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

Sensors ◽  
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.

scholarly journals M-ary nonlinear sine chirp spread spectrum for underwater acoustic communication based on virtual time-reversal mirror method

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Songzuo Liu ◽  
Habib Hussain Zuberi ◽  
Yi Lou ◽  
Muhmmad Bilal Farooq ◽  
Shahabuddin Shaikh ◽  
...  
Keyword(s):  
Acoustic Communication ◽  
Time Reversal ◽  
Spread Spectrum ◽  
Underwater Acoustic Communication ◽  
Half Cycle ◽  
Spreading Factor ◽  
Underwater Acoustic ◽  
Virtual Time ◽  
Chirp Spread Spectrum ◽  
Time Reversal Mirror

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.

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.

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