title: Wireless PBFT consensus blockchain networks
Creators: name: Zhou, Ziyi
Publisher: name: University of Glasgow
Year: 2025

description: As wireless networks evolve towards increasingly heterogeneous environments with a growing number of mobile users, ensuring security and privacy becomes paramount. Blockchain technology, renowned for its decentralization and security features, presents a promising solution to these challenges. Practical Byzantine Fault Tolerant (PBFT), a voting-based consensus blockchain, is suitable for the wireless network because it is not computationally intensive, as most mobile devices are computationally limited due to the battery size and processing limitations. Moreover, PBFT can provide the essential byzantine fault tolerance to provide resistance to network failure and malicious attacks. This thesis investigates the application of PBFT consensus mechanisms to wireless networks, specifically focusing on IEEE 802.11 protocols, base station-enabled architectures and a hybrid network solution.

The performance of the wireless PBFT network using the IEEE 802.11 broadcast scheme under unsaturated conditions is investigated. Through a Markov model, the throughput, transmission success probability, and transaction confirmation delay of such a network are derived. View change is a mechanism incorporated to provide liveness to the PBFT, but frequent view change can undermine the overall performance of the PBFT network by delaying the consensus. The view change delay is introduced and derived in reference to the transaction confirmation delay. The impacts of channel contention from the non-PBFT nodes on the performance of the wireless PBFT network are further investigated. Channel contention impairs the transmission success probability and increases the chance of view change. The findings highlight a critical minimum transmission success probability required for effective PBFT consensus, proposing optimal configurations of the packet arrival rate and contention window size to balance success probability and network performance.

Furthermore, this thesis proposes an innovative PBFT framework leveraging base stations for inter-node communication. This approach reduces communication complexity and node transmit power while enhancing scalability and consensus success probability. The uplink and downlink communication between the base station and nodes are modelled based on the signal-to-interference-plusnoise ratio (SINR) threshold, which measures the strength of the wanted signal compared to the unwanted interference and noise. A good SINR is essential for reliable data transmission speed and integrity. A novel ‘timeout’ mechanism is incorporated to mitigate communication overheads. The performance is evaluated by metrics including consensus success probability, communication complexity, view change delay, view change occurrence probability, average transmit power, consensus delay and consensus throughput. The proposed framework demonstrates improvements in consensus success probability and throughput and reduced consensus delays compared to traditional PBFT implementations. A special case with f deterministic Byzantine nodes is also presented. The optimal configuration for achieving the target consensus success probability to provide analytical guidance for deploying wireless PBFT networks is analysed and demonstrated with numerical results.

To mitigate the influence of the poor wireless connection, which results in increased view changes and reduced consensus success probability, a hybrid PBFT network integrating a private and a public cloud is introduced. The security performance of the hybrid network is assessed in the presence of crashes and malicious attacks with decentralised and centralised coordination modes. This hybrid approach shows enhanced security capabilities compared to conventional PBFT, particularly when the private cloud is secure.

Overall, this thesis provides a comprehensive analysis of PBFT’s application in wireless networks, offering practical insights and solutions to improve security, efficiency, and scalability in future wireless and IoT environments.