Efficient On-Off Keying Underwater Acoustic Communication for Seafloor Observation Networks

Abstract

In the cableless seafloor observation networks (SONs), the links among network nodes rely on underwater acoustic communication (UAC). Due to the energy constraint and the high-reliability requirement of the cableless SONs, the noncoherent UAC has been a preferred choice, even though a noncoherent UAC scheme generally suffers from low spectral efficiency. In this paper, we propose a high-spectral-efficiency noncoherent UAC transmission scheme which is implemented as an orthogonal frequency-division multiplexing (OFDM) system adopting the on-off keying (OOK) modulation. To simultaneously achieve high performance at a low energy consumption, an irregular recursive convolutional code (IrCC) is employed and an accumulator (ACC) is introduced to achieve a modulation with memory at the transmitter side. The ACC enables a turbo iteration between the soft demapper called the ACC-OOK demapper and the soft decoder on the receiver side, and also reduces the decoding error floor. To account for the unknown signal-to-noise ratio (SNR), an iterative threshold estimation (ITE) algorithm is proposed to determine a proper decision threshold for the ACC-OOK demapper. The IrCC is designed to match the extrinsic information transfer (EXIT) curve of the ACC-OOK demapper, lowering the SNR threshold of the aforementioned turbo iteration. Simulations and experimental results verify the superiority of the proposed noncoherent UAC scheme over conventional ones.

Super Permutation Frequency-Shift-Keyed Underwater Acoustic Communication

“…Note that an SPFSK alphabet with M = 1 yields the ON-OFF keying (OOK) (sometimes called OFDM-OOK) alphabet. Hence, an FSK modulation scheme with M carriers can either use an SPFSK alphabet with dimensionality M or map M OOK symbols to the carriers (MC-OOK) (see, e.g., [29]). These two approaches have an equivalent spectral efficiency, and if all symbols are transmitted with equal probability, they both produce the same average number of active carriers per transmission.…”

Robust Underwater Acoustic Communication Using the Overlapped Chirp Spread Carrier Technique in Doubly Spread Environments

“…Underwater acoustic communication is used in various applications, such as underwater navigation, underwater vehicles, underwater sensor networks, marine environment monitoring, and military purposes [1], [2], [3], [4], [5], [6], [7]. However, unlike radio frequency (RF) communication, underwater acoustic communication has many obstacles, such as high propagation loss, frequency selective fading, narrow bandwidth, and fast time variability [8], [9], [10].…”