# Development of User-Participatory Crowdsensing System for Improved Privacy Preservation
## 2 Literature Review
### Related Work  
The risk of personal information exposure in crowdsensing services discourages users from providing sensing data. This prevents the crowdsensing service from operating properly. Therefore, personal information protection is essential in crowdsensing services, and related research should be based on the possible service types. We classify crowdsensing services according to the classification criteria in Reference [24], and we present threats and countermeasures against personal information disclosure in each type of service. Table 1 shows the types of crowdsensing services according to various classification criteria. In terms of the request assignment entity, the centralized type is a method in which a central service provider assigns a request to users, and an attacker who compromises the service provider system can access sensitive personal information such as real-time user location. The distributed type is a method via which a user directly participates in a request allocation by a service provider. In contrast to the centralized type, it is difficult for a specific management entity such as a service provider to access sensitive personal information of a user. However, if a service provider or an attacker masquerades as multiple users and participates in a request assignment, it can access sensitive personal information. In terms of the request assignment target, the partial type is a method in which a request is transmitted only to a user who can provide appropriate sensing data, considering the location and status of the user. Thus, the service provider assigning the request should monitor user location and status in real time. The overall type is a method in which a request is transmitted to all users without considering their location or state, and the service provider does not check sensitive personal information. However, the efficiency of the overall type is low because all requests should be sent to all users. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Classification Criteria**} & \multicolumn{2}{c}{**Classification**} \\  & **Vulnerability to Privacy Exposure** & **Resistance to Privacy Exposure** \\ \hline Request assignment entity & Centralized [15] & Distributed [16] \\ Request assignment target & Partial [17] & Overall [18] \\ Participation willingness & Push [19] & Pull [20] \\ Data providing cycle & Periodic [19] & Participatory [15] \\ Data preprocessing & Extensive [21] & Non-extensive [22] \\ Data type & Spatiotemporal [22] & Non-spatiotemporal [23] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Classification of crowdsensing services. Figure 2: Kaa Internet of things (IoT) platform architecture. In terms of participation willingness, the push type requires that the service provider continuously communicates with the user application so that a request is directly sent to the user application. In this process, the service provider can find sensitive personal information such as real-time user location or mobile phone status. The pull type is a method in which the user directly confirms the request information disclosed by the \(SP\). Therefore, as the \(SP\) and the user application need not communicate continuously, the risk of exposure of personal information is relatively low compared with the push type. All pull-type crowdsensing services are partial type. In terms of the data providing cycle, the persistent type is a method in which sensing data are periodically received without user interference, and the service provider can access real-time user location and status information. The participation type is a method in which sensing data are provided according to user intention when it is determined that the risk of personal information exposure is low or when such an exposure does not become a serious problem. Some crowdsensing services require extensive data preprocessing, as, for example, in the case of parking lot pictures for smart parking systems [21].