Pilot-Based Adaptive Channel Estimation for Underwater Spatial Modulation Technologies

Abstract

Spatial Modulation Technologies (SMTs) are schemes that reduce inter-carrier interference (ICI), inter-channel interference, inter-antenna synchronization (IAS), and system complexity for multiple-input multiple-output (MIMO) communication systems. Moreover, high spectral and energy efficiency have rendered SMTs attractive to underwater acoustic (UWA) MIMO communication systems. Consequently, this paper focuses on SMTs such as spatial modulation (SM), generalized spatial modulation (GSM), and fully generalized spatial modulation (FGSM) in which one constant number and one multiple number of antennas are active to transmit data symbols in any time interval for underwater acoustic communication (UWAC). In SMTs, the receiver requires perfect channel state information (P-CSI) for accurate data detection. However, it is impractical that the perfect channel knowledge is available at the receiver. Therefore, channel estimation is of critical importance to obtain the CSI. This paper proposes the pilot-based recursive least-square (RLS) adaptive channel estimation method over the underwater time-varying MIMO channel. Furthermore, maximum likelihood (ML) decoder is used to detect the transmitted data and antennas indices from the received signal and the estimated UWA-MIMO channel. The numerical computation of mean square error (MSE) and bit error rate (BER) performance are computed for different SMTs like SM, GSM and FSGM using Monte Carlo iterations. Simulation results demonstrate that the RLS channel estimation method achieves the nearly same BER performance as P-CSI.

Fully Quadrature Subcarrier-Index Shift Keying for Efficient Underwater Acoustic Communications

“…The pilot subcarriers are used for channel estimation, and their number and location are varied according to the channel. Moreover, in an underwater acoustic communication scenario, the channel estimation uses a larger number of pilots compared to free space communication [16], [17]. Therefore, the remaining data subcarriers can be any number (not 2 i ).…”

“…Further, owing to the low propagation speed of acoustic waves and the wide-band nature of the UWC, a severe Doppler shift is generated [1], [10], [15]- [17]. Moreover, due to the acoustic band limitations, it becomes necessary to divide the acoustic bandwidth between as many OFDM number subcarriers as possible for generating a long OFDM symbol interval to cope with UAC wide multi-path delay spread [1], [16], [17]. Therefore, a high ICI results from the UWC Doppler shift, which degrades the overall system performance.…”

Data-Driven Signal Detection for Underwater Acoustic Filter Bank Multicarrier Communications

“…Furthermore, the classical signal processing method cannot be directly used, which makes the signal detection of FBMC system more challenging. Researchers have proposed many signal detection approaches based on pilot to counter imaginary interference including interference approximation method [11,12] and interference cancellation method [13][14][15], so as to maximize the symbol amplitude at the pilot after demodulation. The interference approximation method is designed to calculate the value of the neighborhood symbol interference, and the interference cancellation method makes full use of the odd symmetry of the filter fuzzy function, but the performance of these systems still depends on the accuracy of channel estimation and the pilot overhead is high.…”

Underwater Image Transmission Using Spatial Modulation Unequal Error Protection for Internet of Underwater Things

“…There are four communication technologies used as a physical layer for underwater communication: optical, electromagnetic, magnetic induction, and acoustic waves. Until now, the acoustic waves is the most used one in long distance underwater communication [2,3]. However, the acoustic bandwidth is limited, and it consumes high power transmission and IoUTs nodes are battery-based with no capability for recharging.…”

“…The SPIHT coder based on wavelet algorithm is the most employed algorithm in image compression as well as being an essential type of compression for all subsequent algorithms. Spatial modulation technologies have been proposed to deal with the second research direction [3,5]. There are some other research articles, where researchers tried to tackle with improving the underwater multimedia application using combined ideas of two research directions: unequal error protection (UEP) techniques via hierarchical quadrature amplitude modulation (HQAM) [4,6].…”