1. Introduction
Urbanisation, characterised by the growth and expansion of cities, is a significant global trend involving population migration from rural towns or villages to cities. Cities possess complex systems interconnected with their residents and infrastructure, such as transportation, communication networks, advanced services, businesses, and utilities supporting a high living standard. Technological advancements, economic opportunities, and social innovations drive cities’ emergence and growth, which attracts people seeking improved living conditions and employment prospects [
1,
2]. In recent years, many people have relocated to urban areas, and forecasts suggest that by 2030, approximately 60% of the global population will live in cities. Furthermore, according to the United Nations, projections indicate that this trend will continue, with around 68% of the world’s population expected to reside in urban areas by 2050 [
3]. Rapid urbanisation and an increasing city population bring numerous challenges, including technical, socio-economic, and organisational issues, threatening urban environmental and economic sustainability [
2,
4]. For instance, in developing countries and modern cities, it has resulted in problems such as increased pollution and depletion of natural resources [
5], overcrowding, and socioeconomic inequality [
6,
7,
8]. Additionally, unplanned urbanisation can increase the burden on public services, including transportation and waste management [
9,
10]. This has further intensified the need for sustainable solutions to address the growing demands on urban infrastructure, climate change, and resource constraints [
11], which necessitates innovative technological approaches to urban planning and management to create resilient, efficient and sustainable urban environments.
As the urban population grows, various applications have been introduced to provide solutions, contributing significantly to the development of smart urban ecosystem through smart cities [
12,
13]. A smart city is one where traditional networks and services are enhanced using digital and telecommunication technologies to improve the efficiency and quality of life for its inhabitants and businesses [
14]. Additionally, smart cities not only help mitigate urbanisation effects but also drive entrepreneurship and economic development [
15], as evidenced by the 2008 financial crisis, in which several countries pioneered smart city initiatives to boost economic growth. These cities offer a futuristic, adaptable approach that promotes environmental conservation and transformation across social, economic, and environmental domains while ensuring residents’ well-being [
16]. The development of smart cities is heavily influenced by advanced information and communication technologies (ICTs), such as cloud and fog computing [
17,
18], machine learning (ML) [
19], Internet of Things (IoT) [
20], blockchain [
21], and artificial intelligence (AI) [
13,
22], to create a smart ecosystem [
23].
In recent years, the Metaverse has emerged as an innovative virtual environment where digital and physical worlds converge, offering a new layer of technological integration for smart cities with the potential to enhance urban sustainability. It has evolved to represent an immersive, interactive space where users engage through digital avatars and digital twins (DTs), which are digital replicas of physical objects or systems [
24]. The Metaverse integrates extended reality (XR), including virtual reality (VR), mixed reality (MR), and augmented reality (AR), to varying degrees [
25], enabling users to experience alternate lives through their avatars [
26]. High-quality 3D models, advanced communication technologies like 5G/6G, and AI create intelligent environments in the Metaverse. The combination of Metaverse and smart city technologies enhances city management and development. Smart cities utilise real-time monitoring and data collection through sensors, which collect information about various aspects of the city, including the environment, transportation, and energy sectors. This information improves resource management, emergency response, and public safety and optimises energy use. Integrating the Metaverse introduces immersive and interactive virtual environments, allowing residents to engage with city services in new ways, enhancing city planning and overall user experience. Therefore, the Metaverse enables smarter decision-making, resource allocation, and citizen engagement through real-time data analysis and virtual simulations [
27], creating a more interconnected urban ecosystem.
Notably, AI is integral to the Metaverse’s foundation and development [
28] and has numerous applications for Metaverse in smart cities. For instance, AI plays a crucial role in enhancing automation and connectivity [
29], allowing the Metaverse to support smart city applications in intelligent transportation systems [
30] and other urban sectors. This enables smart cities to address the needs of citizens and municipalities more effectively [
13,
31]. For instance, AI-driven deep learning (DL) models have demonstrated the ability to detect early air pollution [
32] and support sustainable agriculture within smart cities, aiding in yield prediction, quality evaluation, and pest detection [
33]. Implementing and designing the urban ecosystem for administrative services like transportation, energy, environment, and culture in smart cities while ensuring ethics and security poses challenges but could offer potential improvements through AI-enabled data analytics [
28] and Metaverse technologies. Furthermore, using AI-based technologies [
34], cities can efficiently analyse the vast amounts of data generated by stakeholders and sources, such as IoT devices, video cameras, and Metaverse-based interactions, helping city officials manage these data quickly and effectively [
35]. However, while AI offers significant benefits, it also presents challenges that must be addressed to ensure the seamless coexistence of humans and machines, both in physical smart cities and their digital counterparts within the Metaverse.
Nevertheless, key technologies such as AI, XR, digital twins, blockchain, 5G/6G and IoT will fully enable Metaverse applications in smart cities to aid users in interacting and collaborating within virtual environments. However, even though AI is crucial in the foundation and development of the Metaverse, it is less prominently discussed how it can or is integrated into the Metaverse, with other key technologies, to actualise a sustainable smart city. For instance, to provide animated 3D building models, state-of-the-art computer vision can be utilised, enabled by AI/ML/DL models. However, utilising the 3D content for the Metaverse is challenging due to the scalability of the current infrastructure. Therefore, it is essential to develop tools and infrastructure that allow developers to create more scalable 3D/AR/VR experiences across various platforms and purposes [
36]. Furthermore, as the Metaverse is massive and creates interpretability challenges, developing explainable smart city applications is essential [
37]. The AI-enabled Metaverse will rely on explainable AI to ensure transparency and explainability in integrating and functioning various key technologies, enabling efficient, trustworthy, and immersive experiences across smart city applications. Motivated by the evolving technologies and foreseen challenges, we survey the state-of-the-art AI-enabled technologies and how they are integrated with other key technologies in the context of Metaverse for a sustainable smart city to answer the following question: How can AI-enabled technologies, integrated with key technologies like XR, digital twins, blockchain, 5G/6G and IoT, drive the development of a sustainable smart city within the Metaverse? In the following subsections, we review the related surveys and outline the contribution and structure of this review.
1.1. Related Surveys
In this subsection, we examine the latest surveys on various technologies related to smart cities. Numerous studies have recently been conducted to explore the potential of smart city technologies, their implementation, applications, and future research directions [
2,
22,
27,
28,
30,
38,
39,
40,
41,
42,
43,
44,
45].
For instance, Wang et al. [
38] present a comprehensive framework for integrating Artificial General Intelligence (AGI) and parallel intelligence into Metaverse-based smart cities, emphasising human ethics, social responsibility, and ecological sustainability. Similarly, the authors in [
39] examine the ethical implications of the Metaverse as a virtual form of data-driven smart cities, focusing on privacy, surveillance capitalism, data surveillance, geo-surveillance, human health and wellness, and collective cognitive echo chambers. The researchers in [
42] also provide an extensive overview of potential and already implemented Metaverse applications in smart cities, discussing various benefits and challenges associated with these applications. Similarly, [
41] highlights the Metaverse’s potential to enhance environmental, economic, and social sustainability in smart cities, focusing on integrating digital twins and AI technologies. Bibri et al. [
40] provide a comprehensive overview of the potential applications, opportunities, and challenges associated with deploying XR technologies in IoT applications within the broader framework of IoCT, emphasising the synergy between XR and AIoT technologies. Furthermore, the integration of Metaverse technologies into intelligent transportation systems is studied, highlighting their potential to enhance transportation safety, reliability, and efficiency through secure communication, virtual simulations, and real-time analytics [
30]. The role of AI, including machine learning algorithms and deep learning architectures, in the foundation and development of the Metaverse is explored, providing a comprehensive investigation of AI-based methods concerning several technical aspects and AI-aided applications, such as healthcare, manufacturing, smart cities, and gaming, in virtual worlds in [
28]. Similarly, Chen et al. [
27] provide a detailed review of smart cities based on Metaverse technologies. Alahi et al. [
2] discuss the role of IoT and AI in developing smart cities, focusing on recent advancements, potential applications, and future trends, emphasising integrating these technologies to enhance urban sustainability and productivity. Yaqoob et al. [
45] reviewed the enabling technologies, opportunities, challenges, and future directions of the Metaverse for smart cities, highlighting its potential to enhance infrastructure, services, and sustainability. Arora et al. [
22] examine the role of multi-agent systems in smart city applications, providing a detailed description of AI paradigms, critical application areas, and future research directions, while the researchers in [
43] study the integration of advanced technologies for sustainable smart cities, focusing on the role of IoT, AI, blockchain, and other technologies in enhancing various smart city domains and addressing sustainability challenges. A summary of these studies compared to our study is presented in
Table 1.
1.2. Method
Studies were identified by searching databases, including IEEE Xplore, ACM Digital Library, Springer, MDPI and Science Direct. The additional literature was collected from Google Scholar, archive databases and other sources, with a publication date range limited to the past six years. We present details in
Table 2. The selected articles comprised early-access materials and published peer-reviewed research from technical conferences and journals. For screening, we focused on the core elements of each paper relevant to our research topic. To ensure the inclusion of unique and relevant studies, we implemented a rigorous screening process to remove redundant references. Duplicate entries across multiple databases were identified and removed.
The searching keywords comprised key technologies supporting the smart city applications in the Metaverse: this included AI for Metaverse, digital twins, Metaverse, explainable AI, IoT enabled Metaverse, 6G powered for the Metaverse, communication, edge and cloud computing for the Metaverse, smart city, sustainable smart city etc. Based on these keywords, we use boolean (AND, OR, and NOT) combination searching to broaden or narrow the searches. After searching all related studies, we screened titles, abstracts, conclusions and introductions. We examined them by the inclusion criteria, which should apply the key technologies supporting the AI applications in the Metaverse. This was followed by assessing the quality of all the screened studies, sorting, and summarising the key technology related to Metaverse for smart cities.
1.3. Contributions
It is clear from the above discussion that some of the existing surveys have focused on very narrow perspectives of AI and relevant technologies, while others have investigated the role of the Metaverse in terms of societal, economic, and digital value, as well as covering limited applications in the context of smart cities. The exploration of how AI enables the key technologies in the Metaverse to attain sustainable smart cities is still unexplored. In contrast, our review specifically focuses on the AI-enabled Metaverse, where AI is leveraged to map the physical world into a digital reality in the virtual world. As such, the review’s key contributions are:
- 1)
It provides a comprehensive review of advancements in AI and examines its role within the Metaverse’s layered architecture for smart cities. By exploring how AI as the core intelligence enables data analysis and decision-making, enhances user experiences through Computer Vision (CV) and Natural Language Processing (NLP), optimises connectivity with 6G and Edge AI, strengthens security through blockchain applications, and manages the creation of digital twins, the study explains the technical integration of AI into key Metaverse-enabling technologies to deepen the understanding of AI’s capabilities in improving user engagement, connectivity, efficiency, and services, laying the foundation for developing advanced Metaverse applications that address challenges in smart cities.
- 2)
Building upon the technical insights, it reviews the integrated role of AI and key technologies in realising the Metaverse for sustainable smart cities. By presenting potential AI-enabled applications and use cases in smart environments, mobility, energy, health, governance, and the economy, it offers a practical roadmap for implementing sustainable solutions to enhance citizens’ quality of life, promote economic growth, and achieve sustainability.
- 3)
It identifies and analyses the challenges and future research directions in integrating AI and key technologies within the Metaverse for sustainable smart cities by highlighting existing gaps, guiding future research and development efforts to overcome these challenges, and informing policymakers to facilitate the implementation of solutions that enhance the quality of life for citizens and promote economic growth and sustainability.
The rest of the article is organised as follows:
Section 2 includes the background and technical aspects of the smart city and the Metaverse.
Section 3 presents the state-of-the-art AI and its role in realising the Metaverse and enabling key supporting technologies.
Section 4 highlights the integrated role of AI and key technologies in realising the Metaverse for sustainable smart cities, along with potential applications and use cases.
Section 5 summarises the analysis of the findings, while
Section 6 discusses the future research directions.
Section 7 concludes the paper.
7. Conclusion
We presented a comprehensive review highlighting the crucial role of AI in enabling the Metaverse to develop sustainable smart cities. AI, combined with the Metaverse technologies like digital twins, IoT, blockchain, and 5G/6G, offers numerous advantages in smart cities, including improved resource management, enhanced urban planning, energy efficiency, and better overall user experiences. However, challenges such as data privacy, cybersecurity, interoperability, and the need for scalable infrastructure remain critical issues that must be addressed to integrate these technologies seamlessly. Looking ahead, the success of sustainable smart cities within the Metaverse relies on developing distributed AI systems that enable decentralised, interoperable, and scalable data processing and storage while ensuring privacy, security, and explainable, responsible decision-making. AI-enabled Metaverse promises to revolutionise how smart cities are designed and managed, fostering sustainability through innovative, real-time solutions for urban challenges. By leveraging advanced technologies and fostering collaboration among stakeholders, an interconnected, sustainable smart city environment can be created that improves quality of life and addresses pressing environmental and social issues. Achieving this vision will require continued research, innovation, and policy development to ensure the responsible and equitable deployment of AI-enabled Metaverse-driven technologies for sustainable smart cities.