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

Abstract

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.

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

“…It is widely used due to its robustness and computational efficiency [33]. Matching pursuit along with VTRM used in [26,34], 35 proves to be very useful. The channel is estimated by sending a training signal through a sparse UWA channel.…”

“…However, the performance of the system is degraded as multipath increases. M-ary-based cyclic shift keying spread spectrum using VTRM presented in [26] requires a high spreading sequence for a higher data rate. The M-ary linear chirp spread spectrum proposed in [27] used matched filter to detect chirp signals.…”

Long-Range Acoustic Communication Using Differential Chirp Spread Spectrum

“…The channel measured the LFM pings with a length of 0.128 ms by repeatedly transmitting 200 times. A measured CIR is expressed as s Rx (t) = h(t) ⊗ s Tx (t), (10) where s Rx is the received signal; s Tx is the transmitted signal; and h is the CIR. In Equation (10), h is cut to the length of the ping and is expressed again in matrix H, which is expressed as…”

“…where 𝑆 𝑅𝑥 is the received signal; 𝑆 𝑇𝑥 is the transmitted signal; and ℎ is the CIR. In Equation (10), ℎ is cut to the length of the ping and is expressed again in matrix 𝐇, which is expressed as…”

“…Especially in the military arena, LRAC should not only have reliable communication, but also confidentiality. The spread spectrum (SS) technique is a good method in terms of confidentiality of communication, and research on the SS method has recently been underway [6,[8][9][10][11]. When the SS technique is applied, the energy of the signal spreads widely in the frequency domain, making it difficult to detect signals in the interceptor.…”