# Development of User-Participatory Crowdsensing System for Improved Privacy Preservation
## 5 Performance Evaluation
### Processing Performance  
To demonstrate the sensing data processing efficiency of the proposed system, the request processing time for the allocated sensing data was measured for varying number of data processing nodes. The request processing time is the time required for completing all the sensing data processing requests from the time when the first request is allocated and opened to the time when the sensing data for the last request is transmitted to the data requester and the reward information is updated (Steps 5-16 in Figure 8). The number of sensing data requests was set to 10, 50, and 100. Ten data providers generated and sent random values as sensing data as soon as they received a new sensing data request. The experiment was performed on the implemented system, as explained in Section 4, and all nodes were connected with a network of virtual machines. The final results were obtained by averaging the results of 10 independent runs of the same experiment. In order to analyze the efficiency of distributed processing of data processing nodes, we compare the proposed system with the method of performing all data processing in one \(SP\). The processing method using the conventional approach is shown in Figure 12. This method is also implemented to  
Figure 11: Compromised processing nodes vs. number of consecutive works allocated to compromised processing nodes. store sensing data, reward information, and user information using PostgreSQL, and the data provider encrypts and transmits the publicly disclosed public key of \(SP\) instead of exchanging a session key with the service provider. The Kaa framework used for data processing node participation, sensing data transmission, and so on is not used in the central \(SP\) processing experiment. The request processing time measured in the conventional method is the time required for processing Steps 3-10 in Figure 12.  
Figure 13 shows the request processing time of proposed and traditional methods according to the number of data processing nodes. When the central \(SP\) processes all the sensing data, it takes 519.858 s to process 100 requests, which is faster than the processing by one data processing node which takes 534.985 s. This difference can be analyzed because the \(SP\) processes the sensing data, unlike the case in which the data processing node processes the session key exchange and reward information transfer. However, even if only one data processing node is added, the processing speed of the proposed system that distributes and processes the sensing data is faster. In particular, it can be seen that, as the number of data processing nodes increases, the request processing time clearly decreases. The results demonstrate that the presence of a larger number of data processing nodes in the proposed system implies better sensing data processing performance. However, even if a data processing node is configured with a relatively small number of nodes, a significant performance improvement can be expected. That is, distributed processing (i.e., the involvement of several data processing nodes) can significantly reduce processing time. In addition, the proposed system not only has superior security compared to the central \(SP\) processing method, but also has an advantage in the processing efficiency of sensing data. Table 7 shows the average time required to process one sensing datum. The participation request and sensing data encryption/decryption time is less than 1 ms and does not affect the total time. Most of the total time is required for session key sharing using asymmetric encryption, for encrypting the sensing data with the requester ID, and for sending the data. Regardless of the total number of requests, the case of a single data processing node involved the longest processing time, as it can be expected that a single data processing node should perform all steps up to issuing a session key for all sensing data and processing time-consuming sensing data. The case of 10 data processing nodes involved the shortest total request processing time.