# Improved PBFT Algorithm Based on Comprehensive Evaluation Model
## 1 Introduction
[PERSON] [11] uses a speculative BFT algorithm that can reduce the communication overhead to near-optimal if all nodes are normal, otherwise, it will adopt a reconfirmation mechanism to reach consensus, but the decision-making with two mechanisms will lead to higher delay. In addition, the number of nodes participating in the consensus has a direct impact on the communication complexity of the PBFT consensus algorithm, so researchers try to reduce the number of nodes participating in the consensus. Algorithms such as DBFT [12] and Tendermint [13] are based on PoS to elect committees, these algorithms associate nodes with margins to solve the noninterest issues of native PoS. The T-PBFT algorithm [14] combines the Eigen-Trust model with a consensus algorithm to evaluate the trust level of nodes, selects some nodes with higher credit to participate in the consensus, and uses the nodes with higher quality in the network to build a consensus group instead of a single primary node. To prevent the selected nodes from being too concentrated to pose a threat to the security of the system, the Algorand algorithm [15] uses VRF [16] to randomly select a subset of network nodes as committees to ensure the unpredictability of committee members and improve the security of the system. These consensus algorithms of the \"committee + PBFT\" model improve the performance and scalability of the algorithm due to the reduction of the consensus network scale. However, the functions of the committee node are higher than those of the general node, and the power is too concentrated in the committee node, which violates the decentralized nature of the blockchain. The Byzantine fault tolerance algorithms are improved by increasing the number of tolerable malicious nodes in the communication network, using methods including timely detection and hardware assistance to improve the fault tolerance of the blockchain. Minbft [17] combines the BFT consensus algorithm with trusted hardware and constrains the evil node with trusted hardware so that only non-Byzantine faults can be generated by Byzantine nodes. With the introduction of trusted hardware, the fault tolerance rate of the BFT algorithm is increased from \(1/3\) to \(1/2\)SDMA-PBFT [18] proposes a scalable dynamic multi-agent hierarchical PBFT algorithm, which divides nodes into several groups. Each group selects an agent and then executes the PBFT algorithm in each group. Multi-layer PBFT [19] proposes a scalable multi-layer PBFT-based consensus mechanism, which significantly reduces the communication complexity and provides guidance for the design and performance analysis of hierarchical systems. However, the instability of the primary node will lead to poor fault tolerance of the system and higher delay in the multi-layer structure. It can be seen from the previous work that the design of the consensus algorithm is a compromise and balance among efficiency, security, and stability on the premise of specific application scenarios. However, whether it is the PoW algorithm, PoS algorithm, or BFT algorithm, the design of the blockchain consensus algorithm needs to face a complex environment, and there are many difficulties and problems to be solved. How to adaptively design a consensus mechanism for a specific performance evaluation target in combination with specific requirements and application scenarios to achieve the purpose of optimizing the algorithm [20; 21] is an urgent problem to be solved. Therefore, we solve the problems of the PBFT algorithm, such as high communication complexity, arbitrary selection of primary nodes, and poor node scalability, and improve the applicability of the blockchain in large-scale scenarios. In this paper, an improved PBFT algorithm based on a comprehensive evaluation model is proposed. Specifically, the main contributions of this paper are as follows:  
First, nodes are divided into several groups based on the multi-formation control strategy of a UAV cluster.