A Blockchain with Parallel Chain Structure to Increase Scalability

Abstract

Blockchain technology solves the centralization problems of the third party in an unreliable network. However, the existing blockchain systems including Bitcoin have relatively long transaction processing time and limited scalability due to the linear chain structure. Scalability in the blockchain system means fast processing of pending transactions. To resolve this limitation, we propose a blockchain protocol with a parallel chain structure that redesigns Bitcoin-NG to increase the scalability. Unlike the linear blockchain, which processes blocks one by one, blocks can be processed in parallel by selected leaders in the proposed structure. However, this structure has four problems: conflicting transaction, fork, reward, and synchronization. First, conflicting transactions occur because multiple leaders collect transactions in the common mining pool. We solve this problem by indexing conflicting transactions in the key block. Second, as the structure changes, forks that were not seen in the existing blockchain are generated. We present solutions for three types of the fork that can be generated in this structure. Third, the reward scheme must be changed due to conflicting transactions and multiple leaders. Finally, it is difficult for all nodes to maintain the same blockchain because many blocks are created in the proposed protocol. We present how to synchronize the blockchain through a key block. Furthermore, we analyze the number of leaders that affects network congestion by calculating the block propagation delay. Therefore, we figure out the optimal number of leaders when the proposed protocol is applied to the existing linear blockchains. According to our mathematical analysis, the proposed protocol improves the throughput of Bitcoin by up to 631 times, of Ethereum by up to 34 times, of Bitcoin Cash by up to 4, and of Litecoin by up to 25.