Martian: Message Broadcast via LED Lights to Heterogeneous Smartphones

Visible light communication (VLC) has been shown to have several advantages over traditional wireless communication. In this paper, we envision an LED-light-to-smartphone VLC protocol for delivering messages to a group of randomly arriving smartphone receivers. Our goal is to increase the throughput for large message delivery, as well as to reduce the delay of message broadcast. Key challenges for implementing such a VLC message broadcast protocol are: 1) the imperfect synchronization among receivers and the transmitter; 2) the receivers' arbitrary arrival times; and 3) the diversity of receivers' smartphones (e.g., location, capability, and frame-rates). In this paper, we propose a new modulation scheme and design link-layer protocols for improving the network data rate. We carefully design and implement our protocol, MARTIAN, which allows smooth communication from the LED lights to a group of smartphone embedded cameras. Across several phone models, MARTIAN can achieve data rate of about 1.6 kb/s even with NLOS-light. It also has a stable and small delay for broadcasting messages to the randomly arriving receivers.