scholarly journals Pilot-Assisted OFDM for Underwater Acoustic Communication

2021 ◽  
Vol 9 (12) ◽  
pp. 1382
Author(s):  
Mohsin Murad ◽  
Imran A. Tasadduq ◽  
Pablo Otero
Keyword(s):  
Channel Estimation ◽  
Underwater Acoustic Communication ◽  
Intercarrier Interference ◽  
Wireless Data ◽  
Error Performance ◽  
Acceptable Error ◽  
Underwater Acoustic ◽  
Channel One ◽  
Wireless Data Transmission ◽  
Time Variations

Multicarrier techniques have made it possible to wirelessly transmit data at higher rates for underwater acoustic (UWA) communication. Several multicarrier techniques have been explored in the past for wireless data transmission. OFDM is known to fight off inter-symbol interference due to the orthogonality of its subcarriers. However, due to time variations, OFDM suffers from intercarrier interference. As the UWA channel is both a time and frequency variant, channel estimation becomes complex. We propose a pilot-based channel estimation technique and explore two equalizers for improving the error performance of an OFDM-based UWA system. Both the equalizers employ pilot subcarriers to estimate the UWA channel. One equalizer is a least squares (LS) equalizer and the other is a zero forcing (ZF) equalizer. Using computer simulations, it is observed that, for an acceptable error performance, the number of pilots should be one-fourth the number of subcarriers. Moreover, if the energy of the pilots is increased without changing the overall symbol energy, the error performance degrades. It is also noted that both the LS and ZF equalizers give an acceptable error performance with the ZF performing marginally better than the LS. Furthermore, the error performance of the proposed system is evaluated as a function of the transmitter-receiver distance and an acceptable error performance is observed even at 1250 m.

scholarly journals Direct-Mapping-Based MIMO-FBMC Underwater Acoustic Communication Architecture for Multimedia Signals

2019 ◽  
Vol 10 (1) ◽  
pp. 233 ◽  
Author(s):  
Chin-Feng Lin ◽  
Tsung-Jen Su ◽  
Hung-Kai Chang ◽  
Chun-Kang Lee ◽  
Shun-Hsyung Chang ◽  
...  
Keyword(s):  
Channel Estimation ◽  
Multimedia Communication ◽  
Error Rates ◽  
Transmission Mechanism ◽  
Underwater Acoustic Communication ◽  
Underwater Acoustic ◽  
Communication Architecture ◽  
Direct Mapping ◽  
Mean Square Errors ◽  
The Voice

In this paper, a direct-mapping (DM)-based multi-input multi-output (MIMO) filter bank multi-carrier (FBMC) underwater acoustic multimedia communication architecture (UAMCA) is proposed. The proposed DM-based MIMO-FBMC UAMCA is rare and non-obvious in the underwater multimedia communication research topic. The following are integrated into the proposed UAMCA: A 2 × 2 DM transmission mechanism, a (2000, 1000) low-density parity-check code encoder, a power assignment mechanism, an object-composition petrinet mechanism, adaptive binary phase shift keying modulation and 4-offset quadrature amplitude modulation methods. The multimedia signals include voice, image, and data. The DM transmission mechanism in different spatial hardware devices transmits different multimedia packets. The proposed underwater multimedia transmission power allocation algorithm (UMTPAA) is simple, fast, and easy to implement, and the threshold transmission bit error rates (BERs) and real-time requirements for voice, image, and data signals can be achieved using the proposed UMTPAA. The BERs of the multimedia signals, data symbol error rates of the data signals, power saving ratios of the voice, image and data signals, mean square errors of the voice signals, and peak signal-to-noise ratios of the image signals, for the proposed UAMCA with a perfect channel estimation, and channel estimation errors of 5%, 10%, and 20%, respectively, were explored and demonstrated. Simulation results demonstrate that the proposed 2 × 2 DM-based MIMO-FBMC UAMCA is suitable for low power and high speed underwater multimedia sensor networks.

scholarly journals Cost Function based Soft Feedback Iterative Channel Estimation in OFDM Underwater Acoustic Communication

2019 ◽  
pp. 29-37
Author(s):  
Gang Qiao ◽  
Zeeshan Babar ◽  
Lu Ma ◽  
Xue Li
Keyword(s):  
Channel Estimation ◽  
Cost Function ◽  
Orthogonal Frequency Division Multiplexing ◽  
Matching Pursuit ◽  
Decision Feedback ◽  
Underwater Acoustic Communication ◽  
Soft Decision ◽  
Iterative Receiver ◽  
Iterative Receivers ◽  
Underwater Acoustic

Underwater Acoustic (UWA) communication is mainly characterized by bandwidth limited complex UWA channels. Orthogonal Frequency Division Multiplexing (OFDM) solves the bandwidth problem and an efficient channel estimation scheme estimates the channel parameters. Iterative channel estimation refines the channel estimation by reducing the number of pilots and coupling the channel estimator with channel decoder. This paper proposes an iterative receiver for OFDM UWA communication, based on a novel cost function threshold driven soft decision feedback iterative channel technique. The receiver exploits orthogonal matching pursuit (OMP) channel estimation and low density parity check (LDPC) coding techniques after comparing different channel estimation and coding schemes. The performance of the proposed receiver is verified by simulations as well as sea experiments. Furthermore, the proposed iterative receiver is compared with other non-iterative and soft decision feedback iterative receivers.

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