Autonomous, Localization-Free Underwater Data Muling Using Acoustic and Optical Communication

Abstract

We present a fully autonomous data muling system consisting of hardware and algorithms. The system allows a robot to autonomously find a sensor node and use high bandwidth, short range optical communication to download 1.2 MB of data from the sensor node and then transport the data back to a base station. The hardware of the system consists of an autonomous underwater vehicle (AUV) paired with an underwater sensor node. The robot and the sensor node use two modes of communication -acoustic for long-range communication and optical for high bandwidth communication. No positioning system is required. Acoustic ranging is used between the sensor node and the AUV. The AUV uses the ranging information to find the sensor node by means of either stochastic gradient descent, or a particle filter. Once it comes close enough to the sensor node where it can use the optical channel it switches to position keeping by means of stochastic gradient descent on the signal quality of the optical link. During this time the optical link is used to download data. Fountain codes are used for data transfer to maximize throughput while minimizing protocol requirements. The system is evaluated in three separate experiments using our Autonomous Modular Optical Underwater Robot (AMOUR), a PANDA sensor node, the UNET acoustic modem, and the AquaOptical modem. In the first experiment AMOUR uses acoustic gradient descent to find the PANDA node starting from a distance of at least 25 m and then switches to optical position keeping during which it downloads a 1.2 MB large file. This experiment is completed 10 times successfully. In the second experiment AMOUR is manually steered above the PANDA node and then autonomously maintains position using the quality of the optical link as a measurement. This experiment is performed two times for 10 minutes. The final experiment does not make use of the optical modems and evaluate the performance of the particle filter in finding the PANDA node. This experiment is performed 5 times successfully.

An End-to-End Signal Strength Model for Underwater Optical Communications

“…All three convert incident radiant power into current. 1 The output current is linearly related to the incident power . For a given sensor, this relationship, called responsivity, can be expressed as a constant (15) The incident power can be computed from the signal irradiance arriving at the detector (10), the incident angle , and the area (assumed flat) of the detector as (16) This yields a PD output current of (17) Equations (16) and (17) hold for a cosine response system.…”

“…Second, the information provided by the model can be used for location estimation. We showed previously that an AUV can use the optical signal strength to maintain position within communication range without external localization [1]. We believe that an optical signal strength model together with a Bayesian filter will enable enhanced localization.…”

A Compact Acoustic Communication Module for Remote Control Underwater

“…However, radio-frequency signals are rapidly attenuated in saltwater, severely restricting the feasible transmission range [7]. Optical communications are a common alternative choice for aquatic data transmission, and works such as [22,10,11] have used optical systems to transmit data. However, visible light is subject to significant scattering, and ambient light near the surface can introduce noise in the communication channel.…”

“…An additional bit is included to toggle video recording. These 11 bits are expanded into a 16-bit word via a (15,11) Hamming encoding with an additional parity bit.…”

Underwater Optical Wireless Communication Systems: A Concise Review

“…In Ref. [44], a robot estimating its position according to a sensor node in a data mulling application-another usage of Aquaoptical IIwas described.…”