Towards sustainable smart cities: A review of trends, architectures, components, and open challenges in smart cities
Introduction
The concept of connecting everyday objects via the existing networks became highly favorable with the emergence of smart devices and their recent advancements. Internet of Things (IoT) resulted from the evolution of conventional networks that connect zillions of connected devices. Technological advancements in ubiquitous computing (UC), wireless sensor networks (WSN), and machine-to-machine (M2M) communication have further strengthened the IoT notion (Silva, Khan, & Han, 2017a; Khan, Silva, Jung, & Han, 2017). Facilitating UC via uniquely identifiable smart devices without or minimal human interaction is being the de-facto principle of IoT (Gubbi, Buyya, Marusic, & Palaniswami, 2013; Khan, Silva, & Han, 2017). Moreover, connected smart devices share own information and access authorized information of other devices to support contextual decision-making (Vermesan et al., 2015). Owing to the extensive attention gained from various interest groups, IoT notion has pioneered striking applications with its expansion i.e. smart home, smart city, smart warehouse, smart health, and so forth (Islam, Kwak, Kabir, Hossain, & Kwak, 2015; Jabbar, Khan, Silva, & Han, 2016; Jin, Gubbi, Marusic, & Palaniswami, 2014; Khan, Silva, & Han, 2016). Smart city has become the spotlight in last few decades, due to dramatic urbanization all over the world. Performing city operations with aid of ICT made cities efficient in various aspects. However, incorporating ICT to perform city operations does not fully interprets a smart city (Hollands, 2008). Smart city has been favored among other urban models i.e. telicity, information city, and digital city, since it represents the abstraction of all other models (Mohanty, Choppali, & Kougianos, 2016). The smart city is an application of the IoT (Silva et al., 2016), hence it inherits the underlying operational mechanisms from IoT. As shown in Fig. 1, IoT provides essential building components for smart cities i.e. data generation, data management, and application handling.
In generic terms, smart city is an urban environment that utilizes ICT and other related technologies to enhance performance efficiency of regular city operations and quality of services (QoS) provided to urban citizens. In formal terms, experts have defined smart city considering various aspects and perspectives. A popular definition states that a smart city connects physical, social, business, and ICT infrastructure to uplift the intelligence of the city (Harrison et al., 2010). In another comprehensive definition smart city is defined as an advanced modern city that utilizes ICT and other technologies to improve quality of life (QoL), competitiveness, operational efficacy of urban services, while ensuring the resource availability for present and future generations in terms of social, economic, and environmental aspects (Kondepudi, 2014). The utmost goal of initial smart cities was to enhance the QoL of urban citizens by reducing the contradiction between demand and supply in various functionalities (Zanella, Bui, Castellani, Vangelista, & Zorzi, 2014). Accommodating QoL demands, modern smart cities especially focus on sustainable and efficient solutions for energy management, transportation, health care, governance, and many more, in order to meet the extreme necessities of urbanization (Ejaz, Naeem, Shahid, Anpalagan, & Jo, 2017).
The United Nations (UN) projected that 66% of the world population will be urban by 2050 (United Nations, 2014). In this era a large portion of resources of the world is preoccupied by cities, as a fact in modern world, 75% of the total energy is consumed by the cities (Mohanty et al., 2016). This perpetual energy consumption generates nearly 80% of the greenhouse gases that causes unfathomable adverse effects on the environment (Nam and Pardo, 2011a). Considering the fact, experts in both industry and academia agreed upon smart city as the ideal solution to address the challenges occur from drastic urbanization, population growth, deterioration of energy sources, environmental pollution, etc. Nevertheless, not every smart city are essentially similar in requirements, contributions, components, and characteristics. Therefore, International Organization for Standardization (ISO) provides globally agreed standards to assure the quality, safety, and performance of a wide range of smart cities. Hence, we can claim that adherence with smart city standards offer innumerable benefits in deploying and managing smart cities, while facilitating real-time performance monitoring (The British Standard Institution, 2014).
The research community came up with a plethora of experimental and real-time smart city solutions owing to expedience and significant attention drawn towards sustainability during the recent past. However, a majority of the proposed works belongs to experimental lab based testbed category. Transforming a testbed scenario into the real world is a laborious and a complicated task, since testbed limitations i.e. limited scalability, lack of user environment, mobility restrictions, and lack of heterogeneity preclude the practical implementation. Even though, Oulu smart city architecture (Ojala, 2010) and Citysense (Murty et al., 2008) offer service provision and experimental testbed, these architectures lack in compensating heterogeneity of IoT devices, scalability, and mobility support. Some testbed experiments (e.g. Kanseigenie (Sridharan et al., 2010)) serve heterogeneity of IoT devices, though the deployed environment is extremely different from the actual urban environment. Hence, direct extension of original tools and mechanisms used in testbed setting is not feasible in real-world deployments. WISEBED (Coulson et al., 2012) is another testbed based solution that provides a comparatively large heterogeneity in IoT devices. Moreover, SmartSantander testbed was proposed to offer mobility experiments exploiting a large-scale IoT device framework, which involves real urban citizens in the experiments (Sanchez et al., 2014).
The rest of the paper is organized as follow: Section 2 elaborates on different features of a smart city. Following to thorough analysis of recent works, in Section 3 we present a generic smart city architecture, which confirms with many proposed architectures. Section 4 elaborates on the composition of a smart city. Real-world implementations of smart cities around the world are presented in Section 5 and challenges and future trends are identified in Section 6. Finally, the conclusions are presented in Section 7.
Section snippets
Features of a smart city
Smart city comprises of attributes, themes, and infrastructure. Attributes of a smart city are also known as characteristics of smart city. Since the continuous progression of a smart city relies on themes, they are also called as pillars of the smart city. In fact, infrastructure is an essential feature for any smart city, which provides the operational platform. This section elaborates on aforementioned features considering a generic smart city deployment.
Smart city architecture
Researchers earnestly work on defining an apparent smart city architecture to alleviate real-world deployment of smart cities. However, feasibility of defining a universal smart city architecture for real world deployment is far from reality, though theoretically feasible. Drastic variations in the required features restrict the universal architecture to be speculative, but not realistic.
After thorough analysis of multiple existing architectures, we derived the bottom-up architecture
Composition of a smart city
Fig. 6 illustrates a few from various components that constitutes a smart city. Smart community, smart energy, smart transportation, and smart healthcare are some of those key components. However, the smart city composition varies from one smart city to another depending on the areas of interest. For example, a particular smart city might consider including a disaster management system to the smart community, while another city plans to integrate a waste management system. Following sub
Smart city rankings
Smart city deployment is ascertained to improve the competitiveness of cities, in order to enhance the sustainability and livability of real-world smart cities. Cities in motion index (CIMI) was introduced to scrutinize 77 city indicators covering 10 dominant categories in urban life i.e. the economy, technology, human capital, social cohesion, international outreach, environment, mobility and transportation, urban planning, public management, and governance (Berrone & Ricart, 2016). Exploiting
Smart city challenges and opportunities
Even though smart city concept is widely accepted and practically implemented in real world, addressing existing issues in certain areas has become crucial to achieve further improvement. This section provides a brief discussion on challenges and promising opportunities for realistic implementation of smart cities. The challenges were identified through extensive literature review performed on recent research on smart cities. Similarly, the opportunities were identified through existing works
Conclusions
Smart city concept emerged as an application domain of IoT. Among various concepts that utilize ICT in urban environments i.e. digital city, green city, sustainable city, intelligent city, etc. smart city stands out owing to its holistic vision. In other terms, smart city act as a composition of other forms of urban environment management strategies.
This paper presented fundamentals of a smart city in terms of definitions, standards, and implications. The characteristics and features are
Acknowledgments
This work was supported by Institute for Information & communications Technology Promotion (IITP) grant funded by the Korea government (MSIP) (No.2017-0-00770).
This study was supported by the BK21 Plus project(SW Human Resource Development Program for Supporting Smart Life) funded by the Ministry of Education, School of Computer Science and Engineering, Kyungpook National University, Korea (21A20131600005).
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