Hybrid-band relay based underwater video broadcasting systems with applications to entertainment and exploration

Underwater communications are critical to applications of remotely operated vehicles (ROV) and autonomous underwater vehicles (AUV) to both entertainment and research purposes. Among others, underwater video transmission is rather difficult due to the demand of high data rate (bandwidth) transmission through the water medium which leads to large attenuation for electromagnetic (EM) waves. In this situation, appropriate relays are usually required for transmission range extension. In this paper, a novel hybrid-band relay based analog/digital video transmission (broadcasting) system is proposed from system design to hardware implementation. By taking the EM wave transmission properties of water into account, 700 MHz-band relays are used for underwater transmission range extension and 2.4 GHz-band relays are used for off-water transmission range extension. One of the advantages of the proposed hybrid-band system is significant reduction of self-interference from the transmitter to the receiver within a relay. This is critical to practical ROV and AUV design in which only a small space is allowed for separating the transmitter and receiver of a relay. Regarding the modulation approaches, a low-cost frequency modulation (FM) scheme and a coded orthogonal frequency division multiplexing (OFDM) scheme are adopted for analog video sources and digital video sources, respectively. Experimental results shows that, with transmission power specified to 100 ~ 500 mW, the video captured by an ROV can be transmitted through an underwater distance of 2 ~ 3 m with two underwater relays. Prototypical toys for a game of underwater battle of ROVs through remote-controlled operation have been developed using the proposed video transmission system.