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

Abstract

Linear 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.

Timing estimation of multiple hyperbolic frequency‐modulated signals based on multicarrier underwater acoustic communication

“…In underwater acoustic communication, using LFM pulse to detect data frames is a mature technology 19 . In a particular frequency band, the amplitude‐frequency characteristic of the LFM signal is relatively flat, but outside this frequency band, the amplitude decreases rapidly; that is, the signal energy is mainly concentrated in this frequency band.…”

Multi‐user underwater acoustic communication using binary phase‐coded hyperbolic frequency‐modulated signals

“…The residual is updated after every iteration and the process continues until the threshold is met. The expression for x n at the nth iteration for which the X has a rank-one projection of maximum value is given in Equation (26).…”

“…A virtual time-reversal mirror is a well-established technique used in UWA communication for equalization [24,25]. VTRM has been proven to minimize the effect of ISI due to the large delay spread of UWA communication not only in single-carrier UWA communication [19,26] but also in multi-user scenarios [7,27]. Moreover, the time-reversal mirror method also proves to be effective in the time-varying channels [28].…”

Code index modulation method with multidimensional invisible data mapping

“…Firstly, the data in original DSSS is still defined as onedimensional data D 1 ðnÞ, and the data added in the MID-CIM is two-dimensional invisible data D 2 ðnÞ and threedimensional invisible data D 3 ðnÞ respectively. Meanwhile, the ratio of the two-dimensional invisible data rate R 2 to the onedimensional data rate R 1 is defined as the index order k, as shown in Equation (3). The relationship between the threedimensional invisible data rate R 3 and the one-dimensional data rate R 1 is defined as the shift order λ, as shown in Equation (4).…”

“…With the increasing demand for applications, especially the requirements of data transmission rate and spectrum utilisation, the advantages of traditional direct spread spectrum are tested, because its anti‐multipath, anti‐interference and multiple access multiplexing capabilities are at the cost of broadening the signal spectrum, which makes it impossible to meet the requirements of effective transmission when transmitting in the channel with narrow bandwidth and high processing gain requirements. Therefore, on the basis of multi‐ary spread spectrum (soft spread spectrum) [1–3] and parallel combinatory spread spectrum [4, 5], index modulation technology [6, 7] is proposed to map some data bits into specific indexes (values) and transmit them in the modulation signal. Therefore, this part of data will not consume extra energy, so as to improve the transmission rate and energy efficiency of the system.…”