Index Terms — Blockchain, Federated Learning, Machine Learning.

I. INTRODUCTION

II. BACKGROUND KNOWLEDGE
B. Brief Introduction to Blockchain

III. FOUNDATIONS OF BCFL
A. Architectures of BCFL
B. Blockchain Types in BCFL
C. Learning Devices in BCFL

IV. FUNCTIONS OF BCFL
A. Verification of Model Updates
B. Aggregation of Global Model
C. Utilization of the Distributed Ledger
D. Incentive Mechanism

V. APPLICATIONS OF BCFL
A. BCFL for IoT
B. BCFL for Healthcare
C. BCFL for Business and Finance
D. BCFL for Smart City

VI. CHALLENGES AND FUTURE RESEARCH DIRECTIONS
A. Privacy and Security
B. Training Efficiency
C. Resource Consumption
D. Future Research Directions

VII. CONCLUSION