Lightweight consensus for blockchain–IoT in smart cities: hierarchical framework

The integration of blockchain technology with Internet of Things (IoT) devices in smart city deployments presents significant technical challenges, particularly regarding consensus mechanism design. Traditional blockchain consensus protocols such as Proof of Work (PoW) and standard Proof of Stake (PoS) impose computational, energy, and latency requirements that exceed the capabilities of resource-constrained IoT devices, motivating the development of lightweight alternatives. This paper examines lightweight consensus mechanisms specifically designed for edge-optimised blockchain deployments, evaluates hybrid on-chain/off-chain architectural patterns, and presents a comparative analysis of emerging solutions. We propose four research hypotheses (H1–H4) regarding hierarchical consensus performance and validate them through extensive discrete-event simulation across five smart city domains, using a 500-node testbed calibrated to representative urban workloads. A novel Business Process Model and Notation (BPMN)-based process model formalises the three-tier consensus workflow, and security analysis quantifies Byzantine fault tolerance guarantees. The proposed three-tier framework achieves a 94.7%± 2.3% reduction in on-chain transactions while maintaining cryptographic auditability, with consensus latency under 500 ms for district-level operations (p < 0.001 vs. single-tier baseline). District-level throughput reaches 1247±89 transactions per second (TPS), representing an 8.0× improvement over city-wide consensus, with energy consumption per transaction at the edge tier 95% lower than single-tier implementations. The simulation of 10,000 Byzantine attack attempts yielded a 99.97% detection rate. All improvements are statistically significant (p < 0.001, Cohen’s d > 0.8). Hierarchical consensus architectures, combined with selective off-chain processing, offer the most promising pathway towards scalable, secure blockchain.