Design of Adaptive and Scalable Protocols for Permissionless Blockchain Systems

Abstract

Blockchain technology enables consensus on a distributed ledger without a central trusted authority, providing transparent, immutable, and decentralized platforms for various applications. Despite its great potential, the adoption of blockchain is constrained by scalability and adaptability issues. In permissionless blockchain networks, user transaction demands are highly dynamic, leading to network congestion during peak times and the creation of empty blocks in low activity periods. These inefficiencies result in resource wastage and degrade the overall performance of the network. There is an urgent need for blockchain systems that can adjust their throughput adaptively in response to fluctuating transaction demands.

This thesis develops adaptive and scalable protocols for permissionless blockchain systems, maximizing resource utilization without compromising security and decentralization. First, we propose AdaptChain, a Proof-of-Work (PoW) based protocol that can adjust blockchain throughput adaptively in response to transaction demands while eliminating duplicate transactions. When the transaction demands are high, the mining difficulty decreases, and the blockchain expands exponentially; when the transaction demands are low, the mining difficulty increases, and the blockchain shrinks exponentially. Second, we present PuffChain, a Proof-of-Stake (PoS) based protocol that provides fine-grained throughput adjustment by decoupling the functionalities of blockchain nodes. We also develop a theoretical model to analyze PuffChain's throughput and derive the optimal parameters to achieve maximal effective throughput. Third, we introduce X-shard, a protocol enhancing sharding-based blockchain scalability through optimized cross-shard transaction processing. X-shard takes an optimistic strategy, achieving high effective throughput and low processing latency. Extensive theoretical analysis and experimental results demonstrate that these protocols significantly improve the adaptability and scalability of blockchain systems across various consensus mechanisms and architectures. We prove the effectiveness and practical applicability of these protocols in real-world scenarios, contributing valuable solutions to blockchain technology.

Date of Award	2 Sept 2024
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Xiaohua JIA (Supervisor)