| With the rapid proliferation of wireless communication technology and sensor technology and the widespread popularization of mobile smart devices,mobile crowdsensing,a newly-emerged data collection paradigm,has attracted extensive attention in academia and industry.Mobile crowdsensing has many advantages such as wide coverage,low deployment cost and high flexibility and soon.Mobile crowdsensing relies on a sufficient number of sensing users to provide a large amount of high-quality sensing data.When users collect data,it is inevitable that takes time and effort,consuming multiple resources of smart devices.In addition,users also expose themselves to potential privacy threats by uploading sensing data.Therefore,there is a need to design a rational incentive mechanism to motivate users to actively participate in sensing tasks.At the same time,malicious users may upload falsified sensing data that affect the data aggregation results in order to obtain rewards,or violate the data privacy of honest users.Therefore,the design of incentive mechanism also needs to consider how to prevent malicious users.In addition,most existing mobile crowdsensing systems rely on centralized server that is vulnerable to single point of failure,and is prone to privacy leakage and injustice.(1)Distributed mobile crowdsensing system is studied.Blockchain is regard as an effective solution to overcome the untrusted of centralized server due to its characteristics of decentralization,immutable,traceability,openness,transparency and anonymity.In this paper,a blockchain-based framework for mobile crowdsensing system is proposed,blockchain is applied to build a decentralized trusted environment in mobile crowdsensing system.The task requester,the sensing platform and sensing users are used as nodes on the blockchain,and the process of crowdsensing between nodes is regarded as transactions,which are verified by miners on the blockchain and then packaged into block and added to the blockchain.(2)A blockchain-based mobile crowdsensing incentive mechanism is proposed.Based on the reverse auction model,the incentive process between the sensing platform and sensing users is constructed,and the incentive factor is designed to attract users to actively participate in sensing tasks.The sensing platform selects users based on the ratio of the bid price to the total value of the tasks,and distributes rewards based on data quality and the number of bids.The miners use EM algorithm for truth discovery of sensing data,and users embed digital watermarking in sensing data to prevent miners from potentially launching fake attacks in order to gain rewards.The theoretical analysis illustrates the security and effectiveness of blockchain-based incentive mechanism.The experiments show that the mechanism can effectively motivate users to participate in sensing tasks,and enhance the utility of users and the platform.(3)A blockchain-based user reputation updating mechanism is designed.Blockchain and edge computing are combined to construct a blockchain-based mobile crowdsensing system.By deploying blockchain on edge nodes,utilizing computing and storage resources of edge servers to support the consensus mechanism and store transaction ledgers on the blockchain.To resist malicious users and protect sensing data privacy,miners select users based on reputation value.The sensing platform uses lightweight additive secret sharing technology to safely aggregate sensing data,adopts MCEM algorithm to evaluate data quality,updates users’ reputation based on data quality and historical tasks performance.The security analysis illustrates the security of blockchain-based user reputation updating mechanism.The experiments demonstrate the feasibility and efficiency of the mechanism. |
