# Reputation-Based Blockchain for Spatial Crowdsourcing in Vehicular Networks
## 2 System Model
### Blockchain  
A block consists of a block head and a block body. The block head plays an important role in blockchain networks by ensuring immutability [29]. Only by changing the block head, can an attacker tamper with the blockchain ledgers from the genesis blockchain, rendering their chance of success nearly impossible. The block body is responsible for recording transactions and information during the generation process, e.g., storage and processing. The details are as follows. (1) The block head is mainly composed of the data version, block hash, merkle root, timestamp, etc. The data version records the attributes and types of accessed data. The block hash consists of both the previous and current block, thus the immutability arises precisely because the hash of the currently created block is determined by the hash of the previous block, and will act as the index of the next block hash. The Merkle root is the binary hash tree created from all transactions in the block, and each data record is hashed into Merkle tree. (2) The block body is mainly composed of data size, block interval, action \begin{table}
\begin{tabular}{l l} \hline \hline
**Notations** & **Meanings** \\ \hline \(\mathcal{M}\) & the set of all miners \\ \(\mathcal{L}\) & the set of all pools \\ \(i\) & the \(i\)-th pool \\ \(j\) & the \(j\)-th miner \\ \(-j\) & the miners except miner \(j\) \\ \(R_{j}(n)\) & the local reputation of miner \(j\) in the \(n\)-th round \\ \(R_{j}^{\mathcal{O}}(n)\) & the local objective reputation of miner \(j\) \\ \(R_{j}^{\mathcal{S}}(n)\) & the local subjective reputation of miner \(j\) \\ \(\tilde{R}_{j}\) & the comprehensive reputation of miner \(j\) \\ \(\mathcal{B}_{Cs}\) & the crowdsourcing side-chain \\ \(\mathcal{B}_{-Cs}\) & the remaining chains except \(\mathcal{B}_{Cs}\) \\ \(N_{j}^{\mathcal{B}_{Cs}\to\mathcal{B}_{-Cs}}(n)\) & the interactions in the crowdsourcing chain \\ \(X_{j}^{\mathcal{S}}(n)\) & the minimum number of interactions \\ \(R_{j}^{\mathcal{S}}\) & the estimations of reputation obtained \\ \(R_{j}^{\mathcal{S}}(n)\) & the normalized reputation evaluation of miner \(j\) \\ \(E_{j}^{(i)}\) & the fixed reward \\ \(E_{p}^{(i)}\) & the performance reward \\ \(E_{r}^{(i)}\) & the participant reward \\ \(|\mathcal{L}^{(i)}|\) & the number of miners in the pool \\ \(|\mathcal{H}^{(i)}|\) & the number of honest miners in the pool \\ \(u_{j}(n)\) & the utility function of miner \(j\) in the \(n\)-th round \\ \(h^{(i)}\) & the entry threshold of pool \(i\) \\ \(f_{j}\) & the reputation fluctuation of miner \(j\) \\ \(T_{j}\) & the survival times \\ \(Q_{j}\) & the probability of being dishonest for miner \(j\) \\ \(\tilde{u}_{j}(n)\) & the accumulated estimated reward of miner \(j\) \\ \(d\) & the distance attribute of individual subtasks \\ \(v\) & the volume of budget segments \\ \(\mathcal{L}^{(i)}\) & the set of miners in pool \(i\) \\ \(D^{\text{tar}}\) & the distance threshold set by the requesters \\ \(\kappa\) & the number of continuous credibility \\ \(R_{Signal}^{(i)}\) & the value of unit reputation for each segment \\ \(f_{Soren}^{(i)}(n)\) & the screening threshold of pool \(i\) \\ \(E\left(R_{j}^{(i)}(n)\right)\) & the expected reputation of pool \(i\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the key notations. counter, block lock timer, data, etc. The block size indirectly defines the maximum number of transactions transferred within a block, mainly determined by the amount of data in the generated block. The block interval defines the waiting time for data to be written into the blockchain ledger, which is measured by the complexity of crowdsourcing tasks. The block lock timer records the last block of transactions. Further, the data part is mainly responsible for all data operations, i.e., interactions, packaging, and chaining, etc.