• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2018.05a
• /
• pp.68-71
• /
• 2018

In this paper, we propose a synchronization protocol for underwater acoustic networks which aims to minimize the effects of long propagation delay and uncertain delay variations and employs packet train scheme with considering low data rate. The proposed protocol uses an one-way delay measurement method by transmitting consecutive packets and acquires synchronization only considering propagation delay variations by calculating packet arrival time differences. We perform simulations under various network conditions, such as node mobility, time interval for packet transmission, network range, and elapsed time after synchronizing. The simulation results shows the superiority of our protocol, compared with a previously proposed protocol.

• The Journal of the Acoustical Society of Korea
• /
• v.36 no.1
• /
• pp.39-48
• /
• 2017

CDMA (Code Division Multiple Access) is promising medium access control schemes for underwater acoustic sensor networks because of its robustness against frequency-selective fading and high frequency-reuse efficiency. In this paper, we design diversity schemes of underwater CDMA transceiver for the forward and reverse links. User data are multiplexed by Walsh code and a pseudo random noise code acquisition process is added for phase error correction before decoding the user data at the receiver. Then, the diversity reception using equal gain combining and maximal ratio combining is performed in order to minimize performance degradation caused by rich multipath fading of underwater acoustic channel. We evaluated the performance of diversity transceiver through lake experiment, which was performed at Lake Kyungcheon, Mungyeong city using two transmitters and two receivers placed 460 m apart at an average depth of 40 m. The lake experiment results show that user data are recovered with error-free in both of the forward and reverse links.

• The Journal of the Acoustical Society of Korea
• /
• v.28 no.8
• /
• pp.774-780
• /
• 2009

This paper proposes a transmitted power saving method for underwater acoustic sensors considering the acoustic wave propagation characteristic that propagation loss increases more rapidly in higher frequency band. In the proposed scheme, sensor nodes are divided into a few groups based on the distance between sink node and the sensor node, and each group uses its own frequency band. The node group with longer distance uses lower frequency and the node group with shorter distance uses higher frequency. By means of such a distance-dependent frequency allocation, all sensor nodes are able to maintain a certain target signal-to-noise ratio (SNR), but also save transmitted power. In addition, the optimum size of node group is obtained, and also a frequency allocation algorithm is proposed accordingly. Numerical results show that the proposed scheme saves transmitted power by more 10 dB comparing non-grouping methods.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.4B
• /
• pp.405-411
• /
• 2011

As the interest in ocean environment monitoring and ocean development has been increased, the need for researches on underwater wireless sensor network (UWSN) and low power consuming acoustic modem for UWSN has been arisen. In this paper, we design and implement a micro-modem equipped with a tiny and omnidirectional transducer for underwater acoustic communications. In addition, we make experiments in a water tank and a pond in order to verify the performance of the developed modem in terms of supply voltage and communication distance, and analyze the results. According to the outdoor experiments, the modem can send data wirelessly in underwater at a distance of 40 meter with a data rate of 200 bps and a bit error rate of $10^{-5}$ when the supply voltage is 12 V. Due to its small size, low power consumption and omnidirectional property, it is expected that the modem which is implemented in this paper could be utilized for various applications based on UWSN.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.22 no.6
• /
• pp.1-10
• /
• 2021

The interest in underwater acoustic sensor networks (UWASNs), along with the rapid development of underwater industries, has increased. To operate UWASNs efficiently, it is important to adopt well-designed medium access control (MAC) protocols that prevent collisions and allow the sharing of resources between nodes efficiently. On the other hand, underwater channels suffer from a narrow bandwidth, long propagation delay, and low data rate, so existing terrestrial node pairing schemes for non orthogonal multiple access (NOMA) cannot be applied directly to underwater environments. Therefore, a multi-dimensional node pairing scheme is proposed to consider the unique underwater channel in UWASNs. Conventional NOMA schemes have considered the channel quality only in node pairing. Unlike previous schemes, the proposed scheme considers the channel gain and many other features, such as node fairness, traffic load, and the age of data packets to find the best node-pair. In addition, the sender employs a list of candidates for node-pairs rather than path loss to reduce the computational complexity. The simulation results showed that the proposed scheme outperforms the conventional scheme by considering the fairness factor with 23.8% increases in throughput, 28% decreases in latency, and 5.7% improvements in fairness at best.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.39C no.3
• /
• pp.275-281
• /
• 2014

Recently, the need for various underwater application systems targeting efficient resource exploration and aquatic ecosystem monitoring is rapidly increasing in littoral sea and inland waters. In this paper, we focus on the research and development of digital module of acoustic micro modem which can be used for underwater mobile communication systems and underwater sensor network systems. Specifically, a digital module of acoustic modem embedding digital signal processor is designed and implemented. On top of the developed hardware platform, physical layer frame generation and recovery and channel coding algorithms are mounted and tested in a water tank and a pond to verify its functionality and performance. According to experimental results, less than 1 percent of total computational power is consumed in the processing of frame control and convolutional code with the data rate of 1 kbps. Thus, the performance of micro modem could be improved by loading efficient baseband algorithms into the processor while maintaining the implemented hardware.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.15 no.1
• /
• pp.33-40
• /
• 2011

In this paper, underwater acoustic communication experiment was carried out to test a performance of single carrier digital modulation schemes. The communication experiment was performed at real sea and tested modulation schemes are ASK, FSK with non-coherent detection and QPSK with coherent detection. A modulated image data was transmitted with data rates of 600bps~3Kbps. From the results of BER of the demodulated signal, ASK and FSK show the achievable BER of $10^{-3}{\sim}10^{-4}$ without compensation techniques and QPSK show that of $10^{-4}$ with linear equalizer.

• Journal of Navigation and Port Research
• /
• v.35 no.10
• /
• pp.811-816
• /
• 2011

In this paper, we analysis to consider the performance of PSPM (Phase Shift Pulse-position Modulation), the one of the low power communication technique, in near-field underwater sound channel by sea trial. PSPM is a QPSK(Quadrature Phase Shift Keying) modulation combined with PPM(Pulse Position Modulation) for low power communication in WBAN(Wireless Body Area Network). It is known that the bandwidth efficiency of PSPM is lower than conventional PSK but the power efficiency increases. In this paper, we will analyze the BER performance of PSPM using data acquired from the sea trials. The BER of QPSK was $6.04{\times}10^{-2}$, PSPM was $3.5{\times}10^{-1}$. Also, PSNR of QPSK was 9.37 dB and in case of PSPM was 9.11 dB.

• The Journal of the Acoustical Society of Korea
• /
• v.28 no.6
• /
• pp.499-505
• /
• 2009

Main design issues for MAC (Medium Access Control) protocol in underwater sensor networks are long propagation delay caused by the low speed of sound, difficult synchronization, and energy-limited node's life. We aimed to mitigate the problems of strict synchronization and channel inefficiency of TDMA and also the throughput degradation induced by unavoidable collisions in contention based MAC protocols. This proposed protocol improved not only the energy efficiency by adopting a sleep-mode, but also the throughput by reducing collisions and increasing channel efficiency.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.5B
• /
• pp.539-548
• /
• 2011

We propose an efficient cooperative ARQ (Automatic Repeat reQuest) scheme for single-hop and multi-hop underwater acoustic communications, in which cooperative nodes are used to provide more reliable alternative paths for a specific source-to-destination connection. This alternative path has higher channel quality than that of the direct source-destination path. In addition, during a packet-relay through multiple hops, the typical acknowledgement (ACK) signal is replaced with overhearing data packet returned back from the next hop. The usage of overhearing as an ACK improves the system performance. In this paper, we evaluate the proposed scheme by comparing it with a conventional S&W ARQ in terms of throughput efficiency. Computer simulation results show that the proposed cooperative retransmission scheme can significantly improve the throughput by increasing the probability of successful retransmission.