning; blockchain technology; internet of things; analysis +
Footnote †: journal: _Future Internet_  
Capitalizing on the previous studies, several focus areas were identified i.e., the importance of secure and scalable frameworks and data-driven decision-making, which guided the further exploration of how ML, blockchain, and IoT collaborate to create intelligent and resilient urban infrastructure. Nowadays, with IoT generating large-scale data, ML is essential for deriving insights, while blockchain ensures the need for data integrity and security. The insights gained from these studies helped to frame the survey's focus on the synergies and challenges of these technological fields. These areas are reflected in the structure and content of the paper and direct the literature review. The executed study was motivated by the need to make a focused presentation of works aimed at analyzing how the combination of ML, blockchain, and IoT can address these rising issues in smart cities in the era of rapid urbanization. More specifically, this survey makes the following contributions:  
* It examines the application of ML in IoT systems and the role of blockchain in enhancing security within smart cities.
* The survey identifies potential synergies between ML, blockchain, and IoT to create more intelligent and secure urban environments.
* It highlights key challenges, such as scalability and ethical considerations, and outlines future research directions.  
The key topics explored in the subsequent sections are depicted in Figure 1, which reflects the structure of the work. The paper is organized as follows. Section 2 details the integration of ML into IoT systems for smart cities. Section 3 explores blockchain for security and data integrity in smart cities. Moreover, Section 4 discusses the synergy of ML, blockchain, and IoT in smart cities. Section 5 outlines challenges and future directions. Finally, Section 6 summarizes the findings of this survey.