# Reputation-Based Blockchain for Spatial Crowdsourcing in Vehicular Networks
## 2 System Model  
### System Architecture  
As shown in Figure 1, we consider a reputation-based crowdsourcing platform for vehicular networks. The red EVs in Figure 1 are requested to obtain real-time road conditions, and then broadcast the task to the blockchain-based crowdsourcing platform. The crowdsourcing platform employs blockchain to conduct crowdsourcing transactions and update reputation scoring. In this context, all vehicles (white vehicles represent candidate miners and blue vehicles depict miners in service) are considered as potential miners for participating in the mining process of the crowdsourcing task.  
The edge network deconstructs large-scale services originally handled by the cloud into smaller and easier-to-manage parts, and distributes them to the edge nodes for processing. This process reduces latency, improves efficiency, and enhances security and privacy protection. For vehicular networks, vehicles, base stations, and edge servers will serve as edge nodes for computing, processing, and storage, which can reduce latency and improve the real-time performance of high-bandwidth applications [26]. The edge-based vehicular networks move a portion of the computational capability of the core network to the edge. The computing tasks can be selected according to real environmental conditions and constraints to perform calculations locally in the vehicle or offload to the nearest edge nodes for computing. In vehicular networks, the vehicle acting as the miner node uses its hardware capabilities to perform specific tasks, such as mining. Meanwhile, the BSs and edge servers can be utilized as trusted nodes to realize offline storage/interaction/processing. Complex and sensitive transactions can also be offloaded to high-level entities with rich computational resources. Vehicle users with weak computational capabilities are primarily utilized for securing their interaction connectivity and basic processing. Weak-capability nodes act as miners to perform normal sensing and actuation tasks, and essential blockchain functions (e.g., verification, mining, and transactions). In addition, complex PoW puzzles and corresponding benefits will also prompt vehicle users to increase their computational capability in order to obtain benefits.  
The blockchain-based crowdsourcing task execution approach mainly centers on the distribution and execution of vehicle/customer tasks. Specifically, crowdsourcing task solutions are mainly divided in to distribution, execution, and recovery. For crowdsourcing distribution, we deploy execution of the transaction within the block, using the blockchain network for broadcasting. When vehicle miners receive information about crowdsourcing tasks, they will join in the computing after weighing private information (i.e., hardware capability) acting as miners. This details the mining process. Once vehicles/miners finish and publish the unverified block to the blockchain, the verification nodes/vehicles (which also contain the miners) will verify the results, representing the verification of crowdsourcing users. The first miner/vehicle to succeed is rewarded, representing recovery of the crowdsourcing task. That is, crowdsourcing within the vehicular networks is executed as a process of generating new blocks.  
To fully utilize the vehicles' redundant hardware resources, the established crowdsourcing tasks are mainly aimed at lightweight applications (e.g., collaboration, feedback, collection, etc.), which is enough to support most lightweight blockchain applications. Even for computationally intensive crowdsourcing tasks, different approaches [27; 28] can be adopted: offload to a higher layer network; or encourage customers to increase their  
Figure 1: System model for performing spatial crowdsourcing tasks via blockchain-based interaction approach in vehicular network.  
budgets, incentivizing vehicles to enhance their computational capability. To improve readability, Table 1 list the key notations.