Doppler Estimation, Synchronization with HFM Signals for Underwater Acoustic Communications

2012 ◽  
Vol 198-199 ◽  
pp. 1638-1645 ◽  
Author(s):  
Lan Zhang ◽  
Xiao Mei Xu ◽  
Wei Feng ◽  
You Gan Chen
Keyword(s):  
Multipath Propagation ◽  
Delay Spread ◽  
Underwater Acoustic Communication ◽  
Good Prospect ◽  
Underwater Acoustic Communications ◽  
Frame Synchronization ◽  
Large Delay ◽  
Underwater Acoustic ◽  
Moving Platforms ◽  
Testing Performance

This paper presents the application of the hyperbolic frequency modulated (HFM) signal to acoustic propagation in order to improve the performance of underwater acoustic (UWA) communications. Due to the large delay spread caused by multipath propagation and the severe Doppler Effect of the channel, we propose the using of double HFM signals as preambles for Doppler estimation, frame synchronization in UWA communications. A theoretical analysis about Doppler-invariability of HFM signals was provided firstly, then some numerical simulations about Doppler estimation were implemented, and experiments on testing performance of double-HFM preambles for frame synchronization in the pool were carried out as well. The simulation and experimental results show that using double-HFM signals as preambles has the capability to take an explicit Doppler estimation and retiming for frame synchronization, demonstrating that it has a good prospect in underwater acoustic communication system, especially for moving platforms.

Experimental Multipath Delay Profile of Underwater Acoustic Communication Channel in Shallow Water

2016 ◽  
Vol 2 (2) ◽  
pp. 351 ◽  
Author(s):  
Yasin Yousif Al_Aboosi ◽  
Ahmad Zuri Sha'ameri
Keyword(s):  
Shallow Water ◽  
Acoustic Communication ◽  
Multipath Propagation ◽  
Water Channel ◽  
Underwater Acoustic Communication ◽  
Communication Performance ◽  
Underwater Acoustic ◽  
Research Fields ◽  
Different Depths ◽  
Major Factors

<p>The shallow water channel is an environment that is of particular interest to many research fields. An underwater acoustic channel is characterized as a multipath channel. Time-varying multipath propagation is one of the major factors that limit the acoustic communication performance in shallow water. This study conducts two underwater acoustic experiments in Tanjung Balau, Johor, Malaysia. A transducer and a hydrophone are submerged at different depths and separated by different distances. Linear frequency modulated (LFM) pulses are chosen as the main transmit signal for the experiments. The cross-correlation between the transmitted and received signals represents the impulse response of the channel (multipath profile). The results show that the amplitude of the successive paths will not rapidly decline, and vice versa, when the distance between the sender and the receiver increases. Moreover, the time difference between the different paths will be small in the case of distance increase. In other words, the successive paths will converge in time.</p>

OFDM Demodulation Using Virtual Time Reversal Processing in Underwater Acoustic Communications

2015 ◽  
Vol 23 (04) ◽  
pp. 1540011 ◽  
Author(s):  
Yanling Yin ◽  
Songzuo Liu ◽  
Gang Qiao ◽  
Yue Yang ◽  
Yue Yang
Keyword(s):  
Time Reversal ◽  
Orthogonal Frequency Division Multiplexing ◽  
Estimation Methods ◽  
Delay Spread ◽  
Underwater Acoustic Communications ◽  
Ofdm Systems ◽  
Acoustic Communications ◽  
Underwater Acoustic ◽  
Single Input Single Output ◽  
Virtual Time

The extremely long underwater channel delay spread causes severe inter-symbol interference (ISI) for underwater acoustic communications. Passive time reversal processing (PTRP) can effectively reduce the channel time dispersion in a simple way via convolving the received packet with a time reversed probe signal (PS). However, the PS itself may introduce extra noise and interference (self-correlation of the PS). In this paper, we propose a virtual time reversal processing (VTRP) for single input single output (SISO) orthogonal frequency division multiplexing (OFDM) systems. It convolves the received packet with the reversed estimated channel, instead of the PS to reduce the interference. Two sparse channel estimation methods, matching pursuit (MP), and basis pursuit denoising (BPDN), are adopted to estimate the channel impulse response (CIR). We compare the performance of VTRP with the PTRP and without any time reversal processing through MATLAB simulations and the pool experiments. The results reveal that VTRP has outstanding performance over time-invariant channels.

scholarly journals Combined Hybrid DFE and CCK Remodulator for Medium-Range Single-Carrier Underwater Acoustic Communications

2017 ◽  
Vol 2017 ◽  
pp. 1-11
Author(s):  
Xialin Jiang ◽  
Wei Su ◽  
En Cheng
Keyword(s):  
Frequency Domain ◽  
Multipath Propagation ◽  
Underwater Acoustic Communications ◽  
Acoustic Communications ◽  
Detection Scheme ◽  
Underwater Acoustic ◽  
Time Frequency ◽  
Single Carrier ◽  
Medium Range ◽  
Underwater Acoustic Channels

Advanced modulation and channel equalization techniques are essential for improving the performance of medium-range single-carrier underwater acoustic communications. In this paper, an enhanced detection scheme, hybrid time-frequency domain decision feedback equalizer (DFE) combined with complementary code keying (CCK) remodulator, is presented. CCK modulation technique provides strong tolerance to intersymbol interference caused by multipath propagation in underwater acoustic channels. The conventional hybrid DFE, using a frequency domain feedforward filter and a time domain feedback filter, provides good performance along with low computational complexity. The error propagation in the feedback filter, caused by feedbacking wrong decisions prior to CCK demodulation, may lead to great performance degradation. In our proposed scheme, with the help of CCK coding gain, more accurate remodulated CCK chips can be used as feedback. The proposed detection scheme is tested by the practical ocean experiments. The experimental results show that the proposed detection scheme ensures robust communications over 10-kilometre underwater acoustic channels with the data rate at 5 Kbits/s in 3 kHz of channel bandwidth.

scholarly journals Underwater Acoustic Channel Characterization of Shallow Water Environment

2018 ◽  
Vol 6 (1) ◽  
pp. 137-150 ◽  
Author(s):  
Tri Budi Santoso ◽  
Endang Widjiati ◽  
Wirawan Wirawan ◽  
Gamantyo Hendrantoro
Keyword(s):  
Shallow Water ◽  
Channel Model ◽  
Delay Spread ◽  
Underwater Acoustic Communication ◽  
Underwater Acoustic Channel ◽  
Underwater Acoustic ◽  
Acoustic Channel ◽  
Measurement Result ◽  
Maximum Delay

Understanding of channel propagation characteristics is a key to the optimal design of underwater acoustic communication. Generally, modelling of underwater acoustic channel is performed based on measurement result in certain site at certain times. Different sites might have different characteristics, each of which can generally be described by a model obtained by averaging measurement results at multiple points in the same environment. This paper describes a characterization of the underwater acoustic channel of tropical shallow water in a Mangrove estuary, which has sediment up to 60 cm at the bottom. Such a channel model is beneficial for the design of communication system in an autonomous underwater vehicle, for instance. The measurement result of delay spread parameter from three different points with the distance of 14 ~ 52 m, has various values. The root mean square (RMS) of delay spread ranges between 0.0621 ~ 0.264 ms, and the maximum delay spread varies with the value of 0.187 ~ 1.0 ms. The pdf fitting shows that Rayleigh distribution describes the fading variation more accurately than Nakagami and Ricean.

Research of FH-MFSK Underwater Acoustic Communication Based on Non-Binary LDPC Codes

2014 ◽  
Vol 519-520 ◽  
pp. 945-952
Author(s):  
Wei Wei Fan ◽  
Bo Li ◽  
You Wen Zhang ◽  
Da Jun Sun
Keyword(s):  
Error Rate ◽  
Ldpc Codes ◽  
Doppler Frequency ◽  
Wireless Channel ◽  
Underwater Acoustic Communication ◽  
Frame Synchronization ◽  
Underwater Acoustic ◽  
Channel Codes ◽  
Binary Channel ◽  
Synchronization Signal

Compared with binary-modulation, Multiple-modulation can obtain higher rate of transmission in the condition of same symbol-rate. If using binary channel codes with multiple-modulation, there exists an problem of information-loss of the probability from bit to symbol conversion. Underwater acoustic channel is an multipath, time-variation, high-noise and strong doppler-effect wireless channel, which leads to high error-rate caused by signal distortion. To solve the problems above, we adopt FH-MFSK modulation to overcome the inter-symbol interference by multipath. The PN sequence is used as a frame synchronization signal and frequency energy accumulation method is used to detect the frame-synchronization. PN hopping signal is chosen to estimate the doppler frequency-shift and using non-binary LDPC codes based on symbol for channel error codes. Finally, We perform numerical simulations and the experiments on the lake to show that compared with binary LDPC codes, non-binary LDPC codes for multiple-modulation can achieve same error-rate under lower SNR.

Recent Technological Trends in Underwater Acoustic Communications

2015 ◽  
Vol 49 (6) ◽  
pp. 161-165 ◽  
Author(s):  
Pierre-Philippe J. Beaujean
Keyword(s):  
Communication Technology ◽  
Multiple Input Multiple Output ◽  
Underwater Acoustic Communication ◽  
Underwater Acoustic Communications ◽  
Acoustic Communications ◽  
Underwater Acoustic ◽  
Marine Industry ◽  
Multiple Input ◽  
Input Multiple Output ◽  
Point To Point

AbstractAs underwater acoustic communication technology is becoming more mature, it is increasingly used in the marine industry, scientific community, and military. This article enquires about the latest developments produced by academia and identifies new technological trends in this field. The latest trends in point-to-point communications, multiple-input multiple-output technology, and underwater acoustic networking are reviewed.

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