Broadband communications, Networks, and Systems: Theory and Applications -- A Machine Learning-based Elastic Strategy for Operator Parallelism in a Big Data Stream Computing System -- End-to-End Dynamic Pipelining Tuning Strategy for Small Files Transfer -- Containers' Privacy and Data Protection via Runtime Scanning Methods -- Digital Twin For Cybersecurity: Towards Enhancing Cyber Resilience -- Differential Privacy-based Permissioned Blockchain for Private Data Sharing in Industrial IoT -- Efficient Privacy-Preserving User Matching with Intel SGX -- Developing an Online Examination Timetabling System Using Artificial Bee Colony Algorithm in Higher Education -- A Topology-Aware Scheduling Strategy for Distributed Stream Computing System -- Data Stream Prediction Strategy for Elastic Stream Computing Systems -- Blockchain Enabled Integrity Protection for Bodycam Video -- Road Rage Recognition System Based on Face Detection Emotion -- A Drip Irrigation Remote Control System using 5G-IoT Technology -- Multipath QUIC - Directions of the Improvements -- One New Adaptive Elliptical Weighting Model Combining with the Tikhonov-ffp-norm for image reconstruction -- Calculation and Numerical Simulation of Building Integrated Photovoltaic System Based on Connected Autonomous Vehicle Platoon Control through Multi-Agent Deep Reinforcement Learning -- 5G-enabled Smart Building: Technology and Challenge -- Accurate Estimation on the State-of-Charge of Lithium-ion Battery Packs -- Fire Simulation and Optimial Evaluation Based on BIM Technology -- Discrete Sliding Mode Control of PMSM with Network Transmission -- Smart Medical and Nursing Platform Based on 5G Technology -- Time-domain predictable trajectory planning for autonomous driving based on Internet of Vehicles -- 5G: The Advances in Industry -- Rate-compatible shortened polar codes based on RM code-aided -- Research on wheat impurity image recognition based on convolutional neural network -- Based on Energy Router Energy Management Control Strategy in micro-grid.

This book constitutes the refereed post-conference proceedings of the 12th International Conference on Broadband Communications, Networks, and Systems, Broadnets 2021, which took place in October 2021. Due to COVID-19 pandemic the conference was held virtually. The 24 full papers presented were carefully reviewed and selected from 49 submissions. The papers are thematically grouped as a session on broadband communications, networks, and systems; 5G-enabled smart building: technology and challenge; and 5G: The advances in industry.