Saudi Arabian researchers investigate new techniques for underwater wireless optical communication (UWOC)
While the capabilities of robots and underwater equipment get better by the week, fast wireless communication in water remains a hurdle. Myriad forms of wireless data transfer options are available, each with various pros and cons, but the fact remains that few will be comparable to a signal sent by wire.
Existing technologies like acoustic communications and low-frequency radio waves are limited by narrow bandwidths and the need for large antennae and high-transmission powers, making them unsuitable for streaming good-quality, real-time video.
A new project by the Saudi Arabia-based King Abdullah University of Science and Technology (KAUST) has sought to pursue one avenue for sending and receiving video signals. In particular, researchers have been aiming to improve signal bandwidth to achieve better video quality.
The research was undertaken by PhD student Abdullah Al-Halafi, with supervisor Associate Professor Dr. Basem Shihada and colleagues. The group used underwater wireless optical communication (UWOC) systems, which consume significantly less power and offer the higher bandwidths required for streaming live video.
“We first built the real-time video transmission system and then integrated it into an UWOC setup,” Al-Halafi said. “Although the design and development of the system were very challenging, its ability to be programmed enabled us to reconfigure the system into several different arrangements.”
The team used a technique called quadrature amplitude modulation to increase the representation of information carried by the signal for a given bandwidth. Dr. Shihada explained to InnovOil via email that this “is a coding technique that is commonly used in digital telecommunications and wireless applications. Its main benefit comes from increasing the effective bandwidth, as the basic implementation is based on combining two amplitude modulated signals into a single channel.”
The signal was then compared with phase-shift keying, which changes the phase of the carrier signal, while optimising the transmission for each configuration. To check how well the system performed, the team developed an innovative algorithm to measure errors that occur during transmission called the bit error rate.
Also, by passing the signal through a 5-metre trough containing water of differing turbidity, they were able to test the quality of the video under different types of ocean water.
All in all, the system showed a tested bandwidth of 2.3 Gb/s. “Our system produced the highest-quality video streaming so far achieved in UWOC systems and provides a reconfigurable and cost-effective communications system for underwater live video streaming,” said Al-Halafi.
In terms of using the technology in commercial applications, Dr. Shihada pointed to a number of different possibilities: “Being able to demonstrate a video transmission over underwater visible light communication over (D) metres is novel. The distance (D) can vary, as we can always place mirrors to reflect the laser light at different angels and make (D) longer, [but in general] the longer the distance the worse the signal is. This is due to the fact that the signal fades over the transmission medium.”
“As for our experiments performed in the lab, the 5-metre value was selected because of the size of the water tank used. I anticipate that we can go beyond 5 metres, but we will need more mirrors and repeaters to strength the signal,” he added.
The team is now analysing the end-to-end delay component of sending live video traffic into underwater optical channels.