## 2 IoT Intelligent Car Parking System  
ITS and other systems, such as electrical energy systems, water-, heating- and gas supply systems, city fire protection and security systems, eHealth/mHealth systems, _etc._, provide intelligent IoT services to make the city smarter [17]. ITS locates in the business layer of IoT, communicates with the cloud-based information centre of the smart city, and delivers 'best' transport-related services to users, such as traffic monitoring & control, route planning, car parking service, _etc._ Figure 3 depicts a high-level view of a centralized IoT platform, which could serve as a generic architectural foundation for a'smart city' establishment, operation, administration, and management. This top-level generic architectural design can unify the development of business applications as an efficient and economical process. For instance, if an ITS service provider wants to deploy a car parking service within a smart city's shared cloud infrastructure, it will only need to focus on the operating model to realize the smartness of the car parking. Here we propose an intelligent car parking system for integration into a smart-city IoT architecture, which consists of three layers--A sensor layer, a communication layer, and an application layer (Figure 4). At the application layer, an information centre provides cloud-based services [18], _i.e._, Platform as a service (PaaS), Software as a service (SaaS), and Infrastructure as a service (IaaS); _i.e._, for allocating computing/storage resources for different car parking services. An IoT management centre administrates the smart city via an IoT integrated services portal. At the bottom, a number of business services explore a common interface to the communication layer. These include car parking locator, supervision, and information services, GIS/GPS services, vehicle license plate patrolling, car tracking services, _etc._At the communication layer, various wireless technologies provide connection between the application- and the sensor layer, based on the ABC&S communication paradigm. A 3-tier InfoStation-based network architecture [10] could be integrated in this layer to enable 'anytime-anywhere-anyhow' communication functionality in smart cities. Different sensing technologies could be utilized at the sensor layer for embedded parking solutions, such as the Radio Frequency Identification (RFID) for car parking access control; laser, passive infrared, microwave radar, ultrasonic, passive acoustic array sensors, or Closed-Circuit Television (CCTV) with video image processing for detecting the status of the car parking lots; license plates with installed 3G/4G communication module for cars' tracking and tracing; _etc._  
Figure 4: An IoT intelligent car parking system for a Smart City. Figure 3: A high-level view of an IoT-based Smart City. To enable the car parking system to work as an operational platform in a smart city, different car parking areas must be distinguished in providing 'best' car parking lots by executing different business roles and applications. Based on their properties, the car parking areas could be divided into four main categories (Figure 5): A transportation hub area; a residential/community area; a ground/street area; and a shopping mall/hotel/restaurant area. The relevant management and control entities, including a highway centre, emergency centre, traffic control centre, and police can get access to the information managed by the car parking information centre with high authority. The sensors deployed in the car parking area periodically send updated information as regards occupancy of the car parking lots to the car parking meters, which push this data to the information centre. Users can interact with the system by installing the corresponding car parking application on their mobile devices. Facilitated by a personal assistant agent, each user can set up a personal profile which will be used by the application for finding, allocating, reserving, and paying for the 'best' parking lot in each particular scenario.