# Smart Parking: A Literature Review from the Technological Perspective
## 3 Smart Parking Solutions  
Vehicle production has grown considerably in the last 30 years as pointed out in [29]. Having more vehicles around the streets implies more fuel and time consumption and a growing demand for parking  
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spaces. These problems can be addressed by smart parking solutions. They are one of the most popular use cases within the concept of smart city and seek to improve the quality life cycle of a city [29].  
The architecture of smart parking solutions is mainly represented by three elements: sensors, networking protocols, and software solutions. Sensors are the most important element as they collect information and feed the whole system. Networking protocols are governed by a gateway that implements wireless IoT protocols and connect sensors to the software systems. Finally, software solutions ensure that information is available for everyone through some sort of service. For instance, people can use this information to view heat maps of zones with the highest parking slots occupancy [30].  
To implement a smart parking solution, several technological components are involved, such as sensors, networking infrastructure, and software solutions, among others. Regarding smart parking architectures, there are several works that have been presented by industry and the scientific community. Some of them focus on the solution, others on the algorithms, software, or systems, whereas others briefly state the technology of the sensors. For instance, the authors of [31] propose an approach based on artificial intelligence (agents) to find available spots. In [32], the authors discuss different approaches to implement Smart Parking solutions; it considers the whole ecosystem of such type of solutions which basically involves sensors, gateway selection, edge processing, and data center analysis. For its part, the authors of [33] depict an architecture totally based on ZigBee technology. Moreover, the authors of [9] suggest artificial intelligence for optimizing park search, but barely specify the technical details of implementation, such as specific protocols or sensor types. Likewise, the work proposed in [34], shows the use of Bluetooth Low Energy (BLE) as a protocol for connecting sensors and gateways. Bluetooth is a wireless protocol that supports connection between end-devices. The BLE version consumes very few energy and is part of the wireless IoT stack protocol. Other solutions, like those in [35], suggest the use of IR sensors for its architecture. Smartphones are also considered in these solutions particularly to find available spaces [36]. Considering the aforementioned, it can be seen that there are no international standards or base architectures defined for implementing smart parking systems. Therefore, it is necessary to analyze how different components are being used as well as identify tendencies in regards to their use in order to implement a smart parking solution.  
Smart parking solutions were developed with many technologies and approaches; therefore, a classification will be performed considering the established points. In this case, three different perspectives were selected: sensors, network infrastructure, and service provided to users. The aforementioned perspectives were selected based on the importance given in [37].