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Content Synchronization with Feedback in Smart City Device-to-Device Communication

With the acceleration of IP traffic and urbanization, Device-to-Device (D2D) communication has appeared as a promising solution to delivering contents to mobile users in a timely manner in smart cities by offloading traffic from the overburdened cellular infrastructure. The process to distribute the new content to all the interested devices is called content synchronization. After all the interested devices have been synchronized, the existence of a large number of content copies in the network reduces resource utilization and network performance. Removing these redundant copies in D2D communication networks with multiple interested devices and no guaranteed end-to-end path between devices is challenging. In this paper, we propose two novel feedback mechanisms namely the acknowledgement-based feedback mechanism (AFM) and the non-acknowledgement-based feedback mechanism (NAFM) built into the relay-assisted synchronization algorithm under the City Section mobility model to address the issue. AFM relies on acknowledgements and NAFM relies on the estimation of synchronization latency to remove redundant copies without adding extra overhead. Simulation results show that both are effective in removing redundant copies: NAFM removes all the copies with little overhead by good estimation of the synchronization latency and AFM has a tradeoff between synchronization latency and number of copies removed.