The Development of LoRa Image Transmission Based on Time Division Multiplexing

Recently, a new IoT wireless technology, LoRa (Long Range), with spread spectrum modulation was proposed. It has the features of remote transmission, low power and high receiver sensitivity; therefore it becomes one of the most important IoT technologies. For various IoT applications, transmitting images is always essential. However, due to the limited frequency resources in LoRa transmission, to simultaneously achieve the multi-signals transmission by using the multiplexing method is inevitable. Therefore, the LoRa based time division multiplexing (TDM) was proposed in the study for the transmission between sensor nodes and gateway. The LoRa image transmission system is divided into three parts: the three image capturing sensor nodes, gateway and server. The three image sensor nodes use the Raspberry Pi as the platform and are responsible for capturing images as well as transmitting the JPEG compression images to gateway. The gateway also used the Raspberry Pi as the platform to decode the image pixel data transmitted from the sensor nodes and combined the image pixel values to restore the image. Finally, the restored image was transmitted to the server by internet. In addition, broadcasting the timing from gateway to the three sensor nodes achieves the synchronization mechanism of the time division multiplexing. The experimental results showed that the single image of 200x150 pixels can be transmitted by LoRa about 1 minute for the distance of 2 km. By the time division multiplexing technology, we can thus simultaneously transmit three images and monitor three environmental states in the experiment.