  Message exchange among vehicles plays an important role in ensuring road
safety. Emergency message dissemination is usually carried out by broadcasting.
However, high vehicle density and mobility usually lead to challenges in
message dissemination such as broadcasting storm and low probability of packet
reception. This paper proposes a federated learning based blockchain-assisted
message dissemination solution. Similar to the incentive-based Proof-of-Work
consensus in blockchain, vehicles compete to become a relay node (miner) by
processing the proposed Proof-of-Federated-Learning (PoFL) consensus which is
embedded in the smart contract of blockchain. Both theoretical and practical
analysis of the proposed solution are provided. Specifically, the proposed
blockchain based federated learning results in more number of vehicles
uploading their models in a given time, which can potentially lead to a more
accurate model in less time as compared to the same solution without using
blockchain. It also outperforms the other blockchain approaches for message
dissemination by reducing 65.2% of time delay in consensus, improving at least
8.2% message delivery rate and preserving privacy of neighbor vehicle more
efficiently. The economic model to incentivize vehicles participating in
federated learning and message dissemination is further analyzed using
Stackelberg game model.
