IoTorch: Reliable LED-to-Camera Communication Against Inter-Frame Gaps and Frame Drops

LED-to-camera communication for smartphones promises to enable low-cost, small-size, and intuitive data access to Internet-of-things (IoT) devices. However, for fast and reliable communication under the rolling shutter effect, the packet losses caused by inter-frame gaps and frame drops must be dealt with. In this paper, we introduce LED-to-camera communication between a commercial smartphone and an IoT device with LED flashlight, where the user can intuitively acquire the desired data transmitted from the IoT device to the smartphone. Specifically, we present IoTorch, a fast and reliable LED-to-camera communication that efficiently prevents the packet losses. IoTorch consists of two core mechanisms: 1) a minimum-repetition one-way reliable transmission focusing on the periodicity of inter-frame gaps and 2) an acknowledgement mechanism to overcome frame drops by using a smartphone's built-in flash focusing on its delay characteristics. Additionally, we propose an optimization method to increase the throughput up to 2.92 kbps (i.e., 2.43 times faster than that of the state-of-the-art method that overcomes the inter-frame gaps). Furthermore, we realize a remote wake-up function by using the smartphone's flash as the data transmission trigger. To demonstrate the benefit of IoTorch, we present a sensor data viewer using Arduino and a smartphone console system on TelosB.