Joint virtual time reversal communications with an orthogonal chirp spread spectrum over underwater acoustic channel

AbstractLinear chirp spread spectrum technique is widely used in underwater acoustic communication because of their resilience to high multipath and Doppler shift. Linear frequency modulated signal requires a high spreading factor to nearly reach orthogonality between two pairs of signals. On the other hand, nonlinear chirp spread spectrum signals can provide orthogonality at a low spreading factor. As a result, it improves spectral efficiency and is more insensitive to Doppler spread than the linear counterpart. To achieve a higher data rate, we propose two variants (half cycle sine and full cycle sine) of the M-ary nonlinear sine chirp spread spectrum technique based on virtual time-reversal mirror (VTRM). The proposed scheme uses different frequency bands to transmit chirp, and VTRM is used to improve the bit error rate due to high multipath. Its superior Doppler sensitivity makes it suitable for underwater acoustic communication. Furthermore, the proposed method uses a simple, low-power bank of matched filters; thus, it reduces the overall system complexity. Simulations are performed in different underwater acoustic channels to verify the robustness of the proposed scheme.

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Multiuser Chirp Spread Spectrum Transmission in an Underwater Acoustic Channel Applied to an AUV Fleet

Sensors ◽

10.3390/s20051527 ◽

2020 ◽

Vol 20 (5) ◽

pp. 1527

Author(s):

Christophe Bernard ◽

Pierre-Jean Bouvet ◽

Antony Pottier ◽

Philippe Forjonel

Keyword(s):

Spread Spectrum ◽

Multiple Access ◽

Autonomous Underwater Vehicle ◽

Matched Filter ◽

Underwater Acoustic Communication ◽

Underwater Acoustic Channel ◽

Underwater Acoustic ◽

Acoustic Channel ◽

Chirp Spread Spectrum ◽

Code Division Multiple

The objective of this paper is to provide a multiuser transmission technique for underwater acoustic communication in the framework of an Autonomous Underwater Vehicle (AUV) fleet. By using a variant of a Hyperbolically Frequency-Modulated (HFM) signal, we describe a new family of transmission techniques called MultiUser Chirp Spread Spectrum (MU-CSS), which allows a very simple matched-filter-based decoding. These techniques are expected to provide good resilience against multiuser interference while keeping good robustness to Underwater Acoustic (UWA) channel impairments like Doppler shift. Their implementation for the UWA scenario is described, and the performance results over a simulated shallow-water UWA channel are analyzed and compared against conventional Code-Division Multiple Access (CDMA) and Time-Division Multiple Access (TDMA) transmission. Finally, the feasibility and robustness of the proposed methods are verified over the underWater AcousTic channEl Replay benchMARK (Watermark), fed by several channel responses from sounding experiments performed in a lake.

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Performance Analysis of Passive Time Reversal in AWGN Channel and Underwater Acoustic Channel

i-manager s Journal on Communication Engineering and Systems ◽

10.26634/jcs.2.4.2475 ◽

2013 ◽

Vol 2 (4) ◽

pp. 20-24

Author(s):

N.R. Krishnamoorthy ◽

C.D. Suriyakala

Keyword(s):

Performance Analysis ◽

Time Reversal ◽

Underwater Acoustic Channel ◽

Underwater Acoustic ◽

Acoustic Channel ◽

Awgn Channel

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LOSS OF RESOLUTION FOR THE TIME REVERSAL OF WAVES IN RANDOM UNDERWATER ACOUSTIC CHANNELS

Mathematical Models and Methods in Applied Sciences ◽

10.1142/s0218202513500267 ◽

2013 ◽

Vol 23 (11) ◽

pp. 2065-2110 ◽

Cited By ~ 1

Author(s):

CHRISTOPHE GOMEZ

Keyword(s):

Time Reversal ◽

Underwater Acoustic Channel ◽

Underwater Acoustic ◽

Acoustic Channel ◽

Coupled Mode ◽

Transverse Profile ◽

Underwater Acoustic Channels ◽

Separation Of Scales ◽

Propagation Medium ◽

Spatial Focusing

In this paper we analyze a time reversal experiment in a random underwater acoustic channel. In this kind of waveguide with a semi-infinite cross-section a propagating field can be decomposed over three kinds of modes: the propagating modes, the radiating modes and the evanescent modes. Using an asymptotic analysis based on a separation of scales technique we derive the asymptotic form of the the coupled mode power equation for the propagating modes. This approximation is used to compute the transverse profile of the refocused field and show that random inhomogeneities inside the waveguide deteriorate the spatial focusing. This result, in an underwater acoustic channel context, is a counterexample of the classical results about time reversal experiment in other configurations for which randomness in the propagation medium enhances the refocusing.

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M-ary Cyclic Shift Keying Spread Spectrum Underwater Acoustic Communications Based on Virtual Time-Reversal Mirror

Sensors ◽

10.3390/s19163577 ◽

2019 ◽

Vol 19 (16) ◽

pp. 3577

Author(s):

Zhou ◽

Liu ◽

Nie ◽

Yang ◽

Zhang ◽

...

Keyword(s):

Time Reversal ◽

Spread Spectrum ◽

Underwater Acoustic Communications ◽

Cyclic Shift ◽

Acoustic Communications ◽

Underwater Acoustic ◽

Underwater Acoustic Channels ◽

Shift Keying ◽

Virtual Time ◽

Time Reversal Mirror

Underwater acoustic communications are challenging because channels are complex, and acoustic waves when propagating in the ocean are subjected to a variety of interferences, such as noise, reflections, scattering and so on. Spread spectrum technique thus has been widely used in underwater acoustic communications for its strong anti-interference ability and good confidentiality. Underwater acoustic channels are typical coherent multipath channels, in which the inter-symbol interference seriously affects the performance of underwater acoustic communications. Time-reversal mirror technique utilizes this physical characteristic of underwater acoustic channels to restrain the inter-symbol interference by reconstructing multipath signals and reduce the influence of channel fading by spatial focusing. This paper presents an M-ary cyclic shift keying spread spectrum underwater acoustic communication scheme based on the virtual time-reversal mirror. Compared to the traditional spread spectrum techniques, this method is more robust, for it uses the M-ary cyclic shift keying spread spectrum to improve the communication rate and uses the virtual time-reversal mirror to ensure a low bit error rate. The performance of this method is verified by simulations and pool experiments.

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Virtual Time-Inverse OFDM Underwater Acoustic Channel Estimation Algorithm Based on Compressed Sensing

Journal of Sensors ◽

10.1155/2020/5910585 ◽

2020 ◽

Vol 2020 ◽

pp. 1-12

Author(s):

Yun Li ◽

Xihua Chen ◽

Sanlin Sun ◽

Zhicheng Tan ◽

Xing Yao

Keyword(s):

Channel Estimation ◽

Compressed Sensing ◽

Doppler Shift ◽

Estimation Algorithm ◽

Underwater Acoustic Channel ◽

Underwater Acoustic ◽

Focusing Effect ◽

Acoustic Channel ◽

Channel Information ◽

Virtual Time

The severe multipath delay of the underwater acoustic channel, the Doppler shift, the severe time-varying characteristics, and sparsity make it difficult to obtain the channel state information in the channel estimation of the virtual time-reverse mirror OFDM, which makes the virtual time mirror subcarrier orthogonality easy to suffer damage; the focusing effect is not obvious. Therefore, this paper proposes a virtual time-inverse OFDM underwater acoustic channel estimation algorithm based on compressed sensing. The algorithm extracts the detection signal, constructs a sparse signal model of the delay-Doppler shift, and then performs preestimation of the underwater acoustic channel based on the compressed sensing theory. Then, by predicting the timing of the underwater acoustic channel and convolving with the received signal, the algorithm improves the focusing effect better. Experimental simulations show that compared with LS and OMP algorithms, the algorithm can accurately recover channel information from a small number of observations, reduce the bit error rate by 10%, and improve the accuracy of channel estimation and the time-inverse OFDM performance of virtual time.

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